Question

Copper is extracted from copper pyrites. After roasting, the ore is mixed with silica and coke and then smelted in a blast furnace. The matte obtained from the blast furnace is charged into a silica lined converter. Some silica is also added and a hot air blast is thrown into the mixture to obtain blister copper which is purified by electrorefining.

During roasting, copper pyrites are ultimately converted into a mixture of:

• A. $FeS+C{u}_{2}S$
• B. $FeS+C{u}_{2}O$
• C. $FeO+C{u}_{2}S$
• D. $FeS+C{u}_{2}S\to FeO+C{u}_{2}O$

Answer 1

Answer: (D)

$FeS+C{u}_{2}S\to FeO+C{u}_{2}O$

Process:

Copper pyrites contains only 2-3% of copper. The rest of ore contains iron as sulphide, silica, silicious materials, sulphur, arsenic etc as impurities. Froth floatation is carried out by xanthate and pine oil. The froth is collected and dried when concentrated ore is obtained which contains 25-30% of Cu. Then smelting of the roasted ore in blast furnace is done.

The minor reactions that occured during roasting continue here. Ferrous oxide combines with sand to form a fusible slag. Cuprous oxide formed combines with ferrous sulphide to give ferrous oxide and cuprous sulphide. This is because iron has more affinity for oxygen than copper.

$FeO+Si{O}_2\to FeSi{O}_3$

During roasting, copper pyrite converts into a mixture of

$FeS+C{u}_{2}S\to FeO+C{u}_{2}O$