Removal of heavy metal ions from aqueous medium using Kuluncak (Malatya) vermiculites and effect of precipitation on removal

• The affinity of vermiculite for heavy metals changed in the order of Pb > Cr > Zn.
• Even the modest concentration of Cr could drastically change the ZP of vermiculite.
• Metal hydroxide formation and its precipitation profoundly affected ions removal.
• The interaction mechanism between metal ions and clay can be explained well by ZP.

The removal of heavy metal ions, Cr3 +, Pb2 + and Zn2 +, by vermiculite was studied by batch adsorption tests. Influence of experimental parameters (e.g., medium pH and initial ion concentration) on removal was examined separately. Metal hydroxide formation in the dispersions and their precipitation was also investigated to assess the effect of precipitation on ion removal. For this purpose, some removal tests were carried out in the absence of vermiculite at various pH and initial ion concentrations. Electrokinetic and other properties (e.g., specific surface area, thermal and chemical analysis) of vermiculite were determined to explain the experimental results and the interaction mechanisms between solid surface and the ions. Zeta potential data were found to be a very useful means to explain the interaction mechanism between the adsorbent and adsorbate. The affinity of vermiculite for ions changed in the order of Pb > Cr > Zn. At the lowest studied pH of 2.5, 15.81, 10.71 and 9.18 mg of Pb, Cr and Zn ions could be removed by 1 g of the adsorbent, respectively.