Remediation of soils contaminated by heavy metals can be defined as the implementation of a range of techniques to remove heavy metals contaminated in soils or to reduce the activity and effective components of heavy metals in the soil in order to restore soil ecological functions and to reduce the release of heavy metal pollutants to the food chain and Groundwater migration. As the most typical factor of heavy metal pollution, chromium is the main method for the remediation of soils contaminated by it. There are two main ways: One is to make a substantial change in the chemical nature of chromium in the soil, such as changing the valence state of chromium ions, reducing the six chromium ions to trivalent or converting the exchangeable and carbonate bound states to relative Stabilize other forms, through these measures to reduce the mobility of chromium in the soil environment, eliminate biological activity; Another approach is to use some means to remove the chromium, a pollution factor, directly from the soil environment. According to these two repair methods, domestic and foreign experts and scholars have done a lot of experimental research and application demonstration. This paper introduces the research status of the remediation technology of chromium contaminated soils, analyzes some problems existing in the application of the various technologies and puts forward some work that needs to be done to promote the remediation of chromium contaminated soils. The remediation methods summarized in the remediation technologies of chromium contaminated soils mainly include the physical remediation method, the chemical remediation method, the bioremediation method, and the integrated remediation method with various technologies. At present, the main technologies used in China are as follows. 1 curing / stabilization technology Curing stabilizing technology is to add a certain agent to the soil polluted by chromium, and then fully mixed. By adding these agents, the migration of chromium into the surrounding environment is reduced. S Wang and Cipulanandan Soil samples were prepared from a mixture of sand (79%), kaolin (20%) and organic matter (1%), which contained Cr (VI) at 7000 mg / kg and Cr (VI) (273mg / L). The content of Cr (VI) in the leachate was reduced by 37% when adding cement treatment (cement-soil ratio was 0.2). After adding 10% FeCl2, the soil was contaminated with Cr (VI) (III), the content of Cr (VI) in leachate decreased by 92%, and the efficiency of 99% was achieved by combining Cr (VI) reduction technology and S / S treatment. Xu Xiaoxi et al. Compared the solidification / stabilization effects of single-doped Portland cement clinker, FeCl2, and composite silicate cement clinker and FeCl2 on the chromium-contaminated soil. The results show that the hydration products of clinker encapsulate and connect soil particles, Filled pores and ion exudation channels, while FeCl2 still has good reducibility under alkaline conditions. Both of them work together to obtain higher strength of the soil and lower the leaching concentration of Cr (VI). "The premise of this technical operation is the need to dig out the original location of soil cleared in other work areas mixed curing, the curing process requires a lot of manpower, material and financial resources, and curing uniformity and curing effect is still not clear , But also follow-up tracking, and the technology still needs further improvement. 2 electric repair Electric repair technology is in the soil under acidic conditions, the DC pass through the soil, remove heavy metals in the soil. The disadvantage of this method is that it has certain requirements on the pH value of the soil and can only be carried out in a low pH soil environment. The whole process needs to add some chemicals to reduce the pH of the soil, and the soil has a certain buffer , The buffer capacity of different soil is also very different, when the need to control the chromium-contaminated soil self-cushioning, which means that the buffer capacity of the soil is high, there may be processing can not achieve the desired Soil acidic environment, making the technology can not achieve the desired results. In addition, this technique takes a long time and can take days to years. "This method does not apply to higher permeability, poor conductivity of the sandy soil, so the scope of application of this method is subject to some limitations.Although chromium contaminated soil can be electrically repaired and retrieved, but in-depth study of chromium and soil Colloids in the physical and chemical effects of this method is less applicable, the use of soil pollution should be taken into account and its basic physical and chemical properties. 3 soil washing technology Soil washing technology is the use of chemical reagents to contaminate soil heavy metal ions from the soil into the liquid phase, making the concentration of heavy metal pollution in soil reduced, and ultimately achieve the purpose of soil remediation. At present, commonly used eluent with inorganic solution, chelating agent, surfactant, a large number of scholars have made a lot of research on the selection and application of different eluent. The results showed that 2mol / L HCl can effectively remove Cr from the heavy metal contaminated soil in chemical plant by 80.75%, EDTA is 0.05mol / L, pH is 7, liquid to soil ratio is 10: 1, leaching time is Under 18 h condition, the removal rate of Cr was 6.29%. Under the condition of citric acid concentration of 0.05 mol / L, the extraction efficiency of sand, loam and clay was good.
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