CA2638521A1 - Method of selectively dissolving minerals from a carnallite or sylvenite source - Google Patents

Abstract

A method for producing high grade potassium chloride from a source of carnallite. The method solubilizes and purifies the carnallite to produce potassium chloride having low levels of contaminants and resistance to hygroscopic behaviour.

Description

METHOD OF SELECTIVELY DISSOLVING MINERALS
FROM A CARNALLITE OR SYLVENITE SOURCE

The present invention relates to potassium chloride production and more particularly to potassium chloride production from a carnallite source.

As is known in the fertilizer art, camallite is a valuable compound in view of the fact that it contains potassium chloride, which is valuable to various industries and in particular, to the fertilizer industry. Carnallite is described by the formula KC 1-MgC12 -6H20.

Currently, when potassium chloride ore is mined, it must undergo significant unit operations for iipgrading, which is costly and significantly increases the price of this commodity. For example, a typical mine is at least a kilometre deep and is of the shaft variety.
Accordingly, this involves a tremendous amount of expenditure in terms of the drilling of the shaft and additionally involves specialized tunnelling to accommodate work areas. Generally speaking, tunnels in these types of mines can exceed six kilometres in length and take inordinate amounts of time to drill. Once mined, the material must then be crushed, ground and deslimed as initial unit operations.
Typically, this source of potassium chloride is affected by unacceptably high levels of salt (sodium chloride) contamination, which makes it un-saleable. In order to diminish the quantity of sodium chloride present, the mined product must undergo flotation to remove the excessive sodium chloride. Once this is done, the product must then be dried and sized with further processing in terms of compaction and crystallization. One of the problems with the latter stages of processing is the storage aspect. Storing the potassium chloride for lengthy periods of time is problematic, since the product is inherently hygroscopic. This results in coagulation and agglomeration of the crystals in to lumps.

Even with the degree of flotation that is typically employed to produce a commercial grade of potassium chloride fertilizer, the existing product in the marketplace is typically impure and has occluded impurities as well as a significant degree of magnesium chloride and sodium chloride contamination.

40248143.1

-2-In order to attempt to circumvent the limitations in conventional potassium chloride production, solution mining has been employed.

Solution mining is a widely known mining engineering technique and has been used extensively to extract evaporite values from subterranean formations for many years.

The intrinsic value of the evaporites is realized in the fact that contained potassium is the progenitor for potash production. The necessity of potash for crop production, animal feed inter alia is well known. The value of potash has increased and now approximates that of crude oil.
The escalating price of potash is based on unprecedented pressure currently experienced by farmers for greater and greater food production. Demand has increased prices.

In light of the foregoing, production has increased absent concomitant improvements in the existing solution mining techniques.

The techniques for solution mining currently followed involve the formation of a cavern into which water is injected as a solvent. This in and of itself is fine, however, volume control of the cavern is often uncontrolled and this results, depending on tectonics, in eventual subsidence of the formation. This is exacerbated by the fact that the formation pressure is not maintained during growth of the cavern. Accordingly, the mine is productive though with environmental consequences.

Perhaps one of the most significant limitations with existing techniques is the issue concerning tailings. By present methods, the tailings can be significant, require special handling and occupy large areas for storage.

It would be desirable to realize the benefits of solution mining in a carnallite deposit also having sylvinite contained therein without the limitations of existing methodology.

As is demonstrative of the existing limitations of the art, current process engineering of the potassium chloride results in a product that is at best 95% pure potassium chloride.

This is what the fertilizer market, generally made up of the golf course industry and agriculture air-seeding industries, must accept. The particles that are produced with current technology are 40248143.1

-3-non-uniform and are plagued with dust problems from disintegrating granules.
There can be as much as 30% discrepancy in the size of the particles in any one sample. This makes it extremely difficult to provide for a consistent, uniform application of the product. As will be readily apparent, since the size fluctuation exists in application, there can be significant variations in concentration from one area to the next. This makes for wastage of the product and also can result in over-fertilization in some areas and under-fertilization in adjacent areas.

The present invention provides for a uniform pellet product, which has a high degree of hardness, resistance to hygroscopicity, can be stored for lengthy periods and allows the user to apply the product in a consistent and even concentration while avoiding the dusting problems, which contribute to product waste.

In view of the limitations noted in the prior art, the present invention overcomes the limitations and provides an improved potassium chloride product as well as a method for producing the same.

One object of the invention is to provide an improved formulation for potassium chloride fertilizer pellets and a more robust and inexpensive method of producing such pellets.

Yet another object of one embodiment of the present invention is to provide a potassium chloride granule having a purity of 96.5% and 99% and a binder content of 4.5%
and 1%.
As a preface, it is known that ore consists of camallite and sylvinite and this is a mixture of sylvite (KCI, or potassium chloride) and halite (NaCI, or sodium chloride. The remainder consists of insoluble clays.

Carnallite dissolves rapidly from the mixture with the water having a temperature of between 20C and 100C with a more desirable range comprising between 40C
and 60C. This dissolution step allows for effective dissolution of potassium chloride from the sylvinite in situ. With maintenance of the temperature, sodium chloride is precipitated while the potassium chloride dissolves to produce a high density brine which sinks to the bottom of the cavern (discussed herein after). In this manner, the bottom of the cavern may be managed to concentrate potassium 40248143.1

-4-chloride brine and settle fine salt and clay to leave the salt crystals in the cavern.
Alternatively, the elevation of the cavern can be adjusted to settle out fine salt and from the production brine.

And the aspect of one embodiment of the present invention is to provide a method of separating potassium minerals from sodium minerals from a formation containing sylvinite and/or carnallite, comprising the steps of:

- providing a subterranean formation containing sylvinite andfor camallite;

- introducing water at a temperature of between 20C and 100C into contact with the formation to generate a cavern and dissolve the sylvinite;

- maintaining an undersaturated concentration of magnesium chloride in the cavern to enable selective dissolution of potassium compounds from sodium compounds;
- forming, through passive cooling, in the cavern, a concentration gradient of crystallized sylvinite at the base of the cavern and a solution of carnallite;
and - removing the carnallite solution from the cavern.

By practicing the methodology set forth herein, the result is a potassium chloride product, which has less than 1% sodium salt as an occluded impurity with significantly reduced dust levels, compared to competing products.

It has been found that the beneficial consolidation of the potassium chloride, the resistance to hygroscopicity and propensity to dust can be controlled if the pellets are granulated, using specific binders in a pan-granulation environment. The process involves the use of gluten extracted from grains. Suitable grains may be selected from raw rice, barley, wheat, etc. The important factor is to have gluten as the binding agent. It has been also discovered that the concentration range of 1% to 4.5% of the gluten is particularly effective for granulation of the potassium chloride.

40248143.1

-5-A still further aspect of one embodiment of the present invention is to promote a method of separating potassium minerals from sodium minerals in situ from a subterranean formation containing sylvinite and/or carnallite, comprising the steps of:

- providing a subterranean formation containing sylvinite andfor carnallite;

- forming a brine solution cavern within the formation by injection of water into the formation;

- maintaining the water temperature to at least 40C to precipitate sodium chloride and dissolve potassium chloride from the sylvinite and/or camallite;

- maintaining an undersaturated concentration of magnesium chloride in the cavern to enable selective dissolution of potassium compounds from sodium compounds;
- forming, through passive cooling, in the cavern, a concentration gradient of crystallized sylvenite at the base of the cavern and a solution of carnallite;
and - removing the carnallite solution from the cavern Regarding product formulation, as an example, the potassium chloride product does not absorb moisture below the 60% relative humidity factor. This is ideal for most conditions under which the product would be granulated. In terms of moisture content, it is obvious that granulated product must be exposed to some moisture in order to induce nucleation and accordingly, the so-called greenballs can typically contain between 5% to 10% by weight moisture.

With the foregoing general description of the invention, reference will now be made to the accompanying drawings, illustrating preferred embodiments.

Figure 1 is a schematic illustration of the overall extraction process of the invention according to one embodiment;

Figure 2 is a schematic illustration of a salt cavern;

Figure 3 is a schematic illustration of a multi cavern system;
40248143.1

-6-Figure 4 is a detailed process flow diagram illustrating the process according to a further embodiment; and Figure 5 is schematic illustration of a granulation process employed to synthesize the potassium chloride granules.

It will be noted that throughout the appended drawings, like features are identified by like reference numerals.

Referring to Figure 1, shown is the overall schematic illustration of the extraction phase of the potassium chloride. The origin of potassium chloride is a carnallite ore source from a subterranean formation, designated by numeral 10. The ore source may be mined in a shaft mine as noted herein previously but preferably by solution mining. Water from an external source (not shown) or from a water-bearing formation 12 may be used to solubilize the carnallite or otherwise render the camallite fluid so that the same can be pumped by pump 13 to a purification stage, which stage may comprise crystallizers 14. In the example, a grouping in series of crystallizers 14 are shown; however, it will be apparent to those skilled in the art that the same may be arranged in parallel or may include any number of crystallizers, depending upon the intended load of the overall circuit. The crystallizers are useful to purify the potassium chloride, which is essentially impure when it is introduced into the crystallizers. The potassium chloride contains magnesium chloride as an impurity as well as sodium chloride and by making use of the crystallization circuit, the KCl is progressively purified without risk of significant amounts of sodium chloride or magnesium chloride being occluded within the potassium chloride.

Waste brine from the purification process is pumped by a pump 15 to a subterranean formation, denoted by numeral 16. This offers an opportunity for the brine to be re-introduced into an environment which is not detrimentally affected by spent brines.

The potassium chloride is then dried with a conventional dryer 17 and subsequently forwarded to the granulation phase noted in Figure 5.

As noted previously, the ore body upon dissolution with water comprises a cavern 18, shown in Figure 2 and produces a brine having the composition as follows: between 8%
and 23% MgC12, 40248143.1

-7-12% to 25% or more KCl and less than 5% NaCI. As is illustrated in Figure 2, the cavern 18 has a solubilized camallite layer 20 and a crystallized sylvinite layer 22. A
distinct advantage in the process is that the underground process selectively dissolves the magnesium chloride and potassium chloride minerals into a brine and does not significantly dissolve the sodium chloride, which is at the top and the bottom of the formation. The brine is evaporated to magnesium chloride saturation at 120C and then cooled in the evaporative crystallizers noted herein previously to the natural equilibrium of potassium chloride at the temperature. A product of 0.15 t of potassium chloride can be produced for every ton of feed brine. The high grade potassium chloride has an impurity of magnesium chloride residual. To remove this, it is best to transform the magnesium chloride into magnesium carbonate with soda ash and centrifuge the magnesium carbonate and potassium chloride solids as final product. In this manner, the feedstock of the potassium chloride for the granulation phase becomes ideal.

Figure 3 illustrates a further embodiment of the present invention where a multiple cavern system is employed. In the embodiment shown, a central cavern 18 is networked in fluid communication with a series of peripherally arranged subsidiary caverns 18'.
In this manner, the caverns can continue to dissolve the mineral and extraction from a larger area becomes progressively greater, eventually mining the entire area.

Referring now to Figure 4, shown is a detailed flow diagram for the process described generally above. Numeral 30 denotes the overall process. Brine 32 from the solution mining discussed above is introduced into a thickener 34 for thickening. A flocculent 36 may be included to augment the thickening process. Once thickened, the material is transported to filter 38 for filtration into a liquid and solid phase. Wash water 40 may be added to the liquid phase and the subsequently washed liquid reintroduced by a circulation loop 42 to the introduction of thickener 34. The solid material 44 may be optionally introduced into a re pulping device. This is an optional operation as indicated in chain line denoted by number 46. In the event that the insoluble re pulping stage is included, brine 48 may be introduced into the re pulping operation.
In any event, insolubles from the solid filtered phase may be introduced into tailing pond, the global operation being denoted by numeral 50.

40248143.1

-8-As a further alternative, the insolubles could be transported with a vehicle directly to the pond.
The transportation step being indicated by numeral 52.

Returning to the filtration of a solid 44, at least a portion may be introduced into a further filter 54 together with wash water. The so washed solids are then subjected to a sodium chloride dissolution step 56 into which brine or water 58 may be introduced into the operation with subsequent discharge of the sodium chloride brine to a tailings pond, the latter step being denoted by numeral 60.

The liquid phase from filter 54, the liquid being denoted by numeral 62 will be discussed hereinafter in greater detail.

Returning to the thickening stage, denoted with thickener 34 at least a portion of the material may be introduced into an evaporating stage and particularly an evaporator 64 with the subsequently increased concentration material being filtered in filter 65. The liquid from the filter 65, may be passed on via line 66 to a magnesium chloride brine tailings pond, denoted by numeral 68. To the pond may be added additional brine from the sodium chloride evolved from the process. Additionally, further brine from the low magnesium crystallization phase of 76 may also be added to the tailings pond at this point. This addition is denoted by numeral 72. A
condensing operation 74 may be included to receive material from the tailings pond 68 for condensing with hot water from condensing operation being introduced into a magnesium feed re pulping stage 876 a liquid 62 from filter 54 may then be combined with the magnesium feed re pulping material and optionally flocculent 78 into a magnesium thickening operation using thickener 80. The thickened magnesium containing material is then introduced to a crystallizer 82 to which may be introduced brine from the tailings pond, the introduction being denoted by numeral 84. The crystallized material then is subjected to filtration phase using filter 86 to which wash water 88 may be added. The separated liquid then may be passed into a heat exchanger 90 and subsequently returned to the magnesium feed re pulping stage denoted by numeral 76.

40248143.1

-9-Solvents from filter 86 which solids contain residual magnesium chloride on the surface of the potassium chloride crystals are introduced into a sodium bicarbonate surface conditioning operation, denoted by numeral 90 to which sodium bicarbonate is added at 92.

This operation assists in converting the magnesium chloride to a non reactive form of magnesium carbonate. This is an important step in the procedure since it contributes to the stability of the final potassium chloride product. As is known, magnesium chloride is significantly hygroscopic and will absorb moisture from the air when the relative humidity exceeds 30%. By providing this operation, Applicant ensures that the contaminated potassium chloride crystals are "conditioned" so that the hygroscopic issue is alleviated. Once conditioned, the solution is passed through a filter 94 where the liquid is returned via line 96 to evaporator 64.
The salt from the filtration is washed with water 96 and the solid subsequently passed into a drying and formulation operation, denoted by numeral 98. In this operation dryer and bag house exhaust are discharged to the atmosphere at 100 and the bag house and dry air dust denoted by numeral 102 are introduced into the magnesium crystallizer 82. The dried and prepared product is then either stored or packaged, the broad step being denoted by numeral 104.

Referring now to Figure 5, in the embodiment shown, the circuit is representative of a ten ton per hour circuit. Reference to numeral 106 denotes the introduction of potassium chloride feedstock initially in a size distribution of between -30 mesh and 100 mesh.

The potassium chloride may be introduced along with suitable binder material 108 set forth herein previously. The feedstock and binder may be then introduced together into a pulverizer 110 to pulverize the feedstock such that a product is produced having 90% -200 mesh. The pulverizer 110 may be a classifying pulverizer or air sweep pulverizer or any other suitable pulverizer known by those skilled in the art. Once pulverized, the stream, generally represented by numeral 112, is introduced onto a pan granulator globally denoted by numeral 114, which includes scrapers 116 and 118. The disposition of the scrapers 116 and 118 can be positioned to establish the desired size distribution. Nucleating material 120 may be added in an amount between 0% and 3% by weight. The nucleating material may be in a size distribution of -30 to 40248143.1

-10-+100 mesh and assists in initiating the granulation process. Water 120 may be added to augment the moisture on the pan when required.

Once the granules are formed, they are dried in a dryer 122 which may be of the air float carrier type. Other suitable options are well within the purview of one skilled. The dry granules are then screened with screen for classification with granules in the size distribution -14 to +30 mesh either being recycled to pan 114 as indicated by 126 or alternatively sold as product 126. The oversized material, i.e. +4 mesh can be returned to pulverizer 110 as indicated by 128. The product is also screened to a size distribution of -4 to +14 mesh to result in a product having at least 95% by weight potassium chloride.

It will also be readily appreciated that the process is interruptible and therefore can be custom designed to produce granules having a variety of layers of material to produce a host of valuable granules. It will be clear to those skilled in the art that the process is effective for producing a number of different forms of fertilizer and has particular utility with respect to the formation of high grade fertilizer for use on golf courses, etc.

To this end, the particles may include a compound having reduced solubility relative to the fertilizer in order to facilitate a timed release of the fertilizer. Examples of such material include sulfur reducing agents, nitrogen fixing compounds, urea, etc. The dissipation of the fertilizer could also be timed with the growth cycle of the material receiving the fertilizer or the requirement thereof.

Depending upon material being granulated, a range of binders may be selected for use.
Examples include lignosol, sugars, saturated salts and proteins, water, calcium sulfate, sodium sulfate, potassium chloride, dry glutens, wheat grains, barley grains, rice grains and calcium phosphate among others. The choice of the binder will depend on the desired characteristics of the granule and accordingly, the aforementioned binders are only exemplary.

With respect to the feedstock and binder, when the binder chosen contains a higher moisture content, i.e. 5% to 10% the use of additional moisture may not be necessary.
By making use of the fine powder feedstock and progressive layering of the material, a solid uninterrupted cross 40248143.1

-11-section for the granule is obtained with homogeneously dispersed feed throughout. This obviates the inconsistencies in product content within the granules formulated using existing technologies.
As a further very significant advantage, the magnesium chloride conversion to magnesium carbonate using the soda ash ensures that the surfaces of the potassium chloride granules do not absorb moisture. It has been found that storage life is interminable provided the relative humidity remains below 60%. This is in marked contrast to existing compactor prepared granules which have a short storage life, typically approximately three months.

Although embodiments of the invention have been described above, it is limited thereto and it will be apparent to those skilled in the art that numerous modifications form part of the present invention insofar as they do not depart from the spirit, nature and scope of the claimed and described invention.

40248143.1

Claims (24)

1. A method of separating potassium minerals from sodium minerals from a formation containing sylvinite and/or carnallite, comprising the steps of:

- providing a subterranean formation containing sylvinite and/or carnallite;

- introducing water at a temperature of between 20C and 100C into contact with said formation to generate a cavern and dissolve said sylvinite;

- maintaining an undersaturated concentration of magnesium chloride in said cavern to enable selective dissolution of potassium compounds from sodium compounds;

- forming, through passive cooling, in said cavern a concentration gradient of crystallized sylvinite at the base of said cavern and a solution of carnallite; and - removing said carnallite from said cavern.

2. The method as set forth in claim 1, wherein said temperature of said water is between 40C
and 60C.

3. The method as set forth in claim 1, further including the step of maintaining the formation pressure during dissolution and removal.

4. The method as set forth in claim 1, wherein said dissolution is in situ within said formation minimizing withdrawal of said sodium compounds from within said formation.

5. The method as set forth in claim 1, wherein said method includes the step of initially dissolving said sylvinite at a temperature of at least 40C.

6. The method as set forth in claim 1, further including the step of providing a central receiving cavern interconnected for fluid communication with a plurality of auxiliary caverns.

7. The method as set forth in claim 1, further including the step storing crystallized sylvinite within a carnallite depleted cavern.

8. The method as set forth in claim 7, including extracting crystallized sylvinite.

9. A method of separating potassium minerals from sodium minerals in situ from a subterranean formation containing sylvinite and/or carnallite, comprising the steps of:

- providing a subterranean formation containing sylvinite and/or carnallite;

- forming a brine solution cavern within said formation by injection of water into said formation;

- maintaining the water temperature to at least 40C to precipitate sodium chloride and dissolve potassium chloride from said sylvinite;

- maintaining an undersaturated concentration of magnesium chloride in said cavern to enable selective dissolution of potassium compounds from sodium compounds;

- forming, through passive cooling, in said cavern a concentration gradient of crystallized sylvinite at the base of said cavern and a solution of carnallite; and - removing said carnallite from said cavern

10. The method as set forth in claim 9, optionally including withdrawing brine from within said cavern while retaining crystallized sylvinite in said cavern, said withdrawn brine comprising production brine.

11. The method as set forth in claim 10, further including treating said brine to remove fines and clay there from.

12. The method as set forth in claim 9, including maintaining the pressure of said formation to reduce subsidence.

13. The method as set forth in claim 9, including altering a height within said formation of said cavern to induce settling of fine salt .

14. The method as set forth in claim 13, including decanting production brine.

15. A method of formulating a potassium chloride granule from a source of sylvite as set forth in claim 9,consisting of:

- forming potassium chloride crystals in a size range of between 30 mesh to mesh;

- commingling said crystals with between 1.5% and 4% by weight of gluten containing binder material to form a mixture;

- introducing said mixture onto a single pan granulator containing potassium chloride in a size range of between 30 mesh to 100 mesh and progressively layering potassium chloride contained on said pan thereon; and - forming granules having a uniform solid cross section with homogeneously dispersed potassium chloride therein resistant to moisture absorption below 60%
relative humidity.

16. The method as set forth in claim 15, wherein said granules contain 5% and 10% moisture.

17. The method as set forth in claim 15, wherein said gluten containing binder material is selected from the group consisting of raw rice, barley, wheat...

18. The method as defined in any one of claims 1, 9 or 15, including step of purifying said potassium chloride.

19. The method as defined in claim 1, wherein said purifying comprises crystallization.

20. The method as defined in claim 19, wherein said crystallization comprises re-crystallization for removing impurities from said potassium chloride.

21. The method as defined in claim 18, wherein said purification further includes removal of magnesium chloride from said source of carnallite.

22. The method as defined in any one of claims 1, 9 or 15, further including the step of discharging brine formulated during extraction of said potassium chloride.

23. The method as defined in claim 22, wherein said discharging comprises deep well injection of said brine.

24. The method as defined in claim 23, wherein said deep well injection comprises injection of said brine into an aqueous subterranean formation.