Optimization Of Hydrochar Preparation Process Based On The Improvement Of Heavy Metal Adsorption And Retention Capacity

Hydrothermal carbon（HC）is a new type of carbon material with homogeneous,hydrophobic,rich in oxygen-containing functional groups and porous structure characteristics of submicron to nano-sized carbon spheres（or fragments）on the surface.Due to the existence of a variety of oxygen-containing groups on its surface,including hydroxyl（-OH）,carbonyl（-C=O）and carboxyl（-COOH）,it provides a large number of oxygen-containings functional group sites to adsorb pollutants in water,which has attracted the attention on many scholars.After surface chemical modification,the heavy metal adsorption performance of HC has been improved,but there is a lack of systematic research on the modification mechanism.Considering that cellulose is an important part of biomass raw materials,understanding the change law of cellulose HC surface microspheres and structure,and exploring the adsorption mechanism of cellulose HC for typical cations and heavy metals in the form of oxonate anions is beneficial for oriented modified preparative measures in practical applications,enhance the adsorption effect of HC on specific heavy metal ions,and reduce the risk of secondary pollution caused by structural instability of surface microspheres in the practical application of HC.In the study,the preparation process conditions were optimized and the acid-base solution was modified by post-treatment.The changes of cellulose HC surface structure and oxygen-containing functional groups were studied by three-dimensional fluorescence spectroscopy,SEM,TEM,FT-IR and XPS.Combined with the study of adsorption kinetics and PZC potential,the adsorption mechanism of cellulose HC for typical negative and positive heavy metal ions was deduced,and the modification technology of cellulose HC was putting forward.:（1）In the process of hydrothermal carbonization,increasing temperature,reaction time and pressure can improve the yield.Temperature and reaction time are positively correlated with HC specific surface area,porosity,particle size and new energy.（2）The effect of alkali treatment was more obvious and strengthened with the increase of alkalinity;HC agglomerated after acid-base treatment;HC-Na OH modified by Na OH changes from carbon sphere aggregation structure to transparent lamellar structure,and nano fragments are distributed;The specific surface area and pore volume of alkali modified HC increased by 98%and 83%respectively.After modification,the proportion of hydroxyl and carboxyl increased significantly and the proportion of carbonyl decreased.（3）The results of Cr（VI）and Cd（II）adsorption experiments on modified HC showed that the adsorption capacities of HC-Na HCO₃ and HC-Na OH were 127 mg/g and116 mg/g,123 mg/g and 128 mg/g respectively,which were higher than those of unmodified HC（84 mg/g and 72 mg/g）;The study of adsorption mechanism shows that the adsorption of Cr（VI）by HC is mainly electrostatic adsorption,and the adsorption of Cd（II）is mainly surface complexation and cation-πinteraction.（4）According to the adsorption mechanism of HC on cations and heavy metals in the form of oxyradical anions,the directional optimization measures for two heavy metal ions were proposed,including adding carbonic acids,adding high oxidizing substances,adding alkali and increasing reaction residence time,which were verified by characterization and adsorption experiments.