Effects Of Fe-rich Materials And Redox Condition On The Stabilization Of Exogenous Arsenic In Soils

Chemical solidification/stabilization method is one of the most popular in repair of arsenic(As)contaminated soil.However,now with some of the repair materials are often too expensive to be suitable for field trials,and people often ignore the impact of change of environment conditions such as redox condition on the As repair soil arsenic processes for curing agents in practice.Focusing on the problems,exogenous As solidification/stabilization mechanism and efficiency in soil amended with the three of lower cost additives including iron-rich red soil,sponge iron filter material,water treatment residue was study,using improved sequential extraction technique and indoor cultivation experiment,respectively.On the basis,the discrepancy of stabilization mechanism of As in soil amended with the additive which possessing better effect of stablaiztion effect under under different redox condition was discussed.And the study of As aging mechanism in soil under the redox conditions alternate carried out,based on the oscillating redox conditions in practical field.The results would provide reference for the screening of repair agent and the remediation effect of As in soil.The scientific reference and basis will be provided in term of obtaining the cost-effective fixing agents of As in soil.At the same time,the results would also provide the reference basis of ecological risk assessment,after the As-contaminated soil was restored.The main results are as follows:1)Iron-rich red soil and sponge iron filter material and water treatment residue would all promote the decrease of relatively mobilizable fractions such an non-specifically sorbed As and the increase of relatively immobilizable fractions like residual As,indicating all the three kinds of materials can paly a role in stabilization of exogenous As in soil,and The higher the amount of addition,the stronger the stabilizing effect.Besides,The exogenous As stabilizing process in soil amended with the three Fe-bearing materials can all be divided into different several phase.And,the As bond with amorphous and poor crystalline Fe/Al hydrou oxides occurred the redistribution in soil amended with the three additives.2)After 180d incubation,the effect of curing exogenous As with songe iron filter in soil was best,result into the lowest As ecological risk in soil,followed the water treatment residue.In contrast,the effect of fixing exogenous As with iron-rich red soil in soil is the worst.In addition,the effect of curing exogenous As with the three kinds of materials in soil increased with the increase of dosage,and the impact of both type and dosage of admentents on pH in soil was ignored.So,sponge iron filter is the most suitable restorer of exogenous As in soil.3)Compared to anoxic condition,Aerobic conditions could promoted more labiled As tansformed into unlabiled As and shorten the stabilizing time of As in soil.And the stabilizing process of exogenous As in soil amended iron filter can be characterized by two stages and the increase of crystallization of Fe oxides,decomposition of organic matter,molecular diffusion,and the occlusion within Fe-(hydr)oxides cocontrolled the stabilization process of As in sponge iron-amended soils under different redox conditions.4)The stabilization process of exogenous As in upper and the lower column soil,could be divided four periods under oscillating redox conditions during the entire incubation period,with the labiled As tansformed into unlabiled As,on the whole.The exogenous As in lower column soil stabilization degree is higher and corresponding ecological risk is lower,compared to upper column soil.The reason may be that the redox potential in lower column soil is higher that in surface level and more As(III)was is oxidized into As(V),resulting into more exogenous As adsorption on the surface of Fe/Al oxide in bottom.