Heavy metals sorption/desorption on competing clay minerals; an experimental study

The adsorption /desorption behaviour of Cd, Cu, Pb, Zn and Ni on illite, beidellite and montmorillonite was investigated using a multichamber device. This method allows one to study the adsorption/desorption rates and metal transfer reactions simultaneously on a few different solids. Sorption experiments show the highest enrichment of metal ions on smectites, but for Pb ions also on illite. The adsorbed amounts of Pb and Cu ions were very high: 80% and 70% of the total concentration of the metal ions, whereas the Zn, Ni and Cd ions were adsorbed in smaller (40–50%) amounts. A desorption experiment of metals adsorbed on clay minerals shows the following sequence of metal mobility from investigated minerals: Pb > Cd ⪢ Cu > Ni > Zn for beidellite, and Pb > Cd ≌ Cu > Ni > Zn for illite and montmorillonite. The lower metal accumulation on clay minerals after reaction with ferrous sulphate is supposed due to the premature iron hydroxide precipitation in the system, which has caused beside metals sorption their precipitation as well. Data from the sorption/desorption studies provides information regarding the different type of metal surface complexes formed with selected clay minerals and will help to predict the fate of metals in soils and sediments.