Adsorption of Heavy Metals by Sodium Polyacrylate-Humic Acid-Rectorite Composite as a Novel Adsorbent

Abstract

A novel organic-inorganic composite sodium polyacrylate-humic acid-rectorite was prepared by polymerization reaction of acrylic acid, humic acid and rectorite in aqueous solution and used as adsorbent for removal of heavy metals Pb(II), Cd(II), Cu(II) and Zn(II) ions from aqueous solution. The effects of contact time, pH, temperature and adsorbent dosage on adsorption capability were investigated. Adsorption kinetics, adsorption isotherm and desorption of adsorbed heavy metal ions were also researched. The results indicated that the adsorption reaction of heavy metals was rapid and reached equilibrium in 30 min. Adsorption capacities of heavy metals increased with increasing initial pH, temperature and adsorbent dosage. Adsorption reaction is endothermic. The optimum pH for all the four ions adsorption was observed at 5.5-6.5. The removal rate of Pb(II), Cd(II), Cu(II) ions with initial concentration of 50mg/L are more than 98%, and Zn(II) ions removal is about 90%. The suitability of adsorption kinetics for heavy metals to a pseudo-second-order kinetics model suggested that the adsorption rate may be governed by chemiadsorption involving ions exchange or sharing between adsorbent and metal ions. The adsorption equilibrium data was well interpreted by Langmuir and Freundlich isotherm model. The adsorption behaved as monomolecular layer. The maximum monolayer adsorption capacity was 1666.7, 666.7, 303.0 and 454.6 mg∙g-1 for Pb(II), Cd(II), Cu(II) and Zn(II) ions, respectively, at 25°C. Adsorbed metal ions were desorbed effectively by 0.1M HCl solution. Desorption rate was about 95.2, 92.4, 98.7 and 94.3% for Pb(II), Cd(II), Cu(II) and Zn(II) ions, respectively. Adsorbent can be reused for three cycles without any significant loss in adsorption performance.