Green selective recovery of lanthanum from Ni-MH battery leachate using aqueous two-phase systems

Abstract In view of the importance of resource recycling and the use of environmentally safe systems to extract the metals contained in wastes, the present study concerns the extraction/separation of lanthanum from spent Ni–MH batteries. Investigation was made of the extraction behavior of lanthanum using aqueous two-phase systems (ATPSs), and a new environmentally safe hydrometallurgical method was developed for the selective extraction of La from Ni-MH battery leachate. The extraction behavior of La was evaluated considering the influence of the following parameters: concentration of different extractant; pH; ATPS-forming electrolyte (Li 2 SO 4 , Na 2 SO 4 , MgSO 4 , Na 2 C 4 H 4 O 6 , or Na 3 C 6 H 5 O 7 ); ATPS-forming polymer (L64 or PEO1500). The recovery efficiency was evaluated by analyzing the extraction percentage (%E), and the best conditions for analyte extraction were achieved using the ATPS formed by PEO1500 + Li 2 SO 4 , at pH 6.00, with 1,10-phenanthroline as the extractant agent (%E = 74.1%). The method was applied to a real Ni-MH battery leachate. After three successive extraction steps, high separation factor (S) values were obtained for the separation of lanthanum from concomitant metals (S La,Ce  = 180; S La,Pr  = 184; S La,Nd  = 185). A stripping assay was carried out, and after a single step, 88.5% of the lanthanum was available for a possible electrowinning step.