ORTHOKINETIC AGGREGATION DURING PRECIPITATION - A COMPUTATIONAL MODELFOR CALCIUM-OXALATE MONOHYDRATE

Smoluchowski's theory for orthokinetic coagulation of spheres is exten ded to aggregation during precipitation of calcium oxalate monohydrate . Physical models for hydrodynamics and deposition ill a binary aggreg ation event are combined to determine the success of collisions with d ifferent orientations to the shear field. Consequently, an efficiency term is introduced that represents the proportion of collisions result ing in aggregates. The model is used to investigate the effect of shea r rare: crystal size and ion concentration on the aggregation rate con stant, beta(agg). A maximum in beta(agg) is observed with shear rate t hat corresponds to two opposing effects; increasing rate of collisions and increasing tensile stress between crystals. By contrast Smoluchow ski's theory predicts direct proportionality. Compared with Smoluchows ki's theory, beta(agg) is relatively insensitive to crystal size. Fina lly, beta(agg) is highly sensitive to solution ion concentration, an e ffect Smoluchowski's theory does not consider.