بررسی توانایی زئولیت اصلاح شده با اسید برای جذب کادمیم درمحیط آبی

Abstract Background and purpose: Natural zeolites are widely used for the purification of water and wastewater. Nevertheless the selectivity of clinoptilolite (a common zeolite mineral) for cadmium is known to be particularly low. In order to enhance the zeolites’ sorption capacity for cadmium, we treated natural clinoptilolite with sulfuric acid solutions and investigated the sorption of cadmium to acid-modified clinoptilolite by a series of batch experiments. Materials and methods: The batch method has been employed using metal concentrations in solution ranged from 25 to 100 mg/l and adsorbent ranged from 0.2 to 1.8 g/l. The influence of acid concentration, contact time, solution pH, adsorbent particle size, initial cadmium concentration and adsorbent mass has been studied. Results: It was found that the acid modified clinoptilolite exhibits higher adsorption to cadmium than unmodified clinoptilolite and adsorption of the cadmium is influenced by several parameters such as cadmium initial concentration, adsorbent dosage and solution pH. Maximum absorption efficiency was achieved at pH of 6. Meanwhile maximum absorption efficiency of acid modified clinoptilolite in cadmium removal shows improvement due to 1 molar sulfuric acid. The equilibrium adsorbed amount also increased with the initial concentration of the metal ions, as expected. Adsorption capacities of the acid- modified clinoptilolite for cadmium increased as the particle size decreased down to 0.5 mm in diameter, but no difference was observed for a diameter less than 1.5 mm. Conclusion: The best results in terms of efficiency are obtained for the clinoptilolite modification with 1 molar sulfuric acid and it was more favorable than natural clinoptilolite in removing cadmium and thus was a better adsorbent as low-cost alternatives in wastewater treatment for cadmium removal.