Red Mud-Sepiolite Composites For Remediation Of Heavy Metal Contaminated Soil

Heavy meatal contamination turns into a severe issue hindering soil security at present.The use of alumina industrial waste residue-red mud and red mud-sepiolite composite materials for remediation of soil contaminated by heavy metals is a new approach for the utilization of red mud resources.This thesis focuses on the use of sepiolite as an adjunct to further improve the effective silicon content in modified red mud,based on the author's previous experiment of the modification of red mud to stimulate the activity of the silicon.In order to explore the red mud-sepiolite composites in the stabilization of cadmium and the inhibition of cadmium uptake by rape in contaminated soil,the determination of available silicon,transformation of cadmium in soil growth status,and cadmium uptake of rape are studied theoretically and experimentally.The thesis examines the method promote mechanism of the stabilization of cadmium in soil by red mud-sepiolite composite materials,and conducts the soil column leaching test.The impact of the application of the composite material on the migration of heavy metal cadmium that caused by the increase of soil silicon activity is investigated.The results of this study were obtained as followed:?1?The compound modification test was conducted with a red mud-sepiolite mass ratio of 1:1.At room temperature,sepiolite was first mixed with 0.056g/g soluble phosphorus,and the red mud was mixed and allowed to stand still for 2h.The effective silicon content was 1507.31 mg·kg^-1,which was 65.41%higher than the red mud raw material.?2?The addition of different ratios and different amounts of red mud-sepiolite composites all can increase the content of available silicon in the soil,and the maximum increase of effective silicon content in soil in the middle and later stages were 11.27%.At the same time,the addition of red mud-based materials has enabled the conversion of available cadmium from cadmium-contaminated soils to residual cadmium which is not easily absorbed by plants,and the decreasing range of exchangeable cadmium in the soil with 5%compounded red mud-sepiolite was between 3.96%and 73.49%.The increasing ratio of residual cadmium was between15.78%and 58.82%.?3?The rapeseed pot test results showed that the red mud base material has little effect on the aboveground biomass and growth index of rapeseed,but has appropriate impact on cadmium uptake.In rapeseed planted with 2%red mud-sepiolite composite soil,the cadmium content in the underground part has increased by 10%,while the cadmium content in the aboveground part has decreased by 5.88%compared to the blank group.?4?In the column leaching test,the concentration of cadmium in the upper layer soil was lower in the treatment groups added with the red mud-based material than in the control group,and the effective silicon content in the middle layer was significantly increased.After adding 5%modified red mud-sepiolite composite treatment in group L5,the cadmium content of the upper and middle layers decreased significantly with the increase of treatment time,and the decrease ranged from 22.33%to 28.78%.Although the enhancement of soil silica activity promotes strong cadmium migration to a certain extent in the vertical profile,it was still difficult to migrate to deep layers.