Micro precipitation of lead on the surface of crab shell particles

Crab shell particles were used as a biosorbent to remove lead from aqueous solutions. The equilibrium isotherm showed that crab shell particles took up lead to the extent of 1300 mg Pb g(-1) crab shell. The optimum pH range for maximum lead removal was increased to 5.5-11.0 compared to the shell-free control pH of 8.5-11.0. pH values of solutions with crab shell material added were increased spontaneously to about 10 as a result of the CaCO3 present, which formed complexes with lead according to pH. Electron spectroscopy, Fourier transform infrared spectrometry, scanning electron microscopy and X-ray diffraction results confirmed that -NHCOCH3 and CO32- were involved in binding of lead. In addition, the removal of lead occurred mainly through dissolution of CaCO3 followed by precipitation of Pb-3(CO3)(2)(OH)(2) and PbCO3 near the surface of crab shell. Micro precipitates formed were then adsorbed to the chitin on the surface of the crab shell particles. (C) 1997 Elsevier Science Ltd.