The adsorption of propionic acid and benzoic acid on anion-exchange resins
was analyzed, and an adsorption equilibrium equation of carboxylic acids wa
s proposed. The adsorption of carboxylic acids on the anion-exchange resins
was considered to be the sum of the physical adsorption of the molecule an
d the ion-exchange adsorption of the ion, which were independent of each ot
her. For the physical adsorption of carboxylic acids, it was conformed to t
he Freundlich equation. For the ion-exchange adsorption of carboxylate ions
, the equilibrium equation corresponded well with the experimental results
for wide ranges of concentration and pH. The equation contains a selectivit
y coefficient S-Cl(A), for the chloride ion versus the carboxylate ion, whi
ch was considered essentially a constant. The influent of the bicarbonate i
on from carbon dioxide in air could also be expressed by the additional equ
ilibrium equation with the selectivity coefficient S-Cl(HCO3) for the chlor
ide ion versus the bicarbonate ion. Consequently, an adsorption equilibrium
equation can estimate the equilibrium adsorption amounts. Even the effect
of a coexisting bicarbonate ion is inconsequential when the parameters of t
he Freundlich isotherm equation and the selectivity coefficients of the car
boxylate ion and the bicarbonate ion in each resin are determined in advanc
e. (C) 2001 Academic Press.