Study On The Performance Of Sodium Alginate Composite Adsorbent For Adsorption Of Heavy Metal Ions In Waste Leachate

The presence of a large amount of heavy metal ions in waste leachate has a significant environmental impact and affects the resource utilization of leachate.In this paper,a simple,economical and efficient adsorption method was used to remove heavy metal ions from water.Cr（VI）and Ni（II）were used as target removers,and sodium alginate（SA）,which is widely available and environmentally friendly,was used as the substrate,and SA-L-As gel spheres were obtained by modifying SA with ascorbic acid（L-As）to adsorb Cr（VI）;chitosan（CS）and ferric tetroxide（Fe₃O₄）modified SA to obtain SA-CS-Fe₃O₄gel spheres to adsorb Ni（II）.Static adsorption experiments investigated the effects of solution p H,dosage,adsorption time,initial concentration,reaction temperature and other factors on the adsorption performance;dynamic adsorption experiments investigated the effects of adsorbent packing height,inlet water flow rate and inlet water concentration on the dynamic adsorption process;the chemical groups,microscopic morphology,elemental chemical state,chemical crystal shape of the gel spheres were analyzed by FTIR,SEM,EDS,XRD characterization means and The adsorption mechanism was explored;the static and dynamic adsorption of Cr（VI）and Ni（II）binary wastewater in waste leachate environment by mixing two adsorbents at a certain mass ratio was studied to provide theoretical basis for the practical application process.（1）Preparation and characterization of SA-L-As and SA-CS-Fe₃O₄:The optimal ratios of SA-L-As gel spheres were obtained from orthogonal experiments:c（SA）=0.03 g/m L,m（L-As）=2 g,and crosslinking time（t）=5 h.Preparation of SA-CS-Fe₃O₄gel spheres:The optimal ratios of SA-CS-Fe₃O₄gel spheres were obtained from orthogonal experiments:m（SA）:m（CS）:m（Fe₃O₄）=2:1:1.The best ratio of SA-CS-Fe₃O₄gel spheres was m（SA）:m（CS）:m（Fe₃O₄）=2:1:1.The results of FTIR,SEM,EDS and XRD illustrated the increased surface roughness and better crystal shape of SA-L-As gel spheres;the internal pores of SA-CS-Fe₃O₄gel spheres increased and the surface showed an amorphous structure.（2）Static adsorption experiments showed that:SA-L-As gel spheres had the best p H of 3and the maximum adsorption capacity of 68.49 mg/g,the adsorption process was mainly multilayer adsorption,and the temperature rise was favorable to the adsorption process,and the coexisting ions had less influence on the process of Cr（VI）,but its cyclic regeneration performance was poor.SA-CS-Fe₃O₄gel spheres had the best p H of 6 and the maximum adsorption capacity of 10.85 mg/g;the adsorption process was dominated by monolayer adsorption,and the temperature rise was not favorable to this adsorption,and the coexisting ions did not have a large effect on the adsorption process of Ni（II）;after conducting four adsorption-desorption experiments,the adsorption amount was maintained at more than 60%of the original base,which showed good adsorption performance.（3）The dynamic adsorption experiments showed that the dynamic adsorption of Cr（VI）and Ni（II）by SA-L-As gel spheres and SA-CS-Fe₃O₄gel spheres was proportional to the packing height and inversely proportional to the inlet water flow rate and inlet water concentration.The results of data fitting by BDST model and Yoon-Nelson model showed that both models could accurately predict the dynamic adsorption runtime.（4）Adsorption mechanism analysis:The EDS energy spectrum after adsorption showed that Cr（VI）and Ni（II）were successfully adsorbed on the surface of SA-L-As gel spheres and SA-CS-Fe₃O₄gel spheres.FTIR after adsorption showed that-OH and-COOH were the main functional groups in the adsorption process of SA-L-As,and-NH₂,-OH and-COOH were the main functional groups in the adsorption process of SA-CS-Fe₃O₄,and the adsorption mechanism of Cr（VI）was mainly the coordination reaction of-COOH,and the adsorption mechanism of Ni（II）was the coordination reaction of-NH₂,-OH and-COOH.（5）Practical application investigation:When p H is 5.5 and m（SA-L-As）:m（SA-CS-Fe₃O₄）is 2:3,the SA-based mixed adsorbent has the best effect on static adsorption treatment of Cr（VI）and Ni（II）mixed wastewater;dynamic adsorption experiments found that the adsorbent still has good removal effect in leachate environment,and the BDST model and Yoon-Nelson The data fitting results of BDST model and Yoon-Nelson model showed that SA-L-As and SA-CS-Fe₃O₄have good application prospects.