US3037624A - Beneficiating potash ores - Google Patents

Description

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United States Patent ()fidce Patented June 5, 152-8?v 3,637,624 BENEFKCIATWG PQTASH ORES Frank L. Jackson, Weston, (Iona, and Bernard M. Fisher and Gilbert L. Jordan, Carlsbad, N. Mex., assignors to National Potash Company, New York, N.Y., a corporation of Delaware Filed Aug. 20, 1958, Ser. No. 756,174 2 Claims. (Cl. 209-4) This invention relates to a new and improved process for beneficiating potash ores and, more particularly, to a process for recovering from a sylvinite ore a sylvite concentrate of desirable particle size which does not contain burdensome quantities of fines and is substantially free of dis-persible clay and other dispersible water-insoluble material.

Heretofore, beneficiation of sylvinite ores to recover potassic values has been generally limited to those ores which contain a relatively small percentage of dispersible clay, and other dispersible, water-insoluble material, i.e., about 3%, or less. However, as these ore deposits diminish, more eificient methods of processing ores having a higher content of dispersible clay-like materials have been needed, but have not been forthcoming. The major problems which arise in the beneficiation of potash ores are usually attributed to the transformation of these dispersible materials into slime form. It is generally believed that the dispersible clay constitutes a large percentage of the slimes formed, and accordingly, the term dispersible clay will be used hereinafter to mean dispersible clay and other dispersible, water-insoluble material present in potash ores. Likewise, since the major beneficiation problems are associated with the amount of clay present, the terms low-clay ore and high-clay ore are used herein to refer to ores which respectively contain 3% or less of dispersible clay and more than 3% of dispersible clay.

Several methods of processing low-clay ores have been employed to recover the sylvite concentrate therefrom. Customarily, these processes include the steps of wet grinding and classifying the ore, passing the ground ore to a pulping tank, usually of the barrel type, where the ore is suspended in a brine solution saturated with respect to sylvite and halite from which the ore is delivered to a hydro-separator where the coarse sylvite and halite concentrate is separated from the clay and fines. The Wet grinding has been considered to contribute importantly to the effective operation of the process. The concentrate obtained in this manner is then processed in several steps including flotation separation, where separation of sylvite and halite is effected.

Although this conventional type of processing has been found sufliciently economical to be commercially acceptable for low-clay ores, it is not practical for the treatment of high-clay ores containing more than about 3% of dispersible clay. As the clay in potash ore increases, various separation problems arise which cannot be overcome readily by adjustment of these customary methods of operation.

Among the disadvantages of known processes, especially when applied to high-clay potash ores, are the following:

Wet grinding produces a large percentage of fines making it desirable to process the fines separately to recover sylvite values, thereby adding to processing costs; the sylvite particles are excessively reduced in size during the processing, thereby reducing the market value of the recovered sylvite concentrate; insuflicient scouring action is provided to separate effectively the clay and particulate sylvite present in the ore; unremoved clay impedes conventional flotation separation of potassium-containing concentrate and absorbs large quantities of flotation agent; and finally, known procedures for classifying and desliming wet-ground high-clay ores are highly ineflicient.

It is an important object of this invention to provide an efficient and uncomplicated process for recovering a sylvite concentrate from both high and low clay potash ores.

It is a special object of this invention to provide a method for producing a mill feed, substantially free of dispersible clay, from a high-clay sylvinite ore without the production of an undesired quantity of fines.

It is another special object of this invention to provide a process whereby a coarse sylvite concentrate can be derived from a high clay sylvinite ore which permits a conventional flotation separation of KCl in very high yields equivalent to and more, of the KCl content of the ore.

Other objects and advantages of the invention will be apparent from the more detailed description of the invention which follows.

These and other objects of the invention are attained by: (1) Dry grinding all of the ore obtained from the mine, to a desirable particle size, suitably, to a maximum of 10 mesh or preferably to about 12 or 14 mesh, (2) Strenuously scrubbing the ground ore in an aqueous medium to separate the clay from the sylvite particles and disperse it in the aqueous medium, and (3) Centrifugally separating the dispersed clay and other fines from the scrubbed ore particles to provide the sylvite ore concentrate.

The invention can be readily understood from the important illustrative embodiment, schematically represented on the accompanying flow sheet, as applied to the continuous processing of a sylvinite ore. The ore treated was a sylvite-halite ore having the following analysis:

Dispersible clay and other dispersible water-insoluble materials 4.98 Combined H O .61

The raw ore, as it came from the mine, was mostly inch mesh sizeand was run over a inch scalping screen to remove A1 inch ore particles. The coarser particle fraction was conveyed to a primary impactor crusher, and the minor fine particle fraction containing a major portion of the clay to an ore dryer and then to a 12 mesh screen. The crushed ore from the primary crusher was likewise conveyed to the 12 mesh screen. The +12 mesh ore particles were conveyed to a secondary impact crusher and the crushed ore reconveyed to the 12 mesh screen. The 12 mesh ore particles were ready for the scrubbing treatment.

More particularly, it has been discovered that drying the fraction of the ore which contains the major portion of the clay and fines substantially reduces blinding of the 12 or 14 mesh screens which control the particle size of the ore being processed. Although the larger particles from the inch scalping screen make up the bulk of the ore being processed, i.e., about of the ore, it has been discovered that this fraction, although later ground and screened contributes only negligibly to the blinding of the 12 or 14 mesh screens. Furthermore, it has been discovered that while drying of the inch ore from the scalping screen considerably improves the efficiency of the 12 or 14 mesh screening of the ore, drying of the 4- /4 inch fraction or the recycle from the 12 or 14 mesh screens has not been found to be of any additional advantage. Rather, it has been found that drying these fractions can be deleterious to the overall efficiencyof the process. The fact that the process operates very effectively by drying only a fraction of the ore, results in important savings in equipment and fuel and avoids excessive rises in the temperature of the brine and the resulting excessive dissolution of potash compounds which must be recovered by expensive recrystallization.

The crushers were operated continuously in closed circuit with the screens. Intermediate screening and removal of undersize particles was not necessary. By adjusting the speed of the impactors to the proper rate, recycling of the oversize material was controlled and overgrinding was avoided. Through this control of the grinding operation, the product contained a larger proportion of coarse particles, and as a result, the final purified ore product produced had a premium value in the market.

A typical sample of the crushed ore had the following particle size distribution, as determined by screening: l2 to +28 mesh, about 42.8%; 28 to +100 mesh, about 40.7%; 100 to 200 mesh, about 9.7%; and less than 200 mesh, about 6.8%. Only the material passing through the 200 mesh screen is considered fines, and analysis along the path of flow of the ore showed that this material was rich in clay.

The dry crushed ore together with approximately an equal weight of an aqueous brine saturated with respect to potassium chloride and sodium chloride were introduced continuously into the first compartment of a compartmented attrition scrubber. This brine was obtained from a later stage of the process and was sufiicient only to provide a fluid mass of high solids content. About 50% of brine, by weight, in the fluid mass was sufiicient. Each compartment of the scrubber was provided with a high speed impeller agitator. By operating the device at an adequately high speed, the particles were vigorously agitated, thereby forcing a high degree of inter-particle impingement at comparatively high velocities and effecting strenuous scouring and scrubbing action on the granular particles, which action removes clay without materially reducing grain sizes. This action also broke up cemented particles and exposed new surfaces, with the result that more effective scrubbing was accomplished. Unless the particulate KCl is scrubbed free of clay, the flotation reagents used for separating KCl from NaCl in the flotation cells, will not be effective.

The ore was underfiowed continuously from compartment to compartment in the scrubber and was then flowed to a dilution tank suitably of cylindrical shape. The number of compartments required in any particular operation is determined by the tenacity with which the clay adheres to the granular particles and the degree of scrubbing desired in this phase of the process. The process can be accomplished in a single scrubbing compartment, but, in this instance, not with an acceptable efficiency.

The mixture was maintained in the dilution tank in a continuous state of high agitation by a stirrer and sui'iicient saturated brine was added to reduce the solids content of the liquor from about 50% to about Agitation may be facilitated by providing the dilution tank with four baflles mounted vertically and radially, equidistant around the wall of the tank.

The diluted pulp was then pumped continuously under pressure to a hydrocyclone separator where a first stage desliming was carried out. The diluted pulp was fed continuously and tangentially into the upper end of the elongated cyclone, clay and fines of relatively small particle size were removed axially and continuously as a stream of restricted diameter from the center of the upper end of the cyclone while a concentrate of the coarser ore particles was forced to the outer area and removed continuously as a stream of restricted diameter from the lower end of the cyclone. The pressure used and the relative size of the outlets in the upper and lower part of the cyclone were adjusted to remove a coarse product having to solids from the bottom of the cyclone and to remove the remainder of the liquid containing the lower specific gravity fines and dispersed clay from the top of the cyclone. The brine was recovered from the clay and fines in a slime leach system in conventional manner.

The partially purified coarse product obtained was next flowed continuously to a second scrubber provided with an impeller agitator. The brine containing the ore particles was vigorously agitated again to force the particles to impinge upon one another and effect an inter-particle scouring action. While various types of scrubbers may be used, it was found, as in the first treatment, that a compartmented scrubber obtained the greatest scouring action per unit of retention time.

After substantially all of the dispersible clay and other material to be removed had been forced from the particles of ore, the suspension was flowed continuously to a second agitated dilution tank where it Was mixed with sufiicient fresh saturated brine to reduce its solids content to about 17%. Then the resulting diluted suspension was pumped continuously to a second centrifuge or hydrocyclone, where a major part of the brine containing substantially all of the remaining dispersible clay and lines was separated from the coarse concentrate and returned to the first dilution tank. The coarse efiluent contained less than 2% of particles of -200' mesh.

The granular sylvite ore concentrate, substantially free of all clay and fines, was passed to a conditioning tank Where flotation agents were added, then brine, in preparation for the flotation separation of the sylvite and halite in a known manner.

After the flotation separation and related crystallization, a coarse sylvite product was obtained containing KCl in a quantity at least equaling a potassium oxide equivalent of 60.5%. In this way, approximately or more of the available KCl was recovered from the core.

In the illustrative embodiment of the invention specific details have been given with reference to procedures and apparatus, but it will be apparent the invention is not limited to these details. For instance, the impeller scrubbing of the ore body may take place in a single attrition machine when a low-clay ore is used or the clay adheres to the ore with less tenacity. Likewise, greater clay separation may be effectuated by increasing the number of compartments. Also, hydrocyclones have proven especially advantageous for separating the scrubbed ore from the dispersed clay, fines, and other water insoluble but dispersible materials. However, other known types of centrifugal separators may be used, somewhat less advantageously. In general, two scrubbing steps and two centrifugal separatory steps are preferred when high-clay ores beneficiated. Thus, it should be understood that this invention extends to all equivalent operations and apparatus which will occur to those skilled in the art upon consideration of the principles of the invention and the disclosed manner of practicing the invention.

What is claimed:

1. A method of beneficiating as-mined high-clay sylvinite ore containing at least about 3% of bound but waterdispersible clay, comprising separating the mined ore into (1) a major fraction of relatively large particles which upon subsequent dry grinding .do not tend to blind a 10 mesh screen and (2) a minor fraction of relatively smaller particles of a size and moisture content which normally tend to blind a 10 mesh screen, drying only said minor fraction of relatively smaller particles, subjecting said major fraction of relatively large particles to dry grinding, combining the resulting dried minor fraction and the resulting dry-ground major fraction and subjecting the resulting combined dry-ground major and the resulting dried minor fractions to a screening treatment on an about 10 mesh screen, feeding the particles of ore which pass through said 10 mesh screen and an aqueous brine solution saturated with respect to potassium chloride and sodium chloride into a scrubbing zone to form a fluid aqueous mixture, said brine solution containing essentially only potassium chloride and sodium chloride, agitating the mixture with such force that the ore is suspended in the brine and the ore particles are forced into contact with one another at high velocities and the clay is scrubbed from the ore particles and becomes dispersed and suspended in the brine, and centrifugally separating the particulate ore from the dispersed clay and fines.

2. In the treatment of as-rnined potash ores containing at least about 3% of bound but Water-dispersible clay to produce an ore concentrate, the steps comprising separating the mined ore into (1) a major fraction of relatively large particles which upon subsequent dry grinding do not tend to blind a mesh screen and (2) a minor fraction of relatively smaller particles of a size and moisture content which normally tend to blind a 10 mesh screen, drying only said minor fraction of relatively smaller particles, grinding the ore particles of said major fraction of relatively large particles to reduce the size thereof only by dry grinding, combining the resulting dried minor fraction and the resulting dry-ground major fraction and subjecting the resulting combined dry-ground major and the resulting dried minor fractions to a screening treatment on an about 10 mesh screen, feeding the particles of ore which pass through said 10 mesh screen and an aqueous brine solution saturated with respect to potassium chloride and sodium chloride into a scrubbing zone to form a fluid aqueous mixture, said brine solution containing essentially only potassium chloride and sodium chloride, agitating the mixture with such force that the ore is suspended in the brine and the ore particles are 5 forced into contact with one another at high velocities and the clay is scrubbed from the ore particles and becomes dispersed and suspended in the brine, and centrifugally separating the particulate ore from the dispersed clay and fines.

References Cited in the file of this patent UNITED STATES PATENTS 2,596,407 Jackson May 13, 1952 2,836,297 Smith et a1 May 27, 1958 2,846,068 Smith et a1. Aug. 5, 1958 2,950,007 Smith Aug. 23, 1960 OTHER REFERENCES Craiglow: Electric Heating of Screens, reprint from Ceramic Bulletin, 1950.

Rock Products, Lenhart, February 1952, pp. 100-103. Chemical Engineering, Tangel, June 1955, volume 62, Number 66, pp. 234-238. Mining Engineering, Weems, August 1951, pp. 685-

Claims (1)

1. A METHOD OF BENEFICIATING AS-MINED HIGH-CLAY SYLVINITE ORE CONTAINING AT LEAST ABOUT 3% OF BOUND BUT WATER DISPERSIBLE CLAY, COMPRISING SEPARATING THE MINED ORE INTO (1) A MAJOR FRACTION OF RELATIVELY LARGE PARTICLES WHICH UPON SUBSEQUENT DRY GRINDING DO NOT TEND TO BLIND A 10 MESH SCREEN AND (2) A MINOR FRACTION OF RELATIVELY SMALLER PARTICLES OF A SIZE AND MOISTURE CONTENT WHICH NORMALLY TEND TO BLIND A 10 MESH SCREEN, DRYING ONLY SAID MINOR FRACTION OF RELATIVELY SMALLER PARTICLES, SUBJECTING SAID MAJOR FRACTION OF RELATIVELY LARGE PARTICLES TO DRY GRINDING, COMBINING THE RESULTING DRIED MIONOR FRACTION AND THE RESULTING DRY-GROUND MAJOR FRACTION SAND SUBJECTING THE RESULTING COMBINED DRY-GROUND MAJOR AND THE RESULTING DRIED MINOR FRACTIONS TO A SCREENING TREATMENT ON AN ABOUT 10 MESH SCREEN, FEEDING THE PARTICLES OF ORE WHICH PASS THROUGH SAID 10 MESH SCREEN AND AN AQUEOUS BRINE SOLUTION SATURATED WITH RESPECT TO POTASSIUM CHLORIDE AND SODIUM CHLORIDE INTO A SCRUBBING ZONE TO FORM A FLUID

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