JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III NON-FERROUS EXTRACTIVE METALLURGY Previous Question Paper (February - 2022 - R18)

The extraction of copper from sulfide ores typically involves pyrometallurgical processing. The process flow sheet includes the following key stages:

1. Mineral Beneficiation: The ore is crushed and ground followed by froth flotation to produce a copper concentrate (typically chalcopyrite, CuFeS₂), increasing copper content from < 1% to 25-30%.
2. Roasting: The concentrate is partially oxidized to remove excess sulfur as SO₂ gas and to convert iron sulfides into iron oxides.
3. Smelting: The calcine or raw concentrate is smelted in a flash furnace with silica flux at 1200-1300°C. This produces matte (Cu₂S-FeS) and slag (iron silicates).
4. Converting: The molten matte is transferred to a Peirce-Smith converter. Air or oxygen-enriched air is blown through the melt to oxidize iron (forming slag) and then to oxidize sulfur, resulting in blister copper (approx. 98-99% Cu).
5. Fire Refining: Blister copper is melted in an anode furnace where air is blown to remove remaining sulfur, followed by poling (using hydrocarbons) to reduce copper oxide to metallic copper, casting it into anodes.

Key parameters include the Fe/SiO₂ ratio in slag to ensure fluidity, oxygen potential to control matte grade, and temperature control to maintain the fluidity of both matte and slag phases.

Electrowinning is the final stage of hydrometallurgical copper extraction, where copper is recovered from a purified pregnant leach solution (PLS) by electrolysis.

1. Cell Setup: The process uses an electrolytic cell with insoluble anodes (typically Pb-Ca-Sn alloy) and starter sheets or permanent stainless steel cathodes.
2. Electrolyte: The electrolyte consists of copper sulfate and sulfuric acid.
3. Electrochemical Reaction: Upon applying a direct current, copper ions in the solution are reduced at the cathode, while water is oxidized at the anode.

The process is controlled by current density, which must be optimized to ensure a dense, non-porous copper deposit. Additives like thiourea or glue are often introduced to the electrolyte to improve the morphology and smoothness of the copper cathode. The acidity of the electrolyte increases over time due to the generation of H⁺ ions at the anode, which is then recycled back to the leaching stage.