US3695711A

US3695711A - Method of recovering underground deposits of soluble minerals, and apparatus for carrying out the method

Info

Publication number: US3695711A
Application number: US4727A
Authority: US
Inventors: Ernst Messer; Arno Singewald
Original assignee: Wintershall AG
Current assignee: Wintershall AG
Priority date: 1970-01-21
Filing date: 1970-01-21
Publication date: 1972-10-03
Anticipated expiration: 1989-10-03

Abstract

A method of recovering underground deposits of soluble minerals, and an apparatus for carrying out the method. An access shaft is sunk to the region of the deposit and a tunnel is driven from the shaft to the deposit, whereupon an upright working shaft is advanced from the tunnel into the deposit. From the working shaft a plurality of vertically spaced substantially horizontal and at least substantially parallel flushing passages are driven into the deposit, and intermediate these passages the deposit is formed with a plurality of slots each connecting two adjacent ones of the passages and inclined thereto. Water is forced through the passages and slots to dissolve soluble minerals from the deposit and the thus-obtained solution is collected in the respectively lower of the passages. The collected solution is at least substantially saturated with dissolved minerals by supplying it together with fresh water through the deposit to the next lower of the passages. The saturated solution is collected underground and thereupon pumped from below ground to above ground where the dissolved minerals are recovered and where residual water remaining after recovery of the minerals is returned into the passages. An apparatus for carrying out the method is also disclosed.

Description

United States Patent 1 3,695,71 1 Messer et al. 51 Oct. 3, 1972 METHOD OF RECOVERING UNDERGROUND DEPOSITS OF [57] ABSTRACT g fi MINERALS AND A method of recovering underground deposits of solu- A ARATUS FOR CARRYING OUT ble minerals, and an apparatus for carrying out the THE METHOD method. An access shaft is sunk to the region of the [72] Inventors; Ern t M w thli A deposit and a tunnel is driven from the shaft to the Singewald, Kassel-Wilh., Germany Primary Examiner-Ernest R. Purser Attorney-Michael S. Striker deposit, whereupon an upright working shaft is advanced from the tunnel into the deposit. From the working shaft a plurality of vertically spaced substantially horizontal and at least substantially parallel flushing passages are driven into the deposit, and intermediate these passages the deposit is formed with a plurality of slots each connecting two adjacent ones of the passages and inclined thereto. Water is forced through the passages and slots to dissolve soluble minerals from the deposit and the thus-obtained solution is collected in the respectively lower of the passages. The collected solution is at least substantially saturated with dissolved minerals by supplying it together with fresh water through the deposit to the next lower of the passages. The saturated solution is collected underground and thereupon pumped from below ground to above ground where the dissolved minerals are recovered and where residual water remaining after recovery of the minerals is returned into the passages. An apparatus for carrying out the method is also disclosed.

15 Claims, 2 Drawing Figures METHOD OF RECOVERING UNDERGROUND DEPOSITS OF SOLUBLE MINERALS, AND APPARATUS FOR CARRYING OUT THE METHOD BACKGROUND OF THE INVENTION The present invention relates generally to the recovery of underground deposits of soluble minerals, and more particularly to a method of effecting such recovery and an apparatus for carrying out the method.

Different methods are known for recovering underground deposits of minerals, including of course the driving of shafts into the deposit in order to permit chunks of the deposit to be brought above ground for further processing. Such deposits include a variety of mineral deposits, for instance sylvin (KCl) which is usually admixed in granular form with rock salt NaCl). Rock salt is also frequently found in almost pure deposits or in form of salt layers which contain relatively insignificant quantities of other minerals, such as anhydrite (CaSO KCl and clay.

In addition to the physical removal of chunks of such deposits for processing above ground it is also known to recover such soluble minerals by a leaching process. On e method of this type which may be used for recovery both of pure salt deposits as well as mixed deposits of NaCl and KCl, requires that the deposit is made accessible by drilling into it an access shaft, in which suitable conduits are installed and into which thereupon water is introduced. The soluble salts of the deposit become dissolved in the water and after the latter has become saturated and forms a brine, the brine is pumped out and further processed. This is repeated until the entire mineral deposit about the access shaft has been leached out.

However, this known process has certain disadvantages. One of these is its limited applicability, particularly for the recovery of kalium-chloride (KCl). It is possible only to economically recover the minerals from deposits or layers which are horizontal or substantially horizontal and which are of regular and relatively significant thickness. Furthermore, it it very difficult and frequently possible only by utilizing expensive aids, to so carry out the leaching process that the floor and/or bottom of the hollows which develop during the leaching process and removal of the soluble minerals, are protected against further leaching when the edge of the deposit has been reached, that is that no leaching of minerals other than those desired will occur. A further difficulty in this latter context is in the use of the additives which are used during the leaching process and which have a higher or lesser specific weight than water or the brine and therefore tend to accumulate on the ceiling and/or floor of such hollows and thus to prevent leaching of minerals from beyond the deposit which it is intended to recover. This, however, often is not an operational safeguard with the result that leaching of minerals from outside the deposit-that is minerals not intended to be obtained-occurs. Aside from the recovery of minerals which are not intended to be obtained there is the further fact that this prevents an adequate saturation of the solution with KCl so that the process is not economical.

A further process of recovery by leaching is known which is used for NaCl deposits which are of horizontal orientation. In this case leaching passages are drilled horizontally through the deposit in parallelism with one another, and thereupon filled completely with water. The solution is pumped out as soon as saturation has taken place. The process is repeated until recovery to the desired extent has taken place. However, this approach can be used only in compact deposits which are even and nearly horizontal. It has not been used to our knowledge for the recovery of KCl and appears to be impossible of utilization for irregularly configurated deposits, particularly for those which extend not horizontal but instead upright, particularly steeply upright.

Spackeler Berg-und Aufbereitungstechnik, Vol. II/9b, 1957, pages 260-263) describes a leaching process for rock salt deposit where access shafts transversely of the deposit are spaced at 260 meter intervals, with chambers being formed of these shafts having a height of 9 meters, a width of 20 meters and a length of 100 meters. Between these chambers walls of salt remain. Each of the thus-obtained underground cavities was filled and the obtained solution pumped out for a requisite number of times until the final size was reached. Each filling period required several weeks if a saturated solution was to be obtained. While the publication specifies that the filling period can be reduced if instead of sweet water or fresh water the water used for the leaching process is partially enriched brine, it is to be understood that even then the filling period still requires weeks.

On pages 263-265 the publication deals with the leaching of KCl-NaCl deposits. It states that it is possible only to obtain solutions of 40 and g/l KC] although the saturation point is at 164 g/l. The publication points to the lack of controllability of the solution process and points out that the brine obtained did not come up to expectations because it was not sufficiently saturated. It was thought that to obtain an adequately concentrated brine it would be necessary to use not water below ground, but instead to use steam. The solution process will thus always remain incomplete.

SUMMARY OF THE INVENTION The present invention has as a general object to improve the state of the art in the above field.

Particularly the present invention is concerned with an improved method of recovering underground deposits of soluble minerals.

The invention is also concerned with an apparatus for carrying out the method.

According to one aspect of the novel method, particularly for the recovery of KCl and NaCl, or NaCl alone from natural KCl and NaCl or NaCl-alone containing underground deposits, an access shaft is sunk to the region of the deposit, a tunnel is driven from the access shaft to the deposit, and from the access shaft a working shaft is driven into the deposit, following the inclination of the same. This working shaft is leached out with water until it has a configuration of approximately 4-lO m Subsequently, from this working shaft a plurality of vertically spaced substantially horizontal and at least substantially parallel flushing passages are formed in the deposit at predetermined distances from one another. This is accomplished by using water supplied via conduits and an apparatus according to the present invention, and the spacing between the flushing passages varies in dependence upon the thickness of the deposit, being approximately 10 m if the thickness of the deposit is 3 m, and approximately up to 25 m if the deposit has a thickness of 10 m. Intermediate the passages a plurality of slots is formed each connecting two adjacent ones of the passages and being inclined thereto. The spacing of such slots is between substantially 0.5 and approximately 5 m and their number per passage length depends upon the thickness of the deposit, for instance two where the deposit is small and 3-5 if the deposit is large. Water is forced through the flushing passages and slots, and the unsaturated solution obtained and containing KC] and NaCl or NaCl alone passes through the slots into the next lower passage, becoming enriched in the process with additional KC] and NaCl, or NaCl alone, and simultaneously increasing the free surface of the next lower passage. The solution is new advanced via valve controlled conduits and water whose quantity can be cally controlled, to the next lower passage where it arrives further enriched to the point of at least substantial saturation. The thus saturated solution is now passed via further valve controlled conduits to a collecting basin from where it is pumped upwardly above ground and further processed to obtain KC] and NaCl, or NaCl alone, and the water obtained on evaporation of the solution is recirculated into the flushing passages until the deposit has been completely recovered.

It has been found that the solution obtained by the use of this method on a sylvinite deposit containing K 0 contains between approximately 30-40 g/] KC] and approximately 80-90 g/] NaCl, and that it becomes enriched --while turning into a saturated solution-by passage through an approximately 10 m long inclined slot and by the solution of further KC] and NaCl, whereupon the concentration is increased by approximately 10-15 g/] KC] and approximately -30 g/] NaCl.

It has further been found that fresh water can advantageously be sprayed against the walls of the deposit containing KC] and NaCl, or NaCl alone, particularly under the influence of the natural hydrostatic pressure, and that the flushing passage can always be automatically extended for a length of approximately 2 m, with the KC] and NaCl, or NaCl solution passing through the slots into the next lower passage.

The slots may be formed with known drilling machines or other apparatus known, or by means of length-adjustable steel tubes through which fresh water is directed against the wall surrounding the passages, utilizing hydrostatic pressure, and thus forming the slots by a leaching process. The accumulation of brine or saturated solution is advantageously held to approximately 1 m below the surface of the flushing passage in which the brine accumulates, by regulating the supply of water, and the flushing passages themselves can be arranged to form two or more groups in form of chambers which are separated by residual walls of the deposit which are not penetrated by passages and/or slots.

It is advantageous to provide three such groups arranged in form of chambers, which are operated in such a manner that in one of the chambers flushing takes place to obtain the initial solution, in a second of the chambers saturation of the solution takes place and in the third of the chambers pumping-out of the saturated solution takes place. If this is the case, and if above ground the further processing of the solution is carried out continuously, dwell-times for the solution in the chambers are on the order of 6-8 hours.

The invention is also utilizable for the recovery of KC], MgC], and NaCl from carnallitite deposits which may be either rich or poor in natural rock salt. In this case, it will be KC], MgCl and NaCl which becomes dissolved in the water and is removed in the manner discussed above. Above ground the saturated solution is processed to obtain MgCl and a crystalline byproduct is obtained containing KC] and NaCl. In the passages where the solution is accumulated, sludge deposits form on the bottom walls or ground which contain KC] and NaCl; these are flushed out by means of the saturated solution or are removed by mechanical means to be brought above ground for further processing.

The underground carnallitite deposits may have kieserite content of up to 5 percent, especially between approximately 1 and 2 percent.

If, for instance, the rock salt poor carnallitite deposit has a composition of 93.8 percent carnallitite and 6.2 percent rock salt with the other aforementioned materials also included, then the saturated solution obtained in accordance with the method of the present invention will have a saturation of approximately 95 percent with reference to MgCl and a composition of 320 g/l MgCl g/l KC], 23 g/l NaCl at an operating temperature of approximately 30 at depth of approximately 500-600 m. The aforementioned sludge deposits contain approximately 70% KC] (44% K 0), 29% NaCl and approximately 1% water unsoluble matter, such as CaSO and clay.

If, on the other hand, the method is executed in a kieseritic carnallitite deposit rich in rock salt, for instance having a composition of 62.3% carnallitite, 29.5% rock salt, 0.6% sylvine, 0.5% MgSO 4.2%

, CaSO 2.9% water unsoluble, a saturated solution of approximately 94% saturation relative to MgC], is obtained, having the composition of 360 g/l MgC],, 45 gl] KC], 34 g/l NaCl at an operating temperature of 29.5% C at depths of approximately 750 m.

In this case, the aforementioned sludge which is obtained contains approximately 27.6% KC], 57% NaCl, 8.5% CaSo 0.9% MgSO, and 6% water unsoluble.

To produce 200 T MgC], per day in form of the substantially saturated MgCl solution with 320 g/l MgCl corresponding to 0.32 t/m, a brine quantity of approximately 625 m lday is required. This contains 540 m water, and an additional 360 m fresh water per day is required. There is further obtained per day approximately 164 T KC] and T NaCl in form of the aforementioned sludge.

The invention is also usable for recovery of KC], NaCl, K MgSO MgCl from deposits containing natural hard salts. Here, the water is used to dissolve KC], NaCl, MgSO MgCl Again, fresh water may be sprayed under the influence of hydrostatic pressure as before.

If the deposit contains hard salts of the composition 34.1% KC], 36.0% NaCl, 23.4% MgSO 0.2% MgCl 0.4% CaSO a solution of approximately the following composition is obtained: ]28 142 g/l KC], 177 220 g/l NaCl, 11 22 g/l MgCl 66 98 g/l MgSO at an operating temperature of approximately 30 C at depths of approximately 500 600 m. The sludge obtained contains predominantly NaCl, KCl and MgSO.,, in smaller quantities of MgSO MgCl and CaSO The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a somewhat diagrammatic illustration showing the formation of the various bores and passages in a deposit to be recovered; and

FIG. 2 is a somewhat diagrammatic illustration of an apparatus for carrying out the method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 4, there is first sunk an access shaft 1 to the region of the deposit to be recovered. From this access shaft 1 a tunnel 2 is driven to the deposit at the level of the upper region of the deposit. Once the deposit has been reached, an upright working shaft 3 is driven in the deposit and has its size increased by flushing with water under pressure to between 4 and in cross section. It is now fortified in the usual manner of below ground shafts so that personnel and material can move through it.

A plurality of horizontal vertically spaced at least substantially parallel flushing passages 4 are driven outwardly from the shaft 3. The spacing of these passages 4 from one another is determined in accordance with the mean thickness of the deposit, for instance a 10 m spacing if the thickness is 3 m. The cross section of the passages 4 is approximately 3 4 m The passages 4 are connected with the bore 3which by now has been increased in cross-sectional dimension-via connecting passages 5 having a length of at most 5 m. This permits the subdivision into sections or chambers 6 each having 1 4 layers 7. Vertical pillars 8 of approximately 10 m thickness remain between the bore 3 and the passages 5. The individual chambers are horizontally limited by the pillars 10 located at opposite sides of the cross passages 9. The thickness of the pillars above the cross passages 9 is selected to be between approximately 5 and 10 m, that of the pillars below the cross passages 9 to be approximately 3 5 m. It has been found that the horizontal pillars are hardly attacked when solution is removed from the region above them, because the soluble salts are dissolved while the insoluble salts such as clay and anhydrite will sink and quickly form a bottom layer which provides protection against solution, and because in accordance with the specific weight the salt solution will immediately after entry become differentiated so that at the lowers locations there quickly develops saturated solution with the result that even at the beginning of the leaching process and before formation of the protection bottom layer the hollowing out process on the bottom of the working area proceeds only slowly.

A down supply conduit 11 serves to supply fresh water from above, and interposed in the conduit 1 1 are containers 12 at different heights which serve to regulate the flushing pressure.

The apparatus 13 according to the present invention is shown in FIG. 2. It comprises a movable support 23 with for instance two pairs of flushing tubes 24a arranged in parallelism with the elongation of the flushing passage, and with a transversely extending spray tube 24b. This support is advanced, with the tubes in withdrawn condition, to the leading end of a respective flushing passage (see FIG. 1, left-hand side) and arrested by means of the device 34 with respect to the bottom and roof of the passage. Then the conduit 30 is utilized, in conjunction with the distributor 31 and the hoses communicating with the tubes, to supply water to the latter. This water issues from the tube in finely divided spray through the

apertures

27, 28 and 29 and dissolves the soluble salts. The tubes are slidably guided in the guide tubes 25 and are automatically advanced to approximately 2 m lengths in accordance with the formation of hollow space ahead of them (resulting from the solution of the soluble salts) by the device 26a and 26b. The transversely extending spray tube serves to smooth the bottom wall. When the end position has been reached, the device 34 is operated to release the apparatus 13 so that it can be advanced by the available newly created hollow space, for instance approximately 2 m. If for instance the cross sectional area to be treated is 3 m and 6 tubes and l transverse tube are utilized, quantity of 50 60 m water per hour must be sprayed and a rate of advancement of 20 30 cm/h is obtained.

Because of the spraying of the water against the leading wall of the respective flushing passage 4, the water dissolves salt such as 30 40 g/l KC] and g/l NaCl in a sylvanite deposit containing l5% K 0. The unsaturated solution 14 shown in FIG. 1 flows along the bottom wall of the respective passage 4 to the slots 15 and from them passes to the lowest location 1611.

The inclined slots may be provided in conventional manner with suitable drilling apparatus, or with longitudinally extendable tubes through which water is driven to hollow out the material and form the slots in this way. They serve for further enrichment of the solution and permit a controlled brine formation. The spacing between the individual slots is selected in dependence upon the thickness of the deposit and within any one layer it is approximately identical; usually the distance is between substantially 0.5 and 5 m.

The solution passing through the slots dissolves and absorbs further salts, for instance if the slots have a length of 8 10 m and an initial diameter of 30 40 mm, with the deposit containing 15% K 0, the solution will absorb between approximately 10 15 g/l KCl and 20 30 g/lNaCl. This of course results in an increase of the diameter of the inclined slots. The location 16a receives not only the unsaturated solution coming through the inclined slots, but also additional fresh water which is supplied through the conduits 11b. The supply can be locally controlled by valves 17 so that the brine formation can be locally influenced in this manner. It is advantageous to maintain the quantity of solution or brine 18 approximately I m below the upper surface of the location 16a. After the solution is saturated, with the dwell time in a deposit having a lpercent K 0 content requiring approximately 6 8 hours, the solution is pumped above ground via valve controlled conduits 19 which are cemented into the horizontal pillars and which communicate with the conduit 20 from where the solution is first passed to a collecting basin 21 to be pumped above ground through the conduits 22 from there.

Filling of the below-ground spaces just discussed with unsaturated solution and fresh water is repeated as many times as necessary to obtain the desired degree of mineral recovery. The water which is obtained on evaporation of the saturated solution above ground is continuously recirculated. It is advantageous to operate at least three different sections or chambers simultaneously and these may be located vertically or horizontally. In this manner the operation above ground may be continuously supplied with saturated solution. Once the chambers 16b are hollowed out, they can be filled up in the manner usual in underground operations.

To obtain a yearly yield of approximately 50,000 jato K 0 at 90 percent yield and 250 working days, a daily yield of 220 T x,o is necessary which corresponds to a quantity of KCl amounting to 350 T. If the deposit contains 15% K 0, the KCl quantity going into solution within the 6 8 hour dwell time amounts to 125 g/l and the NaCl quantity amounts to 255 g/l at 22 operating temperature at 500 m depth. A daily brine quantity of approximately 2,800 m is required. At continuous operation the brine supply is to be approximately 120 m lh. At a spacing between adjacent layers of 10 m for a deposit having an average thickness of 3 m, 63 T of raw salt and approximately 8.2 T K,O are obtained per running meter of length of the deposit and a cross section of 3 m for the flushing passages.

It follows that per day approximately 36 m advancement of the flushing passages is necessary. To obtain this a brine requirement of at least 1,500 m necessary, assuming an absorption factor of 35 g/l KCl and 85 g/l NaCl, and this total quantity used once for flushing absorbs approximately 52.5 T KCl and 33.2 T K 0. These 1,500 m unsaturated solution (with reference to KCl and NaCl) adsorbs on passing through the slotted slots an additional l5 g/l KC] and 30 g/l NaCl, that is an additional 22.5 T KC] and 14.2 T K 0. This is based on the assumption that two of the flushing passages 14 are simultaneously operated at three shifts with a brine supply of 35 40 m lh. The unsaturated solution, together with the remaining approximately 900 m fresh water is supplied to the lowest point of the working station, and the fresh water is supplied via the conduit provided with valves to the upper side, so that after approximately 6 8 hours dwell time a final content of approximately 125 g/l KCl and 255 g/l NaCl is obtained. The quantity of water which is to be circulated above ground amounts to approximately 2,400 m because at 125 g/l KCl and 255 g/l NaCl salt content the content of the water in the brine is 855 g/l.

It will be seen that with the present invention and in contradiction to the statements of the aforementioned Spackeler publication-dwell times to saturation of only approximately 6-8 hours are necessary, as opposed to many weeks. In this time, and assuming that a deposit contains 15% K 0, brine contents of approximately l25 g/l KCl and 255 g/l NaCl can be obtained.

This considerable advantage in the state of the art is made possible by the fact that the inclined slots 15 open up the deposit for easier dissolution of the soluble minerals and simultaneously increase the free surface of the cavities for the leaching process. In addition, the provision of the slots 15 provides for a very advantageous relationship of the soluble surface versus quantity of soluble matter.

The present invention further affords the advantage that the solutions obtained in the flushing passages are passed to the lower portions of the cavities through the inclined slots 15 and in so doing further undergo enrichment with soluble matter.

A further advantage of the present invention with respect to the state of the art is to be seen in the fact that the locally regulatable supply of water quantities permits a control over the hollowing-out of the cavity, so that even deposits can be leached out whose thickness is different at different locations.

Contrary to Spackeler which teaches as the state of the art that the leaching approach is not economically practical, the present invention overcomes this heretofore existing disadvantage and makes it possible to obtain, for instance, a daily recovery rate of 222 T K 0 continuously under recirculation of the solvent brine, at three-shift operation, with economic dwell times of the brine to solution, and with the possibility of controlling precisely the hollowing-out below ground.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of applications differing from the types described above.

While the invention has been illustrated and described as embodied in a method and an apparatus for the recovery of underground deposits of soluble materials, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, for foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

We claim:

1. A method of recovering underground deposits of soluble minerals, comprising the initial steps of sinking an access shaft to the region of said deposit; driving a tunnel from said access shaft to said deposit; driving an upright working shaft from said tunnel into said deposit; driving from said working shaft into said deposit a plurality of vertically spaced substantially horizontal and at least substantially parallel flushing passages at a predetermined distance from one another; forming in said deposit a plurality of slots each connecting two adjacent ones of said passages and being inclined thereto; and the recovery steps of forcing water through said passages and slots to thereby dissolve soluble minerals from said deposit and collect the thus obtained solution in the respectively lower of said passages at least substantially saturating said solution with dissolved minerals by supplying said solution together with fresh water to the next lower of said passages through the intervening zone of said deposit; collecting the saturated solution underground; pumping the collected solution from below ground to above ground; recovering the dissolved minerals from the solution; returning the residual water remaining after recovery of the dissolved minerals, into said passages; and repeating said recovery steps until exhaustion of said deposit.

2. A method as defined in claim 1, wherein the step of driving said passages comprises spacing said passages in accordance with the thickness of said deposit.

3. A method as defined in claim 2, wherein said passages are spaced from one another by substantially m if the thickness of said deposit is on the order of 3 m, and by substantially 25 m if said thickness is on the order of 10 m and more.

4. A method as defined in claim 1, wherein the step of forming said slots comprises spacing said slots from one another by a distance of between substantially 0.5 m and 5 m.

5. A method as defined in claim 1, wherein said deposit is of KCl and/or NaCl, and wherein the dissolved and recovered minerals are KCl and/or NaCl.

6. A method as defined in claim 1, wherein said deposit is a sylvinite deposit containing substantially K 0, wherein said solution contains substantially 30 40 g/l of KC] and 80 90 g/l of NaCl, and wherein said saturated solution has a content of KCl which is higher by substantially l0 15 g/l and an NaCl content which is higher by substantially 30 g/l.

7. A method as defined in claim 1, wherein said deposit is elongated in substantially vertical direction; and wherein the step of driving said passages comprises driving a first set of passages and at least one additional set of passages vertically spaced from said first set and separated therefrom by a region of said deposit which is free from said passages.

8. A method as defined in claim 1, wherein said passages are arranged in at least three separated groups of passages; and further comprising the concurrent steps of forcing water through the passages of a first one of said groups, saturating the solution contained in the passages of a second one of said groups, and pumping collected saturated solution from a third one of said groups.

9. A method as defined in claim 1, wherein said deposit is a hard-salt deposit containing KCl, NaCl, K MgSO and MgCl and wherein said solution and said saturated solution contain dissolved quantities of KCl, NaCl, K 80 MgSO and MgCl and wherein the step of recovering said dissolved minerals comprises subjecting said saturated solution to evaporation and crystallization treatment.

10. A method as defined in claim 1, wherein the step of forcing water through said passages comprises forcing fresh water against the walls bounding said passages whereby minerals are dissolved and the thus obtained solution passes through said slots to the next lower passage.

11. A method as defined 11'] claim 10; and further comprising the step of regulating the quantity of solution so as not to exceed a level of l m below the upper surface bounding the respective passage.

12. A method as defined in claim 10, wherein the step of forcing fresh water against the walls bounding said passages comprises spraying such water under the influence of prevailing hydrostatic pressure.

13. A method as defined in claim 1, wherein said deposit is a carnallitite deposit ranging between rich and poor in its rocksalt content, and wherein said solution and saturated solution contain dissolved KC], MgCland NaCl; and further comprising the step of treating said saturated solution subsequent to pumping above-ground so as to recover MgCl and a crystalline byproduct containing KCl and NaCl.

14. A method as defined in claim 13, wherein sludge containing KC] and NaCl forms in said next-lower passage; and further comprises the step of flushing said sludge out of said next-lower passage with said saturated solution, and conveying said sludge aboveground for further processing.

15. A method as defined in claim 13, wherein said deposit contains up to substantially 5 percent of kieserite.

Claims

2. A method as defined in claim 1, wherein the step of driving said passages comprises spacing said passages in accordance with the thickness of said deposit.
3. A method as defined in claim 2, wherein said passages are spaced from one another by substantially 10 m if the thickness of said deposit is on the order of 3 m, and by substantially 25 m if said thickness is on the order of 10 m and more.
4. A method as defined in claim 1, wherein the step of forming said slots comprises spacing said slots from one another by a distance of between substantially 0.5 m and 5 m.
5. A method as defined in claim 1, wherein said deposit is of KCl and/or NaCl, and wherein the dissolved and recovered minerals are KCl and/or NaCl.
6. A method as defined in claim 1, wherein said deposit is a sylvinite deposit containing substantially 15% K2O, wherein said solution containS substantially 30 - 40 g/l of KCl and 80 - 90 g/l of NaCl, and wherein said saturated solution has a content of KCl which is higher by substantially 10 - 15 g/l and an NaCl content which is higher by substantially 20 - 30 g/l.
7. A method as defined in claim 1, wherein said deposit is elongated in substantially vertical direction; and wherein the step of driving said passages comprises driving a first set of passages and at least one additional set of passages vertically spaced from said first set and separated therefrom by a region of said deposit which is free from said passages.
8. A method as defined in claim 1, wherein said passages are arranged in at least three separated groups of passages; and further comprising the concurrent steps of forcing water through the passages of a first one of said groups, saturating the solution contained in the passages of a second one of said groups, and pumping collected saturated solution from a third one of said groups.
9. A method as defined in claim 1, wherein said deposit is a hard-salt deposit containing KCl, NaCl, K2SO4, MgSO4, and MgCl2, and wherein said solution and said saturated solution contain dissolved quantities of KCl, NaCl, K2SO4, MgSO4 and MgCl2; and wherein the step of recovering said dissolved minerals comprises subjecting said saturated solution to evaporation and crystallization treatment.
10. A method as defined in claim 1, wherein the step of forcing water through said passages comprises forcing fresh water against the walls bounding said passages whereby minerals are dissolved and the thus obtained solution passes through said slots to the next lower passage.
11. A method as defined in claim 10; and further comprising the step of regulating the quantity of solution so as not to exceed a level of 1 m below the upper surface bounding the respective passage.
12. A method as defined in claim 10, wherein the step of forcing fresh water against the walls bounding said passages comprises spraying such water under the influence of prevailing hydrostatic pressure.
13. A method as defined in claim 1, wherein said deposit is a carnallitite deposit ranging between rich and poor in its rocksalt content, and wherein said solution and saturated solution contain dissolved KCl, MgCl2 and NaCl; and further comprising the step of treating said saturated solution subsequent to pumping above-ground so as to recover MgCl2 and a crystalline byproduct containing KCl and NaCl.
14. A method as defined in claim 13, wherein sludge containing KCl and NaCl forms in said next-lower passage; and further comprises the step of flushing said sludge out of said next-lower passage with said saturated solution, and conveying said sludge aboveground for further processing.
15. A method as defined in claim 13, wherein said deposit contains up to substantially 5 percent of kieserite.