Common technical methods for heavy metal remediation of farmland soil

According to incomplete statistics, at present there are nearly 10 million hm2 of cultivated land in China with varying degrees of pollution. Each year, 12 million tons of heavy metal-contaminated food are produced. Most of the cities in China's suburbs of the farmland have been subject to varying degrees of heavy metal pollution. Heavy metal pollutants in farmland soil mainly include Cd, Pb, Cu, Hg, Cr, Zn, Ni and metal-like As, which enter the farmland mainly through agricultural materials such as atmospheric sedimentation, sewage irrigation and the application of solid wastes. For example, the heavy metals contained in tail gas from automobiles and motorcycles enter the atmosphere in the form of aerosols and enter the soil through natural sedimentation and precipitation; the untreated heavy metals in industrial wastewater enter the soil through groundwater; the heavy metals in industrial fixed wastes And unused heavy metals in agricultural materials are spread to the surrounding soil by the sun and rain; untreated heavy metal pollutants enter the soil through wetting and drying and cause pollution to the soil. Heavy metal soil remediation technology mainly includes engineering measures, agronomic regulation, physical and chemical remediation and bioremediation technologies. Technology measures to repair techniques include: guest soil method, tillage mix method and engineering removal method. In the case of farmlands contaminated by heavy metals and with a small pollution area, the soil and land method can effectively reduce the impact of heavy metals on the environment. However, for the farmland with large pollution area, the project management is heavy and costly, affecting the surrounding geology. For contaminated area larger farmland. Tillage mixing method is suitable for farmland with lower degree of pollution, and heavy metal pollution level is too high, which will lead to no obvious decrease in the concentration after tilling mixing, and thus can not achieve the role of heavy metal repair. Engineering removal method is effective, but should pay attention to the lower soil heavy metal pollution. Overall, the use of engineering measures to repair farmland soil heavy metal pollution is a temporary solution, requiring a lot of manpower and material resources, and easily lead to secondary damage to cultivated land, can be used for sudden pollution incidents, does not promote widespread use. Agronomic measures include adjusting soil pH and regulating soil moisture content. Agronomic control measures with low cost, does not affect soil production features, but only for less polluted areas. Changes in the soil environment are likely to re-release of heavy metals. Relatively speaking, agronomic regulation measures are more mature, lower cost and less impact on soil environment, and are recommended for farmland with less heavy metal pollution. Chemical repair techniques include electric repair, washing, chemical curing / stabilization and other methods. Electric repair simple operation, high efficiency, but easily lead to changes in soil physical and chemical properties. The leaching technology can completely remove the heavy metals in the soil, but it is less effective in remediation of the soil with poor permeability and permeability, and the eluent is expensive and can cause secondary damage to the soil. Although chemical curing / stabilization techniques are simple and easy to use, this method simply changes the form of heavy metals that remain in the soil and may also re-release into the soil when the soil environment changes. Chemical repair technology in addition to chemical curing / stabilization of low-cost technology, the repair of other high repair costs. Bioremediation refers to the use of specific biological, absorption, transformation, removal or degradation of environmental pollutants, including phytoremediation, animal repair and microbial repair. Plant restoration is divided into plant stability, plant volatility and plant extracts. Animal remediation refers to the use of low-grade animals can absorb heavy metals in the soil enrichment method. Microbial remediation refers to the use of active microorganisms on the adsorption of heavy metals or converted into low-toxic products, used to repair the bacteria are bacteria, fungi and actinomycetes. In the actual restoration work, we need to select specific restoration technologies according to the pollution of farmland soils, and we need to study and improve the technology of plant extraction, agronomic regulation and control, chemical curing / stabilization, and explore the joint application of these technologies in actual restoration , Get the best repair effect and applicability.