Precipitation of scandium from pregnant leach solution of high-pressure acid leaching of nickel laterite ore and its re-leaching behavior from the precipitate

Scandium is one of the rare earth metals that has been widely developed as an alloying element for aluminum, solid electrolytes in solid oxide fuel cells (SOFCs), and several other modern world applications. However, its rare existence and high production costs cause the price of scandium is still very high. One of the primary sources of scandium is nickel laterite ore which is reported to have Sc contents in the range of 50 – 60 ppm. This research aims to study two-stage iron precipitation behavior as a part of the purification process of pregnant leach solution of nickel limonite ore obtained from high-pressure acid leaching (HPAL) at 240°C and to investigate the effect of several variables of the extraction of scandium from the precipitate re-leaching at atmospheric pressure. The experimental results show that in the first stage of iron precipitation at pH 2.75, Fe precipitation was 72.19%, with the co-precipitation of Sc, Ni, Co, and Al of 4.00, 0.88, 0.95, and 4.03%, respectively. Meanwhile, in the second stage of the iron precipitation at pH 4.75, Fe precipitation was 88.32% with Sc, Ni, Co, and Al co-precipitations of 99.81, 42.88, 36.66, and 99.88%, respectively. The best condition for Sc re-leaching was obtained at a leaching duration of 90 minutes, temperature 35°C, H₂SO₄ concentration 100 g/L, and solid-liquid ratio 0.2 g/mL with 98.61% Sc extraction and co-extraction of Ni, Co, Fe, and Al of 83.75, 93.93, 81.29, and 91.64%, respectively. The two-stage iron removal from the HPAL pregnant solution and re-leaching of scandium from the stage-two precipitate can increase Sc levels from 72 ppm in the ore to 241 ppm in the precipitate from the second-stage iron precipitation.