Many researchers use "traditional" Langmuir, Freundlich and other methods to model the equilibrium, even when mechanism is suggested to be ion-exchange and more a competitive due to the nature of the solid.
Dear David,
The main reason for this is because it´s a simpler approach and it works rather well in a number of cases of practical importance.
Yes because of their simplicity, most researchers use them. I noticed some researchers used them even in precipitation and some in ion-exchange, I think the researcher should find firstly the mechanism of removal and decide latter to use them or not.
One example is the defluoridation by calcined gypsum, I published a paper showing that the mechanism is precipitation even some others dealt with as adsorption. See this paper: Advances in Environmental Research, Vol. 2, No. 1 (2013) 35-49.
One basic reason why researchers model ion-exchange is that the same reactive and active sites on surfaces of adsorbents are considered to be accessible for both modes of uptake. Therefore, the ratio of the uptake of the solute via molecular adsorption and ion exchange depends on the solution pH. However, some researchers do not distinguish between molecular adsorption and ion exchange depending on the pH of interest. It is safer to model the reaction mechanism and validate which mode of uptake predominates.
Dear David
May I refer you to Helfferich "Ion Exchange" published by McGraw -Hill in 1962! Page 193 where he points out that use of Langmuir and Freundlich equations to interpret
ion exchange "are but of historic interest". The correct approach is that used by Barrer and Rees. Please contact me [email protected] if I can be of further help. I am still active in ion-exchange after some 60 years experience and rejecting papers which persist in these totally incorrect approaches.!!.I live near Blackburn and collaborate with Dr Linda Campbell in Manchester's Dept of Earth Sciences
Alan
Prof Alan Dyer. RSC Award in Chromatography and Separation Science. 1994