An innovative process for extracting scandium from nickeliferous laterite ore: Carbothermic reduction followed by NaOH cracking

摘要

Laterite ores account for > 60% of the world's nickel resources. This ore contains considerable amount of scandium, a strategic material in increasingly high demand in various industries. Here, an innovative two-step process was developed in which scandium is first concentrated in a slag phase using carbothermic reduction and then is leached using NaOH cracking process. The byproduct of the first step is metallic iron enriched with nickel and cobalt (ferronickel alloy). The carbothermic reduction process was performed at 1400-1600 degrees C using lignite as a reductant and calcia and/or silica as a fluxing reagent. A systematic study was carried out using a fractional factorial design methodology to investigate the quantitative effect of four variables. Utilizing the results, an empirical model was built to optimize the process for maximizing scandium concentration. Under the optimum conditions, scandium was successfully concentrated in the slag phase > 14 times compared with that in the feed material, while at the same time a high-grade ferronickel alloy was produced. Furthermore, fundamental investigations were performed to elucidate the carbothermic reduction reaction mechanism. For NaOH cracking process, the investigated operating parameters were baking temperature, NaOH-to-slag ratio, baking time, and liquid-to-slag ratio. After optimization, 88% of scandium was recovered, indicating the predictability of the empirical model for scandium recovery.