Removal of cadmium and lead from heavy metals loaded PVA–SA immobilized Lentinus edodes

Abstract

This study, relates to results of Cd(II) and Pb(II) adsorption and removal efficiency from polyvinyl alcohol–Na-alginate (PVA–SA) immobilizing cells of Shi-take mushroom (Lentinus edodes) by H2SO4, HNO3, HCl, Na2CO3, NaHCO3, and NH4Cl solutions. Of these desorbing agents, H2SO4, HNO3, and HCl had strong desorbing potential, while HCl and HNO3 did better. The bio-sorbent particles, after desorption by both H2SO4 and HNO3 were found to be corroded. H2SO4 solution was most severe and it caused formation of amorphous matter at the surface that wrapped bio-sorbent particles and caused their round-shape coagulation. This membranes formed, further blocked desorption of Cd(II)/Pb(II). After desorption by HNO3, the particles were broken down due to strong oxidative power of the acid itself; while no obvious surface corrosion happened after desorption of the bio-sorbent particles when HCl was used as desorption agent. Since HCl solution had a weak influence on the bio-sorbent’s surface features, this acid was used as desorbing agent. An optimal time at equilibrium for Pb(II) desorption by 1 mol/L HCl was 90 min and for Cd(II) by 0.1 mol/L HCl was 60 min, with maximum efficiency of 90% and 81%, respectively. The pseudo-second-order model well-fitted to Cd(II)/Pb(II) desorption rates and the correlation coefficients (R2) were 0.9989 and 0.9969, respectively. From trial to trial as regeneration of bio-sorbent continued, its absorptive potential gradually weakened. Nevertheless, after three regeneration trials, the absorptive potential of reused bio-sorbent still reached 69% for Cd(II) and 85% for Pb(II), and what was displayed is that the immobilizing technology with the abandoned stipe of Shi-take mushroom can be feasible in practical application. After Pb(II) bio-sorption, the surface of bio-sorbent became rich in Pb(II) and energy spectra confirmed that the crystals found in scanning electron microscope (SEM) analysis were Pb(II) salts. On the other side, the spectral peak from Cd(II) was not as clear as from Pb(II). After desorption phase of Pb(II) and Cd(II), there were no spectral peaks from these heavy metals at the surface of the regenerated bio-sorbent.