Study On Adsorption Of Heavy Metal Ions From Water By Novel Biosorbents

Toxic heavy metal pollution is one of the most significant environmental problems due to their hazards to organism. Biosorbent is receiving increasing attention because of its advantages such as low cost, less energy consumption and environment-friendly. The present study investigated the adsorption characteristics of the polyethyleneimine modified eggshell membrane and garlic peel for Cr(VI) and Cu2+from water.In first work, the polyethyleneimine (PEI) functionalized biosorbent which uses an eggshell membrane (ESM) as a model was synthesized based on the cross linking reaction between aldehydes in glutaraldehyde and functional groups such as amines and amides in ESM. The as-prepared biosorbent (PEI-ESM) strongly interacted with chromium(VI). After modification, the dynamic uptake capacity of the PEI-ESM increased by105%compared with the control, and the maximum equilibrium adsorption capacity for Cr(VI) can reach about160mg.g-1. The Langmuir adsorption isotherm was applicable to fit the removal process. Kinetics of the Cr(VI) removal were found to follow a pseudo-second-order rate equation. The results obtained by Raman spectroscopy and X-ray photoelectron spectroscopic analysis (XPS), performed on the as-prepared biosorbent before and after Cr(VI) adsorption, suggested that some of adsorbed Cr(VI) anions were reduced to Cr(III) in Cr2O3or Cr(OH)3during the sorption process, demonstrating that the PEI-ESM could detoxify Cr(VI).Then PEI-ESM was used for Cu2+adsorption. The adsorption process was found to be highly dependent on the pH of solution, as well as the solution temperature. The results showed that the adsorption process followed the Langmuir isotherm with the theoretical maximum adsorption capacity of17.06mg.g-1for Cu2+. In addition, it was found that pseudo-second-order model was suitable to fit the Cu2+adsorption processes, and some divalent metal ions existed in water body almost did not affected the adsortion processes.Finally’0.5mol.L-1HCl was used to successfully desorb Cu2+on the biosorbent,and the recovery was kept above90％.Finally,garlic peel was used as biosorbent for Cu2+adsorption.The scanning transmission electron microscopy(SEM) and FT-IR spectra were used to characterize the garlic peel.The results indicared that the initial pH did not afiect the adsorption processes.It was also found that the pseudo-second-order model was fit to the Cu2+adsorption processes and the theoretical maximum adsorption capacity is higher than most of the natural adsorbent.