Biosorption of uranium from aqueous solutions by Azolla sp. and Limnobium laevigatum.

Abstract

The main goal of this study was to assess alternatives to the current challenges on environmental quality and circular economy. The former is here addressed by the treatment of radioactively contaminated solutions, and the latter by using abundant and low-cost biomass. In this paper, we examine the biosorption of hexavalent uranium (U(VI)) in a batch system using the macrophytes Limnobium laevigatum and Azolla sp. by three operational parameters: biomass dose, metal ion concentration, and contact time. Simulated solutions were firstly addressed with two biomasses, followed by studies with real liquid organic radioactive waste (LORW) with Azolla sp. The batch experiments were carried out by mixing 0.20g biomass in 10mL of the prepared solution or LORW. The total contact time employed for the determination of the equilibrium times was 240min, and the initial U(VI) concentration was 0.63mmol L-1. The equilibrium times were 15min for L. laevigatum and 30min for Azolla sp. respectively. A wide range of initial U(VI) concentrations (0.25-36mmol L-1) was then used to assess the adsorption capacity of each macrophyte. Isotherm models validated the adsorption performance of the biosorption process. Azolla sp. presented a much higher U(VI) uptake (0.474mmolg-1) compared to L. laevigatum (0.026mmolg-1). When in contact with LORW, Azolla sp. removed much less uranium, indicating an adsorption capacity of 0.010mmolg-1. In conclusion, both biomasses, especially Azolla sp., can be used in the treatment of uranium-contaminated solutions.