Selective extraction process of scandium from nickel laterite waste through hydrometallurgy

Scandium (Sc) extraction from iron and aluminum waste is a promising technique for the recycling and valorization of laterite nickel ore waste. Iron and aluminum waste is one source of scandium during preparation of nickel and cobalt hydroxide by wet smelting of laterite nickel ore. The content of Sc is notably higher than that of the raw materials, as the element is enriched in the iron and aluminum waste. As the main element in the waste samples, Al exhibits significant interference in the selective separation of Sc. In this work, taking the production line for laterite nickel ore wet leaching as the research object, the trend and distribution of trace Sc were systematically analyzed. A series of leaching experiments was conducted under varied conditions of leaching pH (2.6-3.5), leaching time (0.5-2.0 h), volume of evaporated concentrated solution (0.2-1.0 L), mass of waste added (200-800 g), reaction temperature (240-260 °C), reaction time (0.5-1.5 h), H₂SO₄ addition amount (50-300 mL L^-1) and (NH₄)₂SO₄ addition amount (150-350 kg m^-3). Experimental results revealed that the optimum leaching conditions were observed at a pH value of 3.0 and a leaching duration of 1 h. The optimum condition for evaporation and concentration was at 0.35 L, while the optimum conditions for impurity removal were at a waste mass of 300 g, a reaction temperature of 255 °C and a reaction time of 1 h. Under these optimum conditions, scandium content was approximately 14.67%. The product was identified as a complex salt of Sc through XRD, which could be converted to high-purity Sc₂O₃ after roasting.