Ferrous sulfide nanoparticles can be biosynthesized by sulfate-reducing bacteria: Synthesis, characterization and removal of heavy metals from acid mine drainage

Ferrous sulfide nanoparticles ( n FeS) have proven to be effective in removing heavy metals (HMs) from wastewater. One such approach, which has garnered much attention as a sustainable technology, is via the in situ microbial synthesis of n FeS. Here, a sulfate-reducing bacteria (SRB) strain, Geobacter sulfurreducens , was used to initially biosynthesize ferrous sulfide nanoparticles (SRB- n FeS) and thereafter remove HMs from acid mine drainage (AMD). SRB-nFeS was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) coupled to an energy dispersive spectrometer (EDS), three-dimensional excitation-emission matrix (3D-EEM) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Such characterization showed that SRB mediated the reduction of SO 4 2- to S 2- to form n FeS, where the metabolized substances functioned as complexing agents which coordinated with n FeS to form biofunctional SRB- n FeS with improved stability. One advantage of this synthetic route was that the attachment of n FeS to the bacterial surface protected SRB cells from HM toxicity. Furthermore, due to a synergistic effect between n FeS and SRB, HM removal from both solution and AMD by SRB- n FeS was enhanced relative to the constituent components. Thus, after 5 consecutive cycles of HM removal, SRB- n FeS removed, Pb(Ⅱ) (92.6%), Cd(Ⅱ) (78.7%), Cu(Ⅱ) (76.0%), Ni(Ⅱ) (62.5%), Mn(Ⅱ) (62.2%), and Zn(Ⅱ) (88.5%) from AMD This study thus provides new insights into the biosynthesis of SRB- n FeS and its subsequent practical application in the removal of HMs from AMD.