The chemical bonding of copper ions on kaolin from Suzhou, China

Reactions of copper with kaolin are important in determining copper fate in the environment. Adsorption characteristics of Cu by the kaolin from Suzhou, China were investigated at varying Cu concentrations (0 to 100 mg/l), pH values (approximately 2 to 11) and temperature (25, 40 and 50 °C). Cu adsorption by the kaolin was well described by the Langmuir and Freundlich adsorption equations. The kaolin did not exhibit the adsorption maximum, 666.67 mg/kg, as determined by the linearized form of the Langmuir equation. The kd values decreased exponentially with increasing initial Cu concentrations in the solution. A unit increase in pH resulted in approximately 8.47, 9.61 and 10.82% increase in Cu adsorption by the kaolin at the initial Cu concentration 5, 50, 100 mg/l, respectively. The pH50 values increase with increasing initial Cu concentration. Desorption of Cu was well described by the linear model (y = 0.0917x + 0.7136) with correlation coefficient R2 = 0.9994. Most of the adsorbed Cu is nonspecific adsorption; the mobility of Cu in the kaolin from Suzhou, China is high under low pH conditions.