| The chromium emitted by industrial and mining enterprises is discharged into the soil in the form of wastewater,waste residue,and waste gas,and accumulated in the soil,affecting crop growth,and endangering the environment.The fixed stabilization method has low implementation cost and good effect and can effectively reduce the harm of heavy metal chromium.In this study,a chitosan gel material CSBT hybrid with bentonite was prepared with chitosan as the basic material,and its adsorption in water and immobilization in soil for chromium was studied through batch experiments in aqueous solutions and soil immobilization experiments,respectively.At the same time,the effects and mechanism of CSBT on hexavalent chromium adsorption and immobilization were explored.The main results are as follows:?1?When the content of chitosan and pillared bentonite is 1%,the removal effect of Cr?VI?is the best.The characterization results of CSBT show that chitosan enters the interlayers of pillared bentonite and reduces the interlayer distance of pillared bentonite AlBT.Infrared spectroscopy showed that hydroxyl and amino groups played a key role in the preparation of CSBT,forming a composite material with a smoother surface and larger particles.CSBT has been combined successfully using chitosan and AlBT?2?The adsorption experiment results in aqueous solution show that CSBT has a good adsorption effect on hexavalent chromium.Under the environmental conditions of pH=3 and25?,88.31%of hexavalent chromium in 10 mg·L-1 potassium dichromate solution can be removed by CSBT.The adsorption process is affected by pH,temperature,the initial concentration of potassium dichromate solution,the amount of CSBT added,and the adsorption time.Among them,the adsorption process is most affected by pH.When pH=3,88.31%of Cr?VI?can be removed.But the removal rate dropped to 27.14%when the pH of the solution was increased to 4,indicating that CSBT requires a large amount of hydrogen ions to participate in the adsorption of hexavalent chromium.The adsorption process was fitted in pseudo-second-order kinetic model and Langmuir isotherm model.The adsorption process can reach equilibrium within 1.5 h,and the maximum adsorption amount is 137.43 mg·g-1.The mechanism study shows that the adsorption process mainly occurs on the surface of CSBT.The entropy and enthalpy decrease during the adsorption process.Recycling experiments show that CSBT can maintain a high hexavalent chromium removal rate after six cycles of use,and more than 60%of Cr?VI?can be desorbed and recovered by sodium hydroxide solution.?3?Immobilization experiments in soil show that CSBT has a significant effect on the exchangeable,oxidizable,and residual chromium content,and can significantly reduce the exchangeable and oxidizable chromium content and increase the residual chromium content.The immobilization time and the amount of CSBT affect the immobilization effect of Cr.The addition of CSBT at 0.2 g·kg-1 reduced the exchangeable chromium content by 63.7%,the oxidizable content by 12.6%,and the residue content increased from 2.34 mg·kg-1 to 46.91mg·kg-1.CSBT has little impact on soil pH,and soil pH can return to its original level.Time and the amount of CSBT affect the immobilization effect of CSBT.The immobilization effect increased rapidly in the first 14 d,and the equilibrium was reached at 28 d and basically maintained in the next 28 d.When the CSBT concentration was increased from 0.2 g·kg-1 to 5g·kg-1,and the immobilization effect was significantly reduced.In summary,the bentonite-doped chitosan gel composite material successfully prepared in this research is effective in the removal of hexavalent chromium pollution in aqueous solution and soil.It can provide references for the application of natural materials and the treatment of chromium pollution in soil. |
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