Chemical Reactions During the Electric Smelting of Nickel-Copper Calcines

Abstract

The smelting behaviour of nickel-copper calcines in the electric furnace was studied by a thermogravimetric-gas chromatographic technique in conjunction with chemical and micrographic analysis. The sequence and nature of reactions during the heating of calcines from 25 to 1250°C were defined by the temperature range and magnitude of weight changes and the characteristics of SO₂, CO and CO₂ gas evolution. Major variables in the tests were:<list list-type="simple"><list-item>

(1) Gas atmosphere (nitrogen and air).</list-item><list-item>

(2) Degree of sulphur elimination from calcine (50–75%).</list-item><list-item>

(3) Coke addition (0–5%).</list-item><list-item>

(4) Lime addition.</list-item></list>

In the lower temperature range (<900°C), substantial SO₂ evolution occurred from decomposition and oxidation reactions in the charge, and CO₂ evolution from coke combustion in air. Above the fusion temperature, the dominant reaction was oxide reduction by coke in the presence of liquid matte.

Experimental results are discussed in the context of their application to environmentally clean electric smelting with high metal recoveries. Consideration is given to the characteristics of SO₂ release during smelting, coke utilization and the implications of increasing the degree of roast of concentrate.