METHOD FOR TREATING A SALT SOLUTION USING MULTISTAGE SEPARATION PROCESSES, AND TREATMENT SYSTEM FOR THIS PURPOSE

Abstract

A method is used for treating a salt solution using a treatment system. The treatment system has an evaporation device to which the salt solution produced in an upstream operation is supplied. A crystallizate suspension having kainite, halite, and sylvite is obtained from the evaporation device, and the kainite is then separated from the crystallizate suspension. The method for separating the kainite from the crystallizate suspension has at least the following steps: supplying the crystallizate suspension to a preliminary classifying device in which kainite is partly separated from the crystallizate suspension by means of a preliminary removal process based on the particle size of the kainite, thereby obtaining a kainite-reduced fraction, and transferring the kainite-reduced fraction to a flotation device in which the remaining content of kainite is separated from the kainite-reduced fraction.

Claims

1: A method for treating a salt solution with a treatment system, wherein the treatment system comprises an evaporating device, the method comprising: supplying the salt solution formed in an upstream operation to the evaporating device, obtaining a crystallizate suspension comprising kainite, halite, and sylvine from the salt solution, subsequently removing the kainite from the crystallizate suspension by at least the following steps: supplying the crystallizate suspension to a preliminary classifying device, in which kainite is partly removed from the crystallizate suspension by a preliminary removal process based on the particle size of the kainite, to give a kainite-reduced fraction, and transferring the kainite-reduced fraction to a flotation device, in which the remaining proportion of kainite is removed from the kainite-reduced fraction.

2: The method as claimed in claim 1, wherein the preliminary classifying device comprises a sorting spiral, wherein the removal of the kainite from the crystallizate suspension is performed by a preliminary removal process which is based on the particle size of the kainite, by the sorting spiral.

3: The method as claimed in claim 1, wherein the preliminary classifying device comprises a hydrocyclone, wherein the removal of the kainite from the crystallizate suspension is performed by a preliminary removal process which is based on the particle size of the kainite, by the hydrocyclone.

4: The method as claimed in claim 1, wherein the preliminary classifying device comprises an up-current classifier, wherein the removal of the kainite from the crystallizate suspension is performed by a preliminary removal process which is based on the particle size of the kainite, by the up-current classifier.

5: The method as claimed in claim 1, wherein a kainite-enriched fraction is transferred from the preliminary classifying device into a thickening device, in which liquid is taken off from the kainite-enriched fraction, so that a useful kainite fraction is taken out from the thickening device.

6: The method as claimed in claim 5, wherein the kainite-reduced fraction, before or in the flotation device, is supplied with an anionic flotation assistant and/or a kainite concentrate is taken out from the flotation device and supplied to the useful kainite fraction.

7: The method as claimed in claim 1, wherein a flotation residue comprising halite and sylvine is taken out from the flotation device and supplied to a further flotation device, in which a proportion of sylvine is removed from the flotation residue.

8: The method as claimed in claim 7, wherein the flotation residue from the flotation device, before or in the further flotation device, is supplied with a cationic flotation assistant.

9: The method as claimed in claim 7, wherein a sylvine-reduced and halite-enriched first fraction and a sylvine-enriched and halite-reduced second fraction are removed from the further flotation device, and/or the sylvine-enriched and halite-reduced second fraction is supplied via a return line to the useful kainite fraction and/or the sylvine-enriched and halite-reduced second fraction is supplied to a further, secondary treatment method.

10: A treatment system for implementing a method as claimed in claim 1, comprising: a preliminary classifying device and a flotation device downstream of the preliminary classifying device, and/or a further flotation device downstream of the flotation device.

11: The method as claimed in claim 6, wherein the anionic flotation assistant is a sulfated fatty acid or alkali metal salt thereof.

12: The method as claimed in claim 8, wherein the cationic flotation assistant is a primary amine.

13: The treatment system as claimed in claim 10, wherein the preliminary classifying device comprises at least one selected from the group consisting of a sorting spiral, a hydrocyclone, and an up-current classifier.

14: The treatment system as claimed in claim 10, wherein the treatment system further comprises a thickening device.

Description

PREFERRED EXEMPLARY EMBODIMENT OF THE INVENTION

[0025] Further measures, improving the invention, are set out in more detail below, together with the description of a preferred exemplary embodiment of the invention using the figures, in which

[0026] FIG. 1 shows a schematic view of the treatment system for implementing a method for treating salt solutions in accordance with the invention, and

[0027] FIG. 2 shows a further schematic view of the treatment system in accordance with FIG. 1, with a sequential flotation, comprising a first flotation device for kainite flotation and a further, second flotation device for sylvine flotation.

[0028] FIGS. 1 and 2 show a schematic view of a treatment system 100, where the treatment system 100 comprises an evaporating device 10, which is supplied with the salt solution 1 formed in an upstream operation and from which a crystallizate suspension 11 comprising kainite, halite, and sylvine is obtained, and where subsequently the kainite is at least partly removed from the crystallizate suspension 11.

[0029] In this case, the crystallizate suspension 11 is first supplied to a preliminary classifying device 12, in which kainite is partly removed from the crystallizate suspension 11 by means of a preliminary removal process based on the particle size of the kainite, to give a kainite-reduced fraction 13. The kainite-reduced fraction 13 is subsequently transferred to a flotation device 14, in which the remaining proportion of kainite is removed, especially predominantly removed, from the kainite-reduced fraction 13.

[0030] The preliminary classifying device 12 comprises, for example, a sorting spiral, in which case the kainite is removed from the crystallizate suspension 11 by means of a preliminary removal process based on the particle size of the kainite, by means of the sorting spiral. Further details of this are set out below.

[0031] Furthermore, a kainite-enriched fraction 15 is transferred from the preliminary classifying device 12 into a thickening device 16, in which liquid is taken off from the kainite-enriched fraction 15, and so a useful kainite fraction 17 is taken out from the thickening device 16, said fraction 17 being reduced in liquid and being transferred, for example, into a reservoir 21.

[0032] With particular advantage a kainite concentrate 18 is taken out from the flotation device 14, and this kainite concentrate 18 is supplied to the useful kainite fraction 17. The supplying therefore takes place after the thickening device 16, and so the kainite concentrate 18 as well can be supplied to the reservoir 21. This reservoir 21 is not absolutely necessary, and the useful kainite fraction 17 in conjunction with the kainite concentrate 18 may also be supplied directly to a further dewatering and/or further-processing system, in order, for example, to produce potassium sulfate fertilizer.

[0033] With reference to FIG. 1, a flotation residue 19 comprising halite, sylvine, and possibly residues of kainite is taken out from the flotation device 14 and supplied, by way of example, to a reservoir 20; the flotation residue 19 may also be supplied, directly or from the reservoir 20, to a further, otherwise undepicted secondary treatment process, such as a dissolution facility, for example.

[0034] With reference to FIG. 2, a flotation residue 19 comprising halite, sylvine, and possibly residues of kainite is taken out from the flotation device 14 and supplied to a further flotation device 22. In the further flotation device 22, a sylvine flotation takes place, from which a sylvine-reduced and halite-enriched first fraction 23 and a sylvine-enriched and halite-reduced second fraction 24 are removed. The advantage is in particular that, in the case of sylvine flotation with primary amines, kainite still present can be floated out along with the sylvine, and so enters the product fraction.

[0035] The first fraction 23 can be disposed of, and for this purpose is supplied, by way of example, to a reservoir 25, and the second fraction 24, which contains essentially sylvine and has merely remnants of halite and also kainite, can be used for the manufacture of fertilizers. The second fraction 24 in this case is supplied, by way of example, to a reservoir 26 for further use, or can be combined with the fraction of the kainite concentrate 18 from the kainite flotation stage from the flotation device 14, as indicated with the return line 27. A further possibility is for the second fraction 24 to be supplied to a further, otherwise undepicted secondary treatment process, such as, for example, a dissolution facility, or to further flotation steps.

[0036] Considered in more detail below are two classifying methods using the preliminary classifying device 12. The first embodiment relates to preliminary removal by a sorting spiral, and the second embodiment relates to preliminary removal by a hydrocyclone, with which sorting spiral/hydrocyclone the preliminary classifying device 12 is accomplished.

[0037] With regard to the sorting spiral embodiment, trials were carried out on the preliminary classifier. Tables 1 and 2 below show the trial results for the classifying of the crystallizate suspension feed, consisting of kainite (47.4%), halite (38.3%), and sylvine (14.3%), by means of the sorting spiral. Trial 1 was aimed at a mode of operation for kainite yield, trial 2 at a mode of operation for kainite quality, in which case the target kainite content is high. Both modes of operation were tried twice (a/b).

[0038] The results show a significant enrichment of kainite in relation to the crystallizate suspension, and therefore a depletion in the fraction still to be floated, the kainite-impoverished fraction, so resulting in the advantages described above. Depending on the mode of operation of the sorting spiral, kainite qualities of between 80% and 86% were obtained. The yield of kainite in the kainite-enriched fraction here was between 24% and 30%. The halite content of the kainite fraction was found to be 8%, the values being reported in percent by weight.

TABLE-US-00001 TABLE 1 Results for classifying using sorting spiral (Operation optimized for yield) Trial 1a Trial 1b Kainite- Kainite- Kainite- Kainite- enriched impoverished enriched impoverished in [% by wt.] fraction fraction fraction fraction Mass yields 16.3 83.7 17.1 82.9 Kainite content 80.8 40.3 81.2 39.9 R(kainite) 28 72 30 70 Halite content 7.9 44.4 8.0 44.5 R(halite) 3 97 4 96 Sylvine content 11.3 15.3 10.9 15.5 R(sylvine) 13 87 13 87 R(mineral) = Yield of(mineral)

TABLE-US-00002 TABLE 2 Results for classifying using sorting spiral (Operation optimized for quality) Trial 2a Trial 2b Kainite- Kainite- Kainite- Kainite- enriched impoverished enriched impoverished in [% by wt.] fraction fraction fraction fraction Mass yields 14.2 85.8 13.6 86.4 Kainite 85.8 40.7 85.6 41.9 content R(kainite) 26 74 24 76 Halite 5.1 43.9 5.6 43.2 content R(halite) 2 98 2 98 Sylvine 9.1 15.4 8.8 14.9 content R(sylvine) 9 91 9 91 R(mineral) = Yield of(mineral)

[0039] In order to reproduce the trials obtained by means of the sorting spiral, further trials were conducted with a continuous mode of operation. The results for this are set out in table 3.

TABLE-US-00003 TABLE 3 Results for kainite classification using sorting spiral with continuous operation Kainite Kainite Kainite Yield of Halite Sylvine content content content useful Mass content content [% by [% by [% by substance yield [% by [% by wt.] wt.] wt.] [% by [% by wt.] wt.] Flotation Trial Feed Concentrate wt.] wt.] Concentrate Concentrate fraction 3 51.7 81.6 30.5 19.3 6.0 12.5 44.6 4 52.6 80.4 26.9 17.6 6.3 13.3 46.7 5 47.8 84.7 16.5 9.3 3.6 11.7 44.0 6 46.4 84.2 16.5 9.1 4.3 11.5 42.6 7 48.2 79.3 36.4 22.2 7.7 13.0 39.4 8 48.5 79.8 35.5 21.6 7.5 12.8 39.9 9 73.0 90.5 46.8 37.7 5.3 4.2 62.4 10 67.5 89.2 43.9 33.2 6.3 4.5 56.7 11 67.3 88.9 52.7 39.9 6.5 4.6 52.9 12 56.8 91.2 30.9 18.3 5.1 3.7 45.5 13 58.6 90.1 26.5 17.2 4.9 5.0 52.0 14 65.7 89.4 51.0 37.5 5.9 5.0 51.4 15 64.8 90.1 45.1 32.5 4.9 5.0 52.7

[0040] In the context of the trials carried out by means of the sorting spiral, a removal is possible in which at least 20% of the total amount of crystallizate can be removed with the required concentrate quality (table 3).

[0041] In the course of the trials, concentrate fractions having a halite content of 8% were obtained. The concentrate quality in terms of the kainite content in this case was around 80%-91%, and the yield of useful substance was between around 16% and 53%, depending on the parameter setting of the spiral.

[0042] These results as well show a significant enrichment of the kainite in the concentrate fraction in relation to the feed crystallizate, and therefore a depletion in the fraction still to be floated, in other words in the kainite-impoverished fraction. It was observed, indeed, that in the case of relatively high kainite contents in the feed, the preliminary removal tends to be better in terms of the yield of useful substance.

[0043] The trials relating to classification by means of a hydrocyclone in the preliminary classifying device 12 likewise show the possibility of selective kainite enrichment in principle even with relatively high halite contents (and relatively low kainite contents) in the crystallizate suspension.

[0044] In the classification, primarily kainite is obtained in the overflow fraction of the hydrocyclone, and primarily halite and/or sylvine, and reduced proportions of kainite, in the underflow fraction. The results in this regard are shown in table 4 below.

TABLE-US-00004 TABLE 4 Results for the classification using a hydrocyclone Mineral phase Cyclone Cyclone distribution Feed A overflow A underflow A Halite [% by wt.] 60.1 3.7 77.1 Sylvine [% by wt.] 8.0 6.5 8.5 Kainite [% by wt.] 31.2 89.8 13.7 Cyclone Cyclone Feed B overflow B underflow B Halite [% by wt.] 61.7 8.5 86.7 Sylvine [% by wt.] 7.8 8.4 6.3 Kainite [% by wt.] 30.5 83.1 7.1 Trial A: Lower throughput (around 1.5 m.sup.3/h); trial B: higher throughput (around 2.0 m.sup.3/h).

[0045] With reference to the sequential flotation, sylvine contents of around 62% and sylvine yields of >80% were obtained in the second fraction 24 in the second step, in the sylvine flotation concentrate fraction (laboratory trial), and the values obtained were therefore significantly higher by comparison with the values in the residue fraction of the kainite flotation in the first step.

[0046] The halite content of the second fraction 24, with values of around 25.9% (laboratory trial), is reduced significantly relative to the residue fraction of the kainite flotation. In production-scale trials for a continuous regime, as well, sylvine contents of around 61.4% and sylvine yields of around 84% were obtained in the second fraction 24 of the sylvine flotation. Here again, the halite content, with values of around 9.5%, is significantly reduced relative to the residue fraction of the kainite flotation. On the production scale, both the kainite flotation and the sylvine flotation each took place in two stages, while both flotation steps in the case of the laboratory trials were carried out each as one stage. With this method, it is also possible to combine the concentrate fractions from the first flotation stage 14, to give the kainite concentrate, and from the second flotation stage 22, to give the sylvine concentrate (second fraction), and therefore both concentrates 18 and 24 can be combined. This is represented by the return line 27. The method of sequential flotation therefore, by means of a simple reconditioning without substantial cost and complexity of apparatus, enables the recovery of considerable quantities of further useful substance, formed here by kainite and sylvine, with consequent significant technical, economic and environmental advantages. Table 5 shows the results of the sequential flotation for a continuous mode of operation.

TABLE-US-00005 TABLE 5 Results of two-stage sylvine flotation Content Content Yield Mineral conc. Yield conc. return return phase [% by wt.] [% by wt.] [% by wt.] [% by wt.] Sylvine 61.4 84 4.0 16 Kainite 29.1 65 6.0 35 Halite 9.5 3 90.0 97 K.sub.2O 44.4 80 3.9 20

[0047] In terms of its embodiment, the invention is not confined to the preferred exemplary embodiment indicated above. Instead, a number of variations are conceivable, making use of the solution shown even with embodiments of a fundamentally different nature. All the features and/or advantages apparent from the claims, the description or the drawings, including construction particulars, spatial arrangements, and method steps, may be essential to the invention not only in themselves but also in a host of different combinations.

LIST OF REFERENCE NUMERALS

[0048] 100 treatment system [0049] 1 salt solution [0050] 10 evaporating device [0051] 11 crystallizate suspension [0052] 12 preliminary classifying device [0053] 13 kainite-reduced fraction [0054] 14 flotation device [0055] 15 kainite-enriched fraction [0056] 16 thickening device [0057] 17 useful kainite fraction [0058] 18 kainite concentrate [0059] 19 flotation residue [0060] 20 reservoir [0061] 21 reservoir [0062] 22 flotation device [0063] 23 first fraction [0064] 24 second fraction [0065] 25 reservoir [0066] 26 reservoir [0067] 27 return line