Biosorption of Pb(II) and Co(II) Ions from Aqueous Solutions Using Pretreated Rhizopus oryzae (Bread Mold)

Abstract

Biosorption of Pb(II) and Co(II) ions from aqueous solutions was studied in a batch mode by using NaOH-pretreated Rhizopus oryzae. The optimum biosorption conditions were studied and determined by investigating pH, time course, initial metal concentration, temperature, co-ions and others. Optimum experimental parameters were determined to be pH (4 for Pb(II) and 7 for Co(II)), contact time 60 min, biomass dose 2 g L−1 of solution, and temperature 25 °C. Metal biosorption reached a saturation value at about 200 mg L−1. At this concentration, the biosorbed Pb(II) and Co(II) reached 69.73 ± 1.48 and 13.56 ± 0.37 mg g−1, respectively. Contrary to Co(II) biosorption, Pb(II) biosorption was unaffected by the presence of many competing ions, but significantly decreased when \({{\rm PO}{_{4}}^{3-}}\) was added. The Langmuir constant (qmax) values are close to the experimental, indicating the ability of this model to describe biosorption process. According to qe values obtained from pseudo-second-order model and values of R2 (0.964 for Pb(II) and 0.992 for Co(II)), the kinetic studies indicated that the biosorption process for both metals followed well pseudo-second order model. Regarding thermodynamic parameters, the values of ΔGo at 25 °C were −26.58 kJ mol−1 for Pb(II) and 20.70 kJ mol−1 for Co(II), ΔSo (69 J mol−1 K−1 for Pb(II) and Co(II)), and ΔHo (2.82 kJ mol−1 for Pb(II) and −0.47 kJ mol−1 for Co(II)). The results showed that metal biosorption by R. oryzae is feasible, spontaneous, endothermic in nature for Pb(II) and exothermic for Co(II). FTIR spectral analysis indicated the involvement of –COOH, –OH and –NH groups in the biosorption process.