The recovery of Platinum (IV) from aqueous solutions by hydrazine-functionalised zeolite

The recovery of platinum group elements (PGEs) which are normally lost during processing, can add value especially in times of declining commodities prices, high operational costs and weak economic growth. The recovery of platinum (Pt(IV)) from aqueous solutions with zeolite functionalised with hydrazine mono hydrochloride (NH2NH2 center dot HCl) was studied. The zeolite was characterised with powder X-ray diffraction (PXRD), X-ray fluorescence (XRF) and Fourier transform infrared (FTIR) spectroscopy. The effect of pH (2-9), concentration (0.5-10 mg L-1), contact time (0-540 min), adsorbent dosage (50-500 mg), competing ions (Fe3+, Ca2+, Mg2+, K+, Co-2+,Co- Ni2+, Hf4+, Zn2+ and PGEs) on the recovery of Pt(IV) was studied. The recovery of Pt (IV) was found to be more effective in acidic pH (2-5). The adsorption capacity increased with concentration from 0.5 mg L-1 to 5 mg L-1 and remained constant beyond 5 mg L-1. A slight increase (9%) in the adsorption capacity of Pt(IV) was observed in the presence of competing ions which could be due to the synergistic Pt-Fe interaction. The experimental data was best described by Langmuir isotherm model (R-2 > 0.99), indicating a monolayer adsorption. The adsorption behaviour was best described by pseudo second-order kinetic model (R-2 > 0.99), implying a chemisorption process through Pt-N interaction. A cost-benefit analysis was done and indicated that similar to 120 g Pt can be recovered per kg adsorbent and this would amount to around $3355 profit under the optimum conditions. These findings demonstrate the potential of this adsorbent for use in recovering low level concentrations of Pt and other PGEs.