Selective removal of Fe(Ⅲ) from HNO3 leach liquor of saprolitic laterite ore: Precipitation efficiency, hydrolysis mechanism, and removal strategy

HNO3 leach liquor of saprolitic laterite ore contains Fe3+, Al3+, Sc3+, Ni2+, Co2+, Mg2+, etc. Efficient removal of Fe3+ while reducing the loss of valuable metals is the key to solution purification. In this paper, a detailed study was carried out on the removal of Fe3+ by hydrolysis precipitation. First, thermodynamic calculations were conducted to analyze the precipitation pH changes and possible hydrolysis products at different temperatures. Subsequently, the experimental results show that more than 99 % Fe can be removed via low-temperature hydrolysis at 25–80 ℃ and pH = 3.0–3.5, but over 40 % Al and 30 % Sc also precipitate together, causing valuable metals losses. Differently, under high-temperature conditions (180 ℃, pH = 1.0, 0.5 h), 99.49 % of Fe can be selectively removed as Fe2O3 product, while other valuable metals hardly precipitate. It was found that the low-temperature Fe removal residue exhibits irregular agglomeration and uneven particle size, and contains 9.48 % NO3– and 25.86 % Fe. The high-temperature Fe removal residue presents a nanoscale spherical shape with uniform particle size and only contains 0.087 % NO3–, and the Fe content is up to 69.07 %. Finally, the Fe3+ hydrolysis mechanism was analyzed and an efficient Fe removal process from the HNO3 system including pH adjustment of leach liquor, selective Fe removal at high temperature, flash evaporation to recover free HNO3, and solid–liquid separation to obtain Fe2O3 products was proposed.