Sorption behaviour of lead(II) ions from aqueous solution onto Haro river sand

The sorption of lead(II) ions onto Haro river sand has been studied using voltammetric methods as well as the effect of different acid concentrations on the sorption process. The maximum sorption of Pb(II) ions onto the adsorbent surface was achieved from de-ionized water. It was found that the sorption data could be fitted by the Freundlich and Dubinin-Radushkevich (D-R) isotherms. Values of 1/n = 0.71 +/- 0.003 and of A = 15.4 +/- 6.86 mmol/g were estimated from the Freundlich isotherm while the D-R isotherm gave beta = -0.00478 +/- 0.00022 mol(2)/kJ(2), X-m = 23.26 +/- 0.05 x 10(-2) mmol/g and E = 10.23 +/- 0.23 kJ/mol. The influence of temperature on the sorption process over the temperature range 283-323 K under optimized conditions yielded Delta H-0 = 24.87 +/- 0.44 kJ/mol, Delta S-0 = 95.8 +/- 1.5 J/(mol K) and Delta G(0) = -3.6 +/- 0.02 kJ/mol at 298 K. These values demonstrate the endothermic and spontaneous nature of the sorption process. The addition of chloride, calcium or zinc ions to the system enhanced the sorption of Pb(II) ions whereas the corresponding addition of sulphate, cadmium, copper(II) or chromium(III) ions tended to reduce the extent of sorption.