Transformation of YF₃ into Y(OH)₃ by a Mechanochemical Process: Extracting Yttrium from Rare Earth Smelting Slag under Mild Conditions

The yttrium (Y) element in the calciothermic reduction YF₃ smelting slag (YSS) has a recovery value, and the conventional direct alkali transformation-acid leaching method of recovering rare earth elements (REEs) from solid waste, which contains rare earth fluoride, has encountered problems of high energy and alkali consumption and low leaching rate. In this study, a green process for the transformation of YF₃ to Y(OH)₃ at room temperature was achieved by employing a mechanochemical method. The process is environment-friendly, with zero emission, less acid/alkali consumption, and water recyclability. It was found that YF₃ will be “passivated” by a newly formed Y(OH)₃ product layer under the alkaline condition, resulting in the unsustainable transformation of YF₃ to Y(OH)₃. However, the mechanical force could destroy the coating of Y(OH)₃ and promoted the transformation of YF₃ to Y(OH)₃ completely; as such, the transformation efficiency of YF₃ reached 98.2%. On this basis, the process of extracting Y from YSS was further studied, and the results showed that YF₃ in YSS was successfully transformed into Y(OH)₃ and the leaching rate of Y reached 96.2%. Therefore, it is expected to be a new technology to recover REEs from waste slag or minerals that contain rare earth fluoride and has good industrial application prospect.