A Study on the Adsorption of Cr(VI) on a Synthetically Prepared Zn-Al-Cl Layered Double Hydroxide(LDH)

Abstract

A Zn-Al-CI layered double hydroxide (LDH) has been synthetically prepared. The LDH has been characterised and extensively studied with reference to Cr(VI) adsor-ption in aqueous solutions The chemical composition of the LDH has been characterised as [Zn069Al028(OH)207]Clo 18 0.33H2o with a particle size in the range of 100-200 nm. The synthesised LDH has been found to be a good adsorbent of Cr(VI) (as Cr2O72) in the chromium concen-tration range of 25-250 ppm with a maximum loading capacity of 48 x 10-3 kg/kg at around 125 ppm. Adsorpt- ion of Cr(VI) on the Zn-Al-Cl surface follows a first order kinetics. Cr(VI) adsorption on the Zn-Al-CI LDH surface increases with increasing pH. There is no leach-ing of Al from the LDH in the pH range of 4-10. Zn leaching is also low beyond pH 7. There is practically no Cr(VI) desorption from the LDH surface in the p11 range of 7-9. Cr(VI) adsorption on the LDH surface primarily proceeds through Cl' exchange but there exists at least one more Cr(VI) adsorption mechanism other than anion exchange. Presence of associated anions in the solutioninterferes Cr(VI)) adsorption (in the Zn-Al-Cl LDH.