Reducing rare earth loss by adding acetic acid in the aluminum removal process of rare earth leaching solution

Abstract

The ionic-type rare earth ore, abundant in medium and heavy rare earth elements, is a strategic mineral resource. The removal of aluminum from ionic rare earth leaching solution results in over 8% loss of rare earths. Preliminary research has found that adding acetic acid (HAc) during aluminum removal process can effectively reduce the loss of rare earth elements. In this paper, through the calculation of the species distribution in the La2(SO4)3-Al2(SO4)3-HAc-H2O system, it is found that HAc forms an AlOH-Ac+ complex with aluminum ions, with a proportion of up to 70%, which will increase the initial precipitation pH of aluminum hydroxide. Furthermore, HAc and lanthanum form a LaAc2+ complex, and the proportion can reach more than 20%. Moreover, the zeta potential, FT-IR, and XPS tests of aluminum hydroxide, obtained by neutralization precipitation, revealed that the complexation of HAc and aluminum can reduce the precipitation rate of aluminum hydroxide, so that its particle size increases, the specific surface area decreases, and the van der Waals force adsorption sites are reduced. HAc can be chemically adsorbed on aluminum hydroxide, thereby increasing the zeta potential of aluminum hydroxide and ultimately reducing its electrostatic adsorption effect on rare earths. Additionally, the complexation of HAc and rare earth elements can reduce the local supersaturation of rare earth hydroxides and decline the coprecipitation of rare earth elements. Finally, under a precipitation endpoint pH of 5.2, HAc concentration of 0.006 mol/L, aluminum concentration of 0.2 g/L, rare earth concentration of 0.8 g/L, magnesium ion concentration of 0.5 g/L and magnesium oxide slurry concentration of 0.45 mol/L, the aluminum removal efficiency obtained with rare earth leaching solution reached 98.47%, and the rare earth loss efficiency was 2.62%. Compared with the control, the rare earth loss efficiency was reduced by 5.59%. This paper provides guidance for the efficient and green development of ionic-type rare earth ore.