Study On The Adsorption Of Heavy Metal Ions By Carboxymethyl Chitosan

With the rapid development of the global industry, the pollution of heavy metal ions also gradually aggravates. It has bad effect on biological and humanity's survival and physical and moral health, through the water, the soil, the air, especially the food chain. In the 1960s there was public nuisance disease which called Minamata disease and Itai itai disease in Japan, it shocked the world. This was because the mercury containing waste water and cadmium containing waste water polluted water respectively. How to deal with heavy metal pollution effectively has become urgent concern of all humanity, so varieties of researchers committed to search for the method of solving the problem of heavy metal pollution. Effective treatment method should be efficient, convenient, and no secondary pollution. It include: oxidation and reduction, chemical precipitation, electrolysis, membrane separation, ion exchange and adsorption, etc. because the way of adsorption is easy and feasible, it has aroused widespread attention.Chitosan can be synthesized through chitin deacetylation; chitin is one of the most abundant natural polymers. There were hydroxyl and amine active groups in the molecular chain of chitosan. Each unit of molecular structure has a primary amino; the lone pair electrons of nitrogen atom can be put into air orbit of metal ions, with the formation of valence bond, so coordination reaction occurs, which can be used as adsorbent of heavy metal ions. However, chitosan itself has many drawbacks, it has poor sulfuric acid resistance, and the presence hydrogen bonds also influence its adsorption capacity, limiting the further expansion of its scope of application.The molecular structure of chitosan contains a variety of functional groups with strong reactivity, and it can introduce into lots of functional groups using chemical modification in order to have different function and effect, carboxymethyl chitosan derived from chitosan by adding carboxymethyl of hydrophilic, and it turn into insoluble metal chelated polymer when it chelate with heavy metal ions, even if the concentration of metal ion is very low, and the two are easy to separate. Carboxymethyl chitosan can chelate with heavy metal ions because of the presence of carboxyl and hydroxyl of the molecular structure. So it can be adsorbed heavy metal ions to purify the wastewater.In this paper, we studied absorption behavior of Zn²⁺, Ni²⁺, Co²⁺ onto carboxymethyl chitosan such as the time, temperature, initial concentration, pH and so on, and studied the adsorption kinetics and thermodynamics, getting the corresponding model and its adsorption kinetics and thermodynamics parameters.