METHOD FOR THE PROCESSING OF POTASSIUM CONTAINING MATERIALS

Abstract

A method for the processing of potassium containing materials comprises: (i) Separation of a potassium containing mineral from gangue minerals; (ii) Acid leaching whereby substantially all potassium, iron, aluminium and magnesium is solubilised and mixed potassium/iron double salt formed; (iii) Selectively crystallising the mixed potassium/iron double salt formed in the leach step (ii); (iv) Second separation to separate the mixed potassium/iron double salt formed in step (iii); (v) Thermal decomposition to produce an iron oxide, a potassium salt and one or more phosphates; (vi) Leaching the product of the thermal decomposition; (vii) Third separation to separate the iron oxide and phosphate from the potassium salt; (viii) Recovering the potassium salt by crystallisation; (ix) Separating the iron oxide and phosphate of step (vii) by leaching and subsequent solid liquid separation; and (x) Precipitating phosphate from liquor produced in step (ix) through the addition of a base.

Claims

1. A method for the processing of potassium containing materials, the method comprising the steps of: (i) Passing a potassium containing material to a first separation step in which a potassium containing mineral is separated from gangue minerals present; (ii) Leaching the potassium containing mineral in acid in a leach step whereby substantially all potassium, iron, aluminium and magnesium present is solubilised and a mixed potassium/iron double salt formed; (iii) Selectively crystallising the mixed potassium/iron double salt formed in the leach of step (ii) in a crystallisation step; (iv) Passing a liquor from the crystallising step (iii) to a second separation step to separate the mixed potassium/iron double salt formed in step (iii); (v) Passing the double salt to a thermal decomposition step to produce an iron oxide, a potassium salt and one or more phosphates; (vi) Leaching the product of the thermal decomposition step; (vii) Passing a leach liquor from step (vi) to a third separation step to separate the iron oxide and phosphates from the potassium salt; (viii) Recovering the potassium salt by crystallisation; (ix) Separating the iron oxide and phosphate of step (vii) by leaching and subsequent solid liquid separation; and (x) Precipitating phosphate from a liquor produced in step (ix) through the addition of a base thereto.

2. The method according to claim 1, wherein the potassium containing mineral comprises one or more of glauconite, biotite and/or phlogopite.

3. The method according to claim 1, wherein the iron oxide separated in step (ix) is in the form of one or more of Fe.sub.3O.sub.4, Fe.sub.2O.sub.3 or FeO.

4. The method according to claim 1, wherein the leaching step (ii) is conducted under atmospheric conditions at a temperature close to boiling.

5. The method according to claim 1, wherein the leaching step is carried out with an excess of sulfuric acid allowing for a free acid concentration of >50 g/L H.sub.2SO.sub.4.

6. The method according to claim 5, wherein the total sulfate concentration is such that it is close to the saturation limit of the solution at the leaching temperature.

7. The method according to claim 5, wherein the total sulfate concentration is 6.0 M S at >90° C.

8. (canceled)

9. The method according to claim 1, wherein the retention time is between about 2 to 12 hours.

10. The method according to claim 1, wherein a metal extraction of greater than 70% is achieved during the leaching step (ii).

11. (canceled)

12. The method according to claim 1, wherein the separation of leach liquor from leached solids is conducted at or near the leach temperature to prevent the crystallisation of metal salts on cooling.

13. The method according to claim 1, wherein the selective crystallisation step (iii) is conducted at or close to the leaching temperature and forced by increasing the sulphur concentration to above saturation.

14. The method according to claim 13, wherein the sulphur concentration is >6 M sulphur at >90° C.

15. The method according to claim 14, wherein the increased sulphur concentration is achieved by the addition of concentrated sulfuric acid and/or evaporation.

16. The method according to claim 1, wherein KFe(SO.sub.4).sub.2, MgSO.sub.4 and phosphate salts are crystallised in the crystallisation step (iii), the KFe(SO.sub.4).sub.2 being washed to remove entrained impurities with a saturated solution of one or more of K.sub.2SO.sub.4, K and Mg sulfates, K.sub.2SO.sub.4/Fe.sub.2(SO.sub.4).sub.3, H.sub.2SO.sub.4 and water.

17. (canceled)

18. The method according to claim 16, wherein the wash solution is recycled to the KFe(SO.sub.4).sub.2 crystallisation stage.

19. The method according to claim 16, wherein a wash filtrate is recycled to the KFe(SO.sub.4).sub.2 crystallisation stage to increase the K/Fe ratio in the liquor.

20. (canceled)

21. The method according to claim 16, wherein the crystallisation step (iv) is achieved by forced cooling of the mixed KFe(SO.sub.4).sub.2, MgSO.sub.4 and phosphate crystallisation filtrate to between about 20 to 60° C.

22. (canceled)

23. (canceled)

24. The method according to claim 1, wherein the thermal decomposition step (v) is operated at about 500-700° C., thereby substantially preventing the conversion, if present, of MgSO.sub.4 to MgO.

25. The method according to claim 24, wherein a decomposition product is quenched with water to dissolve K.sub.2SO.sub.4 and MgSO.sub.4, the amount of water being sufficient to ensure K.sub.2SO.sub.4 and MgSO.sub.4 are close to saturation at a temperature close to boiling.

26. (canceled)

27. The method according to claim 25, wherein after a solid liquid separation, the crystallisation of K.sub.2SO.sub.4 and/or mixed potassium and magnesium double salts from solution is achieved by a combination of cooling and forced evaporation, the conditions being controlled to crystallise K.sub.2SO.sub.4 selectively in a primary crystallisation stage and a mixed potassium and magnesium double salt is crystallised from the primary crystallisation filtrate in a secondary crystallisation stage.

28.-32. (canceled)

33. The method according to any claim 1, wherein the precipitation step (x) is forced by the addition of apatite, recovered from greensand, thereby producing a precipitate containing a high concentration of phosphorus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The process of the present invention will now be described, by way of example only, with reference to one embodiment thereof and the accompanying drawings, in which:

[0047] FIG. 1 is a flow sheet depicting a process for the recovery of potassium, iron, magnesium and aluminium from glauconite rich magnetic concentrate by acid leach, KFe(SO.sub.4).sub.2 crystallisation, KFe(SO.sub.4).sub.2 decomposition, Fe.sub.3O.sub.4 recovery, K.sub.2SO.sub.4 and potassium and magnesium double salt crystallisation, and Al.sub.2(SO.sub.4).sub.3 crystallisation, in accordance with the present invention.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

[0048] The method of the present invention is anticipated to be applicable to a broad range of potassium containing minerals, including potassium containing micas, of which glauconite, biotite and phlogopite are representative. Whilst the large part of this description is directed to glauconite alone it is to be understood that the method of the present invention is broadly applicable to potassium containing micas, with particular efficacy in respect of the minerals glauconite, biotite and phlogopite.

[0049] Glauconite is an iron potassium phyllosilicate (mica group) mineral of characteristic green color with very low weathering resistance and very friable. Its chemical formula is (K,Na)(Fe.sup.3+,Al,Mg).sub.2(Si,Al).sub.4O.sub.10(OH).sub.2. Glauconite can range from 2-8% K.sub.2O and is the component in greensand that contributes to the green colour. Greensands also contain gangue minerals such as quartz, kaolinite, feldspar and apatite.

[0050] The glauconite in greensand can be separated from the gangue minerals by high intensity magnetic separation, due to its low magnetic susceptibility. Magnetic concentrate, which contains a high proportion of glauconite, is treated as shown in FIG. 1 and described hereinafter. The relative grades of the metals in glauconite are described by way of example only, and the method of the present invention is expected to treat any glauconite bearing material, not dependent on grade.

[0051] In FIG. 1 there is shown a method for the processing of potassium containing materials, specifically in the form of a flow sheet for the processing of glauconite containing magnetic concentrate 1 to recover potassium as K.sub.2SO.sub.4 25 and potassium and magnesium as K-Mag 27, iron as Fe.sub.3O.sub.4 31 and aluminium as Al.sub.2(SO.sub.4).sub.3.xH.sub.2O 13.

[0052] The glauconite containing magnetic concentrate 1 is passed to a leach step 40 in which at least a proportion of the contained potassium, iron, magnesium and aluminium are extracted into solution forming a pregnant leach solution (“PLS”). Sulfuric acid 2 and recycled final filtrate 15 are added to the leach step 40. The leach reactors employed in the leach step 40 are heated to provide high metal extractions and relatively short retention time, for example greater than 70% metal extraction in between 2 to 24 hours, more specifically greater than 90% metal extraction in up to 12 hours. The leach step 40 is conducted under atmospheric conditions at a temperature close to boiling. Further, the leaching step 40 is carried out with an excess of sulfuric acid allowing for a free acid concentration of >50 g/L H.sub.2SO.sub.4. The total sulfate concentration in the leach step 40 is such that it is close to the saturation limit of the solution at the leaching temperature. For example, the total sulfate concentration may be 6.0 M sulphur at >90° C. Under these conditions >90% metal extraction is achieved within 12 hours.

[0053] A leach discharge or slurry 3 is passed from the leach step 40 to a solid liquid separation step, for example a belt filter 50, which enables the leach discharge or slurry 3 to be filtered at or near the leaching temperature. The separation of leach liquor from leached solids is conducted at or near the leach temperature to prevent the crystallisation of metal salts on cooling.

[0054] The filtration stage produces a pregnant leach solution or PLS 7 containing the bulk of the extracted potassium, iron, magnesium and aluminium, and a leach residue 5. The leach residue 5 is washed with water 4 and/or an impurity bleed stream. A wash filtrate can be collected separately forming a low grade PLS 6, which can be used as make-up water where required.

[0055] The PLS 7 from the filter 50 is passed to the KFe(SO.sub.4).sub.2 crystallisation stage 60. Sulfuric acid 8 is added to force the crystallisation of KFe(SO.sub.4).sub.2. The crystallisation tanks are heated to maintain the temperature at or close to the leaching temperature. This is best controlled by indirect steam addition to prevent water from entering the crystallisation tanks. Further, the crystallisation forced by increasing the sulphur concentration to above saturation, for example a sulphur concentration of >6 M sulphur at >90° C. MgSO.sub.4 and phosphate salts are also crystallised in the crystallisation stage 60.

[0056] KFe(SO.sub.4).sub.2 crystallisation slurry 9 is passed through a solid liquid separation stage 70, for example a centrifuge, which enables the solids and liquid to be separated at or close to the temperature of the crystallisation stage. A filtrate 10 is passed to an Al.sub.2(SO.sub.4).sub.3.xH.sub.2O crystallisation stage 80 and the solids are washed with part of a potassium and magnesium solution 23, to be described hereinafter. Washed KFe(SO.sub.4).sub.2 is stockpiled for further treatment.

[0057] A wash filtrate 27, which contains K.sub.2SO.sub.4 and entrained impurities including Al.sub.2(SO.sub.4).sub.3, is recycled to the KFe(SO.sub.4).sub.2 crystallisation stage 60 to recover aluminium and increase the K/Fe ratio, which allows for a higher iron recovery. The amount of K.sub.2SO.sub.4 recycled can be controlled to target a specific iron recovery.

[0058] The filtrate 10, which contains mainly Al.sub.2(SO.sub.4).sub.3, is fed to the Al.sub.2(SO.sub.4).sub.3.xH.sub.2O crystallisation stage 80. In this stage the temperature of the solution is reduced by cooling and Al.sub.2(SO.sub.4).sub.3.xH.sub.2O crystallises. The cooling rate can be increased by indirect contact with cooling water 11. The crystallisation slurry 12 is passed to a solid liquid separation step, for example a belt filter. The filtration stage producers a final filtrate 15, which has a high concentration of H.sub.2SO.sub.4 and some soluble iron and aluminium, and solid Al.sub.2(SO.sub.4).sub.3.xH.sub.2O 13. The Al.sub.2(SO.sub.4).sub.3.xH.sub.2O can be washed with a saturated solution of Al.sub.2(SO.sub.4).sub.3 to remove impurities such as H.sub.2SO.sub.4 and iron. The wash filtrate can be combined with final filtrate 15 and then recycled to the leach stage 40. Al.sub.2(SO.sub.4).sub.3.xH.sub.2O can be dried and stored prior to sale, with varying degrees of hydration. In this manner an expensive K-alum decomposition stage is avoided.

[0059] The KFe(SO.sub.4).sub.2 16 is fed to a kiln 100 which operates between about 450° C. to 800° C., for example at >500° C., for thermal decomposition. This enables KFe(SO.sub.4).sub.2 to be converted to Fe.sub.3O.sub.4, K.sub.2SO.sub.4 and SO.sub.2 under slightly reducing conditions. SO.sub.2 gas 18 is recovered and fed to an acid plant 110. Sulfuric acid 19 is produced and used at various stages in the method of the present invention. Operation of the kiln 100 between about 500° C. to 700° C. substantially prevents the conversion, if present, of MgSO.sub.4 to MgO.

[0060] A calcine 20 is discharged from the kiln 100 and is quenched with water 21 in the quench tank and subsequent calcine leach tanks 120. K.sub.2SO.sub.4 and MgSO.sub.4 dissolve in the water 21 and recycled K-mag crystallisation filtrate 28.

[0061] The addition of water 21 and K-mag crystallisation filtrate 28 is controlled to ensure K.sub.2SO.sub.4 and MgSO.sub.4 are at or near saturation at or near the boiling point of the solution. A water leach slurry 22 is passed through a solid liquid separation stage 130, for example a centrifuge, generating a potassium and magnesium solution 23 and a leached calcine 24. Part of the K and Mg solution 23 can be used to wash the solids in the FeK(SO.sub.4).sub.2 filter 70 and the remainder is fed to a conventional crystalliser 140 in which K.sub.2SO.sub.4 is selectively crystallised. A K.sub.2SO.sub.4 product 25 is separated from a K.sub.2SO.sub.4 crystallisation filtrate 26 and dried prior to sale.

[0062] Potassium and magnesium, present in the K.sub.2SO.sub.4 crystallisation filtrate, are co-crystallised in a conventional crystalliser 150. A resulting K-mag product 27 is separated from the K-mag crystallisation filtrate 28 and dried prior to sale. The K-mag crystallisation filtrate 28 is recycled to the quench leach 120 to recover more potassium and magnesium.

[0063] The solids from the calcine leach filter 130, a leached calcine 24, can be washed with water to remove entrained potassium and magnesium solution and then fed to a calcine acid leach 160 to dissolve phosphate. Sulfuric acid 29 is added. A resulting acid leached calcine slurry 30 is passed through a solid liquid separation stage 170, such as a belt filter, generating a phosphate liquor 32 and Fe.sub.3O.sub.4 product 31, which can be washed with water to remove entrained phosphate liquor and stockpiled for sale.

[0064] Phosphate can be recovered from the phosphate leach liquor 32 by the addition of a basic compound, for example limestone 32, lime or apatite concentrate, in precipitation tanks 180. The phosphate slurry is passed through a solid liquid separation stage 190, such as a belt filter, and phosphate containing solids 35 are collected and dried prior to sale. The resulting precipitate is generally similar in composition to commercial grade Single Superphosphate (N 0%, P 8.8%, K 0%, S 11%, and Ca 19%). A phosphate precipitation filtrate 36 is recycled to the calcine acid leach 160 to recover more phosphate.

[0065] Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.