US3442553A

US3442553A - Slurry mining of carnallite

Info

Publication number: US3442553A
Application number: US592119A
Authority: US
Inventors: Kenneth J Kutz
Original assignee: Texas Gulf Sulphur Co
Current assignee: E A DEVELOPMENT Inc; Texasgulf Inc
Priority date: 1966-11-04
Filing date: 1966-11-04
Publication date: 1969-05-06
Anticipated expiration: 1986-05-06
Also published as: BR6794396D0; OA02528A; ES347168A1; DE1288538B

Description

K. J. KUTZ SLURRY MINING OF CARNALLITE May 6, 1969 Sheet Filed Nov. 4, 1966 INVENTOR. hlwvsm d /(urz.

May 6, 196 9 K. J. KUTZ v 3,442,553

SLURRY MINING o CARNALLITE Sheet Filed Nov. 4, 1966 INVEN'IOR. KEN/Yam 1/. 'Vu 72 BY May 6, 1969 K. JfjKUTZ SLURRY MINING OF CARNALLITE Sheet Filed Nov. 4, 1966 May 6, 1 K. J. KUTZ 3,442,553

SLURRY MINING OF CARNALLITE Filed Nov. 4. 1966 Sheet INVENTOR. Ker/war d Aurz May 6, 1969 K. J. KUTZ SLURRY MINING OF CARNALLITE Sheet Filed Nov. 4, 1966 Ti ti a.

y 6, 1969 K. J. KUTZ 3,442,553

SLURRY MINING OF CARNALLITE Filed Nov. 4, 1966 Sheet 6 0r 7 KEN/76TH J. Ku rz May 6, 1969 K. J. Kufrz SLURRY MINING OF CARNALLITE Sheet Filed Nov. 4, 1966 United States Patent 3,442,553 SLURRY MINING 0F CARNALLITE Kenneth J. Kutz, Salt Lake City, Utah, assignor to Texas Gulf Sulphur Company, New York, N.Y., a corporation of Texas Filed Nov. 4, 1966, Ser. No. 592,119 Int. Cl. E21c 43/20, 43/28; C22b 27/00 U.S. Cl. 299-4 13 Claims ABSTRACT OF THE DISCLOSURE This disclosure is directed to a process for the slurrymining of a salt bed, such as carnallite, by introducing water into said bed, thereby leaching a soluble salt (magnesium chloride) therefrom and forming a cavity. The leaching of the soluble salt leaves a less soluble salt (potassium chloride) as a slurry in the bottom of the bed, or in a sump below the bed. This less soluble salt is then removed as a slurry entrained by a substantially saturated solution of the soluble salt.

This invention relates to a process for slurry mining of carnallite and for recovery of potassium chloride therefrom.

Carnallite is a double salt of potassium chloride and magnesium chloride, having the formula This mineral is valuable chiefly as a source of potassium chloride, which is used in the fertilizer industry. The magnesium chloride is at present of comparatively little value. Extensive deposits of this mineral occur in southeastern Utah as well as other locations in the world such as Canada, Ethiopia, East Germany, West Germany, Brazil, and the Congo. In southeastern Utah these deposits may also contain other minerals, for example, about 0 to 20% by weight of sodium chloride, approximately by weight of sylvite (potassium chloride), and small amounts of bromides, sulfates, calcium salts, and water-insoluble materials. These deposits are located at considerable depth below the ground. Since the mechanical strength of carnallite is quite low, mining by conventional methods would be impractical.

Although solution mining of carnallite has been previously attempted, efforts have proved unsuccessful. A major contributing factor to the failures is that the desired product, potassium chloride, is much less soluble in water than magnesium chloride. Introduction of water into an underground bed of carnallite results in dissolution of carnallite and formation of a magnesium chloriderich brine with most of the potassium chloride remaining in the undissolved solid state. No practical method of bringing this undissolved potassium chloride to the surface has been proposed prior to the present invention.

An object of this invention is to provide a mining process for carnallite in which potassium chloride is obtained and brought to the surface in the form of a slurry of undissolved particles.

This object and other objects of this invention will be apparent from the description which follows.

According to this invention, carnallite is dissolved in an underground bed where it occurs by introducing water or an unsaturated aqueous salt solution into the bed, dissolving the magnesium chloride, and forming a potassium chloride slurry. The particles of potassium chloride forming the slurry are entrained in the magnesium chloride solution and pumped to the surface, where pure potassium chloride is recovered by conventional means. The term unsaturated aqueous salt solution, as used in the specification and claims, is defined as an aqueous solution with a sufliciently low salt content so that it will lea-ch out or dissolve magnesium chloride from carnallite, and thus cause the potassium chloride from the carnallite to fallout or form a slurry; this selective solubility results in the decomposition of the carnallite.

This invention will now be described in greater detail with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic view, as seen in vertical elevation, illustrating the slurry mining of carnallite in an underground bed;

FIG. 2 is a diagrammatic plan view of a carnallite bed, as seen from above, showing the location of wells and the development of cavities in the bed;

FIG. 3 is a vertical sectional view illustrating the first phase of operations in which a sump is formed in a salt formation below the carnallite bed in preparation for slurry mining of the carnallite;

FIG. 4 is a vertical sectional view illustrating the second phase of operations, in which water is introduced into a carnallite bed and a solution of magnesium chloride and a slurry of potassium chloride particles is formed;

FIG. 4A is a vertical sectional view illustrating the second phase of operations, similar to FIG. 4 but showing a modified form of apparatus;

FIG. 4B is a vertical sectional view illustrating the second phase of operations, similar to FIG. 4 but showing a further modified form of apparatus;

FIG. 5 is a vertical sectional view illustrating the third phase of operations, in which the undissolved particles of potassium chloride are brought to the surface;

FIG. 6 is a diagrammatic vertical sectional view showing mining technique which is particularly advantageous for obtaining carnallite from steeply inclined beds; and

FIG. 7 is a plan view of the carnallite bed of FIG. 6, showing the location of wells therein, as seen from above.

Referring now to FIG. 1, a carnallite bed 10 is located at substantial depth below the ground -11. In a typical formation, a salt bed 12 containing sodium chloride or other water-soluble salt may be located immediately below the carnallite bed 10. The space 13 between the carnallite bed 10 and the surface of the ground 11 may contain a plurality of strata, including sandstone, shale, anhydrites, limestones, dolomites and a number of sodium chloride beds for example. It will be assumed in this description that the stratum immediately over the carnallite bed 10 consists of a material such as anhydrite or shale which is insoluble in water, although the process is also applicable to deposits in which the overlaying stratum is water soluble.

A plurality of wells are drilled from the surface of the ground to the carnallite bed. Each well includes a rig or derrick 14, and tubinglS comprising a plurality of concentric or adjacent tubing strings which provide inlet and outlet conduits for introducing aqueous fluids into and removing aqueous fluids or slurry from the wells. The structural details of tubing 15 will be described later with reference to FIG. 3. Both the rigs or derricks 14 and tubing 15 are similar to their counterparts in oil wells.

FIG. 1 also illustrates the formation of cavities in the carnallite bed 10 as water or an unsaturated solution is introduced into the bed and brine and slurry are removed therefrom. A plurality of cavities 16, each extending outwardly from a well, comprise the carnallite bed after it has been mined. The progressive growth of cavities 16 during the course of mining operations is illustrated by dotted lines 17. Pillars 18 of undissolved carnallite, which are substantially remnants of removing a plurality of inverted cones, remain in a carnallite bed after it has been mined.

FIG. 2 is a plan view showing the location of wells in a carnallite bed being mined. In the embodiment illustrated, the wells are located in staggered arrangement in a plurality of parallel rows. This gives a maximum recovery of carnallite from the bed. The number and location of wells is chosen to give a maximum recovery of carnallite from the bed 10, consistent with economic considerations. As the number of wells is increased for a given area, the amount of carnallite mined increases, but at greater cost for well drilling.

Referring now to FIG. 3, tubing 15 consists of a plurality of concentric tubing strings 20, 21 and 22 of progressively larger diameter. The innermost tubing string 20 and the next adjacent tubing string 21 are vertically movable and form inlet and outlet conduits for liquid or slurry. The outermost tubing string 22 is cemented to the sides of the well in the strata 13 above carnallite bed 10, and ordinarily terminates at the top of carnallite bed 10. This outermost tubing string 22 serves as a protactive casing.

When a bed of water-soluble salt 12 occurs immediately below carnallite bed 10, the well is drilled from the surface through the carnallite bed and terminates in the salt bed 12 near the top thereof. The tubing 15 is inserted in the bed so that the innermost tubing string is located below the level of the carnallite bed 10 and in the upper portion of salt bed 12. A slick joint and stuffing box (not shown) are provided above the surface of the ground and supported by rig or derrick 14, permitting telescoping vertical movement of inner tubing string 20 with respect to the next adjacent tubing string 21. A hoist located on rig 14 is used to raise and lower tubing 20. Tubing string 21 is also vertically movable, and a stufiing box and slick joint are provided above the surface of the ground and supported by rig 14 for raising and lowering this tube. Initially, when a cavity is being dissolved out in salt bed 12, this tubing string 21 is located so that its tip is several feet below the boundary between carnallite bed 10 and salt bed 12.

After the wells have been drilled, the first phase of operations is to form a small sump for collection of potassium chloride slurry. This is done by circulating water downwardly in the annulus between tubing strings 20 and 21, and bringing out brine through tubing string 20. For best results the direction of fiow of water and brine is periodically reversed. The tip of innermost tubing string 20 is generally near the bottom of the desired cavity in salt bed 12. Dissolution of carnallite in bed 10 can be prevented at this stage of operations by injecting a thin blanket of a hydrocarbon oil through the annulus between

tubing strings

21 and 22 and through the annulus between tubing string 21 and the sides of the well in carnallite bed 10. The use of such a hydrocarbon oil blanket in solution mining operations is conventional.

FIG. 4 illustrates the dissolution of carnallite in bed 10 by injection of water or an unsaturated aqueous salt solution into the bed and the removal of magnesium chloride brine therefrom. Where an unsaturated aqueous solution is used, the salt most frequently is magnesium chloride. This operation is carried out after a sump 25 of desired size has been formed. During the carnallite dissolution operation, as shown in FIG. 4, the tip of the innermost tubing string 20 is approximately at the boundary of carnallite bed 10 and salt bed 12. The tip of the adjacent tubing string 21 is raised to a location in the upper half of the carnallite bed after formation of sump 25 and before the start of dissolution of carnallite. Water or an unsaturated aqueous salt solution is then piped downwardly through the annulus between tubing strings 20 and 21. This water or unsaturated aqueous salt solution circulates in the carnallite bed 10 in the immediate vicinity of the tubing 15. The magnesium chloride content of the carnallite is leached out, forming a cavity 16 and giving a magnessium chloride brine solution. Cavity 16 is in communication with sump 25 so that each is in effect a continuation of the other.

FIG. 4A illustrates the dissolution of carnallite in a bed 10 by injection of water or an unsaturated aqueous salt solution and the removal of magnesium chloride brine therefrom. The operation depicted in FIG. 4A is the same as that shown in FIG. 4. Instead of using tubing 15 having a plurality of concentric pipes, the tubing 15a in FIG. 4A includes a pair of tubes 20a and 20b surrounded by a pipe 21. The tips of tubes 20a and 20b are at approximately the boundary between carnallite bed 10 and salt bed 12 therebelow. It may be desirable for the tip of tube 20b to terminate slightly higher than the tip of tube 20a as shown. The tip of pipe 21 is raised to a location in the upper half of the carnallite bed after the formation of sump 25 and before the start of dissolution of' carnallite. Water or an unsaturated salt solution may be introduced into the carnallite bed 10 through the space enclosed by pipe 21 and surrounding tubes 20a and 20b. A solution about saturated in magnesium chloride is pumped upwardly through tubes 20a and/or 20b. The direction of flow may be reversed or coursed through difierent combinations of tubings and annuluses if desired.

FIG. 4B illustrates the dissolution of carnallite in bed 10 using a modified form of apparatus. The operation depicted in FIG. 4B is the same as that shown in FIG. 4. The apparatus of FIG. 4B includes a pair of

tubes

20c and 21, which are surrounded by tubing string 22 which is cemented to the sides of the well.

Tubes

20c and 21 may have the same diameter. Water or unsaturated salt solution may be introduced into the carnallite bed through tube 200, A solution about 90% saturated in magnesium chloride is pumped up through tube 21. The direction of flow may be reversed if desired. As shown,

tubes

20c and 21 are positioned for supplying water or unsaturated salt solution through tube 200 and for removing 90% saturated magnesium chloride brine through tube 21. For this direction of flow, the tip of tube 20c is in the upper part of cavity 16, and the tip of tube 21a extends into sump 25.

Water or unsaturated aqueous salt solution may be supplied at ambient temperature. The beds are typically at a depth of about 6000 feet, and at this depth may be as hot as 40 C. This sensible heat of the ore will help to supply the heat of solution of the carnallite and will raise the temperature of the solution, thereby increasing the capacity of the well. It is most advantageous to supply water in an amount and at a rate to give a solution which is approximately 90% saturated with respect to magnesium chloride. A small portion of the potassium chloride content of the carnallite is also dissolved. Sodium chloride and sylvite, when present, are also dissolved to a small extent. However, the water solubilities of potassium chloride and sodium chloride are much lower than that of magnesium chloride. For example, if pure carnallite is dissolved in water at 35 C. to saturation, the resulting solution will contain about 27.3% magnesium chloride and 3.8% potassium chloride, balance water. This compares with 34.3% of magnesium chloride and 26.8% of potassium chloride in the carnallite. When sodium chloride is present in the carnallite bed, the percentage of each salt in a saturated solution would differ from the amounts given here. For example, if carnallite and halite (sodium chloride) are dissolved in water at 35 C. to saturation, the resulting solution will contain about 27.88% magnesium chloride, 2.0% potassium chloride, 1.45% sodium chloride, and 68.67% water. It can be seen that only a small proportion of the potassium chloride will be dissolved. The remainder falls out as a slurry as the carnallite is leached, Sodium chloride, and potassium chloride present as sylvite, also fall out predominantly in the slurry. Most of this slurry 26 falls to the bottom of sump 25. Some of the potassium chloride particles collect in a thin layer 27 on the sides of pillars 18, because ordinarily the sides of the pillars are not sloped steeply enough for the particles to fall by gravity into sump 25. During this phase of operations, no attempt is ordinarily made to bring the potassium chloride slurry to the surface. Instead, water or unsaturated aqueous salt solution is piped downwardly into the well and the aforesaid magnesium chloride solution which is approximately 90% saturated is pumped up to the surface. It will be understood that the solution as it is pumped to the surface may contain a greater or smaller amount of magnesium chloride, if desired. Dissolution takes place more slowly as saturation is approached, so that it is not usually worthwhile to attempt to form a saturated solution. On the other hand, the solution pumped to the surface must not be too dilute because its holding power for potassium chloride in solution increases with dilution and causes a decrease in slurry recovery of potassium chloride.

In FIG. 4 the initial rate of fluid flow downwardly through the annulus between tubing string 20 and 21 and upwardly inside tubing string 20' is fairly low, As the size of cavity 16 formed by dissolution of carnallite in bed increases, the flow rate of water may be speeded up. Initial flow rates would be a few tens of gallons per minute with final flow rates of a few hundred gallons per minute being desirable. The gradual dissolution of carnallite in cavity 16 is illustrated by lines 17, which show the progressive boundaries of the cavity as dissolution of carnallite is continued.

The third phase of operations is to recover the potassium chloride slurry 26 which collects in the bottom of sump 25. The magnesium chloride brine brought up to the surface is stored in holding tanks or ponds or the like (not shown) which are located above the ground.

FIG. 5 illustrates the third phase of operations of this invention, in which potassium chloride particles are brought up to the surface. In this phase of operations, a substantially saturated solution of magnesium chloride is introduced into the well in the annulus between tubing strings 20 and 21. This phase of operations is carried out most conveniently by placing the tip of the innermost tubing string 20 at or near the top of the slurry bed 26, and placing the tip of the next tubing string 21 at a short distance above the tip of tubing string 20. This provides for fluid circulation which entrains the solid potassium chloride particles in the magnesium chloride solution flowing downwardly between the annulus and the tubing strings 20 and 21. The tips of tubing strings 20 and 21 are moved up or down by an operator as required to obtain maximum potassium chloride removal, which is indicated by maximum density in the slurry brought to the surface and consequently by maximum pressure build-up on the discharge side of the pump which brings the slurry to the surface,

The magnesium chloride solution is substantially saturated with respect to magnesium chloride and potassium chloride, to minimize dissolution of potassium chloride. Ordinarily this solution is the solution obtained in the second phase of operations, or a portion thereof, containing a solution of magnesium chloride which is approximately 90% saturated.

The solution flowing downwardly into the well entrains potassium chloride particles, which are brought up through tubing string 20 entrained in the magnesium chloride solution. The fluid velocity in tube 20 must exceed the settling rate of the potassium chloride particles in order to bring these particles up to the surface. It is desirable to reverse the direction of flow periodically to prevent plugging of tubing strings 20 and 21 with potassium chloride particles.

While tubing strings 20 and 21 have been illustrated in FIGS. 3, 4 and 5 as concentric, it will be understood in the art that they may actually be two similar size strings located adjacent to each other within string 22. Such embodiment is illustrated in FIG. 4A. The entire sequence of operations, illustrated with respect to concentric tubing strings in FIGS. 3, 4, and 5, may be carried out with the apparatus shown in FIG. 4A. The wells and tubing strings therein are not necessarily absolutely vertical, in which case each tubing string shown will usually touch the adjacent tubing strings.

The second and third phases of operations may be combined in a single operation. In that case water is introduced into the wells, and magnesium chloride brine containing entrained potassium particles is withdrawn.

FIG. 6 illustrates an embodiment of the invention which is particularly suitable to the slurry mining of carnallite in steeply inclined beds. According to this embodiment of the invention, a plurality of wells arranged in parallel rows as illustrated in FIG. 7 are drilled. Each of these wells is surmounted by a derrick 14 in the same manner as described with reference to FIG. 1. Tubing 30 containing an inlet conduit and an outlet conduit is placed in the deepest well and extends from the ground downward to the bottom of the carnallite bed 31 or a short distance therebelow. This tubing contains both an inlet conduit and an outlet conduit and may be identical to that shown as tubing 15 in FIG. 1. The other wells extending to points in carnallite bed 31 at lesser depths require only an inlet conduit, although these tubings may also include concentric tubing strings forming inlet and outlet conduits. According to the procedure in this embodiment of the invention, a sump 33 is formed in a salt bed below carnallite bed 31 at the bottom of the deepest well. After this sump has been formed, water is then introduced through the inlet conduit of tubing string 30 into sump 33. This results in formation of a cavity 34 which gradually grows larger as dissolution proceeds, the stages of growth of the cavity being illustrated by lines 35. Either simultaneously with the introduction of water through tubing 30 or after the cavity has progressed so that it reaches the other wells, water may also be introduced through tubing 32 in these other wells. Magnesium chloride is leached out and removed through the outlet conduit of tubing 30 and may also be removed through outlet conduits in tubing 32. Most of the potassium chloride remains undissolved and forms a slurry which accumulates in sump 33. At intermittent intervals, this potassium chloride slurry is removed through tubing 30 as described earlier in FIG. 5. The potassium chloride slurry particles tumble downwardly along the boundary between the carnallite bed and the salt bed therebelow. Dissolution of carnallite is far more nearly complete in a. steeply inclined bed as shown in FIG. 6 than it is in a level bed or one having a gentle slope as shown in FIG. 1 because the pillars 18 of undissolved carnallite which remain after mining operations are completed are only a small percentage of the carnallite bed. A steeply inclined bed as described herein refers to one in which the angle at which the bottom of the bed is inclined is steeper than the angle of repose of potassium chloride particles. The angle of repose is the minimum angle at which particles on a slope will retain their position; at steeper angles the force of gravity exceeds the frictional force tending to prevent falling of the particles, and the particles tumble toward the lowest point. This tumbling is precisely the thing desired, since it makes possible the nearly complete dissolution of the carnallite bed with only small pillars remaining.

In some instances the material directly below the carnallite bed is an insoluble material rather than a water-soluble salt. In this instance it is not possible to form a sump 25 as illustrated in FIG. 3 of the drawings. Instead, this sump must be formed in the carnallite bed itself, with the result that a smaller percentage of the carnallite is recovered per well than is the case when the sump can be formed below the carnallite bed. In essence, cavity 16 comes to a point at the bottom of the carnallite bed, instead of having a substantial area at this horizon as it has when there is a sump 25.

After the potassium chloride particles have been brought to the surface, they may be recovered by conventional means. For example, centrifugation or filtration can be used to separate the potassium chloride particles from the magnesium chloride solution. The magnesium chloride may be recovered from the solution by solar evaporation, and may be utilized in the manufacture of magnesium metal. Potassium chloride particles may be processed by known techniques including recrystallization in order to obtain a substantially pure and salable product.

While this invention has been described with particular reference to the recovery of potassium chloride from carnallite, it will be apparent that the same principles are equally applicable to the recovery from beds of other double salts which form incongruently saturated solutions.

This invention has been described with reference to certain specific embodiments thereof. These are merely for the purpose of illustration; it is to be understood that changes and additions may be made by those skilled in the art without departing from the scope and spirit of the invention.

What is claimed is.

1. A process for slurry mining of a salt from a bed containing said salt as the less soluble component of a double salt which forms an incongruently saturated solution to recover the less soluble salt therefrom, which comprises:

(1) introducing water or an unsaturated aqueous salt solution into said bed, thereby leaching the more soluble salt and forming a cavity, said leaching resulting in the formation of a substantially saturated solution of said more soluble salt and a slurry of the undissolved less soluble salt;

(2) withdrawing a substantially saturated solution of said more soluble salt having undissolved particles of the less soluble salt entrained therein; and

( 3) recovering said less soluble salt.

2. A process for slurry mining of carnallite to recover potassium chloride therefrom which comprises:

(1) introducing water or an unsaturated aqueous salt solution into a bed of carnallite, thereby leaching magnesium chloride and forming a cavity, said leaching resulting in the formation of a substantially saturated solution of magnesium chloride and a slurry of undissolved potassium chloride;

(2) withdrawing a substantially saturated solution of magnesium chloride having undissolved particles of potassium chloride entrained therein; and

(3) recovering potassium chloride.

3. A process for slurry mining of a salt from a bed containing said salt as the less soluble component of a double salt which forms an incongruently saturated solution to recover the less soluble salt therefrom, which comprises (1) introducing water or an unsaturated aqueous salt solution into said bed, thereby leaching the more soluble salt and forming a cavity, said leaching resulting in the formation of a substantially saturated solution of said more soluble salt and a slurry of the undissolved less soluble salt, and withdrawing said solution from said deposit;

(2) thereafter introducing a substantially saturated solution of said more soluble salt into said cavity, circulating said solution through said slurry, thereby entraining undissolved particles of said less soluble salt, and withdrawing said solution and the particles of said less soluble salt entrained therein; and

(3) recovering said less soluble salt.

4. A process for slurry mining of carnallite to recover potassium chloride therefrom which comprises (1) introducing water or an unsaturated aqueous salt solution into a bed of carnallite, thereby leaching magnesium chloride and forming a cavity, said leaching resulting in the formation of a substantially saturated solution of magnesium chloride and a slurry of undissolved potassium chloride, and withdrawing said solution from said bed;

(2) thereafter introducing a substantially saturated sol-ution of magnesium chloride into said cavity, circulating said solution through said slurry, thereby entraining undissolved particles of potassium chloride, and withdrawing said solution and the particles of potassium chloride entrained therein; and

(3) recovering potassium chloride.

5. A process for slurry mining of carnallite from a deposit including a bed of carnallite and a bed of a different water-soluble salt therebelow, which comprises (1) drilling a well extending from the ground to the bed of said different water-soluble salt;

(2) providing an inlet conduit and an outlet conduit for aqueous fluids in said well;

(3) dissolving a portion of said different salt while preventing dissolution of carnallite so as to form a sump in the bed of said different salt;

(4) introducing water or an unsaturated aqueous salt solution into the carnallite bed, thereby leaching magnesium chloride and forming a cavity in communication with said sump, said leaching resulting in the formation of a substantially saturated solution of magnesium chloride and a slurry of undissolved potassium chloride, and withdrawing said solution from said deposit;

(5) thereafter introducing a substantially saturated solution of magnesium chloride into said cavity, circulating said solution through said slurry, thereby entraining undissolved particles of potassium chloride, and withdrawing said solution and the particles of potassium chloride entrained therein; and

(6) recovering potassium chloride.

6. A process for slurry mining of carnallite from a steeply inclined bed thereof which comprises (1) drilling a plurality of wells extending from the ground to a carnallite bed, said wells terminating at different depths corresponding to differences in depth of the bottom of said bed at the respective locations of the wells;

(2) providing inlet conduits for aqueous fluids in all of said wells and an outlet conduit in the deepest of said wells;

(3) introducing water or an unsaturated aqueous salt solution into said bed, thereby leaching magnesium chloride and forming a cavity, said leaching resulting in the formation of a substantially saturated solution of magnesium chloride and a slurry of undissolved potassium chloride, said slurry collecting adjacent the bottom of said deepest well, and withdrawing said solution from said bed;

(4) thereafter introducing a substantially saturated solution of magnesium chloride into said cavity, circulating said solution through said slurry, thereby entraining undissolved particles of potassium chloride, and withdrawing said solution and the particles of potassium chloride entrained therein through said outlet conduit in said deepest well; and

(5) recovering potassium chloride.

7. A process for slurry mining of a salt from a deposit including a bed containing a double salt which forms an incongruently saturated solution and a bed of different water-soluble salt therebelow, which comprises (1) dissolving a portion of said difierent salt while preventing dissolution of the double salt so as to form a sump in the bed of said water-soluble salt;

(2) introducing water or an unsaturated aqueous salt solution into the bed of the double salt, thereby leaching the more soluble component and forming a cavity in connection with said sump, said leaching resulting in the formation of a nearly saturated solution of the more soluble salt and a slurry of the less soluble component, and withdrawing said solution from said deposit;

(3) thereafter introducing a substantially saturated solution of the more soluble salt into said cavity, circulating said solution through said slurry, thereby entraining undissolved particles of the less soluble salt, and withdrawing said solution and the particles of less soluble salt entrained therein; and

(4) recovering said less soluble salt.

8. A process for slurry mining of carnallite from a steeply inclined bed thereof which comprises (1) drilling a plurality of wells extending from the ground to the carnallite bed, said wells terminating at diiferent depths corresponding to differences in depth of the bottom of said bed at the respective locations of the wells;

(2) introducing water or unsaturated aqueous salt solution into said bed, thereby leaching the magnesium chloride and forming a cavity, said leaching resulting in the formation of a substantially saturated solution of magnesium chloride and a slurry of undissolved potassium chloride;

(3) withdrawing a substantially saturated solution of magnesium chloride having undissolved particles of potassium chloride entrained therein; and

(4) recovering potassium chloride.

9. A process for slurry mining of a salt from a steeply inclined bed containing this salt as the less soluble component of a double salt which forms an incongruently saturated solution to recover the less soluble salt therefrom, which comprises 1) drilling a plurality of wells extending from the ground to the salt bed, said wells terminating at different depths corresponding to differences in depth of the bottom of said bed at the respective locations of the wells;

(2) introducing water or an unsaturated aqueous salt solution into said bed, thereby leaching the more soluble component and forming a cavity, said leaching resulting in the formation of a substantially saturated solution of the more soluble component and a slurry of undissolved less soluble component, said slurry collecting adjacent the bottom of said deepest well, and withdrawing said solution from said bed;

(3) thereafter introducing a substantially saturated solution of the more soluble component into said cavity, circulating said solution through said slurry, thereby entraining undissolved particles of the less soluble component and withdrawing said solution and the particles of the less soluble component entrained therein through said outlet conduit in said deepest well; and

(4) recovering the less soluble component.

10. A process for slurry mining of a salt from a steeply inclined bed containing this salt as the less soluble component of a double salt which forms an incongruently saturated solution to recover the less soluble salt therefrom, which comprises (1) drilling a plurality of wells extending from the ground to the salt bed, said wells terminating at different depths corresponding to differences in depth of the bottom of said bed at the respective locations of the wells;

(2) introducing water or an unsaturated aqueous salt solution into said bed, thereby leaching the more soluble component and forming a cavity, said leaching resulting in the formation of a substantially saturated solution of the more soluble component and a slurry of the less soluble component;

(3) withdrawing a substantially saturated solution of the more soluble component having undissolved particles of the less soluble component entrained therein; and

(4) recovering the less soluble component.

11. A process for slurry mining of a salt from a bed containing said salt as the less soluble component of a double salt which forms an incongruently saturated solution to recover the less soluble salt therefrom, which comprises,

(a) drilling a well extending into said bed, said Well having at least inlet and outlet conduits;

(b) introducing water into said bed, thereby leaching the more soluble salt and forming a cavity, said leaching resulting in the formation of a subsantially saturated solution of said more soluble salt and a slurry of the undissolved less soluble salt, said slurry gravitating to the bottom of said cavity and forming a slurry deposit, and withdrawing said solution;

(c) lowering an outlet conduit to a point in said cavity substantially adjacent said slurry deposit;

(d) circulating a substantially saturated solution of said more soluble salt through said cavity at a fluid velocity which exceeds the settling rate of said slurry, thereby entraining undissolved particles of said less soluble salt, and Withdrawing from said outlet conduit said solution and the particles of said less soluble salt entrained therein; and,

(e) separating said less soluble salt from said saturated solution.

12. The process of claim 11 wherein said soluble salt is carnallite, said insoluble salt comprises potassium chloride and said soluble salt comprises magnesium chloride.

13. A process for slurry mining of carnallite from a deposit including a bed of carnallite and a bed of a different water-soluble salt therebelow, which comprises,

(a) drilling a well extending from the ground to the bed of said different water-soluble salt, said well having at least inlet and outlet conduits;

(b) positioning said inlet and outlet conduits to introduce water into the bed of said different salt, and to withdraw a solution of said different salt;

(c) flowing water through said conduits to form a sump in the bed of said different salt;

(d) raising said inlet conduit;

(e) introducing water into the carnallite bed, thereby leaching magnesium chloride and forming a cavity in communication with said sump, said leaching resulting in the formation of a substantially saturated solution of magnesium chloride and a slurry of undissolved potassium chloride, said slurry gravitating into said sump to form a slurry deposit, and withdrawing said saturated solution;

(f) positioning an outlet conduit at a point in said sump substantially adjacent said slurry deposit;

(g) thereafter circulating a substantially saturated solution of magnesium chloride through said slurry, thereby entraining undissolved particles of potassium chloride, and withdrawing from said outlet conduit, said saturated solution and the particles of potassium chloride entrained therein; and

(h) separating said potassium chloride from said saturated solution.

References Cited UNITED STATES PATENTS 2,685,438 8/1954 Cross 299-5 3,355,212 11/1967 Day 299-5 ERNEST R. PURSER, Primary Exalminer.

US. Cl. X.R. 23-38