Presentation on theme: "MINE 292 Introduction to Mineral Processing Lecture 21 John A Meech"— Presentation transcript:
1 MINE 292 Introduction to Mineral Processing Lecture 21 John A Meech HydrometallurgyMINE 292Introduction to Mineral ProcessingLecture 21John A Meech
2 Hydrometallurgical Processing Comminution (Grinding)Leaching Metal (Quantity - %Recovery)Removal of Metal from Pulpa. Solid/Liquid Separation- CCD thickeners- Staged-washing filtrationb. Adsorption (Carbon-in-Pulp and/or Resin-in-Pulp)(CIP/RIP or CIL/RIL)- granular carbon or coarse resin beads
3 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)
4 Hydrometallurgical Processing 5. Electrowinning or Precipitation followed by Smelting
7 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%solidsLeach Density = 40% solidsClassifier O/F Density = 40%solidsPregnant Solution Flowrate = 300%Barren Bleed Flowrate = 25%Gold in Barren Solution = 0.05 g/tCalculate 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?
8 Metal Recovery by Dissolution Primary extraction from oresUsed with ores that can't be treated physicallySecondary extraction from concentratesUsed with ores that can be beneficiated to a low-grade level
12 Nickel Lateritic Ores acid heap leaching method similar to copper H2SO4 much higher than for copper (1,000 kg/t)patented by BHP Billitonbeing commercialized byCerro Matoso S.A. in ColumbiaVale in BrazilEuropean Nickel Plc in Turkey, Balkans, Philippines
13 Metal Recovery by Dissolution Applied toAluminum (alkali)Al2O3 + 3H2O + 2NaOH → 2NaAl(OH)4Gold and Silver (cyanidation / alkali)Uranium (acid and alkali)
15 Aluminum SmeltingFused Salt Electrolysis – Hall-Herault Process
16 Aluminum SmeltingFused Salt Electrolysis – Hall-Herault Process
17 Uranium Acid LeachingOxidize tetravalent uranium ion (U4+) to hexa-valent uranyl ion (UO22+) using MnO2 or NaClO4About 5 kg/t of MnO2 or 1.5 kg/t of NaClO4UO22+ reacts with H2SO4 to form a uranyl sulfate complex anion, [UO2(SO4)3]4-.
19 LixiviantsLixiviant 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.- H2SO NH4OH- HCl NH4Cl or NH4CO3- HNO NaOH/KOH- HCN >> NaCN/KCN
20 Tank versus Vat Leaching Tank leaching is differentiated from vat leaching as follows:Tank LeachingFine grind (almost full liberation)Pulp flows from one tank to the nextVat LeachingCoarse material placed in a stationary vesselNo agitation except for fluid movement
21 Tank versus Vat Leaching Tanks are generally equipped withagitators,baffles,gas nozzles,Pachuca tanks do not use agitatorsTank equipment maintains solids in suspension and speeds-up leachingTank leaching continuous / Vat leaching batch
22 Tank versus Vat Leaching Some novel vat leach processes are semi-continuous with the lixiviant being pumped through beds of solids in different stagesRetention (or residence) time for vat leaching is much longer than tank leaching to achieve the same recovery level
23 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 needhigher retention times
24 Important Efficiency Factors Particle Size- material ground to size to expose desired mineralto the leaching agent (“liberation”),tank leach >>> size must be suspendable by an agitationvat leach >>> size must be most economically viable- high recovery achieved as liberation increases orkinetics faster is balanced against increased cost ofprocessing the material.Pulp density - percent solids determines retention time- determines settling rate and viscosity- viscosity controls gas mass transfer and leaching rate
25 Important Efficiency Factors Pulp density- percent solids determines retention time- determines settling rate and viscosity- viscosity controls gas mass transfer and leaching rate
26 Important Efficiency Factors Numbers of tanks- Tank leach circuits typically designed with 4 tanksDissolved gases- Gas is injected below the agitator or into the vatbottom to achieve the desired dissolved gas levels- Typically, oxygen or air, or, in some base metal plants,SO2 is used.
27 Important Efficiency Factors Reagents- Adding/maintaining appropriate lixiviant level is critical- Insufficient reagents reduces metal recovery- Excess reagents increases operating costs and may leadto lower recovery due to dissolution of other metals- recycling spent (barren) solution reduces need forfresh reagents, but deleterious compounds maybuild-up leading to reduced kinetics
28 Pressure Leaching Sulfide Leaching more complex than Oxide Leaching Refractory nature of sulfide oresPresence of competing metal reactionsPressurized vessels (autoclaves) are usedFor example, metallurgical recovery of zinc:2ZnS + O2 + 2H2SO4 → 2ZnSO4 + 2H2O + 2SReaction proceeds at temperatures above B.P. of water (100 °C)This creates water vapor under pressure inside the vessel.Oxygen is injected under pressureTotal pressure in the autoclave over 0.6 MPa.
29 Sulfide Heap Leaching Ni recovery much more complex than Cu Requires stages to remove Fe and MgProcess 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
30 Bio-LeachingThiobacillus ferrooxidans used to control ratio of ferric to ferrous ions in solution (Tf acts as a catalyst)4Fe2+(aq) + O2(g) + 4H3O+ → 4Fe3+(aq) + 4H2OFerric sulfate used to leach sulfide copper oresBasic process is acceleration of ARDTypical plant leach times for refractory gold ore is about 24 hours
32 Bio-Leaching at Snow Lake, Manitoba BacTech to use bio-leaching to deal with As and recover gold from an arsenic-bearing waste dumpTwo productsChemically-stable ferric arsenate precipitateGold-rich Residue Concentrate110 tpd of concentrate for 10 yearsAnnual production = 10,400 oz plus some AgCAPEX = $21,400,000 OPEX = $973/ozGold Recovery after toll-smelting = 88.6%
33 SX - Solvent Extraction Pregnant (or loaded) leach solution is emulsified with a stripped organic liquid and then separatedMetal is exchanged from pregnant solution to organicResulting streams are loaded organic and raffinate (spent solution)Loaded organic is emulsified with a spent electrolyte and then separatedMetal is exchanged from the organic to the electrolyteResulting streams are stripped organic and rich electrolyte
44 In-situ Leaching In 2011, 45% of world uranium production was by ISL Over 80% of uranium mining in the US and KazakhstanIn US, ISL is seen to be most cost effective and environmentally acceptable method of miningSome ISLs add H2O2 as oxidant with H2SO4 as lixiviantUS ISL mines use an alkali leach due to presence of significant quantities of gypsum and limestoneEven a few percent of carbonate minerals means that alkali leach must be used although recovery does suffer
45 In-situ LeachingAverage grades of sandstone-hosted deposits range between 0.05% to 0.40% U3O8.
48 In-situ LeachingAcid consumption varies depending on operating philosophy and geological conditionsIn Australia, it is only a fraction of that used in KazakhstanIn 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