The effect of sulfur in rotary kiln fuels on nickel laterite calcination

Abstract

Rotary Kiln - Electric Furnace (RKEF) process is the most commonly used pyrometallurgical technique for processing nickel laterite ores and is mainly suited for saprolite deposits. Sulfur is one of the harmful elements in crude ferronickel obtained via the RKEF process. Typically, laterite ores contain insubstantial sulfur content; hence, it is hypothesized that most of the sulfur in crude ferronickel originates from the coal added as the fuel and the reductant during calcination in the rotary kiln. This study investigates the role of sulfur content of rotary kiln fuels on the composition of the calcine. The calcination-partial reduction experiments were conducted at 900 °C for a 2-h residence time. Various reducing gas mixtures representing combustion products of rotary kiln fuels (e.g., coal) were contacted with the ore. At constant PCO, the sulfur content of the calcine increases linearly with an increase in PSO2 in the input gas mixture. Similarly, at fixed PSO2, the percentage of sulfur in the calcine and the percentage of sulfur deportation increase with PCO. However, an exceptional case is observed at PSO2 = 0 atm in the input gas mixture; the sulfur content and sulfur deportation slightly decrease by increasing PCO in the input gas. The sulfur content and the percentage of sulfur deportation drop at a lower input flow rate of the reducing gas mixtures.