| Arsenic（As）is a metalloid element with high toxicity and strong carcinogenicity,which has attracted widespread attention because of the huge threat to human health and ecological safety.As the main food crop in China,rice is important for humans to ingest As.Therefore,the current researchers have focus on how to reduce the bioavailability of As and alleviate As pollution in paddy soil,thereby reducing the accumulation of As in rice.Schwertmannite（Sch）has a high specific surface area,and a large numbers of hydroxyl groups,sulfate groups and other groups on its surface,showing a strong affinity for arsenic（As）.However,it is still unclear whether it is feasible to reduce the transfer of As in paddy soil to rice via introducing Sch into the paddy soils.In addition,the metastable structure of Sch is easy to transform into a better crystalline form.It is also still unclear whether the phase transformation of Sch would influence the reduction of As in rice by introducing Sch into paddy soils.Therefore,the objectives of the present study are（1）to study the phase transformation of Sch in paddy soil,（2）to investigate the effect of introducing Sch on the behavior of As in paddy soil,（3）to explore the feasibility of reducing the accumulation of As in rice via introducing Sch into paddy soil.It provides a certain technical reference for the remediation of arsenic-contaminated soil by Sch,and is of great significance to the practice of chemical remediation of soil pollution.Mainly results can be concluded as follows:1.The phase transformation of Sch in paddy soil and the associated influencing factors have been clarified.The XRD results showed that under aerobic conditions,Sch in paddy soils were for 90 days;however,in flooded anaerobic environments,Sch was reduced and dissolved on the 15th day,its phase transformation occurred,and the degree of phase transformation was 5%Sch>1%Sch>control,with goethite as the final product.It showed that the moisture content played an important role in controlling the transformatiol of Sch.The concentration of Fe2+ was much higher than that of Fe3+ in pore water during flooding,which reached up to 1384 mg·L-1.This result indicated that Fe2+ was an important driver for catalyzing the transformation of Sch.The introduction of Sch into paddy soil reduced the soil pH and increased the soil Eh value,both of which affected the phase transformation of Sch.2.The effect of introducing Sch into paddy soil and its consequent phase transformation on the behavior of arsenic in soil were studied.Under flooding and intermittent irrigation conditions,the introduction of Sch drastically reduced contents of the total As and As3+ in the soil solution.In addition,sequential extraction procedure showed that Sch also immobilized non-specific and specific adsorbed arsenic in soil.The immobilizing ability of arsenic by applying 5%Sch is obviously greater than that of applying 1%Sch.After applying 5%Sch,the total arsenic concentration in pore water remained at 10 μg·L-1 within 90 days incubation.More importantly,although Sch have undergone mineral phase transformation in a flooded anaerobic environment,the arsenic immobilized by Sch did not release into soil solution,which means that Sch had the ability to efficiently reduce arsenic mobility and its effectiveness lasted for a in long time.3.The effect of introducing Sch into paddy soil on the growth of rice plant and the accumulation of As in rice were further investigated.The addition of 5%Sch had a toxic effect on rice and prevented rice growth;the application of low concentration（0.1%,0.5%Sch）of schwertmannite had a promoting effect on rice fresh weight and tiller number,while the high concentration（1%Sch）of schwertmannite reduced the grain yield.Fe2+ concentration and pH value may be the main factors affecting rice growth.Application of Sch reduced the accumulation of As in rice roots and brown rice to a certain extent,showing the effectiveness of Sch in reducing the mobility of As in paddy soils. |
PDF Full Text Request