The Modification Of Chitosan And Its Adsorption Properties For Heavy Metal Ions

With the development of industry, the pollution of heavy metal ions from industrial wastewater has become increasingly serious. The removal of toxic heavy metal ions from wastewater has received much attention in recent years. Traditional treatment methods that have been used to remove heavy metal ions from various industrial effluents usually include chemical precipitation, ion-exchange, membrane filtration, adsorption etc. The search of methods for removing toxic heavy metal ions required the consideration of effective, economic and without secondary polution.Chitosan (CTS) is a crude macromolecular compound, the active functional groups (-NH2 and -OH) of chitosan can chelate heavy metal ions. So, chitosan can be used as a macromolecular adsorbent to remove heavy metal ions. Furthermore, chitosan is avirulent and it would not bring secondary polution, moreover, chitosan can disassemble by biologic catabolism. Chitosan can dissolve in acid solution, and it limits the use of chitosan. In our study, we have Synthesized tow adsorbent from chitosan and studied they adsorption capacity. The effects of different conditions, such as, pH value, initial concentration, temperature, contact time, have been studied. The main contents are listed as follows:1 Carboxylated chitosan (CKCTS) was prepared by using chitosan, alpha-ketoglutaric acid and monochloroacetic acid. The adsorbent obtained was tested for the remove of Cd(II), Pb(II) and Cu(II) from aqueous solutions. From the result we can see that the maximum adsorption capacity for Cd(II), Pb(II) and Cu(II) were 0.555 mmol/g, 0.733 mmol/g and 0.827 mmol/g respectively. Adsorption capacity of Cd(II), Pb(II) and Cu(II) increases with increasing the pH of the solution. It was shown that a rapid adsorption of metal ions from aqueous solution, it can reach adsorption equilibrium in 20 min. The adsorption equilibrium data were fitted well with the Langmuir isotherm, which revealed that the adsorption is monolayer. Adsorption capacity decreased with the increase of temperature, which revealed the process is exothermic. 2 We prepared CTOS by grafting the thiosemicarbazide onto chitosan. The adsorption properties of the CTOS for Ag~+ have been studied. It found that the adsorbent did not dissolve in acid water, so it can be used in a large range. At 25℃, pH=5 the maximum adsorption capacity of CTOS for Ag~+ is 1.78 mmol/g, much high than chitosan. Compare with Freundlich model, the adsorption process fits well with Langmuir model. Adsorption capacity increased with the increase of temperature, which revealed the process is endothermic. In the mixed solution of Ag-Cu, Ag-Zn and Ag-Pb, the selectivity coefficient of Ag~+ are 74.86, 5.36, 13.86 respectively, and the CTOS has a good selectivity for Ag~+.