期刊
GEOSCIENCES
卷 8, 期 9, 页码 -出版社
MDPI
DOI: 10.3390/geosciences8090309
关键词
allophane; adsorption; precipitation; interface processes; environment; heavy metals; nano-structure; short-range order aluminosilicate; wastewater treatment; aqueous geochemistry
资金
- NAWI Graz Geocentre, Graz University of Technology [F-AF7-221-01]
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 Ba2+, 12.4, 19.3, and 29.0 mg/g for HCoO2-; 7.2, 15.9, and 34.4 mg/g for Sr2+; and 20.9, 26.9, and 36.9 mg/g for Zn2+, 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.
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