Influences of chemically controlled Ca-bearing minerals in chitosan on Pb²⁺ removal efficiency

Highly purified chitosan was generally preferred for heavy metal (HM) removal and the preparation parameters varied largely without any agreement. This study investigated to the influences of chitin with different purities on the HM removal of corresponding chitosan. Sea shrimp waste was used as raw materials and Pb²⁺ was used as target HM. The results of orthogonal experimental analysis 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 minerals (CBM) but not free -NH₂ group of chitosan played a major role in the removal of Pb²⁺ from solution. Partly purified chitosan mainly removed Pb²⁺ by precipitation and then biosorption. The dissociation of Ca²⁺ from CBM 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. This research found the unexplored information for the industrial application of chitosan with minimum cost but the highest HM removal efficiency.