DEHYDRATION, DIFFUSION AND ENTRAPMENT OF ZINC IN BENTONITE

Interactions with bentonile are important in the chemical speciation a nd fate of heavy metals in soils and other ecosystems. The interaction s of Zn with bentonite were studied using X-ray diffraction (XRD), deh ydration, kinetic and sequential extraction procedures. The species an d activity of Zn retained by bentonite were affected markedly by pH. T he Zn(OH)(+) was retained by bentonite prepared at pH greater than or equal to 6.9. The extent of dehydration of Zn(OH)C-bentonite was highe r than that for Zn-bentonite. At a relative humidity of 55.5%, the bas al spacing of the Zn(OH)(+)-bentonite was from 1.21 to 1.26 nm with 1 water sheet and that of the Zn-bentonite was 1.51 nm with 2 water shee ts. The greater affinity of Zn(OH)(+) for bentonite than Zn was associ ated with a lower degree of hydration. When an aqueous suspension of C a-bentonite was incubated with soluble Zn, the concentration of Zn ret ained by the Ca-bentonite was Linearly related to the square root of t ime. The rate of the interaction was controlled probably by tile inter layer diffusion and subsequently by the diffusion into the ditrigonal cavities in bentonite. The Zn retained by bentonite was dehydrated in situ so as to increase the bonding of Zn with surfaces of bentonite. W ith hydrothermal treatment the retained Zn could diffuse easily into t he cavities and transform increasingly to the residual forms that are associated with the entrapped form.