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Natural and modified clinoptilolite were used to remove zinc and cadmium ions from aqueous solution. The raw material was characterized by XRD and XRF analysis. Clinoptilolite was modified with benzyldimethyltetradecylammonium chloride (BDTA) to increase the adsorption of neothorin [2-(2-arsenophenylazo)chromotropic acid disodium salt, C 10 H 11 AsN 2 Na 2 O 11 S 2 ]. All experiments were undertaken using a continuous method. The ultimate goal of these studies was the selective removal of trace amounts of Cd(II) and Zn(II) ions from aqueous solution using a modified form of clinoptilolite.The results obtained showed that Cd(II) and Zn(II) ions were adsorbed quantitatively onto modified clinoptilolite over the respective pH ranges of 4.0-5.4 and 3.3-4.5. The influence on the adsorption process of various parameters such as the ionic concentration, the flow rate, the particle size, the pH value and the presence of other cations was studied to obtain the optimum conditions. Although clinoptilolite and its surfactant-modified form were not capable of the selective adsorption of the cations studied, on the basis of the results obtained it was possible to selectively remove Zn(II) and Cd(II) ions from aqueous solution by modified clinoptilolite using a two-step process, i.e. initial treatment with BDTA followed by treatment with neothorin.

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ABSTRACT:The removal of radionuclides such as 129 I and 131 I from radioactive liquid wastes was studied. Two natural zeolites were modified with different quaternary alkylammonium ions to replace the exchangeable cations from the zeolite surface and used as adsorbent materials. The quaternary ions used for such purpose were hexadecyltrimethylammonium, tetradecyltrimethylammonium, dodecyltrimethylammonium, tetrabutylammonium and tetramethylammonium, respectively. Some of the modified forms exhibited an adsorption capacity much higher than those of the respective natural samples. In contrast, the adsorption capacity was negligible when tetrabutylammonium and tetramethylammonium ions were used. Adsorption experiments were conducted by batch and continuous experiments, and adsorption isotherms constructed from the data obtained. The effect of interfering anions on the adsorption capacity was also investigated as were the breakthrough behaviours of radioiodide in a column charged with the various adsorbents. Desorption of iodide from the modified zeolites into different solutions was also investigated. It was concluded that, in some cases, surfactant modification was an efficient process for the uptake and immobilization of iodide.