Study On The Remediation Effect Of Nano-materials On Cadmium-polluted Soil

Due to the acceleration of industrialization and urbanization,there are a series of environmental problems,among which heavy metal pollution in the soil environment is difficult to be naturally transformed into harmless substances,resulting in food security,life safety and other issues.Soil heavy metal pollution has become one of the hot issues for scholars at home and abroad.In recent years,applying nano materials to repair heavy metal contaminated soil has become a hot research.Based on literature research,nano ferrous sulfide?NFeS,homemade?,carboxymethylcellulose stabilized ferrous sulfide?CMC-NFeS,homemade?and nano-hydroxyapatite?NHAP,commercially available?were tested with heavy metal cadmium?Cd?as the target pollutant.Through soil culture experiments,this paper studied the ability of the above three different nano materials to fix heavy metal cadmium in soil during 60 days cultivation,and selected a suitable nano material.Through the wheat seedlings experiment,this paper studied the effects of different dosage of nano materials on wheat plant enzymes and soil enzyme activities.The pot experiment was conducted to study the how pH and Eh change in the soil after applying the nano materials in different concentrations of cadmium contaminated soil,and the absorption and enrichment amount of cadmium in rape and Beta vulgaris var.cicla L.and how microbial community change in soil.The feasibility and control effect of the nano materials applied to repair heavy metal cadmium contaminated soil were clarified,which can provide theoretical basis and technical support for practical,efficient and safe heavy metal contaminated soil remediation technology.After the above experimental research,the paper obtains the following conclusions:?1?Comparing the effects of three kinds of nano materials NFeS,CMC-NFeS and NHAP on soil pH,soil TCLP extraction and Cd concentration in soil,and the Cd distribution after 60 days of soil culture,and screening a nano-repair material with the best performance.The results show that after applying three kinds of nano materials NFeS,CMC-NFeS and NHAP,the soil pH varies from 6.41 to 7.53,and NHAP significantly increases the soil pH by 0.6-0.86.According to the TCLP toxicity leaching experiment,the three kinds of nano materials can reduce the effective concentration of cadmium,and its degradability is NHAP>CMC-NFeS>NFeS.By comparing the effects of three kinds of nano materials NFeS,CMC-NFeS and NHAP on the morphological distribution of cadmium,it can be seen that the three kinds of nano materials can significantly promote the exchangeable and carbonate-bound cadmium convert into residual cadmium in soil.After treatment with NFeS,CMC-NFeS and NHAP,the proportion of exchangeable cadmium in the soil was 34.5%-39.5%,27.5%-36.5%,and 24%-28%,respectively.The proportion of exchangeable cadmium in the soil treated by NHAP is lower than that of the soils treated by CMC-NFeS and NHAP.After treatment with NFeS,CMC-NFeS and NHAP,the proportion of residual cadmium in the soil was 20.5%-24%,21.5%-29%,and 27.5%-30%,respectively;Compared with the other two types of nano materials,the proportion of residual cadmium treated by NHAP is higher.The three kinds of nano materials have good passivation and fixation effects on cadmium,and NHAP has the best passivation and fixation effect.Therefore,NHAP was selected as the best nano material for repairing heavy metal cadmium contaminated soil for further experimental research.?2?Applying NHAP as the tested material,the effects of concentrations of NHAP on wheat plant enzymes and soil enzyme activities were studied by wheat seedling experiment.Compared with the control group,NHAP with the content of 0.5%,1%and2%?w/w?could increase the activity of SOD and CAT in wheat,but it did not achieve obvious effect on the activity of POD in wheat.When the amount of NHAP was 1%,the activity of POD and CAT in wheat was lower than that applied with other dosages,indicating that wheat had the lowest resistance to oxidative stress.For soil enzyme activity,the NHAP increased soil catalase activity.On the 14^th day,the urease activity increased with the increasing NHAP dosage,but it had little effect on soil alkaline phosphatase activity,so the amount of NHAP is preferably 1%.?3?This paper studied the treatment effect and feasibility of NHAP combined with rape and Beta vulgaris var.cicla L.to repair heavy metal cadmium contaminated soil with different concentrations.Pot experiments showed that the NHAP could increase the pH of rhizosphere and non-rhizosphere soils and reduce the Eh of rhizosphere and non-rhizosphere soils.The addition of NHAP increased the dry weight of the above-ground parts of rape and Beta vulgaris var.cicla L.by 0.4%-1.5%and 0.7%-2.3%,it can reduce the concentration of Cd in plants,reduce the enrichment of heavy metal Cd in plants,and fix heavy metal Cd in soil.Under the Cd pollution load of 0.3 mg/kg,the Cd concentration in the above-ground plants of rape applied with NHAP was found to be 0.25 mg/kg lower than that without NHAP,the Cd concentration in the above-ground plants of Beta vulgaris var.cicla L.applied with NHAP was found to be 0.67 mg/kg lower than that without NHAP.Under the Cd pollution load of 5 mg/kg,the Cd concentration in the above-ground plants of rape applied with NHAP was found to be18.08%lower than that without NHAP,the Cd concentration in the above-ground plants of Beta vulgaris var.cicla L.applied with NHAP was found to be 21.64%lower than that without NHAP;After adding NHAP,the total enrichment of Cd in leaves of Beta vulgaris var.cicla L.was 31.88 mg/pot higher than that of rape.The addition of NHAP can increase the abundance and diversity of microbial species,and increase the abundance of Actinobacteria and Gemmatimonadetes.The rape and Beta vulgaris var.cicla L.can enhance the abundance of Proteobacteria.The studies show that NHAP has good governance effects in treating and repairing heavy metal cadmium contaminated soil.In conclusion,this study screened a type of nano material NHAP suitable for cadmium-contaminated soil restoration.Under the experimental conditions,its optimum dosage was 1%.NHAP has a excellent ability to fix heavy metal cadmium.When the soil cadmium pollution load is 0.3-5mg/kg,NHAP can effectively reduce the absorption and enrichment of cadmium in rape and Beta vulgaris var.cicla L.and increase the abundance of microbial communities.NHAP has good governance effects in treating and repairing heavy metal cadmium contaminated soil.