Development Of Hydrothermal Carbon Preparation Process Of Reed Straw And Its Application In Cadmium Contaminated Soil Remediatio

In recent years,with the development of mining,nickel-cadmium battery,metal coating and other industries,the discharge of cadmium-containing wastewater and waste residue has caused some cadmium pollution to the surrounding soil environment.Concurrently,hydrothermal carbon（HTC）,a new low-cost,novel green material with abundant surface functional groups,has attracted attention and been extensively researched by scholars worldwide for its potential in heavy metal pollution remediation.Reed,widely distributed in our country,often results in environmental pollution and resource wastage when the post-harvest straw is discarded or burned.Using reed straw as raw material to prepare HTC for the remediation of cadmium-contaminated soil can play a good role in"treating waste with waste".In this thesis,the optimization of preparation parameters of HTC from reed straw was studied,the adsorption effect of HTC on Cd²⁺in solution was investigated,the adsorption mechanism was analyzed,and the effect of preparation temperature on physicochemical properties of HTC was discussed.On these basis,the improvement effect of the prepared HTC on the available cadmium in soil and soil nutrients was discussed through the culture experiment of cadmium-contaminated soil.The main research conclusions are as follows:（1）The effect of preparation temperature,solid-liquid ratio and residence time on the yield of reed straw HTC was investigated by orthogonal tests.The primary and secondary factors affecting the yield of HTC were discussed by range analysis and variance analysis,and it was found that the preparation temperature had the greatest influence on the yield,followed by solid-liquid ratio and residence time,and the optimal process parameters were obtained under the above combination.（2）The SR220 with the highest adsorption capacity could be preferred by the cadmium solution adsorption test.The adsorption isotherms of HTC is more consistent with the Freundlich isotherm model,and the adsorption kinetics is more consistent with the pseudo-second-order adsorption kinetics,indicating that the multimolecular layer adsorption plays a dominant role,and the adsorption process is mainly chemical adsorption and supplemented by physical adsorption.The surface morphology,pore structure,surface composition,crystal structure and surface functional groups of the HTC before and after adsorption were analyzed by Scanning electron microscope（SEM）,SEM-Energy dispersive spectrometer（SEM-EDS）,X-ray diffraction（XRD）and Fourier infrared analysis（FTIR）,and the adsorption mechanism was found to mainly include ion exchange interaction,surface complexation and cation-πinteraction.（3）A series of reed straw HTC were prepared at 180℃,220℃and 260℃,respectively.Through the analysis of the physicochemical properties of these HTC,it can be found that with the increase of preparation temperature,the specific surface area,pore volume,fixed carbon content,stability,aromaticity and cation exchange capacity increased,volatile matter,yield and oxygen-containing functional groups decreased,pH slightly increased and ash slightly decreased.The main reason is that dehydration and decarboxylation reaction are intensified with the increase of preparation temperature.（4）The test of reeds straw HTC remediation of cadmium-contaminated soil showed that the appropriate dosage could increase cation exchange capacity（CEC）and soil organic matter（SOM）more effectively,and reduce the content of available cadmium.HTC is rich in nutrients such as organic matter,and its application can directly increase the nutrient content in soil.With the increase of adding time,CEC and SOM showed a slow decline trend,but there was still a significant improvement compared with blank control,indicating that the effect of HTC on soil nutrient enhancement was relatively stable.The available cadmium content decreased first and then increased,mainly because the performance of HTC decreased under the influence of some soil microorganisms or soil environment.HTC with higher preparation temperature has higher stability,can increase CEC and SOM more effectively,and reduce the the content of available cadmium.