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Extractive metallurgy of ironThe following raw materials are involved in manufacturing iron:

Iron ores (magnetite, hematite)iron oxides with earth impurities; Coke, which is both reducing agent and fuel, providing heat for melting the metal and

slag.

Coke is produced from coking coals by heating them away from air.

Limestonecalcium silicate fluxes, forming a fluid slag for removal gangue from the ore.Iron is produced in a blast furnace, schematically shown in the picture.

It the shaft-type furnace consisting of a steel shell lined with refractory bricks.

The top of the furnace is equipped with the bell-like or other system, providing correct chargingand distribution of the raw materials (ore, coke, limestone).

Air heated to 2200F (1200C) is blown through the tuyeres at the bottom.

Oxigen containing in air reacts with the coke, producing carbon monoxide:

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2C + O2= 2COHot gases pass up through the descending materials, causing reduction of the iron oxides to ironaccording to the follwing reactions:

3Fe2O3 + CO = 2Fe3O4 + CO2Fe3O4 + CO = 3FeO + CO2FeO + CO = Fe + CO2Iron in form of a spongy mass moves down and its temperature reaches the melting point at thebottom regions of the furnace where it melts and accumulates.

The gangue, ash and other fractions of ore and coke are mixed by fluxes, formig slag which iscapable to absorb sulphure and other impurities.

The furnace is periodically tapped andthe melt (pig iron) is poured into ladles, which aretransferred to steel making furnaces.

Pig iron usually contains 3-4% of carbon, 2-4% of silicon, 1-2% of manganese and 1-1.2% ofphosphorous.

Extractive metallurgy of aluminumAluminum is the most abundant metal in Earth.

It occurs in the nature in form of aluminum oxide and other combined forms.

The ore containing aluminum compound, which is commercially used in the extractivemetallurgy is called bauxite.Bauxite is a hydrated aluminum oxide.Extraction of aluminum from bauxite is carried out in three stages:

Ore dressingcleaning ore by means of separation of the metal containing mineral fromthe waste (gangue).

Chemical treatment of bauxite (Bayer process) for converting the hydrated aluminumoxide to pure aluminum oxide (Al2O3).

At this stage crushed and ground bauxite is mixed with hot sodium hydroxide solution, whichdissolves the aluminum hydroxide, forming solution of sodium aluminate.

The residual impurities (oxides of silicon, iron and titanium), which called red mud, areseparated from the sodium aluminate solution.

The solution is then treated in precipitator tanks, where aluminum trihydrate precipitates fromthe solution.

The aluminum trihydrate after separation from the sodium hydroxide is converted into pure

aluminum oxide by heating to 1800F (1000C).

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Reduction of aluminum from aluminum oxide by the electrolytic process.As aluminum oxide is a very poor electricity conductor its electrolysis is carried out in a bath ofmolten cryolite (mineral, containing sodium aluminum fluorideNa3AlF6).

The technology is called Hall-Heroult process.

Schematically the process is presented in the picture:

The electrolytic cell for aluminum production consists of a pot with carbon lining, serving asnegative electrode (cathode) and positive electrodes (anodes), connected to the current conductor(bus bar).The anodes are immersed into the bath of molten cryolite.

The aluminum oxide is added to the cryolite and dissolved in it. When electric current passesbetween the anodes and the cathode through the cryolite, aluminum oxide decomposes to metallicaluminum deposited at the cathode and oxygen liberated at the anode.

The molten aluminum is periodically tapped from the furnace into a crucible and cast into ingots.

Extractive metallurgy of copperManufacture ofcopper and its alloys has a long history of thousands of years.

The basic compounds contained by the copper ores are either copper sulfide or copper oxides.Copper ores are poor; therefore commercial extraction of copper involves several dressingoperations before the smelting stage.

The following technological operations are carried out for copper production from sulfide ores:

Crushing and grinding the ore in order to free the gangue from the copper mineral. Concentratingseparation of the copper mineral from the gangue.

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This operation is conducted in a flotation chamber where the ground ore mixed with water istreated by air bubbles which move upward and cause flotation of the mineral particles to the topof the chamber.

The copper concentrate formed in this stage contains about 15% of copper.

Matte smelting.At this stage the concentrate is smelted in a reverberatory furnace to produce a mixture of copperand iron, called matte.

The gangue is absorbed by the slag and removed.

Blister copper production.At this stage the matte is converted into molten copper and iron-rich slag by blowing air throughthe matte.

The resulted copper melt contains about 98% of copper.

Casting copper anodes which are used in the followed electrolytic refining stage. Electrolytic refining.

Impure copper anodes are immersed in a sulfuric acid bath. Pure copper foil (starting sheet)serves as the cathode where copper deposits.

Cathodes produced as a result of the electrolytic refining process contain 99.9% of copper.

The pure copper cathodes are used for manufacturing copper and copper alloys products.

Extractive metallurgy of magnesiumMagnesium is the sixth most abundant element in the earths crust.

The main sources of magnesium compounds are:

seawater (magnesium chloride, MgCl2)and minerals:

dolomite (CaCO3MgCO3), magnesite (MgCO3), carnallite (KClMgCl26H2O).

There are two principal magnesium extraction processes: silicothermic process and electrolyticprocess.Silicotermic process (Pidgeon, Magneth erm, Bolzano).The process involves reducing molten magnesium oxide slag by ferrosilicon under low gaspressure at a temperature of about 2500F (1400C).

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The metallic magnesium, formed in the process, evaporates and then condensates away from thehot region.

The condensed magnesium, having purity of 99,95% is then remelt and cast.

Electrolytic process.The first stage of the process is a preparation of magnesium chloride feed which is followed bythe electrolytic dissociation of magnesium chloride.

Industrial cell feeds consist of a mixture of dehydrated magnesium chloride, partly dehydratedmagnesium chloride or dehydrated carnallite.

Dehydrated magnesium chloride is prepared by one of two methods: chlorination of magnesiumoxide (IG Farben process) or dehydration of magnesium chloride brines.

The electrolytic cell consists of a brick-lined vessel, divided into anode and cathode compartmentsby a semi-wall. Air- or water-cooled Graphite plate anode and steel cathode are submerged inelectrolyte composed of alkaline chlorides with addition of magnesium chloride.

The operating temperature is 1260F to 1380F (680C to 750C).

Magnesium chloride decomposes in the electrolytic cell according to the reaction:

MgCl2 Mg + Cl2(g)Metallic magnesium is formed at the cathode. It floats up (it is lighter than electrolyte) collectingin the cathode compartment.

Chlorine, which is by-product of the process, is collected in the anode compartment.

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Extractive metallurgy of nickelNickel occurs in ores of two general types:

nickel-iron sulfides, hydrous nickel silicate (laterite).

Both of them typically contain 1-3% of nickel.

Extraction of nickel from su lfide oresExtraction of nickel from sulfide oresis carried out by the following process:

Crushing and grinding the ore in order to free the gangue from the nickel sulfide mineral. Concentratingseparation of the nickel sulfide mineral from the gangue.

This operation is conducted in a flotation chamber where the ground ore mixed with water istreated by air bubbles which move upward and cause flotation of the mineral particles to the topof the chamber.

Smelting or roasting with partial converting sulfides to oxide form. Matte smelting.

At this stage the concentrate is smelted in the Bessemer converter to produce a mixture of nickel,copper and other metals called matte.

The gangue is absorbed by the slag and removed.

Electrolytic or chemical refining of nickel.Extraction of nickel from the laterite oresExtraction of nickel from the laterite ores is carried out by either pyrometallurgical orhydrometallurgical process:

Hydrometallurgical process involves ammoniacal or sulfuric acid leaching followed bynickel precipitatation.

In the pyrometallurgical process the ore is dried and calcined in a rotary kiln and thensmelted in an electric furnace with addition ofcarbon. The resulted nickel-iron mattemay be either further refined or used as desired product (in this case sulfur in form ofgypsum or elemental sulfur is added to the kiln).

Extractive metallurgy of titaniumTitanium is the ninth most abundant element in the earths crust.

The ores used for commercial production of titanium are:

Rutile (titanium dioxide TiO2),

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Ilmenite (FeTiO3).Titanium is produced by theKroll process developed by William Justin Kroll in 1946:

Concentrating - separation of titanium dioxide from the gangue and iron oxide (inilmenite).

Carbochlorination - chemical treatment of titanium dioxide in fluid bed reactor withchlorine and petroleum coke at the temperature 1650F (900C) resulted in formation ofimpure titanium tetrachloride:

TiO2 + Cl2 + C = TiCl4 + CO2 Purification of the liquid impure titanium tetrachloride using fractional distillation and

precipitation to remove iron chloride and other impurities.

Titanium sponge productionreaction of pure titanium tetrachloride with magnesium ina stainless retort at 2010F (1100C) under argon atmosphere:

TiCl4 + 2Mg = Ti + 2MgCl2The resulted magnesium chloride is liquid and it is separated from the solid titanium which isobtained in form of porous sponge.

Melting of titanium sponge in vacuum arc furnace or under inert atmosphere and castingthe melt to ingots.