The Dissolution of Calcium Oxalate Kidney Stones. A Kinetic Study

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Abstract
The rates of dissolution of calcium oxalate monohydrate (COM) and dihydrate (COD) and of [human] kidney stones containing these phases was studied in 0.15 M NaCl solution at 37C. In contrast to the diffusion controlled dissolution of the pure synthetic phases, the kidney stones appear to dissolve considerably more slowly by a predominantly surface controlled process, independent of fluid dynamics. The differences between the dissolution rates of the synthetic and stone minerals become greater as the reactions approach equilibrium. As was found for the COD mineral, the dihydrate stone material transforms into the thermodynamically more stable monohydrate phase. The COD stone phase is significantly stabilized in the presence of inhibitors such as polyphosphate and Mg. This may be an important factor in explaining the observed presence of dihydrate as a surface phase in many reported cases of calcium oxalate lithiasis.