Mineral bio-processing: an option for recovering strategic metals?

D. Barrie JohnsonCollege of Natural Sciences,

Bangor University, UKBangorAcidophileResearchTeam

• Professor of Environmental Biotechnology at Bangor University

• also Guest Professor at Exeter University (UK) and Changsha University (China)

• Director of Research & Head of BART(Bangor Acidophile Research Team)

• Royal Society Research Fellow, Fellow of the Learned Society of Wales & Distinguished Lecturer of the Mineralogical Society (UK)

• research going research collaboration with groups (universities, research organisation and industries) throughout the world (Chile, China, South Africa, France…..)

Topics covered in this talk:

• Brief outline of the development and current status of biominingtechnologies

• The roles of microorganisms in mobilizing and immobilizing metals•• Recent and projected developments in biomining technologies

• “Strategic metals” defined and their potential for extraction and recovery using biohydrometallurgical approaches

Biomining

Technology based on the oxidative dissolution of sulfide minerals by prokaryotic microorganisms that facilitates the recovery of metals

• Bioleaching: metals are brought into solution (e.g. Cu)

• Bio-oxidation: metals are made accessible for chemical extraction (e.g. Au)

Biohydrometallurgy

• A sub-division of hydrometallurgy (“the use of aqueous chemistry for the recovery of metals from ores, concentrates, and recycled or residual materials”) that uses microorganisms in one or more stages of a process

• Usually (but not always) constrained to operate in conditions where microorganisms are metabolically active

1. A brief history of biomining

Late 1940’s:A novel bacterium isolated from water draining an abandoned coal mine that could oxidize both iron and sulfur at low pH“Thiobacillus ferrooxidans”

Early 1950’s:Other similar bacteria isolated; also found that these bacteria could solubilize pyrite

Fe2+ + 0.25 O2 + H+ → Fe3+ + 0.5H2O

S0 + 1.5 O2 + H2O → SO42- + 2H+

8 FeS2 + 30 O2 + 18 H2O → Fe8O8(OH)6SO4 + 30 H+ + 15 SO42-

Some milestones in the development of bioprocessing of mineral ores using acidophilic prokaryotes ("biomining")

Date Location Operation

18th & 19th centuries Spain, U.K. Leaching of copper ores in “precipitation ponds”

1960s U.S.A. Copper dump leaching(Kennecott Corporation)

1960s-1990s Ontario, Canada In situ mining of uranium

1980-1996 Lo Aguirre, Chile Bioheap leaching of copper (with SX/EW)

1986- Fairview, South Africa Bioprocessing of gold ore concentrate in aerated stirred tanks.

1995- Nevada, U.S.A. Bioheap leaching of gold ore.

1999-2013 Kasese, Uganda Bioprocessing of cobaltiferous ores in stirred- tank bioreactors

2004-2005 Chuquicamata, Chile Thermophilic leaching of chalcopyrite concentrate

2008- Talvivaara, Finland Bioheap leaching of a polymetallicblack schist (Ni, Zn, Cu)

acid irrigation

Pregnant Leach Solution

First “biomining” operation, mid 1960’s: Bingham copper mine, Utah

“Dump” leaching of low grade (run-of-mine) waste rock

Dexing copper mine, China

Cementation:Cu2+ + Fe0 Cu0 + Fe2+

irrigation

PLS stream

Kennecott Chino Mine, New Mexico

ROM dumps

1970’s: in situ bioleaching of uranium (Canada)

• Used to extract uranium from otherwise worked-out mines

• Underground workings blasted, flooded for a period and then drained

• UO22+ recovered from leach liquors

In situ biomining had been used long before the discovery of bacteria:Periodic flooding of underground working at the Mynydd Parys copper mine (Wales) allowed Cu to be recovered for >100 years after active mining had ended

1980’s: heap bioleaching of copper (mostly Chile)

Escondida, copper mine, Chile

2 km

5 km

electrowinning acid irrigation

copper ore heap

solvent extraction

copper metal

PregnantLiquorSolution

raffinate

impermeable membrane

air blowers

inoculation

Typical circuit design: copper bioheap operation

Acidicaldus

Sb. acidophilus YTF1

Sb. thermosulfido

Irrigation and inoculation: Talvivaara Ni Mine (Finland)

Heap aeration

Talvivaara Escondida

Stirred tank leaching

• Used for mineral concentrates (chiefly refractory gold) and at pulp densities of ~20%

• Most stirred tanks operate at between 35 and 45C; cooling is a major operating cost

• Tanks are generally constructed of high-grade stainless steel

• Tanks are actively aerated

• Agitation (stirring) is another major operational cost

• Minerals are processed in a matter of days (~3-6)

1980’s: tank leaching of refractory gold (Fairview: South Africa)

Initially processed14 tons concentrate/day, now 55 t/day

Suzdal BIOX plant (Kazakhstan): 192 t gold concentrate/day in sub-zero temperatures

A more recent operation at Kokpatas (Uzbekistan) is designed to process over 160,000 t of refractory gold concentrate/year

Gold Biomining in Asia

2. Using microorganisms to mobilize and immobilize metals

• by effecting redox transformations

• by mediating changes in pH

• via production of metabolic products/wastes

Pyrite Talc Diamond Goethite

Hardness(Mohs scale)

6.5 1 10 5.25

Density (g/cm3)

5.0 2.7 3.5 3.8

Many transition metals form hard and dense sulfide minerals

The reduced sulfur present in these minerals (oxidation state of -2 in chalcocite (Cu2S) and -1 in pyrite (FeS2) represents a potential energy source for some highly specialised bacteria and archaea)

In iron-containing sulfide minerals (e.g. pyrite and chalcopyrite (CuFeS2) the iron is present in its reduced (Fe2+) form, which again is a potential energy source for some life forms

The problem is how to access this energy!

→ sulfide mineral-degrading bacteria use ferric iron (Fe3+) as the tool to unlock the energy-rich sulfides

FeS2

6Fe3+

7Fe2+

Abiotic dissolution of pyrite at low pH by ferric iron

S2O32-

3H2O

6H+

FeS2

Fe3+

2Fe2+

Fe3+

Fe2+

Dissolution of pyrite at low pH: role of primary* microorganisms

*Fe-oxidizing acidophiles

O2

FeS2

Fe3+

2Fe2+

Fe3+

Fe2+

Dissolution of pyrite at low pH: role of primary* microorganisms

*Fe-oxidizing acidophiles

Contact leaching Non-contact leaching

FeS2

Fe3+

2Fe2+

Fe3+

Fe2+

S2O32-Polythionates, S0

Fe3+Fe2+

SO42-, H+

Dissolution of pyrite at low pH: role of secondary* microorganisms

*S-oxidizing acidophilesO2

O2

FeS2

Fe3+

2Fe2+

Fe3+

Fe2+

S2O32-Polythionates, S0

Fe3+Fe2+

SO42-, H+

Dissolution of pyrite at low pH: self inhibition by autotrophs

DOC*

DOC*

DOC*

X

X

X

*Dissolved Organic Carbon

FeS2

Fe3+

2Fe2+

Fe3+

Fe2+

S2O32-Polythionates, S0

Fe3+Fe2+

SO42-, H+

Dissolution of pyrite at low pH: role of tertiary* microorganisms

DOC

DOC

DOC

CO2

*heterotrophic acidophiles

Microorganisms that can be anticipated to be found* in mineral bioleach liquors -

1. Primary Group: iron-oxidisers (autotrophs)

2. Secondary Group: sulfur-oxidisers (autotrophs)

3. Tertiary Group: heterotrophic acidophiles- iron-oxidisers- iron-reducers- sulfur-oxidisers

*occurrence does not imply that the organism(s) is fulfilling a useful function, so far as the commercial objective is concerned

Lithotrophic (“rock eating”) prokaryotes

Unexposed rock

Pitted rock due to selective dissolution of sulfidic minerals

Bioleaching of base metal sulfides:target metals are solubilised

SiO2

FeS2(Fe,Ni)9S8

FeS2

Fe/S bacteriaSiO2

Ni2+

Fe3+ SO42-

Bio-oxidation of refractory gold ores:dissolution of sulfide minerals exposes metallic gold

Au

FeS2FeAsS

Au

FeS2

FeS2

CN-

Fe/S bacteria

Au(CN)4-

Bioleaching of uranium ores:ferric iron oxidizes insoluble U(IV) to soluble U(VI)

Fe3+

Fe2+

UO2

UO2 2+

Acidithiobacillus spp.

Leptospirillum spp. etc.

Physiological restrictions in using microorganisms for mineral processing

• Temperature

• pH

• Pressure

• Osmotic/salt stress

Leptospirillum ferrooxidansAcidithrix ferrooxidans

Sulfolobus sp.

Temperature/pH

65

At. ferrooxidans

T. prosperus/"Fm.acidiphilum"

L. ferrooxidans

L. thermoferrooxidans

Ac. brierleyi

Sc. yellowstonensis

Sb. thermosulfidooxidans/acidophilus

Fp. acidiphilum

Metallosphaera spp.

Fp. acidarmanus

Sb.montserratensis

Am.ferrooxidans

S.metallicus

pH

Tem

pera

ture

(o C)

0.0 1.0 2.0 3.0 4.0

35

45

55

75

Metal recovery via biosulfidogenesis

• Bacteria can generate H2S from inorganic S-sources (sulfate, elemental sulfur etc.)

• They require an electron donor (energy source) to do this

• H2S reacts with many metals to produce highly insoluble metal sulfides

4 C3H8O3 + 7 SO42- + 14 H+ → 12 CO2 + 7 H2S + 16 H2O

H2S + Me2+ → MeS↓ + 2 H+

Acidophilic sulfidogenic system using an

Upflow Biofilm Reactor (UBR)

Packed bed(immobilized SRB)

pH electrodeFeed in(pH 1.5‐4)

Effluent out(pH 2‐5)

meterpump

pH electrode

Feed in(pH 1.8-4)

Effluent out(pH 2-5)

pumpH2S stream →

In-line metal precipitation bioreactor Off-line metal precipitation vessel

meter

Colonised beads

(immobilised SRB)

Can be used for off-line and in-line metal precipitation

Selective on-line and off-line precipitation of metals using a single acidophilic sulfidogenic bioreactor

Off-line precipitation of CuS

In line precipitation of ZnS and CoS

3. Some more recent developments in biomining technologies

- thermophilic bioleaching

- indirect bio-oxidation of sulfide minerals

- reductive dissolution of oxidized ores

- selective removal of metals from leach liquors using biomineralization at low pH

2004-2005:

Thermophilic (70-80C) stirred tanks for processing chalcopyrite concentrates (Chuquicamata, Chile)

Objectives:• efficient bioleaching of chalcopyrite (CuFeS2)• faster rates of mineral dissolution• reduced cooling costs

Indirect leaching of mineral concentrates

• mineral oxidation (by ferric iron: abiotic) is separated from ferrous iron oxidation (biological) in a two-stage process

• each process can be operated at optimum conditions of temperature, pH and oxygen concentration

• demonstrated at pilot-scale for processing zinc sulfide concentrates (BioMinEproject)

ZnS bacteria

PLSZn2+ & Fe2+

Zn stripping

Two-stage (“indirect leaching) of zinc sulfide concentrate

Mineral leaching reactor(anoxic; 80-90˚C)

Fe3+ regeneration reactor (aerated; ~45˚C)

Fe3+

Fe2+

Ferric iron-regenerating bioreactor

The BioMOre project (2015-): deep in situ (bio)leaching of a sulfidic ore body

• an indirect bioleaching process is envisaged, whereby acidic ferric iron-rich leach liquors are regenerated in surface bioreactors and injected through boreholes into the fractured ore deposit

Bio-processing of oxidized ores using reductive dissolution

“biomining in reverse gear”

• a process for using bacteria to extract metals from ores and waste materials in

which the primary reaction is that of ferric iron reduction rather than ferrous iron

oxidation

Ni-laterite ore, Western Australia

FeO.OH NiFeO.OH Ni

FeO.OH Ni FeO.OH Ni

FeO.OH Ni

FeO.OH Ni

FeO.OH Ni

FeO.OH Ni

FeO.OH Ni

FeO.OH NiFeO.OH Ni

Ni FeO.OHNi FeO.OH

Ni FeO.OHNi FeO.OH

Ni FeO.OH

Fe2+, Ni2+ , OH-

S0 SO42-

In contrast to conventional mineral bio-processing, “reverse gear” biomining uses acidophilic bacteria to catalyse the reductive dissolution of

oxidized minerals at low pH

Selective precipitation of metal sulfides by using acidophilic SRB

• The solubility products of chalcophilic metal sulfides show great variation

• The concentration of the key reactant (S2-) varies with pH

([Me2+ ] [S2-] > Ksp for MeS to form)

• This facilitates selective recovery of transition metals as their sulfide phases, by varying and controlling pH

pH 2 pH 4 pH 7

Fe2+ Fe2+ Fe2+ FeS

Zn2+ Zn2+ ZnS

Cu2+ CuS

Log Ksp

Cu2+

Cd2+

Zn2+

Co2+

Ni2+

Fe2+

Mn2+

-35.9

-28.9

-24.5

-22.1

-21.0

-18.8

-13.3

Modular units for treating and recovering metals from mine-impacted waters and mine process waters

Zn-capturing reactor Cu-capturing reactor

schwertmannite-generating reactor

4. Where do “strategic metals” fit into this?

(i) E-tech elements (in bold & italics), from Critical Metals in Strategic Energy Technologies, Critical Metals Strategy and Critical Metals for the EUS

(ii) EU Raw Materials Initiative COM (2008) 699. Critical raw materials for the EU

(ii) “E-tech elements”; Natural Environment Research Council (UK), 2013.

Importance to environmental technologies

Science op

portun

ity

(a) Cobalt has already been successfully biomined from pyritic tailings (via oxidative bioleaching) in Kasese (Uganda)

Tailings waste (from copper mining)Acid mine drainage

Bioleaching of cobaltiferous pyrite in tanks is followed by electrowinning, producing a high-quality product (~99.9% Co)

Stirred tank bioleaching: Kasese

Man

gane

se s

olub

ilise

d (m

g L-

1 )

Cob

alt s

olub

ilise

d (m

g L-

1 )

Co

Mn

anaerobic

aerobic

Time (days)

Ni laterites also contain significant amount of Co (mostly associated with Mn(IV) minerals); this too can bioleached using a reductive approach

(Ni,Co)xMn(O,OH)4.nH2O Ni2+ , Co2+ , Mn2+

asbolane Fe2+ Fe3+

A variety of biological options exist for downstream capturing of Co from PLS

Reduced ores(sulfides)

Oxidized ores (laterites etc.)

Oxidative(bio)leaching

Reductive(bio)leaching

PLS Other solubilized metals

H2S

SRB

fungi

oxalate

CoC2O4 CoCO3urea

carbonate

CoS

Fungal leaching

Abiotic (chemical) leaching

• Low carbon/energy (“green”) extractive technologies

• Cobalt products may be sourced for the metal or used directly in other applications (as nanoparticles)

Direct reductive bio‐conversion

Bio‐nanomaterials

(b) Indium:

• Found in association with ZnS in sulfide ore bodies

• ZnS is readily bioleached (directly or indirectly), potentially facilitating the extraction and recovery of In

(c) Gallium:

• By product of the production of Al (bauxite) and Zn (sulfide ores)

• Extraction/recovery of Ga from bioleached ZnS ores is a possibility

(d) REE (and PGM):

• Unlikely to be susceptible to bioleaching

• Biooxidation and/or bioreduction could be used to remove encapsulating minerals

Removal of ferric iron deposits coating valuable minerals/precious metals

- rare earth element (REE) minerals (monazite etc.)

- silver, gold, PGMs

monazite(REE phosphates)

ferric oxy-hydroxide

bio-reduction+ Fe2+

Process analogous to bio-oxidation of refractory gold ores

Summary:

1. Biohydrometallurgical processes are long established for extracting metals from primary ores and mineral wastes, and also for recovering metals from leachate liquors

2. With the exception of Co, none of the metals on the “critical lists” have so far been targeting for bio-extraction/recovery

3. Innovations in biohydrometallurgy, such as reductive bioprocessing, open up new opportunities for metal extraction and recycling

4. “Urban (bio)mining” (extraction and recovery of metals from waste electrical and electronic equipment:WEEE) provides another opportunity to develop and used biohydrometallurgy. Downstream (selective) recovery of metals would probably be the major technological challenge

Underground workings, Mynydd Parys copper mine (Wales); abandoned for 200 years

Diolch yn fawr!

Bangor Acidophile

ResearchTeam