Extractive metallurgy of iron

 

The 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.

• Limestone – calcium 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 charging and distribution of the raw materials (ore, coke, limestone).

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

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

2C + O₂= 2CO

Hot gases pass up through the descending materials, causing reduction of the iron oxides to ironaccording to the follwing reactions:

3Fe₂O₃ + CO = 2Fe₃O₄ + CO₂

Fe₃O₄ + CO = 3FeO + CO₂

FeO + CO = Fe + CO₂

Iron in form of a spongy mass moves down and its temperature reaches the melting point at the bottom 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 is capable to absorb sulphure and other impurities.

The furnace is periodically tapped andthe melt (pig iron) is poured into ladles, which are transferred 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. 

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Extractive Metallurgy of Copper

Beneficiation and extractive metallurgy of copper ores comprises several steps that have for objectives concentrate and extract the copper present in the ore. The methods to be used vary with the mining operation and depend on the ore characteristics and economical aspects. Thus, initially is common to have the sizing and classification stage which employs crushing, screening, grinding, and sorting operations. In a second step can be required a concentration which can be done by froth flotation, ion exchange, solvent extraction, and precipitation. The next step usually involves pyrometallurgical processes, and finally an electrolytical process that let to obtain metallic copper.

The minerals employed in the copper extraction are usually sulphides that content iron and other impurities with economical interest or not such as arsenic, antimony, lead, bismuth, gold, silver, and nickel. The gangue is usually quartz. Two fundamental methods are used: dry and wet route. The first is the most important and treats concentrates with not less than 24% copper. The second route is the hydrometallurgical option and usually treats ores with less than 2% copper.

With the first route, the copper is concentrate from 0.5 to 1 %Cu until 24 to 30% Cu. In this part is very important to eliminate no useful material. Once the concentrate is obtained, will be sent to a pyrometallurgical process where the concentrate is partially roasted in order to eliminate sulphur, and later is smelted to produce a mate that contains all the material in liquid state. In this part, there is an unproductive material called slag. The latter one is formed from the gangue and iron oxide formed during the roasting, and left a product, the mate (Cu2S, nFeS). This product needs to be oxidized in order to obtain an impure copper. For this operation is used the remanent iron and for several reaction will be obtained a copper no pure.

The copper obtained in the last step needs to be improved in grade and quality. The improving can be done in two steps, the first steps involves a pyrometallurgical process where the metal is introduced into a furnace at the temperature of 1100 ^oC, then is produced an oxidant reaction which forms cuprous oxide and some impurities are liberated by air addition. Once the impurities are eliminated as a slag, is required to reduce the copper to the called blister copper (99% Cu). The second step is to purify electrolytically the impure metal by an acid solution of copper sulphate. Thus, the final product is obtained in cathodes which has a purity of 99.999% Cu. The remanent impurities go to the electrolytic sludge.

The second route is a hydrometallurgical option that is done by acid leaching and metal precipitation. The leaching process can be done in tanks, heaps, vats, or dumps. The election depends strongly of the type of copper mineral present in the ore body. The leaching agent is usually sulfuric acid. The solution obtained is always low in copper (approximately 1 g/l). The metallic copper can be precipitated from the solution by scrap iron. Other possibility is to improve the copper content in the solution by solvent extraction. In this case, the solution is treated electrolytically in an acid bath, and the copper is recovered as cathodes of high purity which are called copper electrowon.

Copper metallurgy

The economic production of pure copper metal, suitable for fabrication and use, from copper ores containing as little as 0.5% Cu. Over 90% of the consumption of primary copper in the Western world is produced from ores containing sulfide minerals (chalcopyrite, CuFeS₂; chalcocite, Cu₂S; and bornite, Cu₅FeS₄) that can be economically treated only by pyrometallurgical processes. See also Pyrometallurgy, nonferrous.
In the main processes used in the production of copper from sulfide ores, the mined ore (0.5–2.0% Cu) is finely ground, and then concentrated by flotation to form copper concentrates containing 20–30% Cu. The concentrates are then smelted at high temperatures (about 2280°F or 1250°C) to form a molten mixture of copper and iron sulfides called matte. The molten matte is converted to blister copper (about 99% Cu) by oxidizing the remaining iron and sulfur. After removing the residual sulfur and oxygen in an anode furnace, copper anodes are cast and then refined electrolytically to produce high-purity cathode copper (99.99% Cu), which is suitable for most uses. See also Ore dressing.
Smelting and converting a typical copper concentrate generates over 0.50 ton SO₂ per ton concentrate (0.50 metric ton SO₂ per metric ton concentrate), and the resulting SO₂ emissions must be controlled to meet local environmental standards. This is generally achieved by converting the SO₂ to sulfuric acid in a contact acid plant, as long as the SO₂concentration exceeds 4% and a viable market for acid exists. See also Sulfur.
Electrorefining is used to remove the remaining impurities in the anode copper (principally As, Bi, Ni, Pb, Sb, and Se) and produce a pure cathode copper (99.99+% Cu). Also, many copper ores contain appreciable amounts of precious metals (Ag, Au, Pt, and so on), which are concentrated into the anode copper during smelting and are recovered as valuable by-products in electrorefining. The impure anodes are suspended alternately with pure copper cathodes in tanks through which an electrolyte of copper sulfate and free sulfuric acid is continuously circulated. When direct current is applied, the copper in the anodes is electrochemically dissolved and then plated as pure copper on the cathodes. Some of the anode impurities, such as arsenic and nickel, are less noble than copper and dissolve in the electrolyte, but they do not plate out at the cathode as long as their concentrations are controlled. The other impurities, such as silver, lead, and selenium, are virtually insoluble in the electrolyte and fall as slimes to the bottom of the tank. These slimes are recovered and processed for eventual recovery of selenium and the precious-metal values. See also Electrochemical process; Electrometallurgy.
Oxidized copper ores are more effectively treated by hydrometallurgical processes. The ore is crushed, ground if necessary, and leached with dilute sulfuric acid, either by percolation through heaps of ore or by agitation in tanks. Copper is recovered from the resulting solution by either cementation or solvent extraction-electrowinning. In cementation, copper is precipitated by contact with scrap iron to form an impure cement copper, which is smelted, then refined. Solvent extraction-electrowinning has become the preferred process. In solvent extraction special organic reagents are used to selectively extract copper from solution. The resulting copper-containing organic phase is then stripped to give a pure and more concentrated aqueous copper solution for electrowinning. Electrowinning is similar to electrorefining except that an inert anode is used and more energy is required. Although electrowon cathode copper is generally not as pure as electrorefined copper, it is still suitable for many applications. See also Copper; Hydrometallurgy; Solvent extraction.