Selective formation of lanthanum phosphate from lanthanum–copper solutions

Abstract

Neodymium–iron and samarium–cobalt–iron–copper alloys are typically used to produce magnets. As neodymium and samarium are rare earth elements, they are precious and expensive; consequently, they are often recovered by recycling processes to reduce costs. Recently, a novel technique to recover neodymium and samarium has been reported that avoids the reported difficulties of previous methods. Because rare earth phosphates are the main components of rare earth ores, a novel phosphate process was suggested. However, the presence of copper cations complicated recovery from samarium–cobalt–iron–copper solutions. Therefore, in this work, to clarify the behavior of copper, we investigated the preparation of lanthanum phosphate from lanthanum–copper solutions. A lanthanum–copper solution was mixed with a phosphoric acid solution and then the pH was adjusted using sodium hydroxide solution. The precipitates formed at various pH values were filtered and dried. The ratio of lanthanum and copper in the precipitates was estimated by inductively coupled plasma optical emission spectrometry. As the ideal, the lanthanum phosphate was filtered out, so the filtrate contained the copper ions. Furthermore, the phosphoric acid concentration was varied to study precipitation in the absence of copper compounds. Lanthanum phosphate containing a small amount of copper was obtained using the developed process. This phosphate process was found to be useful for recovering rare earth elements, and it may be applicable to the recycling and recovery of other rare earth elements of interest.