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Issue 27, 2016
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Sorption mechanism(s) of orthophosphate onto Ca(OH)2 pretreated bentonite

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Bentonite was chemically pretreated with Ca(OH)2 to enhance orthophosphate phosphorus (OPP) sorption capacity (qe). The pretreatment resulted in an increase of qe from about 0.3 mg P per g to about 8 mg P per g at pH 7 and 25 °C, and of OPP concentration 100 mg P per L. The effects of solution pH, OPP concentration, sorbent dosage, and temperature on OPP sorption onto pretreated bentonite were investigated. The variation of initial pH (4–9) did not affect qe, however, re-adjustment of the final pH showed that the variation of the final pH had a significant positive effect on qe. The sorption kinetics showed a low rate, reaching half of qe in the first 4 h and equilibrium after 96 h. The calculated Langmuir qmax was 11.68 mg P per g. Thermodynamic analysis suggests that the sorption process is spontaneous and endothermic. Desorption of OPP was high in solutions of 0.1 M HCl and 0.01 EDTA-Na2 and reached 83% and 98%, respectively. We conclude that the predominant sorption mechanism for OPP uptake is inner-sphere surface complexation (ligand exchange). Other less important mechanisms such as surface precipitation and replacement of P5+ for Si4+ on the tetrahedral sites of montmorillonite may operate during the OPP uptake process by pretreated bentonite with Ca(OH)2.

Graphical abstract: Sorption mechanism(s) of orthophosphate onto Ca(OH)2 pretreated bentonite

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Publication details

The article was received on 24 Dec 2015, accepted on 17 Feb 2016 and first published on 17 Feb 2016

Article type: Paper
DOI: 10.1039/C5RA27638A
Citation: RSC Adv., 2016,6, 22295-22305

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    Sorption mechanism(s) of orthophosphate onto Ca(OH)2 pretreated bentonite

    G. Markou, V. J. Inglezakis, D. Mitrogiannis, I. Efthimiopoulos, M. Psychoyou, P. Koutsovitis, K. Muylaert and I. Baziotis, RSC Adv., 2016, 6, 22295
    DOI: 10.1039/C5RA27638A

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