Adsorption of cadmium on acid-modified Transcarpathian clinoptilolite

Abstract

The adsorption properties of acid-modified Ukrainian Transcarpathian clinoptilolite towards aqueous cadmium(II) solutions under dynamic conditions have been investigated. It has been demonstrated that the adsorption capacity of the H-form of clinoptilolite depends on the nature and concentration of acid as well as the duration of contact of clinoptilolite with acid in the process of modification. The most effective adsorption of cadmium(II) was demonstrated by clinoptilolite pre-treated with 1 M of HCl during 24 h. It has been determined that the optimum for concentration of cadmium(II) is the H-form of clinoptilolite obtained without considerable dealumination. Under optimum conditions (diameter of zeolite grains equal to ca. 0.20–0.30 mm; flow rate of cadmium(II) solution of 500 ng/ml concentration through adsorbent equal to 3 ml/min; pH=5.6) the dynamic absorption capacity is 7.41 mg of cadmium per 1 g of acid-modified clinoptilolite. The conditions of desorption of cadmium from acid-modified clinoptilolite have been investigated. The solutions of potassium salts are the best desorbent of the ones that have been approved. The extraction of cadmium in these solutions reaches 88–92%.