Ag+ sorption on natural and Na-exchanged clinoptilolite from Eastern Rhodopes, Bulgaria

The study was carried out to examine the sorption of silver by natural and preliminary sodium-exchanged clinoptilolite from Beli plast deposit, Bulgaria. The effect of varying the process parameters like pH, adsorption time, and initial metal concentration was tested. It was found that the optimum pH is 4, and that the process has a fast kinetic – reaching equilibrium in 45 min. Preliminary treatment of clinoptilolite by exchange in sodium chloride solution increased its sorption ability towards Ag ions compared with the natural material. The sorption equilibrium was most well described by the Freundlich adsorption model. It was found that the ion-exchange plays main role in Ag+ immobilization on the basis of correlation observed between the Ag+ uptake and the amount of released metal ions (Ca2+, K+, Mg2+ and Na+). The desorption of silver from clinoptilolite by use of 0.1 N HNO3 was investigated.