Neodymium and Palladium Extraction with Phosphorylated Thiacalix[4]- and Calix[4]arenes from Nitric Acid Media

Abstract

A comparison was made between the separate extraction and coextraction of neodymium and palladium from nitric acid solutions with bifunctional phosphorylated thiacalix[4]arene (TCPO) and monofunctional extractants that modeled it—phosphorylated calixarene (CPO), thiacalixarene (TCA), and their mixtures—for evaluating the mutual influence of S- and PO-donor sites of the extractants. A decrease in D_Nd was detected only for TCPO: it was less that 0.1 as against 1.6 for CPO. ³¹P{¹H} and ¹³C{¹H} NMR spectroscopy studies showed that the decrease in the neodymium extraction with TCPO is similar to the inhibition of the catalytic activity of enzymes (TCPO analogs) in the presence of effectors (analogs of rare-earth elements) in phosphorylation—dephosphorylation processes. Their coordination to the allosteric CH₂P(O)R₂ site leads to high chemical shift (4 ppm) of the signal of the ¹³CH₂ spacer and to the formation of TCPO hydrolysis products (n-methylthiacalix[4]arene and, probably, dibutylhydroxophosphinate). The results of the extraction with TCA–CPO mixtures are of interest for a simplified process (PUREX) and a process being developed (CARBEX) as applied to the corecovery of neodymium and palladium from nitric acid solutions and their separation from carbonate solutions after neodymium stripping.