Adsorption of hexavalent chromium onto kaolin clay based adsorbent

DENG Lin(邓林)^{1, 2}, SHI Zhou(施周)^{1, 2}, LUO Lu(罗璐)^{1, 2}, CHEN Shi-yang(陈世洋)^{1, 2}, YANG Ling-fang(杨灵芳)^{1, 2}, YANG Xiu-zhen(杨秀贞)^{1, 2}, LIU Li-shan(刘立山)^{1, 2}

(1. Department of Water Engineering and Science, College of Civil Engineering,
Hunan University, Changsha 410082, China;
2. Key Laboratory of Building Safety and Energy Efficiency of Ministry of Education (Hunan University),
Changsha 410082, China)

Abstract:A low-cost adsorbent modified kaolin clay (MKC) was synthesized and utilized for Cr(VI) removal from aqueous solution. Adsorption experiments were carried out as a function of adsorbent dosage, solution pH, Cr(VI) mass concentration, contact time, electrolyte, and temperature. It is found that the adsorption efficiency is high within a wide pH range of 2.5-11.5, and equilibrium is achieved within 180 min. Increases in temperature and electrolyte concentration decrease the adsorption. The adsorption follows the pseudo-second-order kinetic model. The Langmuir isotherm shows better fit than Freundlich isotherm. The maximum uptake capacities calculated from the Langmuir model are 15.82, 15.55 and 15.22 mg/g at 298, 308 and 318 K, respectively. Thermodynamic parameters reveals the spontaneous and exothermic nature of the adsorption. The FTIR study indicates that hydroxyl groups, NH₄⁺ ions and NO₃^- ions on MKC surface play a key role in Cr(VI) adsorption. The Cr(VI) desorbability of 86.53% is achieved at a Na₂CO₃ solution. The results show that MKC is suitable as a low-cost adsorbent for Cr(VI) removal which has higher adsorption capacity and faster adsorption rate at pH close to that where pollutants are usually found in the environment.

Key words:kaolin clay; adsorption; Cr(VI); kinetics; isotherm; thermodynamics; desorption