Thermodynamic and kinetic parameters of iodine extraction from chloride aqueous solutions

Abstract

Extraction is a versatile and relatively simple method for extracting rare and scattered elements, producing good results at minimal expenses in terms of reagents and equipment. Information about the thermal effects and kinetic dependencies of the extraction process is essential for predicting and counteracting fluctuations in external conditions. In this work, the thermodynamic and kinetic parameters of the iodine extraction process were studied using model solutions that contained sodium chloride with an ionic strength of 0–5 mol/l as a background mineralization. This composition closely corresponds to natural and man-made waters of oil and gas condensate fields. A mixture of tri-n-butyl phosphate and isooctane was used as the extractant. In order to evaluate thermodynamic parameters, extraction isotherms were constructed at temperatures of 278 and 288 K. For different background ionic strength values, equilibrium extraction parameters were determined, including the extraction degree, distribution coefficient and equilibrium constant, as well as changes in the enthalpy, entropy and Gibbs energy of the process. A study of the kinetic dependencies of iodine extraction from aqueous solutions under different ionic strength values at temperatures of 278, 288 and 293 K allowed the true and apparent orders of reaction to be established, along with the activation energy of the extraction process. Across the entire range of the studied ionic strength values, iodine extraction occurs spontaneously with high distribution coefficients and an extraction degree of over 86%. The kinetic parameters of the iodine extraction process (activation energy, temporal and concentration reaction order) indicate the diffusion nature of the rate-determining step, the presence of intermediate complexation stages and the absence of temperature effects on the reaction rate.