Crystallization of calcium oxalate in the presence of sodium dodecyl sulphate. Quantitative assessment of the effect of the surfactant on crystal growth and aggregation

Abstract

A quantitative treatment of the influence of sodium dodecyl sulphate, (Na(C12H25SO4)2; NaDS) on the crystal growth and aggregation of calcium oxalates in spontaneously precipitating system is given. The experiments are carried out under the conditions close to those in urine of stone-formers (310 K, pH=6.5, ionic strength I=0.3 mol dm−3, molar ratio c init (Ca)/c init (C2O4)=33.3). The formation of solid particles (crystal size distribution, CSD) was followed by Coulter counter. Standard methods for crystal phase identification were applied (thermogravimetric analysis, x-ray diffraction, optical microscopy). NaDS inhibits the crystal growth process; the intensity of the effect seems to be concentration dependent. The order of reaction (p) increases with increasing concentration of NaDS and assumes following values: \(p_{NaDS_1 } = 8.5, p_{NaDS_2 } = 11.4\), and \(p_{NaDS_3 } = 11.9\). While for the control system (without NaDS) the integration of the growth units into kinks is the rate determining process, in the presence of NaDS crystal growth is controlled by surface adsorption.