Lanthanum biosorption by a Pseudomonas sp.: equilibrium studies and chemical characterization

Lanthanum biosorption by a Pseudomonas sp. was characterized in terms of equilibrium metal loading, model fitting, kinetics, effect of solution pH, lanthanum-bacteria interaction mechanism and recovery of sorbed metal. Lanthanum sorption by the bacterium was rapid and optimum at pH 5.0 with equilibrium metal loading as high as 950 mg g(-1) biomass dry wt. Scatchard model and potentiometric titration suggested the presence of at least two types of metal-binding sites, corresponding to a strong and a weak binding affinity. The chemical nature of metal-microbe interaction has been elucidated employing FTIR spectroscopy, energy dispersive X-ray analysis (EDX) and X-ray diffraction analysis (XRD). FTIR spectroscopy and XRD analysis revealed strong involvement of cellular carboxyl and phosphate groups in lanthanum binding by the bacterial biomass. EDX and the elemental analysis of the sorption solution ascertained the binding of lanthanum with the bacterial biomass via displacement of cellular potassium and calcium. Transmission electron microscopy exhibited La accumulation throughout the bacterial cell with some granular deposits in cell periphery and in cytoplasm. XRD confirmed the presence of LaPO4 crystals onto the bacterial biomass after La accumulation for a long period. A combined ion-exchange-complexation-microprecipitation mechanism could be involved in lanthanum accumulation by the biomass. Almost 98% of biomass-bound La could be recovered using CaCO3 as the desorbing agent.