Competitive adsorption of the herbicide fluroxypyr and tannic acid from distilled and tap water on activated carbons and
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Competitive adsorption of the herbicide fluroxypyr and tannic acid from distilled and tap water on activated carbons and their thermal desorption C. Moreno-Castilla · M.V. López-Ramón · L.M. Pastrana-Martínez · M.A. Álvarez-Merino · M.A. Fontecha-Cámara
Received: 14 December 2011 / Accepted: 8 June 2012 / Published online: 21 June 2012 © Springer Science+Business Media, LLC 2012
Abstract A study was conducted on batch and column competitive adsorption of fluroxypyr (FLX) and tannic acid (TA) from distilled (DW) and tap water (TW) on activated carbon cloth (ACC) and granular activated carbon (GAC). Thermal desorption of the adsorbates from the spent ACC was also studied. FLX adsorption was higher from TW than from DW at low FLX equilibrium concentrations, and the inverse was observed at high FLX concentrations. The presence of TA diminished the amount of FLX adsorbed from both solvents due to partial blocking of the microporosity, but the same trends as before were observed at low and high FLX concentrations. Carbon consumption, obtained from the breakthrough curves, was lower as a function of superficial contact time with ACC than with GAC. The presence of TA increased carbon consumption, which was related to the microporosity of the adsorbents. Thermal desorption profiles of the spent ACC showed two peaks and one peak after adsorption from DW and TW, respectively. Desorption peaks shifted to higher temperatures with an increase in the heating rate, allowing the apparent activation energies and
Electronic supplementary material The online version of this article (doi:10.1007/s10450-012-9391-5) contains supplementary material, which is available to authorized users. C. Moreno-Castilla () Departamento de Química Inorgánica, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain e-mail: [email protected] M.V. López-Ramón · L.M. Pastrana-Martínez · M.A. Álvarez-Merino · M.A. Fontecha-Cámara Departamento de Química Inorgánica y Orgánica, Facultad de Ciencias Experimentales, Universidad de Jaén, 23071 Jaén, Spain M.V. López-Ramón e-mail: [email protected]
pre-exponential factors of the desorption processes to be determined. Keywords Batch adsorption · Column adsorption · Fluroxypyr · Tannic acid · Activated carbons · Thermal desorption
1 Introduction Activated carbons are used in water treatments to remove organic contaminants. Natural organic matter (NOM) is present in all surface waters due to the decay and transformation of vegetation and microbial remains. This NOM is largely in the form of dissolved organic carbon (DOC), whose composition is a complex mixture of humic substances of variable size and molecular weight. DOC competes with the target contaminant by two major mechanisms: direct competition for adsorption sites within the microporosity of the activated carbons; and pore blocking (Li et al. 2003, 2008). Small DOC molecules directly compete with the contaminant molecules if they are of comparable size. Larger DOC molecules can be adsorbed on mesopores or the external surface of activated carbons, b
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