| Soil is an important part of the ecosystem and the heavy metal Cd in the soil was polluted seriously,which affected human health through the food chain.This paper used low-cost attapulgite and biochar as raw materials to prepare composite passivators to treat cadmium-contaminated soil and discuss its adsorption mechanism.It was of great significance for the development of environmentally friendly heavy metal passivation materials and soil heavy metal pollution remediation.It was beneficial to expand the application range of attapulgite and biochar.In this paper,various types of attapulgite and biochar were selected as raw materials.The attapulgite was used as an inorganic carrier,and iron of Fe(Ⅱ/Ⅲ)and biochar were loaded on the surface of the attapulgite by chemical precipitation to prepare modified composite clay mineral materials;A variety of characterization methods such as field emission scanning electron microscope,X-ray diffraction analysis,Fourier infrared spectroscopy and Zeta potential analysis were used to characterize and analyze materials;we had studied the migration and transformation of heavy metal Cd at the solid-liquid interface,adsorption kinetic behavior(such as: pseudo first-order kinetic equation,pseudo-second-order kinetic equation,Weber and Morris model and Elovich model),isotherm adsorption curve(Langmuir,Freundlich and DR model)for model fitting;The leaching characteristics and bioavailability of the leaching column and pot experiment were studied to study the remediation and passivation effect of the composite material on the heavy metal cadmium in the soil under actual conditions.to study the leaching characteristics and bioavailability,detecting the cadmium content in plants,p H,cation exchange capacity and organic matter of soil.The evaluation index of the repair passivation effect provided an important basis for repairing the cadmium pollution in the soil.The main conclusions of the study were: When the ratio of biochar to attapulgite was 1:10,the prepared composite material has the highest adsorption rate of cadmium.Through FESEM,XRD and FTIR analysis,it can be seen that biochar and Fe(Ⅱ/Ⅲ)were successfully loaded on the surface of the attapulgite,and after adsorption,the heavy metal Cd combined with surface Fe to form a stable covalent bond;The kinetic model was fitted for the adsorption process of Cd on the composite material,and it was found to be in line with the pseudo-secondary kinetic model,indicating that the adsorption process was dominated by chemical adsorption,with the maximum adsorption capacity of 39.9 mg/g;The results of the fitting of the isothermal adsorption model conform to the Langmuir model,indicating that the adsorption process was mainly a single layer adsorption on the surface of the material;and the resolution rate of the material after adsorption was close to zero;Adding 3% composite materials to the soil contaminated by exogenous cadmium had the best passivation effect on Cd in the soil;the cadmium content was reduced by 89.3% in plants,the fresh weight of plants was increased by 514%,and the plant height was increased by 34.6%. |
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