Preparation and characterization of calcium oxalate dihydrate seeds suitable for crystal growth kinetic analyses

This work is focused on a practical procedure by which pure and well-formed COD crystals were obtained. The effect of different type of stirring on the precipitation process and properties of COD crystals is studied. Mechanical and magnetic stirring are two common stirring types for precipitation of calcium oxalate and method using ultrasonic irradiation is newly described. The precipitation processes are systematically investigated varying solution stoichiometry (defined as a ratio of concentrations of the constituent ions in solution, (Ca+/(C2O42−) and concentration of additive (citrate). The differences of the structure, morphology and crystals properties between precipitates were investigated by SEM, FT-IR, TG and PXRD. In the ultrasonically stirred systems, COD was the only precipitated phase regardless of solution stoichiometry. Pure and well formed COD crystals with well-formed planes were obtained in the system with c(Ca2+)/c(C2O42−) = 3.86 and c(citrate) = 0.009 mol dm−3. The results demonstrate that ultrasonically assisted precipitation could be a new way in synthesis of COD crystals having different potential applications (in the fields of medicine and biotechnology).