Precipitation of calcium oxalate and calcium phosphate in the presence of uric acid

The influence of uric acid on the precipitation of calcium oxalate and calcium phosphate from electrolyte solutions with pH(i) 6.5, ionic strength 0.3 mol dm(-3) and temperature 370 K, mimicking urinary conditions, has been investigated. The initial concentrations of precipitation components in the system were as follows: c(CaCl2) = 5 x 10(-3)-1 x 10(-1) mol dm(-3), c(H(2)Ox) = 3 x 10(-4)-5 x 10(-4) mol dm(-3); c(H2U) = 1.5 x 10(-4)-6 x 10(-3) mol dm(-3), and c(H3PO4) = 2.5 x 10(-2) mol dm(-3). Precipitates of calcium oxalate monohydrate, calcium hydrogenphosphate dihydrate, tri calcium phosphate trihydrate and sodium hydrogenurate monohydrate were characterized by X-ray diffraction, FTIR spectroscopy, and chemical and thermogravimetric analyses. (C) 1997 Elsevier Science B.V.