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

D. Barrie Johnson College of Natural Sciences, Bangor University, UK Bangor Acidophile Research Team • 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 biomining technologies

• 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

• A sub-division of hydrometallurgy (“the use of aqueous chemistry for the recovery of metals from , 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

Biomining

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

• : metals are brought into solution (e.g. Cu) • Bio-oxidation: metals are made accessible for chemical extraction (e.g. Au) 1. A brief history of biomining

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

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

2+ + 3+ Fe + 0.25 O2 + H → Fe + 0.5H2O

0 2- + S + 1.5 O2 + H2O → SO4 + 2H

+ 2- 8 FeS2 + 30 O2 + 18 H2O → Fe8O8(OH)6SO4 + 30 H + 15 SO4 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 ores in “precipitation ponds”

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

1960s-1990s Ontario, Canada In situ of

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

1986- Fairview, South Africa Bioprocessing of 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 polymetallic black schist (Ni, Zn, Cu) First “biomining” operation, mid 1960’s: Bingham copper mine, Utah

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

acid irrigation

Pregnant Leach Solution Dexing copper mine, China Kennecott Chino Mine, New Mexico

ROM dumps

irrigation

PLS stream

Cementation: Cu2+ + Fe0  Cu0 + Fe2+ 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

2+ •UO2 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)

5 km

2 km

Escondida, copper mine, Chile

Typical circuit design: copper bioheap operation

inoculation copper metal

raffinate

acid irrigation

electrowinning

copper ore heap Pregnant Liquor air blowers Solution solvent extraction

impermeable membrane Irrigation and inoculation: Talvivaara Ni Mine (Finland)

Sb. acidophilus YTF1

Sb. thermosulfido

Acidicaldus 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 45C; 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 Gold Biomining in Asia

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 2. Using microorganisms to mobilize and immobilize metals

• by effecting transformations

• by mediating changes in pH

• via production of metabolic products/wastes Many transition metals form hard and dense sulfide minerals

Pyrite Talc Diamond Goethite

Hardness 6.5 1 10 5.25 (Mohs scale) Density 5.0 2.7 3.5 3.8 (g/cm3) 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 )

In iron-containing sulfide minerals (e.g. pyrite and chalcopyrite 2+) (CuFeS2) the iron is present in its reduced (Fe 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 Abiotic dissolution of pyrite at low pH by ferric iron

6H+

7Fe2+

FeS2

6Fe3+

3H2O

2- S2O3 Dissolution of pyrite at low pH: role of primary* microorganisms

2Fe2+ Fe2+

FeS2 O2

Fe3+ Fe3+

*Fe-oxidizing acidophiles Dissolution of pyrite at low pH: role of primary* microorganisms

2Fe2+ Fe2+

FeS2

Fe3+ Fe3+

Contact leaching Non-contact leaching

*Fe-oxidizing acidophiles Dissolution of pyrite at low pH: role of secondary* microorganisms

2Fe2+ Fe2+ FeS 2 O2

Fe3+ Fe3+

Fe2+ Fe3+

2- Polythionates, S0 S2O3

O2 SO 2-, H+ 4 *S-oxidizing acidophiles Dissolution of pyrite at low pH: self inhibition by autotrophs

X 2Fe2+ Fe2+ FeS DOC* 2

Fe3+ Fe3+ X Fe2+ Fe3+

0 S O 2- Polythionates, S X 2 3 DOC* DOC*

2- + SO4 , H *Dissolved Organic Carbon Dissolution of pyrite at low pH: role of tertiary* microorganisms

CO2

2Fe2+ Fe2+ FeS DOC 2

Fe3+ Fe3+

Fe2+ Fe3+

0 S O 2- Polythionates, S 2 3 DOC

DOC

SO 2-, H+ 4 *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

Ni2+

(Fe,Ni)9S8 FeS2

SiO2 SiO2 Fe/S bacteria

FeS 2- 2 Fe3+ SO4 Bio-oxidation of refractory gold ores: dissolution of sulfide minerals exposes metallic gold

FeAsS FeS2 FeS2 Fe/S bacteria Au Au

CN-

FeS2 - Au(CN)4 Bioleaching of uranium ores: ferric iron oxidizes insoluble U(IV) to soluble U(VI)

2+ UO2 Fe2+ spp. UO2 Leptospirillum spp. Fe3+ etc. Physiological restrictions in using microorganisms for mineral processing

• Temperature

•pH

• Pressure

• Osmotic/salt stress

Leptospirillum ferrooxidans sp. Acidithrix ferrooxidans Temperature/pH

75 Metallosphaera spp.

Ac. brierleyi S.metallicus

65 Sc. yellowstonensis C) o (

55

Sb. thermosulfidooxidans/acidophilus Temperature Am.ferrooxidans 45 L. thermoferrooxidans

Fp. acidarmanus

L. ferrooxidans Fp. acidiphilum T. prosperus/"Fm.acidiphilum" 35 At. ferrooxidans Sb.montserratensis

0.0 1.0 2.0 3.0 4.0 pH 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

2- + 4 C3H8O3 + 7 SO4 + 14 H → 12 CO2 + 7 H2S + 16 H2O

2+ + H2S + Me → MeS↓ + 2 H Acidophilic sulfidogenic system using an Upflow Biofilm Reactor (UBR)

pump meter

pH electrode Feed in Effluent out (pH 1.5‐4) (pH 2‐5)

Packed bed (immobilized SRB) Can be used for off-line and in-line metal precipitation

H2S stream → pump meter

Feed in pH Effluent out (pH 1.8-4) electrode (pH 2-5)

Colonised beads (immobilised SRB)

In-line metal precipitation bioreactor Off-line metal precipitation vessel Selective on-line and off-line precipitation of metals using a single acidophilic sulfidogenic bioreactor

In line precipitation of ZnS and CoS

Off-line precipitation of CuS 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 (70-80C) 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 sulfide concentrates (BioMinE project) Two-stage (“indirect leaching) of zinc sulfide concentrate

Fe3+ Fe2+

3+ Mineral leaching reactor Fe regeneration (anoxic; 80-90˚C) reactor ZnS bacteria (aerated; ~45˚C)

PLS 2+ 2+ Zn & Fe Zn stripping 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 In contrast to conventional mineral bio-processing, “reverse gear” biomining uses acidophilic bacteria to catalyse the reductive dissolution of oxidized minerals at low pH

Ni FeO.OHFeO.OH Ni FeO.OH Ni S0 SO 2- FeO.OH Ni 4 FeO.OH NiFeO.OH Ni Ni FeO.OH Ni FeO.OH FeO.OH Ni FeO.OH Ni Fe2+, Ni2+ , OH- FeO.OH Ni FeO.OH Ni FeO.OH Ni Ni FeO.OH Ni FeO.OHFeO.OH Ni 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

2+ 2- ([Me ] [S ] > Ksp for MeS to form)

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

Log Ksp

2+ pH 2 pH 4 pH 7 Cu -35.9 Cd2+ -28.9 2+ 2+ 2+ Fe Fe Fe FeS Zn2+ -24.5 Zn2+ Zn2+ ZnS Co2+ -22.1 Ni2+ -21.0 2+ Cu CuS Fe2+ -18.8

Mn2+ -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. opportunity

Science

Importance to environmental technologies

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

Acid mine drainage Tailings waste (from copper mining) Stirred tank bioleaching: Kasese

Bioleaching of cobaltiferous pyrite in tanks is followed by electrowinning, producing a high-quality product (~99.9% Co) Ni laterites also contain significant amount of Co (mostlyassociatedwithMn(IV) Ni lateritesalsocontainsignificantamountof (Ni,Co) minerals); thistoocanbioleached using areductiveapproach soaeFe asbolane x Mn(O,OH) 4 .nH 2 Time O Ni 2+

-1 (days) Manganese solubilised (mg L ) Fe 3+ 2+ , Co 2+ Co aerobic Mn , Mn anaerobic 2+

Cobalt solubilised (mg L-1) A variety of biological options exist for downstream capturing of Co from PLS

Oxidative Reduced ores (bio)leaching (sulfides)

fungi CoC2O4 urea CoCO3

oxalate carbonate Fungal leaching PLS Other solubilized metals Abiotic (chemical) H S leaching 2 SRB CoS

Oxidized ores Reductive (bio)leaching (laterites etc.)

• Low carbon/energy (“green”) extractive technologies Direct reductive bio‐conversion • Cobalt products may be sourced for the metal or used directly in other Bio‐nanomaterials applications (as nanoparticles) (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

bio-reduction + Fe2+

ferric oxy- hydroxide

monazite (REE phosphates)

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 Research Team