Barium and Strontium Sulfate Decomposition in Aqueous Solution

Abstract

The decomposition of barium and strontium sulfates by the action of strong solutions of calcium chloride results in the formation of the soluble modification of anhydrite (CaSO,). Dilution of the reaction mass at this point with water results in immediate reversion to the initially reacting, materials, due to the reactivity of the soluble modification of the anhydrite. The soluble anhydrite is converted to the much less reactive insoluble modification HE production of inorganic salts is often carried out by ordinary double decompositions. Usually such T reactions, involving the formation of insoluble salts, are considered essentially quantitative in one direction. A few double decomposition reactions involving insoluble salts reverse their equilibrium position as the solution is changed from dilute to concentrated. Among them are barium sulfate and calcium nitrate in equilibrium with barium nitrate and calcium sulfate (6, l l ) , barium sulfate and calcium chloride in equilibrium with barium chloride and calcium sulfate (6), strontium sulfate and calcium nitrate in equilibrium with strontium nitrate and calcium sulfate (IO), and barium sulfate and an alkali carbonate in equilibrium with barium carbonate and an alkali sulfate ( l a ) .The change in equilibrium position as the solution medium is changed from dilute to concentrated has been studied in the Purdue Chemical Engineering Laboratories especially in the cases of barium and strontium sulfates decomposed by calcium chloride and calcium nitlate. As the solution is made more concentrated, the reaction proceeds farther in the direction of obtaining the soluble strontium and barium salts. Efforts to produce soluble strontium and barium compounds were reviewed in previous publications (4, 6, 7 ) . I n this work only enough water was used to make the ionic reaction possible. The consistency of the reaction mass was that of a thick mush.The experiments of Shreve and Toner (8) and Shreve and Watkins (9) indicated a possible mechanism for these equilibrium reactions. They and others observed that the solubility of calcium sulfate decreases with a rise in tempera-1 Present address, Standard Oil Company (InJiana:, Whiting, Ind. 1 After this work had been oompleted, a paper appeared on "Thermodynamic Properties of G y p~u m and Its Dehydration Products" [Kelley, Southard, and Anderson, U. S Bur. Mines, Tech. P a p e r 625 (1941) I. by heating the reaction products at elevated temperatures. This procedure makes practical the use of aqueous methanol as an extraction solvent for the recovery of the barium chloride made. Under these circumstances even water alone will extract most of the barium chloride initially formed before the insoluble anhydrite has had time to react. The effect of aqueous extractions on decompositions carried out by fusing the reactants also gives similar results*.ture, the solubilities of strontium and barium sulfates increase with a rise in temperature, calcium chloride lowers the solubility of calcium sulfate, and barium and strontium chlorides are...

Processing Media for Making Inorganic Chemicals. Use of Organic and Other Nonaqueous Solvents

“…The strontium reactions (4,22,23,25,31) give better conversions as a rule than the corresponding barium ones. The nitrates (22) of both barium and strontium are formed slightly more favorably than the chlorides.…”

“…The mechanism of these reactions depends on the change in the solubilities or the relative solubilities of the salts involved (27,22,25). The calcium sulfate is precipitated as anhydrite and its solubility decreases with rising temperature, while the solubilities of barium sulfate and strontium sulfate increase with rising temperatures (75).…”