Removal of microelemental Cr(III) and Cu(II) by using soybean meal waste – Unusual isotherms and insights of binding mechanism

In the present study soybean meal (SBM) waste has been used for the removal Cr(III) and Cu(II) from aqueous solutions. Effect of variable parameters including pH, contact time, biomass dose and initial concentration of metal ions were studied. Biosorption kinetics was very fast and the kinetics data were successfully modeled using nonlinear pseudo-second-order model. A series of isotherm experiments revealed that pH 5 favored Cr(III) and Cu(II) biosorption and the affinity order of SBM was Cu(II) > Cr(III). Biosorption mechanism was confirmed by the functional group blocking, FTIR and scanning electron microscopy/energy-dispersive X-ray results. The biosorption mechanism was due to (i) ion-exchange, (ii) chelation by carboxyl and hydroxyl groups present on the SBM surface, (iii) further precipitation of metal ions on the surface of biomass. Our results revealed that SBM could be employed as an effective and low-cost biosorbent for removal of Cr(III) and Cu(II) from contaminated effluents.

Figure optionsDownload as PowerPoint slideHighlights
► Waste soybean meal biomass biosorbent was used for removal Cr(III) and Cu(II) ions.
► Effect of pH, contact time and initial concentrations on metal removal were investigated.
► Pseudo-second-order and Sips models best described the Cr(III) and Cu(II) biosorption.
► Unusual isotherms and biosorption mechanism was fully explored by characterization.
► The results recommend that soybean meal as potentially low-cost biosorbent.