The modified Song isotherm model: application to multisolute sorption of phenols in organoclays using the ideal adsorbed solution theory

ABSTRACT

The three-parameter (K, b, and n) Song isotherm model was slightly modified to make it possible to obtain analytical integration of the spreading pressure integral. The modified Song model (MSM) allows more efficient and accurate calculation of the ideal adsorbed solution theory (IAST). The MSM also satisfies the Henry’s law and the Freundlich model at low and high concentrations, respectively, and reverts to the Langmuir and the linear models when n equals zero and one, respectively. Approximate values of each parameter could be estimated from a plot of log (q/c) versus log c; the partition coefficient in the Henry’s law region (K) and the Freundlich index (n) can be estimated from the ordinate value of the low-concentration asymptote and the slope of the high-concentration asymptote, respectively, and the parameter (b) can be estimated from the solution-phase concentration of the intersection point of the two asymptotes. The MSM was fitted to the single-solute sorption of 2-chloro-, 3-cyano-, and 4-nitrophenol onto montmorillonites modified with either HDTMA cation or TMA/HDTMA dual cations. The ideal adsorbed solution theory (IAST) combined with either dual-mode model, Khan model or MSM as a single-solute isotherm model was used to predict three bisolute and one trisolute sorption to organoclays. The Sheindorf-Rebhun-Sheintuch (SRS) and Murali-Aylmore (M-A) were also used to predict bisolute sorption to organoclays. The IAST predictions were generally in good agreement with the multisolute sorption data. The advantages of MSM over other three-parameter models were fully discussed.

GRAPHICAL ABSTRACT

KEYWORDS:

• Competition modelling
• ideal adsorbed solution theory (IAST)
• modified Song isotherm model
• organoclay
• spreading pressure

Acknowledgements

This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education [2016R1D1A3B03935482] and Korea Environment Industry & Technology Institute (KEITI) through the Chemical Accident Prevention Technology Development Project, funded by Korea Ministry of Environment (MOE) [2019001960002].

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Dong-Ik Song http://orcid.org/0000-0002-2207-3038

Jiyeon Choi http://orcid.org/0000-0003-3838-5025

Won Sik Shin http://orcid.org/0000-0001-6829-8825