Evaluation of wine production residue grape stalks for Cu(II), Pb(II), Cd(II) ve Cr(VI) removal from aqueous solutions

Heavy metals which are used very common in the form of their alloys and compounds are important pollutants that are cause water pollution. The heavy metal ions have different oxidation state in waters. They must be removed from the wastewaters due to their toxic characteristics.Heavy metal ions are removed from aquatic environments by different methods such as chemical precipitation, ion exchange, reverse osmosis, ultrafiltration, cementation, electrocoagulation and solvent extraction. Because of some disadvantages of these methods, adsorption techniques have been investigated in recent years in order to remove heavy metal ions from aqueous solutions.In this study, the removal of copper, lead, cadmium and chromium ions from aqueous solutions by grape stalk which is residue of grape wine production process has been investigated. For this purpose, the effects of initial pH of solution, adsorbent dosage, particle size, contact time, temperature, initial metal concentration and organic substances content on removal of discussed heavy metal ions from aqueous solutions have been explored. Obtained results have been applied adsorption isotherms and the adsorption capacities of discussed material have been calculated.According to results obtained, it has been determined that pH, temperature, adsorbent dosage and contact time are important parameter affecting the copper, lead, cadmium and chromium adsorption. In order to remove copper ions having the concentration of 10 mg/l, the most suitable pH, adsorbent dosage, particle size and contact time have been determined as pH 5, adsorbent dosage of 10 g/l and contact time of 30 min. Under these conditions, 84.8 % of copper in the solution have been removed by grape stalk. The most effective Pb(II) removal yield (89.12%) has been obtained at pH 5 and in the presence of 5 g/l adsorbent dosage having -140+170 mesh particle size and for a contact time of 60 min. Maximum Cd(II) removal yield (92.02%) in the 10 mg-Cd(II) /l solutions have been achieved at the conditions of pH 6, contact time of 15 min, adsorbent dosage of 10 g/l and particle size of -100+140 mesh. In order to remove chromium ions having the concentration of 50 mg/l, the most suitable pH, adsorbent dosage, particle size and contact time have been determined as pH 2, adsorbent dosage of 22.5 g/l, particle size of -200 mesh and contact time of 60 min. Under these conditions, 77.29 % of copper in the solution have been removed by grape stalk.It has been determined that the adsorption yields decreases with the increasing temperature, initial metal ion concentration and the presence of complex forming organic substances.Copper, lead, cadmium and chromium adsorptions by grape stalk fit the Freundlich, Langmuir, Frumkin and Temkin adsorption isotherms. The copper, lead, cadmium and chromium adsorption capacities of the grape stalk at 25°C have been calculated to be 20.7039; 32.8947; 21.5053 ve 6.6979 mg-metal ion/g-grape stalk, respectively. Copper, lead, cadmium and chromium adsorption capacities of the adsorbent decrease in the order of Pb(II)>Cd(II)>Cu(II)>Cr.Keywords: Heavy metal adsorption, grape stalk, wine production residue, adsorption isotherms, desorption.