REMOVAL OF HEAVY-METALS IN WASTEWATER BY USING COMPLEX OXIDES GELS .2. ADSORPTION AND ELUTION OF CHROMIUM(VI) ON COPRECIPITATED SILICA-TITANIA GEL

The removal of chromium(VI) from the solution in terms of adsorption on coprecipitated silica-titania gel, prepared by homogeneous precipitation method, was investigated in a batchwise operation. Temperature effect on adsorption, recovery of chromium(VI) from diluted solution, selective adsorption, and effect of various alkali-treatments of adsorbent were discussed. As an adsorptive ability of a NaOH-treated adsorbent scarecely changed at temperatures 20~60°C, the adsorption was presumed to be due to both physical and chemical adsorptions. It was proved that the size and shape of micropore of the adsorbent more contributed to the adsorptive behavior than the surface area, when concerning with the surface characteristics. A more 90% of chromium (VI) was selectively removed at lower pH than 2, and a 45~85% of all metal ions were simultaneously removed by this adsorbent at pH 3~10 from the mixed solution containing 10 ppm chromium(VI), 1 ppm cadmium(II), and lppm zinc(II). Moreover, it was possible to concentrate efficiently the solution containing lOppm chromium(VI) to that containing 450 ppm chromium (VI) by adsorption and elution. The Ba(OH)2-treated adsorbent showed the significant removal of chromium(VI) at initial pH 2~10. In this case, amount of adsorption and equilibrium concentration obeyed Freundlich-type adsorption isotherm, x = K·c1/n, where K=17.4 and 1/m=0.14. The amount of adsorption was 17 mg Cr/g at 1 ppm of equilibrium concentration. Despite this value was greater by a factor of 8.5 than that of a NaOH-treated adsorbent2), the elution and regeneration of the adsorbent presented difficulty. © 1979, The Chemical Society of Japan. All rights reserved.