Comparison of the adsorption by rice hulls and Lewatit TP 214 of platinum from chloroplatinic solution

Abstract

Rice hulls, a biomass waste product, and Lewatit TP 214, a thiosemicarbazide sorbent, were investigated as adsorbents for the adsorption of platinum( IV) ions from synthetically prepared dilute chloroplatinic acid solutions. The rice hulls were characterized by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). The effects of the different adsorption parameters, sorbent dosage, contact time, temperature and pH of the solution on the percent adsorption were studied in detail for batch sorption. The adsorption equilibrium data were best fitted with the Langmuir isotherm model. The maximum monolayer adsorption capacities, Q max, at 25 °C were found to be 42.02 and 33.22 mg g-1 for the rice hulls and Lewatit TP 214, respectively. Thermodynamic calculations using the measured ΔH°, ΔS° and ΔG° values indicated that the adsorption process was spontaneous and endothermic. The pseudo-first-order and pseudo-second-order rate equations were investigated; the adsorption of platinum ions for both sorbents was found to be described by the pseudo-second-order kinetic model. The kinetic rate, k2, using 30 mg sorbent at 25 °C was found to be 0.0289 and 0.0039 g min-1 mg-1 for the rice hulls and Lewatit TP 214, respectively. The results indicated that the rice hulls could be effectively used for the removal of platinum from aqueous solution.