Recovery of Pd(II), Ir(III) and Rh(III) from aqueous solutions with Brewer’s Yeast-functionalised bentonite

Abstract

The scarcity of precious elements such as Pd(II), Ir(III) and Rh(III) has been increasing over the years hence, their recovery from wastewaters using efficient and cheap recovery techniques is becoming more important. In this study, the spent yeast collected after brewing was used to functionalise bentonite clay material to obtain very cheap material for recovery. The functionalised bentonite was characterised using Fourier transform infrared (FTIR) spectroscopy and element analyser. The textural properties of the natural and functionalised bentonite were determined. The effect of adsorbent dosage, pH, concentration, contact time and competing ions on the adsorption of Pd(II), Ir(III) and Rh(III) by yeast-functionalised bentonite was determined. The adsorbent dosage of 10 g L−1 and 360 min were chosen as optimum for this study. The pH of 2 was used since; it is the typical pH of the processing plant wastewater under investigation. The adsorption of Pd(II) and Ir(III) decreased as the pH increased whilst that of Rh(III) increased with pH. The adsorption of Pd(II) increased with concentration and this was attributed to the ability of Pd(II) to adsorb on different active sites of the adsorbent. This was substantiated by the adsorption isotherm study since, the adsorption of Pd(II) onto the adsorbent was best described by the Freundlich isotherm, meaning that the adsorption occurs on different active sites. Beyond 2 mg L−1, the adsorption capacity of Ir(III) and Rh(III) remained the same. In the presence of other ions, Pd(II) adsorption increases due to the synergistic Fe-Pd interaction but, the adsorption of Ir(III) and Rh(III) decreased by 57 and 17%, respectively. Therefore, to significantly recover Ir(III) and Rh(III), the old adsorbent which contains a significant amount of other elements should constantly be replaced by the new one and as other elements decrease, the adsorption of Ir(III) and Rh(III) will increase. The yeast-functionalised bentonite is a potential cheap adsorbent for the adsorption of precious elements.