Ion exchange recovery of rhodium from strong ammonium chloride solutions

Abstract

The authors looked at the sorption of rhodium using Puromet MTS9840, Puromet MTS9841 and Puromet MTS9850 weakly basic anion exchange resins with polyamine groups and Puromet MTS9140 ion exchange resin with thiourea groups, and they found that, when HCl is partially replaced with NH4Cl as the source of chloride ions and if the overall concentration of chloride ions remains the same (i.e. 4 mol/l), the rhodium distribution coefficients tend to drop in direct proportion to the rising share of NH4Cl in the solution. When using a mixture of 1 mol/l HCl and 3 mol/l NH4Cl, the rhodium capacities of all tested ion exchange resins are 2.5 to 6 times lower than the capacities reached when using 4 mol/l HCl solutions, with the steady-state concentrations of rhodium being equal. The sorption isotherms for the NH4Cl containing solution remain arc-shaped. At the same time, the presence of NH4Cl is associated with only a slight decrease in the rhodium sorption rates when using polyamine resins, which is demon strated in the case of the MTS9840 resin. In terms of selectivity and rhodium capacity when using chloride solutions both with and without ammonium chloride, the tested ion exchange resins can be arranged as follows: MTS9841 > MTS9840 > MTS9140 > MTS9850. It was found that when rhodium is absorbed in dynamic conditions from the following solution, g/l: Rh(III) 0,2; NH4Cl 133,7 (2.5 mol/l); HCl 54,7 (1.5 mol/l); Fe(III) 5,0; Al(III) 4,2; Zn(II) 4,0; Sn(IV) 6,0, the use of the MTS9841 anion exchange resin results in a higher recovery of rhodium (up to 98%), while the residual concentration of rhodium in the solution drops 4 times (down to 0.005 g/l) as compared with the use of the MTS9840 anion exchange resin. It is shown that the process of rhodium desorption from saturated MTS9841 anion exchange resin with a acidified thiourea solution has a minimum rate of 95%. This research was funded by the Russian Science Foundation; Project No. 21-79-30029.