Effect On Environmental Behavior Of Arsenic In Soil Under Sulfate

The paddy soil affected by acid mine drainage has the characteristics of low pH,high sulfate and riches in heavy metals.Among them,sulfate is the main electron acceptor in paddy soil,which plays an important role in electron transport in anaerobic process and is related to the morphological transformation of iron and arsenic in soil.In this thesis,three kinds of paddy soils under different acid mine waste water irrigation effects in high-arsenic coal mines in Xingren County,Guizhou Province were used as research objects.Field experiment was conducted to study the distribution characteristics of total sulfur and available sulfur in paddy soil.The effect on the transformation of arsenic in paddy soil when sulfate addition was studied by using soil slurry anaerobic constant temperature culture method.The soil was inoculated with synthetic iron-arsenic system.The experimental method of anaerobic constant temperature incubation of extracts was carried out to study the effect on the arsenic species in iron-arsenic system under the action of microorganisms of sulfate addition.To investigate the effects of arsenic in iron-arsenic system under sulfate addition,and environmental behaviors such as arsenic reduction,release and fixation in soil under anaerobic conditions.The study mainly draws the following conclusions:?1?The paddy soil contaminated by different degrees of acid mine waste water was acidified,the content of organic matter was high,and iron and arsenic were enriched in the paddy soil.The acidification was more severe,the sulfur content was higher.The corresponding effective sulfur content of paddy soil was higher,and the content was between 0.10 g/kg and 1.17 g/kg The available sulfur contained mainly adsorbed sulfur,and the content of that was between 0.06 g/kg and 1.11 g/kg.Among them,the effective sulfur had a significant positive correlation with total sulfur?r=0.799**,p<0.01?.In the depth of 0-40 cm,the profile distribution of total sulfur and available sulfur content showed obvious stratification,and the total sulfur and available sulfur content of soil mainly accumulated in Tillage layer.?2?Under the action of indigenous mixed microorganisms,the pH value and Eh value in the arsenic-iron system showed a significant negative correlation,and the conditions required for sulfate reduction and microbial growth were satisfied after the5th day.The addition of Sulphate in the arsenic-iron system not only promoted the change of pH,but also promoted change of Eh.?3?In the anaerobic constant temperature culture experiment of paddy soil mud,sulfate was added to promote the reduction and release of arsenic or iron;In the first stage?from 0 day to 5 day?,the addition of sulphate promoted the release of iron or arsenic,and the concentration of As?III?in liquid phase,solid phase extraction of arsenic,and Fe?II?in the liquid phase reached the maximum value on the fifth day.In the second stage?from 5 day to 15 day?,the release ability of Fe?II?was weakened and gradually fixed.The addition of sulfate controlled the release of Fe?II?and promoted the fixation of arsenic.In the fifteenth day,As?III?in the liquid phase and solid phase extraction of arsenic were reduced;In the third stage?from 15 day to 30day?,the addition of sulfate promoted the activation and re-release of arsenic.?4?In the anaerobic constant temperature culture experiment of paddy soil mud,the reduction release of arsenic and the reductive dissolution of iron had a close coupling relationship.The liquid phase As?III?concentration and the liquid phase Fe?II?concentration,solid phase Fe?II?had a significant positive correlation?r=0.578**,P<0.01;r=0.415***,P<0.01?.And the solid phase hydrochloric acid extracted arsenic had a significant positive correlation with the solid phase hydrochloric acid extracted Fe?II??r=0.353**,P<0.01?.The concentration of As?III?in the liquid phase and the concentration of As?T?in solid phase hydrochloric acid in the whole culture system showed similar kinetic characteristics,and there were significant positive correlation between the two?r=0.592**,P<0.01?.?5?In the anaerobic constant temperature incubation experiment of soil extract,sulfate addition under the action of indigenous microorganisms enhanced the biodissolution or abiotic dissolution of arsenic.And the change of transformation of As species between As?V?-Fe₅HO₈·4H₂O(A_-As)and As?V?-Fe₅HO₈·4H₂O(A_-As)were the same when adding sulfate to in two arsenic-containing iron systems.As?V?was mainly released and As?V?was not reduced from 0 day to 5 day in the culture medium.As?V?in solution was released and partially reduced to As?III?.The ratio of As?III?/As?V?gradually increased with the reaction proceeds.And after 20 days,the arsenic release reduction ability was weakened and the As?V?and As?III?were fixed.In summary,there was a correlation between the transformation of arsenic and iron forms in paddy soil under the action of indigenous mixed microorganisms,The reduction release of arsenic and the reductive dissolution of iron had a close coupling relationship.The addition of sulfate in the arsenic-iron system not only promoted the change of pH,but also promoted change of Eh.With the reaction progressed,the concentration of sulfate in the culture system decreased gradually,and the content of iron or arsenic in the paddy soil decreased.It reflected addition of sulphate under the action of microorganisms in paddy soilhad a certain promoting effect on the reduction and release of iron and the release,reduction,fixation,activation and re-release of arsenic.The results will provide a certain data support and scientific basis for regulating the release of arsenic in anaerobic paddy soil.