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Abstract
The sorption efficiency of Opuntia ficus indica cactus fibres regarding the removal of trivalent europium (Eu(III)) from aqueous solutions has been investigated prior and after the chemical treatment (phosphorylation and MnO2-coating) of the biomass. The removal efficiency has been studied as a function of pH, europium concentration, mass of the adsorbent, ionic strength, temperature and contact time. Evaluation of the experimental data shows that biosorption is strongly pH-depended and that the MnO2-coated product presents the highest sorption capacity followed by the non-treated and phosphorylated material. Results have been analysed by Langmuir, Freundlich and Dubinin–Radushkevich isotherms, and the Langmuir model is more suitable to describe the process. The sorption reactions are entropy-driven, and the kinetics follows a pseudo-first order rate expression, described by Lagergren. In addition, the results show that the fibres of the Opuntia ficus indica cactus possess significantly higher sorption capacity than other biomass by-products reported in literature and that the removal of europium from contaminated waters is expected to be more effective in the case of the chemically treated biomasses.