Journal of Chemical Technology and Biotechnology, Vol.67, No.4, 367-375, 1996
Extraction and Separation of HCl and Rh(III) with Trioctylamine
In this paper the use of trioctylamine (TOA) to extract HCl from Rh(III)-containing solutions generated by a supported liquid membrane (SLM) process is investigated. TOA was found to extract HCl readily (in a single contact of 3 min duration) at a molar ratio [HCl]/[TOA] equal to one. For each mole of HCl extracted an equivalent amount of H2O was found to be extracted as well. As far as Rh(III) extraction of TOA is concerned this was found to depend on the age of the solution and the Cl- concentration. Prolonged aging (accelerated by heating) or [Cl-] greater than or equal to 3 M was found to completely suppress the extraction of Rh(III) by TOA. The chloride ion concentration effect was attributed to Le Chatelier’s principle while the aging effect was attributed to the aquation/conversion of the extractable RhCl63- complexes to RhCl5(H2O)(2-). The aquation reaction was studied with UV-Visible spectroscopy in an effort to substantiate the solvent extraction (SX) results. On the basis of the findings of this work a combined SLM/SX process flowsheet is proposed according to which the Rh(III) and HCl co-transported through the supported liquid membrane are co-extracted by TOA and subsequently separated by differential stripping; Rh(III) with 0.5 M HCl/3 M Cl- medium and HCl with NAOH.