Biosorption of lead using crab shell

Abstract

INORGANIC MICROPRECIPITATION OF LEAD ON THE SURFACE OF CRAB SHELL Protunus trituberculatus is a kind of crab used as biosorbent to treat lead-bearing wastewater. The equilibrium isotherms showed that crab shell took up lead from aqueous solutions to the extent of 1300mg Pb/g crab shell. Removal efficiency of lead by crab shells was pH dependent, but was less sensitive than that of control without crab shell. The optimum pH range for the maximum lead removal by precipitation and adsorption on the surface of crab shells was expanded to 5.5-11.0, whereas that of controls was from 8.5 to 11.0. The major mechanism of lead removal by crab shell seemed to occur mainly through $CaCO_3$ dissolution followed by $PbCO_3$ and $Pb_3(CO_3)_2(OH)_2$ precipitation near the surface of crab shell and then lead crystals formed were adsorbed to the chitin. FTIR spectra confirmed that $NHCOCH_3$- and $CO_3^{2-}$ were effective to the lead removal comparing before and after reaction with lead. CHARACTERISTICS OF LEAD REMOVAL BY CRAB SHELL IN SYNTHETIC WASTEWATER Characteristics of lead removal by crab shell was investigated for the various parameters. The removal efficiency of lead was dependent on the pH, crab shell doses, initial lead concentrations, co-ions, chelating agents, and settling time. When a crab shell dose increased from 0.5g/L to 1.5g/L, 98\% of the lead removal efficiency improved to 99.8\% with lead solution of 20ppm. However, the percentage of lead removal decreased from 99.9 to 65\% at initial pH 5.0 when the initial lead concentration increased from 200 to 1000ppm in the solutions with 0.5g/L crab shell. All the solids formed in crab shell-free solutions were difficult to filter and settle. In contrast, in "crab shell" solutions, the solids filtered quickly, were not flaky that was a result of the adsorption of lead carbonates on the surface of the crab shell. Removal efficiency of lead was not affected by ionic strength up to 0.5M of $NaNO_3$ and the types of ba...