| In this study,magnesium oxide biochar-chitosan composites?MgO-BCR-W?were successfully prepared by MgCl2 impregnation and chitosan coating method.Through batch adsorption experiments,the effects of pH and temperature on the adsorption of Cd???onto biochar-chitosan composites were studied.The Cd???adsorption behavior on biochar-chitosan composites was analyzed by fitting the kinetic equations,the isothermal adsorption equations and thermodynamic equations and parameters.The characterations of surface morphology,mineral components and surface functional groups before and after adsorption were compared to reveal the main mechanism of Cd???adsorption onto biochar-chitosan composites.Through soil experiments,the effects of biochar composites application on soil physicochemical properties,bioavailable cadmium and stabilizing effects were studied in order to provide a theoretical basis for the application for heavy metal removal.The main conclusions of the study are as follows:?1?A pseudo-second-order kinetic model could better describe the Cd???adsorption behavior on four different biochar composites,and chemical adsorption played a major role in the adsorption process.The Langmuir adsorption isotherm was more suitable for Cd???adsorption onto the adsorbent,indicated the adsorption is similar to the single molecule adsorption.The computed values of RL ranged between 0 and 1,suggesting that the adsorption of Cd???onto MgO-BCR-W is favourable.Characterisation of the adsorbent revealed that the complexation of surface functional groups,the precipitation and ion exchange of surface mineral components,and cation-?interactions mainly contributed to the Cd???adsorption onto MgO–BCR-W.?2?The application of biochar can increase the soil pH,cation exchange capacity?CEC?and organic matter content?SOM?,while the larger the biochar addition,the greater the increase in soil pH,CEC,and organic matter content.Significant negative correlation between acid-extractable Cd content and soil pH was found?P<0.05?.There was no significant correlation between the reducible and oxidizable Cd content and soil pH,and there was significant positive correlation between residual Cd content and soil pH?P<0.05?.?3?The BCR treatment partially activated Cd in soil.In other treatment,the bioavaible Cd content in soil decreased by 3.63%to 31.57%,and the order of decline was BCR-W2<MgO-BCR-W2<MgO-BCR2,while MgO-BCR 2%had the best treatment effect.The application of four different biochar materials in a 2%ration reduced the acid extractable Cd by-3.05%,13.13%,7.13%,and 14.77%,while the residual Cd content increased by 0.91%,7.69%,9.96%,and 12.54%,respectively.It can be seen that biochar has a better stabilizing effect on Cd in soil after being coated with chitosan?MgO-BCR-W?.The stability rate of Cd increased with the increase of MgO-BCR-W dosage.Thus,MgO-BCR-W had the potential for medium and long-term stability of soil. |
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