Inorganic particulates in removal of toxic heavy metal ions

Abstract

Adsooption behavior of zinc ions on hydrous zirconium oxide (HZO) in aqueous solution has been studied as a function of concentration (10-2-10-8M), temperature (303-333 K) and pH 3--8 of adsorptive solution applying radiotracer technique. The kinetics of adsorption follows first order rate law and agrees well with the classical Freundlich isotherm in the entire range of adsorptive concentration. The removal was found to be increasing with pH of the adsorptive solution while it was suppressed in the presence of acid concentrations. The overall process is found to be endothemfic and irreversible in nature. While certain heavy metal ions (e.g., Hg, Pb, Cd) are toxic, zinc is an essential trace element for enzyme activators in humans, but also becomes toxic at levels of 100-5~ mg/day. Significant quantity of zinc enter our water ways from metal production finishing units, industries using zinc and its compounds, preparation of paints and fungicides. 1-4 To keep our aquatic life and their habitat from serious threat of its toxic and non-biodegradable nature, the most effective remedial action is almost a complete removal (up to the permissible levels) of these metallic species from effluents and water bodies. Hydrous oxides of polyvalent metals have a great potential to be used as adsorbent for the removal of toxic metal ions from aqueous solution and pH of the bulk aqueous soution is an important variable which controls the adsorption of cation by oxide-water interface. A rapid increase in the uptake of zinc ions on amorphous iron oxide from almost zero upto 100%, was noticed by MUSIC and RISTIC 5 when pH was changed from 5.5 to 8.0. A similar maximum adsorption of zinc on hydrous lead dioxide surface was achieved above pH 6.0. 6 The adsorption of zinc on s-alumina and manganese(IV) oxide was found to be increasing with temperature. 7,8 Whereas, a slrong suppression of