Research On Transformation And Transport And Impact Factor Of Arsenic And Mercury In Rocky Desertification Soil Of Heavy Metals High Background Areas In GuangXi

As being environmental pollution problem,heavy metal contamination in soil has been sustained attention all the world.Air,water and soil systems have been different degree contaminated by heavy metals.Throught investigating the land pollution condition,the researcher found partial area had been seriously contaminated by heavy metals,making heavy metals in grain crop exceed the standard,which has endangered animals or humens health and life when they ate the food.It covers a vast karst landscape in GuangXi,the ecological environment of which being relatively fragile and prone to stony desertification.Karst rocky desertification is not only accompanied by a series of changes in soil properties,but also causing the release of heavy metals in the high background area,resulting in high levels of heavy metals in the soil.Based on the study of the distribution characteristics of arsenic and mercury in soils with different rocky desertification levels,the transport and transformation of heavy metals in rocky desertification soils has been studied,which is conductive to understand the environmental chemical behavior of heavy metals in soils.The adsorption-desorption behavior of exogenous arsenic and mercury in soils was studied.Under different moisture conditions,the distribution and morphological transformation of exogenous arsenic and mercury in soils were investigated.The release characteristics of heavy metals were studied under different temperatures and organic acids,and the vertical migration characteristics of arsenic and mercury were studied in soil through simulating acid rain leaching.The main conclusions were as follows:1.Adsorption-desorption behaviors and release characteristics of As and Hg were studied in rocky desertification soils,showing that adsorption capacity of arsenic was higher than that of mercury.The isothermal adsorption curve of As and Hg could be well fitted by Langmiur and Freudlich equation.The release content of As and Hg inceased in different low-molecular organic acids in contaminated soils,and the release content of As and Hg increased with increasing of extraction temperature.2.With increasing of culture time,the content of As and Hg in the smaller particle size increased under the different moisture holding capacity,and which decreased in the coarse particle size,and the bioavailability of As and Hg decreased.As the incubation time increased,the percentage of arsenic non-specific adsorption and specific adsorption state decreasing,the percentage of weak acid extraction state of Hg decreased,however,which of carbonate bound state,Fe/Mn oxide bound state,and the residual state ratio increased.The value of pH and Eh has changed in different moisture condition in the soil-water system,affecting the distribution and transformation of exogenous As and Hg in different particle size fractions.The transformation tates of heavy metals were in the order of 120%> 90%> 60% field capacity.3.The vertical migration characteristics of heavy metals were studied in the simulated acid rain leaching experiment.The results showed that Ec value of exudate continued to decrease and finally stabilized under continuous leaching,while the pH was just the opposite.In the initial leaching stage,a small amount of As and Hg leached out.As the leaching time increasing,the release content of As and Hg in the leaching solution gradually decreased and finally tended to zero.However,the content of As and Hg and the proportion of morphology are different at different depths of leaching column.