Remoção de Cr(VI) de soluções aquosas utilizando argilas anionicas tipo hidrotalcita

AUTOR(ES)
DATA DE PUBLICAÇÃO

1997

RESUMO

The present work reports Cr(VI) removal from aqueous solutions using calcined and uncalcined hydrotalcite type anionic clay. The synthesis of the hydrotalcite was done by coprecipitation of the cations Mg2+ and Al3+ in a basic solution of NaOH and Na2C03. The product was characterized by chemical, thermogravimetric and infrared analysis as well as by X-Ray diffraction. The chemical and thermogravimetric analysis showed the composition ofthe obtained hydrotalcite to be 27(0H)2(C03)O.135.0.55H2O. An isothermic batch reactor was used for evaluating the effect of initial pH of the solution, particle size, initial chromium concentration, adsorption temperature, and the presence of ions other than chromate on chromium removal. The capacity of reconstruction of the structure of the calcined hydrotalcite at different temperatures by chromium in solution was studied. The Cl- and N03- forms were synthesized by reconstruction ofthe calcinated hydrotalcite at 500°C using NaCI or NaN03 solutions, respectively. In the tests of chromium removal, the variation of the chromium concentration and the pH of the solution was followed in time, and then isotherms were obtained. Results ofthe adsorption of chromium at pH under 5.0 showed that the chromium removal from the solution is better than at higher values of pH, but the hydrotalcite becomes soluble at that condition. Reduction ofthe particle size caused a decrease in the rate of chromium removal in the beginning of the experiment, but hed no effect on the equilibrium state. The presence of ions in solution other than Cr(VI) increased or decreased the chromium removal, depending on the charge, size and affinity by the site. Monovalent ions as Cl- and N03 did not change the amount of chromium removal, but the divalent (SO4)2-. ions did compete with the Cr(VI) ions. The hydrotalcite in the calcined form as well as the chloride and nitrate forms showed a high capacity for Cr(VI) removal from aqueous solution if compared with the original carbonate form. The form calcined at 500°C showed the highest efficiency, but had a lower Cr removal rate than the chlorite and nitrate forms. An increase in the temperature of calcination decreased the final quantity removed and yielded a lower kinetic of adsorption. Higher temperatures of adsorption resulted in better rates of chromium removal. This effect was larger for the calcined forms than for the chloride and nitrate forms

ASSUNTO(S)

troca ionica compostos de cromo argila

ACESSO AO ARTIGO

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