Unit operations of metals production Eetu-Pekka Heikkinen Laboratory of process metallurgy Department of process and environmental engineering

Contents n Unit operations of Mining and enrichment n Pyrometallurgical unit operations n Hydrometallurgical unit operations n Electrochemical unit operations n Casting processes n Thermo-mechanical treatment of metals n Metal product manufacture Not included in this presentation

Water Hydrometallurgical metal production Material sciences Mining & Enrichment Metallurgy: introduction Electro- metallurgy Extractive metallurgy Ores Mining Enrichment Crushing Screening Mechanical separation (...) Properties of metals Physical metallurgy Hot and cold rolling (...) Hydrometallurgy Pyrometallurgy e.g. zinc nickel Electrowinning Cementation Ion exchange Chemical precipitation Solvent extraction Similar methods Reaction kinetics Thermo- dynamics Theory Metal recovery Impurity removal Fluid dynamics Heat transfer Mass transfer Transport phenomena Methods Leaching Iron and steel Sulphide- ores (e.g. Cu) e.g. Roasting Pyrometall. pretreatment Pyrometallurgical metal production e.g. iron/steel copper Sintering Coking Blast furnace Sulphur removal Ladle treatments Converters (LD/AOD/...) Casting Flash smelting Converters (PS) Electric furnaces (...) Acidic Basic Organic Solvents

How to choose a process? Pyromet. unit operations Hydromet. unit operations Electro-chem. unit operations Production chain Products Raw materials Residues € Markets Transport Energy Water needed

Pyrometallurgical unit operations Raw material pre- treatments MetalrefiningMetalextraction Production of metals Raw materials Products Reduction and oxidizing Thermal pre- treatment Metal raffination MatteproductionReduction of oxides Compositioncontrol Impurity removal Temperaturecontrol SinteringDryingCalcination Coking Roasting Pelletizing

Drying n Dangerous to charge wet materials to the high temperature processes –The moisture that is allowed depends on the further processing n Mechanical moisture removal prefered –Thermal drying requires a lot of energy n Counter-current drum-driers are common in the drying of metallurgical raw materials n Utilisation of the process waste heat streams

Sintering n Problems in processing fine materials –Gas permeability –Dusting n Thermal agglomeration –Partial melting –Minimisation of the surface energy as a driving force for agglomeration n Chemical and mineralogical changes in material n Drum-, batch- or belt-sintering –Pretreatment: Micropelletising

Pelletizing n Feeding of concentrates, binding materials and water into the rotating and sloped pelletising drum or plate n Capillar forces caused by moisture as cohesive force n Aftertreatments in order to achieve wanted properties –Sintering –Shaft furnace n Small pellets are fed back to the process

Calcination n Thermal disintegration of a compound (which leads into a formation of gaseous product) –Thermal conductivity (endothermic reactions) –Removal of gas from the reaction surface n e.g. calcination of limestone to produce burned lime  Use of lime in iron and steelmaking slags –CaCO 3 = CaO + CO 2  H R >> 0 –Counter-current shaft furnace or rotating drum n Other examples –Disintegration of CaMg(CO 2 ) 2 or Al(OH) 2

Coking n Pyrolysis of coal in order to modify it to be more suitable for metallurgical processes –Removal of water and volatile components –Agglomeration of coal particles –Porous coke as a result n Dry or wet quenching n Several by-products –Reducing gas (H 2, CO) –Raw materials for chem. industry

Roasting n A process in which an anion of a solid compound is changed without changing the valency of the cation n High temperature processing of the sulphide ores without agglomeration –Often used as a pretreatment for the hydrometallurgical processes n Examples –Oxidising roasting –Sulphating roasting –Chlorine/Fluor/Alkalines/...

Oxidising roasting n Difficulties to reduce sulphide ores using carbon –e.g. 2 ZnS + C = 2 Zn + CS 2 or ZnS + CO = Zn + COS –Equilibrium is strongly on the reactants’ side n Roasting of sulphides into the oxides –MeS + 3/2 O 2 = MeO + SO 2 –Used e.g. in the production of lead, copper, zinc, cobalt, nickel and iron when using sulphide ores as raw materials –SO 2  SO 3  H 2 SO 4 n Fluidized bed, sintering or shaft furnace roasting –Products are either fine material or porous agglomerates

Sulphating roasting n Used in separation of metals from complex materials –Some metals react to sulphates that are soluble to water n MeS + 3/2 O 2 = MeO + SO 2 n SO 2 + 1/2 O 2 = SO 3 n MeO + SO 3 = MeSO 4 –Some are left as oxides (non-soluble) n A pretreatment for hydrometallurgical processes n Usually fluidized bed roasting n Often used to remove iron from more valuable metals (Cu, Ni, Zn, Co) –When T > 600  C  Ferrisulphate is not stable

Reduction of oxides n MeO + R = Me + RO –Me is a metal –R is a reducing component (an element or a compound which forms an oxide which is more stable than MeO in the considered temperature)

Reduction of oxides n Carbo-thermal reduction –MeO + C = Me + CO –In practice: n MeO + CO = Me + CO 2 n C + CO 2 = 2 CO (= Boudouard reaction) n Metallothermal reduction –MeO + M = Me + MO n Gas reduction –Usually H 2 and CO (separately or as a mixture) n MeO + H 2 = Me + H 2 O n MeO + CO = Me + CO 2

Reduction of oxides The largest industrial CO 2 -emissions in Finland and Sweden (Mt) Specific and total CO 2 -emissions of the Finnish steel industry

Matte production n Separation of metals from the sulphides –”Worthless” metal is oxidised  Oxidic slag –Wanted metal is still as a sulphide  Matte n Matte is further refined  Metal n Used e.g. in the production of copper, nickel and lead –2 CuS + O 2 = Cu 2 S + SO 2 –FeS 2 + O 2 = FeS + SO 2 –2 FeS + 3 O 2 + SiO 2 = Fe 2 SiO SO 2

Removal of impurities (from iron/steel) n Carbon removal (hot metal  crude steel) –To achieve wanted properties –Decarburization in BOF-converters n Removal of other oxidising impurities/elements (Si, Mn, P) n Oxygen blowing  Oxide formation  Slag/Gases n Temperature is increased –Scrap melting –Vacuum treatment n Burning of carbon is more efficient in lowered pressure n Partial pressure of CO can also be lowered using inert gases

Removal of impurities (from iron/steel) n Deoksidation / Oxygen removal –Solubility of oxygen in steel melt is appr. 0,2 % (T > 1500  C) –Solubility decreases when temperature is decreased n Causes CO formation, oxidation of alloying elements, etc. –Alloying, diffusion or vacuum deoxidation n Gas removal –Solubilities of gases decrease when T is decreased (cf. O) –Gas removal is based on decreasing the partial pressure of the concerned element in the gas phase (vacuum, inert gas) n Sulphur removal –Formation of CaS  Into the slag

Composition control (Steel) n Alloying of steel is made mainly in the BOF-converters after the blowing n More accurate alloying in the steel ladle –Lumps –Powder injection –Wire injection n Stirring –Inductive –Using an inert gas

Temperature control n Increased significance due to continuous casting n Optimisation of a tap temperature n Inductive heating n Use of fuels n Plasma heaters n Chemical heating (Al, Si) n Electric arcs n Insulation n Scrap cooling n Stirring

Hydrometallurgical unit operations Activation Raw material PoorrawmaterialsImpurerawmaterials WastesBy-productsLeaching Impurity removal Metal recovery ChemicalElectro-chemicalProduct Wastetreatment Waste By-product Cleaning / regeneration of the solvent Pyro-metallurgicalHydro-metallurgical

Leaching n Grinding, enrichment and activation as pre-treatments n Solvents –Water n For sulphates and chlorides –Acids n Sulphuric acid most commonly used n Nitric and hydrochloric acids –more expensive and corroding –Bases n Ammonia water –Organic solvents

Leaching n Direct leaching –For poor ores and residues n Tank leaching (in atmospheric pressure) –For rich ores and concentrates –Smaller reactors and faster processes –Stirring n Autoclave leaching –Tank leaching in which reaction kinetics are enhanced by increasing temperature over the boiling point of the solution (in increased pressure)

Metal recovery n Crystallization –Separation of solid crystal from a homogenic solution –Pure products (impurities only on the surfaces) –Saturated solution –Kinetics? n Chemical precipitation (as sulphides or as metals) –Addition of anions or cations in order to form a compound with a low solubility –Selectivity –Gases (H 2 S, H 2, SO 2, CO) are efficient additives n Electrowinning

Impurity removal n Procedures between leaching and metal recovery n Physical removal of solid materials –Thickening –Filtering n Removal of impurities from the solution –Similar methods as in metal recovery –Ion exchange –Liquid-liquid-extraction

Ion exchange n To remove small amounts of impurities from large amounts of solutions –Best with dilute solutions (< 10 ppm) n Possibility to achieve very low impurity levels n Resin to which metal ions are tranfered from solution –Selectivity n Saturated resin is recovered with other solutions to which the metal ions are transfered –Saturation of metals as chlorides, sulphates, etc.

Liquid-liquid-extraction n Recovery of metal ions from the water solution using an organic extraction agent –Two immiscible liquids n Reaction area is increased using efficient stirring –Formation of complex compounds –Settling in order to separate two liquid phases –Recovery of valued metals from the complex compounds n Selectivity

Cementation n Substitution of a metal ion (M + ) with a less noble metal (Me) –Me(s) + M + (aq) = Me + (aq) + M(s) n Efficiency depends on the difference of the ”nobilities” of the metals

Electro-chemical unit operations n Electrolysis = reduction/oxidation that is controlled with the electricity –Electrolyte that contains ions –Anions (-) are transfered to the anode (+)  Oxidation –Cations (+) are transfered to the cathode (-)  Reduction n Can be hydrometallurgical... –Electrowinning –Electrolytical refining n... or pyrometallurgical –Molten salt -electrolysis

Electrowinning n Anodes are not dissolved (e.g. Pb) –Formation of oxygen as a main reaction –Formation of hydrogen occurs with less noble metals –The amount of H + -ions is increased in the electrolyte n Metal-ions from the solution are precipitated in the cathode –The amount of metal ions is decreased in the electrolyte –Metal-poor electrolyte is recycled back to the leaching process n Used in the production of nickel and zinc

Electrolytical refining n Anodes are dissolving (impure metal to be refined) –Wanted metal is dissolved to the electrolyte –All the less noble metals are also dissolved –More noble metals don’t dissolve  an anode sludge is formed n Cathodes –Precipitation of a wanted metal –Less noble metals are left in the electrolyte from which they can be recovered n Refining of pyrometallurgically produced metals –Especially copper

Electrolysis using molten salts as electrolytes n Halide melts as electrolytes n The principle is same as in hydro- metallurgical electrolyses n Higher temperatures –Refractoriness of the reactors etc. n Used in the production of aluminium, magnesium, beryllium, cerium, lithium, potassium and calcium –i.e. metals that are produced from the raw materials with high melting temperatures