Removal of copper(II) from high-salt water with tin acid phosphate

Tin acid phosphate (SnP) was used as adsorbent for the removal of Cu(II) from aqueous solutions. The extent of adsorption was investigated as a function of pH, contact time, adsorbate concentration, reaction temperature with batch experiments. Adsorption mechanism was probed by thermodynamics analysis and potentiometric titration. The results show that the amount of adsorbed copper ions increases with the increase of solution pH in the examined range (3~6.5) and reaction time. The sorption process follows pseudo-second-order kinetics very well. The equilibrium data fits better to the Langmuir isotherm equation. The maximum sorption capacity amounts to 48.69 mg/g at 20°C. The free energy Es (kJ/mol) got from the D-R isotherm indicates the sorption process is a chemical ion-exchange mechanism. The ion-exchange reaction happens between Cu2+ and H+, which is spontaneous and endothermic. Adsorption experiments conducted in stimulated seawater find satisfactory adsorption capacity, 21.87 mg/g, at the NaCl concentration of 0.6 mol/L, which amounts to 93.3% of the counterpart at fresh water media. So it is feasible for tin acid phosphate in removing Cu2+ from hyper-saline media.