The Speciation Of Iron And Arsenic Associated With The Release Of Arsenic In Flooded Soil

Arsenic is a common metalloid element in the nature,and arsenic has a great toxic effect to animals and plants.In recent years,the arsenic pollution incident happened frequently and bring more and more harm to the production and life of human.People had paid more attention to the prevention and control of arsenic pollution.At the same time,different forms of arsenic in soil have different toxicity and mobility.Changing the distribution of different forms of arsenic can effectively reduce the toxicity and migration of arsenic in soil.Iron reduction has an interaction on the arsenic reduction.The speciation of iron changed can lead the speciation of arsenic changed.The reduction of iron also can lead the release of arsenic from soil.Therefor,this paper study the transform of iron and arsenic and the change of TCLP(Toxicity Characteristic Leaching Procedure)extractable concentration of arsenic in flooded soil.We study the speciation of iron and arsenic associated with the release of arsenic in flooded soil influences by temperature,adding lactate,and adding AQDS and alternating wet and dry conditions.The main research contents and results were as follows:1.Iron was reduced to Fe(Ⅱ)fast in the flooded soil.The concentration of Fe(Ⅱ)is2.26 g/kg after flooded 10 days.The concentration of Fe(Ⅱ)is reached equilibrium by 2.44g/kg after 20 days flooded.The concentration of As(Ⅲ)also rise fast in the flooded soil.The concentration of As(Ⅲ)is17.81 mg/kg after flooded 10 days and 18.09 mg/kg after flooded 30 days.The TCLP extractable concentration of arsenic is rise with the flooding.The TCLP extractable concentration of arsenic is 4.43 mg/kg after flooded 30 days.But the concentration of Fe(Ⅱ)and As(Ⅲ)is only 1.39 g/kg and 2.78 mg/kg when the soil is sterilized.That show the speciation of iron and arsenic is effected by the microorganism.The reduction of iron and arsenic is not a chemical reaction,but a biochemical reaction.2.The speciation of iron and arsenic are also effected by the temperature.Iron reduction is fastest in the temperature at 40℃ and the concentration of Fe(Ⅱ)is 2.52 g/kg after flooded 30 days.Iron reduction is slow in the temperature at 4℃ and the concentration of Fe(Ⅱ)is 1.63 g/kg after flooded 30 days.In the different cultivate temperature,arsenic reduction is slowest in the temperature at 4℃ and it is fastest in thethe temperature at 28℃.When in the hot condition,the reduction of arsenic is inhibited and the concentration of As(Ⅲ)is 15.9 mg/kg.The temperature also had effected the TCLP extractable concentration of arsenic.The TCLP extractable concentration of arsenic increased with the rise of temperature.The TCLP extractable concentration of arsenic is4.76 mg/kg after flooded 30 days.That show the temperature effect the activity of microorganism to effect the speciation of iron and arsenic.3.Adding lactate has a great effect on the the speciation of iron and arsenic.When adding lactate to the paddy soil,the reduction of iron and arsenic both promoted.The concentration of Fe(Ⅱ)and As(Ⅲ)are both increased with the concentration of adding lactate increased.When the concentration of lactate is 3 mmol/L,the concentration of Fe(Ⅱ)and As(Ⅲ)are 2.55 g/kg and 20.55 mg/kg.When the concentration of lactate is 6 mmol/L,the concentration of Fe(Ⅱ)and As(Ⅲ)are 2.57 g/kg and 23.55 mg/kg.Adding lactate can promote the TCLP extractable concentration of arsenic in flooded soil.The TCLP extractable concentration is increased with the increase of the concentration of adding lactate.That show lactate both promote the reduction of iron and arsenic.4.Adding AQDS promote the reduction of iron in flooded soil.The iron reduction is promoted when the concentration of AQDS is 1 mmol/L.When the concentration of AQDS is 0.1 mmol/L,the concentration of Fe(Ⅱ)is maximum and the concentration is 3.23 mg/kg.When adding AQDS,the reduction of arsenic is inhibited.When the concentration of AQDS is 0.1 mmol/L,the concentration of arsenic is minimum.Adding AQDS is also increased the TCLP extractable concentration of arsenic in flooded soil.When the concentration of AQDS is 0.1 mmol/L the TCLP extractable concentration of arsenic is maximum with the concentration of 7.66 mg/kg.That show adding the material of electron shuttle can effected the extracellular breathing of microorganism and it can promoted the reduction of iron and the release of arsenic.But it inhibits the reduction of arsenic.5.The speciation of iron and arsenic are also influenced by the moisture content of soil.When the soil in the condition of flooding,the iron and arsenic is in the condition of reduction,the concentration of Fe(Ⅱ)and As(Ⅲ)are both increased.It is maximum after 5days,and the concentration is 1.99 g/kg and 11.16 mg/kg.When the soil in the condition of drying,the concentration of As(Ⅲ)and Fe(Ⅱ)are both decreased.The TCLP extractable concentration of arsenic is also had a regularly change with the moisture content of soil.When soil in the condition of flooding,the TCLP extractable concentration of arsenic is increased to 2.43 mg/kg,when the soil in the condition of drying,the TCLP extractableconcentration of arsenic is decreased.That show the moisture content of soils had a great effected on the reduction of iron and arsenic and the release of arsenic.