Synthesis Of Dialky Phosphinic Acid With High Purity And Their Separation Properties For Rare Earth

Rare earths are important strategic resource, which has been widely used in industries of aviation, aerospace, military, information and energy. Solvent extraction is the key procedure in the process of separation and purification of rare earths. Common extractants for separating rare earths are P204 and P507, which exhibit low separation coefficients and need high concentration acid to strip. In this study, di-(2,4,4-trimethylpentyl)-phosphinic acid (HTMPA) and di-(2-ethylhexyl)-phosphinic acid (HEHPA) with high purity were synthesized, aiming at exploring an extractant with excellent properties for separation of rare earths. In addition, low-cost and facile synthesis route of trialkyl phosphine (TRPO) which could be used as synergistic extractant with dialkyl phosphinic acid to improve extraction ability and phase separation.HTMPA was synthesized with free radical addition method by using hypophosphorous acid, diisobutylene as starting materials, and di-tert-butyl peroxide as initiators. The crude products were purified by water washing, alkali washing and vacuum distillation. Yield:80%; purity:≥98%。Novel synthesis routes of HEHPA and TRPO were designed. HEHPA and TRPO were synthesized by reacting Grignard reagent with POCl3 and PCl3 respectively. The influences of raw material ratio and feed sequence on the yield and purity of the products were systematically investigated. It was shown that the highest yield and purity could be obtained when n(RMgBr)/n(POCl3)= 1:1 and n(RMgBr)/n(PCb)=4:1 respectively with the addition of RMgBr-ethyl ether solution into POCl3 and PCl3-ethyl ether solution. The crude products were purified by acidolysis, water washing, alkali washing and vacuum distillation. Yield: HEHPA 70%, TRPO 68%; purity:HEHPA 98%, TRPO 90%.The as-synthesized products HTMPA, HEHPA and TRPO were characterized by 31P-NMR,1H-NMR, MS, IR and GC-MS. Some physical properties related to extraction performance, such as density and surface tension, were measured.The extractive separation of Er, Tm, Yb and Lu in the medium of HNO3 solution with HTMPA and HEHPA was studied. The influences of pH value, time and phase ratio on extraction efficiency were investigated. It is shown that the separation coefficients of both HTMPA and HEHPA on heavy rare earths are higher than that of P5O7; the striping acidity and saturated capacity of both HTMPA and HEHPA are lower than P507.