Behaviour and mechanism of Zn(II) adsorption on Chinese loess at dilute slurry concentrations

BACKGROUND: Zn(II) is commonly present in mining drainage in developing countries. Since loess is abundant and always located near mining sites in China, it would be useful to investigate the possibility and efficiency of using loess to remove Zn(II) from aqueous solution.RESULTS: The Zn(II) adsorption capacity of Chinese loess was determined as 215.9 mg g⁻¹. The adsorption followed pseudo-second-order kinetics and took place mainly by surface diffusion. Generally, higher initial pH and solute concentration resulted in higher % Zn(II) removal, while higher temperature and slurry concentration led to lower % Zn(II) removal. A thermodynamic study revealed that the adsorption process was exothermic, with the predicted enthalpy change ranging from -20.87 to -4.06 kJ mol⁻¹. With the assistance of X-ray photoelectron spectroscopy and X-ray diffraction, the high adsorption capacity was ascribed to the growth of micro-organisms and mineral constituents such as kaolinite and goethite.CONCLUSION: Chinese loess proved effective for Zn(II) adsorption in this study. The optimal adsorption conditions included pH > 3.0, temperature