Study On The Passivation Effect And Mechanism Of Cadmium In Tobacco Planting Soil By Several Amendments

In order to reduce the absorption of cadmium in the soil and improve the quality of tobacco,this paper systematically studied cadmium adsorption performance and mechanism of four materials,namely thermally activated attapulgite（ATP）,nano zero-valent iron（nZVI）,rice husk biochar（RHB）and soil conditioner（PT）.The effects of four materials on the morphology of cadmium in soil and soil enzyme activity,and the effects on the content of cadmium in tobacco and the agronomic characters of tobacco growth are mainly studied as follows:1.The adsorption mechanism of cadmium ions in aqueous solution by the four materials were clarified.（1）The adsorption kinetics of cadmium by ATP,nZVI,RHB and PT were in accordance with Elovich model;The adsorption isotherms of cadmium by ATP and nZVI were consistent with Langmuir and Freundlich models;The adsorption isotherms of cadmium by RHB and PT were consistent with Langmuir model.The removal percent of cadmium ions by ATP,RHB and PT increased with the increase of the pH of cadmium solution,but the removal percent of cadmium by nZVI increased first and then decreased with the increase of the pH of the cadmium solution.K⁺,Na⁺,Ca²⁺and Mg²⁺inhibited the removal of cadmium ions by the four materials,and the inhibitory effects were enhanced with the increase of ionic strength of the solution.Humic acid promoted the removal of cadmium ions by ATP,RHB and PT,but inhibited the removal of cadmium by nZVI.（2）The removal mechanism of cadmium from the four materials was further deduced by Fourier infrared spectrum and X-ray diffraction characterization of the materials before and after adsorption.There may be ion exchange,electrostatic and surface complexation between ATP and cadmium ions.The removal of cadmium ions in the solution by nZVI was through electrostatic and surface complexation.The removal of cadmium ions in the solution by RHB and PT was through electrostatic,surface complexation and precipitation.2.The effects of the four materials on the content of available cadmium in soil,soil pH value and soil enzyme activity were clarified.（1）All the four materials added to the soil could reduce the content of available cadmium in the soil.When the four materials were added with the same amount,PT had the most significant effect on the reduction of available cadmium in the soil.（2）When the four kinds of materials were added to the soil,they could increase the soil pH value.With the increase of the amount of the four materials,the soil pH gradually increased.（3）ATP and RHB could enhance the activity of urease and sucrase in soil.The addition of nZVI inhibited the activity of soil urease and enhanced the activity of soil sucrase.Adding low dose PT enhanced soil urease and sucrase activity,while high dose PT could disable soil urease and sucrase activity.3.The effects of four materials on cadmium content in tobacco leaves and agronomic characters of tobacco were investigated.（1）When the four materials were added to the soil respectively,ATP,RHB and PT could significantly reduce the cadmium content in tobacco leaves,while nZVI could not inhibit the cadmium absorption in tobacco leaves.（2）Compared with the blank control,leaf length,leaf width,plant height,stem circumference and the number of effective leaves of tobacco in the soil with ATP,RHB and PT were significantly increased.However,the addition of nZVI to the soil reduced the leaf length,stem circumference and effective leaf number of tobacco leaves.