US2333138A - Recovery of sodium sulphate - Google Patents

Description

c. D. ADAMS 2,333,138

RECOVERY OF SODIUM SULPHATE Nov. 2, 1943.

Filed Oct. 19, 1940 3 Sheets-Sheet l l ATTORNEY.

NOV.. 2, 1943. C, D, ADAMS 2,333,138

RECOVERY OF SODIUM SULPHATE Filed Oct. 19, 1940 3 Sheets-Sheet 2 ATTORNEY.

Nov. 2, 1943. c. D. ADAMS 2,333,138

RECOVERY OF SODIUM SULPHATE Filed Oct. 19, 1940 5 Sheets-Sheet 5 A /ze r /327 INVENTOR.

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4a BY @MM ATTORNEY. l

Patented Nov. 2, 1943 2,333,138 RECOVERY or sonrUM stJLPnATE Charles D. Adams, Pomona, Calif. Application October 19, 1940, Serial No. 361,908

7 Claims.

My invention relates generally to the recovery of sodium sulphate, and more particularly to the separation of the sulphate from the various sub- .stances with which it is usually found in nature.

As will become evident hereinafter, my invention is particularly applicable to deposits where the bulk of the material is sodium sulphate, and the associated salts are either considerably more or considerably vless soluble than said sulphate.

In its preferred form, my process involves generally the flooding of the sulphate deposit with sait water to form a pulp or slurry, conveying the pulp toa settling tank to remove the clay and the greater portion of the gypsum, refrigerating the liquor to precipitate crystals of sodium sulphate, and iinally dehydrating the crystals if anhydrous sodium sulphate isdesired. It is also a feature of my invention to recirculate the solutions so as to get the maximum benefit from the water used and also to utilize the water of crystallization which is driven oil by the drying process.

Another feature of my invention is the recirculation or hot gases in the dehydrator to minimize heat loss and also the provision of a novel heat exchange system whereby the heat of one solution which is to be cooled is used to heat another solution.

In the drawings I have illustrated schematically one application of my method, and suitable apparatus for accomplishing it.

Fig. ll is a ilow sheet illustrating the process diagrammatically.

Fig. 2 is in the nature of a pictorial ilow sheet in elevation showing how the various steps of the process of Fig. 1 are accomplished.

Fig. 3 is an elevational view of a body of salt water and pumping apparatus usable in my process, and indicated by the letter A in Fig. 2.

Figs. 4 and 5 are enlarged plan and elevational views respectively of the basin and dredging equipment indicated at B in Fig. 2.

Fig. 6 is an enlarged elevational view of the settling tank C of Fig. 2.

Fig. 7 is an enlarged elevational view of the refrigerating and separating means D of Fig. 2.

Fig. 8 is an enlarged elevational View of the drier E of Fig. 2.

Fig. 9 is a partial section on an enlarged scale of pipes 20 and 40 showing my novel heat exchange system.

It will be understood, of course, that, all of said gures are purely diagrammatic, and that no attempt has been made to illustrate specific parts or dimensions of the apparatus.

- As previously mentioned, I prefer to use salt (sodium chloride) water as my solvent, since it materially increases the rate of.sodium sulphate crystal growth, and if it is available I prefer to use the natural water of salt lakes, such as the Salton Sea located in the Imperial Valley of California. For the most efficient operation of my process, the sodium chloride content of the water should be from 3% to 4%, although I have found that concentration as low as 2% materially aids in the crystal growth. In Fig. 3

I have illustrated a natural body of salt water indicated bythe letter A, in which a float i0 supporting the inlet end of a pipe I I is anchored offshore. The pipe Il is connected to a pump l2 which pumps the sea water through a pipe I3 to the deposit B shown in Figs. 4 and,5.

While there are, of course, various suitable ways of getting the solids from the deposit B into solution and suspension, such for example as excavating and mixing with the solvent, I prefer to form a relatively shallow basin in the deposit B and to ood it with the salt water pumped from the lake A. Having formed a pond or lake in the deposit, a cheap and eilicient method of extracting the sulphate and associated solids is by means of a barge lll provided with hydraulic dredging machinery indicated generally by the numeral l5, which pumps the mixture of solution and solids in` suspension from the deposit B through the pipe i6 into the settling tank C. In

this connection a power shovel Il in combination with a jet I8 may be used to loosen up the deposit and assist in forming the pulp which is dredged'out of the artificial pond formed in the deposit. In deposits such as found in the vicinity of the Salton Sea, the pulp pumped out of the basin B to the settling tank C shown in Fig. 6,

consists principally .of water, sodium sulphate,

sodium chloride, calcium sulphate, clay, and a small percentage of miscellaneous impurities. If there is no gypsum present in the deposit, I prefer to add a limited amount thereof since I have found that it materially facilitates the speedy settling of the clay. The pulp is allowed to remain in the settling tank C until substantially all of the clay has settled to the bottom,

and then the solution is drawn oi in such a manner as to not materially disturb the sediment 48 in the bottom of the tank. Various means may be employed for drawing off the solution, but I have found that one very satisfactory method is to build the tank with a variable vheight dam at one end formed by a rotatable gate I9, which can be gradually lowered as the depth of the solution in the tank decreases.

From the tank C the solution passes through the pipe 20 to the refrigerating apparatus D which may of course take various forms. In Fig.'1 I have illustrated what I now deem to be the preferred form of refrigerating apparatus suitable for use in my process. The solution drawn off the top of tank C ows through the pipe 20 into a tank or flume 2|, preferably set at an angle to promote the natural flow of the liquid from the inlet end thereof to the outlet. Refrigerating 'means such as cooling coils 22 are provided in the ilume 2| and are maintained at a temperature sufficiently low to lower the temperature of the incoming liquid to approximately 50 F. during the time it is passing through the flume. This reduction in temperature of the liquid which leaves the settling tank at a temperature of preferably around 90 FF. causes a rapid growth of sodium sulphate crystals, it being understood of course that the length of the fiume and the rate of :dow therethrough are such as to allow ample time for said crystal growth. I have found that as the temperature is decreased the rate of growth and the total yield of crystals increases, but below 50 F. the increase in yield is proportionately less, i. e., the slope of the curve plotted with crystal yield against decrease in temperaturedecreases materially in the region of 50 F., and the additional yield is not suflicient to warf rant the extra cost necessitated for the additional cooling. Consequently I prefer to operate the refrigerator at a solution temperature of approximately 50 at which point I have found that I secure the maximum proportional yield per unit of cost.

I have also found that as the percentage of sodium chloride in the solution is increased, the rate of crystallization of the sulphate is increased, but that the curve of sodium chloride concentration plotted against the rate of sodium sulphate crystal growth attens out materially for sodium chloride concentrations in excess of 6%. This is probably due to the fact that a given quantity of water will only dissolve a limited amount of. soluble solids, and consequently an excess of sodium chloride in solutions limits the total amount of sodium sulphate which can be taken up into the solution in the first instance, and consequently the amount which can be precipitated in crystalline form in the refrigerator. As previously mentioned, I prefer to operate with solutions containing in the neighborhood of 3% sodium chloride at which point I obtain the maximum crystal yield per unit cost of operation.

When the liquid has remained in the refrigerating flume for a suillcient length of time to form the required amount of sodium sulphate crystals, it passes to suitable separating means which preferably takes the form of a revolving screen indicated in Fig. '1 by the numeral y23. The :solution flows down through the screen into a sump tank 24 and is pumped back through the pipe 25 to the ume 2|, and recirculated around the refrigerating coils to recover the sodium sulphate which did not come out of solution in the i'lrst run. From the filtering screen 23, the crystals may be passed into a second rotating filter screen 26, which functions as a washer, and is provided with a J'et 21 through which extremely cold water lor a weak solution of sodium sulphate, preferably at a relatively low temperature, ispassed.

By keeping the temperature of the washing solution down to a minimum, the amount of sodium sulphate dissolved from the crystals being washed is kept to a minimum, particularly if the washing solution has some sodium sulphate already in it. The washing solution passes down through the screen 26 to a sump 28 from where it can be recirculated by the pump 29 or otherwise utilized as desired. The washed sodium sulphate crystals now pass into a-centrifuge where they are partially dried, and are then in marketable form as Glauber salts.

However, if it is desired to dehydrate the crystals to produce anhydrous sodium sulphate, the crystals may be spread out on trays and exposed to the sun, which in hot Weather is adequate for drying, this being especially advisable where the crystals are small, as is the case where they are formed quite rapidly. However, if more rapid drying is desired, or if a hot sun is not available, the crystals may be conveyed through the hopper 30 to a drier such as shown in Fig. 8. While it will-be understood, of course, that various types of drying apparatus may be used to produce anhydrous sodium sulphate from the crystals, I have found that a drier of the type illustrated herein is the most effective for my purposes.

. As will be seen fromFig'. 8, the partially driedv sodium sulphate crystals pass from the hopper 30 intoajmixingl chamber or conveyor 3| into which lsome anhydrous sodium sulphate is also passed by means of a chute. The mixture of anhydrous sodium sulphate and hydrated sodium sulphate is conveyed through the chamber 3| by any suitable means to a rotary hot air drier 33, which may be connected to a furnace 34 of conventional type. After the crystals have been dehydrated, thehot air gases and dried sodium sulphate are then blown through an outlet pipe 35 to a separator 36 in which the solids are separated out and allowed to pass through the'hopper 31. The greater portion of the solid material, which is practically pure anhydrous sodium sulphate, pass down through hopper 31 and pipe 38 to a storage bin 39, while a portion of the sulphate is by-passed through pipe 32 into the mixing chamber 3| for the purpose heretofore described. The hotgases from the separator 35 are preferably bypassed back to the furnace 34 by means of pipe 4|, it being understood of course that pipes 35 and 4| are suitably insulatedso as to minimize heat losses, and thereby cut down fuel consumption. In some instances it will be found preferable to pass the hot gases, which have a relatively high vapor content by reason of the evaporation of the water of crystallization from the hydrated sodium sulphate, through condenser coils (not shown) to recover the moisture therein, this being particularly advisable where'thefplantis operating in a desert region in which fresh water is at a premium.

Referring again to Fig. 1, I prefer'to recirculate the liquor vfrom which the sodium sulphate crystals have been removed, since it is largely sodium sulphate, sodium chloride, and some cal- This solution may be taken directly from the sump 24 through the pipe 40 without being recirculated through the flume 2|, but as mentioned I prefer to recirculate it through the refrigerator at least once before sending it back to the basin in the deposit B. In this manner the only losses in water are those of evaporation, and consequently even though a plentiful source of natural salt water is not available, my process can be carried on very econom- .ica11y. since practically none of the sodium chlo- AB to'avoid any waste.

Since the solution flowing through pipe 20 from V tank C to refrigerator D is to be cooled, and since the solution ilowlng in pipe 40 from the refrigerator D back to deposit B is to be warmed, I prefer to use the novel heat exchange system illustrated in detail in Fig. 9, where it will be seen that the pipe 40 is considerably smaller than pipe 20, and passes along the inside thereof. Usually the length of pipe 20 is considerable, and hence ample time is aiorded for the heat exchange to be completed.

Where the sulphate deposits are in desert regions the normal temperature during the summer months will insure the solvent water being at approximately the right temperature, i. e., about 90 F., but for winter operations heating means may be provided, if necessary, in the pond B to raise the temperature i the solvent suillciently to dissolve a high percentage of the sodium sulphate from the deposit.

By the useof my process on deposits such as previously mentioned, I am able to produce at a very small oost anhydrous sodium sulphate which will average about 99% pure, and as will be evident, I recover practically 100% of the sodium sulphate present in the deposit, since any of the sulphate which is not crystallized out in any run is recirculated back to the deposit so that by the time the deposit has been completely worked, all of the sodium sulphate therein has been recovered, except that small portion which remains in the iinai waste solution at the time of shutting down operations. It will also be evident that it will usually be advisable to provide several settling tanks for use with a single deposit basin and refrigerating apparatus to insure continuous operations.

While my process is particularly adaptable to regions Where there is a plentiful ysupply of salt water available, it will be evident that I may mine the sulphate aggregate and form the pulp by mixing the minedaggregate and water in a suitable tank, preferably with the addition of sodium chloride as desired, according to particular conditions.

While the form of my invention described in -detail herein is'fully capable of attaining the objects and providing the advantages hereinbefore stated, it is to be understood that it is merely illustrative of the broad principles of my invention as set forth in the appended claims, which I intend to include all equivalents of the form specifically described.

I claim as my invention:

l. The method of recovering sodium sulphate from a nautral -deposit thereof also containing other substances, which includes: forming a relatively large basin in said deposit; iiowing a substantial quantity of water containing from 2% to 6% of sodium chloride into said basin to form a lake therein of suiilcient size to support a dredge; dredging said lake and passing the pulp obtained thereby to a settling basin; flocculating` and settling the insoluble, portions of said pulp in said settling basin; owing the vcleared sodium sulphate solution from vsaid settling basin through a refrigerating apparatus, thereby reducing its temperature to around 50 F.; and causing the rapid growth oi small crystals of sodium sulphate; separating said crystals lfrom the liquor; recirculating said liquor back to said lake in such a manner as to effect a heat transfer between it and fresh solution passing to said refrigerating apparatus; -washing said crystals with a weak solution of sodium sulphate; and drying said sodium sulphate crystals to thereby produce anhydrous sodium sulphate in granular orm.

2. The method of recovering sodium sulphate from a natural deposit thereof also containing other substances, which includes: forming a relatively large basin in said deposit; owing a substantial quantity of water containing from,2% to 6% of sodium chloride into said basin to form a lake therein; dredging said lake and passing the pulp obtained thereby to a settling basin; and settling the insoluble portions ofsaid pulp in said settling basin; flowing the cleared sodium sulphate solution from said settling basin through a refrigerating apparatus, thereby reducing its temperature to around 50" F.; and causing the rapid growth of small crystals of sodium sulphate; separating said crystals from the liquor; washing said crystals with a weak solution oi sodium sulphate; and drying said sodium sulphate crystals to thereby produce anhydrous sodium sulphate in granular form.

3. I'he method of recovering sodium sulphate from a natural deposit thereof also containing other substances, which includes: forming a re1- atively large basin in said deposit; flowing a substantial quantity of water into said basin to form a lake therein; dredging said lake and passing the pulp obtained thereby to a settling basin: settling the insoluble portions of said pulp in said settling basin; flowing the cleared sodium sulphate solution from said settling basin through a refrigerating apparatus, thereby reducing its temperature to around 50 F.; and causing the rapid growth of small crystals of sodium sulphate; separating said crystals from the liquor; and drying said sodium sulphate crystals to thereby produce anhydrous sodium sulphate in granular form.

4. The method of recovering sodium sulphate from a natural deposit thereof also containing other substances. which includes: forming a relatively large basin in said deposit; flowing a substantial quantity of water into said basin to'form a lake therein of sufficient size to support a dredge; dredging said lake and passing the pulp obtained thereby to a settling basin; flocculating and settling the insoluble portions of said pulp in said settling basin; ilowing the cleared sodium sulphate solution from said settling basin through a refrigerating apparatus, thereby reducing its temperature to around 50 F.; and causing the rapid growth of small crystals of sodium sulphate; separating said crystals from the liquor; washing said crystals with a weak solution of sodium sulphate; and drying said sodium sulphate crystals to thereby produce anhydrous sodium sulphate in granular form.

5. The method of recovering sodium sulphate from a. natural deposit thereof also'containing other substances, which includes: forming a relatively large basin in said deposit; flowing a substantial quantity of water into said basin to form a lake therein; dredging said lake and passing the pulp obtained thereby to a settling basin; settling the insoluble portions of said pulp in said settling basin; flowing the cleared sodium sulphate solution from said settling basin through a refrigerating apparatus, thereby reducing its temperature; and causing the growth of crystals of sodium sulphate; separating said crystals from the liquor; and drying said sodium sulphate crystals to thereby produce anhydrous sodium sulphate in granular form.

6. The method of recovering sodium sulphate from a natural deposit thereof also containing other substances, which includes: forming a relatively large basin in said deposit; iiowing a substantial quantity of water into said basin to form a lake therein; dredging said lake and passing the pulp obtained thereby to a refrigerating apparatus, thereby reducing its temperature; and causing the growth of crystals of sodium sulphate; separating said crystals from the liquor;

and drying said sodium sulphate crystals to thereby produce anhydrous sodium sulphate in granular form.

7. The method of recovering sodium sulphate from a natural deposit thereof also containing other substances, which includes: forming a relatively large basin in said deposit; ilowing a substantial quantity of water into said basin to form a lake therein; dredging said lake and passing the pulp obtained thereby to a refrigerating apparatus, thereby reducing its temperature; causing the growth of crystals of sodium sulphate; and separating said crystals from the liquor.

CHARLES D. ADAMS.

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