Study On The Preparation Of Modified Chitosan And Its Application In Wastewater Treatment

At present,dye wastewater and heavy metal wastewater have caused immeasurable harm to the environment.Therefore,these wastewaters need to be properly treated to reduce their harm to the environment and organisms.Adsorption method is applied to water treatment because it is easy to operate,low cost,high efficiency and recyclable,and is one of the common methods used to treat dye wastewater and heavy metal wastewater.As a natural organic polymer,chitosan is used as a flocculant,metal ion chelating agent,adsorbent,etc.in wastewater treatment,it is a water treatment agent with high research value.This paper studies the modification method of chitosan,using citric acid（CA）as the cross-linking agent,chitosan（CTS）andβ-cyclodextrin（CD）as raw materials to prepare chitosan-citric acid（CTS-CA）and chitosan-citric acid-β-cyclodextrin（CTS-CA-CD）two modified chitosan adsorption materials,then perform SEM,FIRT and XRD on the modified chitosan and raw chitosan characterization analysis to explore the modification mechanism.At the same time,the prepared modified chitosan were applied to the research of adsorbing dye wastewater and heavy metal wastewater.The adsorption properties and laws of modified chitosan on methylene blue and basic fuchsin in dye wastewater and nickel in heavy metal wastewater were investigated in detail,the adsorption mechanism was discussed and the regeneration cycle performance of modified chitosan were studied.The main results obtained are as follows:（1）The modified chitosan CTS-CA and CTS-CA-CD were characterized by SEM,FIRT and XRD.The results show that CTS and CA,CTS and CD are successfully cross-linked.The modified chitosan has a larger specific surface area and lower crystallinity,showing a polymerized and irregular state.（2）Taking methylene blue and basic fuchsin solutions as adsorption objects,the adsorption properties of two modified chitosan were studied.p H has a great influence on the adsorption properties of two modified chitosan dye molecules.The optimal adsorption p H of CTS-CA for methylene blue and basic fuchsin is 8.0,and the adsorption equilibrium is reached at 160 min and 200 min,respectively;For CTS-CA-CD,the optimal adsorption p H of CTS-CA-CD for methylene blue and basic fuchsin are 8.0 and 9.0,respectively,and reach adsorption equilibrium at 120min and 150 min,respectively.The adsorption of methylene blue and basic fuchsin on the two modified chitosan is in line with the pseudo-second-order kinetic adsorption model and the Langmuir adsorption isotherm model,indicating that the adsorption of the two modified chitosan to the dye is mainly single-layer chemical adsorption.The maximum adsorption capacities of CTS-CA for methylene blue and basic fuchsin obtained by fitting are 217.46 and 221.99 mg/g,respectively;the maximum adsorption capacities of CTS-CA-CD for methylene blue and basic fuchsin are 226.54and 219.55 mg/g,respectively.（3）With the heavy metal Ni²⁺as the adsorption object,the adsorption properties of two modified chitosan were studied.The results showed that the adsorption capacity of CTS-CA and CTS-CA-CD for Ni²⁺increased with the increase of p H,and the optimal adsorption p H was 6.0.The adsorption process of Ni²⁺reached equilibrium at90 min and 70 min,respectively.The adsorption of Ni²⁺by modified chitosan is applicable to the pseudo-second-order kinetic model and Langmuir adsorption isotherm model to describe,showing that the adsorption of Ni²⁺by the two modified chitosan is mainly single-layer chemical adsorption,the maximum adsorption capacities of the two modified chitosan for Ni²⁺obtained by fitting were 29.22 and35.23 mg/g,respectively.（4）The adsorption capacities of the two modified chitosan for dye and Ni²⁺increased with the increase of temperature,indicating that the temperature was beneficial to the adsorption process.At the same time,the thermodynamic results showed that the adsorption process of Ni²⁺by the two modified chitosan can proceed spontaneously.The regeneration performance experiment of modified chitosan showed that after 5 cycles of adsorption-desorption,the modified chitosan has better wastewater treatment effects.（5）Two kinds of modified chitosan and chitosan were used to adsorb phosphate wastewater from automobile factories.The removal rate of Ni2+in phosphating wastewater increases with the increase of the dosage of modified chitosan.The removal rate of Ni²⁺by the two modified chitosan was greater than that of chitosan,and the order of removal rate was CTS-CA>CTS-CA-CD>CTS.