Biosorption and biomagnetic recovery of La3+ by Magnetospirillum magneticum AMB-1 biomass

Abstract

Biosorption is a simple, efficient, and eco-friendly method for aqueous waste stream treatment. However, the main drawback is the need for biomass removal after adsorption, which can be expensive and energy intensive. In the present study, biomass from the magnetotactic bacterium Magnetospirillum magneticum AMB-1 is evaluated for trivalent lanthanum (La3+) removal and recovery from an aqueous solution, as this naturally magnetic biomass can be easily separated from solution after adsorption using an external magnet. This is the first report of this common magnetotactic strain utilized for biosorption of a rare earth element. The adsorption capacity is 6.0 ± 0.15 mg La3+/g wet biomass (37.2 ± 1.2 mg La3+/g dry biomass) using 10 g/L AMB-1 wet biomass (1.6 g/L dry basis) in a 100 mg/L La3+ solution at pH 6.0, which is greater than that reported for some other bacterial species. Only a minor decrease in biosorption is observed when the salinity is increased to 1.5 M NaCl, and temperature variations up to 50 °C have little to no impact, suggestive of potential applications for biosorption from saline waste streams. The equilibrium biosorption data best fits the Langmuir isotherm model, and thermodynamic analysis indicates thermodynamically favorable lanthanum binding to AMB-1. Binding of La3+ to the AMB-1 biomass occurs through carboxyl, phosphate, and amide functional groups naturally present in the biomass. AMB-1 biomass can be used for at least five rounds of La3+ adsorption and desorption, as well as the separation and concentration of a mixture of rare earth elements. Rapid adsorption and desorption times of 8 min, as well as a simple magnetic separation, make M. magneticum AMB-1 biomass a promising biosorbent for rare earth metals in aqueous waste streams.