CA1097029A - Recovery of strontium from strontium calcium loaded brine - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Strontium is recovered from a brine containing strontium and calcium salts in a Ca++/Sr++ molar ratio of greater than 20/1 by admixing- with the brine strontium sulfate seed and a water-soluble sulfate, and recovering the thus produced strontium sulfate. The soluble sulfate must be more soluble in the brine than strontium sulfate.

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Description

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RECOVERY OF STRONTI~M FROM BR$NE T~AT
CONTAINS STRONTIUM AND CALCIU~

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This invention relates to the reco~ery of stson-tium compou~ds from brine that ~ontains ~issol~ed strontium salts and especially to the re~overy of strontium as a sulfate rom aqueous brine solut~ons which also contain 5 a very high proportion of aissolved c81c~um salts. Stron- -tium sulfate is a valuable product that is useful in the production of pyrotechnics, c~.am1cst..~s~.a~a ~er~
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- - In the past it has bee~ diffic~lt to extract : strontium val~es from ~rine th~t also contains certain aI~aline earth salts, particularly calci.~. Past methods that have at~empted to solve this p,obleM has ~een generall~
unsatisfactory. For example, ~.S. Patent No. 1,831,251, sued to Jones NoYember 10, 19~1, teaches a method whereby :~ ~trontium chloride is separated from brine~ that contain calcium chloride and magnesium c~lor~de by cool~ng the brine to ~ temperature ~elow 31C, or ju~t 9hort of ~he aturation point o~ calcium chloride,~ wh~le agitating.
Howe~er, this m~thod i5~disadvantageous in that a large amount of CaC12 precipitates~along with SrC12, so th~t in

2~ the procipitate~her~ is a 20 ~o 1 rat~o~of CaCl~ to SrC12.
Therefore, in order to 8eparate the CaC~ from the SrCl~

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~ .S. Patent ~o. 3,029,133, issued to Goodenouc~
Ap.ril 10, 1~62, teaches a method of obt~ining SrSO4 from S an inland brine that contains strontium and calcium salts.
In the process, the inlaRd brine is evaporated until mos-o~ the WaCl in the brine crystallizes ou~ of solution;
the brine is then cooled to 70C whereupon some tachhy-ite (2 MgC12 CaC12 12 H2O) crystallizes o.ut. The brine is ~h~n further cooled to 28.5C, at which temperature cæ -nallite t~Cl MgC12 6R2O) crystallizes out with a ~ubstan-tial portion of the SrC12. The carnallite crystals con-taininq the SrC12 are then washed with water to produce a brine c~ntaining calcium and strontium values with a Ca /Sx + molar ratio of approximately 2.7/1. A soluble sulfate is then admixed with this brine and the solutior, is heated. The reaction mixture of brine and soluble sulfa~e is then filtered to separate the Lmpur~ SrSO4 thus ~rm-e-d whi-ch-i~ h~n ~eache*-wi~ a-m~ al-ae~ h~
the method of U.S~ Patent No. 3,029,133 requires several ` ~ treatments of the bxine in order to reduce the molar ratio of Ca /Sr to below 20/1 and preferably below 7/1.

The pres~nt invention can be employed to extract strontium from brine that contAins a Ca+~/Sr++ molar ratio greater than ~0/1 and therefore the initial steps of the pzocess of U.S. Patent No, 3,029,133 can be eliminatad.
$hu~, brines containing high ratios of calcium to stron-tium values can be directly treated to recover strontium compound~.

$he present invention resi~es in a metho~ of recovering strontium as a sulfate.from a brine that con-tains strontium and calcium in a Ca~+~Sr~+ molar ratio of .
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~`~97Q~9 greater thall 20/1, ~-hich compri.ses mixing with the brine strontium sulfa~e seed and a sulfaLe chat is more soluble in water than i5 strontium sulfate, and recovering the strontium sulfate that is thereby produced.

This operation can ~e contlnuously repeated by adding the precipitate that is recovered from the preceding operation io new brine during the next run as seed.

Any sulfate that is more solubl.e in water than iæ SrSO4 is suitable faî use in the invention. Examples of sulfates that can be used in the practice of -this inven-tion ar~ calcium sulfate, sodium sulfate, magnesium sulfate, ammonium sulfate, and sulfuric acid.

The amount of sulfate added should be sufficient to ~emove the desired quan-tity of Sr from the brine and can be determined stoiclliometrically. The following equa-tions illustrate the reaction thought to take place between the strontium salts in the brine and sodium and magnesium sulfates:
tL) SrC12 + Na2SO4 _ ~ SrSO4 + 2NaCl ~ 2) SrC].2 + ~gSO4 ~ SrSO4 + MgCl~

s~ 20~ Depending upon the purpose and needs of the indi~idual practitioner of this invention, the amount of sulfate:that is used can vary significantly from the amount that:is stoichiometrically sufficient to react with and preclpitate:all:of the Sr~+ in the brine~ A very small 25~ amoùnt of:sulfate ~(e.g., less than lQ percent of the6~toi:chiometxlc~amount)~, when admixed with the brine and the~S:rSO~ .seed~, should~pr~eclpltate~a~corresponding molar amount~of SrS04~ For~practical~purposes, however, the OlO~F :
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recommended percent of the sulfate to employ is between 55 and 7S percel~t of the amount that is stochiometrically sufficient to react with the strontium.

The strontium sulfate seed is introduced into the reaction medium to promote the reaction of Sr~ with SO4 to form SrSO4. The seed is introduced lnto the reaction medium in particulate form, for instance by using the crystals of the mineral ce]estite. One method of introducing the seed i 5 to heat the seed to reflux in a Ca free brine and to mix this slurry with a brine which contains the Sr++ and Ca++ values.

The quantity of seed used has no effect en the yield of strontium precipitated from the brine, but it does affect the rate at which the Sr + is precipitated.
The amount of seed to be used can vary from about .05 percent to about 50 percent, by weight, of the brine.
Since the upper seed limit is 1000 times ~reater than the lower limit, it can be seen that the individual practi~
tioner will have a great deal of latitude in determining which amount of seed is best for his purposes.
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At atmospheric pressure this invention can be practiced within a temperature range between the freezing point and the boiling point of the brine. As the pressure is~increased, the upper temperature limit likewise increases.
For instance, at a pressure of 50 psig the reaction will take place at temperatures up to about 150C. However, it is preferred to conduct the reaction at a temperature within a range of from about 60C to about 105C at atmos- -pheric pressure. Temperatures below 60C will not have 30~ any effect on the yield of the strontium precipitated ` but~do require lon~ reaction times. ~As the temperature inareases so will the reaction rate, which can be further increased if the~reaction components are put under pres~
sure while the temperature is raised.
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There is no specific order in which the soluble sulfate, SrSO4 seed, and brine are to be mixed. More-over, once the reaction components are mixed there are a variety of methods by which this in~ention can be practiced.
For instance, Example 1 illustrates a continuous process whereby the precipitate from a preceding run is added to the next run as seed, to be thereby mixed with fresh brine and additional soluble sulfate. Othe;^ methods of prac-ticing this invention can be seen in the examples discussed below.

The SrSO4 precipitate can be recovered in any of a number of ways that are well-known in t~le art, such as by filtering techniques or settling chambers. Those skilled in the art can readily determine which method of recovery i5 best for their particular purposes.

The following examples illustrate the present invention.

Example 1 A 500 ml sample of brine which contains 0.26 weight percent Sr++ and 3.3 weight percent Ca++ was heated to a temperature of 95C. 100 grams celest~te and 12.5 ml of 15.5 weight percent Na2SO4 (87 percent o~ the sul~ate ;~ needed to precipitate all the Sr~+ in the brine~ were then mixed with the brine. The brine was stirred for two minutes 25 ~ and then filtered~. For the next run, the precipitate (102.45 ` ~ grams) from the above run wa~ added to 500 ml of ~resh bxine as seed along with an additional 12.5 ml of 15.5 weight perGent Na2SO4. No additional seed was added except for the precipitate. After 20 such runs, each run using the precipitate from the previous run as seed, the final precipitate was analyzed and found to contain a 14~6/1 ; SrSO4/CaSO4 ratio.~ The final brine sample was analyzed and found to contain 3~4 weight percent Ca+~ and 0.12 weight 18,010-F

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percent ~r +. The original ccncentra~ions of Ca ~ and Sr in the brine were, respectively, 3.~ weight percent and 0.26 weight percent. It was calculated that 88 p~rcent of the Na2SO4 sulfate reacted to prec-pitate SrSO4.

_ample 2 and Cornparative Run 1 This example and its comparative run illustrate the crucial role of the SrSO4 seed in the practice of this invention. They show that even a small amount of the seed will produce a high yield of SrSO4 pr~cipita~e.

In Example 2, 500 ml of Sr +- and Ca -containing brine was heated to 90C wh;le being stirred. 5 ~rams of SrSO4 seed and 12.5 ml of 15.5 weight percent Na~SO4 (75 percent of the sulfate stoichiometrically needed to pre-cipitate all the Sr~+ in the brine) were then added to the brine. Filtered samples of the brine were taken at various intervals to determine its Sr++ content, and the data from ~he analysis are listed in Table I.

The components and reaction conditions of Com-parative Run 1 are very similar to those of Example 2, with the exception that no seed was added in the run. After one hour, a filtered sample of the brine was taken. The liquid sample contained 0.36 weight percent Sr+~, which was the amount of Sr++ in the original brine. The amounts of Ca~+
in the original hrine and the liquid sample were respec-tively, 3.3 weight percent and 3.2 weight percent. WhileCa reacted to form CaSO4 there was no substantial reac-tion of Sx~+ to form the Sr504 preci~itate. There were approximately 1.8 grams precipitate which analyzed as CaSO4 with a trace of Sr++.

In summary, Example 2 illustxates that even a small amount of SrSO4 seed will cause a significant degree o~ precipitation from a strontium-calcium loaded brine.

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1097~Z9 Comparative l~un L illustrates that, when the molar ratio of Ca+~/Sr~+ is 20/1, strontium will not pre~ipi~ate from the brine in ~ny appreciable amount if SrSO4 seed is not present in the brine.

TABLE I
Elapsed Time from Start Percent Sr Sample No. of Run (Min.) In Brine Sample 1 0* .36 2 15 .30

3 30 .20

4 60 .14 120 .ll *Original Brine e 3 -In this run, 500 ml of a brine that contained -0.3~ weight percent Sr and 3.3 weight percent Ca++ was heated to a temperature of 60C while being stirred. 100 grams of SrSO4 seed and 12.5 ml of 15.5 weight percent Na2SO4 were then added to the brine. The brine was stirred and maintained at a temperature of 60C throughout the run.
Using a procedure similar to that shown in Example 2, fil-tered samples of the brine were taken periodically to determine the Sr++ content in the brine. Table II ]ists 25~ the~amount of Sr+ as peraent by weight of the ~rine taken ;at various time intervals.

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- -Example 4 In this example CaSO4 2H2O, rather than Na2SO4, was used to precipitate SrSO4 from the brine.

500 ml of a brine that contained 0.36 weight per-cent Sr and 3.3 weight percent Ca was heated to a tem-perature of 95C. 100 grams celest~te and 3.3 grams CaSO4 2H2O (which was 75 percent of the stoichiometric amount of sulfate needed to precipitate all the Sr in the brine) were then mixed with the ~rine. The brine was stirred for 10 minutes and then filtered.

After 20 such runs of 10 min~tes each, using procedures similar to those shown in Example 1 (i.e. the precipitate from the preceding run was added, as the only seed, to fresh brine and additional sulfate) the final precipitate was analyzed and was found to contain 88.5 percent SrSO4 and 6.5 percent CaSO4. The final brine sample analyzed contained 3.51 percent Ca plus 0.09 per-cent Sr . Approximately 100 percent of the CaSO4 2H2O
sulfate reacted with Sr to precipitate SrSO4.

Examples 5 to_ These examples illustrate how the precipitate-~-forming reaction rate varies at diffexent temperatures.

In Example 5, a mixture o~ 500 ml brine, 100 grams celestite, and 12.5 ml of 15.5 weight percent Na2SO4 was stirred at 25QC. Filtered samples of the brine were taken at time intervals to determine the ~eactlan rate.
Example.s 6 and 7 are simllar to Example 5, with the excep-tion that the reaction temperatures employed were, res-:
~ pectively, 60C and 90C.
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These e~amples illustrate the effect that the quantity of seed added to the brine has on the rate of the precipitate-forming reaction. In Example 8, 500 ml of S Ca -containing brine that contained 0.235 percent Sr was mixed with 5 ~rams of SrSC4 seed. This mixture was heated to 90C and a 15 weight percent solution of Na2S04 was added in an amount calculated as sufficient to preci-pitate 75 percent of the Sr++ in the brine. Filtered samples of the brine were taken at various time intervals.
Table IV lists, at such various time in~er~als, the weight percent of Sr+~ that was removed from the brine and the weight percent Na2S04 sulfate that reacted with Sr+~ to precipitate SrS04 from the brine.

The procedure of Example 8 was repeated for Examples 9 to 11. In those examples, however, the amount of SrS04 seed added to the brine varied from 10 grams (Example g), to 25 grams (Example 10) to 100 g~ams (Exam-ple 11). Table IV lists information for Examples 9 to 11 similar to that for Example 8.

Examples 8 to 11 illustrate that the quantity of seed added to the brine has a significant effect on the rate of reaction but does not significantly affect the yield of SrS04 precipitate formed. Table IV illus-txates that if the amount of seed added to the brine isdeareasad the reaction time must be increased if one is -~ to achieve yields comparable to thoqe obtained when largo amounts ~f seed are used.
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Example ]2 This ~xample illustrates that, as the Ca++ to Sr molar ratio on ihe brine increases beyond a certain level, increasingly lesser amounts of the soluble sulfate (in this éxample Na2SO4) reacts with Sr~ to precipitate SrSO4 and a correspondingly greatex amount of the sulfate reacts with Ca++ to precipitate CaSO4.

In this example, 500 ml of a brine that contained 0.26 weight percent Sr++ and 3.3 weight percent Ca++ was mixed in a reaction vessel and was then heated to 90C, which temperature was maintained throughout the run. Small increments o Na2SO4 were periodically adda-l to the brine.
Approximately 15 minutes after each increment of Na2SO4 was added, a filtered sample of the brine was taken. This procedure was repeated until the total amount of Na2SO4 added was 115 percent of the amount needed to precipitate all the SrSO4 in the brine. As the Sr~+ is gradually removed from th~ brine by the succeeding additions of Na2SO4, the Ca /Sr ratio in the brine increases. Table V illustrates that as the Ca++/Sr + ratio increases above a certain level the pexcentage o Na2SO4, in total and from each succeeding increment, that reacts with Sr++ to precipitate SrSO4 decreases. For example, when the Ca++/Sr++ mol ratio was approximately 49, 89.6 percent by weight of the next Na2SO4 increment reacted with salt to precipitate SrSO4. However, when the ratio lS increa~ed to 73, only 31 percent by wei~ht o~ the next Na2SO4 increment reacted with salt to precipi-tate the strGntium product. Additional data is provided in TabIe V.

~ ~ It haæ been thereby determined that this inven-tion can be practiced when the mol ratio of Ca /Sr is ; as hi~h as about ~9/1, aIthough the ~upper preferred mol ratio of Ca++/Sr+~ is~about 68/1.

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Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of recovering strontium as a sulfate from a brine that contains strontium and calcium in. a Ca++/Sr++
molar ratio of greater than 20/1, which comprises mixing with the brine strontium sulfate seed and a sulfate that is more soluble in water than is strontium sulfate, and recovering the strontium sulfate that is thereby produced.

2. The method of Claim 1 wherein the mixing step takes place at a temperature between 60°C and 105°C.

3. The method of Claim 1 wherein the sulfate is selected from the group consisting of calcium sulfate, sodium sulfate, magnesium sulfate, ammonium sulfate, and sulfuric acid.

4. The method of Claim 1 wherein the brine has a Ca++/Sr++ molar ratio that is no greater than 99/1.

5. The method of Claim 1 wherein the brine has a Ca++ /Sr++ molar ratio that. is no greater than 58/1.

: 6. The method of Claim 1 wherein the amount of strontium sulfate seed used is from .05 weight percent to 50 weight percent of the brine.

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