Selective preparation of samarium phosphates from transition metal mixed solution by two-step precipitation

Samarium-cobalt alloys are used as materials for powerful magnets with relatively high Curie temperatures. Samarium is a valuable and expensive material because it is one of a group of rare earth elements. In order to utilize this rare earth resource in a sustainable society, it is necessary to recover, reuse, and recycle rare earth elements. With this in mind, a new process for recovering neodymium phosphate from neodymium-iron mixed aqueous solutions has recently been reported, avoiding the difficulties reported with conventional methods. Given that rare earth phosphates are a major component of rare earth ores, this new process was proposed to recover them as phosphates. In this method, neodymium phosphate was selectively precipitated from a neodymium-iron mixture in a two-step process with an adjusted pH value. In this study, we attempted to selectively precipitate samarium phosphate from a mixed solution of transition metals using this two-step precipitation method. The advantage of this method is that the samarium compound can be separated from other metal salts without the use of high temperatures or special equipment. Optimal conditions were determined by evaluating the precipitates by molar ratio, color hue, UV-visible reflectance spectra, X-ray diffraction, and infrared spectroscopy of the precipitates obtained. In Step 1, the pH was adjusted using sodium hydroxide to remove cobalt, iron, and copper hydroxides other than samarium. In Step 2, after adding phosphoric acid, the pH was adjusted so that a precipitate of samarium phosphate was formed.