Removal Of Cadmium In Water By Humic Acid-based Complex Materials

With the development of human industrialization,water pollution has become a major obstacle to human survival and development.Heavy metal pollution has become one of the most serious environmental problems.Cadmium is a non-essential element in human body.Excessive cadmium can seriously damage human liver,kidney and bone,and even accompany the occurrence of cancer.Among the many methods,adsorption method is widely used in the removal of heavy metals in water because of its simple operation,reliability and effectiveness.Humic acid is a widely distributed macromolecular organic matter with abundant functional groups on its surface,which can react with heavy metal ions.It has great application potential in the field of adsorbents,and has been increasingly used in adsorbent materials in recent years.But humic acid also has its drawbacks,it disperses easily in water.At present,it is mainly for the modification of humic acid,or preparation of humic acid composite material,in order to improve the stability and adsorption performance of the material.Based on humic acid,we prepare two kinds of composite materials and applied them to the adsorption of cadmium ion in water.The specific contents are as follows:1.Based on humic acid,magnetic humic acid(m HA)material was prepared by water bath heating method,and then mixed with carboxymethyl cellulose as composite gel,which was dropped into chitosan solution.Finally,CS-m HA/CMC composite gel adsorbent was prepared by freeze-drying method.The morphology,structure and properties of the materials were characterized by FT-IR,SEM,XPS and BET.The influence of different CMC and CS content on the stability of adsorbent in water was tested.And the influence of p H,temperature and HA dosage on adsorption was analyzed.In addition,the adsorption of cadmium ions by CS-m HA/CMC conformed to pseudo-second-order kinetic model and Langmuir model.The maximum adsorption capacity of CS-m HA/CMC was 490.2 mg/g.The adsorption process was endothermic reaction.Finally,the adsorption capacity of CS-m HA/CMC decreased by only 13%after 5 cycles of adsorption-desorption.Therefore,CS-m HA/CMC has good reusability.2.Urea-sodium hydroxide-water was used as solution system,CMC hydrogel was prepared by adding HA and crosslinking agent N,N'-methylene bisacrylamide,and zinc nitrate was added during the preparation process.After soaking in 2-methylimidazole aqueous solution,ZIF-8@HA/CMC composite gel adsorbent was prepared.The materials were characterized by infrared spectroscopy,SEM,XPS,XRD,Zeta potential test and TGA.The synthesized ZIF-8@HA/CMC composite was used to adsorb Cd²⁺,and the influence of p H,HA content,the type of ions and concentration was researched.The adsorption experimental data conformed to pseudo-second-order kinetics and Langmuir model,so the adsorption process of ZIF-8@HA/CMC for Cadmium was chemical adsorption and monolayer adsorption,and the maximum adsorption capacity can reach 105.15 mg/g.According to the thermodynamic equation,?H^?>0,?S^?>0,?G^?<0.The adsorption process was spontaneous endothermic process,increasing the temperature was conducive to the adsorption reaction.Finally,the adsorption mechanism of ZIF-8@HA/CMC was analyzed.The main adsorption mechanism of ZIF-8@HA/CMC was the complexation of-COOH and-OH with Cd²⁺and the exchanged of Zn²⁺and Cd²⁺in ZIF-8.