Study On The Remediation Of Cadmium Polluted Soil By Organic-inorganic Compound Passivator

With the development of industry,the exploitation of mineral resources and the use of chemical fertilizer in agriculture,cadmium pollution in soil is becoming more and more serious.According to the national soil pollution investigation bulletin in2014,the over standard rate of soil cadmium is 7%,which is the most serious in all soil pollution.Compared with other repair methods,chemical passivation has the advantages of short repair cycle,simple operation,economic and practical,so it is widely concerned.The organic-inorganic compound passivator has the advantages of both organic and inorganic passivators.It can effectively improve the soil while repairing the cadmium polluted soil.Therefore,this paper intends to carry out the preparation technology of organic-inorganic compound passivator and the study of the passivation and restoration of cadmium in the soilIn this paper,the effects of five passivators and their combinations on Cadmium in soil were studied.Using humic acid and sepiolite as raw materials,the preparation of compound passivator was studied.The best preparation conditions of compound passivator were studied by single factor experiment and response surface experiment.The passivation effect of compound Passivator on cadmium polluted soil was studied by passivation experiment.The microstructure and phase composition of compound passivator were analyzed by BET,XRD and SEM.The results show that:(1)Five kinds of passivators have certain passivation effect on cadmium polluted soil,and the risk of cadmium release in the soil is reduced after passivation;the combination of humic acid and sepiolite has the best effect in the combination,when the reaction time is 3days,the addition ratio is 1:1,the addition amount is 3%,the passivation efficiency is 26.25%,the activity stability ratio is reduced to 0.96,and the activity coefficient is reduced to 0.226.(2)The effect of organic-inorganic compound passivator prepared with humic acid and sepiolite as raw materials is better than that of direct combination.The optimum preparation conditions are: raw material ratio(humic acid: Sepiolite)= 2:1;reaction time of humic acid and sodium hydroxide is 40 min,reaction temperature is80 ℃;concentration of sodium hydroxide is 0.04g/ml.The best addition of compound passivator is 7%,when the reaction time was 7 days,the passivation efficiency reached 53.29%.At this time,the activity stability ratio of cadmium in soil was 0.65,and the activity coefficient was 0.179.After passivation,the pH value of soil increased,the content of organic matter increased,the risk of Cd release from soil was low,and it became more difficult to be absorbed by plants.(3)The specific surface area of composite passivator is smaller than that of sepiolite and humic acid,the composite passivator does not change the original structure of humic acid,and changes its surface morphology;the composite passivator does not damage the soil micro aggregate.(4)The main function of the compound passivator in the remediation of cadmiumcontaminated soil is adsorption,complexation.The addition of the compound passivator can promote the transformation of cadmium from non residue state to residue state,reduce the migration ability and increase the stability of cadmium So as to repair the cadmium polluted soil.