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Method For Obtaining Caesium From Aqueous Starting Solutions

20200208239 · 2020-07-02

    Inventors

    Cpc classification

    International classification

    Abstract

    The invention relates to a method for obtaining caesium from aqueous starting solutions having caesium contents in the range of 50 ppm to 5000 ppm, in which method the caesium ions in the aqueous solution are, in a first step, precipitated as a double salt having divalent cations with the aid of an at least 1.1-times overstoichiometric amount of solutions containing prussiate of potash, in a pH range of 2 to 12 and a temperature range of 10 to 80 C., the divalent cations either already being present in the starting solutions in an amount at least equimolar to the caesium content or being added as a water-soluble salt, and, in a second step, converted back into a water-soluble form by thermal decomposition and, in a third step, separated from the insoluble residues.

    Claims

    1. A method for obtaining cesium from aqueous starting solutions with cesium ion contents in the range of 50 ppm to 5000 ppm, characterized in that the cesium ions in the aqueous solution are, in a first step, precipitated as a double salt having divalent cations with the aid of an at least 1.1-times overstoichiometric amount of solutions containing prussiate of potash selected from the group consisting of K.sub.4[Fe(CN).sub.6], Na.sub.4[Fe(CN).sub.6], Ca.sub.2[Fe(CN).sub.6] and mixtures thereof, in the pH range of 2 to 12 and the temperature range of 10 to 80 C., wherein the divalent cations are either already present in the starting solutions in an amount equimolar to the cesium content or added as a water-soluble salt, and, in a second step, they are converted back into a water-soluble form by thermal decomposition and, in a third step, separated from the insoluble residues.

    2. The method according to claim 1, characterized in that aqueous starting solutions with cesium ion contents in the range of 100 ppm to 1000 ppm are used.

    3. The method according to claim 1, characterized in that an overstoichiometric amount of solutions containing alkali prussiate of potash in the range of the 1.15- to 1.5-times the stoichiometric amount is used.

    4. The method according to claim 1, characterized in that, as divalent cations, calcium and/or magnesium ions are obtained in at least equimolar amount or added at least until the equimolar amount is reached.

    5. The method according to claim 1, characterized in that the precipitation of the double salt is carried out in a first step in the pH range of 4 to 11.

    6. The method according to claim 1, characterized in that the precipitation of the double salt is carried out with the addition of inorganic filtering aids.

    7. The method according to claim 1, characterized in that the overstoichiometric amount of prussiate of potash remaining in the starting solution is precipitated by the addition of a water-soluble iron(III) salt in the pH range of 4 to 7 to the already formed double salt.

    8. The method according to claim 7, characterized in that iron(III) sulfate is used in an excess of up to 100% by weight with respect to the amount of alkali prussiate of potash remaining in the solution.

    9. The method according to claim 1, characterized in that the thermal decomposition in the second step is carried out in a calcining step under oxidative conditions at temperatures of 400 C. to 800 C.

    10. The method according to claim 9, characterized in that the calcining residue is introduced into demineralized water and the soluble components are separated from the insoluble components.

    11. The method according to claim 10, characterized in that the cesium salts contained in the solution are further purified by recrystallization.

    12. The method according to claim 2, characterized in that an overstoichiometric amount of solutions containing alkali prussiate of potash in the range of the 1.15- to 1.5-times the stoichiometric amount is used.

    13. The method according to claim 12, characterized in that, as divalent cations, calcium and/or magnesium ions are obtained in at least equimolar amount or added at least until the equimolar amount is reached.

    14. The method according to claim 13 characterized in that, as divalent cations, calcium and/or magnesium ions are obtained in at least equimolar amount or added at least until the equimolar amount is reached.

    15. The method according to claim 14, characterized in that the precipitation of the double salt is carried out in a first step in the pH range of 4 to 11.

    16. The method according to claim 15, characterized in that the precipitation of the double salt is carried out with the addition of inorganic filtering aids.

    17. The method according to claim 16, characterized in that the overstoichiometric amount of prussiate of potash remaining in the starting solution is precipitated by the addition of a water-soluble iron(III) salt in the pH range of 4 to 7 to the already formed double salt.

    18. The method according to claim 17, characterized in that iron(III) sulfate is used in an excess of up to 100% by weight with respect to the amount of alkali prussiate of potash remaining in the solution.

    19. The method according to claim 18, characterized in that the thermal decomposition in the second step is carried out in a calcining step under oxidative conditions at temperatures of 400 C. to 800 C.

    20. The method according to claim 19, characterized in that the calcining residue is introduced into demineralized water and the soluble components are separated from the insoluble components.

    Description

    EXAMPLE 1

    [0028] Precipitation of Cs ferrocyanide from concentrated, natural, chloride containing salt solution pH 4 to 10 (brine with 14% by weight NaCl, 7% by weight CaCl.sub.2, 1% by weight MgCl.sub.2, <1% by weight KCl, <1% by weight SrCl.sub.2)

    [00001] 2 .Math. .Math. Na , [ Fe ( CN ) .Math. 6 ] 10 .Math. H 2 .Math. 0 484.07 + 2 .Math. CaCl2 + 4 .Math. CsCl .fwdarw. Cs4 [ Fe .Math. ( CN ) 6 ] .Math. ? .Math. Ca 2 1035.69 [ Fe ( CN ) .Math. + 8 .Math. .Math. NaCl .Math. .Math. 3 .Math. ( Fe ( CN ) 6 ) 4 - + 4 .Math. Fe 3 + .Math. .fwdarw. ? .Math. Fe [ FeFe ( CN ) .Math. e ] 3 .Math. ? .Math. 14 .Math. - .Math. 16 .Math. .Math. H .Math. .Math. 2 .Math. .Math. O .Math. ? .Math. indicates text missing or illegible when filed .Math.

    TABLE-US-00001 TABLE 1 Precipitation of Cs ferrocyanide and subsequent precipitation of Prussian blue Molecular weight Molarity Weight g/mol mmol g Remarks Salt solution amount 15 000 with content of Cs 470 ppm 132.91 53.0 7.05 Ca 2.6% by weight 40.08 9730 390 Mg 0.27% by weight 24.31 1666 40 Addition Na.sub.4[Fe(CN).sub.6] 10 H.sub.2O 484.07 36.7 17.8 Excess: +38% by weight +10.2 mmol Fe.sub.2(SO.sub.4).sub.3 399.88 11.2 6.0 g (75% Excess: (21% by weight Fe) 22.4 mmol Fe by weight) +120% by weight +12 mmol

    [0029] Na.sub.4[Fe(CN).sub.6]10 H.sub.2O is added at room temperature in the form of an aqueous solution or a solid and stirred for 30 minutes. The precipitation occurs spontaneously. Subsequently, Fe.sub.2(SO.sub.4).sub.3 is added in the form of an aqueous solution or a solid and stirred for 30 minutes.

    [0030] The further precipitation also occurs spontaneously. Subsequently, filtration through a folded paper filter is carried out, and the unwashed residue is dried at 100 C.

    [0031] Starting solution 15 000 g with 470 ppm Cs (7.1 g Cs)

    [0032] Filtrate: 15 000 g with 20 ppm Cs (0.3 g Cs)

    [0033] Residue: 25.8 g with 26% by weight Cs (6.7 g Cs, 98% of the theory)

    TABLE-US-00002 TABLE 2 Analysis of the filtered leaching solution Cs Fe Ca Mg Na Sr K % by % by % by % by % by % by % by weight weight weight weight weight weight weight Starting solution 0.047 <0.0001 2.6 0.27 5.5 0.15 0.14 Solution after precipitation 0.003 0.0014 2.6 0.27 5.5 0.15 0.13 of Cs ferrocyanide Solution after precipitation 0.002 0.0041 2.6 0.27 5.4 0.15 0.13 of excess ferrocyanide Residue of the two precipitations 26 10.1 5.3 1.9 3.9 0.15 0.25 (unwashed, dried) Final solution of the residue 4.5 <0.0001 0.001 0.0001 0.9 0.005 0.04 of the thermal decomposition

    [0034] 5.0 g of the residue are heated in a crucible made of Al.sub.2O.sub.3 in the tube furnace at 600 C., the temperature is maintained for 3 h, and 50 l.sub.n/h of air is passed over it. The waste gas is introduced into a solution of H.sub.2O.sub.2 and NaOH, in order to oxidize poisonous waste gases such as CO, (CN).sub.2 and HCN. Residue: 4.0 g (weight loss: 20% by weight)

    [0035] Leaching residue: oxides/hydroxides/carbonates of Fe, Ca, Mg, Sr and K.

    [0036] Table 3 shows the composition of the Cs solution obtained by thermal decomposition of the precipitation residue and leaching of the decomposition residue with at least the amount of demineralized water necessary for complete dissolution.

    TABLE-US-00003 TABLE 3 Analysis of the product solution % by weight meq/g Cs.sup.+ 4.5 +/ 0.2 0.34 Na.sup.+ 0.92 0.40 Ca.sup.2+ 0.0013 0.0003 K.sup.+ 0.04 0.01 Total 0.75 OH.sup. 0.10 CO.sub.3.sup.2 0 0 Cl.sup. 0.67 SO.sub.4.sup.2 0.03 0.006 NO.sub.3.sup. 0.12 0.02 Total 0.79

    [0037] The residue of the thermal decomposition is leached here with at least the amount of demineralized water necessary for complete dissolution and is separated by filtration from insoluble components. The aqueous solution contains 1.4 g Cs (100% of the theory).

    [0038] Composition of the solution: 3.8% by weight CsCl/1.7% by weight CsOH/2.3% by weight NaCl/<0.1% by weight KCl