Adsorption of Zn2+ and Cu2+ onto sulphate and phosphate-modified bentonite

The modification of bentonite with sulphate and phosphate increased the cation exchange capacity (CEC) and adsorption of Cu2+ and Zn2+ but decreased the specific surface area (SSA). Phosphate modified bentonite had the highest adsorption capacity for both metal ions. The Fourier transformed infrared spectra indicated the bonding of sulphate and phosphate bentonite with sulphate and phosphate by the hypochromic and hyperchromic shifts are typical of physisorption and chemisorption mechanisms. Phosphate and sulphate were adsorbed through inner-sphere and outer-sphere complex formation. The isotherms were better fitted by the Langmuir model than the Freundlich model.