Application of chitosan for the removal of metals from wastewaters by adsorption - Mechanisms and models review

Chitin is the world's second most abundant naturally occurring polysaccharide. Much of this is disposed of as waste from seafood crustacean, mainly in shrimps, prawns, crabs, and lobsters, where it occurs as a significant component in the shells/exoskeletons of crustacea. Due to its widespread abundance, its chemical and physical versatility, and the problems of its disposal as a waste material, a wide range of value-added applications of chitin and chitosan is being initiated, investigated, and developed. The widely ranging value-added applications of chitin and chitosan are presented in this review. Chitin and its derivative, chitosan, both highly stable and difficult to degrade materials, can be obtained as 10-20% w/w from the waste seafood shells by suitable chemical processing. One of the significant developments in the new range of applications is the study of the ability of chitosan, as a potentially major environmental treatment material, to remove metal ions from wastewaters. Chitosan is the deacetylated form of chitin, and this process produces a chain of amino groups along the chitosan structure. Many researchers are now looking at the ability of this amino group to adsorb metal ions from industrial wastewaters and leachates. This review presents the developments in this area and identifies the defficiences in existing chitosan research by reviewing the equilibrium studies carried out to determine the capacity of chitosan for various metal ions. Then the kinetic studies are reviewed, as well as the solution methodologies adopted by various researchers to explain and model the rate of adsorption of the metal ions from solution. Both equilibrium knowledge and kinetic knowledge are required in order to design commercial treatment systems.