Abstract

This article investigated the recovery of Gd3+ from real leachate of phosphogypsum (PG) using natural bentonite clay. Firstly, a detailed adsorption study was performed using synthetic Gd3+ solutions. Then, it was investigated the clay performance in the real PG leachate. The characterization results indicate classical bentonite characteristics, such as rugosity and an SBET 91.3 m2 g-1, with meso (Dp =3.82 nm) and macroporous (Dp =52.6 nm). In addition, it was identified that the major functional groups are hydroxyl and silicate, with the presence of organic matter. The initial pH solution effect indicates that the optimum removal of Gd3+ is at pH (6), attributing to the pHpzc being at 5.75 and the negatively charged surface above the pHpzc. The Avrami fractional order model was the most suitable for describing the experimental kinetic data. The Langmuir was the proper model for describing the adsorption isotherms, indicating that the Gd3+ forms a monolayer at the surface of the bentonite. The maximum adsorption capacity at pH 6.0 was 121.5 mg g-1. The thermodynamic parameters indicate that the adsorption is spontaneous, with a standard enthalpy change of - 92.30 kJ mol- 1, indicating an ionic exchange, where the Gd3+ tends to be organized at the surface, according to the standard entropy change of - 206.0 J K-1 mol- 1. The fixed bed adsorption test showed that Gd3+ could be adsorbed for up to 200 min without regeneration. Regeneration results show that the citric acid is more efficient in desorbing the Gd3+ from the bentonite, reaching up to 8 cycles without efficiency loss. Finally, the bentonite clay could selectively recover Gd3+ from the real PG leachate.

Keywords

Gadolinium; Natural clay; Adsorption; Selectivity; Kinetics; Thermodynamics

Published in

Journal of Environmental Chemical Engineering
2023, Volume: 11, number: 3, article number: 109748

SLU Authors

• Simões Dos Reis, Glaydson

  • Department of Forest Biomaterials and Technology, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Physical Chemistry


Publication identifier

DOI: https://doi.org/10.1016/j.jece.2023.109748

Permanent link to this page (URI)

https://res.slu.se/id/publ/122380