abstract
The removal of the hazardous Hg2+ from aqueous solutions was studied by ion exchange using titanosilicate in sodium form (Na-ETS-4). Isothermal batch experiments at fixed pH were performed to measure equilibrium and kinetic data, considering two very distinct situations to assess the influence of competition effects: (i) the counter ions initially in solution are Na+ and Hg2+ (both are exchangeable); (ii) the initial counter ions in solution are tetrapropylammonium (TPA(+)) and Hg2+ (only Hg2+ is exchangeable, since TPA(+) is larger than the ETS-4 micropores). The results confirmed that ETS-4 is highly selective for Hg2+, with more than 90% of the mercury being exchanged from the fluid phase. The final equilibrium attained under the presence of TPA(+) or Na+ in solution was very similar, however, the Hg2+/Na+/ETS-4 system in the presence of Na+ required more 100 h to reach equilibrium than in the presence of TPA(+). The Hg2+/Na+/ETS-4 system was modelled and analyzed in terms of equilibrium (mass action law) and mass transfer (Maxwell-Stefan (MS) formalism). Concerning equilibrium, no major deviations from ideality were found in the range of studied concentrations. On the other hand, the MS based model described successfully (average deviation of 5.81%) all kinetic curves of mercury removal.
keywords
ION-EXCHANGE; LANTHANIDE SILICATE; WASTE-WATERS; PURIFICATION; ADSORPTION; KINETICS; TITANOSILICATES; EQUILIBRIUM; HG2+; CS+
subject category
Chemistry, Physical; Materials Science, Multidisciplinary; Metallurgy & Metallurgical Engineering; Physics, Applied; Physics, Condensed Matter
authors
Cardoso, SP; Faria, TL; Pereira, E; Portugal, I; Lopes, CB; Silva, CM
our authors
Carlos Manuel Silva
Associate Professor
Cláudia Batista Lopes
Assistant Researcher
Inês Portugal
Assistant Professor
Simão Pedro Pereira Cardoso
Post-Doc Fellowshipacknowledgements
This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, FCT Ref. UID/CTM/50011/2019, financed by national funds through the FCT/MCTES. Claudia B. Lopes acknowledges hirings funded by national funds (OE), through FCT-Fundacao para a Ciencia e a Tecnologia, I.P., in the scope of the framework contract foreseen in the numbers 4, 5, and 6 of the article 23, of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19.