The sorption of lead and cadmium from aqueous solutions by grape stalk waste (a by-product of wine production) was investigated. The effects of the contact time, pH of the solution, ionic medium, initial metal concentration, other metal ions present and ligands were studied in batch experiments at 20 degrees C. Maximum sorption for both metals was found to occur at an initial pH of around 5.5. The equilibrium process was described well by the Langmuir isotherm model, with maximum grape stalk sorption capacities of 0.241 and 0.248 mmol g(-1) for Pb(II) and Cd(II), respectively, at pH around 5.5. Kinetic studies showed good correlation coefficients for a pseudo-second-order kinetic model. The presence of NaCl and NaClO(4) in the solution caused a reduction in Pb and Cd sorption, the latter being more strongly suppressed. The presence of other metals in the uptake process did not affect the removal of Pb, while the Cd uptake was much reduced. HCl or EDTA solutions were able to desorb lead from the grape stalks completely, while an approximately 65% desorption yield was obtained for cadmium. From the results obtained it seems that other mechanisms, such as surface complexation and electrostatic interactions, must be involved in the metal sorption in addition to ion exchange.

Grape stalk wastes generated in the wine production process were used for the removal of cadmium and lead ions from aqueous solutions. The experimental breakthrough curves (BTC) were obtained from fixed-bed columns. Experiments were carried out to evaluate the influence of both inlet metal concentration and sorbent particle size. The experimental data were fitted to the Thomas model, a well-established fixed-bed sorption model. The theoretical sorption capacities obtained by the Thomas model were in good agreement with the breakthrough capacities determined from the sorption data. The CXTFIT code was used to determine the transport and sorption parameters of the convective-dispersive equation (CDE) and the two-site deterministic nonequilibrium (TSM/CDE) model by adjusting the models to the experimental breakthrough curves. The results showed that sorption capacities as well as both transport and sorption parameters were affected by the initial metal concentration as well as by the sorbent particle size.