Abstract
In this study, a lead-resistant bacterium, Bacillus subtilis X3, was used to prepare a lead bioadsorbent for immobilization and removal of lead in lead solution. The lead shot precipitate was analysed by scanning electron microscopy combined with energy dispersive X-ray fluorescence microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The adsorbed lead was mainly mineralized to form Pb5(PO4)3OH, Pb10(PO4)6(OH)2 and Pb5(PO4)3Cl; however, other mechanisms that can also promote the mineralization of lead should not be ignored. For example, Na+ and Ca2+ on the cell wall surface were exchanged with Pb2+ in solution, which confirmed that the ion-exchange process occurred before mineralization. Moreover, adsorption bridging caused by extracellular polymeric substances also accelerated the further aggregation of lead, and the biomass was encapsulated by lead gradually. Hydroxyl, carbonyl, carboxyl and amine groups were not observed in lead mineral crystals, but the complexation between lead and these groups still benefited the mineralization of lead. The valence of Pb(II) was not changed after mineralization, which indicated that the biosorption process was not a redox reaction. Finally, biosorption occurred on the outer surface of the cell, but its specific surface area was relatively small, limiting the amount and efficiency of biosorption.
Highlights
Heavy metal pollution is a global environmental problem and has received a great deal of attention
We found the same groups on the lead shot upon Fourier transform infrared spectroscopy (FT-IR) spectral analysis, but we did not find these functional groups upon X-ray diffraction (XRD) analysis of the lead mineral crystals
B. subtilis X3 isolated from the soil in a lead mine plant was able to adsorb lead efficiently in solution
Summary
Heavy metal pollution is a global environmental problem and has received a great deal of attention. Heavy metals are generally stable and not biodegradable, their concentrations are quite low 2 [1,2]. Mining, electroplating, metal processing, textiles and the battery manufacturing industry are the main sources of lead contamination [3]. Once lead is discharged into an aqueous environment, it will be concentrated in fish, vegetables and other foods, which impacts humans via the food chain, resulting in strong toxicological effects on the human heart, liver, kidneys, brain and reproductive systems, especially in children [4 –8].
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