| Farmland soil in China is seriously polluted by heavy metals,especially cadmium(Cd).Excessive Cd in soil is easy to be absorbed by crops,thus entering the food chain,and causing human health risks.Therefore,remediation of Cd-pollution in farmland soil is an important work of ecological environment protection.A variety of remediation technologies for soil Cd pollution have been developed at home and abroad,and widely used in actual remediation projects.However,most of the existing technologies still have some technical barriers that are difficult to solve,such as how to maintain long-term stability after remediation,which is one of the scientific problems in the field of environmental pollution control.In this study,Cd-pollution farmland in typical sewage irrigation area of Hebei Province was selected as the research area.The intercropping technology of Cd accumulation plants(Solanum nigrum L.and Amaranthus hybridus L.)and vegetable crops(Pakchoi)was selected to carry out the field experiment of Cd contaminated soil remediation.Combined with the interdisciplinary research methods of Mineralogy,Environmental Science and Ecology.To reduce the environmental risk of Cd in soil,field experiments,laboratory simulation and mineralogical characterization were carried out.The environmental risk reduction and long-term stability after remediation of soil Cd were discussed from two aspects of "removal" and "fixation".In particular,the possibility and mechanism of using fly ash as immobilization / stabilized soil Cd material were studied.Based on the basic theories of crystallography and mineralogy,the way to solve the key problems of heavy metal pollution in the current environmental field was explored,which opened a new research idea for ecological environment treatment.The main achievements of this paper are as follows:(1)Intercropping a row of Pakchoi with a planting density of 30 cm × 30 cm and a row of Solanum nigrum L.can maximally reduce the accumulation of Cd in edible parts of vegetable crops Pakchoi,with a reduction rate of 50%.It is one of the intercropping systems which can significantly reduce Cd in soil.(2)The diversity of soil bacteria in one row belt intercropping system was higher than that in three rows belt intercropping system.Among them,Proteobacteria,Acidobacteria,Actinobacteria,Bacteroidetes,Chloroflexi accounted for 86.04% of the total sequence,which was the dominant flora in this intercropping experiment.(3)The results show that the application of fly ash to soil pollution remediation has the advantage of "treating waste with waste and green restoration".The combined process of mechanical grinding and adding activator can reduce the content of available Cd by 98.79%,which shows that fly ash is one of the effective materials for soil Cd curing,which is worth further study.(4)The result show that the process of "grinding first,then adding Ca O" is beneficial to improve the solidification performance of fly ash materials for Cd.Especially when the pozzolanic activity of fly ash is stimulated,the crystallinity of quartz increases significantly after adding appropriate amount of water,and a new calcite phase is found,which is of great significance to the long-term stabilization of Cd.(5)In this study,it was noted that intercropping system led to the increase of available Cd content in rhizosphere soil,which should be paid enough attention in the process of practical application.It is suggested that other remediation methods should be considered to solve the problem of increasing available Cd in rhizosphere soil. |
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