Modeling Urotropine adsorption thermodynamic on kaolinite particles

This research looked at how much Urotropine can be adsorbed by kaolinite particles and the thermodynamics of that process. Since Urotropine is important for gel injections and stabilizing clay, understanding how it adsorbs onto clay can help us accurately model various related processes. Initially, X-ray diffraction (XRD) analysis was conducted on kaolinite samples, verifying their high purity (97%) and correct crystal structure. Subsequent experiments focused on the adsorption of Urotropine from solutions of varying concentrations onto the kaolinite particles. By monitoring Urotropine's concentration in the aqueous solution with a UV device, we observed that kaolinite efficiently adsorbs Urotropine, reaching an adsorption capacity of 112 mg/g. Notably, the Langmuir adsorption isotherm model provided the best fit for predicting this Urotropine adsorption behavior. Further experiments at elevated temperatures, coupled with thermodynamic modeling, revealed an enthalpy of 9534 J/mole, confirming the endothermic nature of the adsorption. The consistently negative Gibbs free energy (∆G°) across all temperatures indicated that Urotropine adsorption on kaolinite is spontaneous. Core flooding experiments, using a 10⁵ ppm Urotropine solution injected into kaolinite sand-packs, also confirmed the endothermic reaction. However, these experiments showed a significantly lower adsorption capacity compared to batch experiments. This reduction is attributed to the complexity of the porous media and the presence of inaccessible adsorption sites within the sand-packs.