Investigating the Effect of Temperature on Sulfur Deportment in Nickel Laterite Calcination

Abstract

The majority of the ferronickel production from nickel laterite ores is through the Rotary kiln- electric furnace (RK-EF) process. Calcination and partial reduction of the laterite ore is typically carried out in a rotary fuel fired furnace. Sulfur is one of the most deleterious impurities in nickel alloys and degrades the mechanical properties of the product. Considering the insubstantial concentration of sulfur in laterites, it is assumed that sulfur partially originates from added fuel and reductant in the calcination stage. Investigating the effects of the temperature in the calcination stage on the sulfur distribution can provide valuable information on controlling the level of sulfur in the calcine. In this study, the atmosphere resulted from coal combustion is simulated by purging a gas mixture of N2, CO, CO2, and SO2 to the electrical horizontal tube furnace. The effect of temperature (600, 700, 800, and 900 ⁰C) on the sulfur deportment was studied. Inductively coupled plasma optical emission spectrometry (ICP-OES), and X-ray diffraction tests were used to measure the sulfur content and identify the phase composition of the products. The dominant compound of the calcine that contains sulfur is identified as pyrrhotite. Raising temperature from 600 to 700 ⁰C, increases %S in the calcine from 0.29 to 0.34%; however, promoting the temperature above 700 ⁰C diminishes the sulfur deportation percentage because of decreasing the surface area of solids by recrystallization of magnesia silicate compounds and sintering of oxides.