The Study On Stabilization Effect Of Arsenic Contaminated Soil By Iron Containing Materials

Due to their strong adsorption and long-term stabilization of arsenic,iron containing materials have been widely used to reduce the mobility of arsenic.However,the extreme environmental conditions may influence the mobility and bioavailability of arsenic.In this study,three kinds of iron-containing materials?FeSO₄·7H₂O?FeS and Fe⁰?were added to stabilize arsenic highly contaminated soil,and arsenic leaching concentration,soil pH,arsenic occurrence form,soil phase composition were obtained to analyze the stabilization effect.The effects of different environmental conditions?freeze-thaw cycles,different water conditions and interaction of pH and phosphorus?on the stabilization of arsenic were also studied.Moreover,pot experiments were conducted to study the effects of stabilized soil and fertilizer on plant growth and arsenic uptake.It is expected to provide a theoretical basis for evaluating the stabilization effect of arsenic by iron containing materials under different environmental conditions and the ecological restoration of arsenic highly contaminated sites.The main study results are as follows:?1?Based on the study of arsenic leaching concentration,soil pH,combined forms of arsenic and soil phase composition,Fe⁰ showed the best efficiency for arsenic stabilization,and FeSO₄·7H₂O also had good stabilization efficiency,while FeS was most poor for arsenic stabilization.The addition of 1%FeSO₄·7H₂O caused the marked decrease of soil pH,while the treatment of 1%FeS and 1%Fe⁰ had little effect on soil pH.After stabilization by three kinds of iron-containing materials,arsenic in contaminated soil was mainly transformed from exchangeable state and carbonate bound state into iron-manganese oxide bound state of low mobility and bioavailability.1%Fe⁰ stabilized soil nor-formed iron arsenic mineral showed that the stabilization of arsenic by Fe⁰ was mainly through specific adsorption or formation of amorphous iron oxide binding state.?2?The study of the effect of freeze-thaw cycles and different water conditions on stabilization of arsenic showed that the treatment of freeze-thaw cycles and air drying decreased the content of the amorphous iron oxide and promoted crystallization and aging of the iron oxide,while flooding treatment increased content of the amorphous iron oxide and promoted the activation of iron oxide.The stabilization efficiency of arsenic in 1%Fe⁰ stabilized soil after the treatment of continuous freeze-thaw cycles and air drying was the best,while 1%FeSO₄ stabilized soil was the best in the flooding treatment.?3?The arsenic release tended to be stabilized again over time at low pH,whereas the amount of arsenic release from three kinds of stabilized soils dramatically increased at high pH.The addition of phosphorus promoted the release of arsenic from the stabilized soils at all three pH studied.Especially,under acidic conditions,the increment of arsenic release relative to the treatments in the absence of phosphorus was highest.The stability of 1%Fe⁰ stabilized soil was highest among all the systems studied,1%FeSO₄·7H₂O stabilized soil second,and 1%FeS stabilized soil had most poor stability.?4?According to pot experiments,rape?Brassica napus L.?could grow well in stabilized soils,with highest arsenic absorption in roots(405.62 mg·kg^-1)among five plants studied.5%organic fertilizer treatment promoted the growth of rape and inhibited the absorption of arsenic in this plant.The addition of proper phosphate fertilizer reduced the toxic effect of arsenic,significantly improved the growth of rape and promoted the transport of arsenic from roots to the aboveground parts.High phosphorus fertilizer(?0.568g·kg^-1)significantly promoted the absorption of arsenic by rape roots,but inhibited the accumulation of arsenic in the aboveground parts and had little effect on the growth of rape.