MINE 292 Introduction to Mineral Processing Lecture 21 John A Meech Hydrometallurgy MINE 292 Introduction to Mineral Processing Lecture 21 John A Meech

Hydrometallurgical Processing Comminution (Grinding) Leaching Metal (Quantity - %Recovery) Removal of Metal from Pulp a. Solid/Liquid Separation - CCD thickeners - Staged-washing filtration b. Adsorption (Carbon-in-Pulp and/or Resin-in-Pulp) (CIP/RIP or CIL/RIL) - granular carbon or coarse resin beads

Hydrometallurgical Processing 4. Purification (Quality - g/L and removing other ions) - Clarification and Deaeration (vacuum) - Precipitation (Gold: Zn or Al dust) (Copper: H2S or scrap Fe or lime) (Uranium: yellow cake) (Zinc: lime) - Solvent Extraction (adsorption into organic liquid) - Ion Exchange (resin elution columns) - Elution (contact carbon or resin with an electrolyte)

Hydrometallurgical Processing 5. Electrowinning or Precipitation followed by Smelting

Hydrometallurgical Processing

Hydrometallurgical Processing Classifier

Hydrometallurgical Processing Feed Grade = 5 g Au/t Ore %Recovery during Grinding = 60% >>> solids content = 2.00 g/t %Recovery during Leaching = 35% >>> solids content = 0.25 g/t %Recovery during CCD = 0% %Recovery Total = 95% Underflow Densities = 50%solids Leach Density = 40% solids Classifier O/F Density = 40%solids Pregnant Solution Flowrate = 300% Barren Bleed Flowrate = 25% Gold in Barren Solution = 0.05 g/t Calculate the gold content of the Pregnant Solution and the U/F water from each thickener. What is the actual mill recovery? What difference would occur if fresh solution was added to Thickener E rather than Thickener B?

Metal Recovery by Dissolution Primary extraction from ores Used with ores that can't be treated physically Secondary extraction from concentrates Used with ores that can be beneficiated to a low-grade level

Metal Recovery by Dissolution Applied to Copper (both acid and alkali) CuO + H2SO4 → CuSO4 + H2O Cu+2 + 4NH4OH → Cu(NH3)4+2 + 4H2O Zinc (acid) ZnO + H2SO4 → ZnSO4 + H2O Nickel (acid and alkali) – Nickel Laterite Ores NiO + H2SO4 → NiSO4 + H2O NiO + 6NH4OH → Ni(NH3)62+ + H2O

Ammonia Leaching of Malachite NH4Cl → NH4+ + Cl– (1) NH4+ + H2O → H3O+ + NH3 (2) CuCO3·Cu(OH)2 + 2H3O+ → Cu2+ + CO2 + 3H2O + Cu(OH)2 (3) Cu(OH)2 + 2H3O+ → Cu2+ + 2H2O (4) Overall Leaching Reaction CuCO3·Cu(OH)2 + 4 NH4Cl → 2Cu2+ + 4Cl– + CO2 +3H2O +4NH3 (5) Formation of complex amine ions Cu2+ + 2NH3 → Cu(NH3)22+ (6) Cu(NH3)22+ + 2NH3 → Cu(NH3)42+ (7)

Zinc Roasting/Leaching/Electowinning

Nickel Lateritic Ores acid heap leaching method similar to copper H2SO4 much higher than for copper (1,000 kg/t) patented by BHP Billiton being commercialized by Cerro Matoso S.A. in Columbia Vale in Brazil European Nickel Plc in Turkey, Balkans, Philippines

Metal Recovery by Dissolution Applied to Aluminum (alkali) Al2O3 + 3H2O + 2NaOH → 2NaAl(OH)4 Gold and Silver (cyanidation / alkali) Uranium (acid and alkali)

Alumina Leaching

Aluminum Smelting Fused Salt Electrolysis – Hall-Herault Process

Aluminum Smelting Fused Salt Electrolysis – Hall-Herault Process

Uranium Acid Leaching Oxidize tetravalent uranium ion (U4+) to hexa-valent uranyl ion (UO22+) using MnO2 or NaClO4 About 5 kg/t of MnO2 or 1.5 kg/t of NaClO4 UO22+ reacts with H2SO4 to form a uranyl sulfate complex anion, [UO2(SO4)3]4-.

Leaching Processes Tank Leaching (Agitation) Vat Leaching Pressure Leaching (high temperature/pressure) Biological Leaching (Bacteria) Heap Leaching In-situ Leaching (solution mining)

Lixiviants Lixiviant is a liquid medium used to selectively extract a desired metal from a bulk material. It must achieve rapid and complete leaching. The metal is recovered from the pregnant (or loaded) solution after leaching. The lixiviant in a solution may be acidic or basic in nature. - H2SO4 - NH4OH - HCl - NH4Cl or NH4CO3 - HNO3 - NaOH/KOH - HCN >> NaCN/KCN

Tank versus Vat Leaching Tank leaching is differentiated from vat leaching as follows: Tank Leaching Fine grind (almost full liberation) Pulp flows from one tank to the next Vat Leaching Coarse material placed in a stationary vessel No agitation except for fluid movement

Tank versus Vat Leaching Tanks are generally equipped with agitators, baffles, gas nozzles, Pachuca tanks do not use agitators Tank equipment maintains solids in suspension and speeds-up leaching Tank leaching continuous / Vat leaching batch

Tank versus Vat Leaching Some novel vat leach processes are semi-continuous with the lixiviant being pumped through beds of solids in different stages Retention (or residence) time for vat leaching is much longer than tank leaching to achieve the same recovery level

Important Efficiency Factors Retention time = total volume of tanks / slurry volumetric flow - normally measured in hours - gold: 24 to 72 hours - copper: 12 to 36 hours - sequence of tanks called a leach "train" - mineralization & feed grade changes may need higher retention times

Important Efficiency Factors Particle Size - material ground to size to expose desired mineral to the leaching agent (“liberation”), tank leach >>> size must be suspendable by an agitation vat leach >>> size must be most economically viable - high recovery achieved as liberation increases or kinetics faster is balanced against increased cost of processing the material. Pulp density - percent solids determines retention time - determines settling rate and viscosity - viscosity controls gas mass transfer and leaching rate

Important Efficiency Factors Pulp density - percent solids determines retention time - determines settling rate and viscosity - viscosity controls gas mass transfer and leaching rate

Important Efficiency Factors Numbers of tanks - Tank leach circuits typically designed with 4 tanks Dissolved gases - Gas is injected below the agitator or into the vat bottom to achieve the desired dissolved gas levels - Typically, oxygen or air, or, in some base metal plants, SO2 is used.

Important Efficiency Factors Reagents - Adding/maintaining appropriate lixiviant level is critical - Insufficient reagents reduces metal recovery - Excess reagents increases operating costs and may lead to lower recovery due to dissolution of other metals - recycling spent (barren) solution reduces need for fresh reagents, but deleterious compounds may build-up leading to reduced kinetics

Pressure Leaching Sulfide Leaching more complex than Oxide Leaching Refractory nature of sulfide ores Presence of competing metal reactions Pressurized vessels (autoclaves) are used For example, metallurgical recovery of zinc: 2ZnS + O2 + 2H2SO4 → 2ZnSO4 + 2H2O + 2S Reaction proceeds at temperatures above B.P. of water (100 °C) This creates water vapor under pressure inside the vessel. Oxygen is injected under pressure Total pressure in the autoclave over 0.6 MPa.

Sulfide Heap Leaching Ni recovery much more complex than Cu Requires stages to remove Fe and Mg Process produces residue and precipitates from recovery plant (iron oxides/Mg-Ca sulfates) Final product – Ni(OH)2 precipitates (NHP) or mixed metal hydroxide precipitates (MHP) that are smelted conventionally

Bio-Leaching Thiobacillus ferrooxidans used to control ratio of ferric to ferrous ions in solution (Tf acts as a catalyst) 4Fe2+(aq) + O2(g) + 4H3O+ → 4Fe3+(aq) + 4H2O Ferric sulfate used to leach sulfide copper ores Basic process is acceleration of ARD Typical plant leach times for refractory gold ore is about 24 hours

Bio-Leaching

Bio-Leaching at Snow Lake, Manitoba BacTech to use bio-leaching to deal with As and recover gold from an arsenic-bearing waste dump Two products Chemically-stable ferric arsenate precipitate Gold-rich Residue Concentrate 110 tpd of concentrate for 10 years Annual production = 10,400 oz plus some Ag CAPEX = $21,400,000 OPEX = $973/oz Gold Recovery after toll-smelting = 88.6%

SX - Solvent Extraction Pregnant (or loaded) leach solution is emulsified with a stripped organic liquid and then separated Metal is exchanged from pregnant solution to organic Resulting streams are loaded organic and raffinate (spent solution) Loaded organic is emulsified with a spent electrolyte and then separated Metal is exchanged from the organic to the electrolyte Resulting streams are stripped organic and rich electrolyte

Solvent Extraction Mixer/Settler

Reason for 4 Stages of SX

Solvent Extraction and Heap Leaching

Ion Exchange Resins AMn = synthetic ion-exchange resin (class A - 0.6–1.6 mm) Phenyl tri-methyl ammonium functional groups Macro-porous void structure Similar to strong base anion exchange resins Zeolite MPF (GB) Amberlite IRA (USA) Levatite MP-500 (FRG) Deion PA (JPN)

Resin-In-Pulp Pachuca Tank

Resin-In-Pulp Pachuca Tanks

Resin-In-Pulp Pachuca Tanks

Kinetics of RIP for Uranium

Effect of pH on RIP for Uranium

RIP Recovery in each stage

In-situ Leaching In 2011, 45% of world uranium production was by ISL   Over 80% of uranium mining in the US and Kazakhstan In US, ISL is seen to be most cost effective and environmentally acceptable method of mining Some ISLs add H2O2 as oxidant with H2SO4 as lixiviant US ISL mines use an alkali leach due to presence of significant quantities of gypsum and limestone Even a few percent of carbonate minerals means that alkali leach must be used although recovery does suffer

In-situ Leaching Average grades of sandstone-hosted deposits range between 0.05% to 0.40% U3O8.

In-situ Leaching

In-situ Leaching

In-situ Leaching Acid consumption varies depending on operating philosophy and geological conditions In Australia, it is only a fraction of that used in Kazakhstan In Kazakh , about 40 kg acid per kg U (ranging from 20-80) Beverley mine in Australia in 2007 was 7.7 kg/kg U.  Power consumption is about 19 kWh/kg U (16 kWh/kg U3O8) in Australia and around 33 kWh/kg U in Kazakhstan www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Mining-of-Uranium/In-Situ-Leach-Mining-of-Uranium/#.UUihT1fQhLo

In-situ Leaching – well patterns

EMF Chart