JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III NON-FERROUS EXTRACTIVE METALLURGY Previous Question Paper (September - 2021 - R18)

Smelting is a pyrometallurgical process primarily aimed at separating the metal-bearing minerals from the gangue. It involves the melting of ore or concentrate with flux in a furnace (such as a reverberatory or flash furnace) to produce two distinct liquid phases: a matte (a mixture of metal sulfides) and a slag (oxide-based waste). The primary goal is the concentration of valuable metals into the matte phase.

Converting is the subsequent oxidation process performed on the molten matte. It involves blowing air or oxygen-enriched air through the molten matte in a converter (such as a Pierce-Smith converter). The objective is to remove iron and sulfur from the matte, converting the metal sulfides into crude or 'blister' metal. Unlike smelting, which separates metal from gangue, converting chemically transforms the concentrated matte into a metallic state by oxidizing the remaining impurities.

The grade of copper matte, defined by its copper content, significantly impacts the efficiency and economics of the converting process. Difficulties arise at both extremes:

If the matte is too low grade (low copper, high iron and sulfur):

• The volume of slag produced is excessively high, leading to increased copper losses in the slag and higher refractory wear in the converter.
• The process requires a longer blowing time to oxidize the excess iron and sulfur, which reduces the overall throughput of the converter.
• Higher fuel consumption may be required to maintain the necessary temperature due to the increased mass of material being processed.

If the matte is too high grade (high copper, low iron):

• There is insufficient iron sulfide to provide the heat required for the exothermic converting reaction. This can lead to the 'freezing' of the charge, necessitating the addition of external heat or fuel.
• The rapid oxidation of copper can lead to excessive formation of copper oxide (Cu2O), which dissolves into the slag, resulting in significant metal loss.
• The lack of sufficient iron to form a protective slag layer can lead to increased mechanical and thermal stress on the converter lining.