Common potholes in modeling solid–liquid reactions—methods for avoiding them

The reaction rate of a solid in fluids depends on the reactive surface area rather than its concentration. Even though, analytical techniques have been developed enormously during the past decades, the reliable quantification of solid surface areas during are action still remains a challenge. Due to this, still today indirect methods such as test plots play a key role in determining reaction mechanisms and kinetics. The modeling of solid-liquid reactions is a challenge as several assumptions and simplifications need to be made and distinguishing between different hypothesis is not always straight forward. The influence of the particle size distribution (PSD) and the change in the morphology of the solid phase during the reaction are one of the most crucial factors in determining the kinetics, as they are directly related to the quantification of the reactive surface area. Neglecting to consider these factors in modeling can cause misleading conclusions and wrongful parameter estimation with traditional methodology.Techniques for evaluation when it is adequate to use the traditional methodologies and when these factors need to be accounted for are provided in the current work. If the particle size distribution is close to the Gaussian distribution and if the particles are not very rough or porous, the traditional modeling practices can soundly be used. These properties are measured and quantified with the help of a variation coefficient (PSD) and a shape factor (particle morphology). It is demonstrated that how these factors influence the results obtained with traditional approaches. A practical technique for implementing the PSD into kinetic models by using the Gamma distribution is provided. Moreover, a method for taking into account different particle morphologies with the help of a shape factor and solid phase exponents is presented. The dissolution of gibbsite in NaOH is used as an example case. The methodology can be extended to unconventional changes in particle morphology during the reaction as well as different reaction mechanisms, e. g. product layer formation.