| Effects of phosphate on the adsorption-desorption and kinetic of Copper, Cadmium and Chromium(VI) which were typical anions and cations by aggregates in paddy soil, typical soil in Tai Lake region, were studied by equilibrium adsorption method and shaking in constant temperature method.we could reveal the adsorption mechanism of heavy metal ions by aggregates in fields via comparing the different effects of these three heavy metal ions adsorption and desorption. we could provide theoretical references to prevent and repair the pollution of heavy metal ions in soil.The paper was divided into three parts:Part I:Effects of phosphate on adsorption-desorption of Cu2+, Cd2+and Cr(Ⅵ) by aggregates in paddy soil were studied by isothermal equilibrium adsorption method and desorption method using KC1solution. The results showed adsorption of Cu2+by the paddy soil (including pre-sorption of phosphate) could be best described by the Freundlich equation (R2>0.9805). The effect of phosphate on the inhibition or promotion of Cu2+was increasing while adding the concentration of Cu2+. The effect of phosphate on the adsorption amount of Cu2+and Cd2+showed a valley-like curves with the increase of phosphate amount. Namely, Lower concentration of phosphate restrain adsorption of Cu+and Cd2+, but the higher concentration will enhance, which is more significant for Cu2+However, the of Cr(Ⅵ) showed significant inhibition. The desorption of Cd2+showed decreasing with the increase of phosphate concentration, however, the Cr(Ⅵ) showed increasing at first and then decreasing.Part Ⅱ:Effects of phosphate on the kinetic of Cu2+, Cd2+and Cr(Ⅵ) adsorption by aggregates in paddy soil were studied by shaking in constant temperature method. The kinetic curves of Cu2+, Cd2+, Cr(Ⅵ) adsorption on the aggregates have the same trend, Cu2+Cd2+adsorption rate increased significantly by phosphate-tread aggregates, while the Cr(Ⅵ) adsorption rate decreased. The adsorption of Cu2+and Cd2+was divided into two parts:fast stage and slow stage. In fast adsorption stage of Cu2+, the adsorption could be best described by Elovich equation, and in slow stage,the adsorption could be described by Diffusion equation and Elovich equation; In fast adsorption stage of Cd2+, the untreated aggregate and the phosphate-treated aggregate could be best described by first-order equation; in slow stage, the untreated and phosphate-treated aggregate could be respectively best described by Diffusion equation and Elovich equation, the results reached significant levels of correlation. The adsorption of Cr (Ⅵ) by untreated aggregate and phosphate-treated aggregate could be best described by two-constant rate equation and Elovich equation, respectively.Part Ⅲ:Effects of phosphate on the kinetic of aluminum dissolution in Cu2+adsorption by aggregates in paddy soil were studied by equilibrium adsorption method and shaking in constant temperature method. The results showed that aluminum dissolution was detected at initial Cu2+concentration over20mg?L-1, the dissolution amount of aluminum increased with initial Cu2+concentration increased. The pH was significantly decreased in soil balance solution during isothermal equilibrium adsorption of Cu2+. There was a positive correlation were observed between was increased pH decreased and adsorption amount of Cu2+and dissolution amount of aluminum. The aluminum dissolution could be best described by two-constant rate equation and Elovich equation after adsorbing Cu2+by aggregates. |
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