Study On Mechanism And Stabilization Remediation Of Red Mud In Cd Contaminated Soils

The problem of soil contaminated with Cadmium has recently become serious in our country, choosing appropriate amendment to remediate Cadmium contaminated soils was a common remediation method. Red mud as amendment was applied in this research, alluvial mud soil and yellow clayey soil were chosen. Through paddy pot experiment, the effects of adding red mud on soil physical and chemical properties, exchange of Cadmium fraction in soil, rice uptake of Cadmium and paddy growth were studied. In order to discuss the mechanism of stabilization remediation of red mud in Cadmium contaminated soils, the stabilization efficacy of Cadmium in contaminated soil after application of red was analyzed, and the appropriate application rate of red mud in remediation of Cadmium contaminated soil was defined. The main results in this experiment showed as follows:(1) Red mud application increased the soil pH and cation exchange capacity effectively, and the rate went up with the increase of red mud application. The soil organic matter did not change significantly after red mud application.(2) The distribution of Cadmium fraction in soil were related to the own characteristics of soil. With the application of red mud, the contents of exchangeable Cadmium in soil has decreased, while the contents of carbonate-bound and Fe-Mn oxide-bound and residual Cadmium in the soil increased, the contents of organic matter-bound Cadmium in soil did not change significantly. The greatest change of Cadmium fraction distribution in soil was in the treatment with 12.5 g red mud per 1 kg soil. The remediation efficacy of red mud addition in alluvial mud soil is better than in yellow clayey soil. The change of Cadmium fraction distribution in soil was mainly due to the increase of soil pH and cation exchange capacity after red mud addition.(3) Red mud addition decreased the contents of Cadmium in rice grain and the enriching factor of rice grain. The Cadmium concentration in rice grain went down with the increase of red mud application. In the experiment with alluvial mud soil, compared with the experiment of no red mud application (Cadmium concentration in rice grain is 0.31 mg-kg-1), the rice grain Cadmium concentration (0.18 mg·kg-1) was decreased by 41.9%after red mud application up to 7.5 g·kg-1. In the experiment with yellow clayey soil, compared with the experiment of no red mud application (Cadmium concentration in rice grain is 0.24 mg-kg-1), the rice grain Cadmium concentration (0.17 mg-kg-1) was decreased by 29.1%after red mud application up to 5 g·kg-1.The Cadmium concentration of rice grain in those treatments are less than the national hygiene standard (GB2715-2005). The decrease of Cadmium contents in rice grain was mainly due to the exchange of soil physical and chemical properties and the Cadmium fractions, while the contents of bio-available Cadmium was decreased.(4) Application amount of red mud could promote rice growth. But the rice growth could be inhibited by addition of red mud over a certain range. Considering the efficacy of rice growth and soil remediation, addition of 7.5 g red mud per 1 kg soil (16875 kg red mud per 1hm2 soil) in alluvial mud soil and 5 g red mud per 1 kg soil (11250 kg red mud per lhm2 soil) in yellow clayey soil were suggested.