US1946349A - Process of treating sulphide ores - Google Patents

Description

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Feb. 6, 1934. R, G, RowN 1,946,349

PROCESS OF TREATING SULPHIDE ORES Filed May 23, 1929 Raymond 5 3/0 mm 535 h/S' abbozmma l Patented Feb. 6, 1934 UNITED STATES PATENT; OFFICE PROCESS OF TREATING SULPHIDE ORES Application May 23, 1929. Serial No. 365,397

6 Claims.

It has heretofore been proposed to treat com- .plex ores, including ores containing iron sulphide .and usually containing other values, with air and a certain amount of chlorin to produce a solid discharge consisting of gangue material, iron oxid and the chlorids of various other metals present; and a gaseous discharge containing the nitrogen of the air used, together with sulphur chlorid of indefinite composition and chlorids of metalloids, e. g., arsenic chlorid, etc.

While the underlying idea in this type of process is sound, the .embodiments so far proposed have not gone into successful use because of various practical difiiculties. It is the purpose of the present invention to provide a process avoiding these difiiculties and permitting an economic use of chlorin with ores and concentrates of varied character; not only with complex ores and concentrates poor in iron, but with those rich in iron, like pyrites, pyrrhotite, etc. While the sulphur of the ore can be recovered as sulphur chlorid, it is usually more economic to recover sulphur in the elemental form, and to limit the amount of chlorin used to substantially thatrequired to convert non-ferrous metals and metalloids into chlorids. In so doing, by a proper control of conditions, sulphur practically free of chlorin and either metal or metalloid chlorids can be produced.

A further feature of my invention and one that finds particular application when treating complex ores containing in addition to iron, certain metals, such as copper, nickel and cobalt, consists in so introducing the make-up chlorin as to inhibit oxidation of the chlorids of such metals while permitting the selective oxidation of iron chlorids present in admixture therewith, and in this way conserving the content of such metals in soluble form for convenient separation from the iron oxid formed in the process.

In efiecting the purposes of this invention I find it essential to use the ore or concentrate in a very fine form. With every ore there is a certain necessary degree of fineness requisite for good results which must be determined for each particular class of material. When coarse material is treated reaction becomes so slow after a certain amount of reaction has taken place that it can be said, commercially speaking, to have stopped. Finer grinding than that absolutely necessary serves to speed up the reaction, although there seems to be little advantage in going much beyond 200 mesh; and grinding very much finer than this gives rise to difiiculties due to dust. In most cases 55 the ore must be as fine as 100 or 120 mesh and usually but little of the ore should be permitted I to be coarser than 140 mesh. I have found no material that could be treated satisfactorily when coarser than to mesh unless subjected to extensive attrition or grinding during the chlorinating step. Such extensive attrition or grinding during the chlorinating step I consider for the purposes of this specification and the appended claims as being equivalent to initial fine grinding.

I prefer to transmit the finely ground material as a travelling body or stream against a countercurrent flow of hotgases. In one particular instance I employed pyrites ground to a fineness such that 60 to 70% was minus 200 mesh and substantially none was coarser than 140 mesh. With ore of this order of fineness efiicient and quick reaction with the gaseous countercurrent was afforded. In effecting contact and reaction, rotary kilns or drums of various types may be employed. It is advantageous in many instances to use a horizontal drum containing loosely arranged pebbles or balls substantially filling the cross section, such as shown by way of example in Fig. 1 of the accompanying drawing. This apparatus constitutes one embodiment of the invention described and claimed in the co-pending application of Ernest W. Wescott, Serial No. 343,266, filed February 28, 1929. The characteristics required of any apparatus are that it shall provide highly efiicient contact between finely-divided solids and gases and that it shall permit effective temperature control and preferably, distribution of heat from one portion of the charge to another.

In the present invention, the ore or concentrate in finely divided form is preferably passed through some such apparatus in countercurrent to a stream of gases, these gases entering the system as a mixture of air and chlorin. The path of the materials may be regarded as divided into a succession of zones. One zone may be regarded as a chlorinating zone where the various metal sulphides and metalloids are converted into chlorids with liberation of sulphur in elemental form, and the iron is converted into ferrous chlorid. The ferrous chlorid and other heavy metal chlorids next pass into an oxidizing zoneand come into contact with incoming dry air admixed with dry chlorin. The oxygen of the air converts the ferrous chlorid into ferric oxid and ferric chlorid which latter goes forward as vapor with the gas current. The flow of chlorin into the apparatus is so limited that no chlorin reaches the gas exit end of the system. The outgoing gases carry the liberated elemental sulphur in vapor form from the chlorinating zone and in so doing pass into contact with the incoming sulphides so that these serve eifectually to fix any chlorin present in such gases. While the boiling point of sulphur is 445 C., vapors of sulphur can be effectually and completely removed with a temperature at the gas exit end of'the system of 390 to 350 C. This result ispossible because of the presence of diluting gases, mostly nitrogen, enabling vaporization of sulphur at a temperature far below its boiling point.

'By maintainingthe gas exit end of the systen within this low range of temperatures, under the conditions of operation, metal chlorids do not go forward with the sulphur vapors, although it is permissible for the exit gases to contain chloride of some of the metalloids, such as arsenic or antimony. At the other end of the system, the solid product delivered contains the iron as oxid and the other metals, except gold or silver if present, as soluble chloride which can bereadily recovered by leaching. The gold and silver are also in a form amenable to recovery by leaching operations. The leached solid product, if suficiently high in iron, (that is, not containing too much gangue) may be utilized for the production of iron and/ or steel by known methods. In so doing, it is usually sintered to prepare it for the blast furnace. The present process is however economical and emcient, even where the iron content is low or where there is no ready market for iron oxid.

In the present process, unless an ore relatively low in sulphide material is being treated, external heating is not necessary, since the reactions as a whole are heavily exothermic. As hereinbefore indicated, it is often useful to prOvide means for equalizing and distributing heat along the path of the materials.

In the accompanying drawing,

Figure 1 is a longitudinal, vertical section illustrating more or less diagrammatically certain apparatus susceptible of use in the performance of the present process; and

Figure 2 is a diagrammatic plan view of the apparatus indicating the various reaction zones.

As shown, rotary drum 1 is provided with a loose packing of balls or pebbl s 2 filling nearly the entire cross section. Near each end, the drum is mounted on tires 3. At one end, it is provided with sealing means i, a hopper feed 5 for solids and a conduit 6 for gases and vapors, this conduit leading to a dust catcher connecting to a sulphur condensing apparatus (not shown). The other end of the drum is sealed by sealing means 7 to a stationary housing 8 leading through discharge pipe 9 to collecting means for the solid product (not shown). Inlets 10 and 11 serve respectively for the introduction of air and chlorin in properly proportioned amounts. The drum 1 is provided with a suitable lining l2 and is encased in and integrally joined adjacent its ends to an outer metal shell 13. The shell 13 is spaced from the drum 1 to provide an annular chamber 14 for a suitable heat transfer liquid, such as molten lead, oil, etc. A driving ring 15 is carried by the shell 13 and engages with a suitable driving gear connected to a source of power. At the ends of the drum 1 perforated plates 16 are provided. These plates serve to retain the pebbles 2 within the drum while permitting ingress of ores and gases and the discharge of solid materials. The plates 16 are preferably covered with refractory material 17 on the sides exposed to contact with the pebbles 2.

In Fig. 2 the kiln space is shown diagrammatically as divided into zones designated as A, B1, B2. 6 and D. In carrying out the process, finely ground ore, which may be preheated to as high as 300 to 330 (3%, enters at X. Sulphur vapors and inert gases consisting chiefly of nitrogen exit at X. Dry air and dry chlorin enter at Y; the air 7 may be preheated to temperatures of about 308- 350 C. Solids exit at Y, including iron oxid, gangue and chlorids of copper, zinc, lead, etc., but free from ferrous or ferric chlorids.

Instead of carrying out the chlorinating and oxidizing steps in the same chamber, I may use two chambers or kilns. Generally, however, it will be advantageous to carry out both steps in a single kiln, and, therefore, in the following detailed description reference will be had to the single kiln shown in Fig. 1.

Returning to the entering ore, this passes through zone A, which when the ore is introduced in a preheated state is very short, and wherein nothing of consequence takes place, zohe A serving merely as a definite separation of the gases of zone B1 from the exit. Zones B1 and B2 are the chlorinating zones; these may be considered as a single zone. Chlorination is, however, effectuated in B1 largely by sulphur chlorid and very little by'ferric chlorid. In B1 the absorption of chlorin from the gases is complete with the exception of that amount of chlorin combined with metalloids such as arsenic, antimony and bismuth. The partially chlorinated ore passes'from B1 to B2 and in B2 the chlorination is completed by the action of ferric chlorid vapors coming from zone C. Some sulphur chlorid is formed in B2 and travels forward with residual ferric chlorid to B1. Completely chlorinated ore passes forward from B2 to C where the ferrous chlorid reacts with hot air coming from D. When preheatedair is used, zone 1) is merely a neutral zone serving to define the end of zone C; it is an inactive zone assuring that no unoxidized solid ferrous material reaches the exit Y.

When the ore is not preheated or when the ore is only partially preheated zone A must be made longer and then assumes a more definite function. In this case the ore becomes heated in zone A, acquiring heat in part from the outgoing gases and in part from the walls of the kiln. This operation with cold or partially heated ore requires care as there is risk of sulphur condensing in the cold ore causing th latter to ball up. Similarly if the air is not preheated or only partially preheated, zone D acquires a more definite function as a preheating zone. When operating with zone D as an air preheating zone it is necessary that the counter flow be rather perfect as otherwise there is danger of condensation of solid ferric chlorid which may pass out with the exit solids.

In one way in which the process may be car ried out, fine ground pyrites is supplied in a pre-' heated state to inlet X'; this pyrites being ground so that it all passes through a 140 mesh sieve. This entering pyrites encounters in zone B1 a stream of nitrogen and sulphur chlorid and posled ferrous and other metal chlorids formed, together and more or less sulphur chlorid that goes for ward into zone B1. The chlorids formed in zones 31 and B2 passing into zone C meet air and the ferrous chlorid is broken up with formation of ferric oxid and ferric chlorid. The ferric chlorid formed by the reaction of the oxygen of the air with ferrous chlorid, goes forwarclfrom zone G into zone B2. In zone C, the temperature is sufficiently high to vaporize ferric chlorid but is not sufficient to fuse ferrous chlorid. The air supplied to the system is advantageously preheated to about 350 C. and with it is introduced such an amount of chlorin as will suffice to form chlorids of the non-ferrous metals present, and to make up losses. The solid material discharged through Y consists of gangue, ferric oxid and chlorids of the other heavy metals in the ore treated. Chlorid of manganese where present in usually oxidized along with the iron, but as manganese is not commercially'important in the ores to which this invention is addressed, the term iron oxid where used in the claims is to be taken to include manganese oxid. At the other end of the kiln, the vapors and gases exiting at X pass into a dust catcher (not shown), where any solid materials carried with the vapors and gasses are collectedand returned to the kiln. From the dust catcher the vapors and gases pass to a sulphur condenser (not shown). The temperature of the vapors leaving at X is maintained at about 300-320 C. and by suitably insulating the conduits and dust catcher no substantial temperature drop is permitted until the vapors reach the sulphur condenser. With the temperature so controlled the sulphur finally condensed is pure.

It is an advantage of my invention that all the kiln operations may be carried on at substantially the same temperature and that there is a considerable range of temperature within which the desired results can be obtained.

Variations of temperature within the treating zones are, however, entirely permissible. ,The lower limit of temperature of the gases in zone A is that at which sulphur will condense; that is to say, the lower limit is the dew point of sulphur in the gases as constituted, and usually for practical purposes the gases should leave the furnace somewhat abovethis temperature. In the chlorinating zones B1 and E2 the lower limits of temperature are the temperatures at which ferric chlorid will condense or exist as a solid and the temperature at which sulphur will condense or exist other than as a gas, whichever may be the lower; in other words, the temperatures in zones B1 and B2 must be suihciently high so that neither ferric chlorid nor sulphur can exist therein other than as vapors. The upper limit of temperature in the chlorinating zones B1 and B2 is that at which extensive fusion of the solids present takes place. These solids usually contain progressively larger amounts of ferrous chlorid as the material travels through the chlorinating zones, but the melting point of the mass may be much lower than the melting point of pure ferrous chlorid. Small amounts of fusion, i. e. localized fusion, may do no harm although it is usually undesirable, tending to clog the apparatus. Extensive fusion,-the fusion of the whole or of the great bulk of the material-defeats my purposes, causing very ineificient contact of chlorinating gases or vapors with unattacked solids suspended in the fused mass. Again, temperatures permitting fusion in zones B1 and B2 make is difficult, if not impossible, to

avoid the presence of vapors of copper, zinc and lead chlorids in the exit sulphur-bearing gases.

The lower limit of temperature of zone C is that at which ferric chlorid can exist as a solid. The upper limit of temperature must be such not only as to prevent fusion of the mass of chlorids which enters C, but also sufficiently low so that lower melting chlorids, such as those of zinc, will not collect in fused or pasty masses forming inclusions of unoxidized ferric chlorid.

I believe that the lower limit of temperature in zone C is somewhere around 280 C. A safer index of correct operating conditions than the measured temperature is the presence or absence of solid ferric chlorid. If the ferric oxid leaving the kiln at Y contains solid ferric chlorid, the temperature of zone C is too low. I do not advise temperatures at this end higher than 400 C. and only rarely should 350 C. be exceeded. With temperatures too high, chlorids of other metals, such as zinc, are liable to fuse and by inclusion to prevent oxidation of the ferrous chlorid. The presence of fused chlorids and inclusions of ferrous chlorid therein in the solid materials going to exit at Y indicate that zone C is at too high a temperature.

If desired, the air may be wholly or partially preheated by passing same in countercurrent relation to the ferric oxid and gangue discharging from the zone C. This may be brought about by extending the kiln so as to provide an air preheating zone between zone C and the exit, i. e., by extendin zone D. When the operation is so conducted, care should be taken to insure that the how of air is strictly countercurrentso that there will be no danger of ferric chlorid being condensed in the exit material.

Another advantageous way of preheating the air is by the direct combustion of dry fuel. This can be advantageously done by burning in the air a small amount of carbon monoxid or other hydrogen-free fuel. Carbon monoxid may be obtained suitable for this purpose as air blown producer gas, i. e., produced by the action of dry air on dry coke.

I do not limit myself to a temperature of 359 C. in the incoming air. Satisfactory results may be obtained throughout the range limited, on the one hand, by the temperature at which solid ferric chlorid will be present in the solid residue of iron oxid and gangue, and, on the other, by the temperature at which substantial amounts of ferrous chlorid will become included within or covered by fused portions of other chlorids present.

As a specific example, I may treat a pyrites ore containing approximately 90% FeSz, 1% copper, 1.5% each of zinc and lead, 0.2 to 0.5% of manganese, with the balance gangue. This ore, reduced to a fineness of minus 140 mesh and preheated to about 310 C., is introduced to the hopper 5 and fed into the kiln. I maintain the temperature of the kiln at the shell 12 at 315: 5 C. by regulated cooling of the same.

The gases leaving at 6 are passed through a heat-insulated dust chamber, not shown, and then to a sulphur condenser, not shown. The liquid sulphur should contain less than .05% of chlcrin and usually less than .01%. If these amounts are exceeded, and heavy metals are present in the sulphur, either the shell of the kiln is too hot or the kiln is being driven beyond its capacity. If these amounts are exceeded but heavy metal chlorids are not present, then too much chlorin is being fed into the kiln. Ore

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dust collected in the dust catcher is from time to time fed to the kiln through the hopper 5 either alone or along with the fresh ore. At 10 I feed dry air preheated to a temperature of 290i10 C. and at 11 chlorin calculated to make up losses in chloride or in other ways. If unalterated ferrous chlorid is found in the exit solids the air supply should be increased, unless examination shows that the ferrous chlorid exists as inclusions within fused masses of other chlorids. If appreciable amounts of S62 are found in the exit gases from the sulphur condenser too much air is being introduced. If the fused inclusions referred to are found, then either the kiln is too hot and should be cooled or else the kiln is being driven beyond its capacity for the particular ore.

The reactions in zones B1 and B2 are exothermic, while the reaction in zone C appears to be nearly neutral as to heat absorption or evolution. To conserve the heat that would otherwise be lost from the kiln surfaces surrounding zone C and to effect transfer of heat from the zones B1 and B2 to the zone C, and it may be to zones A and D, I prefer to have the shell provided with a jacket containing a heat diffusing liquid. Ordinarily, I do not find it desirable to control the temperatures in the kiln by controlling the rate of feed of the raw material. The rate of feed for reasons of economy and efdciency preferably should be at or near the maximum dictated by the capacity of the kiln to effectuate contact, and hence reaction, between solids and gases. This is an additional reason for the temperature controlling jacket which furnishes a ready method of obtaining desired uniform temperature. A given kiln will often show large capacity for effecting reactions as regards contact of solids and gases but will be limited in its output by its tendency to overheat in one zone or another. In such cases the useful kiln capacity can often be increased by decreasing the thickness of the refractory lining and by using refractories of the greatest practicable heat conductivity.

Chlorin from any suitable source may be used in the described process; and it may be concentrated, as with commercial tank chlorin or electrolytic chlorin; or weak as in the case of chlorin prepared according to the Deacon process. Chlorin may be regained from the heavy metal chlorids as by electrolysis and sent back into circuit. Whatever the source, the chlorin should be dry, as should also the air used.

It is to be understood that instead of adding chlorin as such to make up the losses of chlorin carried from the system in the non-ferrous chlorids, other chlorinating agents that may be introduced in gaseous or vapor form, such as sulphur chlorid and ferric chlorid, may in many cases be used. The use of chlorin is, however, recommended when either nickel, cobalt, or copper is present in the ore being treated, since in this way the principle of the invention set forth in my U. S. Patent No. 1,933,702, dated November 7, 1933 may be employed to prevent the conversion of the chlorids of these metals to the insoluble oxid form.

As set forth in my co-pending application above mentioned, I have found that for any given oxidizing temperature there is a certain concentration of chlorin that will prevent the loss of solubility (by conversion to oxid) of each one of these elements. Thus when operating at about 350 C. there should be at least 0.4 volume per cent. of elemental chlorin added to the incoming air to prevent loss of solubility of copper and cobalt. At 400 C. a little over one volume per cent. chlorin suffices to protect the copper chlorid and slightly less will protectcobalt. In the range 350-400 0., 0.1 volume per cent, chlorin suffices to prevent oxidation of nickel chlorid.

When the ore being treated contains non-ferrous values such as copper, nickel and cobalt, requirements of the operation as respects make-up chlorin are such that sufficient chlorin may be introduced with the air into the oxidizing zone to insure that the chlorids of such metals are not converted to the insoluble oxids, without at the same time causing sulphur chlorid to be formed in excess of the amounts that will react with fresh ore in the zone B1 and pass off with the sulphur. When the ore contains relatively large amounts of non-ferrous heavy metal values, and as a consequence the amount of chlorin removed from the system is relatively large, it may be desirable to introduce a suificient amount of chlorin in elemental form to prevent formation of insoluble compounds of the elements copper, nickel and cobalt and to introduce additional chlorin in another active form to completely make up for that removed as chlorids or otherwise from the system.

Ordinary types of rotary inclined kilns may be used in lieu of the packed drum'described and shown; but the packed drum has the advantage of offering tortuous, constantly changing passageways for the counterfiow. The ball packing has no substantial grinding action with fine ore usually employed.

While I have described my process as carried out in a single kiln or furnace, it will be understood that the chlorinating and oxidizing reactions may be carried out in separate kilns. When the separate kilns are used in treating an ore containing non-ferrous metal values such as copper, nickel and cobalt, the make-up chlorin or at least a sufficient portion thereof to prevent oxidation of the non-ferrous chlorids formed is introduced with the air led to the oxidizing kiln. Various modifications in the procedure outlined may be made without departing from the invention, which is not to be deemed as limited other than as indicated in the appended claims.

What I claim is:

1. In the recovery of pure sulphur from materials containing iron sulphide and other metal values, the process which comprises reducing said ore to a fineness of minus 50 mesh, supplying the finely divided material to a chlorinating zone, chlorinating iron present to ferrous chlorid with dilute chlorinating gases, removing liberated sulphur as a vapor substantially free from heavy metal chlorids, then oxidizing the ferrous chlorid by means of a preheated oxidizing gas, supplying heat by means of preheat of said oxidizing gas in such amount that the oxidation is effected without permitting fusion of the ferrous chlorid or of any other heavy metal chlorids present, and leading chlorinating gases formed in the oxidizing reaction to the chlorinating zone to chlo rinate additional iron sulphide containing material introduced thereto.

2. The process of treating ores containing iron in combination with sulphur and also containing other metal values, which comprises reducing said ore to a finely divided state, supplying the finely divided material to a chlorinating zone, chlorinating iron present to ferrous chlorid with dilute chlorinating gases, removing liberated sulphur as a vapor substantially free from heavy metal chlorids, then oxidizing the ferrous chlorid by means of a preheated oxidizing gas, leading the chlorinating gases formed in the oxidizing reaction to the chlorinating zone to chlorinate additional ore introduced thereto, and throughout the chlorinating and oxidizing reactions supplying heat by means of preheat of the said oxidizing gas in such amount as to maintain the temperature of the solids present above the dew points of ferric chlorid and of sulphur in the passing gases but below the point of extensive fusion of the solids present.

3. A process of treating ores containing iron in combination with sulphur and including other metal values, wherein such ores, in a heated and finely divided state, are passed through a chlorinating zone in countercurrent to a stream of chlorinating gases to liberate sulphur, thence to and through an oxidizing zone in countercurrent to a stream of a heated oxidizing gas, and are thereafter discharged from said oxidizing zone with the contained iron in the form of oxid and with other heavy metals present in the form of chlorids; the temperature of the chlorinating zone being such that the exit vapors containing elemental sulphur are free from gaseous heavy metal chlorids, the chlorinating and oxidizing zones being above the temperature where ferric chlorid and sulphur can exist other than as gases or vapors in the presence of the amount of inert gases present, the chlorinating zone being below the temperature of fusion of the solids present, and the oxidizing zone being below the temperature of formation of inclusions of ferrous chlorid in the other chlorids present, and throughout the operation supplying heat by means of preheat of said oxidizing gas in such amount that the temperatures in said oxidizing and chlorinating zones are maintained as specified.

4. A process of treating ores containing iron in combination with sulphur and including other metal values, wherein such ores, in a heated and finely divided state, are passed through a chlorinating zone in countercurrent to a stream of chlorinating gases, thence to and through an oxidizing zone in countercurrent to a stream of a heated oxidizing gas, and thereafter discharged from said oxidizing zone with the contained iron in the form of oxid and with other heavy metals present in the form of soluble chlorids; the temperature of the chlorinating zone being maintained between 300 C. and the temperature of fusion of the mixture of solids present, and the oxidizing zone being maintained between approximately 280 C. and the temperature of formation of inclusions of ferrous chlorids in fused chlorids of the other metal values present, and throughout the operation supplying heat by means of preheat of said oxidizing gas in such amount that the temperatures in said oxidizing and chlorinating zones are maintained as specified.

5. A process of treating ores containing iron in combination with sulphur and including other metal values, wherein such ores, in a heated and finely divided state, are passed through a chlorinating zone in countercurrent to a stream of chlorinating gases, thence to and through an oxidizing zone in countercurrent to a stream of a heated oxidizing gas admixed with a controlled amount of chlorin sufficient to prevent the formation of insoluble compounds of copper, nickel or cobalt in the oxidizing zone, and thereafter discharged from said oxidizing zone with the contained iron in the form of oxid and with other heavy metals present in the form of soluble chlorids; the temperature of the chlorinating zone being maintained between 300 C. and the temperature of fusion of the mixture of solids present, and the oxidizing zone being maintained between approximately 280 C. and the temperature of formation of inclusions of ferrous chlorids in fused chlorids of the other metal values present, and throughout the operation supplying heat by means of preheat of said oxidizing gas in such amount that the temperatures in said oxidizing and chlorinating zones are maintained as specified.

6. A cyclic chlorination process for treating iron sulphide-containing materials, which comprises treating such material in a dry way and at an elevated temperature with dilute chlorinating gases to chlorinate the iron present therein to ferrous chlorid and to displace the sulphur as such, removing the displaced sulphur as vapors, then oxidizing the ferrous chlorid formed with preheated air to produce dilute ferric chlorid vapors and iron oxid, using the dilute ferric chlorid vapors so produced as chlorinating agent in repeating the cycle with further amounts of said iron sulphide-containing material, and supplying heat by means of preheat of the air in such amount that the chlorinating and oxidizing reactions are carried out at temperatures above those where ferric chlorid and sulphur can exist other than as gases or vapors in the presence of the inert gases present and below the temperature of bulk fusion of the solids present.

RAYMOND G. BROWN.

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