Enrichment of scandium and aluminum from limonitic laterite during the nitric acid pressure leaching process

The presence of 50-100 (g/t) scandium in limonitic laterite makes it an important source for the extraction of Sc together with nickel and cobalt. This study aims to separate and enrich Sc and Al from limonitic laterite during the nitric acid pressure leaching (NAPL) process for treating limonitic laterite without interfering with the main nickel-cobalt production circuit. Extractions of 86.2% Sc and 71.0% Al were obtained under the most suitable conditions for leaching limonitic laterite. The Sc and Al were selectively, homogeneously precipitated with MgCO3 suspension after adjusting the pH to 4.5 at 60 degrees C. The precipitate contains about 27% Al and 0.037% Sc. Moreover, 0.68% of Ni and 3.62% of Mg were also found in the Sc-containing Al precipitate and their precipitation behaviour and mechanism were examined. Specifically, a small amount of Mg and Al co-precipitate to produce the layered double hydroxides (Mg-Al LDHs). The Sc-containing Al precipitate was leached by NaOH with initial concentration of 20% and liquid-to-solid ratio of 3.5 mL/g at 80 degrees C for 1 h allowing 94.6% of Al to be dissolved. The resultant sodium aluminate solution contains 65.4 g/L of Al, which could be directly applied to the recovery of Al. Scandium enrichment in the leach residue achieved a content of 0.245%. The proposed method demonstrates the potential to enhance the economic value of limonitic laterite through the recovery of Sc and Al.