Impregnating multi-walled carbon nanotubes with Cyanex 923 extractant to improve harmful chromium(VI) adsorption from aqueous media

The performance of C923-impregnated multi-walled carbon nanotubes on harmful Cr(VI) adsorption from acidic solutions was investigated. C923 (Cyanex 923) is a liquid-liquid extraction reagent of the phosphine oxide type. The adsorption was investigated at various experimental conditions: stirring speed (250-1,500 min-1, temperature (20 degrees C-60 degrees C), HCl (0.5-2 M) and metal (0.01-0.2 g/L) concentrations in the aqueous phase, ionic strength of this phase, and adsorbent dosage (0.5-1 g/L). It was found that the metal adsorption is endothermic and spontaneous, responded to the moving boundary rate law and to the Freundlich isotherm. Adsorption dosage responded to two different models, at 0.5 g/L, data were fitted to the first order kinetic equation, whereas at 1 g/L, pseudo -second-order model fitted to the experimental results. Metal loaded onto the impregnated nano -tubes can be desorbed by the use of hydrazine sulphate solutions, at the same time, chromium was recovered in the solutions in the less harmful Cr(III) oxidation state.