Adsorption of Cu(II) ions from synthetic solution by sunflower seed husks

Abstract

Annual production of the sunflower seed in Serbia is between 650,000-720,000 tons. Most of this amount is used in vegetable oil industry. Abundant by-products from this processing are sunflower seed husks. Husks are usually incinerated by vegetable oil producers in order to obtain energy, used as an animal feed, or, unfortunately, landed up at some landfills. In order to promote new, added value for this abundant, renewable resource, the investigation presented in this paper was conducted. For that purpose, adsorption of Cu(II) ions from synthetic solution by unmodified sunflower seed husks was examined. ATR-FTIR was used to identify functional groups as potential active sites for Cu(II) sorption. Zeta potential values were determined to reveal the surface charge, while the cation exchange capacity (CEC) was determined to reveal the amount of exchangeable ions on its surface. ATR-FTIR analysis revealed the presence of specific functional groups (hydroxyl, carboxyl, carbonyl, and amine) responsible for removal of Cu(II) ions. The total CEC of sunflower husk is 47.74 meq/100g and Ca(II) and Mg(II) ions are in dominant exchangeable positions. The study of ion-exchange mechanism involvement was done and results confirmed that this mechanism is not the only mechanism which is involved in copper sorption. Also, the results show that the Cu(II) ions have preference for Mg(II) ions substitution. Sorption experiments were conducted in batch system. The effect of operating parameters (pH, contact time, initial concentration of Cu(II) ions and adsorbent dosage) on the adsorption capacity were investigated. The obtained experimental data were fitted by Langmuir and Freundlich isotherm models. The maximum adsorption capacity for Cu(II) ions calculated from Langmuir adsorption isotherm was 34.89 mg/g which is 15 to 35% higher than the capacity that other researchers reported previously for the same material and pollutant. These results are suggesting that sunflower seed husks have a potential to be applied as an effective adsorbent of copper ions from contaminated waters.