Remediation Of Copper And Cadmium Contaminated Soil With Several Immobilizing Amendments

Currently, many farmland has become abandoned land due to heavy metal contamination of soil, so the remediation and re-use of abandoned land has reached a critical period which can not be delayed any more. Chemical immobilization technology has been paid widely attention for its low-cost, easy operation and quick results.In this paper, the adsorption and desorption experiment, thermostatic incubation experiment and pot trial were done by selecting several immobilizing amendments including natural maifan stone, salt-modified maifan stone, maifan stone coated urea slow release fertilizer and biological soil conditioner, using ryegrass(Lolium Perenne L.) as indicator plant and heavy metal contaminated abandoned farmland which was surrounded one copper smelter factory as experimental soil. Simultaneously, the immobilized remediation effect and functional mechanism of the several immobilizing amendments on soil-plant niche were studied. The main results were as follows.The results of adsorption and desorption experiment of screen the effective immobilizing amendments among six species as fly-ash, limestone, natural maifan stone, salt-modified maifan stone, alkali-modified maifan stone and biological soil conditioner indicated that all six immobilizing amendments have some immobilization effect on copper and cadmium in soil. When adding content concentration of the above 6 chemical immobilizing amendments are 80g/kg, 2g/kg, 10g/kg, 50g/kg, 50g/kg, and 50g/kg, respectively, the immobilization effect could reach its best. Among them, the immobilization percentage of Cu in soil were 85.1%, 89.6%, 96.5%, 89.6%, 96.5% and 96.4 %, and to Cd were 47.8%, 56.3%, 74.2%, 38.6%, 63.94% and 61.96%. Considering both value of economic and usage, we selected four immobilizing amendments to do thermostatic incubation experiment and pot trial which including natural maifan stone, salt-modified maifan stone, biological soil conditioner and maifan stone coated urea fertilizer.The results of thermostatic incubation experiment and pot trial both showed that the four immobilizing amendments can improve soil p H and increase the soil ccation exchange capacity, bring down the activity of Cu, Cd in soil, immobilize copper and cadmium in the combined pollution soil effectively. When compared with the control in thermostatic incubation experiment, the p H of soil increased from 4.74 to 5.53, 6.37, 6.09 and 4.92 respectively, and soil cation exchange capacity has increased by 46%, 52%, 49% and 45%, the percentage of soil Cu acid-soluble fraction decreased from 45.96% to 33.26%, 32.92%, 33.51% and 31.93%, the percentage of soil Cd acid-soluble fraction reduced from 68.04% to 34.04%、27.08%、30.42%、38.33%. It showed a significant negative correlation between the percentage of soil Cu, Cd acid-soluble fraction and residual fraction form percentage, and the same effect between soil p H and CEC. The activity change of soil urease and acid phosphatase could prove this conclusion.We could know the result from the contrast between pot trial and thermostatic incubation experiment, after the application of the above-described four kinds of immobilizing agent, the percentage of soil Cu, Cd acid-soluble fraction kept decline, among which, Cu has declined by 21%, 23%, 30%, and 2%, and Cd has decreased by 26%, 28%, 20%, 8%. Compared to the control group, the Cu content in aerial part of the ryegrass(Lolium Perenne L.) has decreased by 74.35%, 76.91%, 71.78% and 29.21%, the underground part has decreased by 40.02%, 52.52%, 70.16% and 1.36%; the Cd content in aerial part of the ryegrass(Lolium Perenne L.) has decreased by 61.28%, 65.00%, 51.60%, and 52.10%, the underground part has decreased by 38.27%, 41.89%, 46.71% and 18.01%. So we could see that the decreased number of aerial part was much higher than the underground part, immobilizing amendments could effectively inhibit Cu, Cd in soil migrating from the underground part to aerial part, reduced the assimilation and accumulation of winter wheat grass to Cu, Cd in order to achieve the purpose of remediation of contaminated soil.XRD analysis showed that the main composition of maifan stone is Na A1Si3O8(albite), SEM morphology and specific surface area character told us the liminated structure has interlaminar fracture after modification, the specific surface area has increased then increase the absorption area of maifan stone has increased at the same time, which proved modified maifan stone can immobilize the natural maifan stone better from the structure.Chemical immobilization amendments have well immobilize effect on Cu, Cd compound contaminated soil, especially the application of clay minerals as natural maifan stone and its modified materials, which will not only bring no new pollutants in soil, but also avoid risk of secondary pollution, the most important thing was that it could improve the soil environment effectively, which provided a new method to immobilize and remedy the heavy metal contaminated soil.