Effect Of Two Modified Biochar On Cd Passivation Of Yellow Soil

Biochar passivation has an obvious effect on remediation of soil heavy metal pollution,but it still has some limitations.Relevant studies show that biochar has a significantly enhanced ability to adsorb heavy metals after modification.Therefore,in this paper,oil tea residue and roxburgh rose residue were selected to prepare biochar for sulfhydryl modification.The changes of surface structure and functional groups of biochar before and after modification were investigated by scanning electron microscopy and infrared spectroscopy.The adsorption characteristics of Cd and the passivation effect of Cd in yellow soil before and after modification of biochar were determined by indoor adsorption test and culture test.The main results are as follows:（1）The pH of biochar modified by sulfhydryl group changed from basic to acid.Scanning electron microscopy and infrared spectrum analysis showed that the surface of the original biochar was rough and had more impurity particles,while the surface of the modified biochar was smooth and had tiny pore structure.The contents of S and Si on the surface of biochar modified by sulfuric acid catalytic esterification increased significantly,with the maximum increase of 9.86%.The contents of S and Si on the surface of biochar modified by hydrochloric acid catalytic immersion increased by 5.81%and 6.28%,respectively.The increasing effect of biochar at 500℃was greater than that of biochar at 400℃.The surface functional groups of the original biochar were mainly alkanes,and the characteristic peaks of sulfhydryl and ester groups appeared on the surface of the sulfhydryl modified biochar,indicating that the modified biochar surface was loaded with sulfhydryl functional groups.（2）Adsorption experiments showed that the adsorption of Cd²⁺in the original biochar was mainly physical adsorption,the adsorption capacity of biochar at 500℃was greater than that of biochar at 400℃,and the adsorption capacity of mercapto-modified biochar was mainly chemical adsorption,and the adsorption capacity of mercapto-modified biochar was 1.5 times that of the original biochar.The maximum adsorption capacity of original oil tea residue biochar was 9.98mg/g,and that of sulfhydryl modified oil tea residue biochar was 15.97mg/g.The maximum adsorption capacity of the original roxburgh rose residue biochar was 13.22mg/g,while the maximum adsorption capacity of the sulfhydryl modified roxburgh rose residue biochar was 19.30mg/g.The adsorption capacity of the biochar modified by hydrochloric acid catalytic soaking was greater than that of the biochar modified by sulfuric acid catalytic esterification.When the pH of solution ranged from 3 to 7,the adsorption capacity of original biochar was poor when the pH of solution was low.With the increase of the pH of solution,the adsorption capacity of mercapto modified biochar to Cd²⁺gradually increased.The desorption rate of sulfhydryl modified biochar is 4.38～7.75%,which is much lower than 43.28～45.55%of original biochar,showing strong adsorption stability.（3）The culture experiment showed that the original biochar increased the pH of yellow soil in different culture periods,and the maximum increase was achieved when the addition amount was 2%.The improvement effect of biochar at 500℃was greater than that of biochar at 400℃.The original oil tea residue biochar increased the maximum pH in yellow soil after 60 days of culture,which increased by 0.37 units compared with CK.The original roxburgh rose residue biochar increased the maximum pH in yellow soil after 30 days of culture,which increased by 0.51units.The sulfhydryl modified biochar reduced the pH of yellow soil in different incubation periods.When the original biochar was cultured for 30 days,the effective Cd content of yellow soil decreased the most,and the decrease rate increased with the increase of biochar addition,the original oil tea residue biochar decreased by 38.14%and the original roxburgh rose residue biochar decreased by 35.71%.The effective Cd content in yellow soil decreased the most when the thiol modified biochar was cultured for 60 days,and decreased the most when the biochar addition amount was2%.Among them,sulfuric acid catalytic esterification method modified oil tea residue biochar effect is greater than hydrochloric acid catalytic soaking method,the maximum reduction rate of available Cd in yellow soil is 52.38%.The effect of hydrochloric acid catalytic soaking method on the modification of roxburgh rose residue biochar was greater than that of sulfuric acid catalytic esterification method,and the maximum reduction rate of available Cd in yellow soil was 52.42%.Primitive creatures has a little influence on carbon in the form of Cd in the yellow soil,mercapto modification biochar make yellow soil weak acid extract Cd and can still square one Cd content is reduced,increasing oxidation state Cd and residue content of Cd,mercapto modification cili slag biochar is greater than the effect of sulphur modified in hot oil biochar,hydrochloric acid catalytic soaking method modified biochar is greater than the effect of sulfuric acid catalytic esterification method.Among them,the maximum reduction rate of Cd extracted from roxburgh roxburgh residue biochar modified by hydrochloric acid catalytic soaking method was11.12%,and the maximum increase rate of residual Cd was 13.98%.