Analytical Issues:

Making the numbers real

Dr. Rob Bowell – SRK Consulting (UK)

Introduction

Geochemical and mineralogical testwork

Essential components in characterization

of mine waste

Geochemical testwork goals:

• Quantify total reservoir

of acid generation,

metal and salts available

• Quantify reactive portion

of acid generation,

metal and salts available

• Quantify the rate of leaching

or attenuation of acid generation,

metal and salts available

• On realistic samples

• Representative analysis

Gaps in Predictive Knowledge

Sampling approach

• Representation

• Heterogeneity

• Number of samples

Verification of data

Assessment of non-standard

protocols

Application of field tests

Kinetic tests

Assessment of ecotoxicology

Detection limits

on samples in

2007 (ppm)

Perkin - Elmer

Detection limits on samples in 1998 (ppm)

0.001

0.01

0.1

1

0.01 0.1 1 10

Ultra trace four-acid package

Mo

Cu

Tl

Ag Bi

In

Ultra trace aqua regia package

La Pb Sr

Sc

Ni Co

Bi Ag

U,Co,W Nb,Rb

Li

Be Ta

Ga,Ge,Te

Cd

Mo

Tl

Te

Ga, Ge, Sb

Cd

As

+ Reliability + Reduced costs + Turn around

High resolution leading to further drops in DLs

opening up isotopes

Understanding analysis

QA-QC

• Essential role of a geochemist

• Ensure numbers collected are

representative

• Common commodities e.g. gold, copper,

nickel, iron obtain international standards

• New commodity types or data collection

methods need to generate site specific

standards

Data Verification

Steps to Verification • Appropriate containers, preservatives & ensure transport to lab

within holding time at correct temperature

• Know laboratory or practical reporting limits versus minimum detection limit

• Ensure clean sampling equipment in the case of waters

• Use appropriate blank

Determine Precision & Accuracy • Precision, measure of the reproducibility of measurements under a

given set of conditions.

RPD = sample result – duplicate result x 100

0.5 (sample result + duplicate result

• Accuracy is the degree of agreement between an analytical measurement and the true value.

Comparability

Cation-Anion Balance

(Sum of Cations-Sum of Anions) *100

(Sum of Cations + Sum of Anions)

Data assessment

Qualifier Description

R Rejected: The data are rejected due to deficiencies in meeting QC criteria

and may not be used for decision making.

J Estimated: The analyte was positively identified and is an estimate

due to discrepancies in meeting analyte-specific quality control criteria.

B Blank contamination: The analyte was found in an associated blank

above the RL, as well as in the sample.

UJ Estimate: The analyte was not detected; however, the result is an estimate

due to discrepancies in meeting analyte-specific quality control criteria.

D

The reporting limit is elevated due to matrix interference.

This is a laboratory applied qualifier and is incorporated in this report

for completeness.

Mu

ltiv

aria

te d

ista

nce

Probability function

Traditional approach – satellite spotting

Objective – detect samples whose geochemistry appears “anomalous”

Defining Anomalies

Discriminating Variability

e.g, K-means clustering

Clustering and “anomaly” detection

e.g, PCA, FA and SVD

Pattern Recognition

Stretch Process

X1

X3

X2

Lixiviants in environmental studies

Typically we use water

Are there alternatives?

• Simulated mine

or process water

• Actual mine

or process water

• Reagents e.g. H2O2,

H2SO4

• Selective extraction

studies

(based on Gray, 1999)

Carbonates Resistate minerals

Silicates Mn-oxides

& am. Fe-ox.

Soluble phases

Cryst. Fe-oxides

Adsorbed & Exch. species

Organics

Acetate + HOAc

HF / fusion

Aqua regia

Mixed acids

Weak acidified NH2OH

EDTA / H+

Water (US

beer)

Strong acidified NH2OH

Regoleach

HCl

Ammonium acetate

MMI

Guinness

Na-pyro / H2O2

Enzyme Leach / H2O2

Increasing age of mineral phase in regolith Less transitory metal contents

Partial or Selective Extractions

Example of selective extraction

results, heap leach solid

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Antimony Arsenic Copper Beryllium Cadmium Lead Aluminium Nickel Zinc Iron

Residual

Pyrite

Reactive Sulfides

Crystalline FeOx

Amorphous FeOx

Labile

Soluble

What is an ARDML program?

Acid Base Accounting

• Good screening test

• Balances potential to generate acid with potential to neutralize acid

• Acid Potential is proportional to sulfide content

FeS2 + H2O + 3/2O2 = Fe3+ + 2SO42- + H+

CaCO3 + H+ = Ca2+ + HCO3-

• AGP = 31.25* sulfide S (in wt%) is acid generation in equivalent kg CaCO3 per ton required to neutralize acid

• Neutralization is proportional to carbonate content and/or neutralization of acid to a known pH in the lab (Sobek method). Calculate in kg CaCO3 per ton

Assessment of Acid Generation

Geological controls to acid generation

Map areas of high acid generation in pit

Relate to mining plans or geological units

Management criteria

• NAF, Not Acid Forming- > 20 eq.kg CaCO3/ton of rock of buffering capacity

• IND, Indiscriminate, Between ±20 eq.kg CaCO3/ton of rock of buffering capacity

• PAF, Potentially Acid Forming- < -20 eq.kg CaCO3/ton of rock of buffering capacity

Acid Base Accounting

Comparison of Static Test

Methods

• Both Sobek ABA and

Net Carbonate Value methods

are commonly used in Nevada

• Methods differ in both

the quantitation of ANP and AGP

• Are the methods comparable?

• Which method is better?

Comparison of AGP

Comparison of NNP

Comparison of NPR to Sulfide Sulfur

Neutralization Potential

What Defines Neutralization?

Comparison of ANP

Other Methods

• Net Acid Generation

or Hydrogen Peroxide test

• Useful in that it oxidizes

sulfide exposed in sample –

estimate of reactivity

• Measure metals in leachate

• Neutralize to a set pH to determine

acid content and calculate

to equivalent kg H2SO4 per ton

generated by sulfide oxidation

NAG test

Caption/Description of XX 25

Acid Generation Capacity Final NAG pH

(s.u.) Static NAG

(kg H2SO4 eq/ton)

Potentially Acid Forming (PAF)

Higher Capacity < 4 >10

Lower Capacity < 4 <10, >1

Non-Acid Forming (NAF) > 4 0

Comparison of ABA-NAG data

Caption/Description of XX 26

More methods

of XX 27

• Sequential NAG test

• Kinetic NAG test

• Oxygen consumption test

• Rising head test

Compare leach metals to pH

Caption/Description of XX 28

Kinetic NAG

Caption/Description of XX 29

Whole Rock Geochemistry

of XX 30

• Good screening test- determine

potential metals of concern

GAI index

Caption/Description of XX 31

GAI Value Interpretation

0 < 3 times average crustal concentrations

1 3 to 6 times average crustal concentrations

2 6 to 12 times average crustal concentrations

3 12 to 24 times average crustal concentrations

4 24 to 48 times average crustal concentrations

5 48 to 96 times average crustal concentrations

6 >96 times average crustal concentrations

Compare metal abundance

of XX 32

Compare to mineralization

Caption/Description of XX 33

Partial leaching to assess metal mobility

Static approach • TCLP; pH adjusted water:

solid ratio

• SWEP; pH adjusted water:

solid ratio

• EPA 1312 test; 20:1 pH

adjusted water: solid ratio

• Bottle roll test; typically

with DI

• MWMP (Nevada); pH

adjusted water of 1 pore

volume to solid ratio

Kinetic approach • Different columns as an

approach

Standard Cell Tall Cell Broad Cell

94 mm64 mm 144 mm

20

0 m

m

50

0 m

m

150

mm

Adjustable clip with screw to tighten

Rubber bung with glass tube running through centre

Plastic piping for draining cell into collection vessel

Perspex base plate with drilled holes for sample drainage

Filter Funnel, attached to base place with silicone sealant

Example: static tests on a Carlin

waste rock sample

Element

mg/L

SPLP

Test Porewater MWMP

Reaction with 10%

aqua regia 15% H2O2

Aluminium 14.9 11.7 16.3 15.8 10.8

Arsenic 0.766 0.85 1.61 21.3 13.9

Cadmium 0.031 0.024 0.155 2.54 1.66

Copper <0.005 <0.005 0.037 4.15 3.89

Fluoride 0.18 0.21 0.24 Not analysed 1.18

Iron 1.86 0.78 2.33 67.5 59.2

Lead 0.014 0.011 0.022 1.9 1.84

Mercury <0.002 <0.0005 <0.002 1.72 1.65

Nickel 0.71 0.43 0.96 7.91 8.21

Selenium 0.04 0.051 0.076 1.33 0.86

Sulfate 128 146 337 Not analysed 835

Metal Leaching Risk

Test Extractant Water:Rock

Ratio

Comments

MWMP DI water 1:1 Most common test

SPLP (1312) Wk HNO3,H2SO4 20:1 EPA std, very dilute

EN1457 (EU) DI water 2:1 & 8:1 EU approved

Humidity Cell DI water ~1.5:1 / wk Best for assessing rate of

release

Columns Any Progressive $$, most flexible &

representative

NAG Metals

H2O2

100:1

New, holds promise for core

samples

Pilot Tests Meteoric water <<1:1 Early operation stage

Predicting soluble Constituents in Mine Water

NWMA - Reno, NV 36

Metal Leaching Risk

Compared contact water chemistry with:

• MWMP, SPLP (1312), Column tests

Variable agreement between test and result

• Failure to use weathered sample – real need for test that accelerates weathering

• Inappropriate water:rock ratio

• Failure of current test methods mitigated by predictable solubility behavior for some constituents or over certain pH ranges

December 3, 2008 NWMA - Reno, NV 37

38

Comparison of Leachate Values-

Arsenic

Compare parameters – Ficklin plot

Kinetic testing

• Purpose to define rate

of leaching not to remove

all mobile constituents

• The relative rates of acid

generation and neutralisation,

(important in determining

if a sample will “go acid”)

• The time to ARD onset

• Drainage chemistry

and the resulting

downstream loading

Kinetic testing

• Which protocol to run?

• How long do you

operate?

• What parameters to

run?

• Type of cell utilized?

• What lixiviant to use?

• Termination analysis?

Dry air & MoistAir In

Air OutRinse water in

Waste Rock Sample

PerforatedSupport

Leachate Out

PlexiglasTube

Selection of Humidity Cells

• Select on rock

types/alteration types

• Select on highest WRA

constitutes e.g. As

• High/low S/C values

• Proportional to ore

grade?

• Proportional to static

results?

0

1

1

2

2

3

3

4

4

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40

Su

lfid

e S

ulf

ur

(wt%

)

Gold Grade (opt)

Skip Samples

Muck Samples

HCT Samples

Ore

Gra

de

Cu

t-O

ff=

0.1

4 o

pt

Interpretation of Kinetic data

• Use sample volume

of leachate to same mass

of solid

• SG and porosity varies

from rock to rock

so ratio varies

• Convert mg/L from cell

analysis to mg/kg/week leach

rate

• Calculate removal rates-

cumulative or sequential

Example of mine tailings acidification

-40

-20

0

20

40

60

80

100

120

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40

Time (Weeks)

Nu

trali

zin

g P

ote

nti

al

(%)

T3_G4

T3_BH4_30

T3_BH4_10

T10_BH3_05

T10_BH1_220

T10_BH1_130

T10_BH1_7.5

T1_BH7_90

T1_BH7_50

T5_BH25_40

T6_BH24_20

T1_BH9_60,BH27_15

T5_BH25_50,BH12_50

T6_BH23_70

Metal/metalloid release:

Sulfide waste rock

As, Zn, Mn, Ni Leached (mg/kg/week) - Carlin sulfide waste

0

5

10

15

20

25

30

35

40

0 1 2 4 6 10 15 20 24 28 32 36 40 48 52 60 70 80 95

Time (weeks)

Leachin

g R

ate

(m

g/k

g/w

eek)

As

Zn

Mn

Ni

Influence of aeration

Forced aeration common

in kinetic testwork

Periodic cycling of dry

and moist air

Effects questioned e.g. Lapakko

& White, 2000 demonstrated

no appreciable effect

Aerated (APSA) vs.

non-aerated (APSN) cells

Effects of aeration on pH

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0 10 20 30 40 50 60 70

Cycle Number

pH

AP-S-A

AP-S-N

VMS-S-A(1)

VMS-S-A(2)

VMS-S-N(1-6)

VMS-S-N(2)

VMS-S-N(3)

VMS-S-N(4)

VMS-S-N(5)

VMS-S-N(6)

Effects of aeration on sulfate production

0

500

1000

1500

2000

2500

3000

3500

4000

0 10 20 30 40 50 60 70

Cycle Number

Su

lfate

Rele

ase (

mg

/kg

/cycle

)

AP-S-A

AP-S-N

VMS-S-A(1)

VMS-S-A(2)

VMS-S-N(1-6)

VMS-S-N(2)

VMS-S-N(3)

VMS-S-N(4)

VMS-S-N(5)

VMS-S-N(6)

Influence of secondary minerals

Importance of mineralogy

Formation dependent

on reaction rates in cell

Secondary minerals-

are they wanted?

Problems with sulfur

mass balance

Fe:S ratio

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 10 20 30 40 50 60 70

Cycle Number

[F

e] /

[S

O4

2-]

VMS-S-A(1)

VMS-S-N(2)

VMS-S-N (14 day)

VMS-S-N (28 day)

Conceptual model

Influence of Particle Size

pH variation with particle size

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0 5 10 15 20 25 30 35 40 45 50

Cycle Number

pH

IBN-S-N

IBN 2-S-N

IBN 3-S-N

VMS-S-N

VMS 2-S-N

C-S-A

Sulfate variation with particle size

0

500

1000

1500

2000

2500

3000

3500

4000

0 5 10 15 20 25 30 35 40 45 50

Cycle Number

Su

lfa

te R

ele

as

e (

mg

/kg

/cy

cle

)

IBN-S-N

IBN 2-S-N

IBN 3-S-N

VMS-S-N

VMS 2-S-N

C-S-A

Effect of sample mass on pH

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0 10 20 30 40 50 60 70

Cycle Number

pH

VMS-L-N(1)

VMS-L-N(2)

VMS-S-N(1-6)

VMS-S-N(2)

VMS-S-N(3)

VMS-S-N(4)

VMS-S-N(5)

VMS-S-N(6)

Effects of sample mass on sulfate

0

500

1000

1500

2000

2500

3000

3500

4000

0 10 20 30 40 50 60 70

Cycle Number

Su

lfa

te R

ele

ase m

g/k

g/c

ycle

)

VMS-L-N(1)

VMS-L-N(2)

VMS-S-N(1-6)

VMS-S-N(2)

VMS-S-N(3)

VMS-S-N(4)

VMS-S-N(5)

VMS-S-N(6)

Influence of flushing frequency on pH

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0 10 20 30 40 50 60 70

Cycle Number

pH

IBN 2-S-N

IBN 2-S-N (21 day)

VMS-S-N (14 day)

VMS-S-N (28 day)

VMS-S-N(1-6)

VMS-S-N(2)

VMS-S-N(3)

VMS-S-N(4)

VMS-S-N(5)

VMS-S-N(6)

Influence of flushing frequency on sulfate

0

500

1000

1500

2000

2500

3000

3500

4000

0 20 40 60 80 100 120

Test Duration (weeks)

Su

lfa

te R

ele

as

e (

mg

/kg

/we

ek

)

IBN 2-S-N

IBN 2-S-N (21 day)

VMS-S-N (14 day)

VMS-S-N (28 day)

VMS-S-N(1-6)

VMS-S-N(2)

VMS-S-N(3)

VMS-S-N(4)

VMS-S-N(5)

VMS-S-N(6)

How long should they run?

• Consistent release rates

over 3-4 weeks

• No obvious increases

in trace elements

• Is there a Minimum period?

• Comparison to static tests

Comparison HCT to NAG

Compare HCT results

to statics

Gauge if reactions

are complete or

if predictions reasonable

Scale factor from static

testwork to HCT

• useful to apply static data

as a substitute for HCT

release data for preliminary

assessment (factor of 250x)

Alternative Approach

Europe

ARDML assessment still relatively new

Focus from Landfill/ Radionuclide

assessment/ Chemical Contamination –

Risk Based Approach

• Risk Screening test - WRA

• pH solubility testing

• Kappa testing

• Flushing tests

• Diffusion assessment

pH-SolubilityTest

10:1 + KOH + HCl pH 12 pH 2

Develop buffer curve to determine acid or base to add to achieve target pH levels of 2 to 12

Add acid/base to 10:1 LS batch tests

Synthetic GW solution and 4% CO2 atmosphere

Determine concentrations

Conducted on pulverized sample

Kappa test: Short term leach test

2:1

100:1

10:1

Batch tests at 2:1, 5:1, 10:1, 50:1

and 100:1 LS ratio

Synthetic GW solution and 4%

CO2 atmosphere

React for 24 hours

Determine concentrations

Conducted on pulverized sample

CLS = C0 e –κ(LS)

Where CLS is the concentration at any leaching proportion LS

C0 is the first flush concentration,

κ is a derived parameter, kappa

LS is the liquid:solid ratio

Long term flushing test

Simulate flooding

Aerobic and Anaerobic columns

Flow rate 500 mL/d for 40 days

Replenished water removed

for analysis to ensure solubility

controls unlikely i.e. determine

mass removal of solute

Diffusion tests: ASTM C1308

Developed for evaluating diffusive release of radioactive constituents

from cemented waste

Application in assessment of Paste Backfill or Encapsulated tailings

Varying contact time

Uses synthetic groundwater

Numerical evaluation assess whether diffusion or chemical dissolution

is controlling concentrations

𝐶𝐹𝐿 =

𝑎𝑛𝐴0= 𝐼𝐹𝐿 = 2

𝑆

𝑉

𝐷𝑎𝑡

𝜋

1/2

Where an is the mass of constituent in the nth batch solution

Ao is the total available constituent mass in the cylinder

S is the cylinder surface area (cm2)

V is the cylinder volume (cm3)

Da is the apparent diffusivity cm2/s

T is time in s

3 hr 3 hr 12 hr 6 hr 24 hr 24 hr 24 hr

Case Study: Paste backfill, Sappes, Greece

• Underground mine fill

• Corrosive to conventional cement

• Rapid mix-key (less time for oxygen/water reaction)

• Develop understanding of geochemical stability in

order to determine physical stability

• Roaster tailings treated to reduce cyanide levels

• Tailings are hydro-cycloned to obtain coarse fraction

• Cyclone underflow filtered to reduce water content

• Binder added to filtered U/F, mixed and adequate

water added for hydration

• Paste pumped underground. Residual water absorbed

through chemical hydration reactions

• Strength develops as paste cures over several month

period

• Formation of hydrated cement minerals decreases

mobility of constituents in tailings

Short term leach results, Arsenic

Long term leachate results, Arsenic

Diffusion test conditions

Diffusion test results, Arsenic

Static testing metal leaching

• Mobilize labile metals, dissolve reactive

minerals

• Simulates short term rain water

or meteoric rinsing

• Only indicates reactive component, nor

quantitative

• Over estimate versus initial kinetic test

leachates due to high water: solid ratio

• Physical flushing and chemical leaching

Example of mine tailings acidification

-40

-20

0

20

40

60

80

100

120

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40

Time (Weeks)

Nu

trali

zin

g P

ote

nti

al

(%)

T3_G4

T3_BH4_30

T3_BH4_10

T10_BH3_05

T10_BH1_220

T10_BH1_130

T10_BH1_7.5

T1_BH7_90

T1_BH7_50

T5_BH25_40

T6_BH24_20

T1_BH9_60,BH27_15

T5_BH25_50,BH12_50

T6_BH23_70

Metal/metalloid release- sulfide waste rock

As, Zn, Mn, Ni Leached (mg/kg/week) - Carlin sulfide waste

0

5

10

15

20

25

30

35

40

0 1 2 4 6 10 15 20 24 28 32 36 40 48 52 60 70 80 95

Time (weeks)

Le

ach

ing

Ra

te (

mg/k

g/w

ee

k)

As

Zn

Mn

Ni

Ecotoxicology assessment

Receptor impact

Determine uptake issues

Sources of contamination

Pathways

• Ingestion

• Dust

• Water

• Open wounds

Acute vs. Chronic

exposure

Example: Arsenic rich waste in Cornwall

• Exposed mine waste

and processed waste

• Arsenic concentration

reported up to 12%

in soil and waste

• Developed recreational area

• Potential for arsenic

ingestion by humans

and animals

• Balance human health

and cultural sustainability

Arsenic geochemistry

Arsenic occurrence

in nature

• As (III), sulfides,

reducing

• As (V), ambient, oxide

• MMAA/DMAA/organic-

rich environments

Arsenic mobility

• reducing

• low Al/Fe

• v.acidic (pH <2) or

alkaline (pH > 8.5)

Arsenic selective extraction

• Selective extraction to determine potential hosts

of soluble arsenic

• Used approaches of Keon et al. 2001; Hall, 2004

Results of SE

Arsenic release

Arsenic toxicity test

PBET test

Simulate gastrotestinal

consumption

Several sequential

extractions at 37°C

Bioavailability

risk assessment

Correlation with Mineral Phases

Natural Geochemical Attenuation

Interaction of lithologies

with mine waters

Attenuate metals, radio

nuclides and protons

through

• Precipitation

• Adsorption

• Absorption

Groundwater flow path

Surface water flow path

Void water e.g. pit lake

Attenuation assessment

High HFO content

Large columns

Compaction to field densities

Saturate loaded column

Drain column completely

Repeat to obtain break-

through (i.e. loss

of attenuation capacity)

Arsenic attenuation Glamis Attenuation Studies

Arsenic Attenuated (%)

-100%

-80%

-60%

-40%

-20%

0%

20%

40%

60%

80%

100%

PV

1

PV

3

PV

5

PV

7

PV

9

PV

11

PV

13

PV

15

PV

17

PV

19

PV

21

PV

23

PV

25

PV

27

PV

29

Time (Pore Volume)

% A

tte

nu

ate

d

Alluvium

Edna Mountain

Havalla

Valmy

Take Home Points Sampling

• Representation/Repeatability

• Account for Heterogeneity

Field Assessment

• Screening approach

• Provide informed sampling approach

Analysis

• Data verification

• Use of laboratory QA to confirm valid analysis

Data Assessment

• Account for variability

• Identify trends

Kinetic testing influenced by

• Internal factors eg particle size, mineralogy, mineral reactions in cell, biota activity

• External factors eg aeration, sample size, frequency of flush

Protocols

• GARD manual has excellent range of methodologies that cover >90% of requirements

• Consider site specific or problem specific approaches

• Greater use of mineralogy & selective extraction

• Kappa approach as an alternative to humidity cells

• Assess directly potential toxicity – useful where direct receptors can be identified