Relative extraction rates of rare earth ions from weakly acidic solution of binary mixture of rare earth chlorides by di-(2-ethyl-hexyl) phosphoric acid/kerosine

Abstract

Extraction studies on rare earth ions from weakly acidic solutions of binary mixture of yttrium and other rare earth chlorides system, and praseodymium and neodymium chlorides system, by di-(2-ethyl-hexyl) phosphoric acid/kerosine, H 2X 2 as dimer, show that rare earth ions having a smaller artificial atomic number than yttrium (67.5) were extracted faster than it, and also praseodymium was done faster than neodymium, while, those having the larger number than yttrium were extracted slower than it. These results can be explained as follows: The stoichmetry of the reaction can be written by Ln 3+ + 3 (H 2X 2) = Ln(HX 2) 3 + 3 H + and the law is given by V = k′ 1 [Ln 3+] − k′ −1, [Ln(HX 2) 3], supposing that concentrations of H 2X 2 and H + would not affect the extraction rate, where k′ 1 and k′ −1 are the pseudo-first order reaction rate constants of the forward and backward reaction, and both of them are dependent on shaking strength (contact surface area between aqueous phase and organic one). The order of the k′ (= k′ 1 + k′ −1), k′ 1 and k′ −1 value for the yttrium-other rare earth system were k′ Nd > k′ Dy > k′ Ho > k′ Y > k′ Er > k′ Yb, and k′ −1 Nd > k′ −1 Dy > k′ −1 Ho > k′ −1 Y > k′ −1 Er > k′ −1 Yb, while the values of k′ 1 were almost constant for all of the rare earth ions studied. And also, the order of the k′, k′ 1 and k′ −1, value for the praseodymiumneodymium system were k′ Pr > k′ Nd, k′ −1 Pr > k′ −1 Nd and k′ 1 Pr − k 1 Nd.