-The ability of nano-silversol-coated activated carbon (NSSCAC) to adsorb Pb 2+ from aqueous solution has been investigated through batch experiments. The adsorption of lead onto NSSCAC has been found to depend on adsorbent dose, initial concentration and contact time. The experiments were carried out at natural solution pH. Equilibrium data fitted well with the Langmuir model and Freundlich model with a maximum adsorption capacity of 23.81 mg of Pb/g of NSSCAC. The experiments showed that the highest removal rate was 92.42% for Pb 2+ under optimal conditions. The sorption of Pb 2+ on NSSCAC was rapid during the first 30 min and the equilibrium attained within 60 min. The kinetic processes of Pb 2+ adsorption on NSSCAC were described by applying pseudo-first-order and pseudo-second-order kinetic models. The kinetic data for the adsorption process obeyed a pseudo-second-order kinetic model, suggesting that the adsorption process is chemisorption. The NSSCAC investigated in this study showed good potential for the removal of Pb 2+ from aqueous solution.

The removal of hexavalent chromium, Cr(VI), from aqueous solutions under different conditions using an anion-exchange resin (AXR) as an adsorbent was investigated under batch conditions. Such studies indicated that the percentage adsorption decreased with increasing initial Cr(VI) concentration, with the maximum removal of such ions occurred at a pH value of ca. 2.0. Both the Langmuir and Freundlich isotherm models were capable of reproducing the isotherms obtained experimentally. The sorption process was rapid during the first 20 min with equilibrium being attained within 30 min. The process followed first-order kinetics. The results demonstrate that such anion-exchange resins can be used for the efficient removal of Cr(VI) ions from water and wastewater.

The removal of heavy metal ions from water and wastewater has received a great deal of attention. Although adsorption methods are those most frequently used for the treatment of polluted water, such methods generally employ high-cost adsorbents such as activated carbon. The purpose of the present study was the exploration of the use of natural materials as a low-cost adsorbent in such technological applications. Thus, experiments have been conducted to test the efficiency of bael tree leaves in removing heavy metal ions, viz. Zn(II) ions, from wastewater derived from the electroplating industry. The percentage removal of Zn(II) ions was evaluated under varying experimental conditions, i.e. adsorbent dosage, initial metal ion concentration and contact time. To this effect, batch adsorption experiments were undertaken employing 2 g of 40–50 mesh bael tree leaves as an adsorbent in 100 mℓ of synthetic wastewater containing ca. 10, 20, 30, 40 and 50 mg/ℓ of Zn(II) ions. The initial pH of the synthetic wastewater was ca. 5. The experiments showed that the highest removal rate for Zn(II) ions was 88.58% under optimal conditions. Such Zn(II) ion adsorption followed reversible first-order rate kinetics. Thus, the tree leaves investigated in this study showed a good potential for the removal of Zn(II) ions from synthetic wastewater. The ultimate goal of the work described is the development of inexpensive, readily available, effective metal ion adsorbents from natural waste products as an alternative to existing commercial adsorbents.