economical recovery of base metals from leach streams … · economical recovery of base metals...
TRANSCRIPT
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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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
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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