Biosorption of Hg(II) onto goethite with extracellular polymeric substances

•Interactions between Hg(II), EPS and goethite were investigated.•EPS from Chroococcus sp. enhances adsorption capacity of Hg(II) on goethite.•EPS binds with Hg(II) to quench the EEM peaks of proteins on EPS.•Goethite–EPS soil is a larger Hg(II) sink than goethite alone soil.•Biosorption significantly affects the mobility of Hg(II) in goethite soils.

This study characterized the interactions of goethite, EPS from cyanobacterium Chroococcus sp. and Hg(II) using excitation emission matrix (EEM) spectra and adsorption isotherms. Three protein-like fluorescence peaks were noted to quench in the presence of Hg(II). The estimated conditional stability constant (log Ka) and the binding constant (log Kb) of the studied EPS–Hg(II) systems ranged 3.84–4.24 and 6.99–7.69, respectively. The proteins in EPS formed stable complex with Hg(II). The presence of proteins of Chroococcus sp. enhanced the adsorption capacity of Hg(II) on goethite; therefore, the goethite–EPS soil is a larger Hg(II) sink than goethite alone soil. Biosorption significantly affects the mobility of Hg(II) in goethite soils.