Solute Transport Laws Of Se In Soil

The heavy metal pollution in the soil is a growing problem. The solute transport laws and the influence factors of SeO32- in soil under the laboratorial conditions are studied, using miscible displacement technique. In this thesis, numerical model CDE is used to simulate the migration SeO32-, studying the solute transport laws of SeO32 in different soil, different soil structure and different locations slope. The main results obtained from this study are as follows:â‘´The spatial distribution of soil basic natureOrganic matter content is relatively poor on the Loess Plateau, but rich in yunwu mountain of guyuan region. And pH is little difference, the coefficient of variation was 0.2%, the soil in the northern region is weak alkaline. The particle composition of tested soil on the Loess Plateau is slitï¹¥sandï¹¥clay. Silt and sand in the aggregate are more than 94%. Clay content from the south to the north gradually reduced, sand content increased. The texture is growing thicker.⑵Different soil on the impact of migration SeDiffusion coefficient D in the soil of eight laws: aeolian sand soilï¹¥sand loessï¹¥cinnamon soilï¹¥gray-cinnamonic soilï¹¥hard loessï¹¥heilu soilï¹¥silt soilï¹¥huangmian soil. And the difference is larger, the coefficient of variation reach 329.85%. The coefficient of variation of retardation factor R in only 0.23%, hard loess is biggest and sand loess is smallest. R of aeolian sand soil, cinnamon soil, gray-cinnamonic soil, heilu soil, silt soil, huangmian soil is similar. The impact of the basic mature of the soil in diffusion coefficient D is obviously greater than in retardation factor R. Aeolian sand soil and sand loess are all smaller than 1 in retardation factor R, the reasons are the larger pore, the sand content of up to 50% or more, especially aeolian sand soil up to 97.14%, leading to a greater role mechanical dispersion. The factors influencing diffusion coefficient D are silt content, organic matter content and cation exchange capacity. The basic nature of the soil and retardation factor R correlation is not significantly.⑶Sand-soil structure on the impact of migration SeSand content and silt content of the soil particles account for 98%, poses a major sand loess skeleton. Silt content with the increasing slope length in performance for the first decreases, then increase, and the lowest silt content which appears in slop middle. Sand content is opposite. The flow velocity of mixed soil is obviously bigger after accession to aeolian sandy soil, the average growth rate of 3.96%. The increasing rate of diffusion coefficient D is slightly less than the decreasing rate of retardation factor R. The reason is silt content relative lessened and ion exclusion role relative weak after accession to in aeolian sandy soil so that the diffusion coefficient D is relative decrease. The flow velocity of two different mixed soil samples are more or less the same, its coefficient of variation was 2.43%. The results show that increasing role is obviously only accession to a certain amount of aeolian sandy soil, but the growth of flow velocity will be small once over the volume. When silt content in soil is lower than 24.14%, the impact of different sand-soil structure is little. But the impact is bigger when silt content in soil is bigger than 60.80%.â‘·The solute transport laws of Se in slope soilThe retardation factor (R) is smaller in the middle of slope, which is bigger in soil porosity, and R is bigger when soil porosity is smaller. It can be seen from the above conclusions that the soil porosity is an important factor which influences the transport of SeO32- in aeolian sandy soil. The decreasing tendencies of retardation factor (R) in a soil profile with the increase of the depth are obviously different among the different slope positions, the order of the variability along the slope is as follows: the middle > the top> the bottom. And the variability of retardation factor (R) in deeper soil is smaller because of the smaller impact of outside environment. The flow velocity of SeO32- solution in surface layer soil is faster than in deeper soil, and R is decreasing with the increasing of flow velocity when variance coefficient of flow velocity is bigger than 14.14% in the premise of similar mechanical composition. The results show that the flow velocity is also an important factor influencing the transport of SeO₃^2- in aeolian sandy soil.