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The specific adsorption of organic and inorganic phosphates by variable‐charge oxides
Author(s) -
Barrow N. J.,
Feng X. H.,
Yan Y. P.
Publication year - 2015
Publication title -
european journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 1351-0754
DOI - 10.1111/ejss.12280
Subject(s) - adsorption , phosphate , chemistry , surface charge , inorganic chemistry , aluminium , ion , plane (geometry) , organic chemistry , geometry , mathematics
Summary We measured the reaction of inorganic phosphate and of four organic phosphates with three aluminium hydroxides or oxides. We compared the fit of the L angmuir equation with that of an equation designed to allow for the feedback effect of adsorption on the electric potential. We also fitted a four‐plane model to describe the effects of pH on adsorption and ζ potential. For inorganic phosphate, the L angmuir equation described adsorption curves poorly, indicating that there was a large feedback effect of adsorption on the electric potential of the adsorption plane. For the organic phosphates, the deviations from the L angmuir equation were not as marked, indicating that there was little feedback effect. Nevertheless, there was a large effect on the ζ potential of the phosphated aluminium (hydr)oxides. We suggest that when a large organic phosphate molecule is adsorbed, the charge conveyed to the surface is repelled electrostatically to the outside of the new surface. There is therefore a large effect on the ζ potential and a small effect on the potential of the adsorption plane. This suggestion was supported by the fit of the four‐plane model, for which, with increasing molecular weight, the mean position of the charge conveyed to the surface by adsorption was moved further from the plane carrying the potential determining ions ( H + and OH − ).