Use of colemanite in ferronickel smelting

Use of colemanite in metal-slag systems aims primarily to decrease the viscosity of slag and, therefore, achieve better metal-slag separation. Enhanced metal-slag separation is helpful to decrease the number of suspended metal/alloy droplets in slag, i.e. the physical losses. In the literature, successful use of colemanite was reported both in steelmaking and copper matte smelting processes. Ferronickel smelting slags contain nickel in the range of 0.1-0.2% and correspondingly, metal-slag distribution ratio values of nickel are reported even above 200. On the contrary, nickel recoveries are hard to exceed 95%. This can be mostly attributed to the physical losses of nickel due to very high slag volume in ferronickel smelters; for 1 ton of ferronickel, 10-15 tonnes of slag are generated regardless of the type of the laterite, which contains significant quantity of gangue components. The authors thought that use of colemanite could be a solution to decrease physical losses. Therefore, the use of colemanite in ferronickel smelting was investigated in the present work. Laboratory-scale smelting experiments were conducted using calcined and prereduced laterites in a vertical tube furnace under different gas atmospheres. The amount of colemanite added was in the range of 0 - 2.5% of the total charge. The experiments were also performed using ferronickel and slag samples obtained from a ferronickel smelter.

Viscosity and structure evolution of the SiO2-MgO-FeO-CaO-Al2O3 slag in ferronickel smelting process from laterite

The SiO2 fractions in laterite-nickel ores are quite high, thus certain amount of lime should be used as fluxing material to achieve good fluidity and desulfurization capacity in industrial smelting process. However, this operation leads to an additional cost of lime. In addition, the increase of slag volume decreases the effective furnace volume. To avoid such problem, partial reduction of FeO has been suggested. Therefore, the high SiO2, low MgO and FeO and very little CaO slag is formed, which was less studied in the previous literature. Therefore, the viscosity and slag structure are investigated in the present study through FT-IR and Raman analysis methods. Experimental results show that the slag is a mixture of liquid and solid phases under the experimental temperature. The FT-IR and Raman spectra show that the fractions of the complex polymerization structure decrease significantly with the increase of FeO content and slag basicity, resulting in the decrease of apparent viscosity.