Kinetic Study of Denatonium Sorption to Smectite Clay Minerals

Abstract

The denatonium cation, as a benzoate salt, is the most bitter cation known to modern society and is frequently added to consumer products to reduce accidental and intentional consumption by humans and animals. Denatonium can enter the environment by accidental discharges, potentially rendering water supplies undrinkable. Interactions of denatonium with soil components (i.e., smectite minerals) ultimately control the environmental fate of denatonium, but the current literature is devoid of studies that evaluate denatonium sorption to smectite minerals. This study investigated the mechanism and kinetics of denatonium sorption to smectite clay minerals as a function of smectite type, temperature, pH and ionic strength. Uptake by synthetic mica montmorillonite (Syn-1), Wyoming montmorillonite (SWy-2), and Texas montmorillonite (STx-1b) at 305K was rapid, with equilibrium being reached within 2 min for all clays. Complete removal of denatonium was observed for STx-1b at pH 6.9, while partial removal was observed for Syn-1 and SWy-2. Kinetic behavior of SWy-2 and Syn-1 is consistent with a pseudo-second-order model at 305K. An activation energy of + 25.9 kJ/mol was obtained for sorption to Syn-1 and was independent of temperature between 286K and 338K. Activation-free energy (DG*), activation enthalpy (DH*), and activation entropy (DS*) for Syn-1 were found to be + 62.91 kJ/mol, + 23.36 kJ/mol, and -0.130 kJ/(K$mol), respectively. Sorption capacities at pH 3.6, 6.9, and 8.2 were constant at 1.3 · 10 -2 g denatonium/g clay; however, the kinetic rate constant increased by 56%, going from acidic to basic solution conditions. Distribution coefficients were negatively correlated with ionic strength, suggesting cation exchange. Collectively, results suggested that smectite minerals can serve as efficient sinks for denatonium cations. This is much-needed information for agencies developing regulations regarding denatonium usage and for water treatment professionals who may ultimately have to treat denatonium-impacted water supplies.

Ciprofloxacin intercalated in fluorohectorite clay: identical pure drug activity and toxicity with higher adsorption and controlled release rate

“…for the sorption of denatonium onto the synthetic smectite montmorillonite (25.9 kJ mol −1 ). 48 Furthermore, the obtained value is within the range of ion exchange in mesoporous and macro porous materials (24–40 kJ mol −1 ). 49 Together these findings support the idea that the CIPRO's release is governed by cation exchange.…”

Activated Carbon and Clay Minerals for the Sorptive Removal of Denatonium Ions from Denatonium Benzoate Solutions

“…activated carbon or clay minerals) to remove aqueous denatonium benzoate (DB) prior to DB's widespread use and likely introduction into water and wastewater. Recently, our team evaluated the kinetics of denatonium ion sorption to smectite minerals and determined that 1) sorption was rapid (and near complete) when using 200 ppm initial concentrations of DB and 2) sorption likely proceeded via a cation exchange process [21].…”