Kinetics of precipitation of calcium oxalates and phosphates from solutions supersaturated with both solid phases

Abstract

The urine of patients with disorders of calcium metabolism is frequently supersaturated with calcium oxalates and phosphates (6), a state that increases the tendency of such patients to form renal stones. Such stones, containing both calcium oxalates and phosphates, are commonly observed (1). Several studies on crystal growth of calcium oxalates upon seed crystals of calcium phosphates and vice versa have been reported (3,5), but no kinetic study on the spontaneous precipitation of both solid phases from supersaturated solutions has so far been published. Recent observations made under conditions of metastable equilibrium (2) suggest that phosphate ions retard crystal growth and delay equilibration of the calcium oxalate phases. In this paper, the kinetics of precipitation of calcium oxalate trihydrate (COT) and calcium hydrogenphosphate dihydrate, (DCPD) from unseeded solutions supersaturated to both solid phases are described. Attention is given to the mutual interaction of the solid phases and to the influence of excess phosphate ions on the kinetics of COT crystal growth.