CALCIUM-OXALATE MONOHYDRATE PRECIPITATION INVESTIGATION BY THERMOMETRIC METHOD

Calcium oxalate monohydrate (COM) precipitation from diluted solutions of 100 mol M-3 ionic strength at 25-degrees-C was studied by an isoperibolic reaction twin calorimeter. The molar reaction enthalpy was determined as - 17.5 kJ mol-1. Results achieved with a pure system were highly reproducible. Citrate, pyrophosphate and phytate retard COM precipitation that is manifested mainly by an induction period appearance and a decrease of the initial precipitation rate. Effect of the studied impurities on individual precipitation experiments carried out under identical conditions was to some extent ''random'', i.e. the reaction extent reached at arbitrary time considerably differed for individual experiments. Impurity effectiveness in retarding spontaneous precipitation increases in succession citrate < pyrophosphate < phytate.