Stabilization On Cadmium Soil Using Modified Silicon Activated Red Mud Based Material

Red mud was modified to increase the content of available silicon in this research. And this red mud based material was used to promote the stabilization of heavy metal polluted soil and the inhabitation of plant absorption. It is also an innovation of red mud in agricultural resource utilization. Influence on soil physical and chemical properties, heavy metal form transformation and plant absorption of heavy metals were studied in experimengts of simulative contaminated soil and rice pot. Furthermore, the mechanism of stabilizing heavy metals was explored. The main results in experiments were shown as follow.(1) In physical and chemical modifications, hesting red mud could not gain more available silicon. The effect of acid modification was superior to alkalic modification. The preferably compound modification was that red mud was been soaked in HNO3 and then calcined at 200℃. Content of available silicon in the modified red mud was 1148.02mg·kg-1, which increased 50.18% on the base of red mud.(2) Available silicon in soil increased by adding composite modified red mud. Available silicon increment ranged from 26.89 to 986.89 mg·kg-1 in 30th. The best conversional efficiency occurred at the amendment level of 5% composite material(red mud:zeolite=3:1), and the exchangeable Cd decreased 79.31%, while the residue Cd increased 170.84%. The convertion of iron manganese oxide Cd into residue was improved with the rate of red mud increased in the compound materials.(3) Silicon in red mud could be activated by using different phosphates. Compared with red mud, the content of available silicon increased 34.18%～85.69% in modified red mud disposed by 0.5～3 mol·L-1 KH2PO4. When red mud was soaked in 0.5mol·L-1 KH2PO4 at room temperature, there was a 85.69% increase in the modified red mud.(4) There was little influence on soil pH by using phosphate modified red mud. After phosphate modified red mud materials were added, available silicon in the soil obviously improved from 6.37% to 209.66%. Exchange Cdmium in the soil decreased 42.75%～90.97%, and residual Cd increased steeply from 25.66% to 44.91%.(5)Plant height and chlorophyll content increased after application of phosphate modified red mud materials. Accumulation of cadmium in rice root increased, while the cadmium content in leaf, rice husk, rice grain reduced. Of these, Cd in rice was 0.2133 mg·kg-1 under 3% KH2PO4 modified red mud disposal,the best result with a 24.17% decrease compared with blank.