| In recent years,biosorption based on bio-materials has been widely used in dye wastewater treatment.In this paper,natural oyster shells are used as raw materials.Steam kinetic energy pulverized crushed shell powder is used as the raw material.Then t he shells and natural clay minerals attapulgite are added to chitosan solution by the solution blending method.Chitosan based hydrogels are prepared.Then the chitosan/shell powder and chitosan/attapulgite/shell powder aerogels are prepared by freeze-drying method.The adsorption of Congo red and methylene blue in simulated printing and dyeing wastewater was studied by crushing shell powder,chitosan/shell composite aerogel and chitosan/attapulgite/shell powder aerogel.The effects of initial concentration,contact time and the amount of adsorbent on the adsorption capacity of dye wastewater were systematically studied.The experimental data obtained were fitted by quasi first-order and quasi second-order kinetic models,Langmuir and Freundlich adsorption isotherm models.The morphology and particle size of various adsorbents were characterized by scanning electron microscopy,etc.The mechanism of dye adsorption was studied.The results are as follows:(1)For the shell powder comminuted by superheated stea m,it is found that the shell powder can be comminuted efficiently by using superheated steam as the medium of gas comminution.The results of SEM and particle size analyzer show that after comminution,the particle size of shell powder decreases significa ntly,and the average particle size is less than 9μm;Results show that the main component of shell powder is aragonite crystal.It was found that the adsorption capacity of two kinds of different electric dyes(cationic methylene blue and anionic Congo red)on the crushed shell powder was significantly greater than that on the original sample;compared with the two kinds of different electric dyes,the adsorption capacity of Congo red was significantly greater than that of cationic methylene blue due to t he presence of cationic chitin in the shell powder.(2)A certain amount of shell powder can be added into chitosan solution to form stable hydrogel.After freezing and drying,macroporous aerogels can be prepared.C hitosan/shell powder composite aerogel has good water and acid resistance.Because of the presence of abundant amino groups on the chitosan,the composite aerogels have excellent adsorption properties for Congo red.The composite aerogels have a faster adsorption rate and the adsorption equilibrium was reach in 2 h.The composite aerogel with less shell powder has higher adsorption capacity and the maximum adsorption capacity can reach more than 1300mg/g.Results showed that adding shell powder would make the surface of aerogel coarse and conducive to adsorption.(3)Using chitosan and attapulgite as the matrix,adding a certain amount of shell powder and neutralizing acetic acid in the mixed solution,ternary mixed hydrogel can be obtained,and the composite aerogel can be obtained by freeze-drying.The aerogels obtained had higher porosity and specific surface area of aerogels.The adsorption properties of two aerogels prepared for Congo red and methylene blue were systematically studied.The results showed that the composite aerogels had excellent adsorption capacity and high adsorption capacity for Congo red.With the addition of shell powder,the stability of the composite aerogel increased significantly,and its adsorption capacity for methylene blue was much larger than that without shell powder. |
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