Precipitation Of Calcium Oxalate Monohydrate Research Articles

Kinetics of the crystallisation of calcium oxalate monohydrate

The kinetics of precipitation of calcium oxalate monohydrate have been studied conductometrically at 298 K for both spontaneous and seeded growth systems. The rate of growth follows a quadratic dependence upon the relative supersaturation, which suggests a surface-controlled growth mechanism. This rate equation holds fairly well for the various solid/solution ratios used in the range of 2.35–10.18 relative supersaturation and for seed concentrations of 0–200 mg dm–3. The effect of sodium tripolyphosphate and phosphonate additives on the precipitation kinetics of calcium oxalate in the absence and presence of well characterised seeds has been investigated at various levels of additive concentration. The inhibiting activity of these additives is discussed in relation to the surface characteristics of the inoculated seeds and structural features of the additive molecules. The fit of experimental data to the Langmuir adsorption isotherm supports a mechanism of inhibition through molecular adsorption of the foreign ions on the surface of the growing crystals.

Triamterene and Renal Stone Formation

We investigated the influence of triamterene (TA), and its metabolites parahydroxytriamterene (PHTAS), and parahydroxytriamterene sulfate (PHTAS) on the nucleation and crystal growth of calcium oxalate monohydrate (COM), in supersaturated solution at 37C using a new constant composition technique. The spontaneous precipitation of COM is preceded by induction periods which decrease with increasing supersaturation. The addition of the triamterene seed materials substantially reduces these delay periods and induces the crystal growth of COM. Specific surface area and scanning electron microscopic results indicate that the seed materials act as sources for the heterogeneous nucleation of COM. In addition, the surface of the more crystalline PHTAS appears to offer sites from which COM crystals can develop as well formed rosettes. This evidence suggests that in addition to triamterene renal stone formation, TA and its metabolites may catalyze the precipitation of other stone forming minerals with which urines may be supersaturated.