| In order to understand the adsorption mechanism and adsorption capacity of arsenic (V) in soil,arsenic (As5+) of adsorption and desorption characteristics was studied on the bulk soil and micro-aggregates of different size (2-0.25,0.25-0.053,0.053-0.002,(0.002 mm) of the Mingshan River watershed typical paddy soil by laboratory simulationn, equilibrium liquid adsorption and the NaCl as desorbent’s desorption method,a-nd Arsenic (As5+) of adsorption and desorption characteristics under removal of soil components about arsenic’s (As5+) thermodynamics and kinetics of adsorption and desorption characteristics of the process was studied. Our results for the region to be able to predict the environmental capacity of heavy metals arsenic, control point source and non-point source of heavy metal pollution, improve crop quality provide aframe of reference, and also to provide basic data and theoretical basis for unders-tanding migration and transformation of arsenic. The results are as follows:(1) The paddy soil was studied about the thermodynamics of arsenic adsorption and desorption. Arsenic’s adsorption process is divided into fast and slow two reaction stages about paddy soil of the bulk soil and micro-aggregates of different size. Thermodynamic adsorption amount increased with the concentration of the initial As5+. The Freundlich equation was the best fit for thermodynamic adsorption,which was multilayer adsorption. The order of arsenic’s thermodynamic adsorption capacity between the different size of soil was:(<0.002mm)>0.053-0.002mm>the bulk soil>2-0.25mm>0.25-0.053mm, and the distribution was identical with the organic matter,free iron and cation exchange capacity content.Between the rate of easily desorbed and the amount of adsorption was instead about the order in the each particle micro-aggregates.The gordian suck accounted absolute advantage.The specific adsorption was master,non-specific adsorption was su-pplemented about the thermodynaics adsorption.(2) The paddy soil was studied about the kinetics of arsenic adsorption and desorption. Kinetic adsorption process also divided into two reactions of fast and slow, and it was identical with the thermodynamics adsorption.The amount of kinetics adsorption of As5+ gradually decreased with time increases in the paddy soil the bulk soil and the different size of micro-aggregates,and it was reached adsorption equilibrium after the 600min.The Elovich equation was the best fit for the kinetics adsorpt-ion(r=0.9839～0.994 1).The order of arsenic’s kinetics adsorption capacity between the different size of soil was:(<0.002mm)>0.053-0.002mm>the bulk soil>2-0.25mm>0.25-0.053mm,and the distribution was identical with the organic matter, free iron and CEC content.Between the rate of easily desorbed and the amount of kinetics adsorption was instead about the order in the each particle micro-aggregates.The gordian suck also accounted absolute advantage. The specific adsorption was master,non-specific adsorption was supplemented about the thkinetics adsorption.(3) The arsenic’s thermodynamics of desorption and adsorptionwas studied after removal of soil components (organic, free iron oxide). After the three treatments of removal SOM, remove the Fed, and simultaneously removing(SOM、Fed),the variation regular pattern of arsenic’s amount of adsorption was consistent with unremoved component But the equilibrium concentration of arsenic’s maximum adsorption maximum was hysteresised.Af-er the soil components was removal,Freundlich eq-uation was still the best fit (removing SOM:r= 0.9919-0.9989;removing Fed:r=0.9951-0.9989;simultaneously removing SOM, Fed:r=0.9944-0.9976).Under the three treatment of component removal, the order of the reducing amount of adsorption was:(<0.002mm)>0.053-0.002mm>originn al soil>2-0.25mm>0.25-0.053mm, and the Fed had greater influence than SOM on soil adsorption capacity.After removal of the components, the arsenic’s non-specific adsorption capacity(rate) was increased, the obligate adsorption amount(rate) was lowered on paddy soil of the bulk soil and the differrent sizes of micro-aggregates, and the relationshipof the amount(rate) of easily desorption was:simultaneously removal the SOM,Fed> remove the Fed> remove the SOM. Specific adsorption was still based, supplemented by nonspecific adsorption about the arsenic’s thermodynamic dadsorption.(4)The arsenic’s kinetics of desorption and adsorptionwas studied after removal of soil components (organic, free iron oxide).After removal of soil components, the arsenic’s amoutof kinetics adsorption was consistent with unremoved soil component, and it was still divided into fast and slow two stages, and after removal of the soil components; the time of adsorption equilibrium was a certain degree of advance.The best fit of the bulk soil and the different size micro-aggregates for the ars-enic’s kinetics adsorption also was Elovich equation (removing SOM:r=0.9933-0.9977; removing Fed:r=0.9865～0.9953; simultaneously removing SOM, Fed:r=0.9820～0.994), and the the worst fit was the first kinetic equation.The relation of the reduci-ng maximum amount of adsorption were:(<0.002mm)>0.053-0.002mm>the bulk soil>2-0.25m-m>0.25-0.053mm.They were significantly positively correlated between the amount of removing the soil component and the maximum decrease amount of adsorption.After removing the soil components,the arsenic’s desorption amount rate’s change in article size of soil were focus on 60-600min,and the quick response was occurred in 0-60 min,later stage for the slow response. |
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