The adsorption characteristics of precious and base metals on four different ion-exchange resins

[摘要] ENGLISH ABSTRACT:Adsorption tests were conducted with four different ion-exchange resins to determinethe equilibrium adsorption of a range of precious and base metals. The adsorptioncharacteristics were determined for synthetic single metal, as well as for multicomponentand base metal solutions. The effect of the el- concentration on theequilibrium adsorption was established for three different Hel concentrations in theabove solutions. From the ion-exchange characteristics determined, a selectiveadsorption sequence is proposed for the separation of precious and base metals.Pure platinum, palladium and gold were dissolved in aqua regia and diluted to 2000ppm (as metal) in 4M Hel. Ruthenium, rhodium and iridium were dissolved frompure salts in Hel. A 2000 ppm base metal solution was prepared by dissolving all therequired components, including precious metals, to match an in-plant industrial basemetalssolution composition. For each precious metal the equilibrium adsorption wasdetermined for a couple of solution concentrations. Data points for adsorption curveswere established by varying the amount of resin added to the test solution of a specificconcentration. The equilibrium solution concentrations were determined by Iepanalysis after 24 hours of exposure, using the bottle-roll technique.The experimental results obtained indicate a possible process route for the separationof precious metals with ion-exchange resin. The XAD7 resin is highly selective forgold from mixed solutions containing precious and base metals. It is also evident that,with the gold removed from the solution, the A22 resin adsorbs only palladium.IR200 resin adsorbs only the base metals from the solution. With all other preciousmetals removed from the solution (platinum and ruthenium must be extracted by othermeans), iridium can be adsorbed from the solution by IRA900 resin which is highlyselective for iridium over rhodium. For all of the anion resins, XAD7, IRA900, andA22, the chloride concentration of the solution did not have a big effect on theadsorption capacity. However, the adsorption of base metals on IR200 is sensitive tochloride concentration, with a rapid reduction in adsorption at higher chlorideconcentrations.Statistical models were developed for the adsorption of each of the precious metals,as well as for the base metal solution. All adsorption data, obtained for a resin(typically 250 equilibrium data points), was used in the development of the model.The SPSS statistical software package was used to develop linear regression models.The interaction between all the input parameters, e.g. the interaction of gold andchloride ions, was modelled by specifying the product of the gold and the chlorideconcentrations as an input variable. The variables that determine the adsorptionquantities were identified.High solution concentrations of the target adsorption component increase theadsorption quantity. It has been established that a higher platinum concentrationincreases the adsorption quantity of gold on XAD7 resin. However, the adsorptionquantity is reduced at higher ruthenium concentrations. The adsorption quantity ofiridium on IRA900 is reduced with increased rhodium concentration. The adsorptionquantity of palladium on A22 is increased by the presence of rhodium and decreasedby larger concentrations of iridium and platinum. The adsorption of base metals onIR200 is decreased at higher acid concentrations. Higher concentrations of gold in thebase metal solution also decrease the adsorption quantity of base metals. The modelpredicted adsorption of each component compares well with the actual measuredvalues.In batch adsorption tests the counter ion is not removed from the resin. The resincapacity for a specific ion concentration could therefore not be determined. As such,the adsorption models are only valid for the initial part of the ion-exchange process.The effect of kinetics on the adsorption was not determined.

[发布机构] Stellenbosch University