Many industries discharge wastewater from processing into surface and underground waterways, and then, these waste waters must therefore be treated in order to remove heavy metals. The most common treatment used is the activated carbon adsorption, a particularly competitive and effective process; however, the use of activated carbon is not suitable due to the high costs. Then, in order to minimize processing cost, recent investigations have been focused on the use of low-cost adsorbents as zeolites. In particular, clinoptilolite is known to have high selectivity for certain heavy metals. In this paper, the capability of clinoptilolite as a low-cost adsorbent for the removal of zinc and cadmium ions from wastewater was analyzed in a batch system. Preliminary characterization was performed on adsorbent material in order to evaluate the chemical-physical structure. Tests in batch for analyzing adsorbing capacity of clinoptilolite were carried out varying zinc and cadmium concentrations between 10 and 200 mg/L with different amounts of sorbent in the solution (10-60 g/L). For both zinc and cadmium ions, complete adsorption was reached when the concentration was equal to 10 mg/L and adsorption capacity decreased increasing metals amount. In particular, clinoptilolite permitted high Cd2+ abatement, probably due to its greater affinity with adsorbent in the single system. Binary system was then analyzed, and, contrary to previous tests, the adsorbent in the simultaneous presence of the two metals demonstrated a greater affinity toward zinc, showing a higher percentage of absorption, due to a different absorption mechanism in the presence of two ions.
Keywords: Adsorption; Heavy metals; Natural zeolite; Wastewater.