Removal of heavy metals from waste water using locally derived chitosan

Abstract

In this research work natural bio polymer “chitosan” was synthesized using locally available shrimp shells and adsorption of chromium by chitosan was studied. Synthesize of chitosan involved four main stages as preconditioning, demineralization, deprotenisation and deacetylation. “Preconditioning” process is a new step introduced in this research, to remove loosely bound protein. In the preconditioning, the skeletal matrix structure is first weakened which makes easier to remove soluble protein by washing with water. Therefore during deproteination process less alkali concentration can be used. Effect of deacetylation conditions such as alkali concentration, number of times of deacetylation performed and reaction temperature was investigated. Chitosan was characterized using Fourier Transform Infrared Spectroscopy (FTIR), Differential Thermal analysis (DTA), Thermal Gravimetric Analysis (TGA) and X-ray diffraction (XRD). These characterization techniques confirm the existence of chitosan. Degree of deacetylation was calculated using FTIR spectra. This value was highly depending on reaction temperature, reaction time, alkali concentration and number of times of deacetylation. Both characterization techniques confirm the existence of chitosan. The affinity of chitosan for chromium was studied using K2Cr2O7 solution as the heavy metal solution containing Cr (VI) ions. Adsorption of chromium ions by chitosan was investigated under different conditions. The effect of reaction temperature, particle size of chitosan and pH of solution were studied. Amount of chromium absorbed under different conditions was evaluated using atomic absorption spectroscopy.