US1516550A - Manufacture of sodium nitrate - Google Patents

Description

Patented Nov. 25, 1924.

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I. F l E o l ELIAS ANTI-ION CAPPELEN SMITH, OF NEW YORK, N. Y., ASSIGNOR TO GUGGEN- HEIM BROTHERS, A GOPARTNERSHIP OE NEW YORK, N. Y.

MANUFACTURE OF SODIUM NITRATE.

N'o Drawing.

To all whom it may concern:

Be it known that I, ELIAS ANrHoN CAP- IELEN SMITH, a citizen of the United States of America, residing at New York city, in the county of New York, State of New York, have invented certain new and useful Improvements in Manufacture of Sodium N itrate; and I do hereby declare the following to be a full, clear, andexact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to im 'irovemeuts in the extraction and recovery of nitrate from caliche, and involves improvements which are not only particularly adapted to installations of small or moderate capacity, but also to installations of the largest magnitude.

The invention also includes a new and improved sodium nitrate product having new and improved properties which make it particularly suitable for use in the chemical and other industries.

In its preferred and complete form, the process of the invention includes a cyclic process in which the nitrate is extracted from caliche by cold or tepid leaching, and in which the nitrates are recovered from the solution in the form of the new nitrate product by refrigeration, as well as a process in which the refrigeration of the strong solution containing the nitrate is in part accomplished by heat interchange with the cold mother liquor which is thereby warmed before its return for further use in the leaching operation.

The method of extraction of nitrates from caliche, which is at present almost universally used, consists in boiling the caliche together with the mother liquors from former crystallizations so as to obtaina strong solution or caldo, and the subsequent cooling of suclfcaldo and the depositing out of its dissolved nitrate during a period of five or six days. This process is attended withheavy incidental losses, such as the sacrifice of about 33% of the total nitrate present in the caliche treated, while a considerable portion of the caliche is at present rejected on accoupt of its fine state of divislon.

The present invention largely overcomes or avo ds he difliculties and. objections of Application filed January 19, 1922. Serial No. 530,437.

such prior methods of extraction. traction of the nitrate from the caliche by boiling is wholly dispensed with, together with the subsequent slow cooling for a long period of time, While the heavy incidental losses in unextracted nitrate and in the fines are largely avoided. The fines, which are regarded as extremely diflicult of treatment in the present methods, are made fully available in the practice of the present invention. By the expression fines is to be understood not only the fine material resulting at any step o' the process by disintegration of the caliche under treatment, as, for instance, the fine material which in the present practice passes through and gathers under the false bottom of the boiling tank, but also all of that portion of the caliche broken on the pampa which is at present rejected on account of its fine state of division.

In carrying out the cyclic process the caliche, crushed to a size appropriate to the method of leaching adopted, will be exposed, together with its fines, to the dissolving action of mother liquor of suitable composition returned from the crystallization process or of a solution of suitable concentration whose nitrate content is intermediate between that of the mother liquor and that of the solution suitable for recovery treatment. This dissolving or extraction is carried out in such a manner and in such forms of apparatus (appropriate to the method of leaching adopted) and with a leaching solution of such a composition as to bring the available nitrate in the caliche into substantially complete solution. This extraction or leaching of the caliche is carried out at atmospheric or tepid temperatures. for best results, contain sufficient amounts of protective agents of the character described in the prior application of Charles L. Burdick, Serial No. 513,335, filed November 7, 1921.

The caliche under treatment, after it has been subjectedto extraction for the removal of the nitrate, will be subjected to a sulficient number of wash waters, of graded nitrate strength to remove and displace to a great extent the stronger solution produced in the leaching operation. With this leaching procedure and with rational applica The ex-.

The leaching solution, should,

tion of wash Waters of suitable character an extraction of at least 90% of theavailable nitrate is readily obtained and the extraction may be as high as 95%.

It will be understood that, contrary to the usual practice, all of the caliche material broken on the pampas may be charged into the leaching apparatus, thus increasing by a large fraction the amount of caliche commonly treated, inasmuch as the invention permits full use to be made of the fines which have heretofore, in many cases, been entirely neglected. Moreover, inasmuch as extremely high recovery of nitrate from caliche-is realized by the present invention, it will be economically profitable to work a much lower grade of caliche than is feasible in the prevailing practice. For example, in some instances, the so-called over-burden itself (that is to say, the outer stratum of material overlying the caliche and which is usually rejected) may be rich enough in nitrate to warrant treatment along with the caliche proper, thus greatly diminishing the cost of the mining operation.

The enriched liquors withdrawn from the leaching apparatus are sent to the nitrate recovery plant where a portion of their content of nitrate is removed by crystallization, thereby forming a fresh quantity of mother liquor or treatment solution. This crystallization of the nitrate from the saturated or nearly saturated solution received from the leaching plant is brought about by cooling the solution by refrigeration to a lower temperature than that of the cold or tepid leaching. If the solution is .not of proper composition, the nitrate may be admixed with sulfate. In order to avoid the con tamination of the nitrate with sulfate, the solution, which is subjected to refrigeration should be one which contains or which has added thereto a sufiicient amount of protective a ents of the character referred to in the s 1d application of Charles L. Burdick, Serial No. 513,335. When the solution is of suitable composition and is subjected to rapid refrigeration with agitation, the nitrate is separated in the form of the new nitrate product, hereinafter more fully described. In order for the recovery plant to operate to best advantage, it should not only refrigerate the cool 'or tepid saturated or. nearly saturated solutions, in order to induce crystallization, but it must also supply such additional refrigeration as is necessary to balance the heat of crystallization of the sodium nitrate crystals.

The cyclic rocess is also carried out with circulation o the saturated or nearly saturated solutions into heat interchan ing relation with the cold mother liquor cm the crystallization plant. By using heat interchangers, the mother liquor returning from,

the crystallizatibn tanks to the leaching tanks will be warmed, and the refrigeration stored in the refrigerated weak mother refrigerator tanks.

The mother liquor will thus emerge from the heat interchangers at a somewhat lower temperature than atmospheric. This mother liquor can be used to advantage as the cool- 'ing medium in the condenser for the refrigerant (i. e., the ammonia vapors) in which cooling medium the heat of condensation of the vapors of the refrigerant will in turn heat the mother liquor so that it will have a certain quantity of surplus heat stored in it when it returns to the leaching tanks; or, where the mother liquor is circulated through a series of tanks, it may be warmed between successive tanks, or before entering the last leaching tank, thus raising its temperature during or toward the end of the leaching operation, and increasing the strength of the final strong solution. The mother liquor may also be heated from some other source of waste heat and a certain quantity of surplus heat stored in it. t The amount of surplus heat will preferably be suflicient or more than enough to satisfy 105 the heat necessarily absorbed in dissolving the nitrate from the caliche. In the refrigerators and interchangers themselves, the refrigeration applied or recovered must similarly compensate for this absorbed heat, in order to bring about the crystallization of the nitrate.

The sequence of operation is shown in the following flow sheet:

Tepid mother liquor-) Iieaching apparatus (Caliche.

Advance and make-up.

Strong solu- Extracted G raded wash 6 tion. caliche. waters [01- 1 I lowed by Waste heat recovery. Cooling and condensation apparatus.

Mother liquor. Nitrate.

As illustrated in the flow sheet, the strong solution received from the leaching. apparatus enters the heat interchangers at a temperature, for example, of 25 C. The heat interchangers may be of any appropriate type, but preferably they are of such construction as. to present a large surface of contact and a prolonged contact surface between the solutions passing therethrough in counter current flow. In these heat interchangers the strong solutions are cooled by the counter flow against colder mother liquor returning from the refrigeration tanks. The temperature of the strong solution may, for example, be reduced in the heat interchange system, from 25 C. to about 6 C., so that a considerable part of the nitrate will be precipitated and recovered in the tanks of the heat interchanging system in a substantially pure form.

In the refrigerator proper the temperature will be further lowered, for example, to about 0 (3., and a further quantity of nitrate will be precipitated. It will, of course, be understood that, in its passage through the heat interchangers and the refrigerator, the solution loses but part of its nitrate and a large part still remains .dissolved in the mother liquor and returns again to re-enter the solution cycle. The nitrate precipitated in the heat interchang ers and the refrigerator may be discharged therefrom automatically and continuously by any suitable mechanical arrangements. The refrigerator may be provided with any suitable means of refrigeration, as, for instance, by means of ammonia vaporization or cold brine solution. The system of heat interchangers and refrigerators, together with the intermediate connections, may be insulated to eliminate atmospheric influences. Different forms of heat inter changers and refrigerating'devices are well known and need not be specifically described, for example, liquid ammonia may be vaporized at low pressure, in the usual manner, in the refrigerator coils, and then compressed and condensed in the customary manner incident to ammonia cooling processes, and, as above described, the heat of compression and condensation may be utilized in heating the mother liquors to assist in the leaching operation.

The mother liquor from the refrigerators is. preferably returned by counterflow through the heat interchangers where it is warmedto, say 20, more or less. The stored refrigeration in the mother liquor is thus simultaneously transmitted to the fresh incoming strong solution. From the heat interchangers, or, in certain cases from the refrigerators themselves, the mother liquor passes through the ammonia condenser (which, for example, may be of the shell and tube type) or through other forms of waste heat recovery apparatus where it while at-the same time it is itself raised to a' temperature intermediate between its entrance temperature and the temperature of the condensing refrigerant, so that it returns to the leaching tanks at a correspondingly increased temperature.

In the extraction of caliche with Water not only does the nitrate dissolve, but all the other soluble constituents pass into solution. It is not objectionable for these salts to build up in the solutions provided they do not contaminate the nitrate product obtained from the refrigerating process. The chief impurity which is encountered in the solutions is sodium chloride, together with lesser amounts of sulfates, potassium salts, borates, iodates, and magnesium. For example, the concentrations of the major foreign salts dissolved in a mother liquor produced in the operation of the refrigeration process, were found, in one instance, to be a total of 200 grams per liter of chlorine expressed as sodium chloride, and a total of grams per liter of sulfate expressed as sodium sulfate.

The sodium chloride (which occurs in the caliche in large quantities) does not interfere in the operation of the refrigerating cycle, inasmuch as its solubility (in the presence of sodium nitrate) increases as the temperature decreases, so that there is no tendency for it to precipitate along with the nitrate.

Sodium sulfate, however, (which also may occur in considerable quantities in the caliche) presents solubility relations somewhat similar to those of the nitrate, in that, below a certain point, (which in the normal solution encountered is in the neighborhood of 8 its solubility decreases as the temperature is lowered. The concentrations of sodium sulfate encountered in the solutions are, however, such that down to a temperature of at least 4 Chthere is no substantial danger of precipitation, particularly if protective agents are present in the proper amount. Consequently, the sodium nitrate crystals contained in the heat interchanger are practically free from precipitated sulfate.

In the refrigerators, a further precipitation of the sodium nitrate crystals will occur, and, at the same time, there may be precipitated, at the lower temperatures, a quantity of sodium sulfate, which may thereafter he removed by processes understood in the art. However, in the preferred practice of the invention, with the production of solution, in the leaching, of concentrations suflicientlyhigh in nitrate, and with stabilizing agents, such as salts of magnesium and potassium, borates and iodates,

quantity of sodium sulfate in solution (i. e.,

the quantity of sodium sulfate as distinguished from the total sulfate in solution), the concentration of sulfate in the solutions may be maintained below such a value that refrigeration at or below 0 C. can be accomplished with the production of the new nitrate product of a commercially pure and marketable form. Consequently, in accordance with this additional feature of the invention, by proper regulation of temperature, and composition of the solution, the new product substantially free from sulfate can also be obtained in the refrigerators. This feature of the invention is of particular advantage, inasmuch as it avoids the necessity that would otherwise exist of subsequent purification of the nitrate crystals from accompanying precipitated sulfate, and insures in a simple and economical way the obtaining of a new nitrate product substantially devoid of contaminations, and having new and valuable properties from the refrigerators, in the orderly and regular functioning of the system.

The sodium nitrate produced in the manner above described, by refrigeration of a nitrate solution of suitable composition, is-

a new and valuable form of sodium nitrate and forms a new nitrate product. The new product is in the form of firm, hard, regular faced rhombohedra, especially free from imperfectly developed crystal faces, and of improved appearance, being of a fine uni-- form white appearance. The new nitrate product, obtainable by refrigeration in the manner above described,

is of an evenly graded character and of a degree of fineness which makes it particularly suitable for use in the chemical industry. In size, the particles are practically all above 100 mesh and with an average size of the crystals of approximately mesh, the particles practically all being between the sizes of 35 mesh (0.4 mm.) and mesh (0.2 mm), so that approximatelyall of the product will pass through a 35 mesh screen and will remain on a 100 mesh screen. The product is, inthis respect, distinguished from the nitrate product commonly produced from the usual boiling process of extracting calichc, which product is much coarser, the particles ranging around 2 to 6 mm. in size, while the furthercrushing of this material results in a product with a considerable amount of very fine material, as well as particles which are irregular in size and which are lacking in uniformity.

The new product, being made up of small uniform crystals, can be readily dissolved, and completely utilized, while it promotes the regularity and steadiness of the progress of chemical reactions in which it is used, thus further distinguishing it from the un crushed or crushed product produced by the usual boiling process of extracting the nitrate from caliche.

The new product is also of superior appearance, being of a fine uniform white appearance, and it does not set on standing in the same manner as nitrate produced by the present boiling method of extraction. These properties make the product particularly suitable for chemical mixtures and compositions in which the nitrate is introduced as such. Such mixtures are less apt to become non-uniform through segregation of the nitrate, and also less liable to deteriorate through the absorption of moisture.

An important characteristic and advantage of the new product is its improved hydroscopic properties.\ The new product' shows considerably less tendencies to attract moisture from the atmosphere than the ordinary nitrate products. Investigations made under equal conditions with the new product and with the ordinary commercial product (produced by the boiling process of extracting nitrate from caliche) showed the following pronounced difierences and advantages in favor of the new product. Like portions of these two materials were exposed to atmospheres of varying humidities at ordinary tempera? tures with the following results :On one days exposure to an atmosphere of 60% humidity, the old nitrate product absorbed 110% more moisture than did the new product under the same conditions.

sorbed a total of 49% more moisture than did the new product. On exposure to an atmosphere of 90% humidity, for one day,

the old nitrate product absorbed 82% more moisture, and on exposure for sixteen days it absorbed a total of 19% more moisture,

On sixteen days exposure the old nitrate ab character, the new product of the present invention can be more readily kept in storage, and, under normal conditions of storage, it is unnecessary to break up or crush the product to anywhere .near the same extent that is found to be necessary with theordinary nitrate products produce in the usual way. Furthermore, the new product is able to carry a higher moisture content without its physical properties being affected in any objectionable way. The new product is therefore particularly valu able as a component of mixed fertilizers, in which, owing to its improved hydroscopic and other properties, it forms a superior ingredient.

The new product is almost completely free from potassium, the. potassium content ranging only from about 0.5% to 0.7%, whereas the ordinary nitrate product ranges from over 2 or 3% up to 25% or more. This freedom from potassium is an important advantage in many branches of chemical industry where nitrate is used, for example, in nitric acid manufacture and in the manufacture of certain kinds of explosives which contain sodium nitrate.

Another characteristic property and ad'- vantage of the new product is its freedom from salts of perchloric acid, the perchlorates being present in only nominal quantities, averaging less than 0.1% perchlorate, figured as sodium perchlorate. This practically complete freedom from perchlorates is an important advantage of the new product in its application in certain industries, in particular, in its utilization for nitration and the manufacture of certain explosives. In the ordinary commercial nitrates the content of perchlorates may be as high as 2%, depending upon .the method of production of the nitrate.

It will thus be seen that the new product, obtainable in the manner above described, possesses various features which distinguish it and which make it advantageous for use in the industries. It is a uniform product with particles of substantially uniform size r between about 35 mesh and 100 mesh. In

appearance it is a fine white product with uniform regular crystals, giving a sparkling appearance in a beam of sunlight or of directed artificial light. The product is readily distinguishable from the ordinary nitrate product by the smaller and uniform size of crystals, and from pulverized nitrate in which the particles are irregular and uneven in character. The new product also possesses improved hydroscopic properties, absorbing moisture at a rate of from 20 to 25% less than ordinary nitrate under the same conditions of humidity, thus making the new product more valuable where its hydroscopic properties are of importance. The new product is also characterized by an average potassium content in the neighborhood of 0.5 to 0.7%, which content does not in general exceed about 1%; while it is also practically free from perchlorates, the con-' tent of which is not inexcess of about 0.1%.

It will thus be seen that the present invention providesboth a new cyclic process of leaching nitrate from caliche, and a new nitrate product. The cyclic process includes leaching of the caliche at atmospheric or tepid temperatures and the crystallization of the new nitrate product from the resulting solution by refrigeration and resulting rapid cooling, while agitating the solution and maintaining it of proper composition to prevent contamination of the new nitrate product with sulfate or other impurities. The leaching, as hereinbefore stated, may be carried out without extraneous heat, that is to say, at or about ordinary atmospheric temperatures, or the leached liquor may be heated before or during the leaching operation, particularly where a source of waste heat is available. In any event, however, the surplus heat, if any, thus imparted to the leached solutions need not exceed the amount required to maintain the solutions at working temperatures up to but not substantially higher than about 60 (3., which includes the range of temperatures herein referred to as tepid.

I claim:

1. The cyclic method of extracting sodium nitrate from caliche by leaching the caliche at temperatures not exeeding about 60 C. and subjecting the resulting strong solution to refrigeration for the precipitation of sodium nitrate therefrom and returning the cold mother liquor for further leaching, which comprises providing and maintaining in the solution during refrigeration a suflicient amount of stabilizing agents to avoid I any substantial precipitation of sulfate when the solution is cooled to a relatively low temperature, and efi'ecting a heat exchange between the strong solution on its way to the refrigerating step and the cold mother liquor on its return from the refrigerating step to the leaching step.

2. The cyclic method of extracting sodium nitrate from caliche by leaching the caliche at temperatures not exceeding about 60 C.

low temperature, effecting a heat exchange between the strong solution on its way to the refrigerating stepand the cold mother liquor on its return from the refrigerating step to the leaching step, and further ut1lizing the cold mother liquor on its way from the refrigerating step to the leaching step for the condensation of the refrigerant emplayed in the refrigerating step.

3. The cyclic method of extracting sodium nitrate from caliche by leaching the caliche at temperatures not exceeding about 60 C. and su to refrigeration for the precipitation of sodium nitrate therefrom and returning the coldmother liquor for further leaching, which comprises carrying out the refrigeration in successive stages, one of which stages jecting the resulting strong solution involves a heat exchange between the strong solution from the leaching step and the cold mother liquor in the course of which sodium nitrate is precipitated, from the strong solotion, and another of which stages involves refrigeration of the solution at a lower temperature with a resulting precipitation of sodium nitrate and the production of said cold mother liquor.

4. The cyclic method of extracting sodium nitrate from caliche by leaching the caliche at temperatures not exceeding about 60 C. and subjecting the resulting strong solution to refrigeration for the precipitation of sodium nitrate therefrom and returning the cold mother liquor for further leaching, which comprises providin and maintaining in the solution during refrigeration a sufiicient amount of stabilizing agents to avoid any substantial precipitation of sulfate when the solution is cooled to a relatively low temperature, and carrying out the refrigeration in successive stages, one of which stages involves a heat exchange between the strong solution from the leaching step and the cold mother liquor in the course of which sodium nitrate is precipitated from the strong solution, and another of which stages involves refrigeration of the solution at a lower temperature with a resulting precipitation of sodium nitrate and the production of said cold mother liquor.

5. A new sodium nitrate product in the form of firm, hard, regular crystals of practically uniform size between about 35 and 100 mesh, said product having an average potassium content in'the neighborhood of 0.5 to 0.7%, and which content does not in general exceed about 1%, and said product containing an average perchlorate content not in excess of about 0.1%, said product being further characterized by improved hydroscopic properties, being relatively nonhydroscopic in character.

In testimony whereof I afiix my signature.

' ELIAS ANTHON CAPPELEN SNllTl-l.