CA1144738A - Process for purifying potassium chloride particles - Google Patents
Process for purifying potassium chloride particlesInfo
- Publication number
- CA1144738A CA1144738A CA000380450A CA380450A CA1144738A CA 1144738 A CA1144738 A CA 1144738A CA 000380450 A CA000380450 A CA 000380450A CA 380450 A CA380450 A CA 380450A CA 1144738 A CA1144738 A CA 1144738A
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- Canada
- Prior art keywords
- potassium chloride
- leaching
- column
- sodium chloride
- chloride
- Prior art date
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D3/00—Halides of sodium, potassium or alkali metals in general
- C01D3/14—Purification
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Inorganic Chemistry (AREA)
- Extraction Or Liquid Replacement (AREA)
- Manufacture And Refinement Of Metals (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Industrially produced potassium chloride particles containing a minor contaminating amount of sodium chloride are treated to substantially reduce the sodium chloride content of such particles. The disclosed treat-ment comprises, (1) introducing an aqueous slurry of the potassium chloride particles into the top of a leaching column, (2) contacting the particles countercurrently with an aqueous leaching salt solution that is saturated with respect to potassium chloride and contains less than 45 grams of sodium chloride per liter of solution, (3) removing aqueous effluent from near the top of the leaching column and utilizing said effluent for the preparation of further potassium chloride slurry that is introduced to the leaching column, (4) removing a slurry of potassium chloride particles sub-stantially reduced in sodium chloride content from near the bottom of the leaching column, (5) separating and optionally washing leached potassium chloride particles from the mother liquor of the slurry removed from the bottom of the leaching column and recycling the mother liquor to the leach-ing column as leaching salt solution, and (6) drying the potassium chloride particles obtained in step (5), thereby obtaining potassium chloride par-ticles substantially reduced in sodium chloride content.
Industrially produced potassium chloride particles containing a minor contaminating amount of sodium chloride are treated to substantially reduce the sodium chloride content of such particles. The disclosed treat-ment comprises, (1) introducing an aqueous slurry of the potassium chloride particles into the top of a leaching column, (2) contacting the particles countercurrently with an aqueous leaching salt solution that is saturated with respect to potassium chloride and contains less than 45 grams of sodium chloride per liter of solution, (3) removing aqueous effluent from near the top of the leaching column and utilizing said effluent for the preparation of further potassium chloride slurry that is introduced to the leaching column, (4) removing a slurry of potassium chloride particles sub-stantially reduced in sodium chloride content from near the bottom of the leaching column, (5) separating and optionally washing leached potassium chloride particles from the mother liquor of the slurry removed from the bottom of the leaching column and recycling the mother liquor to the leach-ing column as leaching salt solution, and (6) drying the potassium chloride particles obtained in step (5), thereby obtaining potassium chloride par-ticles substantially reduced in sodium chloride content.
Description
73~
PROC~SS FOR PURIFYING POTASSlUM CHLORIDE PARTICLES
C~OSS REFERENCE TO RE~ATED APPLICATIONS
The present application is related to copending, coassigned Canadian Patent application Serial No. 316,780, filed 23 November 1978 for Brett G, Haugrud and entitled Process For Purifying Crystalline Potassium Chloride.
DESCRIPTION OF THE INVENTION
The present invention relates to a process for purifying particu-late potassium chloride containing inorganic salt impurities, e.g., sodium chloride, More particularly, this invention concerns substantially reduc-ing the minor contaminatlng amount of inorganic metal salts ~ound in indus-trially produced potassium chloride by leaching same with an aqueous salt solution saturated with respect to potassium chloride and unsaturated with respect to said contaminating inorganic salts.
Potassium chloride is obtained commercially by the minlng of ores containlng the salt and subsequently separating the potassium chloride erom the other ore constituents. Typically, potassium chloride ores contain other inorganic salts of which the most common are sodium chloride, calcium chloride, magnesium chloride, magnesium sulfate and sodium carbonate, Sodium chloride commonly represents the other principal inorganic salt constituent present in the potassium chloride-bearing ore. Potassium chloride is separated from the other soluble and insoluble constituents present in the ore by methods well known in ~he art, which methods include froth flotation, frac~ional leachlng, selective precipita~ion and solution ,, .
mining.
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In the froth flotation process, ground potassium chloride-containing ore is mixed with a solution saturated with respect to the ore constituents and to which frothing agent3 have been added. In this manner, particulate potassium chloride is separated from the other inorgsnic metal ~alts and other impurities present in the ore. Potassium chloride solids thereby obtained typically contain relatively high levels (about 2-5 per-cent by weighe) of the other inorganic metal salts found in the ore. These salt impurities are believed to have been incorporated, encapsulated or occluded wi~hin the potassium chloride particles during the geological time frame of natural crystal formation. The aforesaid particle3 often have a reddish discoloration due to traces o~ iron and are thought to have a char3cteristically unique distribution of the inorganic metal salt impuri-ties throughout the potassium chloride particle.
In other indus~rial processes, potassium chloride is crystallized from a salt solution rich in both sodium and potassium chloride. Produc- -tion of industrially crystallized potassium chloride invoLve~ dissolving potassium chloride ore in an aqueous solvent to form a solution containing potassium chloride and other soluble inorganic metal salts that are pre3ent in the ore. Subsequently, the potassium chloride is crystallized from or separated, e.g., by precipitation, from the solution. A minor contaminat-ing amount of the inorganic salts, principally sodium chloride, is incor-porated, encapsulated or occluded within the crystal during i~s formation.
Incorporation of such salt impuri~ies in the potassium chloride crystal obtained is unavoidable since the solution from which the potas~ium chlo-ride crystal3 are obtained inevitably contain such salt impurities.
The potassium chloride product obtained by ~he aforesaid indus-trial processes is sufficiently pure for many commercial application~.
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There are, however, some industrial applieations whieh require very low levels of other ~alt impurities, such as sodium chloride. A method for reducing the sodlum ehloride eontent of lndustrially erystalli~ed po~assium chloride is described in copendlng, coassigned Canadian Patent application 316,780 flled 23 ~ovember 1978. In the method deseribed in said applica-tion, industrially crystalllzed potassium chloride, particularly compaeted potassium ehloride particles, are leached under isothermal conditions wlth a leaching solutlon ~hat is saturated with respect to potassium chloride and unsaturated with respeet to sodium chloride for a time sufficient to substantially reduee the sodium chloride eontent of the potassium ehloride crystals.
It has now been discovered that leaching of substantially pure potassium chloride partieles to substantially reduee the minor eontaminat-ing amount of sodium ehloride contained therein can be effected in an effi-cient and facile manner. In this process, industrially produced p~tassium chloride particles (usually as an aqueous slurry) are fed to the top of a leaching column wherein they are contacted eountercurrently with an aqueous leaching solution that is saturated with respect to potassium chloride and unsaturated with respect to sodium chloride. A slurry of the leached par-ticles is removed from the bottom of the column and the entraining liquld phase (mother liquor) of the slurry separated from the leaehed particles.
This mother liquor is recycled as leaching fluid to the leaching column.
Liquid aqueous effluent from the top of the leaching column is removed and utilized for the prepara~ion of resh potassium chloride slurry feed to the leaching column. In this manner, liquor rich in sodium chlor~de is segregated from liquor lean in sodium chloride within the process, thereby resulting in a subs~antial reduction of sodium chloride levels in the ~4~38 potassium chloride particles charged to the leachlng column. In a preferred embodiment washin~ of the leached particles with a saturated potassium chlor-ide aqueous solution containing no sodium chlorlde or washing wi~h water reduces the sodium chloride level of the leached partlcles still further.
The process of the present invention is capable of purifying industrially crystallized potassium chloride to very low levels of con-taminating inorganic metal salt lmpurities, i.e., sodium chloride, calcium chloride and magnesium chloride. It has been found that substantlal reduc-tions, i.e., a reduction of greater than 50%, based on the initlal contami-nating concentration, in the content of such salts can be achieved. It is not unusual, for example, to achieve sodium chloride levels of less than 0.2 weight percent, e.g., less than 0.1 weight percent, by the aforesaid process. In one preferred embodiment, the sodium chloride level of com-pacted, industrially crystallized potassium chloride has been reduced from about 1 weight percent to less than 0.1 weight percent, e.g" 0.07-~.09 weight percent, with an average residence time in the Leaching column of about 6 hours. Calcium and magnesium chloride levels have simultaneously been reduced from about 150 parts per million (ppm) to less than about 60 ppm.
The aforesaid reduction in inorganic salt impuri~ies i9 achieved by the above-described process, which segregates sodium rich liquors ln the system from sodium lean liquors. Thus, ~he overflow from the leaching column (a sodium rich liquor) is used to repulp the solid potassium chloride feed, which is also rich in sodium chloride compared to the aqueous leaching salt solution and leached potassium chloride product.
The latter solution and product are lean in sodium chloride and, in accordance wi~h the present process, are kept separate from the process streams rich in sodium chlorlde, except in the event of inadequate quantities of sodium chlor1de lean make-up liquor.
:, BRIEF DESCRIPTION OF THE DRAWING
The attached drawing is a simplified schematic diagram of the process of the present invention with certain illustrated preferred embodi-ments.
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DETAILED DESCRIPTION
The present process can be best understood by reference to the drawing. In the embodiment described therein, industrially produced potas-sium chloride from a ~ource (not shown) is forwarded by feed line 6 to feed screw 8 and thence into slurry tank 10 by means of flow line 9.
As the potassium chloride feed to the present process, there can be used industrially produced potassium chloride particles having a potas-sium chloride content of at least about 95 weight percent. Often, tbe potassium chloride content will be higher, e.g., from about 96 to about 99.5, e.g., 97.5 to 93.5, weight percent potassium chloride. Accordingly, the potassium chloride feed can contain up to about 5 weight percent sodium chloride. More typically, the feed will contain between about 0.5 and about 2.5, e.g., between about 0.9 or 1 and about 1.5 or 2 weight percent sodium chloride. The calcium and magnesium content of the potassium chloride feed will generally each be le3s than about 300 parts per million (.030 weight percent).
As the principal oetal salt impurity in indu~trially produced potassium chloride particles is by far sodium chloride, the other metal salt impurities, e.g., those of calcium and msgnesium can be and will be disregarded for the =ost part in this discussion. By potassium chloride "particles" is meant that crystAlline body formed by the solidification of potassium chloride having a regular repeating internal arrangement of 473~3 its atoms, including the product formed by consolidating solid potassium chloride by high pressure, in which case the internal arrangement of the potassium chloride may be distorted.
As indicated, the potassium chloride feed used in the present process is industrially produced potassium chloride9 such as an indus- -trially crystallized product, e.g., potassium chloride produced by crys-tallizing the product from a solution saturated wi~h respect to potassium chloride and containing sodiu~ chloride in the ~olution. Preferably, the potassium chloride feed used i9 a compacted industrially crystallized product.
It is preferred that the potassium chloride to be leached in accordance with the present process be so treated before it has been con-ditioned or treated in a manner that seals the surface of the particle3.
For example, treatment of dry potassium chloride with small amounts of water to reduce dusting and improve particle competency renders the process of the present invention less effective. Further, it is generally pre-ferred that the potas~ium chloride to be leached is treated in accordance with the process of the present invention soon after it is produced as the evidence at hand indicates that less sodium chloride is lPached ~rom aged pota~sium chloride produ~t.
Although the particle size o~ the particulate potassium chloride treated is not critical, it is preferred that the potassium chloride feed be larger than 35 Tyler mesh, e.g., -10, ~35 Tyler mesh. While smaller particles than 35 mesh can be used, they can present handl mg problems caused by their poor flowability and tendency to be dusty. Particle~ -larger than 10 mesh generally find applica~ion as a commercial product but such larger particles can also be treated in accordance with the present 73~3 process. Thus, it is contemplated that granular potasaium chloride, which commonly is a compacted product with a size sange of about -4, ~14 mesh, can be treated by the herein described process. More typically, the com-pacted particles treated will have a size range of -14, +35 Tyler mesh.
Referring again to the drawing, the potassium chloride feed introduced into slurry tank 10 i9 repulped therein with an aqueous salt solution that is preferably saturated with respect to potassium chloride and unsaturated with respect to ~odium chloride at the temperature of mixing. Slurry tank 10 is equipped with stirring means, e.g., an agitator, to produce the desired slurry. The aqueous salt solution i9 introduced into slurry tank 10 by means of line 52 and is obtained fro~ the liquid effluent overflo~ of leaching column 20. At start up, the aqueous salt solution used to repulp the potassium chloride crystals in slurry tank 10 can be unsaturated with respect to potassium chloride and contain from none to greater than 50 grams sodium chloride per liter of solution (gpl), e.g., 0 to 45 gpl. The aqueous salt solution will become satura~ed with respect to potas3ium chloride at the expense of dissolving product charged to the slurry tank. The sodium chloride content of this salt solution will be controlled during the leaching process by purging the system of sodium chloride rich brine by means of line 54 and valve 56.
Sufficient aqueous salt solution is added to slurry tank 10 to repulp the potassium chloride feed to a slurry containing between about 20 and about 50 volume percent solids. The percent potassium chloride solids present in the slurry will be determined by the pumpability of the slurry and the contact time available in the leaching column. The highes the level of solids in the slurry pumped to the leaching column at a given flow rate, the larger the column required or the longer the residence time ~4~1738 required in the column in order to achieve the needed inti~ate contact of the solids with the leaching solution to accomplish the desired degree of leaching in a continuous process. Commonly, the slurry will contain between about 20 and about 30 volume percent of potassium chloride solids.
This slurry is removed from slurry tank 10 and pumped by me~ns of pump 12 through line 16 to the top or near the top of leaching column 20. Valve 14 in line 16 regulates the flow of ~lurry to the leaching column.
As used in the specification and claims, the term3 "sop", "near the top", "bottom", or "near the bottom" of the column or terms of like import are intended to mean and include the uppermost or bottommost portion, as the case may be, of the column. The exact location of liquid inlet and outlet streams to the colu=n will depPnd on the design of the column and no specific location (other than a general location) is intended by such terms.
Leaching column 20 is of a size (height and diameter~ such that intimate contact of the potassium chloride solids charged thereto with the leaching solution is obtained for a residence time that is sufficient to substantially reduce the sodium chloride content of the potassium chloride solids. It is contemplated ~hat re~idence times of between about 0.5 and 24 hours, e.g., between 2 and 18, more particularly between 4 and 12, hours, are sufficient to accomplish the aforementioned result. The exact residence time will, of course, depend upon the initial sodium chloride content of the potassium chloride feed and the degree of purification desired, For example, compacted industrially crystallized potassium chloride of a par-ticle size of -14, +35 Tyler mesh and containing a sodium chloride content of about 1 weight percent can be purified to contain a sodium chloride con- -tent of less than about 0.2 weight percent in about 6 hours at steady state conditions by the herein described process. By ~ubstantially reducing the ~4~738 sodium chloride content of potassium chloride particles i9 ~eant tbat the sodium chloride content is reduced to less than 0.5 weight percent, e.g., less than 0.25 weight percent.
The aqueous salt solution used 8S the leaching fluid is forwarded from lèach liquor tank 40 by means of pump 47 and line 46 to or near the bottom of leaching column 20. The rate at which leaching fluid is intro-duced into the column can be regulated by means of valve 48 in line 46.
The leaching 1uid is a salt solution, the solute of which is selected from the group con~i~ting of potassium chloride and mixtures of potas~ium chloride and sodium chloride. The leaching fluid i5 gub9tantially BatU-rated with respect to potassium chloride and substantially unsaturated with respect to sodium chloride at the temperature of the solution. By "sub-stantially saturated" with respect to potas3ium chloride is meant that sufficient potassium chloride is in solution BO that little, if any, of the potassium chloride particles treated will be di~solved as a con~e- -quence of being treated by the process of the inven~ion. The amount of ~odium chloride in the leaching fluid can vary; but, should be maintained at less than 45 gpl of sodium chloride in order to provide a significant driving force to permit removal of substantial quantities of sodium chlo-ride from the potas~ium chloride solids. Preferably thP leaching fluid introduced into the bottom of the leaching column will contain less than 25, e.g., les~ than 20~ gpl sodium chloride. More preferably, the leaching fluid will contain between 5 and 20, e.g., between 10 and 16 gpl of sodium chloride at steady state conditions.
The amount of leaching fluid introduced into the leaching column can vary; however, the amount should be sufficient to provide itlti~ate contact thereof with substantially all of the potassium chloride particle~
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in the column. By intimate contact i~ meant that enou~h leaching fluid i9 used 80 that the entire surface Area of each potassium chloride particle is contacted with leaching fluid for the time required to obtain substantial reduction of the sodium chloride content therein. A ratio of 4000 grams of potassium chloride particles introduced into the leaching column per liter of aqueous leaching solution has been found to be useful. Variations in the ratio, such as down to 200 or 300 grams of potassium chloride per liter of leaching ~olu~ion, would not significantly improve results. Thus, a ratio of from about 300 to about 4000 grams of potassium chloride per liter of aqueous leaching solution can be used. Lower ratios can be used also;
but, are economically unattractive since it would involve the movement of large quantities of liquid per unit weight of potassium chloride particles leached.
The leaching fluid is introduced into the leaching column coun-tercurrene to the flow of potassium chloride solids in the column and in 3uch a manner as to provide a net upward flow of leaching fluid within the column. The leaching fluid is percolated upwardly through a ~ettled bed of the potassium chloride maintained within the column at a rate that is insufficient to cause fluidization or bridging of the bed. A slurry of leached potassium chloride is removed from near or at the bottom of col- -umn 20 by means of line 25 and forwarded to separating me~ns 26 for ~epa-rating the liquid phase (mother liquor) from the solids. The rate at which leached product is withdrawn from the column can be regulated by means of valve 24 in line 25. Some leaching fluid will be withdrawn with the prod-uct from the bottom of the column bscause of the closeness of the point of product withdrawal and the point of leAching fluid entry. Withdrawal of the leached product can be facilitated, if needed, by dilution with the leaching fluid.
The means by which the entraining liquid associated with the leached potassium chloride product is separated therefrom should be chosen to minimi~e degradation of the leached particle and to maximize efficient dewatering. Any conventional apparatus which accomplishes such a separa-tion and allows efficient washing or rinsin~ of the solid product can be used. In the drawing, separating means 26 is shown as a filter for separat-ing the leached potassium chloride withdrswn from the bottom of column 20 from the liquid phase (~other liquor) associated therewith. Examples of apparatus that can be used to separate the leached crystals from its mother liquor include horizontal filters, e.g.J belt, pan and table filters, drum filters, disc filters, and centrifuges. Preferably, a centrifuge is not used for leached compacted potassium chloride particles. ~fficient dewater-ing and washing is to be encouraged for the reason that a significant amount of the remaining sodium chloride is derived from the liquor adhering to the leached particles.
The product slurry is deposited on separating means (filter) 26 and the filtrate (mother liquor) is withdrawn by means of line 27 and for-warded to leach liquor tank 40 with the assistance of pump 34. The moist filter cake can be rinsed with washing fluid forwarded to the filter cake by means of line 41. The amount of washing fluid used can be controlled by means of valve 44 in line 41. The washing fluid can be water or a salt solution of potassium chloride, or potassium chloride with low levels of sodium chloride. If a salt solution is used, it can be saturated or unsa-turated with respect to potassium chloride. It is contemplated that a solution 50 to 60 percent saturated with respect to potassium chloride and containing very low levels of sodium ~hloride be used. The level of sodium chloride present in the washing fluid should be le~s than the amount of 4~3~
sodium chloride remaining in the leached potassium chloride so that such product is not recontaminated with sodium chloride. Preferably, the washing fluid is water or a potassium chloride salt solution substantially free, i.e., less than .05 weight percent of sodium chloride. It i8 contem-plated that the filter cake is washed with up to 15 displacements of wa~h- -ing fluid. By "displacement" i8 meant the amount of water remaining in the filter cake following ~eparation of the mother liquor by the separating means, e.g., filter 26.
The washed potassium chloride product is removed from filter 26, e.g., by a doctor blade, and forwarded by means of line 28 to drier 30 wherein the moisture associated with the product i8 removed. The final dried product i9 removed from the drier by means of line 32 and forwarded to storage or packed out.
Washing fluid for rinsing the filter cake is introduced into the system from a source not shown throu~h line 41 and controlled by valve 44.
Water for make-up is forwarded by line 42 to leach liquor tanlc 40. Thc amount of make-up water introduced into the tank i9 regulated by means of valve 43 in line ~2.
As the leaching fluid proceeds upwardly through the leaching col-umn, it di~places mother liquor as60ciated with and removes sodi~m chloride from the potassium chloride particles descending countercurrently to it.
An aqueous overflow liquor is removed from near the top of leaching col-umn 20 by means of line 22 and forwarded to overflow tank 50. I~e overflow liquor is saturated with respect to potasiium chloride and contains a minor amount of sodium chloride, which amount i~ slightly higher than the ~odium chloride level present in the leaching fluid introduced at the bottom of the column. Also dissolved in the overflow liquor are small amounts of ~44~738 calcium ~nd magnesium salts. Aqueous li~uor in o~erflow tank 50 is for-warded by means of line 52 to slurry tank 10 for utilization in repulping potassium chloride feed, i.e., for preparing further potassium chloride ; slurry feed to the leaching column. In the event that there is insuffi-cient make-up water available in the system for the process, the liquor in overflow tank 50 can be recycled by means of line 53 and valve 55 to leach liquor tank 40. However, the recycling of this liquor from overflow tank 50 to leach liquor tank 40 is not desired for the reason that it results in forwarding a salt solution rich in sodium chloride to tank 40 which con-tains a salt solution lean in sodium chloride.
In order to prevent a build-up of sodium chloride and calcium and magnesium salts in the system, a bleed stream is provided in line 53 by means of line 54 and valve 56. Sufficient of the overflow from column 20 is taken as bleed to maintain the desired sodium balance in the system, which in turn depends on the desired purity of the product. Accordingly, the amount of make-up water required to the system will be equal to the amount of liquid withdrawn by mean~ of the sodium chloride bleed strbam, ~ the moisture removed at the dryer and for other unaccounted losses of - liquid in the ~ystem les~ the amount of water introduced to the system by the filter wash stream 41.
In operating the leaching column, the slurry of industrially produced potassium chloride crystals (about 20-30 volume percent) is intro-duced into ~he top of the leaching column where it slowly descends against the rising countercurrent flow of leaching fluid. A bed o~ potassium chloride of about 90 percent ~ettled solids is formed in the column through which the leaching fluid percolates. As ~he leaching fluid rises in the column, it di~places the mother liquor associated with the solid~ and 11~4~3~
leaches sodium chloride contained therein, thereby increasing it~ sodium chloride content. For example, a saturated potassium chloride aqueous solution leaching fluid containing initially about 13 grams per liter sodium chloride will contain about 15-17 grams per liter of sodium chloride when it is withdrawn from the leaching column as overflow. When the slurry of leached potassium chloride solids is withdrawn from the bottom of the leach-ing column, it is diluted wi~h leaching fluid so that the slurry charged to the filter 26 contains only about 30 to 40 percent settled solids.
The temperature at which the present process is conducted csn vary~ However, the higher the temperature the more potassium chloride required to maintain the various process ~treams saturated therewith and the greater the energy requirements. Consequently, moderate temperatures, i.e., from about 20C. to about 70C., e.g~, from about 75 to about 55C., are preferred for conducting the process of this invention. Typically, the process is operated isothermally, i.e., without the intentional addition or removal of heat.
In performing the process described hereinabove with respect to the Figure, the system, i.e., the lesch liquor tank, leaching column, over-flow tank and slurry tank, are filled with a potassium chloride solution.
Potassium chloride lS then fed to slurry tank 10 by operating feed screw 8.
A stirring system, such as a propellor, within tank 10 induces circulationof the solution in the tank, theraby csusing ~uspension of the particulate potassium chloride charged to the tank. The resulting slurry i~ forwarded to leaching column 20. If the ~olution contained in the syætem is not saturated ~ith respect to potsssium chloride, particulate potassium chlo- -ride will di~solve until ~aturation is reached. Thereafter, a solids bed will build up inside ~he leaching column. The bed height will depend on ~4~38 the desired retention time. Once the target bed height i9 reached, product discharge valve 24 i8 opened and product discharge from the column for-warded to filter 26. The setting for valve 24 is adjusted to maintain a constant bed height.
Following introduction of product to the filter, filter wash is forwarded to the filter and filtrate pump 34 is started to re ycle filtrate to the leach liquor tank. Washed product is forwarded to preheated dryer 30 which removes residual moisture from the product.
The sodium chloride content of the leaching solution forwarded to column 20 through line 46 is determined. If the sodium chloride content of this solution i8 higher than the desired tar~et concentration, valve 56 in line 54 is opened to purge sodium chloride from the system snd make-up solu-tion, which has a lower sodium chloride content, is added through line 42 to compensste for the volume of the sodium chloride bleed stream purged from the system. If the solution has a sodium chloride content less than the target concentration, bleeding is not required and valve 56 is closed.
Make up solution (other than to replace losses) is also not required until the sy~tem reaches !teady state conditions.
The present process is more particularly described in the follow-ing example which is intended as illustrative only since numerous modifica-tions and variations therein will be apparent to those ~killed in the art.
EXAMPLE
In the following example, values and operating conditions given are average values for 28 hours of steady seate operation. Flow rates are in U. S. gallons per minute (gpm) unless noted otherwise.
~4738 Compacted, industrially crystallized potassium chloride having the average sieve analy~es reported in Table I was charged to slurry tank 10 at a rate of about 1.73 tons per hour. The potassium chloride feed contained on the average 0.91 weight percent sodium chloride and 0.023 and 0.014 weight percent calcium and magnesium respectively. An aqueous slurry of the afore~aid compacted potassium chloride feed having about 22 volume percent solids (settled sol;ds) was charged at a rate of 60 gpm to the top of a leaching column in which the settled bed was about 21-22 feet.
A saturated potassium chloride solution containing about 13.1 grams per liter (gpl) of sodium chloride was introduced into the bottom of ; the column as the leaching fluid at about 51.3 gpm. The llquid overflow from the column contained about 15.6 gpl sodium chloride. Retention time in the column was calculated to be about 6.1 hours. Water make-up averaged 6-9 gpm.
Leached potassium chloride was withdrawn from the column and forwarded to a filter. The filter discharge was found to contain about 0.084 weight percent sodium chloride, 0.0036 weight percent calcium and 0.00098 weight percent magnesium. When tried, unrinsed sample~ of the filter cake were found to contain an average of 0.108 weight percent sodium chloride, 0.0035 weight percent calcium, and 0.0016 weight percent magne-sium. Samples of filter cake rinsed for 30 seconds in a potassium chloride ~aturated solution containing no sodium chloride and then dried were found to contain 0.042 weight percent sodium chloride, 0.0022 weight percent cal~
cium and 0.00055 weight percen~ magnesium.
The data of the aforesaid example demonstrates that the sodium chloride content of compacted, industrially crystallized potassium chloride can be reduced to low levels, i.e., from about 0.9 ~o about 0.09 weight percent by the leaching proceBs of the present invention.
~4738 TABLE I
TYL~R SIEVE CUMULATIVE WEIGHT, %
14 23.5 16 48.6 ` 20 ~ 71.7 28 ~ 9I.2 95.7 48 97.5 Although the p~esent process has been described wi~h reference to specific details of certain embodiments thereof, it is not intended that such details should be regarded as limitation~ upon the scope of the inven-tion except ns and to the e~tent that they are included in the accompanying claims.
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PROC~SS FOR PURIFYING POTASSlUM CHLORIDE PARTICLES
C~OSS REFERENCE TO RE~ATED APPLICATIONS
The present application is related to copending, coassigned Canadian Patent application Serial No. 316,780, filed 23 November 1978 for Brett G, Haugrud and entitled Process For Purifying Crystalline Potassium Chloride.
DESCRIPTION OF THE INVENTION
The present invention relates to a process for purifying particu-late potassium chloride containing inorganic salt impurities, e.g., sodium chloride, More particularly, this invention concerns substantially reduc-ing the minor contaminatlng amount of inorganic metal salts ~ound in indus-trially produced potassium chloride by leaching same with an aqueous salt solution saturated with respect to potassium chloride and unsaturated with respect to said contaminating inorganic salts.
Potassium chloride is obtained commercially by the minlng of ores containlng the salt and subsequently separating the potassium chloride erom the other ore constituents. Typically, potassium chloride ores contain other inorganic salts of which the most common are sodium chloride, calcium chloride, magnesium chloride, magnesium sulfate and sodium carbonate, Sodium chloride commonly represents the other principal inorganic salt constituent present in the potassium chloride-bearing ore. Potassium chloride is separated from the other soluble and insoluble constituents present in the ore by methods well known in ~he art, which methods include froth flotation, frac~ional leachlng, selective precipita~ion and solution ,, .
mining.
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73~
In the froth flotation process, ground potassium chloride-containing ore is mixed with a solution saturated with respect to the ore constituents and to which frothing agent3 have been added. In this manner, particulate potassium chloride is separated from the other inorgsnic metal ~alts and other impurities present in the ore. Potassium chloride solids thereby obtained typically contain relatively high levels (about 2-5 per-cent by weighe) of the other inorganic metal salts found in the ore. These salt impurities are believed to have been incorporated, encapsulated or occluded wi~hin the potassium chloride particles during the geological time frame of natural crystal formation. The aforesaid particle3 often have a reddish discoloration due to traces o~ iron and are thought to have a char3cteristically unique distribution of the inorganic metal salt impuri-ties throughout the potassium chloride particle.
In other indus~rial processes, potassium chloride is crystallized from a salt solution rich in both sodium and potassium chloride. Produc- -tion of industrially crystallized potassium chloride invoLve~ dissolving potassium chloride ore in an aqueous solvent to form a solution containing potassium chloride and other soluble inorganic metal salts that are pre3ent in the ore. Subsequently, the potassium chloride is crystallized from or separated, e.g., by precipitation, from the solution. A minor contaminat-ing amount of the inorganic salts, principally sodium chloride, is incor-porated, encapsulated or occluded within the crystal during i~s formation.
Incorporation of such salt impuri~ies in the potassium chloride crystal obtained is unavoidable since the solution from which the potas~ium chlo-ride crystal3 are obtained inevitably contain such salt impurities.
The potassium chloride product obtained by ~he aforesaid indus-trial processes is sufficiently pure for many commercial application~.
;`` ~L~IL~4~73~
There are, however, some industrial applieations whieh require very low levels of other ~alt impurities, such as sodium chloride. A method for reducing the sodlum ehloride eontent of lndustrially erystalli~ed po~assium chloride is described in copendlng, coassigned Canadian Patent application 316,780 flled 23 ~ovember 1978. In the method deseribed in said applica-tion, industrially crystalllzed potassium chloride, particularly compaeted potassium ehloride particles, are leached under isothermal conditions wlth a leaching solutlon ~hat is saturated with respect to potassium chloride and unsaturated with respeet to sodium chloride for a time sufficient to substantially reduee the sodium chloride eontent of the potassium ehloride crystals.
It has now been discovered that leaching of substantially pure potassium chloride partieles to substantially reduee the minor eontaminat-ing amount of sodium ehloride contained therein can be effected in an effi-cient and facile manner. In this process, industrially produced p~tassium chloride particles (usually as an aqueous slurry) are fed to the top of a leaching column wherein they are contacted eountercurrently with an aqueous leaching solution that is saturated with respect to potassium chloride and unsaturated with respect to sodium chloride. A slurry of the leached par-ticles is removed from the bottom of the column and the entraining liquld phase (mother liquor) of the slurry separated from the leaehed particles.
This mother liquor is recycled as leaching fluid to the leaching column.
Liquid aqueous effluent from the top of the leaching column is removed and utilized for the prepara~ion of resh potassium chloride slurry feed to the leaching column. In this manner, liquor rich in sodium chlor~de is segregated from liquor lean in sodium chloride within the process, thereby resulting in a subs~antial reduction of sodium chloride levels in the ~4~38 potassium chloride particles charged to the leachlng column. In a preferred embodiment washin~ of the leached particles with a saturated potassium chlor-ide aqueous solution containing no sodium chlorlde or washing wi~h water reduces the sodium chloride level of the leached partlcles still further.
The process of the present invention is capable of purifying industrially crystallized potassium chloride to very low levels of con-taminating inorganic metal salt lmpurities, i.e., sodium chloride, calcium chloride and magnesium chloride. It has been found that substantlal reduc-tions, i.e., a reduction of greater than 50%, based on the initlal contami-nating concentration, in the content of such salts can be achieved. It is not unusual, for example, to achieve sodium chloride levels of less than 0.2 weight percent, e.g., less than 0.1 weight percent, by the aforesaid process. In one preferred embodiment, the sodium chloride level of com-pacted, industrially crystallized potassium chloride has been reduced from about 1 weight percent to less than 0.1 weight percent, e.g" 0.07-~.09 weight percent, with an average residence time in the Leaching column of about 6 hours. Calcium and magnesium chloride levels have simultaneously been reduced from about 150 parts per million (ppm) to less than about 60 ppm.
The aforesaid reduction in inorganic salt impuri~ies i9 achieved by the above-described process, which segregates sodium rich liquors ln the system from sodium lean liquors. Thus, ~he overflow from the leaching column (a sodium rich liquor) is used to repulp the solid potassium chloride feed, which is also rich in sodium chloride compared to the aqueous leaching salt solution and leached potassium chloride product.
The latter solution and product are lean in sodium chloride and, in accordance wi~h the present process, are kept separate from the process streams rich in sodium chlorlde, except in the event of inadequate quantities of sodium chlor1de lean make-up liquor.
:, BRIEF DESCRIPTION OF THE DRAWING
The attached drawing is a simplified schematic diagram of the process of the present invention with certain illustrated preferred embodi-ments.
';
DETAILED DESCRIPTION
The present process can be best understood by reference to the drawing. In the embodiment described therein, industrially produced potas-sium chloride from a ~ource (not shown) is forwarded by feed line 6 to feed screw 8 and thence into slurry tank 10 by means of flow line 9.
As the potassium chloride feed to the present process, there can be used industrially produced potassium chloride particles having a potas-sium chloride content of at least about 95 weight percent. Often, tbe potassium chloride content will be higher, e.g., from about 96 to about 99.5, e.g., 97.5 to 93.5, weight percent potassium chloride. Accordingly, the potassium chloride feed can contain up to about 5 weight percent sodium chloride. More typically, the feed will contain between about 0.5 and about 2.5, e.g., between about 0.9 or 1 and about 1.5 or 2 weight percent sodium chloride. The calcium and magnesium content of the potassium chloride feed will generally each be le3s than about 300 parts per million (.030 weight percent).
As the principal oetal salt impurity in indu~trially produced potassium chloride particles is by far sodium chloride, the other metal salt impurities, e.g., those of calcium and msgnesium can be and will be disregarded for the =ost part in this discussion. By potassium chloride "particles" is meant that crystAlline body formed by the solidification of potassium chloride having a regular repeating internal arrangement of 473~3 its atoms, including the product formed by consolidating solid potassium chloride by high pressure, in which case the internal arrangement of the potassium chloride may be distorted.
As indicated, the potassium chloride feed used in the present process is industrially produced potassium chloride9 such as an indus- -trially crystallized product, e.g., potassium chloride produced by crys-tallizing the product from a solution saturated wi~h respect to potassium chloride and containing sodiu~ chloride in the ~olution. Preferably, the potassium chloride feed used i9 a compacted industrially crystallized product.
It is preferred that the potassium chloride to be leached in accordance with the present process be so treated before it has been con-ditioned or treated in a manner that seals the surface of the particle3.
For example, treatment of dry potassium chloride with small amounts of water to reduce dusting and improve particle competency renders the process of the present invention less effective. Further, it is generally pre-ferred that the potas~ium chloride to be leached is treated in accordance with the process of the present invention soon after it is produced as the evidence at hand indicates that less sodium chloride is lPached ~rom aged pota~sium chloride produ~t.
Although the particle size o~ the particulate potassium chloride treated is not critical, it is preferred that the potassium chloride feed be larger than 35 Tyler mesh, e.g., -10, ~35 Tyler mesh. While smaller particles than 35 mesh can be used, they can present handl mg problems caused by their poor flowability and tendency to be dusty. Particle~ -larger than 10 mesh generally find applica~ion as a commercial product but such larger particles can also be treated in accordance with the present 73~3 process. Thus, it is contemplated that granular potasaium chloride, which commonly is a compacted product with a size sange of about -4, ~14 mesh, can be treated by the herein described process. More typically, the com-pacted particles treated will have a size range of -14, +35 Tyler mesh.
Referring again to the drawing, the potassium chloride feed introduced into slurry tank 10 i9 repulped therein with an aqueous salt solution that is preferably saturated with respect to potassium chloride and unsaturated with respect to ~odium chloride at the temperature of mixing. Slurry tank 10 is equipped with stirring means, e.g., an agitator, to produce the desired slurry. The aqueous salt solution i9 introduced into slurry tank 10 by means of line 52 and is obtained fro~ the liquid effluent overflo~ of leaching column 20. At start up, the aqueous salt solution used to repulp the potassium chloride crystals in slurry tank 10 can be unsaturated with respect to potassium chloride and contain from none to greater than 50 grams sodium chloride per liter of solution (gpl), e.g., 0 to 45 gpl. The aqueous salt solution will become satura~ed with respect to potas3ium chloride at the expense of dissolving product charged to the slurry tank. The sodium chloride content of this salt solution will be controlled during the leaching process by purging the system of sodium chloride rich brine by means of line 54 and valve 56.
Sufficient aqueous salt solution is added to slurry tank 10 to repulp the potassium chloride feed to a slurry containing between about 20 and about 50 volume percent solids. The percent potassium chloride solids present in the slurry will be determined by the pumpability of the slurry and the contact time available in the leaching column. The highes the level of solids in the slurry pumped to the leaching column at a given flow rate, the larger the column required or the longer the residence time ~4~1738 required in the column in order to achieve the needed inti~ate contact of the solids with the leaching solution to accomplish the desired degree of leaching in a continuous process. Commonly, the slurry will contain between about 20 and about 30 volume percent of potassium chloride solids.
This slurry is removed from slurry tank 10 and pumped by me~ns of pump 12 through line 16 to the top or near the top of leaching column 20. Valve 14 in line 16 regulates the flow of ~lurry to the leaching column.
As used in the specification and claims, the term3 "sop", "near the top", "bottom", or "near the bottom" of the column or terms of like import are intended to mean and include the uppermost or bottommost portion, as the case may be, of the column. The exact location of liquid inlet and outlet streams to the colu=n will depPnd on the design of the column and no specific location (other than a general location) is intended by such terms.
Leaching column 20 is of a size (height and diameter~ such that intimate contact of the potassium chloride solids charged thereto with the leaching solution is obtained for a residence time that is sufficient to substantially reduce the sodium chloride content of the potassium chloride solids. It is contemplated ~hat re~idence times of between about 0.5 and 24 hours, e.g., between 2 and 18, more particularly between 4 and 12, hours, are sufficient to accomplish the aforementioned result. The exact residence time will, of course, depend upon the initial sodium chloride content of the potassium chloride feed and the degree of purification desired, For example, compacted industrially crystallized potassium chloride of a par-ticle size of -14, +35 Tyler mesh and containing a sodium chloride content of about 1 weight percent can be purified to contain a sodium chloride con- -tent of less than about 0.2 weight percent in about 6 hours at steady state conditions by the herein described process. By ~ubstantially reducing the ~4~738 sodium chloride content of potassium chloride particles i9 ~eant tbat the sodium chloride content is reduced to less than 0.5 weight percent, e.g., less than 0.25 weight percent.
The aqueous salt solution used 8S the leaching fluid is forwarded from lèach liquor tank 40 by means of pump 47 and line 46 to or near the bottom of leaching column 20. The rate at which leaching fluid is intro-duced into the column can be regulated by means of valve 48 in line 46.
The leaching 1uid is a salt solution, the solute of which is selected from the group con~i~ting of potassium chloride and mixtures of potas~ium chloride and sodium chloride. The leaching fluid i5 gub9tantially BatU-rated with respect to potassium chloride and substantially unsaturated with respect to sodium chloride at the temperature of the solution. By "sub-stantially saturated" with respect to potas3ium chloride is meant that sufficient potassium chloride is in solution BO that little, if any, of the potassium chloride particles treated will be di~solved as a con~e- -quence of being treated by the process of the inven~ion. The amount of ~odium chloride in the leaching fluid can vary; but, should be maintained at less than 45 gpl of sodium chloride in order to provide a significant driving force to permit removal of substantial quantities of sodium chlo-ride from the potas~ium chloride solids. Preferably thP leaching fluid introduced into the bottom of the leaching column will contain less than 25, e.g., les~ than 20~ gpl sodium chloride. More preferably, the leaching fluid will contain between 5 and 20, e.g., between 10 and 16 gpl of sodium chloride at steady state conditions.
The amount of leaching fluid introduced into the leaching column can vary; however, the amount should be sufficient to provide itlti~ate contact thereof with substantially all of the potassium chloride particle~
_ 9 _ .. . . . ... . . . . .
in the column. By intimate contact i~ meant that enou~h leaching fluid i9 used 80 that the entire surface Area of each potassium chloride particle is contacted with leaching fluid for the time required to obtain substantial reduction of the sodium chloride content therein. A ratio of 4000 grams of potassium chloride particles introduced into the leaching column per liter of aqueous leaching solution has been found to be useful. Variations in the ratio, such as down to 200 or 300 grams of potassium chloride per liter of leaching ~olu~ion, would not significantly improve results. Thus, a ratio of from about 300 to about 4000 grams of potassium chloride per liter of aqueous leaching solution can be used. Lower ratios can be used also;
but, are economically unattractive since it would involve the movement of large quantities of liquid per unit weight of potassium chloride particles leached.
The leaching fluid is introduced into the leaching column coun-tercurrene to the flow of potassium chloride solids in the column and in 3uch a manner as to provide a net upward flow of leaching fluid within the column. The leaching fluid is percolated upwardly through a ~ettled bed of the potassium chloride maintained within the column at a rate that is insufficient to cause fluidization or bridging of the bed. A slurry of leached potassium chloride is removed from near or at the bottom of col- -umn 20 by means of line 25 and forwarded to separating me~ns 26 for ~epa-rating the liquid phase (mother liquor) from the solids. The rate at which leached product is withdrawn from the column can be regulated by means of valve 24 in line 25. Some leaching fluid will be withdrawn with the prod-uct from the bottom of the column bscause of the closeness of the point of product withdrawal and the point of leAching fluid entry. Withdrawal of the leached product can be facilitated, if needed, by dilution with the leaching fluid.
The means by which the entraining liquid associated with the leached potassium chloride product is separated therefrom should be chosen to minimi~e degradation of the leached particle and to maximize efficient dewatering. Any conventional apparatus which accomplishes such a separa-tion and allows efficient washing or rinsin~ of the solid product can be used. In the drawing, separating means 26 is shown as a filter for separat-ing the leached potassium chloride withdrswn from the bottom of column 20 from the liquid phase (~other liquor) associated therewith. Examples of apparatus that can be used to separate the leached crystals from its mother liquor include horizontal filters, e.g.J belt, pan and table filters, drum filters, disc filters, and centrifuges. Preferably, a centrifuge is not used for leached compacted potassium chloride particles. ~fficient dewater-ing and washing is to be encouraged for the reason that a significant amount of the remaining sodium chloride is derived from the liquor adhering to the leached particles.
The product slurry is deposited on separating means (filter) 26 and the filtrate (mother liquor) is withdrawn by means of line 27 and for-warded to leach liquor tank 40 with the assistance of pump 34. The moist filter cake can be rinsed with washing fluid forwarded to the filter cake by means of line 41. The amount of washing fluid used can be controlled by means of valve 44 in line 41. The washing fluid can be water or a salt solution of potassium chloride, or potassium chloride with low levels of sodium chloride. If a salt solution is used, it can be saturated or unsa-turated with respect to potassium chloride. It is contemplated that a solution 50 to 60 percent saturated with respect to potassium chloride and containing very low levels of sodium ~hloride be used. The level of sodium chloride present in the washing fluid should be le~s than the amount of 4~3~
sodium chloride remaining in the leached potassium chloride so that such product is not recontaminated with sodium chloride. Preferably, the washing fluid is water or a potassium chloride salt solution substantially free, i.e., less than .05 weight percent of sodium chloride. It i8 contem-plated that the filter cake is washed with up to 15 displacements of wa~h- -ing fluid. By "displacement" i8 meant the amount of water remaining in the filter cake following ~eparation of the mother liquor by the separating means, e.g., filter 26.
The washed potassium chloride product is removed from filter 26, e.g., by a doctor blade, and forwarded by means of line 28 to drier 30 wherein the moisture associated with the product i8 removed. The final dried product i9 removed from the drier by means of line 32 and forwarded to storage or packed out.
Washing fluid for rinsing the filter cake is introduced into the system from a source not shown throu~h line 41 and controlled by valve 44.
Water for make-up is forwarded by line 42 to leach liquor tanlc 40. Thc amount of make-up water introduced into the tank i9 regulated by means of valve 43 in line ~2.
As the leaching fluid proceeds upwardly through the leaching col-umn, it di~places mother liquor as60ciated with and removes sodi~m chloride from the potassium chloride particles descending countercurrently to it.
An aqueous overflow liquor is removed from near the top of leaching col-umn 20 by means of line 22 and forwarded to overflow tank 50. I~e overflow liquor is saturated with respect to potasiium chloride and contains a minor amount of sodium chloride, which amount i~ slightly higher than the ~odium chloride level present in the leaching fluid introduced at the bottom of the column. Also dissolved in the overflow liquor are small amounts of ~44~738 calcium ~nd magnesium salts. Aqueous li~uor in o~erflow tank 50 is for-warded by means of line 52 to slurry tank 10 for utilization in repulping potassium chloride feed, i.e., for preparing further potassium chloride ; slurry feed to the leaching column. In the event that there is insuffi-cient make-up water available in the system for the process, the liquor in overflow tank 50 can be recycled by means of line 53 and valve 55 to leach liquor tank 40. However, the recycling of this liquor from overflow tank 50 to leach liquor tank 40 is not desired for the reason that it results in forwarding a salt solution rich in sodium chloride to tank 40 which con-tains a salt solution lean in sodium chloride.
In order to prevent a build-up of sodium chloride and calcium and magnesium salts in the system, a bleed stream is provided in line 53 by means of line 54 and valve 56. Sufficient of the overflow from column 20 is taken as bleed to maintain the desired sodium balance in the system, which in turn depends on the desired purity of the product. Accordingly, the amount of make-up water required to the system will be equal to the amount of liquid withdrawn by mean~ of the sodium chloride bleed strbam, ~ the moisture removed at the dryer and for other unaccounted losses of - liquid in the ~ystem les~ the amount of water introduced to the system by the filter wash stream 41.
In operating the leaching column, the slurry of industrially produced potassium chloride crystals (about 20-30 volume percent) is intro-duced into ~he top of the leaching column where it slowly descends against the rising countercurrent flow of leaching fluid. A bed o~ potassium chloride of about 90 percent ~ettled solids is formed in the column through which the leaching fluid percolates. As ~he leaching fluid rises in the column, it di~places the mother liquor associated with the solid~ and 11~4~3~
leaches sodium chloride contained therein, thereby increasing it~ sodium chloride content. For example, a saturated potassium chloride aqueous solution leaching fluid containing initially about 13 grams per liter sodium chloride will contain about 15-17 grams per liter of sodium chloride when it is withdrawn from the leaching column as overflow. When the slurry of leached potassium chloride solids is withdrawn from the bottom of the leach-ing column, it is diluted wi~h leaching fluid so that the slurry charged to the filter 26 contains only about 30 to 40 percent settled solids.
The temperature at which the present process is conducted csn vary~ However, the higher the temperature the more potassium chloride required to maintain the various process ~treams saturated therewith and the greater the energy requirements. Consequently, moderate temperatures, i.e., from about 20C. to about 70C., e.g~, from about 75 to about 55C., are preferred for conducting the process of this invention. Typically, the process is operated isothermally, i.e., without the intentional addition or removal of heat.
In performing the process described hereinabove with respect to the Figure, the system, i.e., the lesch liquor tank, leaching column, over-flow tank and slurry tank, are filled with a potassium chloride solution.
Potassium chloride lS then fed to slurry tank 10 by operating feed screw 8.
A stirring system, such as a propellor, within tank 10 induces circulationof the solution in the tank, theraby csusing ~uspension of the particulate potassium chloride charged to the tank. The resulting slurry i~ forwarded to leaching column 20. If the ~olution contained in the syætem is not saturated ~ith respect to potsssium chloride, particulate potassium chlo- -ride will di~solve until ~aturation is reached. Thereafter, a solids bed will build up inside ~he leaching column. The bed height will depend on ~4~38 the desired retention time. Once the target bed height i9 reached, product discharge valve 24 i8 opened and product discharge from the column for-warded to filter 26. The setting for valve 24 is adjusted to maintain a constant bed height.
Following introduction of product to the filter, filter wash is forwarded to the filter and filtrate pump 34 is started to re ycle filtrate to the leach liquor tank. Washed product is forwarded to preheated dryer 30 which removes residual moisture from the product.
The sodium chloride content of the leaching solution forwarded to column 20 through line 46 is determined. If the sodium chloride content of this solution i8 higher than the desired tar~et concentration, valve 56 in line 54 is opened to purge sodium chloride from the system snd make-up solu-tion, which has a lower sodium chloride content, is added through line 42 to compensste for the volume of the sodium chloride bleed stream purged from the system. If the solution has a sodium chloride content less than the target concentration, bleeding is not required and valve 56 is closed.
Make up solution (other than to replace losses) is also not required until the sy~tem reaches !teady state conditions.
The present process is more particularly described in the follow-ing example which is intended as illustrative only since numerous modifica-tions and variations therein will be apparent to those ~killed in the art.
EXAMPLE
In the following example, values and operating conditions given are average values for 28 hours of steady seate operation. Flow rates are in U. S. gallons per minute (gpm) unless noted otherwise.
~4738 Compacted, industrially crystallized potassium chloride having the average sieve analy~es reported in Table I was charged to slurry tank 10 at a rate of about 1.73 tons per hour. The potassium chloride feed contained on the average 0.91 weight percent sodium chloride and 0.023 and 0.014 weight percent calcium and magnesium respectively. An aqueous slurry of the afore~aid compacted potassium chloride feed having about 22 volume percent solids (settled sol;ds) was charged at a rate of 60 gpm to the top of a leaching column in which the settled bed was about 21-22 feet.
A saturated potassium chloride solution containing about 13.1 grams per liter (gpl) of sodium chloride was introduced into the bottom of ; the column as the leaching fluid at about 51.3 gpm. The llquid overflow from the column contained about 15.6 gpl sodium chloride. Retention time in the column was calculated to be about 6.1 hours. Water make-up averaged 6-9 gpm.
Leached potassium chloride was withdrawn from the column and forwarded to a filter. The filter discharge was found to contain about 0.084 weight percent sodium chloride, 0.0036 weight percent calcium and 0.00098 weight percent magnesium. When tried, unrinsed sample~ of the filter cake were found to contain an average of 0.108 weight percent sodium chloride, 0.0035 weight percent calcium, and 0.0016 weight percent magne-sium. Samples of filter cake rinsed for 30 seconds in a potassium chloride ~aturated solution containing no sodium chloride and then dried were found to contain 0.042 weight percent sodium chloride, 0.0022 weight percent cal~
cium and 0.00055 weight percen~ magnesium.
The data of the aforesaid example demonstrates that the sodium chloride content of compacted, industrially crystallized potassium chloride can be reduced to low levels, i.e., from about 0.9 ~o about 0.09 weight percent by the leaching proceBs of the present invention.
~4738 TABLE I
TYL~R SIEVE CUMULATIVE WEIGHT, %
14 23.5 16 48.6 ` 20 ~ 71.7 28 ~ 9I.2 95.7 48 97.5 Although the p~esent process has been described wi~h reference to specific details of certain embodiments thereof, it is not intended that such details should be regarded as limitation~ upon the scope of the inven-tion except ns and to the e~tent that they are included in the accompanying claims.
:
' :
,:
:
Claims (15)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In the process of purifying industrially produced particulate potassium chloride consisting essentially of potassium chloride and minor contaminating amounts of encapsulated sodium chloride wherein said potassium chloride is leached with a saturated potassium chloride salt solution, the improvement which comprises:
(a) introducing particulate potassium chloride into and near the top of a leaching column, (b) introducing sodium chloride lean, aqueous leaching potassium chloride salt solution into the bottom of said leaching column in an amount sufficient to contact said particulate potassium chloride intimately and in a direction to produce an upward flow of leaching salt solution within said column, said leaching salt solution being saturated with respect to potassium chloride and containing less than 45 grams of sodium chloride per liter of solution, (c) maintaining said particulate potassium chloride in intimate contact with said aqueous leaching solution for a time sufficient to substantially reduce the sodium chloride content of the particulate potassium chloride, (d) removing aqueous liquid effluent from the top of the leaching column, said effluent having a sodium chloride content greater than the leaching salt solution introduced into said column, (e) removing a slurry of leached particulate potassium chloride substantially reduced in sodium chloride content from the bottom of said leaching column, (f) separating leached particulate potassium chloride from sodium chloride lean entraining mother liquor of the slurry of step (e), (g) recycling sodium chloride lean mother liquor of step (f) to the leaching column as leaching salt solution, and (h) segregating recycled sodium chloride lean leaching solution of step (g) from aqueous liquid effluent removed from the top of the leaching column, thereby obtaining particulate potassium chloride substantially reduced in sodium chloride content.
(a) introducing particulate potassium chloride into and near the top of a leaching column, (b) introducing sodium chloride lean, aqueous leaching potassium chloride salt solution into the bottom of said leaching column in an amount sufficient to contact said particulate potassium chloride intimately and in a direction to produce an upward flow of leaching salt solution within said column, said leaching salt solution being saturated with respect to potassium chloride and containing less than 45 grams of sodium chloride per liter of solution, (c) maintaining said particulate potassium chloride in intimate contact with said aqueous leaching solution for a time sufficient to substantially reduce the sodium chloride content of the particulate potassium chloride, (d) removing aqueous liquid effluent from the top of the leaching column, said effluent having a sodium chloride content greater than the leaching salt solution introduced into said column, (e) removing a slurry of leached particulate potassium chloride substantially reduced in sodium chloride content from the bottom of said leaching column, (f) separating leached particulate potassium chloride from sodium chloride lean entraining mother liquor of the slurry of step (e), (g) recycling sodium chloride lean mother liquor of step (f) to the leaching column as leaching salt solution, and (h) segregating recycled sodium chloride lean leaching solution of step (g) from aqueous liquid effluent removed from the top of the leaching column, thereby obtaining particulate potassium chloride substantially reduced in sodium chloride content.
2. The process of claim l wherein the particulate potassium chloride introduced into the leaching column is introduced as an aqueous slurry.
3. The process of claim 2 wherein liquid effluent from the top of the leaching column is utilized for the preparation of further potassium chloride slurry feed to the leaching column.
4. The process of claim 1 wherein a portion of the liquid effluent from the top of the leaching column is purged to control the sodium chloride content within the column.
5. The process of claim 1 wherein the leached potassium chloride of step (f) is washed with a washing fluid selected from the group consisting of water and an aqueous potassium chloride salt solution, said salt solution containing a sodium chloride content no greater than the sodium chloride content of the leached potassium chloride.
6. The process of claim 5 wherein the potassium chloride washing fluid is substantially free of sodium chloride.
7. The process of claims 5 or 6 wherein the potassium chloride washing fluid is substantially saturated with potassium chloride.
8. The process of claim 1 wherein the industrially produced potassium chloride is a compacted particulate potassium chloride.
9. The process of claim 8 wherein the leaching salt solution of step (b) contains less than 25 grams of sodium chloride per liter of solution.
10. The process of claim 8 wherein the residence time within the column is between about 0.5 and 24 hours.
11. The process of claim 8 wherein the temperature at which leaching is conducted is from about 20°C. to about 70°C.
12. The process of claim 3 wherein the industrially produced potassium chloride is compacted particulate potassium chloride, the leaching solution contains less than 25 grams of sodium chloride per liter of solution, the residence time within the column is between about 2 and 18 hours, and a portion of the liquid effluent from the top of the leaching column is purged to control the sodium chloride content within the column.
13. The process of claim 12 wherein the leaching solution contains less than 20 grams of sodium chloride per liter of solution and the residence time within the column is between 4 and 12 hours.
14. The process of claim 12 wherein the leached potassium chloride of step (e) is washed with a washing fluid selected from the group consisting of water and an aqueous potassium chloride salt solution containing a sodium chloride content no greater than the sodium chloride content of the leached potassium chloride.
15. The process of claim 14 wherein the temperature at which leaching is conducted is from about 20°C. to about 70°C.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US17430880A | 1980-07-31 | 1980-07-31 | |
| US174,308 | 1980-07-31 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1144738A true CA1144738A (en) | 1983-04-19 |
Family
ID=22635699
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000380450A Expired CA1144738A (en) | 1980-07-31 | 1981-06-23 | Process for purifying potassium chloride particles |
Country Status (4)
| Country | Link |
|---|---|
| CA (1) | CA1144738A (en) |
| DE (1) | DE3129042C2 (en) |
| FR (1) | FR2487809A1 (en) |
| GB (1) | GB2080779B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2634665B1 (en) * | 1988-07-29 | 1991-12-13 | Solvay | PROCESS AND PLANT FOR CRYSTALLIZATION OF A MINERAL SUBSTANCE AND CRYSTALS OF SODIUM CHLORIDE |
| US4997637A (en) * | 1989-05-09 | 1991-03-05 | Occidental Chemical Corporation | Digestive crystallizing process and apparatus for purification of KC1 |
| ATE128104T1 (en) * | 1993-06-03 | 1995-10-15 | Kali & Salz Ag | METHOD AND DEVICE FOR TREATING A POTASSIUM CHLORIDE MIXTURE. |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB213531A (en) * | 1923-03-29 | 1924-06-12 | Grande Paroisse Azote & Prod C | Improvements in or relating to the purification of minerals and salts |
| FR2411158A1 (en) * | 1977-12-08 | 1979-07-06 | Ppg Ind Canada Ltd | PROCESS FOR PURIFYING CRYSTALLINE POTASSIUM CHLORIDE |
| US4248601A (en) * | 1979-07-12 | 1981-02-03 | Kerr-Mcgee Chemical Corporation | Process for reducing the sodium chloride content of a potassium salt |
-
1981
- 1981-06-08 GB GB8117501A patent/GB2080779B/en not_active Expired
- 1981-06-23 CA CA000380450A patent/CA1144738A/en not_active Expired
- 1981-07-23 DE DE19813129042 patent/DE3129042C2/en not_active Expired
- 1981-07-29 FR FR8114785A patent/FR2487809A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| GB2080779A (en) | 1982-02-10 |
| FR2487809B1 (en) | 1983-08-19 |
| DE3129042A1 (en) | 1982-03-04 |
| GB2080779B (en) | 1984-06-20 |
| FR2487809A1 (en) | 1982-02-05 |
| DE3129042C2 (en) | 1984-05-03 |
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