US 2625384 A
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Jan. 13, 1953 R. D. PlKE ErAL MINING oPERATIoN Filed July 1, '1949 INVENToRs ,471755477- 0. //KE BARRIER .CTRONA BED Patented Jan. 13, 1953 MINING OPERATION Robert D. Pikc and Max Y. Seaton, Greenwich",
Conn., assignors: to Food Machnery and Chemi'cal Corporation, New York, N. Y., a corporation of Delaware Application July 1, 1949, Serial No. 102,599
This invention relates to a novel and economical method for mining trona. There has recently been discovered near Green River, Wyoming, a mineral deposit which is a-n almost' level. bed of trona which is about 95% water soluble, yielding a solution of so'dum sesquicarbonate which' is almost chemically pure, except for: a small amount of coloring matter which may be removed by adsorption. The bed ranges from 10-15 feet thick and lies' at a depthV of approximately' 1500 feet below the surface. This invention is applicable to the minng and recovery of trona and other soluble salts from this andsimilar sal't bede.
NoI bo dy' ofV almost pure trona has hithertu been discover'ed.V This mineral, while. fairly common in. arid regions, as hitherto known, is contaminated with considerable amounts of NaCl and NazSO'4. But' inR the Green River trona, NaCl is present only to the extent of. about 01%, and N`a2SO4 occurs in even smaller percentage'. Nor has any deposit of subterranean. trona hith'erto been discovered, all known dep'osits being on or very near the surface. The discovery, therefore, near Green River, Wyoming, of a Vast' body of almost pure subterranean. trona of mineable thi'ckness, is a unique oocurrence presenting unusual problems in the mining and recovery thereof.
The roof conditions over this deposit are. suitable for mining by the conventional room-andpillar system which we propose tov use for dry mining. In this method the trona ismined' from so-called unit panels, which when m-ined out, contain numerous supporting pillars. of the trona, outlning the rooms from which the ore has been removed from each side ofv the central access and haulageways, which are employed while. the panels are being mi'ned. The room pillars which are left in the panels, support the roof. and the so-called barrier pillars separate the panels from each other and from the surroundi'ng tron'a bed.
In following our method, We proceedv withV dry mining alone until' a. number of' mined out panels are left which are sufficiently remote from the current dry mining operation to enable us to carry out solution mining without encountering the danger of' fioodng the dry mining workings. This may take a number of years, say three to five, depending upon the rate of production by dry mining. At the expiration of this time, in accordance with our invention, We start solution mining of the material in the room pillars and barrier pillars.
We may proceed to thus mine one panel, 01' preferably a pair of panels,. one on each side of the main access and haulageways, which. were used in dry mining. We do'this by laying a water pipe along the bottom surface level of the panel haulageway to' discharge water at approximately ground temperature and about two-thirds of: the way' back towa'rds the rear barrier p-illar. Where the pipe enters the panel, we erect a bulkhead or retaining wall across the accessway, through which wall: the pipe ente-rs at its bottom level and also a drainage pipe is placed at thev same level. Th-isdrainage pipe' is usedto lead the liquor from solution mining to the suznp of a pump. We preferabl-y extenrl this bulkhead to, or` nearly to, the roof. If desired the walls adzjacent the bulkhead may be lined With an insoluble material, such as concrete', for a suitable distance inward fromthe bulkhead. to assure that the walls adja- Acent the bulkhead will not be attacked by the solution.
The. supply pipe, or the: two pipes, if a pair of mined outpanels is to beV treated at' the same time, extends to the surface-Where it receives, the water required for solution. This water entering thepa-nel. at aZ controlled rate of flow, first attacks and. dissolves the bottom of the room pillars in the immediate V-ici-nity of the end of the pipe. This will eventually cause these pillars to coll-apse and as they become dissolvechthe area of unsaturated solution spreads and dissolves more pillars, thusv eventually eausing most of the roof to collapse and most of the` pillars to go into solution.
All of the water introduced through the pipe from the surface necessarily eventually' flows out through the drain pipe in the bottom of the bulkhead asa substantially saturatecl solution 'at the ground. temperature. This solution flows: to the suction of a pump, which wepreferably install nearby in' the main haulage and accessway and this lifts the saturated solution to the. surface. As the solution flow-mg to the pump is: always substantially satu-rated, the material in. the immediate. vic'inity of the bulkhead and. the: pump, although. sol-uble in Water, is not attacked by the saturatecl solution. Of course, if the flow of Water were kept up' long enough,. all. of thesoluble material near thev bulkhead and pump Would eventually be dissolved and the barrier pillar between` the panelA and the main accessways, Would. be at least pa-rtially dissolved. We' prefer to stop the fiow of water considerably short of this, but, if necessary, all. undesired solution of trona near the bulkhead and pump pit can be prevented. by lining the wallsz at these points withV an insoluble material.
Once: having startedl solutionv min-ing', we prefer to carry it on in step relation with the dry mining operation. We thus prefer to bring to the surface each day sufiicient sodium carbonate by solution mining, so that when this has been recovered, the total production formerly had by dry mining alone, will remain unchanged.
The principal object of our invention is to set up mining conditions in the trona whereby a considerable percentage of the total tonnage of iNazCOa produced is from low cost solution mining of the mined out panels. v
A further object of our invention is to combine the production of sodium carbonate by solution mining and dry mining. This we prefer to do by heating the solution pumped up from the solution mining Operations, and dissolving dry mined trona in it. The combined solution may then be clarified and used for the production of sodium carbonate by any suitable method, as for example, running to dryness in a rotary kiln, or
drying in ponds on the surface by solar evaporation. An advantage of this latter method resides in its ability to crystallize out pure sodium carbonates, leaving what NaCl and Na2SO4 may have been picked up in the solution mining operation, in the remaining mother liquor, which is then discarded.
Having described our invention in general terms, we now refer to the drawings of which- Figure 1 shows a diagrammatic layout of a plan for underground mining, embodying our invention; and
Figura 2 shows a longitudinal section through a panel along the accessway in which the pipe is laid.
In the drawings, IO is an Operating shaft which may be either inclined or Vertical, designed to receive mined trona and to raise the same and deposit it on the surface. At H is indicated an escape and air circulation shaft, which with slight modification may be used for full operation. The main entries for access, haulage and air circulation are shown at |2, l3, |4, l5 and IG. A typical mined out panel is shown at I'l and its companion panel in which dry mining is progressing, is shown at |8, although the precise location of 18 is open to considerable choice. While a generally rectangular dry mining operation has been shown, it will be understood that radial operation of mining shafts from 'a central access shaft and other arrangements may be used.
Panel |9, together with H, may be considered as typical panels for solution mining. The room pillars are of various forms, but two types are indicated as 22, 23, the lattei` appearing in both Figures 1 and 2. The so-called barrier pillars are indicated at 24, and 26. The pipe 28 may be laid in accessway 21. The pump sump is indicated at 29 and the pump at 30.
In practice, we supply water in controlled amount from the surface through pipe 28 and we may not open the pump valve 3| until the water has accumulated to a depth corresponding to the top of the bulkhead 32. At this point, or sooner if desired, w-e open valve 3| and pump the solution to the surface. We prefer to continue to add water until attack begins on the barrier pillar 28. At this point we may shut off the water from the surface, but continue to pump solution to the surface until substantially all of it has been pumped out of the panel. By this time most of the roof of the panel will have collapsed, opening up drainage of solution containing both NazCOa and NaI-ICOs and NaCl from overlying structures,
but we have observed that these structures are so dense that they do not provide a sufiicient ilow of brine to be an important factor. In fact, the continuing stream produced by them from an entire mine will only amount to a few gallons per minute and can easily be dealt with.
We have found that it is desirable to supply water to the underground pipe at no lower temperature than the underground temperature of about 70 F., but during the Winter months the water available on the surface is at a considerably lower temperature and should be heated to the ground temperature before being introduced. This is because cold water will dissolve the trona more slowly and less than Water at a higher temperature and also if the temperature of the Water be below about 70 F., there is a tendency to decompose the trona dissolving NazCOs preferentially and leaving solid NaHCO3 behind in the mine. But at temperatures at about 70 F. and above, the tendency is to dissolve trona without decomposition until the solution is saturated when an exchange will begin whereby NazCOa goes into solution and NaHCOz comes out until the trona sodium bicarbonate invariant point is reached, at which point solid trona is in equilibrium with solution. Thus at temperatures below 70 F., trona will be decomposed With preferential solutions of NazCOs leaving NaHCOa behind as a solid but at temperatures of '70 F. and above, there will be more of a tendency for trona to be dissolved as a whole, that is, congruently, although the possibility of sel-ective solution of NazCOz cannot be dismissed because of the large surface of the pillars and the long time of resistance of the water in the panel. Nevertheless, we have found that the more usual condition is solution of trona as such, that is, congruently, under the existing conditions, but our process deals With either condition, that is, congruent solution which leaves no solid sodium bicarbonate in the mine and solution which corresponds to the trona sodium bicarbonate in- Variant point which necessarily leaves a considerable amount of sodium bicarbonate in the mine. Intermediate conditions will often exist between these two extremes.
In citing an example for purpose of illustration, We shall assume that solution of the trona is congruent and that the temperature is '70 F.
In this example, it is assumed that an annual production of 500,000 tons equivalent NazCOz is desired. Principal significant data for such production are given in the following:
Equivalent NazCOx produced by solution mining annually, tons 206,000 Same, by dry mining, tons 294,000
Total, tons 500,000
In this example, a panel has the assumed dimensions of about 1275 feet long by 802 feet wide and contains about 449,160 tons of clear trona, not including the top approximate 3 feet of trona of a 10 foot bed, which is heavily contaminated with shale and which is estimated as being lost, although in practice we recover a considerable amount of it by our process. Of the 449,160 tons recoverable trona estimated as being in the panel, about 52% of the total is recovered by dry mining and of the remaining 48%, a sufiicient amount is recovered so that recovery by solution mining is 41% of the total production.
When the solution of trona from the pump 30, which is an approximately saturated solution at 70 F. reaches the surface, it may be heated to approximately boiling temperature and additional dry mined trona may be dissolved therein.
A boiling hot saturated solution of pure trona or sodium sesquicarbonate and water contains about 2.77 lbs. H2O per pound of equivalent NazCOs, but the solution at 70 F. produced by solution mining contains 7.53 lbs. water per pound equivalent NazCOs, leaving a surplus of 4.76 lbs. Water which Will dissolve 1.73 lbs. equivalent Na2CO3; but only 1.43 lbs. must be dissolved to correspond to the assumed production of dry mined trona, which in turn corresponds to 1 1b. equivalent NazCOs produced by solution mining. This leaves 0.85 1b. surplus water which must be evaporated, corresponding to 2.43 lbs. total equivalent NazCOs, or 0.34 lb. water per pound total equivalent NazCOs. This is not a serious additional load on the evaporative system used where dry mining alone is practiced, because with dry mining alone the necessary evaporation is 2.77 lbs. per lb. equivalent NazCOa if the dry mined trona is dissolved in boiling hot water as a step in its processing so the additional evaporative load is only about 121/2%, which is of little consequence when the value of the sodium carbonate won by solution mining and brought to the surface at little additional cost is taken into consideration. The dried trona may be used as such or may be calcined to produce sodium carbonate.
While we have described a preferred method of applying our invention, it will be understood that solution mining may be carried out in one portion of the bed as described, for example, in the patent to R. D. Pike, No. 2,388,009, while dry mining is being carried out in another portion of the bed, and that the dry mined trona may be added to the solution mined trona in the manner described herein; also that various other modifications and changes may be made in the dry and solution mining operation and the recovery of the trona, and that the processes described herein may be applied to the recovery of other soluble salts, without departing from the spirit of this invention or the scope of the appended claims.
1. A process for recovering sodium carbonate from trona beds, which comprises dry mining the trona, introducing water at substantially the temperature of the trona deposit into the dry mined Sections of the bed to remove residual trona after the dry mining, bringing the solution of trona to the surface, heating said solution and dissolving in it dry mined trona, and processing to produce sodium carbonate.
2. A process for recovering sodium carbonate from trona beds, which comprises dry mining the trona bed, introducing water at a temperature not lower than ground temperature into the dry mined sections of the bed to remove residual trona after the dry mining by solution, bringing 6 the solution to the surface, heating said solution and dissolving dry mined trona in it and processing to produce sodium carbonate.
3. A process for recovering sodium carbonate from trona beds, comprising dry mining the trona bed, removing residual trona after dry mining by solution mining at substantially the temperature of the trona deposit, pumping the solution to the surface, heating and dissolving in it dry mined trona, and processing to produce sodium carbonate.
4. The method of recovering sodium carbonate from underground deposits of trona which comprises introducing water into the underground deposit of trona at substantially the temperature of the underground deposit, withdrawing a solution substantially saturated with trona at the underground temperature and bringing said solution above ground, heating said solution to approximately boiling temperature and dissolvlng more trona therein and processing said solution to produce sodium carbonate therefrom.
5. The method of mining crystallizable salts having two components of different solubilities but each having substantially greater solubility at higher temperatures than at lower temperatures which comprises introducing water into the salt deposit at substantially the temperature of said deposit contacting the deposit with the water until the water is substantially saturated by solubilizing said deposit, removing the solution from the deposit and adding heat thereto, dissolving more of said salt in said solution and recovering the salt from said solution.
6. A method for the continuous mining of the deposits of Green River trona which comprises removing about one half of the trona in a section of the mine by dry mining leaving mined out rooms with the roof supported by pillars of the unmined trona, erecting barriers isolating a portion of the mined out section remote from current dry mining Operations, flooding the isolated area with water at approximately the temperature of the trona deposit, dissolving out the unmined trona with the introduced water until the introduced water is substantially saturated with trona, pumping the aqueous solution to the surface, heating the solution to approximately its boiling point, adding previously dry mined trona until the introduced trona approximates the solubilized trona, and recovering the sodium carbonate content of the heated water whereby new sections are made available for solution mining at substantially the same rate as the trona in solution mined sections is exhausted.
ROBERT D. PIKE. MAX Y. SEATON.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 1,121,225 Bradley Dec. 15, 1914 2,200,665 Bolton May 14, 1940 2,388,009 Pike Oct. 30, 1945 FOREIGN PATENTS Number Country Date 135,722 Germany 1902 198,375 Germany 1908