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 S02' CO and CO 2 gas evolution. Major variables in the tests were:(1) Gas atmosphere (nitrogen and air).(2) Degree of sulphur elimination from calcine (50-75%).(3) Coke addition (0-5%).(4) Lime addition.In the lower temperature range ( < 900°C), substantial S02 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 S02 release during smelting, coke utilization and the implications of increasing the degree of roast of concentrate.

Sulfate Formation and Decomposition of Nickel Concentrates

“…This means that any unreacted FeS in contact with Fe 2 O 3 will react and form magnetite plus SO 2 . This reaction was also proposed by Celmer et al [10] in previous calcine smelting tests.…”

“…[4][5][6][7] This means that the calcine being transferred to the electric furnaces consists of a mixture of unreacted sulfides in addition to various oxides and sulfates. [8][9][10][11][12] One important aspect of this is that during the subsequent heating in the calcine banks of the electric furnace, these sulfates will decompose releasing SO 2 according to reactions such as…”

Hydrogen reduction of oxidized nickel concentrates

“…[10,11] As seen in Figure 4, calcine C97 lost about 2 mass pct upon heating to 850°C. For calcine C92, the total mass loss was about 4 pct upon heating in argon to 850°C.…”

“…This is in accordance with the conclusions of previous investigators. [10,11] Figure 5 illustrates the difference between the low sulfate (C97) calcine and the high sulfate (C92) calcine. As expected, the high sulfate and hematite calcine experiences a faster mass loss and with the evolution of more SO 2 .…”

Mitigation of energy intensity of an industrial off-gas cleaning system using process engineering solutions

“…Each furnace is equipped with electrodes to provide the heat required for the complex reactions (Celmer et al [15]), of which the most important involve the generation of CO, as given below.…”