KINETICS OF DEHYDRATION OF CALCIUM-OXALATE TRIHYDRATE CRYSTALS IN AQUEOUS-SOLUTION

The dehydration of calcium oxalate trihydrate to the stable thermodynamic monohydrate form was studied in aqueous solutions at various supersaturations in the temperature range 25-40.degree. C. Following growth and agglomeration of the trihydrate crystals, solid state nucleation and growth of calcium oxalate monohydrate occurs. The concluding processes involve solution growth and aging of the newly formed monohydrate crystals and the overall dehydration process has an approximate activation energy of 45 kcal mol-1. Calcium oxalate dihydrate was not involved in the transformation process. Sodium pyrophosphate and certain diphosphonates inhibited the solid state formation of calcium oxalate monohydrate and, alternatively, the stability and dissolution of the trihydrate crystals were found to be important factors. The relevancy of these processes to urinary calculi formation is discussed.