The Preparation Of Carboxyl Modified Magnetic Adsorbent And Its Study On Adsorption Of Cr(?)

Cr???is widely used in leather,dyestuff,mining,metallurgy,textile and electroplating industries,due to the production needs a large number of organic acids were added,and combined with heavy metal to form a stable complex state.A large number of free and complex state of heavy metal in the industrial wastewater,increasing the difficulty of heavy metal removal,become a difficulty subject.In this study,Cr???was selected as the target heavy metal,and the DTPA modified ferromagnetic material?Fe₃O₄@SiO₂/Cs-DTPA?,EDTA-silane modified ferrosilicon material?Fe₃O₄@SiO₂-EDTA?and IDA mesoporous ferrosilicon materials?MCM-41@IDA?were used as adsorbents to remove the free and complex state of Cr???in water.The adsorption properties such as p H effect,ionic strength effect,sorption isotherm,adsorption kinetics,regeneration and material stability were studied.Based on the characterization results and adsorption experiments,the important results are shown as follows:?1?Adsorption of Cr???on Fe₃O₄@SiO₂/Cs-DTPA: In the process of synthesis for Fe₃O₄@SiO₂/Cs-DTPA,SiO₂ successfully coated on the surface of Fe₃O₄ to form core shell structure of Fe₃O₄@SiO₂,Chitosan and DTPA dehydration reaction to form amide group,DTPA successfully loaded onto Fe₃O₄@SiO₂ surface,and the coating rate was 34.31%.The adsorbent was superparamagnetic,and easy to separate from adsorbate.In the process of Fe₃O₄@SiO₂/Cs-DTPA adsorption of Cr???,increasing amount of EDTA or citric acid in the solution decreased the amount of Cr???adsorbed by Fe₃O₄@SiO₂/Cs-DTPA.The adsorption of free state Cr???increased with pH,complexing state of Cr???adsorption increased overall,the minimum adsorption at pH 4.0.Na⁺,Ca²⁺ and Mg²⁺ reduce the adsorption of Cr???.The results of adsorption test showed that the adsorption process of Cr???onFe₃O₄@SiO₂/Cs-DTPA is in accordance with pseudo second-order kinetic equation.Under the experimental conditions,the maximum equilibrium adsorption capacity of free and complex Cr???were 39.27 and 22.24 mg/g,the adsorption process conforms to the Sips model equation.Fe₃O₄@SiO₂/Cs-DTPA desorption and regenerated for 4 cycles,the adsorption capacity to the free state and complexing state Cr???remain stable,has a good recycling performance.?2?Adsorption of Cr???on Fe₃O₄@SiO₂-EDTA: The Characterization results show that silane EDTA is successfully modified on the surface of Fe₃O₄@SiO₂ without changing the crystal structure of Fe₃O₄,and Fe₃O₄@SiO₂-EDTA was superparamagnetic,stable and easy to separate.The adsorption of Cr???by Fe₃O₄@SiO₂-EDTA was inhibited by the presence of EDTA in the system.With the increase of pH the adsorption of Cr???increased.The adsorption of Cr???was decreased by the presence of coexisting cations.The experimental results show that the adsorption of free and complex state of Cr???were accorded with pseudo second-order kinetic equation.The theoretical maximum adsorption calculated by BiLangmuir and Sip model gave the best fit to the experimental date,and the maximum adsorption for free and complex state of Cr???under the experimental conditions were 33.14 and28.11 mg/g,respectively.After 4 times of desorption and regeneration,the adsorption of the free and the complex state of Cr???were kept steady,indicating that the material regeneration effect was good and could be recycled.?3?Adsorption of Cr???on magMCM-41@IDA: synthesis of mag MCM-41@IDA magnetic mesoporous materials,IDA coating effect is good.The magMCM-41@IDA specific surface area was 154.08m²/g,the pore volume was 0.287cm³/g,the bore diameter was 6.73 nm,had superparamagnetic,and easy to separate.The adsorption decreased with the increase of EDTA.Under the experimental conditions,as the pH increase adsorption of free and complex of Cr???were promoted.With the increase of Na⁺,Ca²⁺ and Mg²⁺ the adsorption of Cr???decreased,and the order of influence was Mg²⁺> Ca²⁺ > Na⁺.The experiment data of adsorption isotherm gave a best fit for Langmuir model and pseudo-second-order model,and belong to monolayer adsorption,the maximum adsorption for free and complex state of Cr???were 32.24 and 24.15mg/g,respectively.magMCM-41@IDA adsorbent regeneration effect is good,can berecycled.