Synthesis Of Carboxylated Magnetic Composite Adsorbents For The Removal Of Cr(?)from Wastewater

The industrial wastewater discharged from a variety of processes including the leather tanning,chrome-plating,mining,electroplating and wood processing,commonly contains Cr???,and Cr???is often coexist with high concentrations of organic complexing agent,oils,and soluble inorganic salt of Na⁺,SO₄^2-,Cl^-,Ca²⁺and other substances,forming a complex pollution system and increasing the difficulty of Cr???removal.Therefore,how to remove Cr???from waste water in complex pollution systems with high salt and complexing agents has aroused much attention.The magnetic adsorbents modified by multi-functional groups have the advantages of high efficiency,environmental friendly and easy recycling.In this thesis,the succinic acid modified magnetic composited matarial?Fe₃O₄@SiO₂-NH-COOH?,the iminodiacetic acid?IDA?modified magnetic ferrosilicon material?Fe₃O₄@SiO₂-IDA?and ethylene glycol bis-2-aminoethyl ether?EGTA?modified ferrosilicon magnetic material?Fe₃O₄@SiO₂-EGTA?were used as carboxylated adsorbent to remove Cr???from wastewater.The adsorption effect of these three adsorbents on Cr???was studied by isothermal adsorption and kinetic experiments.The effects of pH,cations,organic complexing agents,complex pollution system with high salt and high complexing agent and the desorption and regeneration properties of the materials on the adsorption efficiency were investigated.The intrinsic adsorption mechanism was elucidated by combining the characterization results?FT-IR,XRD,TGA,BETand XPS?and experimental data.The main conclusions are as follows:?1?Adsorption of Cr???on Fe₃O₄@SiO₂-NH-COOH:Succinic acid functionalized adsorbent?Fe₃O₄@SiO₂-NH-COOH?was successfully prepared.By means of a variety of characterization method,it was found that the carboxyl group was successfully modified onto the surface of Fe₃O₄@SiO₂,and the crystal structure of Fe₃O₄ was not changed.The adsorbent was easy to be magnetic separated from adsorbate.Combined with the results of a series of adsorption experiments,we knew that the adsorption capacity of Cr???on the adsorbent was good,and the actual maximum adsorption amount was 19.98mg/g at pH 4.0 and 25?.The langmuir model can further explained the isothermal adsorption curve and the adsorption process is favorable.The kinetic adsorption process follows the pseudo-second-order kinetic reaction model.Due to the effect of Cr???concentration gradient driving force,the adsorption capacity increased with the increase of the Cr???concentration.With the increase of solution pH value,the adsorption capacity increased gradually;The presence of cations,organic complexing agents and the complex system of organic complexing agent and high salt could inhibit the adsorption of Cr???.Desorption and regeneration experiments showed that the adsorbent has good regeneration performance.XPS mechanism analysis showed that the adsorbent was mainly adsorbed by carboxyl complexation of Cr???.?2?Adsorption of Cr???on Fe₃O₄@SiO₂-IDA:The carboxylated adsorbent Fe₃O₄@Si O₂-IDA was successfully prepared.The characterization results showed that IDA was successfully coated on the surface of the materials,the crystal structure of the materials remains unchanged,and the adsorbents have good magnetic separation properties.A series of experiments on the adsorption of Cr???showed that Fe₃O₄@SiO₂-IDA has a good adsorption property,the actual maximum adsorption capacity was 23.47 mg/g at pH 4.0 and 25?.The adsorption isotherm fitting results can be explained by langmuir model and the adsorption process is favorable.The kinetic adsorption curve accorded with the pseudo-second-order reaction model and the adsorption process was very rapid.When the p H value of the solution increased,the adsorption capacity of Fe₃O₄@Si O₂-IDA for Cr???was also increased.The adsorption process of Cr???was inhibited by cations,organic complexing agents and the complex system of organic complexing agent and high salt.The desorption cycle and regeneration experiments showed that the range of the adsorption capacity of Fe₃O₄@Si O₂-IDA on Cr???remains basically constant,the adsorbent has good regeneration performance.The results of XPS analysis showed that the N,O atom in the functional group on the surface of the material forms a complex with Cr???,and thus realizes the adsorption and removal of Cr???in the water.?3?Adsorption of Cr???on Fe₃O₄@Si O₂-EGTA:The carboxylated adsorbent Fe₃O₄@SiO₂-EGTA was successfully prepared.It was proved that EGTA was successfully coated on the surface of Fe₃O₄@SiO₂ by various characterization methods.The crystal structure remains unchanged,and the adsorbent has good magnetic properties.It was easy to realize magnetic separation between adsorbent and adsorbate.According to the results of adsorption experiments,Fe₃O₄@SiO₂-EGTA has good adsorption property for Cr???.The actual maximum adsorption amount was 25.25 mg/g at pH 4.0 and25?.The Cr???adsorption process on the adsorbent can be well explained by the Langmuir model,the pseudo-second-order reaction model was suitable for describing the dynamic adsorption curve of the adsorbent.The increase of pH in solution was favorable to the adsorption of Fe₃O₄@SiO₂-EGTA for Cr???;The existence of cationic,organic complexing agent,organic complexing agent and high salt complex system inhibited the adsorption of Cr???and the adsorbent has good desorption and regeneration performance.The XPS analysis showed that the carboxyl group on the adsorbent surface was the main active site for chelating Cr???.