Experimental and calculated solubilities of magnesium sulfate monohydrate in aqueous nitric acid and related solubilities, 200–350°C; ionization constants of nitric acid at 300–370°C

Abstract

Of interest in predicting high temperature phase equilibria for geothermal power, desalination, general hydrothermal and other evaluations, solubilities of magnesium sulfate monohydrate have been determined in 0–1 m aqueous nitric acid solutions at 200–350°C. These solubilities also have been calculated independently, with good agreement to 300°C, by applying earlier published values of solubility product constants ( K sp ) of the salt, second ionization constants ( K 2) of sulfuric acid, and ionization constants ( K n ) of nitric acid. The experimental solubilities, when treated by iterative equations and the resulting values of solubility products ( Q sp ) extrapolated to zero ionic strength, yielded values of K sp essentially identical with those obtained from earlier solubility studies in aqueous sulfuric acid. From the experimental results at 350°C, a value of K n was obtained that resolved its earlier uncertainty at this temperature and allowed revised thermodynamic functions to be presented at 300–370°C. Comparative solubilities of magnesium sulfate monohydrate in aqueous sodium nitrate solutions and of magnesium and calcium hydroxides in nitric acid are included.