| A large amount of chromium-containing wastewater will be produced in the process of leather tanning,which poses a great threat to the ecological environment and leads to a serious waste of chromium resources.In this paper,chitosan（CS）was chemically modified,and two kinds of chitosan-modified adsorbents were prepared to effectively remove and recover Cr（Ⅲ）from chromium-containing wastewater.Using 0.1 M disodium ethylenediamine tetraacetate（EDTA）solution,Cr（Ⅲ）adsorbed on the adsorbent can be desorbed and recovered effectively,and the adsorbent can be recycled.The main research contents were as follows:（1）Using CS and maleic anhydride（MA）as raw materials,Ceric ammonium nitrate as initiator,and glutaraldehyde（GA）as cross-linking agent,maleic anhydride（MCS）aerogels were prepared by graft copolymerization under the condition of water bath heating.Taking the adsorption capacity of Cr（Ⅲ）in 50 m L simulated chromium-containing wastewater as the reference index,through the single factor experiment and response surface method central composite design（RSM-CCD）optimization experiment,the optimum preparation conditions of MCS were obtained as follows:MA dosage 1.84 g,reaction temperature 50℃,reaction time 3.05 h,GA dosage 1.72 m L,cross-linking time 1 h,initiator dosage 0.87 g,acetic acid concentration 1.0%,CS concentration 1.53%and freezing time36 h.Under the optimum preparation conditions,CS and MCS adsorption properties were preliminarily analyzed and studied.The results showed that compared with CS,the adsorption capacity of MCS to Cr（Ⅲ）increased by 89.04%,which effectively improved the adsorption performance.（2）The adsorption performance of MCS was studied.The effects of initial p H value,adsorbent dosage,adsorption temperature,adsorption time,and initial chromium concentration on the adsorption of Cr（Ⅲ）in 50 m L simulated chromium-containing wastewater were studied by single-factor experiments.The results show that the optimum adsorption conditions of MCS on Cr（Ⅲ）were as follows:the initial p H value of 5.0,the amount of adsorbent 0.04 g,the temperature of 25℃,the adsorption time of 360 min,and the initial concentration of chromium 100 mg·L-1.In the adsorption study,the maximum adsorption capacity and removal rate of Cr（Ⅲ）by MCS are 267.7 mg·g-1 and 97.8%,respectively.The adsorption process accords with the pseudo-second-order kinetic model and Freundlich isotherm model,which indicated that the adsorption process was mainly multi-layer adsorption based on chemical adsorption and ion exchange,and the outer surface diffusion played a dominant role in the adsorption process.The study of desorption and regeneration utilization performance showed that after three adsorption-desorption cycles,MCS still had a high adsorption capacity on Cr（Ⅲ）,and the removal rate of Cr（Ⅲ）was 74.35%.Under the optimum adsorption conditions,the adsorption properties of CS and MCS were preliminarily analyzed and studied.The results showed that the adsorption capacity of MCS on Cr（Ⅲ）increased by 78.26%compared with CS,and MCS had better adsorption performance.（3）Under the condition of water bath heating,maleoylated chitosan@graphene oxide（MCS@GO）aerogel adsorbent was prepared by graft copolymerization using CS,MA,and graphene oxide（GO）as raw materials and Ceric ammonium nitrate as initiator.Taking the adsorption capacity of Cr（Ⅲ）as the reference index,aiming at the simulated chromium-containing wastewater of 50 m L,the optimum preparation conditions of MCS@GO were obtained by single factor experiment and orthogonal experiment:the amount of MA was1.84 g,the amount of MCS@GO was 30 mg,the reaction temperature was 55℃,and the reaction time was 3 h.（4）Study on the adsorption performance of MCS@GO.The effects of initial p H value,adsorbent dosage,temperature,adsorption time,and initial chromium concentration on the adsorption process of Cr（Ⅲ）in 50 m L simulated chromium-containing wastewater were studied through single-factor experiments.The results showed that the optimum adsorption conditions of MCS@GO for Cr（Ⅲ）were as follows:the initial p H value of 5.0,the amount of adsorbent 0.03 g,the temperature of 25℃,the adsorption time of 300 min,and the initial concentration of chromium 100 mg·L-1.The maximum adsorption capacity and removal rate of Cr（Ⅲ）by MCS@GO are 324.3 mg·g-1 and 99.4%,respectively.The adsorption process accords with the pseudo-second-order kinetic model and Freundlich isotherm model,indicating that the adsorption process is mainly multi-layer adsorption based on chemical adsorption and ion exchange,and the outer surface diffusion plays a dominant role in the adsorption process.The preliminary study on the desorption and regeneration of MCS@GO shows that after 6 adsorption-desorption cycles,the adsorption capacity and desorption capacity of MCS@GO for Cr（Ⅲ）are 142.6 mg·g-1 and 131.9 mg·g-1,respectively,indicating that MCS@GO has good regeneration usefulness and is an effective adsorbent for Cr（Ⅲ）removal.Under the optimum adsorption conditions,CS,MCS,and MCS@GO adsorption properties were preliminarily analyzed and studied.The results showed that compared with CS and MCS,the adsorption capacity of MCS@GO to Cr（Ⅲ）increased by 135.33%and 21.37%,respectively,compared with CS and MCS,the number of MCS@GO adsorption-desorption cycles increased by 200%and 50%.This paper prepared two kinds of chitosan aerogel adsorbents by modifying chitosan,which was used to remove and recover Cr（Ⅲ）from simulated chromium-containing wastewater.The results show that the adsorbents have good adsorption and regeneration properties,and have potential application value in the field of removing chromium-containing wastewater containing Cr（Ⅲ）. |
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