ed i t o r s

Fernando ValenzuelaCourtney Young

5th International Seminar on Process Hydrometallurgy

5th International Seminar on Process Hydrometallurgy

ed i t o r s

Fernando ValenzuelaCourtney Young

5th International Seminar on Process Hydrometallurgy

July 10 - 12, 2013

Santiago, Chile

CopyrightGecamin,Chile.Allrightsreserved.Nopartofthispublicationmaybereproduced,storedortransmittedinanyformorbyanymeans,electronic,mechanical,byphotocopying,recordingorotherwise,withoutthepriorwrittenpermissionfromGecamin.

Authors disclaimerAnyviewsandopinionspresentedinthearticlespublishedintheseproceedingsaresolelythoseoftheauthorsanddonotnecessarilyrepresentthoseofGecamin.Theauthorstakefullandexclusiveresponsibilityfortechnicalcontent,style,languageandaccuracyoftheinformationpublishedherein.Thisinformationisnotintendednorimpliedtobeasubstituteforprofessionaladvice.Theeditorsarenotresponsibleforanydamagetopropertyorpersonsthatmayoccurasaresultofuseoftheinformationcontainedinthisvolume.

I.S.B.N.978-956-8504-88-5

GecaminPaseoBulnes197,Piso6Santiago,ChilePostcode:8330336Telephone:+56226521500www.gecamin.com

Online proceedings www.gecaminpublications.com/hydroprocess2013

Contents

11 Organizers 13 Committees 17 Foreword 19 Preface 21 Acknowledgements

chap. 1 Plenary presentations

Impregnated activated carbon for gold extraction from thiosulfate solutions. Courtney Young and Nick Gow

25

Geotechnical lessons learned from the operation of Cerro Verdes Crush Leach Pad 4-A. Helbert Galdos, Javier Guevara and Arnaldo Saavedra

35

chap. 2 Base metals hydrometallurgy

Daily process mineralogy: A metallurgical tool for optimized copper leaching. Wolfgang Baum, Kevin Ausburn and Randy Zahn

49

Direct production of high-purity cobalt sulfate heptahydrate from a NiCo deposit concentrate. Alex Mezei, Michael Johnson, Cornelia Lupu, Ron Molnar, Keith Lee and Robin Goad

59

Copper extraction from oxide ore using sea water. Cynthia Torres, Mara Elisa Taboada, Tefilo Graber, Hctor Galleguillos and Helen Watling

69

Kinetics of chalcopyrite leaching in either ferric sulfate or cupric sulfate media in the presence of NaCl. Tcia Veloso, Johne Peixoto, Michael Rodrigues and Versiane Albis Leo

79

Mineral QTs in place leaching, standard sector. Hugo Letelier, Patricio Gimnez, Carola Gonzlez, Luis Zenteno and Carlos Castillo

87

Study of the steel dust leaching for the recovery of zinc and cadmium. Ernesto de la Torre, Alicia Guevara and Cynthia Espinoza

93

Zinc recovery from electric-arc furnace dust by hydrochloric leaching and bi-electrolyte electrolysis. Jos Ricaurte and Ernesto de la Torre

103

A step closer to the leaching of primary sulfides. Guillermo Velarde111

Controlling the irrigation flow in heap leach piles of El Soldado mine by canopy system with thermal camera. Javier Ruiz-del-Solar, Omar Daud, Mauricio Correa and Marco Torres

119

Hydrothermal mineral replacement reactions and their applications in mining and processing. Jing Zhao, Allan Pring, Jol Brugger, Fang Xia, Kan Li and Yung Ngothai

127

Study of the recovery of silica from the zircon chemical treatment. Laura Rocha and Carlos Morais

135

Maboumine process: Example of a promising process for developing a polymetallic ore deposit. Florent Delvalle, Valrie Weigel and Antoine Greco

143

chap. 3 Cyanidation, leaching and recovery of gold

A theoretical study of sArt precipitate generation: Operational and safety impacts. Humberto Estay, Pablo Carvajal, Karina Gonzlez and Vernica Vsquez

153

Development of a new technique to recover cyanide for gold mining using membranes contactors. Humberto Estay, Miguel Ortiz and Julio Romero

161

Leaching of sulfide gold ores using dithiooxamide, a non-cyanide solvent of low-toxicity. Juan Pablo Serrano and Ernesto de la Torre

171

Copper cyanocomplexes adsorption on activated carbon: Effects on the selectivity of gold dicyanide adsorption. Clauson Souza, Virginia Ciminelli and Daniel Majuste

181

Cyanide leaching of copper-gold-silver ores. Humberto Estay, Pablo Carvajal, Karina Gonzlez, Hctor Yez, Waldo Bustos, Sergio Castro and Francisco Arriagada

191

Successful application of sArt technology for gold-copper ore deposits. Kresimir Ljubetic, scar Lpez, David Kratochvil and David Sanguinetti

201

chap. 4 Solvent extraction and ion exchange

Analysis phase separation profiles in copper extraction. Patricio Navarro and Sebastin Jara

211

Mo recovery process from high acidity solutions via solvent extraction using CYANeX600. Mauricio Salamanca, Alejandro Quilodrn and Osvaldo Castro

217

Use of Nr reagents in presence of nitrate ion in SX: A revision of the present moment. Rodrigo Zambra, Alejandro Quilodrn, Gonzalo Rivera and Osvaldo Castro

225

Advantages and contributions of modifiers to copper extraction. Rodrigo Zambra, Alejandro Quilodrn, Osvaldo Castro and Sara Pascuale

235

Regeneration process for copper solvent extraction reagents. Piritta Salonen and James Kabugo

245

Metallurgical performance of small and medium size copper SX plants: Relevance of the SX reagent formulation. Philippe Joly and Francisco Reyes

253

Removal of some heavy metals from a sulfate-containing residual mining solution using nano-structured calcium silicates. Fernando Valenzuela, Jaime Sapag, Carlos Basualto and Luis Verdugo

261

chap. 5 Electrometallurgical processes and electrochemistry

Electrochemistry of enargite: Reactivity in alkaline solutions. Nick Gow, Courtney Young, Hsin-Hsuing Huang and Greg Hope

265

Effects of organic impurities on zinc electrowinning. Daniel Majuste, Virginia Ciminelli, Eder Martins and Adelson de Sousa

275

SeLe Technology: An alternative to boosting current efficiency and cathode quality in eW plants. Pedro Aylwin, Nicols Lagos and Patricio Melani

285

Tankhouse parameters for transition from lead to alternative anodes. Scot Sandoval, Casey Clayton, Ephrem Gebrehiwot and Jason Morgan

295

CoolBar: A new intercell bar for electrolytic processes. Gerardo Cifuentes and Rodolfo Mannheim

303

Practical determination of galvanic corrosion of steel induced by mineral particles. Genny Leinenweber and Luis Cceres

311

Mirs Starter Sheet Robotic Stripping Machine (ssrsM). Luis Felipe Ramrez

321

chap. 6 Bioleaching processes

Bioaccelerant: A new biotechnological product for bioleaching process optimization. Mara de la Luz Osses, Matas Saavedra and Simn Beard

329

The effect of temperature on column bioleaching of secondary copper sulfide ores. Michael Rodrigues, Klinger Lopes, Hamilton Lencio, Tcia Veloso and Versiane Albis Leo

339

Leaching of copper oxide ore by in situ biological generation of sulphuric acid. Debora Monteiro de Oliveira, Luis Sobral and Diogo de Oliveira Padro

347

A real-time method for detecting active microorganisms in commercial-scale biohydrometallurgical processes. Davor Cotoras and Pabla Viedma

355

Bioleaching of covellite from low grade copper sulfide ore and tails. Vctor Zepeda, Pedro Galleguillos, Cecilia Demergasso, Dina Cautivo, Jos Soto and Yasna Contador

365

chap. 7 Modeling, and optimizing hydrometallurgical operations and circuits

Implications of hydrodynamic testing for heap leach design. Stefan Robertson, Amado Guzmn and Graeme Miller

375

Dynamic model of copper recovery in heaps, Compaa Minera Doa Ins de Collahuasi. Eduardo Flores, Juan Pablo Garcs, Christian Hu and Jess Casas

389

Dynamic simulator of ore preparation processes and leaching. Francisco Reyes, Gabriel Tejeda, Pablo Karelovic, Aldo Cipriano, Miguel Herrera, Fernando Romero, Solange Rojas and Cristian Salgado

401

DroP Project: Leaching process optimization for reducing water consumption in copper mining. Ulrike Broschek, Jorge Lobos, Jorge Cornejo, Luis Bravo, Josu Lagos and Karien Volker

409

Rheometallurgical process risk mitigation through engineering data generation. Alex Mezei and Mike Ashbury

417

chap. 8 Hydrometallurgical processes for producing salt and non-metals compounds

Some improvements in Caliche heap leaching. Javier Ordez, Silvia Valdez, Luis Moreno and Luis Cisternas

429

Author's index439

Editors443

Organizers

The Hydroprocess 2013 Seminar was organized by Montana Tech of the Uni-versity of Montana, UsA and Gecamin, Chile.

Montana Tech of the University of Montana

With more than 2,800 students on two campuses, Montana Tech is composed of the School of Mines & Engineering; College of Letters, Sciences & Profes-sional Studies; Highlands College; Graduate School; and the Montana Bureau of Mines & Geology.

Montana Tech emphasizes teamwork, collaboration, and hands-on learning. Montana Techs vision is to meet the changing needs of society by supplying knowledge and education through a strong curriculum augmented by research, graduate education and service. Its vision is to be a leader for higher education and research in the Pacific Northwest in engineering, science, energy, health, information sciences, and technology.

All programs derive a special character and emphasis from the unique setting and continued tradition of high quality that has characterized Montana Tech since its founding. Montana Tech has a long standing reputation for producing outstanding graduates and is committed to research; resulting in an unprecedented growth in its funded research over the last several years.

Learn more by visiting www.mtech.edu

Gecamin

Powering professional development for sustainable mining

Gecamin is a Chilean company with 15 years of experience organizing technical and international conferences for the mining industry. Our conferences aim to inform and inspire professionals from all over the world, fostering the exchange of best practices and innovative experiences.

Over 12,000 professionals have attended our events and have been trained in areas fundamental to the mining industry. These areas include Geology and

11

Mining, Mineral Processing, Hydrometallurgy, Sustainability and Environment, Water and Energy, Maintenance and Automation, and Human Capital.

Gecamin seeks to contribute to the sustainable development of the mining industry by openly addressing its most pressing concerns and by offering a platform for knowledge exchange that aims at identifying the most sustainable solutions.

In 2012, Gecamin organized 10 conferences and 12 courses, with a total of 501 technical presentations, gathering more than 2600 delegates. A total of 128 mining houses from 37 countries were represented.

Learn more about Gecamin conferences by visiting www.gecamin.com

12

Executive Committee

ch a i r

Gabriel Meruane , r&d Project Director, sQM Industrial, Chile

co - ch a i r sCourtney Young , Department Head and Lewis S. Prater Distinguished Professor, Metallurgical and Materials Engineering, Montana Tech, UsA

Javier Guevara , Hydrometallurgical Process Manager, Sociedad Minera Cerro Verde, Peru

2 0 1 2 ch a i rSergio Castro , Senior Processing Consultant, Arcadis, Chile

e x e cu t i v e d i r e c t o rCarlos Barahona , General Manager, Gecamin, Chile

t e chn i c a l coord i n at o rFernando Valenzuela , Professor, Universidad de Chile

s em i na r coord i n at o rFabiola Bustamante , Gecamin, Chile

a s s i s ta n t coord i n at o rRebekah Zale , Gecamin, Chile

Directing Members

Alejandro Dagnino , Mining Resources and

Development Manager, Minera Gaby SpA, Chile

Marcelo Jo , General Manager of Technical

Support, Xstrata Copper, Chile

Cleve Lightfoot , Global Practice Leader

Technology, Bhp Billiton, Chile

Percy Mayta , Technical Services Manager,

Freeport-McMoran Copper & Gold Inc., Peru

scar Rosas , Plant Manager, El Soldado

Division, Anglo American, Chile

Gustavo Tapia , Technological Innovation and

Process Manager, Antofagasta Minerals, Chile

Advisory Committee

Pablo Amigo , Jacobs Chile s.a.

Corby Anderson , Colorado School of Mines, usa

Francisco Arriagada , Arcadis, Chile

Antonio Ballester , Universidad

Complutense de Madrid, Spain

Directing Members

Alejandro Dagnino , Mining Resources and

Development Manager, Minera Gaby SpA, Chile

Marcelo Jo , General Manager of Technical

Support, Xstrata Copper, Chile

Cleve Lightfoot , Global Practice Leader

Technology, Bhp Billiton, Chile

Percy Mayta , Technical Services Manager,

Freeport-McMoran Copper & Gold Inc., Peru

scar Rosas , Plant Manager, El Soldado

Division, Anglo American, Chile

Gustavo Tapia , Technological Innovation and

Process Manager, Antofagasta Minerals, Chile

Advisory Committee

Pablo Amigo , Jacobs Chile s.a.

Corby Anderson , Colorado School of Mines, usa

Francisco Arriagada , Arcadis, Chile

Committees

13

Antonio Ballester , Universidad

Complutense de Madrid, Spain

Enrique Carretero , amira International

Latin America Ltda., Chile

Dick Celmer , Fluor, Chile

Virginia Ciminelli , Universidade Federal

de Minas Gerais (uFmG), Brazil

Clenilson Da Silva Souza Junior , Instituto

Federal do Rio de Janeiro, Brazil

Ernesto de la Torre , Escuela Politcnica Nacional, Ecuador

George P. Demopoulos , McGill University, Canada

Claudia Diniz , Vale, Brazil

David Dixon , University of British Columbia, Canada

Steve Dixon , GoldCorp, usa

scar Ferrada , Minera Escondida, Chile

Rick Gilbert , Freeport-McMoran Copper & Gold Inc., usa

Manuel Guzmn , Molibdenos y Metales s.a., Chile

Miguel Herrera , Universidad Adolfo Ibez, Chile

Jorge Ipinza , Jri Engineering, Chile

Joaqun Martnez , Royal Institute of Technology, Sweden

Jorge Menacho , De Re Metallica Ingeniera Ltda., Chile

John Monhemius , Imperial College

London, United Kingdom

Miguel Monroy , Xstrata Copper, Lomas Bayas, Chile

Luis Moreno , Royal Institute of Technology, Sweden

Patricio Navarro , Universidad de Santiago de Chile

Felipe Nez , Minera Florida, Yamana, Chile

Manuel Olivares , ara Worley Parsons s.a., Chile

Kwadwo Osseo-Asare , Penn State University, usa

Vladimiros Papangelakis , University of Toronto, Canada

Eduardo Patio , Bhp Billiton Chile Inc.

Sergio Rivera , El Salvador Division, Codelco, Chile

David Robinson , csiro, Australia

Eloy Romn , Hochschild Mining, Peru

Luis Snchez , Bhp Billiton Pampa Norte, Chile

Nathan Stubina , Barrick Gold, Canada

Juan Carlos Tapia , amec International

Engineering and Construction, Chile

Julio Cesar Tremolada , Iberometex s.a.c., Peru

Petrus Van Staden , Mintek, South Africa

Guillermo Velarde , Sociedad Minera Cerro Verde s.a., Peru

Joan Vials , Universidad de Barcelona, Spain

Technical Committee

Fernando Acevedo , Pontificia Universidad

Catlica de Valparaso, Chile

Jaime Alfaro , Xstrata Copper, Tintaya, Peru

Luis Bergh , Universidad Tcnica Federico Santa Mara, Chile

Germn Cceres , Universidad de Atacama, Chile

Francisco Carranza , Universidad de Sevilla, Spain

Jess Casas , Process Consulting, Chile

Gerardo Cifuentes , Universidad de Santiago, Chile

Luis Cisternas , Universidad de Antofagasta/

cicitem/csiro, Chile

Francisco Cubillos , Universidad de Santiago de Chile

Manuel Chvez , Freeport-McMoran, Minera El Abra

Francisco Daz , The Chilean Commission

for Nuclear Energy, Chile

Jos Fernndez , Mantos Blancos

Division, Anglo American Chile

Juan Pablo Garcs , Ca. Minera Doa

Ins de Collahuasi, Chile

Juan Carlos Gentina , Pontificia Universidad

Catlica de Valparaso, Chile

Tefilo Graber , Universidad de Antofagasta, Chile

Nlida Heresi , Jri Ingeniera, Chile

Christian Hu , Ca. Minera Doa Ins de Collahuasi, Chile

Jos Hernndez , Universidad de Chile

14

Juan Patricio Ibez , Universidad Tcnica

Federico Santa Mara, Chile

Hugo Letelier , El Teniente Division, Codelco, Chile

Hugo Maturana , Universidad de La Serena, Chile

Gonzalo Montes-Atenas , Universidad de Chile

Rafael Padilla , Universidad de Concepcin, Chile

Carolina Paipa , Universidad de Playa Ancha, Chile

Nelson Parra , Jri Ingeniera, Chile

Geysa Pereira , Hydrometallurgy, Vale, Brasil

Eduardo Robles , Hatch, Chile

Eladio Rojas , Chuquicamata Division, Codelco, Chile

Leonardo Romero , Universidad Catlica del Norte, Chile

Vernica Rueda , snc Lavalin, Chile

Andrs Soto , Universidad Mayor, Chile

Mara Elisa Taboada , Universidad de Antofagasta, Chile

Jaime Tapia , Universidad Arturo Prat, Chile

Diego Verdejo , Antofagasta Minerals, Chile

Editorial Committeeed i t o r sFernando Valenzuela , Universidad de Chile

Courtney Young , Montana Tech, usa

co p y e d i t o rRebekah Zale , Gecamin, Chile

r e v i ewer s

Versiane Albis Leo , Universidade

Federal de Ouro Preto, Brazil

Jaime Alfaro , Xstrata Tintaya, Peru

Francisco Arriagada , Arcadis, Chile

Pedro Aylwin , New Tech Copper SpA, Chile

Antonio Ballester , Universidad

Complutense de Madrid, Spain

Carlos Basualto , Universidad de Chile

Jess Casas , Process Consulting, Chile

Sergio Castro , Arcadis, Chile

Gerardo Cifuentes , Universidad de Santiago, Chile

Luis Cisternas , Universidad de Antofagasta/

cicitem/csiro, Chile

Davor Cotoras , Biohidrica, Biotecnologas del Agua, Chile

Clenilson Da Silva Souza Junior , Instituto

Federal do Rio de Janeiro, Brazil

Ernesto de la Torre , Escuela Politcnica Nacional, Ecuador

Javier Delgado , Novigi Ltda., Chile

Diana Endara , Escuela Politcnica Nacional, Ecuador

Humberto Estay , Arcadis, Chle

Helbert Galdos , Sociedad Minera Cerro Verde s.a.a., Peru

Nick Gow , FLSmidth, usa

Tefilo Graber , Universidad de Antofagasta, Chile

Alicia Guevara , Escuela Politcnica Nacional, Ecuador

Nlida Heresi , Jri Ingeniera, Chile

Miguel Herrera , Universidad Adolfo Ibez, Chile

Juan Patricio Ibez , Universidad Tcnica

Federico Santa Mara, Chile

Marcelo Jo , Xstrata Copper, Chile

Hugo Letelier , El Teniente Division, Codelco, Chile

Daniel Majuste , Federal University of Minas Gerais, Brazil

Hctor Mlaga , Sociedad Minera Cerro Verde s.a.a., Peru

Joaqun Martnez , Royal Institute of Technology, Sweden

Jorge Menacho , De Re Metallica Ingeniera Ltda., Chile

Gabriel Meruane , r&d Project Director,

sQm Industrial, Chile

Alex Mezei , sGs Mineral Services,

Metallurgical Operations, Canada

John Monhemius , Imperial College

London, United Kingdom

Luis Moreno , Royal Institute of Technology, Sweden

Caroline Muzawasi , University of Cape Town, South Africa

15

Patricio Navarro , Universidad de Santiago de Chile

Rafael Padilla , Universidad de Concepcin, Chile

Vladimiros Papangelakis , University of Toronto, Canada

Jochen Petersen , University of Cape Town, South Africa

Li Qian , School of Minerals Processing and

Bioengineering, Central South University, China

Francisco Reyes , dictuc s.a., Chile

Stefan Robertson , Mintek, South Africa

Julio Romero, Universidad de Santiago de Chile

Javier Ruiz-del-Solar , Universidad de Chile

Scot Sandoval , Freeport-McMoRan Copper & Gold Inc., usa

Ruberlan Silva , Vale, Brazil

Luis Sobral , Centre for Mineral Technology, cetem, Brazil

Andrs Soto , Universidad Mayor, Chile

Clauson Souza , Federal University of Minas Gerais, Brazil

Mara Elisa Taboada , Universidad de Antofagasta, Chile

Luis Alberto Texeira , Pontificia Universidade

Catlica do Rio de Janeiro, Perxidos do Brasil

Csar Ugarte , Hatch, Peru

Petrus Van Staden , Mintek, South Africa

Diego Verdejo , Antofagasta Minerals, Chile

Jacques Wiertz , Universidad de Chile

Rodrigo Zambra , Cytec, Chile

16

In the last three decades the role of hydrometallurgy has changed. What started as a secondary process alternative is now recognized as a primary option with key advantages. Hydro-processes are able to treat lower quality minerals, reduce the environmental impact of mining and recovery processes significantly, and require lower initial capital costs thus giving opportunities to small and medium sized producers.

However, as an established technology further growing faces new challenges. Complex ore mineralogy, including lower grade materials, forces us to look for continuous improvement in chemical processes. It is challenging to move over the standard operation and force continuous innovation cycles to adapt mineral processing to new conditions.

Another critical limitation is water availability. The intensive use of sea water shows new challenges and opportunities. The requirement to increase water reuse and recycling is now not only an environmental responsibility but also a cost factor. Increasing water cycling produces an increase in yield but impurities accumulate as a side effect. New process conditions should be faced and the proper forecast is a key to sustain the operation standard.

Thirdly, we observe that the role of hydrometallurgists has changed in recent years. Ones initial role preparing flow sheets and balances has been superseded by new responsibilities. Safety management, environmental responsibility, operations and human resources management, risk assessment, and finances appear more often. The traditional academic curriculum for mining, metallurgy and chemical professionals should be critically analyzed to include new time requirements. Limitations are observed not only with regards to the availability of qualified professionals but also in their initial toolkit of abilities.

Global markets have given us a very good opportunity to grow. However, we are now facing the instability and uncertainty associated with the European markets. The normal reaction of shareholders is to contain production costs to be more competitive. It is our challenge to support the innovation cycles despite limits in resources. Crisis periods are especially fertile for creativity and innovation.

Foreword

17

Hydroprocess 2013 is an opportunity to look over these and other important challenges in the industry for the coming years. Here we will share our positive results, critical opportunities and foster coming dreams. Certainly we are discuss-ing the state of art in the aqueous processing industry, and we feel proud to be part of it every year.

Many thanks and welcome to you all.

Gabriel Meruane Naranjoch a i rHydroprocess 2013 | 5th International Seminar on Process Hydrometallurgy

18

The realization of the 5th International Seminar on Process Hydrometallurgy is the outcome of great efforts and special dedication from all those involved. This seminar provided an excellent opportunity to work with many renowned professionals and researchers from different countries who have selflessly collaborated with us. Hydroprocess 2013, held from July 10 - 12, 2013 at the Sheraton Hotel in Santiago, Chile, is effectively the fifth in a series of interna-tional seminars on Process Hydrometallurgy initiated in 2006 by Gecamin.

Undoubtedly, this seminar has become the site of an international forum where all professionals and executives involved in Hydrometallurgy can analyze and discuss innovations and developments concerning the liquid processes of ores and materials involving the use of aqueous chemistry and physics. The papers presented in these proceedings of the fifth version of Hydroprocess speak of a consolidated seminar given the important assortment of technical subjects covered and the number of enterprises and countries represented.

As was defined in the initial call, the main objectives of this seminar are to (i) learn about innovations and developments in the hydrometallurgical processing of metals including valuable metals, non-metal compounds and industrial minerals, (ii) identify the best practices and technologies used in hydrometallurgical plant operation and design, and (iii) fortify an international network of collaboration and exchange between professionals related to hydrometallurgy.

This book contains 45 abstracts written by delegates from 11 different countries. The conference has been organized by area of interest, including: Plenary presentations (2); Base metals hydrometallurgy (12); Cyanidation, leaching and recovery of gold (6); Solvent extraction and ion exchange (7); Electrometallurgical processes and electrochemistry (7); Bioleaching pro-cesses (5); Modeling and optimizing hydrometallurgical operations and circuits (5); and Hydrometallurgical processes for producing salt and non-metals compounds (1).

I would like to thank all those whose efforts have helped in making Hy-droprocess a success. Thank you to the authors and their organizations for submitting papers; to all the technical experts, for sharing their expertise,

Preface

19

dedicating valuable time correcting the articles, and for providing insightful comments thus enhancing the quality of this publication and the standard of the seminar. Finally, I would like to thank all the Gecamin personnel for their efforts in ensuring all the goals proposed for the seminar were successfully achieved.

Fernando Valenzuelat e chn ic a l c o or d i n at or a n d e d i t orHydroprocess 2013 | 5th International Seminar on Process Hydrometallurgy

20

The Organizing Committee acknowledges with gratitude the efforts of all the authors for contributing a large variety of high quality, detailed and in-novative papers to the technical program. We also would like to thank the reviewers, Montana Tech of the University of Montana, the employees from Gecamin, and all those involved in the creation of these proceedings for their assistance. The support of the Organizing, Advisory and Technical Committees has been greatly appreciated, as has been the support of the Hydroprocess 2013 Chair, Co-Chairs and the Chairs of the technical sessions.

The Organizing Committee also wishes to thank the following sponsors (as of June 7, 2013 in alphabetical order) for their generous support:

Gold : BASF, GEA Westfalia, Inppamet and SNF FloMin

Silver : BTA, Cytec, Metalex, Outotec, RSR Anodes and Verne SpA

Social : SQM

Official Material : Arcadis and BASF

Institutional Partners : Consejo Minero, Chile; Instituto de Ingenieros de Minas del Per; Servicio Nacional de Geologa y Minera (serNAGeoMiN), Chile; and Sociedad Nacional de Minera (soNAMi), Chile

Official Media : AreaMinera, Chile

Media Partners : Ecoamrica, Chile; Elsevier, United Kingdom; Infomine, Canada; and Mining Engineering, UsA.

Finally, we would like to thank all the delegates who attended the seminar and exchanged their valuable knowledge and expertise, thus contributing to the great success of this 5th edition of the International Seminar on Process Hydrometallurgy, Hydroprocess 2013. We are looking forward to seeing you all again during the next version of Hydroprocess, in the year 2014.

Executive Organizing CommitteeHydroprocess 2013 | 5th International Seminar on Process Hydrometallurgy

Acknowledgements

21

Plenary presentations

ChAP. 1

Hydrometallurgical processing of gold is almost exclusively accomplished with cyanidation. However, cyanidation has been attacked from environmental, health and safety aspects due to cyanide toxicity, poor tailings management, and desires to eliminate open pit mining. Although these attacks are predomi-nantly unwarranted, they have led to an increase in studies about cyanide alternatives, particularly thiosulfate. Thiosulfate leaching of gold is similar to cyanidation; however, gold recovery from thiosulfate solutions is not possible with conventional carbon adsorption. This necessitates the use of more ex-pensive resin adsorption/ion exchange processes to recover the gold from thio-sulfate solution. In order to make gold recovery cheaper as well as cost-competitive against cyanidation, a novel non-resin technology is described and character-ized. In this technology, activated carbon is impregnated with cyano-cuprous species which allows for high gold extraction followed by traditional elution. Elution efficiency depends on how much copper is present with the gold on the activated carbon surface. Optimal conditions for extracting and eluting the gold were identified from computational models developed from statisti-cally designed experiments. The impregnated activated carbon technology has been patented because it makes thiosulfate leaching cost effective compared to cyanidation by replacing resin adsorption/ion exchange; however, the tech-nology needs to be tested on both a continuous and large scale.

Impregnated activated carbon for gold extraction from thiosulfate solutions

Courtney Young. Montana Tech, USA

Nick Gow. FLSmidth, USA

25

INTRODUCTION

During cyanidation, gold (Au) is reacted with cyanide (CN-1) and oxygen (O2) causing its oxidation

and dissolution by forming cyano-aurous complex [Au(CN)2-1] and hydroxide (OH-1) (Marsden &

House, 2006). The process was patented by MacArthur (1916) and was conclusively shown to be

electrochemical in nature by Kudryk & Kellogg (1954) but was not combined with carbon

adsorption for recovering the Au from solution until 1970 (Marsden & House, 2006). If copper (Cu)

is present, it will leach via the same mechanism and form one of four cyano-cuprous species

[CuCN, Cu(CN)2-1, Cu(CN)3-2 and Cu(CN)4-3] depending on the pH (Adams, 1994). Because Cu is

usually present in larger amounts than Au, cyano-cuprous species result in higher concentrations

and compete more with cyano-aurous for the adsorption sites on the activated carbon (Jay, 2000).

Using cyanide toxicity and poor tailings management as excuses (Young, 2001), political groups

have attacked cyanidation to eliminate mining, a foundation of modern society. In response,

researchers in the mining industry have examined alternatives to cyanide leaching including, but

not limited to, chlorine, bromine, ammonia, nitric oxide, thiourea, thiocyanate and thiosulfate

(Young, 2001). Based on its leaching mechanism being similar to that of cyanide including the use

of a neutral pH, thiosulfate leaching is the leading contender even though various chemicals are

needed to stabilize the thiosulfate by preventing polythionate formation. In this regard, Cu has

been found to be the most effective and additionally shown to act as a catalyst (Marsden & House,

2006). Unfortunately, Au recovery from thiosulfate solution can only be accomplished by ion

exchange with resins, which are inherently expensive and suffer from fouling with polythionates.

However, Young et al. (2005) conceived an activated carbon technology that shows great promise

for making thiosulfate leaching cheaper and therefore cost-competitive against cyanidation.

It is well known that activated carbon, by itself, has no affinity for Au thiosulfate (Marsden &

House, 2006) and must be pretreated in order to recover Au from thiosulfate solution. Knowing

that Cu is needed as a catalyst as well as a thiosulfate preservative, Young et al. (2005) suggested

using Cu to impregnate the activated carbon with cyano-cuprous by chemisorption forming

Cu(CN)2-1 ads in order for the following metal exchange reaction to take place:

Au(S2O3)2-3 + Cu(CN)2-1 ads Au(CN)2-1ads + Cu(S2O3)2-3 [1]

and thereby extract the Au from thiosulfate solution. In this paper, the development of this novel,

non-resin technology is reviewed from its proof of concept (Gow, 2006) at low adsorption density of

Cu(CN)2-1 to confirmation (Melashvili, 2009) at high adsorption density and subsequent elution.

Results have been presented in detail elsewhere (Young et al., 2012) but are reviewed here along

with, for the first time, a brief discussion on cost.

CYANO-CUPROUS CHEMISORPTION

Experiments of cyano-cuprous chemisorption on activated carbon were conducted at room

temperature (20C) and elevated temperature (40C) as well as variable pH (9-12). Adsorption

densities averaged near 15,000 g Cu/g C which equates to approximately 1,500 opt Au assuming

Cu and Au exchange in a 1:1 molar ratio according to Reaction 1. Because carbon adsorption

26

during cyanidation yields Au loadings near 300 opt (Marsden & House, 2006), this would more

than satisfy industrial needs. Furthermore, adsorption densities were found to increase with

increasing temperature and therefore to be endothermic yielding maxima of approximately 8,000

g Cu/g C at room temperature (20C) and 20,000 g Cu/g C at elevated temperature (40C) at pH 9.

However, these values were found to increase moderately by approximately 2,000 g Cu/g C at pH

12. The studies were conducted using caustic (NaOH) to adjust the pH and therefore in the absence

of lime [Ca(OH)2] which eliminates Ca+2 adsorption and therefore the formation of ion pairs

(MacDougall et al., 1980). This was done to keep the chemistry of the system as simple as possible

and thereby enable thermodynamic calculations to verify that cyano-cuprous chemisorbs.

After converting the adsorption densities to surface coverages, fitting the resulting values to

Langmuir Isotherms, and using the isotherms to determine reaction constants according to the

Stern-Langmuir Equation, free energies of adsorption (Gads) were determined and then used to calculate enthalpies (Hads) and entropies (Sads) of adsorption as well using the Clausius-Clapeyron Equation and the fundamental thermodynamic expression, respectively (Young 1994).

Results presented in Table 1 show that Gads at 20C and 40C average -27.4 and -32.6 kJ/mol, respectively. Because Gads are negative and Hads are positive, adsorption is both favorable and endothermic. Furthermore, because the free energies are significantly lower than -20 kJ/mol,

adsorption is confirmed to be chemisorption.

In order to optimize chemisorption densities, tests were conducted via full, two-level, factorial-

designed experiments using Stat-Ease software by systematically varying 4 factors between low

and high values, initial Cu concentration (0.001 or 0.1 M); pH (9 or 12); time (1 or 5 hours); and

temperature (20 or 40C), and using mid-point determinations (0.01 M, pH 10.5, 3 hours and 30C).

Resulting models were used to construct 3-dimensional plots to clearly illustrate the conditions that

yield maximum chemisorption. Results were found to be relatively independent of time and were

higher at increased temperature (40C) verifying its endothermic behavior. Taking cross-sections of

the plot at constant pH yields adsorption isotherms similar to those described earlier but as a

function of surface coverage as opposed to adsorption density. Clearly, the optimal conditions for

cyano-cuprous chemisorption on activated carbon occur at shorter time (1 hour), higher

temperature (40C), higher pH (pH 12), and higher cyano-cuprous concentration (0.1M).

Table 1 Thermodynamic Data for Cyano-Cuprous Chemisorption on Activated Carbon

Temperature (C) Gads (kJ/mol) Hads (kJ/mol) Sads (J/mol/K)

20 @ pH 9 -26.8 41.02 223.8

40 @ pH 9 -31.4

20 @ pH 12 -28.1 55.65 276.8

40 @ pH 12 -33.8

GOLD-COPPER ION EXCHANGE

Impregnated carbon prepared under conditions where minimum chemisorption would occur in

anticipation that they would be favored by industry: 1 hour, 20C, 0.001M and pH 9. It was then

contacted with 20 ppm Au thiosulfate solution and characterized with Raman Spectroscopy to see if

the proposed reaction products could be observed (see Reaction 1). Raman spectra of impregnated

27

carbon before and after contact with Au cyanide are shown in Figure 2. Raman shifts near 2100 cm-

1 in Figure 2a are due to cyano-cuprous with the band at 2118 corresponding to dicyano-cuprous

[Cu(CN)2-1] and those at 2096 and 2127 cm-1 representing tricyano-cuprous [Cu(CN)3-2] (Young et al.,

2008). These peaks are slightly shifted from their aqueous counterparts at 2137, 2094 and 2108 cm-1,

respectively (Lukey et al., 1999). Likewise, Raman band at 2227 cm-1 in Figure 2b are due to cyano-

aurous that formed at the activated carbon surface. It is slightly shifted from the 2239 cm-1 band for solid KAu(CN)2 (Parker et al., 2008). It is understood that, as the pH increases, dicyano cuprous

will convert to tricyano cuprous with excess cyanide present (Marsden & House, 2006).

Consequently, it is reasonable to conclude that increased chemisorption at increased pH is due to

the additional tricyano cuprous available.

Figure 1 3-dimensional plot showing the effect of cyano-cuprous concentration and pH on surface coverage

() at 40C after 1 hour of chemisorption (Young et al., 2012)

Surfa

ce Co

ver

age

()

9.00

9.75

10.50

11.25

12.00

0.001 0.026

0.051 0.075

0.100

0.490

0.617

0.745

0.873

1.000

pH

Initial [Cu]

28

Figure 2 Raman spectra of activated carbon showing (a) the appearance of cyano-cuprous bands following

impregnation and (b) their disappearance along with the appearance of the cyano-aurous band following Au

extraction (Young et al., 2012)

Because all of the cyano-cuprous bands disappeared following contact of the impregnated carbon

with Au thiosulfate solution, the Au must have ion exchanged with both of the cyano-cuprous

species, resulting in the formation of cyano-aurous species. Clearly, Reaction 1 is confirmed but the

results also suggest that the reaction mechanism should also include tricyano-cuprous:

Au(S2O3)2-3 + Cu(CN)3-2 ads Au(CN)2-1ads + CN- + Cu(S2O3)2-3 [2]

As with Reaction 1, it is assumed in Reaction 2 that the Cu and Au exchange in a 1:1 molar ratio. To

test this, impregnated carbon was prepared under various conditions to yield different cyano-

cuprous chemisorption densities and then contacted with Au thiosulfate solutions of varying

concentrations (5-50 ppm). Resulting Au concentrations were measured by ICP. Differences

between initial and final Au concentrations were used to calculate the amount extracted. Results

showed that, when the molar ratio of Cu on the impregnated carbon to Au in solution (Cu:Au) was

greater than approximately 1.5:1, Au extraction efficiencies of 100% were observed. Cu

concentrations were also measured but results were indeterminant yielding ratios ranging from 0:1

to 1:1, likely caused by precipitation when excess thiosulfate was not present to keep it solubilized.

Optimization tests of Au extraction via its ion exchange with Cu were also conducted with Stat-

Ease software using full two-level, factorial-design. In this case, three factors were systematically

varied and midpoints were examined: time (1 or 4 hrs), pH (10 or 12) and Au concentration (10 or

20 ppm). The temperature was fixed at 20C and the cyano-cuprous impregnation was established

at approximately 20,000 g Cu/g C so that Cu:Au ratios at the surface would not exceed either 2:1

or 1:1 assuming complete Au extraction. All variables were found to be important but Au extraction

1500 2000 2500 3000

Raman Shift, cm-12050 2100 2150

a) Cu-CN Bands Appear

b) Au-CN Band

Appears

Cu-CN Bands Disappear

29

at high Au concentration was slower. The 3-dimensional plot in Figure 3 shows the effect of time

and pH on Au extraction at the high Au concentration. It indicates that Au extraction is a maximum

at high pH and long times. Projecting the plot onto the base (i.e., pH-Time plane) yields contours of

which five are shown and three are labeled 90, 70 and 50%. For example, the conditions needed to

achieve >90% extraction range from pH 10.5 and 4 hours to pH 12 and 2.5 hours. Clearly, in this

case, the contours allow the conditions to be seen easier.

Figure 3 3-dimensional plot showing the effect of time and pH on Au extraction by impregnated carbon from

Au thiosulfate solution at 20 ppm (Young et al., 2012)

GOLD ELUTION

Au-loaded, impregnated carbon produced in this manner was eluted using the AARL method

(Marsden & House, 2006) and thereby pretreated with 2% NaCN and 1% NaOH solution for an

hour, transferred to a water-jacketed column controlled at 97C, and eluted with distilled water.

Resulting eluant was collected as a function of time, reported in bed volumes (BV), and analyzed

for free cyanide by ISE and Au and Cu concentration by ICP. Example profiles and a Au recovery

curve are shown in Figure 4. Cu is being eluted somewhat selectively which is common in

cyanidation circuits (Marsden & House, 2006). It was not until 5 BVs have passed that the Au

concentration became significant. After approximately 15 BVs, Au concentrations reached a

maximum of 420 mg/L (ppm) which is comparable to cyanidation circuits as well. In this case, Au

recovery reaches a maximum of 83% at 70 BVs but other tests ranged from lows of 5% when Cu

was still present in significant amounts on the surface to 100% when relatively no Cu was on the

surface. Clearly the best results were obtained at low chemisorption densities of cyano-cuprous

such that, after Au extraction, relatively no Cu was left on the surface. However, if some Cu did

remain, it could be selectively eluted or separated by conventional smelting technology.

Au

Ex

trac

tio

n (

%)

10.0

10.5

11.0

11.5

12.0

1.0

1.8

2.5

3.3

4.0

50

64.8

79.5

94.3

109

pH Time

90%

70%

50%

30

Figure 4 Elution (a) and recovery (b) of Au from impregnated activated carbon as a function of bed volume at

97C using distilled water, 2% NaCN and 1% NaOH according to the AARL method (Young et al., 2012)

FLOWSHEET DESIGN AND COST ANALYSIS

Figure 5 shows a conceptualized flowsheet for thiosulfate heap leaching as determined in this study

and compares it to cyanidation. As can be seen, the two processes are virtually identical. In both

cases, a leachant is added to the heap through which it trickles to leach the Au. The pregnant

solution is then extracted of its Au by adsorption onto activated carbon such that the barren

solution is recycled back to the heap and the loaded carbon is sent to stripping. At this point,

because the carbon contains an adsorbed cyano-aurous species, both processes include stripping

with conventional elution technology followed by electrowinning onto steel wool and eventually

smelting to produce Au dore. Stripped carbon will then be reactivated and recycled back to the

carbon columns, and raffinate from electrowinning will be recycled back to stripping. Steps for

carbon reactivation are not shown in these flowsheets.

a) b)

31

Figure 5 Flowsheets for heap leaching and Au recovery by (a) cyanide and (b) thiosulfate using the novel,

non-resin, activated carbon process with cyano-cuprous impregnation (Young et al., 2012)

Clearly, the envisioned thiosulfate process uses the same unit operations as cyanidation. The cost

difference between the two heap leaching operations will therefore be predominantly due to the

impregnation step as well as the consumption of chemicals throughout. The impregnation step will

require conditioning tanks and pumps beyond that needed for cyanidation but capital and

operating costs for these items will be minimal. Although lime/caustic consumption will increase

due to the impregnation step, thiosulfate leaching (at pH 8) has less consumption than cyanidation

(at pH 10.5); hence, the overall consumption rates will be similar. Assuming the leachants (cyanide

vs thiosulfate) have the same costs, the only difference will be the cost for cyano-cuprous reagent

which is available for the plating industry at moderate costs near US$6/kg and in large quantities

on the order of MTPD. With chemisorption densities near 15,000 g Cu/g C, cyano-cuprous costs

will also be negligible. It is additionally noted that, because of the impregnation step, the Au dore

product could become contaminated with Cu. This could be prevented by selective elution, as

mentioned earlier, and/or by the proper management of the smelting step. If Cu is present in the ore

either process may be pursued and consequently these costs are not considered as well.

CONCLUSIONS

A novel carbon adsorption technology for extracting Au from thiosulfate solutions has been

developed and shows promise at becoming a cost effective method allowing thiosulfate leaching to

become economically competitive against cyanide leaching. Unless impregnated, activated carbons

will not adsorb Au thiosulfate. However, by first adsorbing cyano-cuprous species onto the carbon,

Au can be extracted from thiosulfate solution. Thermodynamic analysis of the adsorption data

a) b)

32

verified that the adsorption process was chemisorption and endothermic. Factorially-designed

experiments verified that maximum cyano-cuprous adsorption occurred at high pH and

temperature and verified the tests. Similar tests conducted for Au extraction showed the Au

followed the Cu. Raman spectroscopy revealed that increased adsorption with increasing pH was

due to both di- and tri-cyano-cuprous and the resulting adsorbed Au species was likely cyano-

aurous [Au(CN)2-1]. Flowsheets similar to current cyanidation processes were designed and could

be employed immediately. At question is whether Au and Cu separation can be done in the process

or in subsequent smelting and refining processes. Based on these promising results, a patent has

been granted; however, the technology needs to be tested on a continuous basis.

ACKNOWLEDGEMENTS

Many thanks are extended to Newmont Mining Corporation for their support of this project as well

as the patent granted in the U.S.A. and pending in Canada and Australia.

REFERENCES

Adams, M.D. (1994), Removal of Cyanide from Solution using Activated Carbon, Mineral Engineering,

7(9):1165-1177.

Gow, R.N. (2008), Pretreatment of Activated Carbon for Gold Adsorption from Thiosulfate Leach Liquors,

Thesis, Montana Tech, Butte, MT.

Jay, W.H. (2000), Copper Cyanidation Chemistry and the Application of Ion Exchange Resins and Solvent

Extractants in Copper-Gold Cyanide Recovery Systems, In: Proceedings of Alta 2000 Conference,

Adelaide, Australia.

Kudryk, V. and H.H. Kellogg, (1954), Mechanism and RateControlling Factors in the Dissolution of Gold in

Cyanide Solution, Trans. AIME J. of Metals, 541-548.

Lukey, G.C., van Deventer, J.S.J., Huntington, S.T., Chowdhury, R.L., Shallcross, D.C. (1999), Raman Study on

the Speciation of Copper Cyanide Complexes in Highly Saline Solutions, Hydrometallurgy, 53:233-244.

MacArthur, J.S. (1916), Discovery of Cyanidation, Mining & Scientific Press, London.

MacDougall, G.J., Hancock, R.D., Nicol, M.J., Wellington, O.L. and Copperthwaite, R.J. (1980), The Mechanism

of the Adsorption of Gold Cyanide on Activated Carbon, J. S. Afr. Inst. Min. & Metall., 80: 344-356.

Marsden, J. and I. House (2006), The Chemisty of Gold Extraction, Ellis Horwood Publishers, New York.

Melashvilli, M. (2009), Gold Recovery from Thiosulfate Solutions using Activated Carbon Pretreated with

Copper-Cyanide: Mechanism, Quantification and Elution, Thesis, Montana Tech, Butte, MT.

Parker, G.K., Gow, R.N. and Young, C.A. Twidwell, L.G. and Hope, G.A. (2008), Spectroelectrochemical

Investigation of the Reaction between Adsorbed Cuprous Cyanide and Gold Thiosulfate ions at

Activated Carbon Surfaces, In: Hydrometallurgy 2008: Proceedings of the 6th International Symposium

Honoring Robert S. Shoemaker, C.A. Young, P.R. Taylor, C.G. Anderson and Y. Choi (Editors), SME,

Littleton, CO.

Young, C.A. (1994), Characterization of Adsorbed Oleate at Calcite and Flourite Surfaces by Infrared and

Raman Spectroscopy, Dissertation, University of Utah, pp. 287.

33

Young, C.A. (2001), Cyanide: Just the Facts, in: Cyanide: Social, Industrial and Economic Aspects, C.A. Young, L.G.

Twidwell and C.G. Anderson (Editors), TMS, Warrendale, PA.

Young, C.A., Gow, R.N. and Melashvilli, M. (2011), Method for Aqueous Gold Thiosulfate Extraction Using

Copper Cyanide Pretreated Carbon Adsorption, U.S. Patent Publication Number US 20110259148 A1.

Young, C.A., Gow, R.N., Melashvilli, M. and LeVier, M. (2012), Impregnated Activated Carbon for Gold

Extraction from Thiosulfate Solutions, In: Separation Technologies for Minerals, Coal and Earth

Resources, Proceedings of the Roe-Hoan Yoon Symposium, C.A. Young and G.H. Luttrell (Editors),

SME, Littleton, CO.

Young, C.A., Gow, R.N., Parker, G. and Hope, G. (2008), Cu-Cyanide Adsorption on Activated Carbon, In:

Hydrometallurgy 2008: Proceedings of the 6th International Symposium Honoring Robert S. Shoemaker, C.A.

Young, P.R. Taylor, C.G. Anderson and Y. Choi (Editors), SME, Littleton, CO.

Young, C.A., Twidwell, L.G and Hope, G. (2005), Recovery of Gold from Thiosulfate Leach Liquor Using Activated

Carbon, CAST Proposal, Montana Tech, Butte, MT.

34

The leaching process started in Cerro Verde in the late 1970s. At that time, the leach pad operating criteria centered around metallurgical and production parameters only. Little or no consideration was given to slope stability, phreatic levels or permeability issues. Later on, when new leach pads were started up in the early 1990s, unusual slope stability issues began to take place; however, these did not pose risks to the operation because overall pad heights were small compared to todays permanent pads. In 1996, the Crush Leach Pad 4-A was engineered and constructed using the best technology available at the time. The design considered twenty 4-meter lifts, which quickly became 6-meter and then 8-meter lifts with improvements in ore agglomeration technology, forced air injection and larger and taller stacking equipment. Recently, Pad 4-A has reached its maximum capacity; twenty lifts have been stacked at an average of 5.5 meters per lift. The metallurgical optimization, coupled with changes in ore quality, entailed geotechnical challenges that led to modified variable irrigation rate schemes, ore stacking, lift rinsing practices, dewatering and phreatic level controls. Lessons learned at Pad 4-A, described in this paper, have been taken into consideration in the engineering and construction of the new Crush Leach Pad 4-B. This paper also describes the geotechnical best practices and design considerations implemented at this new leach pad.

Helbert Galdos, Javier Guevara and Arnaldo Saavedra. Sociedad Minera Cerro Verde S.A.A ., Peru

Geotechnical lessons learned from the operation of Cerro Verdes Crush Leach Pad 4-A

35

INTRODUCTION

The main purpose of this paper is to describe the experience gained by Sociedad Minera Cerro

Verde S.A.A. (SMCV) in the geotechnical control of permanent leach pads of crushed and

agglomerated mineral. Proper control is critical to the slope stability of leach operations. The

phreatic levels inside the heaps must be controlled as they can seriously affect safety, the

environment, metallurgy and the operation. Nevertheless, they are not always given the attention

which they deserve.

On the other hand, the geotechnical control of leach heaps has been improving. It has become more

complex and elaborate as the leach heaps, platforms or pads, have grown in size. Furthermore,

governmental and internal mining company regulations have been changing as part of more

demanding risk management programs.

In general, it is clear that the geotechnical control of leach heaps has evolved in a simple, almost

always reactive manner, instead of in a more elaborate preventative way. Experience has taught

that it is much more convenient to incorporate geotechnical controls from the engineering stage

than when the leach platforms have already been started and have several layers of mineral being

treated.

The first part of this paper briefly describes the leach operation at SMCV, then the geotechnical and

operational problems encountered at the leach heap of crushed and agglomerated Pad 4-A will be

described, along with the corrective measures implemented. Next, the geotechnical controls

implemented at Pad 4-A as part of a preventative program will be discussed. Finally, the paper will

show the application of the experience obtained at Pad 4-A for the engineering, construction and

operation of the new leach platform, Pad 4-B, which began operations in December 2012. All of

which were intended to guarantee, from the initial design, the stability of the heap, and its

operational continuity to avoid having to implement much more expensive corrective measures

later.

The leach process at Sociedad Minera Cerro Verde S.A.A.

At Sociedad Minera Cerro Verde, secondary sulfide and transitional coppers are leached. The

leaching of low-grade (ROM) minerals is carried out at the leach heaps MegaPad ROM and Pad 1X.

On the other hand, the leaching of high grade mineral, previously crushed and agglomerated with

sulfuric acid, takes place at the heap Pad4-A and, more recently, at Pad 4-B.

Both processes involve multilayer permanent heaps of the valley-leach type, i.e. the mineral is

stacked up until it reaches the storage capacity of the pad. The heaps at Cerro Verde are unique in

that they are built in small ravines, that are filled until they reach the height of the platform and

then an upright pyramid is formed by continuing to stack the mineral until the maximum area of

the platform is reached. Thereafter, the pyramid is formed with ever decreasing stack area. The

total height of Pad 4-A is 110 meters with 20 layers of mineral and its slopes have global gradients

of 2.5H : 1V.

36

Operational and geotechnical problems of leach heaps

The most common operational, metallurgical and geotechnical problems found at the permanent

heaps are as follows:

Operational problems

The collapse of the leach solution collection pipes and/or their connections occurs due to lack of

quality control during installation, or while the protective geo-membrane material (overliner) is

being put in place, or by the uncontrolled movement of heavy equipment such as tractors or

conveyor belts. These collapses significantly reduce the drainage capacity of the system,

producing an increase in the phreatic level inside the pad, reducing the factor of safety and

increasing the risk of liquefaction of the saturated mineral and destabilization and collapse of

the slopes.

Leakages from the pipes near the slopes affect the geometry of the slopes.

Removing leached material from the bases of the slopes, for example, to open/maintain access

routes to the leach heaps, weakens the base of the slope.

Increasing the rate of irrigation without bearing in mind the limit of permeability of the material,

or the settling of the underlying material with each layer placed on top.

Geotechnical problems

Internal erosion and piping due to the concentration of fluid at the base of the slope. In some

cases, a cavern is developed which grows towards the interior of the heap.

Localized instability of a side (bank) due to an increased phreatic level near the slope.

Interruptions to vertical flow caused by the presence of layers of low permeability due to their

high clay contents, badly scarified interfaces (badly carried out drainage and ripping).

The presence of craters (sink holes) in the surface produced by damaged collection pipes

followed by internal erosion.

Surface channels caused by rain, flow from broken pipes, or the overflow of an area with

ponded solution resulting in superficial slipping on sides or banks.

Internal canalization of the solution through high-permeability zones (due to the presence of

highly permeable or segregated material) and lateral discharge over the perimeter.

Metallurgical problems

Excessive increase in clay content (montmorillonite and kaolinite) and high percentage of fines

(below mesh 100) in the agglomerated mineral stacked on the leach heap.

Low quality agglomerated mineral due to insufficient control during agglomeration and mineral

transportation to the leach platforms.

Pooling (ponding) of the irrigation solution due to the presence of mineral with high-clay and

and content and ore fines, which generate areas of very low permeability.

37

Solutions implemented

The operational, metallurgical and geotechnical solutions implemented were the following:

Operational solutions

The localizing of segments of collapsed main drainage collection pipes with the help of infrared

cameras mounted on small remote-control vehicles moving inside the pipes, or by following the

behavior of craters or sink holes on the irrigated surface.

Excavating until the collapsed main pipes are located, replacing the damaged sections and

replacing the removed material, increasing its permeability by mixing it with coarser material.

Blending of minerals in the mine to reduce the concentration of clays and fines being fed to the

crushing and agglomeration plant.

Inspection and periodic replacement of the main and auxiliary high-density polyethylene

(HDPE) pipes in the irrigation system, which show damage due to a reduction in their thickness

caused by handling or transportation, or excessive contraction and expansion due the daily

fluctuations in ambient temperature. The latter involves the use of ultrasound techniques to

evaluate the integrity of the fused unions of the HDPE pipes.

Geotechnical solutions

The installation in the bases of the slopes of banks of horizontal drains of 38 and 102 milllimeters

of exterior diameter, 100 and 150 meter long, respectively. In the right number and length, these

horizontal drains help to reduce the phreatic levels near the slopes of the leach heaps.

Reconstruction of slopes affected by the incorrect removal of material from the toe of the slope.

The latter can be aided by analysing the stability of the slope before and after the reshaping

work to ensure that the minimally acceptable geotechnical safety factors have been maintained

for static and post-seismic conditions.

The construction of small rock buttresses or retaining walls at the base of unstable slopes. This

method stabilizes the slope and canalizes the solution so that it can be drained, which avoids a

localized increase in ore moisture and saturation.

The installation of French drains to capture and evacuate the pools of solutions which can

accumulate on the surface near the base of the slope. These consist of ditches excavated in the

gravel, which are refilled with selected crushed stone (filter), which contains a perforated or

slotted pipe. The pipe must have a slope of at least 1% and operate at full flow. Before the end of

discharge, the slotted pipe will be replaced by a blind pipe and a low-permeable plug put in

place.

The installation of banks or batteries of vertical dewatering wells with exterior diameters of

between 204 and 356 millimeters of perforated PVC pipe to lower the phreatic levels inside the

leach heap. These wells have submergible pumps, pressure sensors (transducers), and low-level

switches to optimize the recovery of the solution retained inside the heap due the loss of

permeability of the mineral.

38

Stabilization of the craters (sink holes) by refilling with gravel or highly permeable mineral with

particle sizes of from 102 to 204 millimeters; the repaired area is then covered with layers of non-

woven geotextil and geonet to stop the sink hole from affecting underlaying layers.

Repairing of channels in the slopes of the leach heaps, caused by rain or by the spillage of

solution, which result in erosion. The loose material is removed (as it has a high content of fines)

and is replaced by material of an appropriate size distribution, which is wetted and compacted

layer by layer to avoid further erosion.

Stability buttresses are constructed at the base of the principal slopes of the leach heaps, which

due to the high phreatic levels or deterioration in the angle of design of the slope, do not meet

the minimum factors of safety. The main purpose of a buttress is to increase vertical pressure

and to keep the base of the slope in place (only a localized effect). Likewise, as a side-effect, it

strengthens shear resistance when potential faulty zones pass through it. Buttresses are made

from leached material, rubble or waste material from the mine. The material is checked, wetted

and compacted in horizontal layers. Its weight is crucial. These buttresses contain filter zones or

drains of highly permeable gravel to lower or eliminate the phreatic level to ensure their long

term slope stability.

Metallurgical solutions

Optimization of the quality of the agglomerated mineral, ensuring the correct level of humidity,

dosage of sulphuric acid during the agglomeration, transportation and stacking stages of high-

grade mineral. For the above, an instrument has been designed, which by measuring the

conductivity of the agglomerated mineral can optimize both the dosage of leach solution and

acid for curing of the mineral. It should be mentioned that an excessive dosage of acid

deteriorates the matrix of the rock of the mineral.

A widening (coarsening) of the size distribution curve of crushed mineral to reduce the level of

fines in the crushing circuit. This method is adopted after ensuring that an increase in ore size

would not reduce copper recovery any more than that caused by the presence of clays and fines

due to damage to or compaction (settling) of the mineral with every new layer stacked on the

permanent pad.

Implementation of geotechnical controls

The geotechnical controls of a leach heap are by nature almost always preventative, focused on

monitoring the phreatic levels, the surface and depth movements of key slopes, the vertical

pressure on the base of the slope and the settling of the mineral. Alternatively, the settling which

takes place between the layers can be monitored which would allow changes to the dry density and

porosity of the material to be controlled.

If the global hydraulic conductivity of the leached material is to be evaluated, a large-scale

pumping test should be carried out, which would obtain much more realistic results than localized

testing, an example is provided by the Lefranc tests which are made inside perforations. Another

alternative to measure hydraulic conductivity, but only locally, are the water addition (slug) tests

which take place inside an open-tube piezometer. These tests can also determine whether the

instrument can detect, over time, losses in permeability of the surrounding material due to

deterioration (decrepitation) or aging of the mineral.

39

If the leach heap contains gravel which is likely to suffer from liquefaction, seismographs should be

installed to register important seismic events and to correlate these to any resulting damage to the

heaps. A fixed seismograph should be installed on solid rock and a mobile one set up on the crest of

the heap to analyze signal amplification and the filtration of frequencies.

The geotechnical controls used at SMCV are as follows:

a) Periodical evaluations of slope stability

The periodical evaluations of stability analyze the stability of the heap slopes using the limit

equilibrium method. This analysis is bi-dimensional and as part of the hypothesis, the surface is

considered to act like a rigid solid. This method does not measure movements, only the resulting

safety factor. For a given surface, which is likely to suffer a fault, this method divides the block

into vertical slices, calculates and compares the resistance forces with the destabilization forces.

If the forces which are available to withstand movement are greater than the forces which

destabilize the slope (FS1), then the slope is considered to be stable.

FS = (Resistance Forces / Destabilizing Forces) 1

In general, the following conditions can be analyzed in heaps: static (short and long-term),

pseudo-static, post-seismic with reduced shear resistance, and post-seismic with liquefaction.

Given the large size of the slope, local, intermediate and global faults are investigated. The

potential fault surfaces are circular, blocks or random. Each type of analysis has its

corresponding minimum recommended factor of safety, established by the industry and by

technical literature. Normally, several control sections are established and for each one, the

factors of safety are calculated, which are compared with the required minimum values. Table 1

shows the required minimum safety factors for the leach platform Pad 4-A.

Table 1 Factors of Safety Leach Heap Slope Stability

Condition Safety Factor (FOS) Notes

Short-Term Static 1.3 Only for temporary slope cut work

Long-Term Static 1.5 For all important slopes

Pseudo-Static 1.0 Not applicable as the mineral of Pad 4A below the

phreatic level will undergo liquefaction in the event of

a high magnitude seism.

Post-seismic with

degraded resistance

1.3 Not applicable as the mineral of Pad 4A below the

phreatic level will undergo liquefaction in the event of

a high magnitude seism.

Post-seismic with

Liquefaction

1.1 Normal value to control slope stability. This is the most

critical parameter to be complied.

40

b) Maximum permissible phreatic levels

The maximum permissible phreatic levels are limits or threshold values beyond which it is not

safe to operate the leach heap. Below these thresholds, all the applicable safety factors are met

(static, pseudo-static and/or pseudo-seismic with liquefaction). These are established using slope

stability analysis (by the limit equilibrium method); they depend on the properties of shear

resistance of the terrain, the geometry of the slope and the phreatic level. Figure 1 shows an

example of the control of phreatic levels with respect to the maximum permissible values.

Figure 1 Comparison of Phreatic Levels with Maximum Permissible Values

c) Manual of operations

The Manual of Operations is a field document which attempts to standardize criteria, provide

instructions, procedures and recommendations to monitor and control the phreatic level inside

the leach heap by setting a series of maximum permissible operational levels. The manual

indicates the actions to be taken if these permissible limits are exceeded.

d) Prisms

These are optical instruments which facilitate the monitoring of the surface movements of the

slope in three directions; they are fixed to the terrain by a metallic tube which is embedded in a

concrete base. They can detect settling and/or bulging on the face of the slope, and are read

using electronic surveying equipment with accuracies of a few millimeters.

Geotechnical controls incorporated in the design of Pad 4B leach heap

Based on geotechnical experience acquired during the operation of the leach heap of high-grade

mineral, Pad 4-A; it was decided to include, from the engineering stage, the following elements of

41

geotechnical control in the design of the new high grade ore leach platform, Pad 4-B, which was

successfully started-up in December 2012.

a) Vibrating-wire settlement sensors

This type of sensor allows continuous monitoring of the vertical deformation of the foundations

of the leach heap, due to the vertical pressure of the stacked mineral and the phreatic level. This

sensor is especially useful when the terrain of the foundations has compressible layers or there

are thick refills. Furthermore, they allow indirect measurement of geomembrane stretching or

elongation. They are normally placed under the membrane (underliner layer), either on the mass

or on the structure of the refill. They are accurate to a few millimeters.

b) Inclinometers

Inclinometers are used to measure lateral deformation of the terrain of the foundations of the

heap which are caused by deep breaches (shear surfaces). They are installed outside the heap,

either on the containment berm or on the containment wall. An inclinometer consists of a plastic

tube with special grooves in two perpendicular directions which is installed and connected to

the terrain with grout or with slurry of cement and bentonite. Readings are taken with a biaxis

electronic probe (torpedo) which registers, over 50 centimeter sections, vertical deviations of the

tube in two perpendicular directions. They are accurate to a few millimeters.

c) Vibrating-Wire piezometers

Piezometers measure the pore pressure of the fluid contained in the void spaces of the leached

material (ripios) or in gravel when they are completely full of liquid, that is, saturated (100%

degree of saturation). They are based on the vibrating-wire principle and are very accurate.

Knowing the specific density of the fluid, it is possible to calculate the equivalent height of

column of liquid (piezometric height).

d) Vibrating-wire pressure cells

Vibrating-wire pressure cells measure the total vertical pressure increase at the base of the heap

over its useful lifetime. This pressure is that of the weight of the mineral and the solution.

Knowing the height of the heap, it is possible to estimate the average wet density if required,

which is important operational information. The pressure measurements and those taken from

the foundations allow the plotting of the settling curve of the pad against vertical pressure and

hence calculate the rigidity of the foundation terrain, which is important information for future

designs.

e) The main solution collection system

The system of collection of copper pregnant leach solution (PLS) at Pad 4-B has undergone the

following improvements:

A system to collect the main solution has been installed on a cut zone of bedrock material at

the bottom of the ravine to prevent differential settlement (uneven settling), which can

decouple the pipe joints. In other words, by installation of the main collection drains on

42

bedrock, and not on structural fill, the possibility of future differential settlement is

eliminated.

The principal collection pipes are interconnected which prevents the retention of solution

inside the heap due to obstruction of the collection system.

Together with the system of corrugated and perforated pipes, a system of solid perforated

HDPE collection pipes has been installed in order to ensure continued drainage if a collapse

occurs in the corrugated collection pipes.

Collection pipes have been installed inside trapezoidal ditches (canals) to generate an arc

effect in the mineral located above them and thus transfer the vertical loads of the heap

towards the sides and so reduce deformation.

f) Gravel screens

To prevent phreatic levels from exceeding those considered in the geotechnical design of the

leach, Pad 4-B has permeable gravel screens installed in the space formed by the union of toe of

the slopes of two adjacent cells. These gravel screens are installed in two sectors near the front

slope by the PLS weir upstream the PLS ponds. These gravel screens will also be installed in the

upper levels up to Lift 4, so that, they form a permeable front, perpendicular to the flow of leach

solution on its way to the PLS weir. These screens allow the removal of the leach solution from

the leach zones most adjacent to the front slope, avoiding solution build-up and abating high

phreatic levels affecting the factor of safety of the front slope. This area is the most critical area of

the pad from a geotechnical perspective.

Figure 2 Gravel Screen Pad 4B

g) Large diameter wells for the recovery of solution from the phreatic level

The purpose of these large size wells (nominal diameter of 2.50 meters) is to limit the phreatic

levels inside the heap from the beginning of the operation by providing the opportunity of

installing and operating pumps when the phreatic level starts to increase. The idea is to avoid

costly drilling for dewatering purposes. They have the advantage that they are built in stages

with each new lift being stacked on top of the previous. These well rest on the base of the heap,

43

taking advantage of the entire saturated height of mineral; their size ensures that they have the

required capacity. Solid, perforated pipes of 457 millimeters in diameter have been installed.

They have a gravel band of around 1m thick around them. Due to their large diameter, the pipes

remain upright until agglomerated mineral is stacked around them. Before being put into

operation, the wells should be cleaned and developed to remove fines from the filter and the

surrounding gravel to maximize solution collection and recovery pumping.

h) Wick drains

In the future, to eliminate serious permeability problems due to the presence of perched solution

(pockets of solution), wick drains will be installed; these are vertical drains made from a

corrugated plastic center wrapped in a nonwoven geotextile. They are used to manage complex

hydrogeological processes and to hydraulically connect the pad vertically. They allow the

drainage of perched phreatic levels, the crossing of areas of low hydraulic conductivity and the

reduction of pressure in artesian zones. A metallic lance (pole) is used to sink them into the

terrain. They can reach depths from 30 to 35 meters in leach ripios, with a maximum diameter

size of from 19 to 25 millimeters.

i) Horizontal internal drains

In the future, to eliminate serious permeability issues of the mineral and thanks to the presence

of bedrock banks located to the east and south-east of Pad 4-B, a design for the installation

(while stacking) of horizontal internal drains has been developed. It is much more practical to

proactively install drains than to try to perforate horizontal drains once the heap exhibits poor

permeability; these drains will be made from corrugated perforated pipe, 102 millimeters in

diameter, which will be connected to the PLS collection secondary drain pipes located on top of

the bedrock banks.

CONCLUSIONS

The process metallurgists and leach operators should be aware of the geotechnical concepts

involved in heap leaching practice in order to understand the mechanical, physical and hydraulic

phenomena, which occur inside heaps, their affect on process performance and the physical

stability of the slopes.

In light of the concepts described above, it is possible to avoid future slope stability problems, both

in dynamic and permanent multilayer leach pads by developing solutions that integrate

geotechnical, operational and metallurgical concepts to protect personnel from safety incidents,

meet environmental requirements and achieve production targets.

AKNOWLEDGEMENTS

This paper describes the development of solutions for the geotechnical and operational problems

which occurred at the permanent leach heaps of Cerro Verde. These ideas generally came from all

the members of the Hydrometallurgical Processes Area and the consultancy firms with which they

work. We would like to thank all of the people involved for their creativity and effort.

44

REFERENCES

Memorndum Tcnico: Preliminary Extraction Well Design, North Face, Pad 4A, SMCV, Arequipa, Peru, URS,

Febrero 2009

Evaluacin Geotcnica Integral del Pad 4A, Vector S.A.C., Octubre 2009

Leach Pad N 4A Buttress and Slope Regrading, URS, Noviembre 2009

Memorndum Tcnico: Final Cerro Verde Pad 4A - Liquefaction Analysis, Summary of Runout Estimate, URS,

Julio 2010

Memorndum Tcnico 002 - Anlisis de Estabilidad Adicional Seccin C-C Pad 4A, Ausenco vector,

Septiembre 2011.

45

Base metals hydrometallurgy

ChAP. 2

Although future copper ores will increasingly require concentrator operations, heap and stockpile leaching (including bio-leaching of low grade primary sulfides) will continue to represent a significant production segment in copper mining. Future copper leach operations will be faced with lower grades, harder, finer grained and more acid-consuming ores, complex mineralogy and cost increases related to water, power, reagents and steel wear. It is, therefore, imperative that existing and new leach operations are well-designed and have robust data bases and daily control of the ore feed mineralogy. In order to achieve optimal and consistent crushing, best-practice agglomeration, good permeability, efficient curing, and lowest acid consumption, a leach operation will require quantitative routine mineralogy data. Several heap leach operations in Arizona, Peru and Northern Chile have benefited from long-term mineralogi-cal feed and leach residue analyzes. Typically, modern laboratory technology such as Xrd Rietveld, near infrared, optical microscopy and automated mineral analyzers were used. The application of the characterization techniques for daily blast hole analysis in two Arizona mines and select operations in Chile and Peru has minimized ore routing errors, supported a better p80 and throughput in crushing, reduced permeability failures, and optimized hydro-metallurgical treatment. This paper provides application examples and recom-mendations for production mineralogy in conventional copper leaching, bio-leaching and/or hybrid heap-stockpile concepts. The use of automated small to large mineralogy laboratory modules for mine-site mineralogy will be illustrated.

Daily process mineralogy: A metallurgical tool for optimized copper leaching

Wolfgang Baum, Kevin Ausburn and Randy Zahn. FLSmidth, USA

49

INTRODUCTION

Future mining of sulfide ores will be faced with lower grades, harder and finer grained rock

matrices, complex mineralogy, more reagent consumption, remote locations, severe staff shortages,

and cost escalations for power, water, reagents and (steel) wear. To exacerbate these challenges, the

cyclical exploration approach may not be able to provide sufficient re-fills in the reserve

pipelines. High throughput heap leach (and stockpile bio-leach) operations of the future will have

to use considerably better ore characterization and production control mineralogy in order to

achieve good copper extraction while maintaining low operating cost.

These better ore characterization approaches were pioneered in the 1980s and started to become

increasingly accepted in the new copper leach operations in Chile in the 1990s.

One case study example is the step-changing process mineralogy work at the El Indio gold-silver-

copper operation (then owned by St. Joe Minerals Corporation) which resulted in substantial plant

metallurgy improvements and significant gold, silver and copper recovery increases (Baum et al

1989).

A break-through for process mineralogy for copper leach operations was accomplished with the

extensive use of mineralogical ore characterization by both the El Abra and Radomiro Tomic leach

operations. Specifically at Radomiro Tomic, the first robust, semi-quantitative copper and alteration

mineralogy was carried out on large sample numbers and probably contributed to good startup

and continuously high leach extraction (Cuadra C. and Rojas S. , 2001) and Baum 1998b cited in

Cuadra and Rojas).

Challenges in copper leaching

A ground rule for optimized copper leaching (J.Campbell, 2004, pers. comm.) states maximize

your first cycle leach recovery and control your mineralogy

The copper leach operations of the past had the advantage of relatively good ore grades combined

with oxide copper mineralogy. These ore types are becoming depleted and a variety of ores

including secondary sulfide ores, mixed oxide-sulfide ores, bornite-dominated and, finally, low-

grade chalcopyrite ores will make up the feeds of the future. Also, the future ores may be harder

and will have high(er) acid consumption depending on the host rock type and increase of skarns

and volcanic rocks. Finally, in order to compensate for the declining grades, leach operations

require higher throughput. All of the factors mentioned will place considerable demands on good

ore control which is synonymous with reliable ore characterization.

Operating competitive future heap and bio-stockpile leaching will not be economically attractive

without routine quantitative feed and leach residue mineralogy. Mineralogical analyses, today, are

capable of providing daily/weekly data on:

Mineralogical data Process parameters optimized by mineralogy

Overall gangue mineralogy Geo-technical features

Pyrite content Blast indexing & crusher efficiency

Copper deportment Agglomeration

Clay content Curing requirements

50

Acid consumers Permeability failures

Salting potential Acid, Ferric, PLS Impurities, Cu extraction

Although diagnostic extraction tests (i.e. flash leach tests), copper assays, bottle roll, column and

mini heap tests remain baseline metallurgical tools, they cannot and will not provide the answers

for low recoveries, high acid consumption, poor agglomeration and low permeability (to name a

few). Mineralogical analyses are required to assess the cause(s) for poor metallurgy.

The following examples (Tables 1 and 2) illustrate the importance of mineralogy for identifying

leach problems:

Table 1 Variance in Acid Consumption Oxide Leach Ore Northern Chile

Parameter Ore Type A Ore Type B

Leach extraction, % 74.3 58.9

Acid consumption, lbs/t 18.9 29.6

Matrix fracturing, % 26.5 41.2

Iron hydroxides, % 16.2 25.4

Ca-Montmorillonite,% 4.3 15.8

Modified after Baum, Smith & Sepulveda 1996

Table 2 Diagnostic Quick Leach & Copper Deportment Errors

Total Cu = 0.89% - Cyanide Soluble Cu = 69%

Diagnostic Leach Conclusion: 77% Covellite/Chalcocite Mineralogy

Actual Mineralogy

Copper Mineral % Distribution Leach Type

Cu-Fe-hydroxide/Chrysocolla 36 Semi-Refractory

Covellite/Chalcocite 20 Ferric Acid Leachable

Chrysocolla/Malachite 29 Acid Soluble

Chalcopyrite/Turquoise 15 Refractory

Estimated Total Recovery

Mineralogy 60% Diagnostic Leach 77%

Assays 53%

Bottle Roll Tests 65%

45 Day Column Tests 59%

Modified after Baum 1998a

METHODOLOGY

The currently available mineralogical tools consist of 5 major optimized techniques or innovations

which were introduced during the last 20 years:

1. Automated sample preparation for high throughput and fast turnaround

51

2. Polarized Light Microscopy

3. XRD (x-ray diffraction) Rietveld mineralogy (quantitative)

4. NIR or FT-NIR (near infrared or Fourier transform near infrared) analyses

5. Automated mineralogy (via QEMSCAN, MLA, TIMA, others*) *QEMSCAN, QEMSCAN WellSite, MLA, MLA Express, ASPEX: FEI, Hillsboro, OR USA TIMA: Tescan USA, Cranberry Township/PA USA RoqSCAN: Fugro Robertson/Carl Zeiss, Houston, TX USA EVO MA 15 & Particle SCAN VP: Carl Zeiss, Oberkochen, Germany

Further, the availability of larger, automated or central laboratories, permits mineralogical work on

daily blast hole samples and the use of these data for constant ore control, ore blending, ore routing

and, last but not least, for process control (Allen et al. 2007, Baum, 1996a & b, 1998a, 1999, 2007,

2009, 2013).

Automated sample preparation

The introduction and implementation of robotics technology for sample preparation at various

mining companies has been a step change in providing fast and high-throughput laboratory data

(Best et al, 2007). Specifically, for mineralogy, the availability of automated XRD-NIR laboratories

has enabled data feedback for mining and processing on a daily basis (Baum, 2009).

- Both Freeport-McMo-Ran Copper & Gold laboratories, the Central Analytical Service

Center (Best et al 2007) and the AXN XRD-NIR Mineralogy Lab (Baum 2009) are good

examples of integrating the daily use of mineralogy for leach and concentra