Studies On The Distribution And Correlation Of Cadmium And Available Silicon In Different Particle Size Of Yellow Paddy Soil

Due to the different compositional ways of the different size of soil particles and organic minerals, the adsorption capacity of heavy metals is different, thus showing the different distribution and chemical speciation of cadmium in the grain fraction. Silicon as a beneficial element for most plants, the researchers used silicon-containing material for the improvement of cadmium contaminated soil, found that it had ease the plant cadmium toxicity. The study was in-depth analysis on cadmium and silicon distribution of different soil particle size of Yellow paddy soil development from old alluvial parent material collected from Mingshan, Pujiang, Qionglai, through the study of available silicon change corresponding to the cadmium and morphological change of various particle size in natural state, from the soil itself, to analyze the mechanism of action of silicon reduce cadmium toxicity, the main results were as follows.(1)The average content through separation of sand, silt, clay fractions from yellow paddy soil was respectively36.9%,35.78%,27.34%. The average content of the total cadmium was0.369mg/kg in the original soil,0.162mg/kg in the sand particle, probably0.401mg/kg in the silt particle,0.494mg/kg in the clay particle. The heavy metal Cd accumulated significantly in relatively fine particle, the content in the clay was the highest of about1.35times more than the original soil, secondly, which was about1.08times more in the silt. While the lowest accumulation of Cd was in sand particle, only43.9%content of the original soil. The available silicon content of three area samples was the highest in the clay,2356.534mg/kg in it, followed by silt, the least in sand, which was consistent with the trend of total Cd, it is1.28to1.61times in the clay more than the original soil.(2) The same form Cd, exchangeable cadmium content was the maximum in the silt, the other form of Cd content was greater in the clay than other fractions. The different form Cd, the residual Cd content was significantly higher than other forms in the particle group, exchangeable cadmium content was higher in silt, carbonate cadmium content was relatively high in clay particle, Fe-Mn oxide cadmium content was significantly higher in the clay than the other particle size, organic combination of cadmium content was low in various particle size. In three kinds of fractions, the percentage content of effective Cd in the clay was the lowest, only20.85%, while it is relatively high in the silt and sand,32.72%and32.92%respectively, they were higher than the original soil, only19.51%.(3) In the original soil, the available silicon content with exchangeable, carbonate, organic combination of cadmium was negative correlation respectively, which was significant negative correlation with total Cd and positive correlation with Fe-Mn oxide cadmium. The correlation of the available silicon and Cd had some change in different particle size. The available silicon and different form of Cd were negative correlation relationship in the sand particle, but the effect was not obvious was mainly because of less adsorption switch point of the sand itself. Available silicon was also negatively correlated with the different forms of Cd respectively in the silt particle, due to a small amount of colloid powder and less exchange site, so this competitive adsorption force was not large. It was also the negative correlation relationship in the clay particle size, especially with exchangeable Cd and total Cd showing significant negative correlation, the correlation coefficients were respectively0.470and0.446, due to rich exchange site in it, making the competition effect obvious enhancement. Thus, with the available silicon content increasing, the Cd content decreases, this effect was not the same in the different fraction, the most obvious in the clay.Overall, through the analysis of the experiment, the same amount of the heavy metal Cd into three different particle of yellow paddy soil, the toxicity of Cd is the higher into the silt and sand particle, its potential hazards to human body is higher. The Cd into the clay particle is lower toxicity, meanwhile, available silicon to effect on reducing cadmium toxicity is the most obvious. Due to the strong adsorption properties of clay, we can reasonably mix the soil with clay and the silicon material, make large amounts of cadmium in the form of low-activity state to be fixed in the clay to reduce the cadmium toxicity in soil.