University of SaskatchewanUniversity of Saskatchewan

Geological EngineeringGeological EngineeringGEOE 498.3GEOE 498.3

Introduction to Mineral EngineeringIntroduction to Mineral Engineering

Lecture 11 – Mineral Processing 4Lecture 11 – Mineral Processing 4

Mineral Processing OverviewMineral Processing Overview

Mineral Processing Terms, EconomicsMineral Processing Terms, Economics

Comminution and ClassificationComminution and Classification

Physical processing methodsPhysical processing methods

Chemical processing methodsChemical processing methods Waste products treatment and disposalWaste products treatment and disposal

Process plant flow sheets: uranium and potashProcess plant flow sheets: uranium and potash

These course notes are a compilation of work conducted by many people.

Notes have been taken from the following Edumine courses:

The Mill Operating Resource 1&2

Extractive Metallurgy 1&2

Hydrometallurgy 1,2,3,4

Lecture 11Lecture 11

Chemical ProcessingChemical Processing HydrometallurgyHydrometallurgy

Basic CircuitsBasic CircuitsLeachingLeachingSolvent ExtractionSolvent ExtractionPrecipitationPrecipitationDryingDrying

PyrometallurgyPyrometallurgySmeltingSmelting

ElectrometallurgyElectrometallurgyElectrowinningElectrowinning

Chemical ProcessingChemical Processing

Hydro- Versus Pyrometallurgy:Hydro- Versus Pyrometallurgy:

Techniques have competed over the yearsTechniques have competed over the years

Pyrometallurgy: Pyrometallurgy:

Very ancient technologyVery ancient technology

was most successful with high-grade, simple ores, large scalewas most successful with high-grade, simple ores, large scale

High temperature, fast reactionHigh temperature, fast reaction

Problems can include pollution of the environment, high energy Problems can include pollution of the environment, high energy consumption, and excessive dust formationconsumption, and excessive dust formation

Hydrometallurgy:Hydrometallurgy:

works better with low grade, complex ores, smaller scaleworks better with low grade, complex ores, smaller scale

Lower temperature, slower reactionLower temperature, slower reaction

First hydrometallurgical process: alumina from bauxite, at start of 20First hydrometallurgical process: alumina from bauxite, at start of 20 thth centurycentury

Hydrometallurgy TerminologyHydrometallurgy Terminology Hydrometallurgy: aqueous Hydrometallurgy: aqueous

methods of extracting metals methods of extracting metals from their ores from their ores

hydrometallurgical plant: large hydrometallurgical plant: large amounts of water are needed, amounts of water are needed, and a water balance must be and a water balance must be maintainedmaintained

Generally involves two distinct Generally involves two distinct steps:steps:

leachingleaching = Selective dissolution = Selective dissolution of the metal values from an oreof the metal values from an ore

precipitationprecipitation = Selective  = Selective recovery of the metal values recovery of the metal values from the solutionfrom the solution

Sometimes includes Sometimes includes purification/concentrationpurification/concentration

HydrometallurgyHydrometallurgy

Purposes of hydrometallurgy:Purposes of hydrometallurgy:

Recovery of salts – directly from their deposits. examples: common salt, Recovery of salts – directly from their deposits. examples: common salt, sodium carbonate, potash, borax, etc.sodium carbonate, potash, borax, etc.

Production of pure solutions - high purity metals can then be produced by Production of pure solutions - high purity metals can then be produced by electrolysis, examples:electrolysis, examples: zinc, cadmium, nickel, copper, gold, and silver.zinc, cadmium, nickel, copper, gold, and silver.

Production of pure compounds - can be subsequently used for producing Production of pure compounds - can be subsequently used for producing the pure metals by other methods. examples:the pure metals by other methods. examples: aluminum, magnesium, aluminum, magnesium, uranium, and beryllium uranium, and beryllium

Chemical beneficiation - undesirable components of the raw material are Chemical beneficiation - undesirable components of the raw material are leached away and the remaining solids are the valuable product that has to leached away and the remaining solids are the valuable product that has to be processed further. Examples: desulfurization of coalbe processed further. Examples: desulfurization of coal

Direct production of pure metals - suitable for the market after a Direct production of pure metals - suitable for the market after a

subsequent minor treatment. Examples:subsequent minor treatment. Examples: precipitation of cobalt, nickel, and precipitation of cobalt, nickel, and copper from solution by hydrogen under pressurecopper from solution by hydrogen under pressure

LeachingLeaching Before leachingBefore leaching:

usually crushed and groundusually crushed and ground

sometimes beneficiated by physical methods.sometimes beneficiated by physical methods.

In some cases treated by thermal methods, such as In some cases treated by thermal methods, such as oxidation, reduction, before being leached:oxidation, reduction, before being leached:

render the material more amenable to leaching, orrender the material more amenable to leaching, or

exclude an undesirable component. exclude an undesirable component.

Leaching is usually followed by:Leaching is usually followed by:

filtration, washing, and filtration, washing, and solution purification steps.solution purification steps.

LeachingLeaching The choice of a leaching agent depends on the following factors:The choice of a leaching agent depends on the following factors:

SolubilitySolubility. Large and rapid solubility of the material to be . Large and rapid solubility of the material to be leached in the leaching agent.leached in the leaching agent.

CostCost. An expensive reagent is undesirable because any traces . An expensive reagent is undesirable because any traces lost during handling will represent a large economic loss.lost during handling will represent a large economic loss.

Materials of constructionMaterials of construction. If the leaching agent is corrosive and . If the leaching agent is corrosive and has to be handled in tanks made of stainless steel, titanium, or has to be handled in tanks made of stainless steel, titanium, or Hastalloy, the capital cost will be high, and therefore its use will Hastalloy, the capital cost will be high, and therefore its use will be less desirable.be less desirable.

SelectivitySelectivity. An ideal reagent will extract only the desired . An ideal reagent will extract only the desired component.component.

RegenerationRegeneration. Ability of regenerating the reagent for recycle is . Ability of regenerating the reagent for recycle is also an important criteria.also an important criteria.

Leaching - SolubilityLeaching - Solubility

Water moleculesWater molecules - high polarityhigh polarity

But, Hydrogen bonds are weakBut, Hydrogen bonds are weak

Solubility of any substance in water is related to the polarity of water and the association of water molecules together by forming hydrogen bonds.

Ionic crystals: attractive forces between the anions and cations in a salt are reduced by a factor of 80 when water is the medium between them

non-ionic crystals such as metals (metallic bond) or covalent crystals like quartz (SiO2) are insoluble

Slightly soluble electrolytes are more soluble in foreign salts than in

pure water

LeachingLeaching

Water is an ideal leaching agent because it is cheap and Water is an ideal leaching agent because it is cheap and noncorrosive, but its action is only limited to few minerals. noncorrosive, but its action is only limited to few minerals.

Leaching agents commonly used other than pure water are: Leaching agents commonly used other than pure water are: Acids, bases, and aqueous salt solutionsAcids, bases, and aqueous salt solutions

Leaching agents may be used either alone or in combination with Leaching agents may be used either alone or in combination with oxidizing agents. oxidizing agents.

An oxidizing or a reducing agent is sometimes needed during An oxidizing or a reducing agent is sometimes needed during leaching to solubilize certain minerals which do not dissolve leaching to solubilize certain minerals which do not dissolve otherwise.otherwise.

Commonly used oxidizing agents are: oxygen (or air), ozone, hydrogen peroxide, ferric ion, manganese dioxide, sodium nitrate, and sodium chlorate

commonly used reducing agents are ferrous ion, hydrogen and sulfur dioxide.

LeachingLeaching

Sulfuric acid is the most common leaching agent.Sulfuric acid is the most common leaching agent.

Dilute: used for leaching copper oxide ores, zinc oxide, phosphate Dilute: used for leaching copper oxide ores, zinc oxide, phosphate rock, and a variety of other ores. rock, and a variety of other ores.

In combination with an oxidizing agent: used for leaching uranium In combination with an oxidizing agent: used for leaching uranium ores and sulfides.ores and sulfides.

Concentrated: used for treating more resistant minerals such as Concentrated: used for treating more resistant minerals such as sulfide concentrates, laterites, monazite, and titanium slag.sulfide concentrates, laterites, monazite, and titanium slag.

LeachingLeaching

Addition of oxygen to an atom, ion, Addition of oxygen to an atom, ion, or molecule is known as oxidation or molecule is known as oxidation reaction.reaction.

Removal of oxygen is known as Removal of oxygen is known as reduction.reduction.

Electrode (oxidation) potentialElectrode (oxidation) potential - The tendency of a substance to be The tendency of a substance to be oxidized or reduced, measured in oxidized or reduced, measured in voltsvolts

For reactions involving hydrogen For reactions involving hydrogen ions, the electrode potential is ions, the electrode potential is dependent on pH.dependent on pH.

LeachingLeachingLeach general principles:Leach general principles:

percent recovery is a major percent recovery is a major concernconcern

rate of a leaching process - the percent recovery as a function of time

Related factors: particle size, Related factors: particle size, concentration of leaching agent, concentration of leaching agent, temperature, pulp density, temperature, pulp density, agitation intensityagitation intensity

compromise is always made compromise is always made between the increased rate of between the increased rate of leaching and the negative effect leaching and the negative effect of any of the factors influencing of any of the factors influencing this increasethis increase

LeachingLeachingLeach general principles:Leach general principles:

After leaching, slurries obtainedAfter leaching, slurries obtained are usually filtered/thickened to are usually filtered/thickened to recover the leach solution, then washed to remove entrained solution recover the leach solution, then washed to remove entrained solution from residuesfrom residues – CCD circuit

Residues likely also need pH adjustment and heavy metal removal

LeachingLeachingAgitated pulp (tank) leaching:Agitated pulp (tank) leaching:

leaching agent added to finely ground raw material, forms a leaching agent added to finely ground raw material, forms a pulppulp

agitated continuously to prevent the solids from settling, and agitated continuously to prevent the solids from settling, and to terminate the leaching process in the shortest possible time.to terminate the leaching process in the shortest possible time.

Generally used under the following conditions:Generally used under the following conditions:

The metal values are of fine grain size and disseminated in The metal values are of fine grain size and disseminated in the host rock - extensive crushing and grinding to liberate.the host rock - extensive crushing and grinding to liberate.

Raw material is of moderate to high grade.Raw material is of moderate to high grade.

The metal values are difficult to dissolve and that is why The metal values are difficult to dissolve and that is why intensive agitation is needed to increase the rate.intensive agitation is needed to increase the rate.

Agitated LeachingAgitated LeachingAgitation may be accomplished in two ways:Agitation may be accomplished in two ways:

MechanicalMechanical: motor-driven impellers are used. More expensive : motor-driven impellers are used. More expensive capital and maintenance cost.capital and maintenance cost.

Pneumatic (pachucas)Pneumatic (pachucas): compressed air or high-pressure steam is : compressed air or high-pressure steam is used. This has the advantage of low initial cost and low maintenance used. This has the advantage of low initial cost and low maintenance cost because there are no moving parts. Steam is used instead of air cost because there are no moving parts. Steam is used instead of air when heating is desired.when heating is desired.

LeachingLeaching

High-pressure leaching:High-pressure leaching:

uses pressure reactors (or uses pressure reactors (or autoclaves).autoclaves).

Closed vesselClosed vessel

temperature higher than the boiling temperature higher than the boiling pointpoint

Without oxidizing agent: pressure generated is the result of the vapor pressure of the solution

With oxidizing agent: oxygen partial pressure is the controlling factor on leaching rate

LeachingLeaching

High-pressure leaching:High-pressure leaching:

shape may be vertical or shape may be vertical or horizontal cylinders, spherical, horizontal cylinders, spherical, or a long horizontal tubeor a long horizontal tube

Agitation: steam, mechanical impellers, or rotating the whole autoclave

media is hot and corrosive: constructed of special steel alloys, titanium, and other high-grade materials. Interior may be lined with rubber or ceramic.

usually connected in series for continuous operation.

LeachingLeaching High-pressure High-pressure leaching:leaching:

Horizontal autoclave Horizontal autoclave – oxygen addition, – oxygen addition, cascading flow. Fill to cascading flow. Fill to 65-70% to allow space 65-70% to allow space

for the exhaust gasesfor the exhaust gases

Rotating autoclave – contains grinding media to expose mineral surface (titanium ores)

LeachingLeaching High-pressure High-pressure leaching:leaching:

Tube autoclave: slurry is pumped through

High pressure diaphragm-piston pumps (10,000-20,000 kPa) made this design possible.

Used for bauxite

Characterized by extremely short residence time, high thermal efficiency, and low capital cost

In-Situ Uranium LeachingIn-Situ Uranium Leaching Used in USA – carbonate leachUsed in USA – carbonate leach

In Kazakhstan – acid ISLIn Kazakhstan – acid ISL

The ore is simply leached in The ore is simply leached in place over long periods of time place over long periods of time because it is usually too low in because it is usually too low in grade to justify mining and grade to justify mining and

transportation expensestransportation expenses

In Situ LeachingIn Situ Leaching

Two basic criteria required for an underground deposit to be Two basic criteria required for an underground deposit to be considered suitable for leaching in place are:considered suitable for leaching in place are:

The ore body must be enclosed between impermeable strata that The ore body must be enclosed between impermeable strata that will prevent the loss of solution.will prevent the loss of solution.

It must be permeable to the leaching solution.It must be permeable to the leaching solution.

Heap/Dump LeachingHeap/Dump Leaching

clear vegetation then level at a slight inclinationclear vegetation then level at a slight inclination

cover with layer of asphalt or flexible plastic sheetcover with layer of asphalt or flexible plastic sheet

crushed ore transport from the mine to the prepared site by dump crushed ore transport from the mine to the prepared site by dump trucks to a level of 10-15 m hightrucks to a level of 10-15 m high

The leaching agent is sprayed at the top of the dump through The leaching agent is sprayed at the top of the dump through which it percolates and the leach solution is collected at the bottom.which it percolates and the leach solution is collected at the bottom.

When the material is fully leached, the dump is either abandoned When the material is fully leached, the dump is either abandoned or re-used for leaching another batch.or re-used for leaching another batch.

Heap/Dump LeachingHeap/Dump Leaching

Material handling and stock-piling have become enormous Material handling and stock-piling have become enormous engineering operations. engineering operations.

Problems include plugging with fine materials, evaporation losses, leakage at the bottom, and channeling.

Bio-heap leach using bacteria is commercial option

Bio-Heap Leaching example – Talvivaara, FinlandBio-Heap Leaching example – Talvivaara, Finland

IsIs

TakesTakes

Hydrometallurgy TerminologyHydrometallurgy Terminology

purification/concentrationpurification/concentration operation: operation: After leaching.After leaching. Prior to precipitation. Prior to precipitation. Goals: 1) purification and 2) increase solution concentration, Goals: 1) purification and 2) increase solution concentration,

from which the metal values can subsequently be from which the metal values can subsequently be precipitated effectively. precipitated effectively.

methods used are: methods used are: adsorption on activated charcoal,adsorption on activated charcoal, sorption on ion exchange resinssorption on ion exchange resins extraction by organic solvents. extraction by organic solvents.

Common operation scheme: loading, washing, and Common operation scheme: loading, washing, and unloading (elution or stripping) is used in all three unloading (elution or stripping) is used in all three operations. operations.

After the elution step, the material is ready for another cycle.After the elution step, the material is ready for another cycle.

Purification and ConcentrationPurification and Concentration

Activated charcoal Activated charcoal and ion exchange and ion exchange processes are often processes are often conducted in columnsconducted in columns

Two main steps: Two main steps: loading of the desired loading of the desired metal and elution metal and elution (unloading)(unloading)

Water-washing Water-washing between these steps to between these steps to remove the entrained remove the entrained solution. solution.

After the elution step, After the elution step, the column is ready the column is ready again for loadingagain for loading

Purification and ConcentrationPurification and Concentration Adsorption on activated charcoal:Adsorption on activated charcoal:

Used for concentrating gold and silver from cyanide leach Used for concentrating gold and silver from cyanide leach solutionsolution

Can be used for turbid solutions or pulps thus saving an Can be used for turbid solutions or pulps thus saving an expensive filtration step.expensive filtration step.

Low adsorption of metal ion by activated charcoal compared to ion Low adsorption of metal ion by activated charcoal compared to ion exchange; however, activated charcoal is a much cheaper materialexchange; however, activated charcoal is a much cheaper material

Charcoals heated at 400-800 °C produce a highly porous material called "activated charcoal", usually in as pellets of 2 mm diameter

Purification and ConcentrationPurification and Concentration

Carbon Carbon adsorption and elution are slow processes: Typically it takes about 24 hours to adsorb gold from a solution containing about 10 ppm gold and 50 hours to elute.

One ton activated carbon adsorbs about 10 kg gold.

Three variations of the process are used: columns, carbon-in-Three variations of the process are used: columns, carbon-in-pulp and carbon-in-leach.pulp and carbon-in-leach.

Two factors contribute to the choice of the adsorption process:Two factors contribute to the choice of the adsorption process:

filtration properties of the pulpfiltration properties of the pulp

presence of organic matter in the orepresence of organic matter in the ore

Granular Activated CarbonGranular Activated Carbon

columns are used when the columns are used when the ore can be filtered easily and ore can be filtered easily and clear solutions can be clear solutions can be obtainedobtained

Carbon-in-pulp used to Carbon-in-pulp used to treat ores containing clay treat ores containing clay particles which are difficult to particles which are difficult to filter. Pulp is agitated in filter. Pulp is agitated in tanks with the charcoal tanks with the charcoal pellets, then screened to pellets, then screened to collect gold-laden pelletscollect gold-laden pellets

Carbon-in-leach used to Carbon-in-leach used to treat ores containing organic treat ores containing organic matter - gold cyanide complex matter - gold cyanide complex susceptible of being lost in susceptible of being lost in the residue. Granular the residue. Granular activated carbon is added in activated carbon is added in the leaching tanks so that it the leaching tanks so that it can adsorb the gold cyanide can adsorb the gold cyanide complex ASAP.complex ASAP.

Example - GoldExample - GoldGold Cyanidation Gold Cyanidation

Pulp flows through a series of agitated tanks.

Oxidative dissolution by hydrogen peroxide or air (or both).

NaCN (0.32 gm l-1)

pH is maintained at 10.0 by lime addition.

4Au + 8NaCN + O2 + 2H2O

4Na+[Au(CN)2]- + 4NaOH

Gold CyanidationGold Cyanidation

Gold LeachingGold Leaching

Pulp from cyanidation is sent to a second series of agitated tanks.

Carbon adsorption:Carbon adsorption:

[Au(CN)2]- complex is adsorbed onto the surface of activated carbon granules.

washing with water to remove the entrained solutionwashing with water to remove the entrained solution

desorption, usually with a solution of 0.2% NaCN and 1% NaOH at 90 desorption, usually with a solution of 0.2% NaCN and 1% NaOH at 90 °C°C

Loaded charcoal is removed and acid washing to remove CaCO3 acid washing to remove CaCO3 precipitateprecipitate

Dewatering, regeneration by heating in a kiln for 30 minutes at 700 °C Dewatering, regeneration by heating in a kiln for 30 minutes at 700 °C in absence of air, then quenching and recycling.in absence of air, then quenching and recycling.

Carbon is transferred through the series of tanks, counter-current to the flow of pulp.

Waste rock is disposed.

Strip solution is plated onto stainless steel electrodes.

Plates out at 65% gold.

Gold CyanidationGold Cyanidation

Ion Exchange (IX)Ion Exchange (IX) Natural (zeolite) or synthetic (polymer resin) materialNatural (zeolite) or synthetic (polymer resin) material Uranium was the first metal to be recovered commercially Uranium was the first metal to be recovered commercially

using IX – paved the way for other metalsusing IX – paved the way for other metals Especially useful in the treatment of very dilute solutions Especially useful in the treatment of very dilute solutions

with metal ion concentration of the order of 10 ppm or lesswith metal ion concentration of the order of 10 ppm or less An ion exchanger is a framework or a matrix (sponge) An ion exchanger is a framework or a matrix (sponge)

which carries a positive or a negative electric charge. which carries a positive or a negative electric charge. Counter-ions (holes) can be replaced by other ions of the Counter-ions (holes) can be replaced by other ions of the

same sign, while the fixed ions (matrix) are not mobile. same sign, while the fixed ions (matrix) are not mobile.

Ion ExchangeIon Exchange

Types of IX systems:Types of IX systems: Columns – fixed resin bed. Batchwise, Columns – fixed resin bed. Batchwise,

carousel operationcarousel operation

Ion Exchange EquipmentIon Exchange Equipment

Types of IX systems:Types of IX systems:

Resin-in-pulp - Resin-in-pulp - unfiltered leach unfiltered leach liquor fed through liquor fed through tanks with wire-mesh tanks with wire-mesh baskets containing baskets containing coarse-grade resincoarse-grade resin

Continuous – pump Continuous – pump the resin between the resin between loading and elutionloading and elution

Ion ExchangeIon Exchange Types of IX resins:Types of IX resins:

Strong acid: cation Strong acid: cation exchangers, containing -exchangers, containing -SO3H groups SO3H groups

Weak acid: cation Weak acid: cation exchangers, containing -exchangers, containing -COOH groups COOH groups

Strong base: anion Strong base: anion exchangers. Strength of the exchangers. Strength of the resin can be increased by resin can be increased by using substituted amines using substituted amines

Weak base: anion Weak base: anion exchangers, containing exchangers, containing amino groups amino groups

Anion exchange.Anion exchange.. The . The extracted species is a extracted species is a negatively charged ion and negatively charged ion and the extractant is a base, the extractant is a base, e.g., an amine:e.g., an amine:

Solvent ExtractionSolvent Extraction

leach solution is mixed with an immiscible organic solvent so the desired metal ion leach solution is mixed with an immiscible organic solvent so the desired metal ion in aqueous phase is transferred to organic phase in aqueous phase is transferred to organic phase

The two phases are then allowed to separate.The two phases are then allowed to separate.

The process is then reversed by contacting the loaded organic phase with an The process is then reversed by contacting the loaded organic phase with an aqueous (strip)aqueous (strip) solution that transfers the desired metal ion back out of the organic. solution that transfers the desired metal ion back out of the organic.

The aqueous phase obtained is a pure and concentrated solution suitable for metal The aqueous phase obtained is a pure and concentrated solution suitable for metal recovery while the stripped organic phase is suitable for recyclerecovery while the stripped organic phase is suitable for recycle

Solvent ExtractionSolvent Extraction

Pregnant – loaded with the metal of interestPregnant – loaded with the metal of interest Barren – metal of interest has been removedBarren – metal of interest has been removed Pregnant aqueous – the feed solution to SX that contains Pregnant aqueous – the feed solution to SX that contains

the components to be separated.the components to be separated. Solutes – minor components in the feed (or other) Solutes – minor components in the feed (or other)

solutions = dissolved metals.solutions = dissolved metals. Solvent – the immiscible liquid added to a process for the Solvent – the immiscible liquid added to a process for the

purpose of extracting a solute or solutes from the feed.purpose of extracting a solute or solutes from the feed. Organic – the “light” phase, used for extraction from feed.Organic – the “light” phase, used for extraction from feed. Raffinate – the liquid phase left from the feed after Raffinate – the liquid phase left from the feed after

extraction = barren aqueous.extraction = barren aqueous. Strip solution – acts as the solvent to remove metal of Strip solution – acts as the solvent to remove metal of

interest from the organic phaseinterest from the organic phase

Separatory funnel - emulsificationSeparatory funnel - emulsification

Feed

ExtractionSolvent

Feed

ExtractionSolvent

Extract

Raffinate

Extract

Raffinate

Hydrometallurgy EquipmentHydrometallurgy Equipment Solvent extraction mixer-settlersSolvent extraction mixer-settlers mixing chamber: aqueous and organic phases are mixed mixing chamber: aqueous and organic phases are mixed

together by a rotating impellertogether by a rotating impeller settling chamber: mixed phases are given enough time settling chamber: mixed phases are given enough time

to separate to separate

Solvent ExtractionSolvent Extraction

Only clear filtered Only clear filtered solutions can be extracted solutions can be extracted by organic solventsby organic solvents

Usually many stages are used (3 to 5) and are operated in counter-current in the extraction as well as in the stripping steps.

Sometimes, a washing step is inserted between extraction and stripping to remove loosely bound metal ions

Solvent Extraction Solvent Extraction EquipmentEquipment

Krebs mixer-Krebs mixer-settler:settler:

Interphase Interphase regulatorregulator

Mixer and Mixer and conical pumpconical pump

Top launder for Top launder for initial phase initial phase disengagementdisengagement

Solvent Extraction Solvent Extraction EquipmentEquipment

Column cell:Column cell: Discs and Discs and

doughnutsdoughnuts No exposure to No exposure to

airair Gentle mixingGentle mixing

Solvent Extraction Solvent Extraction EquipmentEquipment

Outotec Spirok mixersOutotec Spirok mixers Low shearLow shear

Solvent ExtractionSolvent Extraction

Organic typically has the following components:Organic typically has the following components:

Carrier – main volume of organic, eg. keroseneCarrier – main volume of organic, eg. kerosene

Extractant – active in collecting metal. Eg. amineExtractant – active in collecting metal. Eg. amine

Diluent – Reduces surface tension, aids phase Diluent – Reduces surface tension, aids phase separation, eg. Isodecanol (alcohol)separation, eg. Isodecanol (alcohol)

Example: UraniumExample: Uranium

Uranium Solvent Extraction:Uranium Solvent Extraction:

Aqueous leach solution (3 - 13 g/l uranium) is separated Aqueous leach solution (3 - 13 g/l uranium) is separated from the waste rock and is sent to solvent extraction as from the waste rock and is sent to solvent extraction as the feed solution.the feed solution.

Aqueous feed is mixed with an organic extraction solvent Aqueous feed is mixed with an organic extraction solvent consisting of:consisting of:

kerosene (91%)kerosene (91%) isodecanol (3%)isodecanol (3%) tertiary amine (6%)tertiary amine (6%)

Uranium is selectively transferred to the organic phase.Uranium is selectively transferred to the organic phase.

Barren aqueous phase (raffinate) is recycled to CCD or Barren aqueous phase (raffinate) is recycled to CCD or discarded.discarded.

Solvent ExtractionSolvent Extraction

Uranium SX - Complexation Reactions

2R3N + H2SO4 2 R3NH+ + SO42

Extraction:

4 R3NH+ + UO22+ + 3 SO4

2(R3NH)4UO2(SO4)3

Extraction is selective for uranium

Stripping: (R3NH)4UO2(SO4)3 + 4NH4OH 3R3N + UO22+ + 3SO42- + 4NH4+ + 4H2O

Precipitation: 2UO22+ + 2SO42- + 6NH4OH (NH4)2U2O7 + 4 NH4+ + 2 SO42 + 3H2O

Uranium Solvent Extraction and PrecipitationUranium Solvent Extraction and Precipitation

E1 E2 E3 E4

Aqueous Feed(6-8 g/l)

Raffinate(<0.01 g/l)

S1 S2 S3 S4

Loaded Organic(20-25 g/l)

Barren Organic(<0.1 g/l)

YellowcakePrecipitation

Ammonia Gas

YellowcakeProduct

Barren Strip(<0.1 g/l)

LoadedStrip(50 g/l)

Bleed to Ammonium Sulfate Crystallization

E1 E2E2 E3E3 E4E4

Aqueous Feed(6-8 g/l)

Raffinate(<0.01 g/l)

S1 S2S2 S3S3 S4

Loaded Organic(20-25 g/l)

Barren Organic(<0.1 g/l)

YellowcakePrecipitation

Ammonia Gas

YellowcakeProduct

Barren Strip(<0.1 g/l)

LoadedStrip(50 g/l)

Bleed to Ammonium Sulfate Crystallization

Uranium Solvent ExtractionUranium Solvent Extraction Key Lake SX circuitKey Lake SX circuit

HydrometallurgyHydrometallurgy Precipitation is the final step in many hydrometallurgical processes. Precipitation is the final step in many hydrometallurgical processes. It is also used as a purification step to separate impurities It is also used as a purification step to separate impurities Can be physical or chemical Can be physical or chemical

Precipitation EquipmentPrecipitation Equipment

Solar Crystallizers:Solar Crystallizers: Used for evaporating sea water or brines Used for evaporating sea water or brines

from wells for the bulk recovery of from wells for the bulk recovery of sodium chloride or other salts sodium chloride or other salts (magnesium chloride, lithium chloride)(magnesium chloride, lithium chloride)

Large evaporation ponds are Large evaporation ponds are constructed adjacent to the source.constructed adjacent to the source.

Climate in the region must show high Climate in the region must show high yearly evaporation and low rainfall. yearly evaporation and low rainfall.

Precipitation EquipmentPrecipitation Equipment

Vacuum crystallizer:Vacuum crystallizer: no reagents are added, but the no reagents are added, but the

concentration and temperature concentration and temperature adjustedadjusted

concentrate a solution such concentrate a solution such that crystallize solids by that crystallize solids by evaporation evaporation

Evaporation is conducted Evaporation is conducted under vacuum to decrease the under vacuum to decrease the boiling point of the solution boiling point of the solution and thus economize in heat and thus economize in heat requirement requirement

common procedure for common procedure for obtaining pure salts, e.g., obtaining pure salts, e.g., sodium chloride, ammonium sodium chloride, ammonium sulphatesulphate

However, cooling will also However, cooling will also effectively lead to effectively lead to crystallization of a salt crystallization of a salt provided its solubility is largely provided its solubility is largely dependent on temperature.dependent on temperature.

Precipitation EquipmentPrecipitation Equipment

multiple effect evaporators - steam generated in the multiple effect evaporators - steam generated in the first evaporator is used to heat the charge in the first evaporator is used to heat the charge in the second evaporator, and that from the second is second evaporator, and that from the second is used to heat the charge in the third. used to heat the charge in the third.

Hydrometallurgy EquipmentHydrometallurgy Equipment

Chemical precipitation methods:Chemical precipitation methods: hydrolysis – just add water! Precipitation of hydrolysis – just add water! Precipitation of

oxides, hydrated oxides, hydroxides, or hydrated oxides, hydrated oxides, hydroxides, or hydrated salts salts

Ionic - ions formed are neutralized by a base, Ionic - ions formed are neutralized by a base, example:example:

Reduction - a reducing agent is added which Reduction - a reducing agent is added which results in the precipitation of a metal and the results in the precipitation of a metal and the agent is oxidized:agent is oxidized:

An important sub-group is hydrogen reductionAn important sub-group is hydrogen reduction Substitution – precipitate metal ions from organic Substitution – precipitate metal ions from organic

solvents solvents

PrecipitationPrecipitation

Particle sizeParticle size

Particle size and form of a precipitate depend Particle size and form of a precipitate depend upon the conditions of formation.upon the conditions of formation.

Freshly formed precipitate is sometimes Freshly formed precipitate is sometimes described as amorphous or gelatinous and is described as amorphous or gelatinous and is difficult to separate by filtration.difficult to separate by filtration.

Precipitates undergo continuous Precipitates undergo continuous recrystallization as they age ... accelerated by recrystallization as they age ... accelerated by heating heating

PrecipitationPrecipitation

Precipitation involves two steps:Precipitation involves two steps:

nucleationnucleation

crystal growthcrystal growth

Rate of nucleation is influenced by:Rate of nucleation is influenced by:

concentrationconcentration

agitationagitation

nucleating agentsnucleating agents

Change in valency by adding an oxidizing or reducing Change in valency by adding an oxidizing or reducing agent may be used to effect selective precipitations.agent may be used to effect selective precipitations.

Extractive Metallurgy Extractive Metallurgy Terminology Terminology

Electrometallurgy – use of electrical Electrometallurgy – use of electrical energy to induce a chemical energy to induce a chemical transformationtransformation

Electrowinning – to precipitate a metal Electrowinning – to precipitate a metal from solution using electric potentialfrom solution using electric potential

Electrorefining – to purify a metal by Electrorefining – to purify a metal by dissolving it, then re-precipitating it dissolving it, then re-precipitating it

Electrometallurgy EquipmentElectrometallurgy Equipment

Electrolytic process:Electrolytic process: precipitation of a metal from its aqueous solution is precipitation of a metal from its aqueous solution is

affected by imposing an outside electromotive force affected by imposing an outside electromotive force from a direct current source. This can be represented by:from a direct current source. This can be represented by:

Electrometallurgy EquipmentElectrometallurgy Equipment

Alternating anodes and Alternating anodes and cathodes in a tankhouse cathodes in a tankhouse for electrowinningfor electrowinning

For example, copper, zinc, For example, copper, zinc, cadmium, and nickel are cadmium, and nickel are recovered industrially recovered industrially from leach solutions by from leach solutions by electrolytic methods electrolytic methods

Example: Gold and silver Example: Gold and silver are recovered from the are recovered from the eluate by electrolysis eluate by electrolysis using steel wool cathodes using steel wool cathodes

The aqueous solutions are The aqueous solutions are electrolyzed using inert electrolyzed using inert electrodes; the pure metal electrodes; the pure metal is deposited on the is deposited on the cathode.cathode.

Extractive Metallurgy Extractive Metallurgy Terminology Terminology

Pyrometallurgy – use of heat to induce a Pyrometallurgy – use of heat to induce a chemical transformationchemical transformation

Roasting – convert to oxide form. Often first Roasting – convert to oxide form. Often first step preceding smelting for Cu, Ni, Pb step preceding smelting for Cu, Ni, Pb

Example: 2 CuS2 + 5 O2 → 2 CuO + 4 SO2Example: 2 CuS2 + 5 O2 → 2 CuO + 4 SO2 Equipment – fluidized bed roasterEquipment – fluidized bed roaster

Extractive Metallurgy Extractive Metallurgy Terminology Terminology

Smelting - uses reducing substances that will Smelting - uses reducing substances that will combine with those oxidized elements to free combine with those oxidized elements to free the metal. the metal.

Example: 2 Fe2O3 + 3 C → 4 Fe + 3 CO2 Example: 2 Fe2O3 + 3 C → 4 Fe + 3 CO2 Converter – add back a bit of oxygen to purify, Converter – add back a bit of oxygen to purify,

example: blister copperexample: blister copper

Pyrometallurgy EquipmentPyrometallurgy Equipment

Smelter:Smelter: Add flux (silica or lime) to remove impurities - Add flux (silica or lime) to remove impurities -

waste becomes slagwaste becomes slag Dust and off gas control are big issuesDust and off gas control are big issues

PyrometallurgyPyrometallurgy The molten components coalesce, each forming an individual molten layer The molten components coalesce, each forming an individual molten layer

Slag: top layer with specific gravity 3.6, and is composed of silicates.Slag: top layer with specific gravity 3.6, and is composed of silicates.

Matte: next layer with specific gravity 5.2, and is composed of sulfides.Matte: next layer with specific gravity 5.2, and is composed of sulfides.

Speiss: next layer with specific gravity 6.0, and is composed of arsenides.Speiss: next layer with specific gravity 6.0, and is composed of arsenides.

Bullion: bottom layer with specific gravity > 6, and is composed of metals.Bullion: bottom layer with specific gravity > 6, and is composed of metals.

PyrometallurgyPyrometallurgy

Calcination – Chemical decomposition – but not Calcination – Chemical decomposition – but not oxidation or reduction. oxidation or reduction.

Example: CaCO3 = CaO + CO2(g)Example: CaCO3 = CaO + CO2(g)

PyrometallurgyPyrometallurgy

Multi-hearth calciner/roaster:Multi-hearth calciner/roaster:

Pyrometallurgy – Gold SmeltingPyrometallurgy – Gold Smelting

Gold-bearing sludge is mixed with NaNOGold-bearing sludge is mixed with NaNO33

flux.flux.

Heated to melting.Heated to melting.

Impurities transfer to the slag.Impurities transfer to the slag.

Final gold product (Dore bar) is then Final gold product (Dore bar) is then poured, then to refinery.poured, then to refinery.

Dore product composition:Dore product composition:

90% Au90% Au

5-6% Ag5-6% Ag

<5% Fe, Cu, Ni, ...<5% Fe, Cu, Ni, ...

Pyrometallurgy – SteelmakingPyrometallurgy – Steelmaking

Scrap steel is segregated into piles according to composition.Scrap steel is segregated into piles according to composition.

Each batch (“heat”) has proportions of the various scraps added Each batch (“heat”) has proportions of the various scraps added to yield approximately the correct steel composition.to yield approximately the correct steel composition.

One heat is ~ 135 tonnesOne heat is ~ 135 tonnes

Alloys addedAlloys added

Lime added as flux, leads to the formation of a slag layer above Lime added as flux, leads to the formation of a slag layer above the molten iron.the molten iron.

Impurities in the steel form compounds soluble in the slag:Impurities in the steel form compounds soluble in the slag:

• 2 Mn + O2 2 MnO

• Si + O2 CaSiO3

• 4P + 5 O2 + 6 CaO Ca3(PO4)2

• Mn + S + CaO CaS + MnO

• 4 Al + 3 O2 2 Al2O3

Pyrometallurgy – SteelmakingPyrometallurgy – Steelmaking Current applied through three large carbon electrodes.Current applied through three large carbon electrodes.

Arc generates heat up to 5500 °F which melts the steelArc generates heat up to 5500 °F which melts the steel

Further heat provided by injecting oxygen, which reacts with Further heat provided by injecting oxygen, which reacts with carbon to form COcarbon to form CO

Pyrometallurgy – SteelmakingPyrometallurgy – Steelmaking After slag has been removed, the steel is After slag has been removed, the steel is

poured into a ladlepoured into a ladle

A sample of the ladle is taken and assayedA sample of the ladle is taken and assayed

Based on the results of the assay and the Based on the results of the assay and the desired composition, additional alloys are desired composition, additional alloys are added: Cr, Ti, Ni, V, Moadded: Cr, Ti, Ni, V, Mo

Mixed by injecting argon until homogeneousMixed by injecting argon until homogeneous

Poured into a continuous caster to make Poured into a continuous caster to make steel platesteel plate

Assignment / Tutorial #11 Assignment / Tutorial #11

Tutorial / AssignmentTutorial / AssignmentComplete selected EduMine sections:Complete selected EduMine sections:

Hydrometallurgy 1: Review #3Hydrometallurgy 1: Review #3Extractive Metallurgy 2: Review #2Extractive Metallurgy 2: Review #2

Flowsheet examplesFlowsheet examples

Aluminum:Aluminum: from bauxitefrom bauxite Copper: Copper: from chalcopyritefrom chalcopyrite Iron: Iron: from hematitefrom hematite

GoldGold – – Placer, sulphide and oxide Placer, sulphide and oxide

Dead SeaDead Sea – – IsraelIsrael

AluminumAluminum

CopperCopper

IronIron

GoldGold

Dead Sea brine Dead Sea brine