Forms of rare earth loss and the function mechanism of acetic acid in the aluminum removal process of rare earth leaching liquor

The leaching liquor extracted from ion-adsorption type rare earth (RE) ores contains large amounts of aluminum (Al) ions. The neutralization-precipitation method for Al removal results in the loss of large amounts of RE, leading to the waste of RE resources. Preliminary research has shown that the introduction of acetic acid (HAc) during the Al removal process could effectively reduce RE loss. However, there has been no in-depth study on the forms of RE loss during the Al removal process with the neutralization-precipitation method and the function mechanism of HAc. In this paper, the yttrium element was used as a representation of RE for relevant research. It was found that the forms of RE loss mainly include adsorption loss and coprecipitation loss, and the addition of HAc can simultaneously reduce both types of loss. The addition of HAc can generate Y(Ac)²⁺ and Y(Ac)₂⁺ complexes with Y³⁺, leading to an increase in the initial precipitation pH of yttrium hydroxide from 6.62 to 6.87, thereby reducing the coprecipitation loss of RE. Additionally, HAc was adsorbed on the aluminum hydroxide (Al(OH)₃), which increased the surface potential and decreased the specific surface area of Al(OH)₃, thus reducing the adsorption loss of RE. Finally, through precipitation experiments on a mixed solution of aluminum sulfate and yttrium sulfate, it was found that when the neutralization pH was 5.2, the percentage of yttrium lost decreased from 18.91 % to 12.66 % as the concentration of HAc was increased from 0 to 0.012 mol/L. The above function mechanism of HAc was further verified through XPS, SEM-EDS, and other tests on the precipitate.