ADSORPTION OF HEXAVALENT CHROMIUM FROM AQUEOUS SOLUTIONS ONTO MODIFIED ZEOLITES

Clinoptilolite, which was modified with hexadecyltrimethylammonium-bromide solution (HDTMA-Br) in a proportion of 1/8 (modified zeolite I) and 1/4 w./v. (modified zeolite II), was used for the adsorption of chromate anions from aqueous solutions. Different initial concentrations of chromate anions from 0 to 145 ppm were added as K2Cr2O7 to 1g of each modified zeolite adsorbent. Clinoptilolite was also used for comparison reasons. Equilibrium isotherms of chromate anions were studied for clinoptilolite and modified zeolites at temperature equal to 25 degrees C. Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms were applied to the experimental data. According to the results, the chromate anions adsorption capacity of adsorbents follows the order: modified zeolite I>modified zeolite II>clinoptilolite. Isotherm studies showed that the adsorption data from zeolite and modified zeolite ll are best described by Langmuir isotherm while the adsorption data from modified zeolite I are best described by Langmuir and Temkin isotherm. Clinoptilolite adsorbed a low amount of chromate anions equal to 35.05 mg Kg(-1). Modified zeolite I and ll presented a maximum adsorption of chromate anions equal to 2000.01 and 379.86 mg Kg(-1), respectively. The modification of clinoptilolite with HDTMA-Br leads to the increase of the positive surface charge of zeolite increasing the adsorption of hexavalent chromium in the form of chromate anions. Such modified zeolite adsorbents can be applied as filters for the removal of anions and anionic dyes from wastewaters, where negative charged clinoptilolite presents low adsorption capacity.