Preparation And Adsorption Properties Of Natural Polymer Composite Microspheres

The pollutants generated by industrial production can bring enormous harm to humans and the natural environment.Compared with the removal of cationic pollutants that have been well studied,industrial anionic pollutants(such as Cr（VI）,PO₄^3-,As（V）,and azo anionic dyes)exist in various forms and pose greater harm in the water environment,making it difficult to treat.Therefore,it is urgent to develop efficient anionic pollutant treatment technologies.The adsorption method can effectively remove these harmful pollutants through chemical and physical actions due to its simple equipment,wide sources of active ingredients,easy operation,and flexible methods.In this paper,based on the common natural macromolecule chitosan,lignin,cellulose and other materials,adsorbent microspheres that can efficiently capture anionic pollutants were prepared through lotion polymerization.The detailed research contents include:（1）Chitosan based composite microsphere biosorbent（CP）was prepared by lotion copolymerization of polyethyleneimine（PEI）and chitosan.At an optimal p H of 3,the maximum adsorption capacity of CP for hexavalent chromium Cr（Ⅵ）can reach 299.89 mg g^-1,which is much higher than that of non copolymerized chitosan microspheres(168.91 mg g^-1).When the amount of CP added is 0.25 g L^-1,the removal rates of 50 mg L^-1Cr（VI）and 50 mg L^-1anionic dyes chrome blue black R（EBBR）can reach 95%and 99%,respectively.The time required for the copolymerized composite microspheres CP to reach adsorption equilibrium（180 min）was significantly shorter than that of chitosan microspheres（540 min）.Langmuir’s isothermal model,Pseudo-second-order kinetic model,and thermodynamic calculations reveal the monolayer,chemical adsorption,and spontaneity of endothermic processes.The composition of actual electroplating wastewater was analyzed.When the amount of CP reached 4.0 g L^-1,the content of Cr（Ⅵ）could be reduced to 0.452 mg L^-1.The adsorption experiment of coexisting ions showed that SO₄^2-had a significant impact on the adsorption of Cr（Ⅵ）by CP.The recycling performance of CP was explored through adsorption cycle experiments.（2）PEI/SiO₂/lignin porous composite microspheres（LSPGs）were prepared by inverse lotion polymerization from sodium lignosulfonate.Microsphere LSPGs has good removal effects on various pollutants.The equilibrium time required for adsorption of Cr（VI）,PO₄^3-,and Congo red dyes is 120 min,45 min,and 180 min,respectively,and their removal mainly relies on chemical adsorption.The experiments showed that the maximum adsorption capacities of LSPGs for Cr（VI）,PO₄^3-,and Congo Red were 355.21 mg g^-1,313.48 mg g^-1,and 588.24 mg g^-1,respectively.In the presence of interfering anions,LSPGs exhibit a selective trapping behavior for Cr（VI）,while SO₄^2-has a strong inhibitory effect on the adsorption of PO₄^3-by LSPGs.The attraction of counter charges plays an important role in the removal of anionic pollutants by LSPGs.In addition,LSPGs also play an important role in the elimination of Cr（VI）,PO₄^3-,and Congo Red,as well as in redox,hydrogen bonding,andπ-πstacking.For actual chromium containing electroplating wastewater,the utilization efficiency of the secondary feeding method（adding adsorbent twice）for raw materials is higher than that of the primary feeding method（adding adsorbent once）.The total dosage for reducing Cr（Ⅵ）to 0.5 mg L^-1is 1.5 g L^-1and 2.5 g L^-1,respectively.（3）Due to the poor adsorption selectivity of LSPGs for PO₄^3-,sodium carboxymethyl cellulose is used as the main raw material,and the carboxyl group of CMC can be used to chelate with La（Ⅲ）to cross-link.In order to make the three-dimensional structure of the final microspheres more stable,sodium alginate was also added to the CMC mixed solution to form a lanthanum alginate egg-box structure,and finally a cellulose/lanthanum alginate/La（OH）₃composite microspheres（CSPGs-La）were synthesized.In phosphate solutions,CSPGs-La has excellent swelling properties,unique three-dimensional structure,and mass transfer efficiency,which are important reasons for its strong ability to capture phosphate.In the presence of 500 mg L^-1of SO₄^2-and CO₃^2-,the ability of CSPGs-La to capture PO₄^3-decreased by only 2.92%and9.49%,respectively.However,CSPGs-Ech with protonation amino group as the main adsorption site almost completely lost the adsorption capacity for PO₄^3-.When the dosage of CSPGs-La is1.35 g L^-1,the total phosphorus in actual domestic phosphorus containing wastewater can be reduced to less than 10μg L^-1,providing a green,easy to implement,and promising solution for the preparation of efficient and selective phosphorus removal adsorbents.