23-4-2012

Economical recovery of base metals from leach streams

after gold recovery

Date:

Place:

Author:

In collaboration with:

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• Background

• Metal sulfide precipitation

• Thioteq process

• Case 1

• Case 2

• Economics

• Conclusions

Content

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Common sight near mining operations

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Has been, and still is, accepted treatment, but:

• Moderate effluent sulfate (1500 - 2000 mg/L SO4)

• High Dissolved Solids output

• Long-term environmental liabilities

• Increasing costs for reagents and sludge storage

• Resources are wasted (metals & chemicals)

Reason: Simple lime treatment

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• Acid mine drainage treatment

Consumes 30% of total lime consumption for

wastewater treatment

• Results in approx. 80 Mton/a of heavy metal

polluted gypsum

• Conversion of CaCO3 + fuel to CaO releases CO2

Sustainability?!

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Step 1: Metals

• Metal removal as metal sulfide (not hydroxide)

– Low solubility

– Recovery of metals

– Compact sludge

Step 2: Sulfate

• Removal of dissolved sulfate as:

– Clean gypsum (construction material) or

– Elemental biosulfur

Solution ?

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(In-)Solubility of Metal Sulfides

CdS

PbS

NiS

As2S3

Zn(OH)2

Cd(OH)2

Ni(OH)2

NiS

Ni(OH)2

Cu(OH)2

Pb(OH)2

CuS PbS

ZnS

ZnS

pH

Soluble metal concentration [mg/L]

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• Buy it: Transport and storage

– Dangerous and expensive

• Make it: Chemical production on-site

– High investment costs

– Dangerous

Sulfide!? Where from??

Safe & Reliable biotechnology makes it possible

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• What is Thioteq™ process?

– Safe and economic base metal recovery from low-concentrated (50 ~ 1000 mg/l) leach & bleed streams

• What does Thioteq™ produce?

– Pure & compact high quality sulfide precipitate

• What does Thioteq™ consume?

– Elemental sulfur, ethanol (or equivalent) and fertiliser-like nutrients

•

THIOTEQ™ PROCESS

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Advantages: Cheap and safe H2S production Water conditions no issue Selective MeS recovery possible Better than settling & dewatering, and

lower costs than with NaSH

Block diagram

Disadvantages: No sulfate removal pH drops

Sulfur-feed

E-donor (Alcohol, acetate

or H2)

Rich gas Metal sulfides

product

Process stream with

dissolved metals

Lean gas

23-4-2012

Biologically produced H2S

Solid

elemental

sulfur (S80)

-

Hydrogen

sulfide

(H2S)

- H

Dissolved elemental

sulfur (polysulfide)

- H

Sulfur

reducing

bacteria

Overall conversion:

S0(s) + H2(g->l) -> H2S(l->g)

Mechanism:

23-4-2012

Example: Copper recovery

INFLUENT (mg/l) EFFLUENT (mg/l) Leach water Copper 200 < 1 Ground water Zinc 82 < 0.2 Aluminium 2412 < 2 Calcium 450 50 Copper 44 < 0.1 Iron 512 < 0.1 Magnesium 2640 990 Manganese 200 < 0.4 Sulfate 25000 < 500

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Example of selective metal recovery

Sulfur-feed

E-donor (Alcohol, acetate

or H2)

Rich gas As2S3

Lean gas

CuS

23-4-2012

POX at gold mine

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Case 1: Base metal recovery after pressure leach

PAL Gold

recovery Iron

removal

THIOTEQ

Copper & zinc

recovery

Final

neutralisatio

n

Gold Iron/gypsum

sludge

Zinc

sulfide Copper

sulfide

Gypsum

Water

recycle /

discharge

• Recovery of 50 kton/yr copper as CuS

• Elemental sulfur & ethanol as main consumables

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• CCD wash solution: 1,900 m3/hr

• Zn: ~870mg/L, Cu ~ 285 mg/L

• Base water treatment case:

• Assume metal net back • Zn (38 ton/d) @ 0.65 $/lb & Cu (5.9 ton/d) @ 2.13 $/lb

Base metal revenue possible: 30 M$/yr

Example 2: Mine with POX

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• Optimal solution: Combination of Thioteq with lime/gypsum

Mine with oxidative leach

Iron removal Copper precipitation Zinc precipitation Final neutralisation

CaCO3 CaCO3 / Ca(OH)2

Optional : Air CaSO4 CuS ZnS CaSO4

Fe(OH)3 Al(OH)3

AsO4 H2S gas recycle Fe(OH)2

THIOTEQ bioreactor

Sulphur H2 gas from reforming LPG

Iron removal Copper precipitation Zinc precipitation Final neutralisation

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Economics

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• Effluent: 1,200 m3/hr with Zn: ~880 mg/l & Cu ~ 110 mg/L

• Zn: 24 tpd @ 1.19 US$/lb & 55% Net back

• Cu: 3.2 tpd @ 2.5 US$E/lb & 85% Net back

• Estimated capital investment: 23 million US$

Revenue Zn recovery $ 12,605,505 Cu recovery $ 5,535,297

Chemicals Sulfur $ -698,676

E-donor $ -973,090

Other $ -206,590 Power

Bioreactor $ -185,274 Contactors $ -19,710 Others $ -74,110

Labor $ -700,000

Maintenance $ -690,000 Earnings $ 14,593,352 Depreciation (10 years) $ -3,743,144 Nett annual earnings $ $10,850,208

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• Biobased process enable efficient recovery of low

concentrated metal-containing streams

• Selective recovery of base metals

• High grade concentrate-like products

• Better effluent quality, increase sustainability

• Cleaner gypsum product

• THIOTEQ is flexible, reliable & safe

Conclusions