Adsorption Of Cu²⁺ And Pb²⁺ By Modified Crosslinked Chitosan

With the development of industry,the discharge of heavy metal wastewater,especially copper and lead-containing wastewater,is seriously polluting the environment.Adsorption method using chitosan microsphere as adsorbent has attracted much attention due to its low cost and environmental friendliness.However,chitosan without surface modification has low adsorption capacity for metal ions and poor adsorption selectivity.To this end,this paper carried out a series of studies on the preparation of chitosan microspheres,the specific research results are as follows:（1）.Chitosan microsphere prepared by tow-step methed（CMTSM）,the chitosan microspheres were prepared by cross-linking method,and then the amine-modified chitosan microspheres are prepared by chemical grafting.Effect of cross-linking agent on the structure of microspheres during the preparation process was discussed,and the adsorption performances of amine-based modification were studied.SEM analysis showed that well dispersed microsphere was obtained when 2.5m L gultaraldehyde（7.5%）was added.FTIR analysis shows that TEPA is successfully grafted onto the surface of the microspheres.The results of static adsorption studies showed that the maximum adsorption capacities of chitosan microspheres for Cu²⁺and Pb²⁺before and after modification were 19.84,33.12 mg g^-1and 34.56,74.52 mg g^-1,respectively.The adsorption isotherm curves fitted the Langmuir and Temkin isotherm model well.Dynamic adsorption and desorption experiments indicated that the adsorption capacities of modified microspheres for Cu²⁺and Pb²⁺were 23.68 and23.77 mg g^-1,and the desorption capacities were 22.40 and 20.70 mg g^-1,respectively.Desorption efficiency of the adsorbents for the two metal ions were 94%and 91%,respectively.（2）.Modified porous chitosan microspheres prepared by using Ca（OH）₂ microparticle as the poreforming agent.In the process of chitosan cross-linking,Ca Cl₂and template reagent were added simultaneously,chitosan coated nano-scale Ca（OH）₂particles were prepared by adjusting p H,and then phosphate buffered saline（PBS）was used to obtain porous chitosan microspheres with uniform dispersibility,then preparation of amine modified chitosan microspheres by TEPA modification.Effect of the amount of pore-forming particles on the structure of porous microspheres was discussed,and experimental results show that the optimum amount of anhydrous Ca Cl₂is 3 g.Static adsorption experiments show that the adsorption process of modified porous chitosan microspheres reaches equilibrium quickly,and the kinetic curve fitted thepseudo second-order kinetic model,the adsorption is mainly controlled by the number of active sites.The results of dynamic adsorption experiments showed that the maximum adsorption capacities of the adsorbents for Cu²⁺and Pb²⁺were 30.72 and 45.54 mg g^-1,respectively.（3）.In order to simplify the preparation process of modified chitosan microspheres,Amine-modified chitosan microspheres were prepared by one-step method throgh adding tetraethylene pentamine in the crossing-linking process.Effects of the amount of cross-linking agent and tetraethylenepentamine on the adsorbent structure and adsorption capacity were discussed.Static experiments showed that the adsorbent showed a higher adsorption capacity for Cu²⁺(43.07mg g^-1)and Pb²⁺(95.43mg g^-1),respectively.Results of dynamic experiments show that the adsorbent synthesized by this method further increases the dynamic adsorption capacity of Cu²⁺and Pb²⁺,which are 32.64 and 55.89 mg g^-1,respectively,and the desorption efficiency of the two metals is over 95%.（4）.Adsorption treatment of simulated industrial wastewater containing of Cu²⁺,Mg²⁺,Zn²⁺,Ca²⁺,Cd²⁺and Pb²⁺was carried out by one-step synthesied amine-modified adsorbent packed column,and the adsorption kinetics of each metal ion was discussed.Results show that the breakthrough curve of Mg²⁺and Ca²⁺show an inverted“L”shape,and that curve of Zn²⁺,Cd²⁺and Pb²⁺show obvious overshoot,and while that of Cu²⁺shows“S”type.Breakthrough times are 5,5,40,40,70 and 115 min for Mg²⁺,Ca²⁺,Zn²⁺,Cd²⁺,Pb²⁺and Cu²⁺respectively.According to the breakthrough time curve,the modified chitosan microspheres have the lowest adsorption affinity for Mg²⁺and Ca²⁺,and the breakthrough time is the shortest;Zn²⁺,Cd²⁺and Pb²⁺are competitively substituted and desorbed after selective adsorption;Cu²⁺is adsorbed until equilibrium.The above results indicate that adsorption affinity order of the amine-modified adsorption for each metal ion is:Cu²⁺>Zn²⁺,Cd²⁺,Pb²⁺>Mg²⁺,Ca²⁺.The adsorption capacities for Cu²⁺,Mg²⁺,Zn²⁺,Ca²⁺,Cd²⁺and Pb²⁺on the adsorbent were 0.378,0.00845,0.029,0.00076,0.00064 and 0.086 mmol g^-1.The above results indicate that the one-step synthesis of amine-modified chitosan microspheres has obvious adsorption selectivity for Cu²⁺,and it is expected to be applied in separation and recovery of Cu²⁺form actual industrial wastewater.