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Open AccessArticle

Removal of Barium, Cobalt, Strontium, and Zinc from Solution by Natural and Synthetic Allophane Adsorbents

1
Institute of Applied Geosciences, Graz University of Technology, Rechbauerstraße 12, 8010 Graz, Austria
2
Institute of Technology and Testing of Building Materials, Graz University of Technology, Inffeldgasse 24, 8010 Graz, Austria
3
Institute for Electron Microscopy and Nanoanalysis and Center for Electron Microscopy, Graz University of Technology, Steyrergasse 17, 8010 Graz, Austria
4
BGR, Bundesanstalt für Geowissenschaften und Rohstoffe, Geozentrum Hannover, Stilleweg 2, 30655 Hannover, Germany
*
Author to whom correspondence should be addressed.
Geosciences 2018, 8(9), 309; https://doi.org/10.3390/geosciences8090309
Received: 28 June 2018 / Revised: 13 August 2018 / Accepted: 17 August 2018 / Published: 21 August 2018
(This article belongs to the Special Issue Dynamics and Kinetics of Melt-Fluid-Rock Interactions)
The capacity and mechanism of the adsorption of aqueous barium (Ba), cobalt (Co), strontium (Sr), and zinc (Zn) by Ecuadorian (NatAllo) and synthetic (SynAllo-1 and SynAllo-2) allophanes were studied as a function of contact time, pH, and metal ion concentration using kinetic and equilibrium experiments. The mineralogy, nano-structure, and chemical composition of the allophanes were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and specific surface area analyses. The evolution of adsorption fitted to a pseudo-first-order reaction kinetics, where equilibrium between aqueous metal ions and allophane was reached within <10 min. The metal ion removal efficiencies varied from 0.7 to 99.7% at pH 4.0 to 8.5. At equilibrium, the adsorption behavior is better described by the Langmuir model than by the Dubinin–Radushkevich model, yielding sorption capacities of 10.6, 17.2, and 38.6 mg/g for Ba 2 + , 12.4, 19.3, and 29.0 mg/g for HCoO 2 ; 7.2, 15.9, and 34.4 mg/g for Sr 2 + ; and 20.9, 26.9, and 36.9 mg/g for Zn 2 + , by NatAllo, SynAllo-2, and SynAllo-1, respectively. The uptake mechanism is based on a physical adsorption process rather than chemical ion exchange. Allophane holds great potential to effectively remove aqueous metal ions over a wide pH range and could be used instead of other commercially available sorbent materials such as zeolites, montmorillonite, carbonates, and phosphates for special wastewater treatment applications. View Full-Text
Keywords: allophane; adsorption; precipitation; interface processes; environment; heavy metals; nano-structure; short-range order aluminosilicate; wastewater treatment; aqueous geochemistry allophane; adsorption; precipitation; interface processes; environment; heavy metals; nano-structure; short-range order aluminosilicate; wastewater treatment; aqueous geochemistry
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Baldermann, A.; Grießbacher, A.C.; Baldermann, C.; Purgstaller, B.; Letofsky-Papst, I.; Kaufhold, S.; Dietzel, M. Removal of Barium, Cobalt, Strontium, and Zinc from Solution by Natural and Synthetic Allophane Adsorbents. Geosciences 2018, 8, 309.

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