Effects Of Modified Zeolite On Properties Of Cadmium Contaminated Soil And Pepper Growth

With the rapid development of social economy,soil heavy metal contamination has become one of the current environmental problems that can not be ignored.Cadmium（Cd）is a very toxic heavy metal element,Excessive heavy metal cadmium（Cd）in farmland soil not only affect the absorption of nitrogen,phosphorus,potassium and other nutrients in plants,inhibit crop growth,reduce crop yield,but also can enter the human body along with the food chain even threaten human health.Therefore,how to realize the safe production of heavy metal contaminated land has become the primary task and research focus of soil heavy metal remediation.Zeolite is a potential passivation remediation material for heavy metal contaminated soil with good filtration and ion exchange capacity,and strong adsorption capacity for heavy metal ions such as Cd,Pb and so on.In this study,natural zeolite（NZ）was used as raw material to carry out Na OH modification（JZ）,high temperature modification（HZ）,Na₂S modification（SZ）,humic acid modification（FZ）and ultrasonic modification（CZ）in terms of improving specific surface area and increasing porosity.Based on adsorption and desorption test,the effects of initial Cd²⁺concentration,temperature,p H and adsorption time on the adsorption and desorption properties of zeolite were investigated,and the adsorption mechanism of Cd²⁺on zeolite was explored through adsorption kinetics and isothermal adsorption.Pepper pot experiment was used to explore the remediation effect and passivation effect of different zeolite on Cd contaminated soil.Based on pot experiment of pepper,the effects of zeolite addition on soil available cadmium content,soil enzyme activity,soil p H,growth characteristics and quality of pepper were studied.The results could provide theoretical basis and technical support for remediation of heavy metal contaminated soil by modified zeolite.The main results are as follows:（1）The adsorption capacity of zeolite to Cd²⁺increases with the increase of the initial concentration of Cd²⁺,and finally reaches saturation.The saturated adsorption capacities of Na OH modified zeolite and Na₂S modified zeolite are significantly higher than that of natural zeolite（35.54%and 18.54%,respectively）.The desorption rate of Na OH modified zeolite is0.43%,which is significantly lower than natural zeolite.Moreover,the p H value of zeolite adsorption ranging from 4 to 8,the time of 360 min,and the temperature of 25-35℃are the most conducive conditions to the Cd²⁺adsorption.The Langmuir adsorption isotherm equation could fit the Cd²⁺adsorption process of zeolite well（R~2>0.9765）.The adsorption kinetics analysis results showed that the adsorption kinetics model of Na OH modified zeolite,Na₂S modified zeolite and natural zeolite for Cd²⁺fit the quasi-second-order kinetic equation,and the adsorption concentration at equilibrium is 1.996mg/g,1.994mg/g and 1.779mg/g,respectively.（2）Zeolite with different modification and addition ratio had significant effects on the content of available cadmium in soil,soil p H and soil enzyme activity.With the increase of zeolite addition ratio,the passivation effect of zeolite on Cd gradually increased.Na OH modified zeolite has the best passivation effect on Cd contaminated soil.When zeolite addition ratio is 10%,compared with CK control group,soil available Cd content decreases by 0.09%-46.10%,soil p H increases by 0.02%-6.03%.Catalase and phosphatase activities increased by 27.90%-41.10%and 4.40%-43.01%,respectively.（3）At the 10%application level,the content and enrichment coefficient of Cd in the root and fruit of pepper treated with Na OH modified zeolite were the lowest,which were0.024mg/kg,0.022mg/kg and 0.011,respectively.When the additive proportion was 10%,the plant height,fresh weight,fruit weight and Vc content of pepper treated with Na OH modified zeolite were higher than others.Compared with the control group CK,the plant height,fresh weight,fruit weight per plant and Vc content increased by 14.40%,21.80%,39.60%and25.50%respectively.（4）Compared with other modified zeolites,Na OH modified zeolites and Na₂S modified zeolites can effectively relieve the stress of Cd on pepper,and reduce the bioavailability of Cd in soil.Comprehensive analysis shows that when the zeolite addition proportion is 10%,Na OH modified zeolites has the best evaluation effect,followed by Na₂S modified zeolites.Through cluster analysis,it is found that 5%and 10%Na OH modified zeolite belong to the same category,and their effects are similar.Therefore,5%Na OH modified zeolite is preferred for comprehensive improvement effect and economic situation.