Passivation Effect Of Modified Attapulgite On Cadmium In Agricultural Soil

The soil of agricultural land is the most closely related to people’s life,and cadmium is the primary pollutant in agricultural land.The research on the passivation remediation technology of cadmium contaminated soil is of great significance to the remediation work of soil pollution of agricultural land.Current studies on the passivation effect of modified materials mostly focus on the influence of single modified passivation material on the passivation effect of acid contaminated soil.However,most of the agricultural land in northern China is alkaline soil,and existing studies have shown that the compound material may produce better passivation effect than single material.Therefore,it is of great significance to study the passivation effect of modified composite materials on alkaline soil for soil remediation of agricultural land in North China.In this study,simulated cadmium contaminated soil is the object of remediation.Two kinds of single modified attapulgite and seven kinds of compound modified attapulgite were prepared as passivation materials.Through indoor passivation experiment and pot experiment,three results were explored: difference of modification mechanism between iron modification and alkali modification of attapulgite,effect of modified compound attapulgite on the soil physical and chemical property and the passivation effect of cadmium in soil.The main conclusions of this paper are as follows:(1)Compared with the single application of modified attapulgite,the effects of combined application on soil p H value,cation exchange capacity,organic matter content,DTPA-Cd content,growth status and Cd enrichment of lettuce were different.(2)Compared with the original attapulgite,the physical and chemical properties of alkali-modified attapulgite have the following changes: high degree of crystallization;the surface area decreased;the magnesium oxide and aluminum oxide are dissolved in the internal structure of the crystal,which make the internal microchannel aperture increase.The physical and chemical properties of iron modified attapulgite have the following changes: the surface and inner pore were attached with hydroxyl oxide particles,which increased the specific surface area by 45.95%;the carbonate are dissolved in the internal structure of the crystal,which make the number of microchannels and pore volume increase.(3)Compared with the attapulgite modified by alkali,the soil p H decreased and the cation exchange capacity increased.Compared with the attapulgite modified by iron,the soil p H increased and the CEC decreased.There was no significant difference between single application and combined application of modified attapulgite on soil organic matter content.(4)Under the dosage of 0.50%,1.00%,1.50% and 2.00% soil mass,the content of DTPA-Cd in soil under the optimal configuration of modified attapulgite can be reduced by 0.07～0.19mg/kg compared with that of iron modified attapulgite and by0.01～0.09mg/kg compared with that of alkali modified attapulgite.The decreasing degree of soil DTPA-Cd content was higher with the increase of dosage,and the decreasing degree was the highest with the dosage of 2.00%.(5)Under the addition amount of 2.00% soil mass,combined with the effect of reducing cadmium content in the aboveground part of lettuce and other factors,the optimal allocation mode obtained in this study was the mass ratio of alkali modified attapulgite and iron modified attapulgite at 3:1.