Thermodynamics of Rare Earth Precipitation in NdCl3-AlCl3-H2C2O4 Solution System

Abstract

In the process of rare earth ore leaching, the impurity will be leached into the rare earth feed liquid.The impurity, especially the Al3+ ion has adverse effects on subsequent rare earth extraction process and the purity of rare earth product. According to the simultaneous equilibrium principle, the thermodynamic equilibrium of NdCl3-AlCl3-H2C2O4 system was calculated, and the lgc-pH diagram of soluble ion in the system was drawn. The forming reason of stable precipitates existence zone were analyzed. By changing the oxalic acid concentration, the concentrations of neodymium and aluminum in the solution system and the variation of stable precipitates existence zone with pH were discussed and analyzed. The results show that precipitation of neodymium can be guaranteed under the conditions of 1 11.74, while aluminum does not precipitate out. From the point of actual production, the precipitation of neodymium oxalate under acidic conditions is the focus of the research. When the concentration of oxalic acid exceeds the concentration required by neodymium ion to form neodymium oxalate precipitation, the stable precipitates existence zone of Nd2(C2O4)3 enlarged. In this range, the lower the pH is, the better the Nd2(C2O4)3 precipitation effect would attain.