Urea hydrolysis in solutions from 100 to 150 °C: Thermokinetics and the influence of dissolved Ca2+, Mg2+, and Na+

Urea decomposes through hydrolysis when exposed to ureolytic enzymes, microorganisms, and/or sufficient heat, increasing carbonate alkalinity. By controlling hydrolysis, water-based fluids can be used to precipitate minerals such as calcium carbonate in engineered applications. In this study, thermokinetic data are presented for the hydrolysis of dissolved urea in solutions from 100 - 150 ˚C, with urea concentrations up to 3 M, including the effects of dissolved calcium, magnesium, and sodium. The data from direct urea measurements fit a first-order kinetic dependence on urea and are compared to existing literature. Above 110 °C, reaction rates were higher with 1 M urea than with 3 M urea. Calcium lowered the hydrolysis rate of urea. Magnesium and sodium had no apparent influence on hydrolysis rates. For all temperatures and solutions, the reaction half-life was less than three days, suggesting feasible controllability in environmental technologies such as engineered mineral precipitation or wastewater treatment.