Application of South African heulandite (HEU) zeolite for the adsorption and removal of Pb and Cd ions from aqueous water solution: Experimental and computational study.

The capacity of South African Heulandite HEU zeolite to remove Pb and Cd ions from aqueous solution was investigated using batch experiments and molecular simulations studies. The effect of different factors on the adsorption of these ions onto the zeolite was investigated; contact time, initial metal ion concentration and the amount of HEU adsorbent. Molecular simulations was done using Monte Carlo and density functional theory. Experimental results obtained indicate that the maximum adsorption for the two ions occur at pH 5 and after 240 min of contact time. The percent removal based on contact time of Pb and Cd ions from water by the heulandite zeolite were 99.7 and 76.7 %, respectively. The adsorption of two metal ions onto the HEU zeolite follows the Langmuir adsorption isotherm. From the molecular simulation findings, the adsorption of Pb ions onto the HEU window is equidistant from the two adjacent oxygen atoms within the HEU structure while the Cd ion is adsorbed in the upper left side of the 8-ring HEU window. It was observed that the performance of the zeolite can significantly be improved by doping with germanium, aluminum, thallium indium, and sodium cations. These results indicate that the application of HEU zeolite as an adsorbent holds a great promise in heavy metal removal from aqueous solutions.