Extraction of Rare-Earth Elements from Nitric Acid Solutions by Selected Bifunctional Acidic Organophosphorus Compounds

摘要

The extraction of microquantities of La,Ce,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm,Yb,Lu,and Y from HNO_3 solutions by bifunctional acidic organophosphorus compounds R_2P(O)CH_2P(O)Ph(OH),R=Ph (I),R=Oct (II),R=p-Tol (III),R=CH_3OC_6H_4 (IV),and Ph_2P(O)CH_2 P(O)(OBu)(OH) (V) in organic diluents has been studied.The effect of HNO_3 concentration in the aqueous phase and that of the extractant concentration in the organic phase on the extraction of metal ions is considered.The stoichiometry of the extracted complexes has been determined.The replacement of phenyl radicals in the Ph_2P(O)CH_2 fragment of (diphenylphosphinylmethyl)phenylphosphinic acid (I) by p-tolyl ones has been found to increase rare-earth ion extraction.The introduction of p-methoxy-phenyl or octyl substituents instead of phenyl ones at the same part of molecule I,facilitates the extraction of Eu-Lu and Y or Tb-Lu and Y,respectively.However,the extraction of other lantha-nides from 3 M HNO_3 solutions decreases when p-methoxy-phenyl or octyl-substituted compounds in toluene are used as extractants.The replacement of phenyl radical in the P(O)OH fragment of compound I by a butoxy-group brings about a decrease in rare-earth elements (REE) extraction.The effect of octyl radicals substitution by phenyl ones in compound II on the extraction of lanthanide ions decreases as the atomic number of REE increases.The extraction efficiency of octyl-substituted compound II has been observed to be higher than that of phenyl-substituted compound I when HNO_3 concentration in the aqueous phase decreased or when diluents with a small Schmidt's diluent parameter (DP) were used.