Separation and recovery of neodymium and praseodymium from permanent magnet scrap through the hydrometallurgical route

Abstract

ABSTRACTThe leaching of neodymium (Nd) and praseodymium from scrap permanent magnet bearing 64.37% Fe, 30.57% Nd and 0.42% Pr and 0.71% B was carried out using HCl solution. X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyses study ensured the elements of the above metals as Nd-Fe-B in the solid phase . The leaching parameters – HCl concentration, time, temperature, particle size, pulp density (S/L) – were investigated to obtain the suitable leaching condition for the effective dissolution of both Nd and Pr. At the conditions of 0.2 M HCl, temperature 90°C, leaching time 240 min, particle size 76–105 µm, agitation speed 800 rpm and pulp density (PD) 1%, the leaching efficiencies of Nd and Fe were 99.99% and 61.36%, respectively. The optimum leaching condition was established by minimizing iron co-extraction vis-à-vis the quantitative recovery of Nd and Pr. The iron content of the leach liquor was removed by the precipitation method using lime (Ca(OH)2) at pH 4.0. After the removal of iron, the solvent extraction (SX) parameters were optimized and the McCabe–Thiele diagram for extraction and stripping was developed. The McCabe–Thiele plot for extraction with 0.8 M NaD2EHPA (30% neutralized) and stripping with 8% H2SO4 showed two stages at A:O = 2:1 and O: A = 4:1, respectively, for the quantitative recovery of Nd and Pr. The final strip solution bearing 72 g/L Nd and 1.088 g/L Pr was crystallized to produce (Nd) 2(SO4)3 and (Pr) 2(SO4)3, respectively.