ABSTRACT

Chitosan was prepared from crab shells using standard chemical procedures. 1 he physicochemical properties, degree of deacetylation (74%) and ash content (1.19%) of the prepared chitosan showed that crab shell is a good source of chitosan. The waler binding capacity of the prepared chitosan was 50.4% while fat binding capacity was 37.2%. FT-IR. spectra gave characteristics bands of NI12 at 3449.00 cm'1, carbonyl at 1640.93 em'and hydroxyl at 1435.90 cm'1. Batch adsorption experiments were performed at different concentrations ol metal ions, different temperatures, contact time and pH. The results indicated that the uptake performance ol chitosan biopolymer changed with pH, concentration, temperature and co-ions. The optimum pH for the adsorption of metal ions were observed to be; Cr(VI) (2.0),Zn(ll) (4.0).Ni(II) (8.0), Pb (II) (4.0).Cu (II) (8.0), and Cd(II) (8.0).The Freundlich and Temkin adsorption isotherm models adequately represented the adsorption data obtained in the study. fhc kinetic studies showed that biosorption rates could be described better by a pseudo-second order process and the rate coefficients were determined to be 1.4620 x 1 (Pinin'1 ,1.520x1 O'" min’1. 3.840 x 1 (Pinin’1.4.469 xl(P min’1, 7.12 xKPmin'1, and 1.257 xl(P min 'for CT2O7'. Zn“'.Ni‘',.Pb"',Cu2' and,Cd24, respectively. Adsorption efficiencies of chitosan for removal of the metals were found to range from 73.3% to 90% while desorption efficiencies ranged from 60 to 80%. Chromium and cadmium showed high desorption rates while lead showed lower desorption rate. The presence of chloride ions under the same operating conditions reduced the adsorption of lead and improved adsorption of zinc and cadmium by chitosan. Chitosan biopolymer demonstrated high adsorption capacity for the heavy metal ions investigated.