US2131786A - Roasting of ores, especially zinc sulphide ores containing lead and/or cadmium - Google Patents

Description

Oct. 4, 1938. 1 s. ROBSON ET AL 2,131,786

. ROASTING 0F ORES, ESPECIALLY ZINC SULPHIDE ORES CONTAINING LEAD AND/OR CADMIUM Filed May 15, 1957 2 Sheets-Sheet l 1 INVENTORS I STANLEY RoBsoN THOMAS BENSON GYLES ATTORNEYS Oct. 4, 1938. v s. ROBSON ET AL 2,131,786

ROASTING OF ORES, ESPECIALLY ZINC SULPHIDE ORES CONTAINING LEAD AND/OR CADMIUM Filed May 15, 1957 2 Sheets-Sheet 2 INVENTORS STANLEY ROBSON THOMAS BENSON Gvuas ww w ATTORN E YS Paten ted ett '4; 193 8 I I b I it 2 m'f I I ROASTING or ones, ESPECIALLY. zinc SULPHIDE ORES CONTAINING LEAD AND/R. CADMIUM 1 I v Stanley Robson; Durdham Park, Bristol, Gloucester, and Thomas Benson Gyles,.Clitton',- Bristol, Gloucester, England, assignors to National Processes Limited, London, England, an 1 Englishjoint-stockcompany I I Application; May 15,1937, Serial No. 142,780

In Great Britain May 21, 1936 i v a m 101. 15-1) I p This invention relates to processes and means teririg machineigwhich can be easily-separated- I or or relating to roasting ores particularly zinc into two layerssso that the upper layer or the sulphide ores,'concentrates and the like (allherecake which is relatively free 'from lead or cad-- I -inafter referred to as the ore) in which any suitm y e separated V fromflnd d r d 1 b t; roaster l u a .b empldyed,- separately from the lower layer of the charge .5 for example blast roasting apparatusof the well in which the lead or/aud cadmium is concen:

- known "DwlghtJ-loyd type'in which the ore to rai rmainly eonchtrated- I I .be sintered is delivered on to the surface of travel- I According to the inven i n a pr cess for .ro'ast- I ling grates so as to form thereon-a bed or charge, lng zinc sulp ores, containing l an '10 of such'ore of suitable thickness which travelling cadmium consists in arranging the one charge on .bed of ore or-charge is'caused, to pass beneath, thetravelling d ofa sinteringma in in 3 an ignition burner or burners and over a suction lay s a p t li -r y se a ated, byintera chamber or chambers whereby the ore is sintered' posing afley r 1 m terial which is either (a) inand thereafter delivered-oil the machine, for exert during the rcasting opera 1 n r lbf 11-. x m l as r be 1 mi patent spgciflcatlgn ferent grain size or (c) 01' dliferent sulphur. con-.- 16 v Nix-306.569; or if desired in carrying out the I tentof fuel value from t ma n/char e. where- I present invention any other suitable l'orm of by when the chargeis sintered' a plane of cleav I blast roaster apparatus may be employedin which age in the charge lsj fo med b tweenthe upper 1 cment a of 8417 or oxydizmg' atmosphere is and lower layers of the-ore charge. I r 4 20 blown-or drawn through a charg'e'for bed of ore The lollowing a eexamples three e a i 2,

on a perforated travelling grate, I, I i methods 0! pr due n ythe pl n of c ava in According to this invention the bed-orcharge e s nt r d ake W cha e mp ll of ore to be sintered is composedol 3 layers or I a an in r layer y b 'l e p d be we n 1.: dill g materials in the contiguouslayerswhich the top and bottom a s y spreading over the g are each prepared and laid, superimposed, on one om por i n ttom layer). of the char a another, on the travelling grate so that when the I zinc ore containing nq l h r such for example .7 3

complete bed orore'or charge thus formed on as'calamiue or already desulphurizedzinc'ore-or the trave l lfi grate has been subjected to the S a er- In this case the interp a er wil 7 ,sinterlng operation the thu's sintere'd bed of ore main inert during the roasting pro ess, whereas to or charge will produce 'or provide aplane or easy t e lay ra e n l yer below it being the mm I or ready cleavage whereby this .sintered-t'ravel Inal charge in ng. 1 1' example! en r ling bed or charge of ore ca'n bereadily separated I and returned sinter willform two slnter layers into two layers advantageously when about to s arated by the interposed in t and h s al' r. leave or as same leave the travelling grate. thus Iorming a planeof cleavage.

a 1 This invention refers particularly to-the blast 1 (b) All'ayer of diflering' grain size'may be in roasting or zlnc'sulphide ores (blende' contain. .terbosed by dus n ve y fine slntered returns I ing impurities, notably lead and/or cadmium; 1 on to the bottom layer before eed n n to s n communds :or other ,compoundswhich may bethe top layer material; or by using for the infipresent and which readily volatilize whenttige termediate'layer the same mixed charge mate- 40 said o'res are heated i'n processes. of the type in 1181 as the t pand o m ayers, vbut havin 40 which the roastedproduct is obtained .in a- 5111: "for the intermediate layerra particle size'coarser- Y tered jiorm and we. will proceedto describe our than the rest'oi the charge. In this latter-case,- I presentinyention:withr r r t tm kmd (if 2 although the shrinkage maybe of-or about-the ore., V I same order asgthe upper and lower: layers, yet It has been observed-in practice thatthelead the dlil'erencein particle -size will cause 'thej or/andcadmiu'm present in-thesintered charge coarser material or the' intermediate layer to a 4 j from a 'zinc 'sulphideore (blendel chargedonto form a loose rubbly layer whicheasilyparts be- -.a 'sintering Zmachine is not evenly,,distributed tween the upper and. lower layers. I I v therethrough-on completion oith'e vsinteringj (ciAn interposed layer ol' diilerent sulphur I operation-i. e.-the bottom-portlons-oithe sinter [content orluelvalue can be produced by mak so 1 cakenowhaving a muchgreater proportion. or in: a lflerent mixture of green ore than the v theselelements than the t p portions which latter main charge so as to produce a mixture for-the are relativelyzfre hereof. intermediate layer ha n eithera high r or w- It is an object 01' this invention to pro'duce :a er sulphur contentthan that of the main charge.- aintered cake (on the travelling state, or the sinf In this case, the dilrerent'roasting intensity will cause a different shrinkage between the interposed layer and the layers above and below thus forming a plane of cleavage. The same efiect will also be obtained by forming the interposed layer of desulphurized sinter with which sufficient fuel is admixed which burning in the air current will produce a difierent temperature in the interposed layer and consequently form a cleavage plane. I

The process of the invention may be employed in any well-known sintering processes to which same may be applicable as, for example, in the well-known two-stage process (patent specification No. 1,401,733) in which the material is sintered (after previous roasting in a pre-roasting furnace) using green ore as the additional fuel. The invention may also be applied to similar processes as, for example, where coal or coke or carbon is used as the fuel in the sintering of materials previously desuiphurized.

The invention is, however, particularly applicable in carrying out the process set out in British patent specification No. 306,569 and in carrying out the process set out in British patent specification No. 433,861. In these processes the invention may be employed in any of the ways described above, but a convenient method is for the interposing layer or layers to consist of normal returns" without the addition of any green ore.

In carrying out either or both of these last named processes we have found that an inert layer of returns say from of an inch to about /2 an inch thickness acts very satisfactorily. The roasting actioninitiated at ignition, and passing down through the charge passes satisfactorily through an interposed layer of limited thickness, the necessary heat being transmitted therethrough by air currents and by radiation and conduction. If for any reason, e. g. the desire to maintain higher gas strengths ($02) or higher heat intensities or to use a thicker interposed layer, it is undesirable to use an entirely inert material, then one or other of the means indicated above can be used to increase the fuel value of the interposed layer.

The interposed layer can be inserted by means of any convenient mechanical arrangement. For example, a thickness of the normal charge to form the bottom layer can be fed on to the travelling grate in one or other of the well-known or recognized feeding devices, and then from a similar and separate device the requisite thickness of the intermediate layer (to form the parting layer) can be fed, followed by feeding on of the normal charge to form the top layer. In the case of using simply coarser portions of the charge as the interposed layer to form the parting zone, this can be accomplished by carrying on' the first operation as above, and then passing to the third operation, but arrangingthe feeding on in such a manner as to allow the coarser particles to roll down the feed heap, thus forming the coarser zone in between the other two.

The separate discharging of the layer or layers to be selected at or towards the discharge end can be accomplished by any convenient device, as for example the edge of a metal blade or plate, or a row of prongs or forks on which the top layer, easily detached from the lower, rides over and reaching a conveyor is separately transported. The under portionof the charge together with loose material takes the normal route of the sintering equipment, for example in the proces of British patent specification No. 306,569 is used as returns. Alternatively, the upper portion can be returned or transported, and in general regarded as the normal product, while the under portion at some convenient place in the equipment is diverted as the special output.

The position of the interposed layer within the cake can be chosen to suit the quality requirements of the products, or the characteristics of the process. More than one layer can, if desired, be inserted e. g. two inserted layers, giving three divisions of the charge.

Some practical examples will serve to illustrate various modes of operationz-taking the case of the process of British Patent No. 306,569, with certain zinc ores high in lead, say 4.5% Pb. In the normal process it will be found that the lead percentage in the sintered cake ranges from say 0.5% in the top to as high as 30% in the very bottom. By the use of two inserted layers, it is thus possible to divide the output into three portions:the bottom portion high in lead and cadmium, which can be used for the recovery of lead and cadmium therefrom, the middle portion which can be used as normal output and/or for the supply of returns; the top portion low in lead and cadmium, which can be used for zinc distillation, or zinc oxide production, or other purposes. Any deficiencies in the amount of returns required for the process can be made up from one or other of the other portions, preferably the middle portion in normal modes of operation.

In the accompanying drawings there is illustrated a form of blast roasting apparatus designed for carrying on the process of the present invention; but it is to be understood that any other suitable form of blast roasting apparatus may be employed in carrying on the said process.

Referring to the accompanying drawings:-

Fig. 1 is a local view in side elevation of the upper portion of a blast roasting apparatus and showing diagrammatically the means for separately feeding the respective 3 layers onto the endless travelling grate and the means for effecting the separation of the top and bottom main layers after roasting, and for removing said top layer and discharging the latter (separately from the bottom layer) from the delivery end of the sintering machine;

Fig. 2 is a view in side elevationon a greatly enlarged scale-of: (a) one of the pallets pans or link members, forming the endless travelling grate, in the tilted position which it is caused to assume on its arrival at the discharge end of the endless travelling grate (as shown in Fig. 1) and (b) means for effecting the separation of the top and bottom main layers after roasting and for removing said top layer and delivering the latter separately from the bottom layer, as each said pallet in succession arrives at and passes under said means for separating the top and bottom layers.

Fig. 3 is a fragmentary view, in plan, of Fig. 2;

Fig. 4 is a cross-sectional view on an enlarged scale on line l4 of Fig. 1, of one of the pallets of the endless travelling grate. a

A is the endless travelling grate formed of pallets, pans or link members a (hereinafter referred to as the pallets a) which are linked to one another, in any known or suitable manner to form the endless travelling grate of the blast roasting apparatus.

Each pallet a, on each side of itsupper surface, is provided with a side flange a. '(Figf4), and is provided with flanged wheels I) which run on the guide rails 33, B and D by which the 75 pallets are guided, except during their travel along the longitudinal upper part of the roasting apparatus. During the travel ,of the pallets it along said upper 'part of the roasting apparatus, the bottom part of each pallet a. slides along the upper surface of the longitudinal member C on each side of the apparatus.

"Qio

At the discharge end of the apparatus the wheels b encounter and then run on the rail B which is curved downwards as indicated at B (see Fig. 1) After delivering the sintered material oil the palletsatthe discharge end of the apparatus the pallets ai'pass downwards around 1 saidcurved end rail B their wheels 12 then engagingthe further rail D which runs along the lower part of the apparatus.

c is the knife or plate having knife edgec of .the full width'of the layers'of material carried travelling grate.

example hinged at c so on the endless travelling grate between the flanges a of the palletsja forming the'endless The knifje'or plate cis adjustably mounted, for that. the edge end -c or said 'knife or plate can be raised or lowered (and fixed in its adjusted position) to divide the top layer of any desired thickness from the bottom layer on the grate. d is shoot, down which the top layer divided byjthe knife or plate 0 is separately delivered,

for example to a conveyor (not,shown)..

e is roller, engaging on flange a on each side of the endless travelling grate A.

r is shoot, down which is fed the desired mate-. I for initially forming the. bottom layer 3, (see Fig. 2) of the desired rial or mixture 01' materials thickness, on' the pallets a of the endless travel- :ling grate A.

g is shoot, down which is i'ed-onto the top of the No."3 layer the desired material for forming the intermediate layer 2; (ofthe desired thick- I ness) to be interposed between the top layer l v and bottom layer 3 --s ee Fig. 2.

h is shoot, down which is fed onto the top of the intermediate layer! the desired material or [mixture oi-materials forming the top layer I oi the desired thickness.

i t is the igniter.

v ,A simple mode of operationls'the insertion of only one interposed or parting layer, and with ores as above; assuming that the main aim 'is not only, while sintering, (a) to cause the upper layer to become relatively free from lead or/and cadmium but also (b) to cause the segregation-- of the lead or/and cadmium in. the bottom layer r 55 to enable the lead or/and cadmium 'tobe re-. covered from" said bottom layer alter the latter has been separated, and delivered separately,

from the upper layer; thenthe interposedlayer would be inserted nearthe bottom-oi the charge on the grate." In-this -oase. the top portioncan be utilized for'returns, as well as normaloutput;

while the separated bottom layeris selected and treated as aforesaid for lead or/and. cadmium recovery.- 7 L e5 v of.-a parting. layer near thetop, and the selection 3 With ores lower in leadcontent,'the insertion of the top layer as output gives agood low lead productwhich results his good grade ot'metal (zinc! inthe zinc distillation process ora good grade zinc oxide. g 4 When sintering zinc ores containins 'l.5% Pb, the uneven. lead distribution makes it possivble by the insertion'oi' 'a .cleavage layer to obtain a top portionjassaying10.01%'1 b and lower.-

1 With the production of sintered material exilorming the'intermediate layer as in either of travelling grate of a blast roasting apparatus and travelling grate of a blastroasting apparatus and sintered on the travellinggrate, which consists in delivering the charge tobe sintered onto said high grade zinc oxides and/or high grade metallic zinc can be produced therefrom.

,With' a negligible or very low lead and cadmium contentin the top layer when sintered, the 6 metal fromboth vertical and horizontal retort distillation processes can be delivered substan: tially free from lead and cadmium.

-.Further, we. have found that with these low or negligible leadsinters treated in the horizontal distillationprocess any small amounts of lead left in the sinter come over in the earlier taps of the process, while the metal from the later taps is almost entirely free from lead and cadmium.

This is contrary to experience with/sinters or can be seen, therefore, that with these low lead sinters produced by the present invention, a high grade of zinc metal substantially free from both lead and cadmium can be obtained during the latter part of the distillation period.

It will be obvious that the present invention may be employed for re-sintering already sintered ore for the purpose of separately de-leading or de-cadmiumizing. such already sintered ore; namely by the addition to and admixture with the already sinter'e'd ore of carbon (e. g. coal .or

. coke) in that part of the charge for forming the top and bottom layers of such sinter mixture and the/foregoing Examples (1, or b or 0; except that in the case of Example cbeing employed a dif; ferent coke mixture would be employed in the intermediate layer insteadoi' green ore.

. If desired the processor method of the present invention maybe employed in the blast roasting" of any ore or ores (as well'as for zinc sulphide ore) to which same maybe applicable. 7

What weclaim isz+ t 1. In the operation of sintering ore on the the removal or substantial removal from the ore, during the sintering' operation, of lead and/or cadmium and/orother' impurities present in the ore; the method of forming the charge. to be sintered on the travelling grate which consists-in delivering onto said travelling grate the charge material in three superimposed :layers of diifer-' ing. characteristics by interposing. between the top and bottom layers of the charge material, an 5n intermediate layer of charge material having (iii- 7 ieringcharacteristics from the top and bottom layers andsuch that after the completion of. thesinterin'g operation this intermediate layer 'will constituteja plane orzone of cleavage in the sintered charge thereby to enable the now substantially impurities-tree sintered top layer of the T charge to be-readily separatedfrom the bottom layer and to. be separately delivered Irom the travelling grate; and separating said top layer from thebottomlayer and delivering Qfromthe grate said top layer'separately fromsaid bottom layer. z. l -2. Inthe operation of 'sintering ore. on the the'removal or substantial removatiromdzheore, during the .sinteringioperation, of lead and/or; cadmium and/or other impurities present in the ore; the method of forming the charge to be travelling grate in more than three superimposed layers of material of difl'ering-characteristics in r such wise that an intermediate layer, i'ormed oi material of diflering characteristics from the v other layers, is interposed between the top layer and bottom layer and will, after completion of the sintering operation constitute a plane or zone of cleavage in the slntered charge thereby to enable the now substantially impurities-free slntered top layer to be readily separated from the lower layers and to be separately delivered from the travelling grate and separating said top layer from the lower layers and delivering said top layer separately from said lower layers.

3. In the method of sintering ore according to claim 1, forming an intermediate layer between the top and bottom layers of a material which remains inert throughout the sintering operation.

4. Inthe method of sintering ore according to claim 1, forming an intermediate layer between the top and bottom layers of a material of coarser grain size than that of the layer next above and below said intermediate layer.

' 5. In the method of slntering ore according to claim 1, forming an intermediate layer between the top and bottom layers of a material of finer grain size than that of the layer next above and below saidintermediate layer.

6. In the method of sintering ore according to claim 1, forming an intermediate layer between the top and bottom layers oi! a material of different fuel value from that of the layer next above and below said intermediate layer.

'7. In the method of sintering ore according to claim 1, forming an intermediate layer between the top and bottom layers of a material of different sulphur content from that of the layer next above and below said intermediate layer.

STANLEY ROBSON. THOMAS BENSON GYLES.

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