US2030627A - Process of making iron oxide and sulphur dioxide from iron sulphide ores - Google Patents

Description

Feb.. M, i936. H FREEMAN PROCESS 0F MAKING IRON OXIDE AND SLPHUR DIOXIDE FROM iRoN SULPHIDE oREs Filed MaIOh 5, 1950 search Corporation oi poration lof Canada Application Match s. 1 1o Claim. i

. f This invention relates to improvements in the treatment of sulphide iron ores, such as pyrite and pyrrhotlte and one object oi' the .inventionl is to `eillciently produce simultaneously sulphur 5 dioxide and an iron oxide product, preferably magnetic and" of high iron content and low sulphur content suitable for production oi' metallic iron.

Various other objects, featuresfa'nd advantages m of the invention may be ascertained from theA following description.

` This application comprises a 4continuation in part of my fcopending application, led Januaryv -17,- 1929, Ser. No. 333,222, nowv Patent No. 1.812,-

,5 397, granted June 30, 1931, the present application embodying certain alternative and additional features and improvemen l In thepast, sulphide iron ores have been largely used in the production 1 of sulphur dioxide by Yroasting or burning the orev withair. Of late,

this has been" accomplishedusually in roosters in which the ore is caused by mechanical means to move slowly counter current to air. This type oi' roaster is welliliustrated in multiple hearth apparatus in which `the ore is introduced on the top hearth andmoved Vby rakes across the hearth l to fail onto the hearth below, the operation being. repeated o n each successive hearth. In this and other types otroasters infgeneral use. the combustion of the sulphide is comparatively slow.

While considerable 'heat is generated, the temv perature oi `the burningsulphide rarely exceeds 1.000 C. and usually does not exceed 700 to 800? C. The iron oxide product resulting is in -the' form oi' unfuse'd and unagglomerated small particles varying from` red to purple in colour and is notmagnetic toany appreciable or signiilcant degree'.l In' the operation oi' .these mechanical roasters, the ore is cold asit enters the roaster;

10 and thus cools the gases leaving the roaster, soV

that acons'iderable partei the sulphur dioxide is oxidized to sulphur trioxide. At no 'time durjing passage through the rooster ls it ordinarily attempted to heat the. ore 'sumcientlv for fusion if, to result andthe temperature in any part of the urnacels substantially the same as the tern- V perature of the ore in that part. The solid residual product of this treatment is uniused iron oxide containing varying amountsl oi' sulphur..

o usually'from 2% to 8%.depending' on the ore,

;thetype`ot :toasterl and the mannerot operatiom For example, if itris desired to produce from such roosters gasof sulphur dioxide content.

this can be done only by usinga ininimumoi'l higher temperature in the s airand the result isra- MAKING gIlHUB DIOXIDE FROM IRON oi- 'the particles, relatively widely se pass into contactwith [in the air almost the -whole volume and are fused. 'I'he oxidized f rima IRON xma AND' mama gan Falls, Quebec, Canols Engineering 'da Re- Canada. Limited, a' corroaster causing somewhat excessive deterlo'ration of the apparatus and a high sulphurresidue in thc iron cxidc product. Y f According to this invention; the ore, reduced to finely divided form. is burned in suspension` in air during slow passage through a combustion chamber. the amount of alr'being not materially in excess of thatl necessary for oxidation oi all the sulphur and iron. Infthe absence of cooling by excess of air and by reason of the suspension parated, in he combusmplete comon is brought'about with liberation of heat air and their slow passage through t tion chamber, a very-rapid and co busti In greater deta Theore particles" entering the combustion chamber pass rst throu gh hot gases ilowing to thegas outlet and are thereby heated to the temperature of ignition and of fusion. The hot particles'then' air and-combustion ensues ai; thesuriaces of the particles. In the finely divided state in which the ore is treated, the ratio of suiace to 'volume isvery high and the particles being relatively widely separated-and suspended of each particle, is presented at one time for oxidation, so that Valmost every particle burns completely and all the particles burn very rapidly. of sulphur is more complete than is possible with mechanical roasters.- The rapid oxidation liberates heat which is absorbed by the particlesand serves to complete and maintain la state of fusion. 3g In all probability the temperature of the fused particlesis higher than can be -obtained by other methods of roasting. This is evidenced lby the factthatthe resulting iron oxide isfound to be ,fused, black in colour and highly magnetic. It is 4o known that if red iron oxidei which is non4magc netic, is' heated to or above 1650? C., it is'i'used and converted to a black magnetic oxide and from thislfact it is concluded that, although temperatures of the order of 1650 C. in; the combustion chamber` may not be recorded, nevertheless the individual particles have been heated by their heat of combustion to. this or higher temperature ore particles nally n chamber through are 'therebyV chilled. bc subjected to inaglmination of'non-magnetic mpletely oxidized particles silica and other impurities which have en- I6 The removal emerge from the combustio the cool entering air and The produced .oxide may netic separation tor el material such as ylirico 'and il. the process is as follows:-

" cess of air and to the high temperature by rapid and complete combustion of the ore, the` sulphur trioxide that this process is 4forms of apparatus may tered with' the o re. The sulphur content of the product is very low, ranging from 0.3% to 12% according to the fineness of the ore. Owing to limitation of the air supply to that necessary in practice to effect complete combustion of the sulphur and iron, the amount of air admixed with the sulphur dioxide leaving the combustion chamber is much less than in the case of mechanical roasting. Also, owing to the absence of cooling by exattained sulphur dioxide leaves the combustion chamber at a temperature well above that at which is oxidizes to sulphur trioxide. The exit gases are preferably passed through a steam boiler `wherein the sulphur dioxide is chilled so rapidly through the temperature range at which it oxidizes to practically none of this latter gas is formed. Also. owing to limitation of the air supply, the sulphur dioxide produced by less diluted than that produced from mechanical roasters.

It is found most convenient and practical to =introduce the finely divided ore vertically downwardly into the top of a combustion chamber by means of a gentle current of air in amount much less than is necessary for combustion 'of the ore.

' and to supply the further air necessary for combustion by drawing the same upwardly through the combustion chamber. By adjusting the velocities of the two opposed air currents relatively to one another and to the force of gravity acting on the particles, the period of time occupied by the particles in descending through the combustion chamber may be regulated to provide ample time for combustion. In other words, the de scentof the particles, due to their initial downward velocity and the acceleration of gravity, may be retarded by the upwardlyv moving current of air.

A form of apparatus which has been found suitable for carrying out the process, but to use of which the invention is not confined as other be used,is illustrated more or less .diagrammatically inthe accompanying drawing.

Referring more particularly to the drawing, il l designates yo. gas-tight furnace shell. preferably of metal, having a refractory lining i2 and an internal refractory division wall i3 extending from the bottom of the furnace nearly to the top thereof. The dimensions of the furnace are such that the division wall constitutes two chambers il and i5, the 'greatest dimension of each of which is its height. The chamber i4, which is the combustion chamber, ls open .to the atmosphere at the bottom I6 while the chamber I5, which is a settling chamber. is closed to the atmosphere at vits bottom il.. Any suitablemeans for 'coiiectins and removingthe solid furnace product is provided at suchdistance beneath lthelcnjainber Ail that it does not interfere with the free entrance of air into the chamber. Any suitable means I9 is provided at the-bottom of the chamber I5 for removing solid furnace product while excluding air. Conveniently. the means I9 may discharge into the means IB but this is not obligatory.' A gas cooler 20, preferably in the form of a ilre tube `steam boiler, is connected to the furnace to receive gases from the lower part oi.' the chamber i5. Preferably the boiler shell is connected l directly to the furnace shell, as shown. and the a large exit opening aoaobsv nected to the end of the boiler remote from the furnace in such manner as to draw gases from the furnace through the boiler. A damper 22 may be provided between the blower boiler. The boiler is provided with the usual water supply pipe 23 and steam delivery pipe 24.

Ore to be treated is delivered in finely divided form into a hopper bottom bin 2 5 from which it is fed through a regulating device 28 into a hopper 21 open to the atmosphere and connected at its bottom to the suction inlet of a fan or centrifugal blower 28. The discharge pipe 29 of the blower leads downward into the top of the combustion chamber i4 and terminates in any suitable sort of heat resisting nozzle 3|).

The operation of the apparatus described is as 2i and the.

follows:-Dry, flnely divided metal sulphide. such as a flotation concentrate or finely crushed iron pyrites, is delivered to the bin and is fed from the bin at measured rate through 'the regulator 28 into the open hopper 21, where it is caught by the current of air and drawn into the blower 2l and fed by it vertically downward into the top of the combustion chamber Il. By regulating the feeding device 2B andthe speed of the blower 2s, the rate of feed of ore into the furnace and the amount and velocity of air entering with the ore may be regulated as desired. -The suction of the blower 2i draws air into the bottom of the combustion chamber and upwardly through this chamber and also drawsv the furnace gases and any residual air downwardly through the chamber I6 and through the boiler 20. The amount and velocity of air entering the bottom of the combustion chamber may be regulatedby means of the damper 22 and by regulating the speed of the blower 2i. The regulation is preferably such that the upwardly movingI current of air offsets the initial downward velocity of the ore particles feeding finely divided sulphide downwardly into the combustion chamber with less air than necessary f'or combustion .of the sulphide and at the same time drawing the additional air necessary in practice for complete combustion of the sulphide upwardly through the combustion chamber. and the furnace is in full operation, three clearly defined cones-established, the dimensions of whichI depend on the amounts and velocities of air and sulphide foci.V

When the temperatures have been built up there are- The upper zone, or heating sone. extends some distance downwardly from the homie 80. The atmosphere inherent phur dioxide and nitrogen rising` from the zones below. The temperature is too high to permit oxidation ofthe sulphur dioxide by the air enterin g with the sulphide vand little, if any. airrises from vthe zones below. The 'sulphide particles passing down through vthis zone are heated to ignition and fusion temperature. If there is free sulphur in the ore. some of it may be volatilized and burned. n

The middle zone. or vzone of primary ombustion, is quite clearly and visibly defined om the zones above and below.

This zione extends downto this zone is. largely sui- (ifi atf the a .zone of intense combussuipnmdioxide with the sir ustion, extends downwerdiy from the level at l Iwhich the sulphide particles become incandescent tonearly the bottom ofthe chamber. In this zone the highly heated particles meet an excess of comparatively undiluted air drawn in at the lbottom of the chamber. 'I'he particles are indi-` vidually visible as a shower of brightly sparkling points of light and it is presumedthat in this zone most of the iron and the residual-sulphur is burned. The intense heat uofthe individual particles, indicated by the condition 'of incan- .25V desoence, is largely absorbed by the-particles, at

the moment of liberation, in maintaining the fused state of iron oxide so that the temperature of the atmosphere in this zone is probably much below the temperature of the individual particles.

30 The Ascintillating effect in this zone diminishes toward the bottom of the zone.

Below the bottom zone the fused particles are chilled and solidified inthe incoming air and serve in some measure to preheat the air. The solid material collected is inthe form of a heavy Vblack powder composed of minute fused particles usually hollow.

'From the foregoing description, it' will be observed that the sulphide is rstburned'with less if air is necessaryfor complete combustion,

the' 'amount being, however, sufficient, for oxidation of moet of the sulphur, andy is later burned tion' of theiron and remainingsulphur. A

It will also beobserved that the sulphide par. '.ticles are maintained in suspension in air during Ythe entire process ofoxidation. By regulating 50 the velocities of the two air supplies. the period of time during which the particles are held in on, may be `materially longer than would, be normally occupied in -the gravitation of the particles to the bottom of the combustion Y with perhaps less air than necessary for' comev plete combustion. the secondary airsupilly being i materially in excess of that required-foroxida-VA com ar.

runen in wmen most or the with' thev sulphide.andfwitn` the bottom er the i sores, t here followingmay bepartlcularly noted. The free entrance of air substantially unobstructed by the roasted product at the bottom air inlet Il is such that airmay `be-drawn in over the entire area through whiclrthe treated orel falls out of the furnace. `Thus there is free access of air to all parts of the lower, portionof the furnace and substantially uniformly to all areas through which the treated Particles fall and are chilled during their passage out of the furnace. Yet despite the fact'thatthis entrance of air `may take place over a considerable area. the quantity n of air thus admitted may be carefully regulated by regulation ofthe damperV 22 Yon the. suction fan 2l, this regulation being effected without disturbing the uniformity of the draft at one part of the furnace bottom as compared with any other part. In thetreatment of many forms of it 'isrof advantage to use the suction-method disclosed, of `drawing the auxiliary air into the bottom of the roasting chamber in lieu of forcing the air into the bottom of the chamber. as indicated in my priorpatent above referred That is, by the suction method, I have found hat the suspension of the ore particles during their passage through the `furnace may be made more uniform at each level in the furnace by using the suction draft at the top ofthe furnace instead of forcing the air in at the bottom of the Vzones of treatmentabove described are obtained.`

furnace. Also by using the suction fan 2| in lieu of forcing theair in at the bottomof-the furnace, the travel of the gases throughthe settling chamber I5 and the boiler 20 may be made somewhat more uniform.V In short, by properly regulating the damper 22 and by properly adjusting the-flow of the ore into the apparatus by the regulator 26, the. desirable roasting conditions within the furnace may be readily achieved for various -grades'of o'resand so that the various With proper regulation of the roasting conditions. as above described. the relatively free admission of air-into the bottom ofthe vfurnace also has the advantage thatthe ore particles are individuallyl chilled somewhat while still in suspension and before the saine reach the.con' Vveyor or other carrying device It. With the individual fused particles thus chilled in suspension, any substantial agglomeration thereof on theconveyor may be avoided. While theonly oxidizing medium mentioned is air, it willbe obvious that any gas mixture Y which contains'` the requisite free oxygen and no -c. so reduces the time during wmen the stupeur 1 dioxideispassing through the temperature range of oxidation that practically no sulphur trioxide is formed. l t

0 With the process as carried out in the above described apparatus. the temperature and time of treatment of the ore in the various zones of the roasting vchamber may be very accurately regulated. There are several important features l to this possibility, among which the `tail with-respect to particular preferred exampies, l1t winne understood by those skiuedi in the components which will react undesirably with the sulphide or formed oxides may be substituted `for air. Inthefollowing claims, the term air"` is to be construed as including such gas While the sulphide introducing current of gas has been stated to be air. it'will be understood that a non-oxidizing gas may be substituted and all 'the oxidizing effect obtained from a countercurrent of oxidizing gas or, alternatively, both of the countercurrents of gas may be nonoxidizing and serve merely to maintain the suiphide particlesin suspension and exposed. to an oxidizingas introduced separately from the two countercurrentstreams. l i

While the invention has been described in deart after understanding the invention. that various changes and further modifications may be l made without departing from the spirit and scope of the invention, and it is intended therefore in and modifications.

What is claimed a s new and desired tobe secured by Letters Patent of the United States is:

l. A process of oxidizing iron sulphide ores by 'passing the same downwardly through a roasting chamber of substantial height, which comprises introducing the ore in finely divided form into a heated zone at the top of the chamber where the ore is preheated to ignition temperature by contact with rising hot furnace gases, allowing the ore to settle into a second zone in which it is heated to fusion temperature and burned with a deficiency of gaseous oxidizing agent whereby most of the sulphur is oxidized, allowing the ore to settle into athird zone in which it is further heated in a state of fusion and is burned with an excess of gaseous oxidizing agent whereby substantially all of the iron and the remaining sulphur is oxidized, andv finally passing the ore through an incoming stream` of said' gaseous oxidizing agent as the ore passes out at the bottom of the furnace, said incoming stream being of such temperature that the fused particles are individually chilled while in suspension suillciently to substantially avoid agglomeration.

2. Process for forming magnetic iron oxide in the form of finely divided fused particles, which comprises injecting with a gaseous medium finely divided iron sulphide ore into the top of a hot roasting chamber, allowing said particles to settle in the chamber through a rising current of oxidizing gas, the particles finally passing out at the bottom of the furnace through a relatively cold incoming stream of said oxidizing'gas. the movement of the ore particles and the gases within the chamberbeing so controlled that the sulphur content of the ore is largely burned and the ore particles are individually `fused while in suspension and are then chilled in suspension as they pass out through the incoming stream of oxidizing gas. l

3. Process according to claim 2 and in which the gaseous products of combustion are withdrawn by suction through an outlet at the ton of the chamber.

a. Process according to claim 2 and in which the gaseous products'of combustion are withdawn by suction through an outlet at, the top of the chamber, and including regulating the draft through such outlet to produce the desired uniform flow of incoming oxidizing gas at the bottom of the chamber.

5. Process of forming magnetic iron oxide in the form of finely divided fused particles, which comprises roasting finely divided iron sulphide ore particles in suspension, the roast being so controlled that the particles are individually ing the particles to gravitate` against an upwardly flowing stream of relatively `cool oxidiz ing gas of such temperature that the -partlcles while still in suspension are chilled sufficiently to avoid agglomeration. i

6. Processof forming magnetic iron oxide in the form of finely divided particles, which comprises roasting finely divided sulphide ore parthe temperature of i fused in suspension, and allowi 4 fticles are individually ticles in suspension in an oxidizing gas, 'at l temperature causing fusion of the particles, the particles being allowed to gravitate from the area of roasting against an upwardly flowing stream of a relatively cool gaseous medium such that the particles while still in suspension are chilled sufficiently to substantially avoid agglomeration.

'7. Process of forming magnetic ironl oxide in the form of finely divided particles but substantially free of dust. which comprises roasting finely divided iron sulphide ore particles in suspension in an oxidizing gas, at a temperature causing fusion of the particles. allowing the particles to gravitate from the area of roasting against an upwardly flowing. gaseous medium oi' such temperature that the particles while still in suspension are chilled sufciently to substantially avoid agglomeration, and withdrawing upwardly by suction means .from the area of roasting the gaseous products of the roast together with the dusty material.

8. Process of oxidizing metal sulphides which comprises introducingthe sulphide in finely divided form carried' in a gaseous medium into the top of a hot combustion chamber, introducing a countercurrent of to substantially completely oxidize the sulphides in suspension, withdrawing the gaseous products at the top of the chamber and through a settling chamber by suction means, such a said countercurrent of air being maintained by adJusting said suction means so that combustion chamber and the settling chamber is maintained above that at4 which sulphur trioxide may be formed, and nnally between said settling chamber and suction means passing the gases through means which quickly cools them to a temperature below that at which sulphur trioxide forms.

9. Process of oxidizing metal sulphides which comprises vroasting the same in finely divided form in suspension in an oxidizing gas. at a temperature causing fusion of the particles, allowing the particles to gravitate from the area of roastinit4 against an upwardly flowing stream of relatively cool oxidizing gas of such temperature that the particles while still in suspension are chilled sufliciently to sugstantiaily avoid agglomeration when collected. withdrawing upwardly from the area lof roasting the gaseous products of combustion together with any dust occurring at said area. and then passing said products of combustion and dust Adownwardly through a settling chamber.

l0. The process of producing iron oxide in the form of finely divided fused particles, which comprises oxidizing and roasting finely divided iron sulphide particles in suspension in an atmosphere of oxidizing gas, the temperature of the roasting andloxidfizingbeing sofc'ontrolled that the parl fused and Vcaused to be-A come hollow while in Suspension. and thereafter' while the particlesare"still insuspension.` applying. air thereto of such amount that the particles while still in suspen' lsion are chilled sumciently to avoid agglomeraf the temperature in the.

temperature and` stream of relatively cool air in an amount sufficient v ssl

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