INTERACTION OF METALS AND PROTONS WITH ALGAE .4. ION-EXCHANGE VS ADSORPTION MODELS AND A REASSESSMENT OF SCATCHARD PLOTS - ION-EXCHANGE RATES AND EQUILIBRIA COMPARED WITH CALCIUM ALGINATE
Rh. Crist et al., INTERACTION OF METALS AND PROTONS WITH ALGAE .4. ION-EXCHANGE VS ADSORPTION MODELS AND A REASSESSMENT OF SCATCHARD PLOTS - ION-EXCHANGE RATES AND EQUILIBRIA COMPARED WITH CALCIUM ALGINATE, Environmental science & technology, 28(11), 1994, pp. 1859-1866
Sorption is frequently described in terms of adsorption isotherms (Lan
gmuir, Freundlich), but metal sorption on algae has been recognized to
be an exchange process where sorption is accompanied by the release o
f ions. An experimental ion-exchange constant for Zn displacing Ca fro
m Rhizoclonium was used to calculate concentrations over a wide enough
range to assess interpretations given to Langmuir and Scatchard plots
. While such plots may be convenient to describe maximum sorption and
systematize data, misinterpretations can occur at low metal concentrat
ions in an ion-exchange system. Values of K-ex for seven metals displa
cing Ca from Vaucheria correlated with formation constants of the meta
l acetates and with K-ex of the metals on calcium alginate, a model of
cell wall components, indicating the bonding of metals to carboxylate
groups of algal cell walls. Rates of metal desorption from Vaucheria
by EDTA-Li are inversely related to binding strengths, and rates of Cd
desorption from calcium alginate justify assumptions in the K-ex expr
ession. Removal of Cd with a calcium alginate column was investigated
for possible application to water treatment.