THE KINETICS OF CRYSTAL GROWTH OF CALCIUM OXALATE

Calcium oxalate is a major component of renal stones which crystallize in the urinary tract. The kinetics of crystal growth of calcium oxalate was studied using two highly reproducible techniques. In the first, well-characterized seed material was added to stable supersaturated solutions of calcium oxalate and the rate of growth was followed by monitoring the calcium concentration. In order to model more closely the relatively constant concentrations encountered in the body, a second technique was developed using a calcium electrode to control, automatically, the addition of the calcium and oxalate ions to the system as the crystallization reaction proceeds. The solid phases were examined by x-ray powder diffraction, scanning electron microscopy and by particle size distribution. Since calcium oxalate can exist as the mono-, di- or trihydrate, the interconversion processes were investigated. The crystallization reactions were studied using various seed materials such as the synthetic hydrates of varying morphology and natural stone materials. Different solution compositions of varying degrees of supersaturation, ionic strength and calcium to oxalate molar ratio were also studied. The influence of various potential inhibitors, including natural inhibitors found in the urine, on the crystallization of the calcium oxalate hydrate phases was investigated.