Preparation Of Adsorbent Materials From Shrimp/Crab Shells And Their Applications In Heavy Metal Adsorption And Stabilization

The preparation of chitosan has been investigated for more than half century;however,the application of chitosan for heavy metal(HM)adsorption is still under research.The application of chitosan as low-cost adsorbent in treatment of HM contaminated water has drawn much research interest.Highly purified chitosan was generally preferred for HM removal/adsorption.Some of them did not follow any uniform parameters and only emphasized on the chitin yield and chitin quality.As a result,the preparation parameters varied largely without any agreement.Municipal solid waste incineration fly ash(MSWIFA)is considered as hazardous waste due to its high content of HM.Therefore,MSWIFA should be treated properly prior to landfill disposal and application as construction materials.Very few studies investigated the influences of chitosan on solidification/stabilization(S/S)of HM in MSWIFA.The investigation results in this thesis are showed as follows:1.This study used shrimp waste for chitosan preparation.The prepared chitosan was applied to remove/adsorb Pb2+ from aqueous solution.The results showed that only acid concentration played an important role in the deproteinization and demineralization processes of the chitin preparation under HCl,H2SO4 and CH3COOH treatment.Ca-bearing contents(CBC)but not free-NH2 group of chitosan played a major role in the removal of Pb2+ from aqueous solution.Partly purified chitosan mainly removed Pb2+ by precipitation and then by biosorption.The dissociation of Ca2+ from CBC elevated pH value of Pb2+ solution which benefited to precipitation and the formation of NH2-Pb2+.Partly purified chitosan prepared from HCl and CH3COOH treated chitin showed 720-753 mg/g of Pb2+ adsorption at the initial pH value of 6.0;however,highly purified chitosan prepared from HCl treated chitin showed only 45-160 mg/g.Chitosan prepared from H2SO4 treated chitin showed 720-752 mg/g of Pb2+adsorption.The adsorption data of Pb2+ onto chitosan was well fitted by Langmuir isotherm model and Pseudo-second-order model with correlation coefficient(R2>0.98 and R2>0.94,respectively).It indicated that the adsorption capacity strongly depended on CBC and-NH2 group in chitosan.2.This study utilized sea crabs to prepare chitosan.The target HM for adsorption test were Pb2+,Cd2+ and Cu2+in aqueous solution.The results showed that highly purified chitosan showed the optimum HM adsorption at the initial pH values of 4.14 and 6.13,and the adsorption mechanism was chemisorption involving valence forces through sharing or exchange of electrons between the chitosan and HM ions.Highly purified chitosan prepared from HCl treated chitin only showed effective for Pb2+,however,those prepared from CH3COOH treated chitin showed effective for HM adsorption due to a little amount of CBC.The HM adsorption mechanisms of partly purified chitosan were precipitation due to CBC and biosorption.Chitosan with 73%CBC showed the optimum adsorption of Pb2+(755 mg/g)at an initial pH value of 2.10 while Cd2+(979 mg/g)and Cu2+(877 mg/g)at the initial pH values of 4.14 and 6.13.High Ca(OH)2-bearing chitosan prepared from HCl and H2SO4 treated chitin showed the optimum Cd2+(978 mg/g)and Cu2+(852 mg/g)adsorption at an initial pH value of 2.10.Biosorption isotherm and kinetics models showed that the adsorption data of HM onto the surface of chitosan was well-fitted by Langmuir model and Pseudo-second-order model with correlation coefficient(R2>0.95 and R2>0.91,respectively).Pseudo-second-order model showed that the adsorption capacity strongly depended on CBC in chitosan and initial pH value of HM solution.3.High concentrated(0.5M)H2SO4 treated chitosan sample CS-SA-2 was applied for S/S of HM in MSWIFA.The addition of chitosan increased calcium silicate hydrate(C-S-H),which meant chitosan was helpful for hydration of CFBCFA,which was due to the water adsorption ability of chitosan.The distribution of HMs changed little except for Pb after adding CFBCFA in S/S mixtures.The addition of chitosan lowered down the HM appearance in S/S solids,which meant that chitosan helped S/S of HM.Only the amount of Pb exceeded the thresholds prescribed in GB5085.3,which was due to the high calcium content in CFBCFA and chitosan.As the curing age was only 24h the calcium in CFBCFA cannot be largely consumed.After S/S MSWIFA using CFBCFA and chitosan,the HM decreased except for Pb,Zn,As and Hg.However,the Zn,As and Hg decreased when the addition of chitosan decreased to 0.1%,which suggested that these three HMs came from chitosan.With the decrease in the addition of chitosan the S/S effects of other HMs decreased.This research found the unexplored information for the industrial application of chitosan with minimum cost but the highest HM removal/adsorption efficiency.The chitosan preparation process of this study is easy and economically feasible,so it can be applied in industrial preparation of chitosan specifically for the treatment of HM contaminated water.High CBC in chitosan acts as supporting binding materials in rapid S/S of HM in MSWIFA.So it can be utilized in industrial disposal of MSWIFA as well.