Preparation, Characterization And Adsorption For Cu²⁺, Pb²⁺and Cd²⁺ Of Chitosan And Its Derivative Resin

For the past few years, with the development of industry and the increase of allkinds of human activities, various types of heavy metal pollutants are discharged intothe air, the water, and the soil ecological environment, all of these have brought aserious threat to the human health and the environment. Adsorption method occupiesan important position in the many methods of treatment of heavy metal pollutants inwater, the development of some low cost, high performance and safety andenvironmental protection adsorption materials is the future direction in the field ofheavy metal treatment. Chitosan is abundant reserves marine biologicalpolysaccharide. It has the advantage of good biocompatibility, biodegradable,non-toxic, etc. and has been widely used in the pharmaceutical, food, environmentalprotection and other fields, and has caused extensive concern of the researchers inrecent years. There are a larger number of amino（-NH2） and hydroxy（-OH） reactivegroups in chitosan molecular chain, and these groups can have coordination reactionwith a variety of heavy metal ions. These properties of chitosan can be applied to theseparation and purification of heavy metals in water, but the easy loss and the difficultrecovery of chitosan in heavy metal medium limited its widespread application in thefield of metal processing.In this study, the orifice titration method and the emulsion crosslinking methodare used to prepare two chitosan spherical resins, the physical structure and chemicalstructure of these two resins are characterized. The double aldehyde of glutaraldehydecan have Schiff base reaction with chitosan, based on this principle,the glutaraldehydecan have cross-linking reaction with chitosan to increase the stability and mechanicalstrength of the chitosan in the acidic medium. The resin prepared using differentmethods were used to adsorb the heavy metal ions in the aqueous solution, the studyshows that the resins which prepared by emulsion crosslinking method have a good adsorption of heavy metals and have good mechanical strength, it is a very nicematerial for heavy metal adsorption. The chitosan resin prepared by emulsioncrosslinking method was used to adsorb Cu²⁺, Pb²⁺and Cd²⁺ions in the aqueoussolution, it was found that different pH, contact time and initial concentration hadinfluence on the adsorption amount. maximum adsorption of Cu²⁺ions was observedat pH5，Pb²⁺and Cd²⁺ions was observed at pH6. Under the condition of optimumpH, the maximum adsorption quantity of these three heavy metal ions were150min,210min, and240min, and the adsorption kinetics was fit well with the pseudosecond-order kinetic model. Adsorption amount increased with the increase of theinitial concentration and eventually reached equilibrium, the experimental data werefitted with Langmuir and Freundlich isothermal adsorption model, the resinadsorption of these three kinds of heavy metal ions were in accordance with Langmuirisotherm model. The maximum adsorption capacities were163.93mg/g,188.67mg/gand151.51mg/g. The adsorption characteristics of the coexistence of a variety ofheavy metal ions, and found that the resin has a certain selective adsorption of Cu²⁺.Carboxymethyl chitosan is an important derivative of chitosan, and it has strongcoordination ability for heavy metal ions. CMCS were prepared into a spherical resinby emulsion crosslinking method, and the resulting adsorbent was characterized bymeans of SEM and FTIR. The amino （-NH2）, hydroxyl （-OH） and carboxymethyl（-CH₂-COO-） were involved in the coordination reaction with heavy metal ions. Theresin adsorption behavior of heavy metal ions in aqueous solution was studied, andfound that in the optimal conditions, the adsorption of resins for Cu²⁺, Pb²⁺and Cd²⁺would reach equilibrium, respectively, in the90min,120min and150min, theadsorption process accorded with the two order kinetic model, the adsorption amountof these three heavy metal ions were respectively156.25mg/g，222.22mg/g and178.57mg/g. The experimental data were fitted with Langmuir and Freundlichisothermal adsorption model, the resin adsorption of these three kinds of heavy metalions were in accordance with Langmuir isotherm model too. It shows that comparedto chitosan resins, the carboxymethyl chitosan resins have a stronger adsorption capacity, and shorter time to reach equilibrium. When there are varieties of heavymetal ions coexist in the solution, the resin for the selective adsorption capacity ofheavy metal ions are Cu²⁺＞Pb²⁺＞Cd²⁺,it also has a better selective adsorption of Cu²⁺, desorption of the resin with EDTA had achieved good removal efficiency, it showsthat the resin has a renewable ability.These two species of marine biological resin prepared in this study areadsorption materials safety and environmental protection, don’t produce secondarypollution, for this reason, they can be used for the removal of heavy metal ions in theproduction of Chinese herbal medicine. In this paper, honeysuckle extract and ginkgoleaf extract were used as models to research the resin removal efficiency of heavymetal ions in the extract of Chinese herbal medicine and its impact on the activeingredients of the Chinese herbal medicine. The results showed that carboxymethylchitosan resin for these two kinds of Chinese herbs extracts of heavy metal ions Cu²⁺,Pb²⁺and Cd²⁺had better adsorption capacity, the removal rate reached more than90%.After the adsorption, the loss rate of chlorogenic acid and total flavonoids, the activeingredients of Chinese herbal medicine were small, The resin has certain applicationvalue in the treatment of heavy metals in Chinese herbal medicines.