Rh(III) Extraction by Phosphinic Acids from Nitrate Media

The demand for platinum group metals (PGMs), such as rhodium, continues to rise at a rate that could exceed current mining yields. An alternative source for rhodium is present in spent nuclear fuel as a fission product. This work examines the use of phosphinic acids, diphenylphosphinic acid (DPPA), and diphenyldithiophosphinic (DPDTPA) acid, to extract Rh(III) from nitrate media. The results suggest that extraction of Rh(III) using DPPA and DPDTPA is non-spontaneous at room temperature. Lowering the pH and/or increasing the nitrate ion concentration in solution suppressed extraction.