Selective preconcentration of platinum and rhodium from hydrochloric acid media containing tin (II) chloride using polyurethane foam

Master Thesis


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University of Cape Town

The potentially quantitative and selective sorption of chloro-(trichlorostannato)-platinum(II) and -rhodium (III/I) complex anions by polyurethane foams has been examined. Quantitative separation of platinum(II) from iridium and ruthenium has been achieved. Rhodium( III) is similarly sorbed by polyurethane foam in the presence of sufficient tin(II) chloride and-its clean separation from iridium has been achieved using this method. Ruthenium, although not significantly sorbed under the same conditions as platinum and rhodium, appears to inhibit the extraction of the rhodium(III/I)-tin(II) species. A procedure has been developed for the quantitative recovery of both platinum and rhodium. The polyurethane foams are dissolved in hot nitric acid, followed by flame AAS. Near-quantitative recovery of these metals has been achieved by means of foam stripping using a suitable eluent. The rate of formation of the chloro-(trichlorostannato)platinum( II) complex anions is rapid when PtCl₄²⁻ is treated with an excess of tin( II) chloride. On the other hand, the reaction of cis-Pt(NH₃)₂Cl₂ with stannous chloride is very slow and forcing conditions are required to achieve quantitative sorption of the platinum(II)-tin( II) species by polyurethane foams for this complex The potential of the foam to selectively extract platinum from solutions containing certain base metals was studied. Results obtained show that in all cases complete extraction of platinum was achieved. Of the base metals investigated, namely Fe( III), Co( II), Ni(II), Cu(II) and Zn(II), only copper(II) co-extracts to a small extent with the noble metal.

Includes bibliographical references.