United States Patent Office Patented Nov
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3,848,055 United States Patent Office Patented Nov. 12, 1974 2 (f) recovering strontium values from the separated solu 3,848,055 tion. EXTRACTION OF STRONTUMWALUES DETAILED DESCRIPTION FROM CELESTTE Allan C. Kelly, Pleasanton, Calif., assignor to Kaiser The celestite used may be either a natural ore, or an Aluminum & Chemical Corporation, Oakland, Calif. 5 ore which has been beneficiated, for example by froth No Drawing. Filed July 13, 1973, Ser. No. 379,125 flotation. Preferably all the celestite passes a 100 mesh Int. Cl. C22b 3/00, 29/00, C01f 1/00, 11/00 screen and at least 30% passes a 325 mesh screen. This U.S. C. 423-158 0 Clains sizing may be achieved by grinding a high purity natural O ore, or may result from the grinding performed prior to ABSTRACT OF THE DISCLOSURE froth flotation of a lower grade ore. It will be under stood that generally the finer the celestite ore, the more Strontium hydroxide is produced directly from celestite rapidly it will react with the sodium hydroxide to form (SrSO4) by forming a slurry of finely divided celestite in strontium hydroxide. a sodium hydroxide solution of such concentration that The amount of the sodium hydroxide solution used to it contains at least 10 g./l. NaOH after reaction of the 15 slurry the celestite will be adequate to produce a readily celestite with sodium hydroxide to form strontium hy agitated slurry. While relatively dilute slurries can be used, droxide. The strontium hydroxide formed is washed to for efficiency one will use as high a concentration of solids remove any sodium sulfate also precipitated, and then as is consistent with getting good stirring action. For ex dissolved in hot water to separate solid impurities. ample, a slurry of 100 grams of celestite ore in 1 liter of 20 sodium hydroxide solution has been successfully used. BACKGROUND OF THE INVENTION The concentration of the sodium hydroxide solution is chosen so that after the strontium sulfate and other con It has been known for many years to extract strontium stituents (for example BaSO4) in the celestite ore have compounds such as the oxide, carbonate, hydroxide, and reacted with the sodium hydroxide to form strontium nitrate, from the strontium sulfate (SrSO) contained in 25 hydroxide or other hydroxides (for example Ba(OH)2), celestite ore. However, recently developed uses for stron the concentration of the solution will still be at least 10 tium compounds, for example, in glass for color television g./1. NaOH, and preferably will be at least 30 g./I. NaOH. picture tubes and in permanent ceramic magnets, have Again, for the sake of efficiency, much higher concentra caused a search for more efficient methods of extracting tions, for example 250 g./l., will ordinarily be used. strontium values from natural ores, and for methods 30 The reason for maintaining a certain minimum concen which can be used to extract strontium from lower grade tration of sodium hydroxide in the aqueous solution is OS, that the solubility of strontium hydroxide in sodium hy Prior processes for extracting strontium values from droxide solution is much lower at higher concentrations, celestite ore include the black ash process, wherein celes being for example about 0.5 g./l. at an NaOH concen tite is calcined in the presence of carbon to form stron 3 5 tium sulfide which is then dissolved in water. Another tration of 30 g./I. and as low as 0.1 g/l. at an NaOH prior process converts strontium sulfate to strontium concentration of 300 g/l. carbonate by reaction with sodium carbonate, and purifies Digestion of the celestite ore is carried out at a tem the strontium carbonate by calcination and slaking the perature below the boiling point of water, preferably be 40 low 50° C. and most preferably below 20° C., since the resulting SrO to form strontium hydroxide. It is also solubility of strontium hydroxide increases rapidly with known to dissolve barium or strontium sulfate in fused increasing temperature. For example it is about 25 g./I. in sodium hydroxide at elevated temperatures, the resulting 50° C. water, but less than 10 g/l. in 20° C. water. The barium or strontium hydroxide being extracted from the objective of the digestion reaction is to precipitate as solidified fusion with an ethylene glycol and methanol much strontium hydroxide as possible, probably as the solvent, as set forth in U.S. Pat. 2,225,633. octahydrate, while at the same time taking into solution These previous processes all involve the use of rela as much sodium sulfate (Na2SO4) as possible. tively high temperatures, whereas the process of this in Although the solubility of sodium sulfate in a sodium vention enables the production of strontium hydroxide hydroxide solution is much greater than that of strontium from celestite by aqueous processes carried out below hydroxide, it is still relatively limited and also decreases the temperature of boiling water. 50 as the concentration of the sodium hydroxide solution in SUMMARY OF THE INVENTION creases. For example, at 25 C. the solubility of sodium It has now been found, according to this invention, sulfate in 150 g./l. NaOH is about 200 g/l. and drops to that strontium hydroxide can be produced from celestite about 50 g./l. for a sodium hydroxide solution of 300 by g/l. concentration. Accordingly, if it is desired that all the sodium sulfate produced by digestion of the celestite (a) reacting a finely divided celestite with sufficient aque go into solution, relatively dilute sodium hydroxide, within ous sodium hydroxide solution to form a slurry, the the limits set forth above, will be used. However, as previ solution containing sufficient NaOH to maintain a con ously explained, it will generally be more efficient to oper centration of at least 10 g/l. NaOH after reaction of ate at higher sodium hydroxide concentrations, and under the sodium hydroxide in the solution with the celestite 60 these conditions the solution will become saturated with to form strontium hydroxide, the reaction being carried sodium sulfate, the excess sodium sulfate produced being out at a temperature below the boiling point of water; precipitated along with the solid strontium hydroxide and (b) separating the solid material resulting from step (a) undigested impurities from the celestite ore. from the aqueous solution; It is also possible to add a source of sodium ion, for (c) washing the solid material separated in step (b) to 65 example sodium chloride, to the sodium hydroxide solu dissolve and remove any solid sodium sulfate present; tion to increase the sodium ion concentration and thus (d) dissolving the strontium hydroxide in the washed salt out solid sodium sulfate, as is well known. The ad solid material produced in step (c) in Water at a tem vantage of this approach is that sodium chloride is a perature of at least 90° C.; much cheaper source of sodium ion than is sodium hy (e) separating the strontium hydroxide solution produced 70 droxide. However, the concentration of sodium hydroxide in step (d) from the remaining solids; and specified above must be maintained in order to prevent 3,848,055 3 4 any significant amounts of strontium hydroxide remaining dried solids were recovered. About 10 g. of the dried in solution after the digestion. solids were added to 100 ml. of 300 g./I. NaOH, mixed, In addition to promoting the rate of reaction by using centrifuged, and the clear liquor decanted. This was re finely divided celestite, it has been found that carrying peated with NaOH solution, 0° C. Water, and then twice out the reaction in the presence of attrition, for example with alcohol. After this washing the solids were leached in a rotating chamber containing rods or balls, also en 5 with hot water, filtered, and repeatedly washed with hot hances the rate of reaction. (80-90° C.) water, using a total of about 1 liter. The After the digestion reaction, the sodium hydroxide leachate was carbonated with CO2 to produce solid stron solution is separated from the solids, principally precipi tium carbonate, cooled to 16° C. and the solids filtered, tated strontium hydroxide (probably in the form of the O producing 4.4 g. SrCO3. Calculation indicated that about octahydrate), solid impurities, and any excess sodium 94% of the strontium values in the celestite digested were sulfate produced. While it is possible to discard the spent recovered in the strontium carbonate. It can also be cal hydroxide solution, and use fresh solution for the next culated that the 60 g. of solids obtained by digestion of batch of ore processed, it will generally be found more 40 g. of ore contained about 50 g. Sr(OH)28H2O, 5 g. economic to reuse the solution after adding sodium hy 5 Na2SO4, and 5 g. impurities. droxide to make up for that consumed in the reaction The careful washings of the example were used because and, if desired, removing sodium sulfate from the solu it was desired to make a quantitative determination of tion by known methods, for example by evaporating the the yield of the process; in a commercial operation, less solution to concentrate it and salt out the Na2SO4. care would be needed since quantitative recovery is not It will be understood that, if desired, a sodium hy 20 necessary. droxide solution which is already saturated in sodium In the specification and claims, percentages and parts sulfate can be used for the digestion, in which case all are by weight unless otherwise indicated. Mesh sizes the sodium sulfate produced will be precipitated along referred to herein are Tyler standard screen sizes which with the strontium hydroxide.