Optimizing Conditions for the Formation of Calcium Oxalate Trihydrate Using Response Surface Methodology

Abstract

Calcium oxalate (CaOx), the main component of kidney stones, occurs in several hydrated forms, among which calcium oxalate trihydrate (COT) is a rare and metastable phase believed to act as a transient precursor to the thermodynamically stable monohydrate. In this study, Response Surface Methodology (RSM), a statistical data analysis method that combines a specific experimental design with mathematical modeling, was applied to quantitatively evaluate and predict the influence of temperature, pH, and ionic strength on the formation of COT. The resulting precipitates were characterized using optical microscopy, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and powder X-ray diffraction (PXRD). The results demonstrate that COT formation is favored at moderate temperatures, while higher temperatures promote the formation of calcium oxalate monohydrate (COM), whereas ionic strength exerts no significant effect under the investigated conditions. Overall, temperature was identified as the dominant parameter governing CaOx hydrate phase selection.