Fast Method to Determine Solubility Products of Sparingly Soluble Salts by Combining Titration Experiments and Thermodynamic Modeling: A Case Study on the Example of Cu/Zn Based Catalyst Precursors and Ni/Mn Based Precursors for Cathode Active Material

Solubility products are essential for the thermodynamic and kinetic modeling of (co-)precipitation processes. However, due to the complexity in the determination of solubility products of sparingly soluble salts, models often rely on the limited data for minerals, which may differ in the elemental composition or crystallographic properties when compared to their synthetic counterparts. Thus, we developed an easily accessible method to determine solubility products for synthetic precipitate phases as a function of the temperature and elemental composition based on simple titration studies and a thermodynamic equilibrium model. By applying this method, we determined solubility products for the synthetic precursor phase zincian georgeite ([Cu,Zn]2CO3(OH)2), which is relevant in the preparation of Cu/Zn-based catalysts, as a function of temperature and its Zn fraction. The data significantly differ from the data for the mineral rosasite (Cu1.16Zn0.84CO3(OH)2) which is used so far, and applying the new data resulted in an improved model accuracy. Furthermore, we identified Ni8(OH)14SO4 as a phase that is possibly responsible for the incorporation of sulfate ions into the precursor for cathode active material (PCAM) and determined its solubility product. Using these results, we were able to predict the phase composition of Ni/Mn-based PCAM and the degree of sulfate incorporation as a function of pH. Both examples show the applicability and relevance of our method to determine solubility products for the modeling of industrial relevant (co-)precipitation processes.