United States Patent Oflice 3,329,265 Patented July 4, 1967 The invention herein described and-claimed may be manufactured and used by or for the Government of the United States of America for governmental purposes Without the payment of royalties thereon or therefor.Inquiry Online
This invention relates to beneficiation of mica ores by flotation, and is a modification and improvement of patent application Ser. No. 320,576 of Frank W. Millsaps and James S. Browning, filed Oct. 31, 1963, now US. Patent No. 3,278,028. The improvement is based on the fact that the process described in this invention is more positive and selective in the flotation of high quality mica concentrates, and that the process enables a selective separation of muscovite mica and biotite mica.
Mica ores normally occur in pegmatites associated with such minerals as quartz, feldspars, tourmaline, apatite, spodumene, beryl, kaolinite and limonite. Domestic production of scrap and flake mica used in producing ground mica is presently dependent almost entirely on crushing and screening and on gravity methods for recovering the mica. In the few cases where flotation is utilized, the ore must be thoroughly deslimed, usually at 100 mesh. These methods are inetficient and result in considerable losses of mica. Furthermore, the concentration of mica ores by flotation has presented many problems, not the least of which, is the production of slimes during conditioning and flotation.
A further object of the invention is to provide a process by which muscovite mica may be concentrated from biotite mica and associated gangue materials regardless of their varying proportions or surface alterations.
It has now been found that the above objects may be achieved by means of a process employing a combination of a cationic and an anionic reagent as a flotation agent and an alkaline inorganic material and a lignin sulfonate to disperse and retard flotation of the gangue materials.
Both cationic and anionic reagents have been used in flotation processes, including mica flotation. US. Patents 2,132,902 to Lenher and 2,885,078 to Fenske disclose the use of cationic reagents while Patent No. 2,303,962 to Tartaron et al. discloses anionic reagents. Alkaline inorganic materials and lignin sulfonates have also been used in various flotation processes. However, as is well known, the art of flotation is a highly empirical one in which a Wide variety of factors may have substantial or even critical effect on the degree of separation attained. Such factors include the nature of the collector, the depressant,
deflocculating agents, activators, pH, etc. Determination of the optimum combination of ingredients for separation of a particular material is largely unpredictable and can be determined only by extensive tests and experiments. As stated above, the combination of cationic and anionic reagent and the alkaline inorganic material and lignin sulfonate, according to the present invention, has been found surprisingly etfective in flotation of mica, particularly in the presence of slimes.
Tallow amine acetate has been found to be particularly elfective as the cationic reagent; however, other cationic reagents, however, other cationic reagents, such as those disclosed in the aforementioned patents to Lenher and Fenske, may be employed. Suitable cationic reagents are saturated or unsaturated amine acetates whose alkyl' groups contain 8 to 22 carbon atoms. Other examples are octyl amine acetate, Coco amine acetate and soya amine acetate.
Oleic acid has been found to be highly effective as the anionic reagent; however, other anionic reagents such as those referred to in the above-mentioned patent to Tartaron et a1. may be used. Suitable anionic reagents'are saturated or unsaturated fatty acids containing 8 to 20 carbon atoms or salts thereof. Examples are linoleic acid, linolenic acid, stearic acid, palmitic acid, rosin acids (distilled tall oil) or mixtures of these acids.
The preferred alkaline inorganic reagent is soda ash; however, other reagents such as sodium hydroxide or sodium silicate may be substituted in whole or in part for the soda ash. The function of this alkaline material is to retard flotation of the gangue materials and control the pH of the pulp. The exact mechanism. of this retard ing action has not been definitely determined but its effectiveness may be due to removal and dispersion of slime coatings on the mineral surfaces.
The lignin sulfonates that we prefer to utilize as a slime dispersant and gangue depressant are the calcium, magnesium, or sodium lignin sulfonates derived from the by-product of the sulfite process of papermaking, commonly known as sulfite liquor. These liquors, separated as waste from the cellulose pulp, contain soluble salts of the lignin sulfonic acids resulting from the decomposition of the wood by the acid solutions used in the pulping process.
The mechanism of the retarding action of the lignin sulfonate in our method of mica flotation. has not been definitely determined and this invention is not limited to any theory of action. It seems probable, however, that the lignin sulfonate coats the surfaces of the gangue minerals so as to prevent their attachment to the bubbles in froth flotation. It is assumed that the mica particles in the pulp exhibit less tendency than the gangue particles to become coated by the lignin sulfonate, and the mica particles are thus made floatable. The lignin sulfonates are effective slime dispersants and may aid flotation by assisting in proper removal and dispersion of slime coatings on the mineral surfaces.
The quantities of the various reagents are not critical and may vary considerably with the type and amount of ore treated, state of subdivision of the ore, amount of water etc. Optimum quantities are best determined empirically. In general, however, amounts of reagents, in pounds per ton of ore, will be approximately as follows: alkaline inorganic reagent, 0.5 to 4.0; lignin sulfonate, 0.5 to 4.0; cationic reagent, 0.1 to 0.5 and anionic reagent,
The general procedure used in the process of the invention is a conventional froth flotation procedure in which the ore is first ground to relatively fine particles, water is added to form a pulp and the pulp is passed to a flotation cell where reagents are added and air is introduced.
The invention will be further illustrated, but is not intended to be limited, by the following examples. The high percentage of mica recovered by the process of the invention is apparent from the data given in the tables accompanying the examples.
Example 1 A sample of mica ore was obtained from an Alabama pegmatite deposit. Analysis indicated the ore contained 22.4 percent mica. In addition, the ore contained quartz, feldspar, limonite and clay-like materials.
In carrying out the flotation process according to this invention, the ore was first ground to a suitable size for conventional flotation methods. With the ore cited, grinding to 28-mesh yielded satisfactory liberation of the mica.
A 250-gram sample of the ore was wet ground to pass 28-mesh using a laboratory Abbe mill containing various size flint pebbles. The ground charge was then deslimed by decanting to remove part of the clay from the pulp. The pulp was then transferred to a small mechanical cell of standard design, and sufficient tap water added to give a pulp containing about 40 percent solids. The pulp was conditioned for 5 minutes with 2.0- pounds of soda ash and 110 pound of calcium lignin sulfonate per ton of ore, followed by 5-minute conditioning with 0.80 pound of oleic acid per ton of ore, and an adidtional l-minute conditioning with 0.40 pound of tallow amine acetate per ton of ore. The pulp was diluted to 20 percent solids with tap water. Air was allowed to enter the cell, resulting in the formation of a heavily mineralized froth. A rougher froth was collected for 5 minutes, whereupon flotation was complete. The rougher froth was cleaned twice to further retard the gangue collected with the mica in the rougher operation. The finished concentrate had an average analysis of 99.5 percent mica with a recovery of 87.1 percent of the total mica content. The results of the test were as follows:
A sample of mica ore was obtained from a North Carolina pegmatite. Analysis indicated that the ore contained about 10.1 percent mica. In addition to mica, the ore contained quartz, feldspar, limonite, and kaolinite.
A ZSO-gram sample of the ore was ground to pass 28-mesh in a laboratory Abbe mill. The ground charge was then partly deslimed by decanting to remove part of the clay. The pulpwas transferred to a small mechanical flotation cell, and diluted to about 40 percent solids using tap water.
The pulp was conditioned for 5 minutes with 2.0 pounds of soda ash and 1.0 pound of calcium lignin sulfonate per ton or ore, then 5 minutes with 1.60 pounds per ton of ore of a mixture of oleic acid, linoleic acid, and rosin acids (distilled tall oil), and finally 1 minute with 0.40 pound of tallow amine acetate per ton of ore. Suflicient tap water was added to dilute the pulp to about 20 per- 4 cent solids. The pH of the diluted pulp was 9.8. Air was allowed to enter the cell, resulting in a heavily mineralized mica froth. A rougher froth was collected for 5 minutes at which time flotation was completed. The rougher froth was cleaned twice to further retard the gangue minerals collected with the froth in the rougher operation.
Example 3 A sample of mica ore was obtained from a North Carolina pegmatite deposit. Analysis indicated the ore contained 8.5 percent muscovite mica, and 1.5 percent biotite mica. In addition, the ore contained quartz, feldspar, and clay-like materials.
A ZSO-gram sample of the ore was wet ground to pass 28-mesh using a laboratory Abbe mill containing various size flint pebbles. The ground charge was then deslimed by decanting to remove part of the clay from the pulp. The pulp was then transferred to a small mechanical cell and sufficient tap water added to give a pulp containing about 40 percent solids. The pulp was conditioned for 3 minutes with 2.0 pounds of soda ash and 1.0 pound of calcium lignin sulfonate per ton of ore, followed by 3 minute conditioning with 0.8 pound of a mixture of oleic acid, linoleic acid, and rosin acids at a pH of 9.2; 040 pound of tallow amine acetate per ton of ore was then added and the pulp conditioned for an additional 1 minute. Sufiicient tap was then added to give a pulp containing 20 percent solids. Air was allowed to enter the cell, resulting in formation of a heavily mineralized mica froth. The froth was collected for 4 minutes at the end of which flotation was complete. The rougher concentrate was cleaned twice to further retard the gangue collected in the froth during the rougher operation. The resulting concentrate analyzed 94.8 percent muscovite mica and accounted for 77.1 percent of the total muscvite mica content. Over 93 percent of the biotite mica was retarded in middling, tailing and slimes. The results of the test were as follows:
1. A process for beneficiating mica ore wherein the mica content of said ore is a member of the group consisting of predominantly muscovite mica and mixtures of muscovite mica and biotite mica by selective flotation of muscovite mica comprising adding to an aqueous pulp of the ore in a flotation cell (1) a depressant for the gangue materials in the ore comprising an alkaline inorganic reagent and a lignin sulfonate and (2) a collector for the mica comprising a combination of a cationic reagent and an anionic reagent selected from the group consisting of fatty acids, rosin acids and salts thereof and then froth floating the desired mica.
This report is part of the collection entitled: Technical Report Archive and Image Library and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Alkaline Anionic-Cationic Flotation MethodThe alkaline anionic-cationic method of micaflotation provides a very effective method for re-covery of mica in the presence of slimes. The oreis normally deslimed sufficiently to remove theclay slimes, but not so drastically as to removethe fine-size mica and other granular material.Particles as coarse as 20 mesh may be floated bythe process.Briefly described, the process included condi-tioning the finely. ground ore pulps at 40 to 45percent solids with sodium carbonate and cal-cium lignin sulfonate and floating the mica witha combination of anionic and cationic collectors.The separation was not particularly sensitiveto pulp pH, and excellent mica recoveries wereobtained in a pH range of 8.0 to 10.5.The function of the sodium carbonate is toretard flotation of the gangue minerals and con-trol the pH of the pulp. The exact mechanismof the retarding action of the sodium carbonateis not known. It seems probable, however, thatits effectiveness may be due to removal anddispersion of slime coatings on the mineralsurfaces.The mechanism of the retarding action of thelignin sulfonate has not been definitely deter-
mined. It seems probable, however, that selec-tive adsorption of the lignin sulfonate at gan-gue mineral surfaces effectively prevents adsorp-tion-attachment of the collector at these sur-faces. On the other hand, mica particles, beingrather devoid of adsorbed lignin sulfonate, arefree to react with collector and are thus madefloatable. The lignin sulfonates are effectiveslime dispersants and may aid flotation by assist-ing in proper removal and dispersion of slimecoatings on the mineral surfaces.Anionic-type reagents, such as oleic acid andcombinations of oleic and linoleic acid, werefound to be the most effective collecting agentsfor floating mica. Increased selectivity in thepresence of slimes was imparted to anionic col-lectors by incorporating small amounts of cat-ionic amine acetate collecting agents in thesystem.The most effective ratio of anionic andcationic collector for mica flotation was 2 to 3parts fatty acid to 1 part cationic collector. Anyappreciable change in the ratio decreased boththe grade and the recovery of mica.A comparison of the advantages and disad-vantages of the two processes for mica flotation,acid cationic vs. alkaline anionic-cationic, isgiven in table 3
Table 3.-Comparison of the two mica flotation methodsAlkaline anionic-cationic method Acid cationic method1. Does not require acid proof equipment. 1. Requires acidproof equipment.2. Recovers mica from ore pulps containing slimes. 2. Will not tolerate slimes.3. Depresses limonite and biotite. 3. Does not effectively depress limonite and biotite.4. Will float finer size material than will acid circuit. 4. Will float coarser size material than will alkalinecircuit.5. When coarse mica is recovered by differential grinding 5. Requires more desliming equipment than alkalineand screening prior to alkaline flotation, the coarse circuit, thus increasing operating costs and lossesmica is not coated with reagents. in fine mica.6. Overall recovery is higher because a larger percentageof mica is subject to recovery by screening andflotation
CONTINUOUS FLOTATION PILOT PLANTUpon completion of preliminary studies, acontinuous pilot plant to treat about 300 poundsof ore per hour was assembled. The flowsheetincluded concurrent grinding, screening, clas-sification, conditioning, and flotation. The pilotplant was designed so that with a minimumalteration of piping and equipment the circuit
could be changed to accommodate either theacid cationic flotation procedure, the alkalineanionic-cationic procedure, or combinations ofthe two procedures. The initial pilot plantoperations were devoted to shakedown runs,during which various equipment units and flow-sheets were tested and the several unit opera-tions were integrated. Flowsheets of the circuitsare shown in the following sections of this re-
Browning, James S. Mica Beneficiation, report, 1973; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc12807/m1/9/: accessed March 1, 2021), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.
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The invention relates to a process for the recovery of micas by flotation starting with slurried ore from which the fines have been optionally removed, comprising a stage of bringing the said slurry into contact with a suitable cationic collector, followed by an actual flotation stage and recovery of the supernatant formed for subsequent treatment and optional rewashing
Micas are minerals which consist of a double silicate of aluminium and of another metal, for example sodium, potassium or magnesium, with, additionally traces of iron, particularly in the form of iron oxide (FeO)
The process of separation by flotation consists in suspending the ore in water and adding to the slurry obtained a collecting agent which will be deposited on one or more of the compounds constituting the ore and which, when a vigorous air stream is introduced, will enable the air bubbles to attach themselves around the said compounds, the said bubbles ensuring the levitation of the said compounds in the form of froth with the aid of a frothing agent. These compounds are then discharged and optionally reprocessed (rewashing)
The ores containing micas frequently also include calciferous materials such as calcite. One of the additional problems to be solved consists in separating the micas from these limestones because, in this case, the conventional flotation method at acidic pH cannot be employed
Ores containing micas also frequently include sulphur-containing minerals such as iron sulphides and, in this case, one of the additional problems to be solved consists in separating the sulphur-containing minerals from the micas either by floating up the micas during the flotation or, conversely, by floating the sulphur-containing minerals, the micas then remaining at the bottom of the reaction vessel
Within the scope of the present description the expression "flotation process" will be applied to the flotation process, from slurrying to the stage of bringing the air stream into contact with the slurry, whereas the expression "flotation stage" will be applied to the actual bringing of the air stream into contact with the said slurry
Adair et al. have described, in the periodical US Govt. Res. Develop. Rep. 1969, 69(16), 80, a process for the flotation of muscovite starting with Alabama ore based on schist and graphitic mica. After a preconcentration of the ground ore on a Humphrey spiral, the process of flotation of the mica, already purified to more than 89%, is ensured by bringing the slurry in an acidic medium into contact with a cationic collector, the purity of the mica obtained being of the order of 98%
Nevertheless, this process requires, on the one hand, a preliminary grinding followed by a stage of preconcentration and, on the other hand, a stage of acidification of the slurry. In fact, normally, the ores containing micas are naturally at basic pH
Tiunof et al., CA98(18):147267z, describe a process for the recovery of muscovite from ore containing it by flotation in an alkaline medium in the presence of a cationic collector and addition of hydroxamic acid to the medium as a muscovite-activating agent. This process requires the introduction of sodium carbonate in order to buffer the medium because of the addition of hydroxamic acid
In CA102(2):10118h, Gershenkop has described a process for mica flotation resulting in a muscovite whose purity is higher than 95%, in the presence of a cationic collector and of a frothing agent, the said flotation being activated by the addition of sodium fluorosilicate
In the journal Scand. J. Metall. 12(3), 117-20 Bolin et al. describe a mica flotation process consisting in grinding pegmatite, removing the fines and floating the slurry at an acidic pH (approximately 3-4) in the presence of a diamine collector. It is indicated that a better selectivity is observed when the mica flotation is carried out in the presence of iron ions. Nevertheless, this process requires the slurry, which is normally in a basic medium, bearing in mind the origin of the ores, to be placed in a relatively highly acidic phase
Another objective of the present invention is to propose a process for the recovery of micas which does not require the substantial modification of the pH of the slurry as obtained by mixing the natural ore with water
In this case it is impossible to use the conventional method of mica flotation at acidic pH≦4 because calcite is attacked in an acidic medium, and this would result in a considerable and costly consumption of acid. The fact that the process according to the invention can be performed at natural (and thus basic) pH represents an important advantage in the case of the ores containing calcite
The process according to the invention is characterized in that it is used at a pH higher than 6 and in that the stage of bringing the said slurry into contact with the cationic collector is preceded by a stage of bringing the said slurry into contact with an activating agent chosen from soluble metal salts
In general, micas are double silicates of aluminium and of another metal (sodium, potassium or magnesium) with traces of iron. Among the micas which are lean in iron there may be mentioned phlogopite and muscovite, which are micas containing between 0 and 5% of Fe2 O3, and biotite, which is a mica rich in iron (up to 13% Fe2 O3)
Although the process according to the invention is not restricted to a particular abovementioned form of mica, it is nevertheless particularly suitable for the recovery of micas which are lean in iron, such as muscovite and, preferably, phlogopite
Also preferably, the process is used for the treatment of ores containing iron sulphides and oxides, it being possible for this proportion to be between 0 and 10%, but capable of ranging up to 30% in some cases
In technical parlance this removal of the fines is called desliming. This desliming operation may, of course, be performed before the slurrying although from an industrial viewpoint this solution is not desirable
As already indicated above in the discussion of the prior art, in its principle, the flotation operation requires the materials to be recovered as supernatants, normally in the form of froth, to be used in combination with a collector which makes its surface hydrophobic, enabling the binding of the air bubbles ensuring the floating of the said material
In the case of the process according to the invention, which is used at a neutral or basic pH, although it is still possible at a weakly acidic pH (between 6 and 7), the collector is a cationic collector, that is to say that it contains anion acceptor groups such as, for example, NH4 + groups. The cationic collectors will therefore be chosen, in a known manner, from amines containing a hydrophobic chain, such as linear C18 amines
Within the scope of the present invention the term "stage", for example "stage of bringing the said slurry into contact with an appropriate cationic collector", generally implies that an aging period is provided so that the various ingredients can perform the function which is attributed to them. The term "flotation stage" does not, exceptionally, imply this aging period, insofar as the flotation by definition involves bringing the slurry into contact with the air stream for a certain period
The process is preferably used without the pH of the subsequent slurry being modified in relation to the natural pH. In general, this pH is basic and normally varies between 9 and 11. An additional advantage of the invention is therefore involved, of avoiding an additional stage of pH modification, since the pH of flotation is the natural pH
One objective of the present invention is to make it possible to separate, on the one hand, the said sulphur-containing minerals and, on the other hand, the micas. The micas are recovered in the supernatant in the form of froth, while the sulphur-containing minerals fall to the bottom of the vessel and can thus be removed. In order to improve this separation, it has been found that it is very advantageous to introduce, during the stage of bringing the slurry into contact with the activating agent, an agent which depresses iron sulphides, such as sodium or potassium cyanide, sodium sulphites or sulphur dioxide. Among these iron sulphide-depressants preference will be given to sodium cyanide. It is obvious that in this case the process according to the invention cannot be used industrially at an acidic pH for safety reasons
In a known manner, during the stage of bringing the said slurry into contact with a cationic collector, this collector is used in combination with a frothing agent such as pine oil and an agent which makes it possible to control the formation of this froth, such as light fuel oil. During this stage of bringing into contact with a cationic collector the following composition is preferably employed:
In order to improve the performance of the process further it is often preferable to precede the stage of bringing the slurry into contact with the activating agent (optionally used in combination with the depressing agent), with an additional stage in which the slurry is brought into contact with a dispersing agent, especially sodium silicate, and optionally with a calcite-depressing agent, especially Cataflot P40®
This flotation process which is also known by the name of a "roughing" operation, may be optionally followed by one or more rewashing operations, characterized in that the supernatant in the form of froth formed is recovered and transferred to a vessel where the various stages of the roughing operation which are described above are reproduced optionally with the various variants with the exception of the stage of removal of fines and the optional exception of the introduction of the frothing agent and the antifoam agent. A person skilled in the art will be capable of assessing the advantage or otherwise of introducing such frothing and antifoam agents, depending on the conditions
These rewashing operations may be recommenced a number of times. The process according to the invention will be preferably characterized in that, after the roughing operation, three rewashing operations are performed, resulting in micas whose purity is higher than 95%
One of the prominent features that the invention displays--although in its most general aspect it is not limited thereto--is the process of recovery of phlogopite by flotation using a cationic collector, especially an amine, after activation of the slurry with the aid of lead nitrate, resulting in a phlogopite of an exceptional purity in addition to the advantages linked with the use of the process
Obviously, any of the alternative forms and explanations indicated above apply to this preferred alternative form. In order to improve the quality of the phlogopite further it is advantageous to perform subsequent rewashing operations
The roughing process is consequently advantageously followed by one or more rewashing operations consisting in that the supernatant obtained previously is recovered and transferred to a vessel where the various stages are reproduced, with the exception of the stage of removal of fines and the optional exception of the introduction of the frothing agent and of the antifoam
It is also possible to perform a magnetic separation of the concentrate obtained by the process according to the invention in order to lower the iron content of the mica. This additional stage may be replaced by a screening operation
After dilution of the ore with an appropriate quantity of water in order to obtain a slurry, an operation of removal of the fines with a particle size of less than 63 micrometres makes it possible to remove 12.7% by weight of the ore introduced. This operation is called "desliming" in technical parlance
In a second stage 1 g of sodiumsilicate (Na2 SiO3) is added, acting as a dispersant and depressant for quartz, together with 0.3 g of a depressant for calcite and the calciferous minerals such as anortite
In a third stage 0.2 g of sodium cyanide, which is a depressant for iron sulphides (FeS2, FeS) is added first of all, followed by 0.6 g of lead nitrate (Pb(NO3)2), which is an activator for the micas, as has been found according to the present invention
The slurry thus obtained is subjected to the actual flotation stage by introducing a vigorous air stream resulting, on the one hand, in the flotation of a froth and, on the other hand, the sedimentation of tailings
The first rewashing stage consists in reproducing the roughing stage by adding, respectively, 0.1 g of sodium silicate and 7.5×10-2 g of depressant for the calciferous minerals, in aging the slurry obtained for 10 min and then adding firstly 4×10-2 g of sodium cyanide and then 5×10-2 g of lead nitrate and aging the slurry obtained for 5 min
The said slurry is then subjected to a flotation stage for 1.25 min, which results in the recovery of a froth constituting 5.1% of the ore introduced, that is 102 g, whose potassium oxide content is 9.5% and in the recovery of a tailing which has settled, which constitutes 1.8% of the ore introduced and whose potassium oxide content is 3.3%
A froth is thus obtained constituting 4.3% of the weight of the ore introduced (86 g), whose potassium oxide content is 9.94%, and a settled tailing is also recovered constituting 0.8% of the ore introduced (16 g), whose potassium oxide content is 7.09%
The supernatant obtained as froth constitutes 3.6% by weight of the ore introduced, that is 72 g, whose potassium oxide content is 10.04%. 14 g of tailings are additionally recovered, whose potassium oxide content is 9.34%
A 1,000-g sample whose potassium oxide content is 2.2% is slurried with the appropriate quantity of water and is then subjected to a desliming operation to remove the fines whose particle size is less than 63 micrometres
0.1 and then 0.05 g of C18 primary amine are added to the slurry and then, in two lots, 0.02 g of MIBC and 0.1 g of light fuel oil. The pH of the slurry is then 9.9. After 2 min of aging, flotation is carried out for 0.75 min and a supernatant is obtained as a froth constituting 1.9% of the ore introduced, that is 19 g, whose potassium oxide content is 2.33
It is therefore found that, in comparison with the preceding example, the roughing operation results in an increase in the potassium oxide content by a factor of less than 1.1, whereas it is greater than 3.5 in the case where lead nitrate is added
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