US1128874A - Process of treating natural phosphate-rock. - Google Patents

Description

F. K. HOOVER & A. J. MASON.

PROCESS OF TREATING NATURAL PHOSPHATE ROCK. APPLICATION FILED JUNE 9, 1911.

Patented Feb. 16, 1915.

FRANK K. HOOVER AND ARTHUR J. MASON, OF CHICAGO, ILLINOIS.

' PROCESS OF TREATING NATURAL PHOSPHATE-ROCK.

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Specification of Letters Patent.

Patented lFeb. to, 1915.

Application filed June 9, 1911. Serial No. 632,234.

T all whom it may concern:

.Be it known that we, FRANK K. Hoover: and ARTHUR J. MASON, citizens of the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented a new and Improved Process of Treating Natural Phosphate-Rock, of which the following is a specification.

This invention relates to a new and improved method of treating natural phosphate rock which is extensively used at the present time as a fertilizing agent. Phosphate rock is a natural mineral deposit occurring to a considerable extent in Tennessee and other parts of the country, being usually found at a depth of from five to thirty feet below the surface of the ground and existing in strata of varying thicknesses beneath an over-lying stratum of clay. The phosphate or brown rock deposit in its natural state is found .in pieces varying from rocks of considerable size down to fine powder. The larger pieces are comparatively pure, and the present somewhat wasteful method consists in utilizing principally the larger pieces and roughly washing them to obtain the desired percentage of purity, discarding the finer material which contains a considerably greater percentage of clay and other foreign matter. proportion of the total material existing in the fine form is, in many localities, a very considerable percentage of the whole, it is highly desirable from the viewpoint of economy to save such fine material; but to increase its commercial value it is necessary to purify it of the contained clay; and it is the chief purpose and object of the present invention to efiect such a cleaning or purification of the entire body of material, including the finer part, so as to bring the whole up to the desired or required standard of purity. We have found from extensive work on a considerable variety of the brown rock of Tennessee that the portion represented by the finer particles, that'is, those smaller than one-twentieth of an inch in diameter, if properly washed, will retain nearly the same percentage of phosphate of lime as the large pieces, and our present process consists in a method of treament whereby the whole deposit consisting of the so-called phosphate sand as well as the large lumps and rocks may be caused to yield a As the I resulting product which will grade substantially the same as when the large pieces only are selected.

Our process, as to its main or essential steps or operations, consists in, first, the rubbing and grinding of the material on itself to bring all the clay to a solvent condition; second, diluting the same thoroughly with sufficient water; and, third, the separating of the rock from the dirty water. A

preliminary operation of grinding or crushwherein we have illustrated, somewhat diagramatically, a group of devices well adapted for the carrying out of the several steps of the treatment; although it is to be understood that the performance of the several acts and operations involved in the process is by no means dependent upon the particular devices herein illustrated for this purpose.

The material as received from the mine consists of a mass generally very wet and composed of pieces ranging in'size from that of a mans head down to extremely fine material such as impalpable powder, containing intermixed therewith a considerable amount of clay, iron and sand,chiefly clay. For convenience we first provide a receiving hopper A for this rock preferably of considerable capacity for the purpose of guarding against the intermittent operations at the mine due to weather conditions and other causes. At the lower portion of said hopper we provide a rotary feed gate B, preferably of the form and type disclosed in our Patent No. 753,076, granted Feb. 23, 1904-. The rock is emitted from the receiving hopper in a continuous and regulated stream and is passed through one or more pairs of crushing rolls, two being herein indicated at C and D, the rolls of the two pairs be (ing spaced at different distances apart, the

upper rolls being set about four inches apart and the lower rolls about a half inch apart, so as to insure the crushing 'of both the larger and smaller pieces and effecting the reduction of the wholeto the desired size for treatment. From the rolls the material falls into a device which we have denominated a m'ulcher shown at E. We have found in treating this phosphate rock to cleanse the same-of the associated clay that something more is necessary than the customary tumbling in the presence of water. We have demonstarted that if this same material is first subjected to a' thorough rubbing action, such as a person subjects his hands to in washing them with soap, in the presence of just sufficient water to soften and render plastic the mass, it is then brought to acondition highly favorable for the next step in the process of its cleansing.

A microscopic examination of phosphate rock as now maiketed reveals the fact that a large proportion consists of grains very much like ordinary building sand, each grain more or less coated with clay carrying some iron. If these grains be vigorously rubbed against each other in the presence of a small amount of water, a scouring effect is had, so that on-further rinsing with more water they will appear clean and free from this coating of clay and iron. The object of this mulcher, therefore, is to subject the mass of material to this rubbing andscouring .action. This device, which forms the subject matter of another application filed by us June 9, 1911, Serial No. 632,235, consists, generally stated, of a number of superimposed ring-shaped holders e and e, alternate holders being mounted to rotate and the intermediate holders being either stationary or rotating in the opposite direction. As-the material feeds down between these holders, theportions contained in adjacent holders are rubbed against each other,'and

as the material is constantly and slowly passing through the holders, a very thorough and intimate rubbing of the particles -of the entire mass upon and against each other is obtained. We find that this rubbing and scouring action is best obtained when the material has about a consistency a little stiffer than that of mortar usually employed in plastering buildings, and for this purpose we add a small tempering stream of water through a pipe-F which is controlled in a manner similar to that employed in brick making in the preliminary preparation of the day. From between the rings e and e the material'falls upon a rotating plate E, from the periphery of which it is uniformly withdrawn by-'a stationary plow indicated at E ,After the material is passed through this mulcher, its appearance and behavior i indicate a marked change in its condition,

and it is obvious from ins ection that all the clay has been softene and loosened from the particles of phosphate rock. this time the material resembles a pulpy mass, the majority of the particles of which are phosphate rock of varying sizes.

The next step in the operation consists in bringing the clay into a condition of complete suspension in water. For this purpose the material discharged from the mnlcher is passed through a chute Ginto what we term a dasher H, which consists of a rotatable cylinder set slightly out of the horizontal and having set around its interior a series of longitudinal buckets h, and to which water is continuously supplied, as through a perforated pipe h lying in the upper part of the cylinder. The revolution of the dasher causes the material and water intermixed therewith to be lifted by the buckets h and frequently drepped'upon itself. In this way the added waterthoroughly mixes with the clay, and on emission from the lower end of the dasher the material is in a suitable condition to begin the proce% of separation,

containing at this time about one and oneing an opening at. its bottom sealed by a ball valve 3' and provided at its top with a seriesof channels 7' laid across the same for 'the purpose of diffusing the over-flow over substantially the whole area of the cone and thus producing a uniform upward current, the cone J being normally filled and brimming over. This over-flow contains, of course, mud in suspension, and with it some of the -finer particles of phosphate rock. The bulk of the phosphate rock, however, piles up at the bottom of the cone, and is, from time to time, discharged by opening the valve'j, and delivered, accompanied by about an equal quantity of muddy water, into an underlying tank K which constitutes the lower part of the separator. The purpose of this latter device is to thoroughly expel with clear water the mud that fails to pass off in the overflow from the cone .l and rinse the solid particles of phosphate rock. .To facilitate this operation we provide within the tank K a zigzag annular passage formed between outer and inner corrugated partitions Z, Z. clean water being ,let into the lower portion of the tank K a i m wardly through a zigzag annular passage to the top of the tank K, and in so doing meets and intercepts with a rinsing action the descending particles of phosphate rock, the latter falling to the bottom of the tank K, and the mud rising with the upflowing stream of water. To render the upward flow in the tank K as uniform as possible and efiect its diffusion over the whole area of the tank We likewise provide at the top of mud and other impurities passln through the overflow trough m By means of the latter a number of channels similar to the channels 7' of the upper separator, through which the rising volume of water with the balance of the mud and some finer particles of phosphate rock in suspension therein flows, together with the overflow from cone J into a trough L, whence the entire overflow passes into a further separator operating upon the water-fall or cascade principle and consisting essentially of a tank M containing a number of vertical transverse partitions m of gradually decreasing height and forming a row of compartments having a gradually stepped relation,'thereby producing a series of minute cascades delivering in succession to each other from the front to the rear end of the tank, the fine particles of the heavier phosphate rock settling to the bottoms of the several successive compartments, and the lighter pargiclefis of this auxiliary separator, thefinest particles of phosphate rock, running froin 1/80 to 1/500 of an inch in diameter, and represented generally by the impalpable powder constituent, and which would be otherwise wasted in the overflow from the main separator, are recovered. Returning to the main separator, the. bulk of the phosphate rock falls to the bottom of the tank K and is from time to time withdrawn through a cen-. tral hole in said bottom by opening a ball valve 70 the material falling through a chute N into-a skip-car 0, whence it is conveyed through delivery troughs P into a series of draining-tanks Q. We prefer to employ two or more such draining tanks with delivery to and from each in succession in order to give time for the contained water to drain. Each tank has at its bottom a filtering-bed q composed of coarse material, such as coarse phosphate rock,

crushed limestone, cinder, or any suitable material, through which and the bottom of the tank is set a delivery spout q. The water is drained ofi through a drain-pipe g and in order to accelerate the draining we introduce into each drain pipe a steam ejector jet or nozzle indicated at g When the drainage tank has been filled with the washed phosphate rock and given time for drainage, and is ready for the drying operation, we find that it has assumed a condition so water-packed that it will not flow even when a very large opening as large as three feet in diameter is made in the floor of the tank or receptacle. In order to cause it to flow out of the tank, we first bore ahole through the exit opening g from below upwardly to' the full height of the material in the tank, using for this purpose an earthboring augerzof suflicient size (actually about nine inches in diameter). The material is then shoveled from the top into this hole and passes thence into an underlying feed-hopper R at the bottom which regulates the supply of material to the drying devices. While it is true that this material packs in the manner above described, yet after it has been drained and once loosened it remains in the loose condition, like ordinary building sand, and flows freely in any desired manner. The expeditious removal of the drained phosphate rock from these draining tanks has heretofore presented quite a serious problem; but operating in the manner above described the material is easily removed and the capacity of a single operator becomes very great, as high as ten tons per hour. y

We find that if a tank be filled with the material described, Within an hour or two, by means of a steam-ejector, it may be brought to a condition wherein the water is only about seventeen per cent. of the weight of the Whole, whereas in the customary method of treating phosphate rock this material passes to the drying apparatus containing not less than twenty-five per cent. of water. When it is borne in mind that a great preponderance of the heat required to dry phosphate rock is expended in merely evaporating the contained water, it will be seen that the preliminary draining which We employ effects a substantial reduction in the fuel necessar to effect the final and artificial drying. on the material in each drain-tank is ready for drying by artificial heat, the valve 1* at the lower end of the deli-very nozzle 9 is opened, and the material ejected in the manner above de-- scribed flows out into the hopper R and is delivered thence by the feed-rollerrthrough a chute S to the drier T. This latter, which forms the subject matter of another application filed by us June 9, 1911, Serial No. 632,239, consists substantially of a rotary drum t made up of a plurality of endwise connected cast-iron sections, and slung by wire ropes t from pulleys t on an overhead rotating shaft t said drum being set within an ordinary. furnace chamber 15. The drum is suspended at a slight angle and is formed interiorly with a number of integral longitudinal concaves or scallops which pick up and tumble the material upon itself, and the drum is provided near its discharge end with an annular row of ppenings which serve the double function of delivering the combustion through the interior, as well as around the exterior, of the drum; such gases.

and products of combustion passing off through a casing W underlying the feed devices and a flue X to the chimney. As the drum t of the drier revolves it causes the material therein to be constantly alive and moving, and therefore in a favorable condition to release the steam constantly being generated. The material is thus subject to direct and intimate contact with the hot gases and likewise to direct contact with the hot metal which receives its heat largely from the external exposure.

In order to clearly describe a practical mode of treatment of phosphate rock beginning with the material as it comes from the mine or ore-bed and ending with the clean and dried material ready for the market, we have described all of the various steps or operations which We preferably employ, including those for recovering the finest particles which have heretofore been Wasted. It should be understood, however, that not all of these operations are indispensable tothe obtainment of a satisfactory product in accordance with our present invention; the main and distinguishing acts or operations residing in the loosening of the rock from the adhering clay, the bringing of the latter thoroughly into suspension in water, and

the separation of the rock from the loosened and suspended clay; the other described operations being ancillary thereto and preferably carried out to secure the most satisfactory results in the character of the prodnot and the economy and efficiency of theprocess.

We clalm I 1. The method of removing foreign matter from a natural mineral deposit such as.

phosphate rock, which consists in subjecting the phosphate ore to a mutual attrition of the components thereof in the presence of suflicient water only to form a plastic mass, thereafter-subjecting the material to a tumbling action in the presence of an added quantity of Water to suspend all the mateterial to a mutual rubbing movement to,

effect an attrition.of said foreign matter and the consequent formation of a plastic mass consisting of a mixture of the said water, mineral and triturated foreign matter, then adding to said mixture a sullicient quantity of water to suspend all of the material in water, and finally removing the clean ore by gravity while subject to cleaning currents of water.

FRANK K. HOOVER. ARTHUR J. MASON. W itnesses SAMUEL N. POND, C. A. KnNYoN.

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