| 【Objective】The present study aimed to reveal the reaction characteristics of Cr( Ⅵ ) adsorbed by
paddy soil and examine the reduction effect of Cr( Ⅵ ) by zero-valent iron ( ZVI,) in the soil, and analyze the effect of
relative factors on the above-mentioned process. 【Method】The batch isotherm adsorption and kinetics experiments were
performed to investigate the effects of reactant concentration, reacting time, pH, ionic strength and accompanying anions on
the adsorption and reduction of Cr( Ⅵ ) in the mixed system of paddy soil and ZVI. The experimental data was also analyzed
with adsorption and kinetic model.【Result】The adsorption saturation was not obtained with the initial concentrations
ranging from 0.1 to 2.0 mmol/L and the adsorption isotherm could be well fitted by Langmuir equation (R2=0.9963). The
increase in pH and ionic strength was unfavourable for Cr( Ⅵ ) adsorption and the kinetic curve could be properly fitted by
pseudo-first-order kinetic equation (R2=0.9935). With the introduction of ZVI, the added Cr( Ⅵ ) (0.20 mmol/L ) was totally transformed to Cr( Ⅲ ) under the present reaction condition, and the calculation of aqueous Cr mass balance indicated that a
certain amount of the generated Cr( Ⅲ ) were adsorbed by the solid surface. The presence of phosphate and 1,10-phenanthroline
could inhibit the Cr( Ⅵ ) reduction. Moreover, Cr(VI) reduction would be suppressed as the solution pH increased, evidenced
by the reduction percentage decreased from 100% at pH 4.34 to 56.3% at pH 6.87. 【Conclusion】The electrostatic adsorption
was involved in Cr( Ⅵ ) adsorption by the paddy soil. The enhancement of electrostatic repulsion between the soil surface and
Cr( Ⅵ ) and the competitive adsorption between Cr( Ⅵ ) and chloride ions contained in the supporting electrolyte could jointly
decrease the Cr( Ⅵ ) adsorption in the soil. Low pH was favourable for the occurrence of Cr( Ⅵ ) reduction by ZVI in the soil,
and the reduction would be inhibited in the presence of phosphate and 1,10-phenanthroline. |
