Environmental insights from Langmuir adsorption site capacities
2011
Ghabbour, Elham A. | Davies, Geoffrey
Adsorption by soil humic acids (HAs) regulates the bioavailability of nutrients and pollutants, and adsorption studies can lead to useful environmental models. Langmuir's model of reversible adsorption of a gas on a solid surface as it applies to adsorption of a dissolved substance B on insoluble adsorbent A to give insoluble state A·B is examined in terms of the measured site capacity vₒbₛd (mmol solute/g adsorbent) at equilibrium concentration [B], adsorbent site capacity v at infinite concentration [B], and the maximum site capacity of the adsorbent, vₘₐₓ. The relationship v=Smfvₘₐₓ=S/〈Mw〉, where S is the number of solute entities per adsorbent site, mf is the mass fraction of adsorption sites and 〈Mw〉 is the adsorbent's mass-average molar mass, is discussed. This relationship is applied to analysis of (1) different adsorption sites on a solid, municipal compost-derived HA and on a proposed HA building block, (2) adsorption of herbicide acifluorfen on a solid HA and (3) adsorption of herbicides alachlor and metachlor on activated charcoals. Practical applications of the relationship are listed.
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