US1921743A - Process for purifying zinc ore - Google Patents

Description

Aug. s, 1933. o, GERLACH 1,921,743

PROCESS FOR PURIFYING vZINC ORE Filed July 2l, 1930 2 Sheets-Sheet 2 Patented Aug. 8, 1933 UNITED STATES PATENT OFFICE PROCESS FOR PURIFYING ZINC ORE Oscar Gerlach, Peru, Ill., assignor to Matthiessen & Hegeler Zinc Co., La Salle, Ill., a Corporation of Illinois This inventionv relates to' improvements in processes and apparatus for purifying zinc ore and the present invention is an improvement upon that described and claimed in my prior co-pending application Serial No. 243,840, filed December 31, 1927, which has matured into United States Patent No. 1,773,991, datedAugust 26, 1930. In said prior application there is disclosed an improved process of purifying zinc ore according to which the ore is freed of lead,

cadmium and sulphur compounds and other impurities by the application of heat in such a way that a portion of the body of the ore is heated at a temperature and pressure at which lead and cadmium vaporize while the remaining portion of the body of ore is maintained at a substantially lower temperature so that the lead and cadmium which are volatilized from the rst named portion are condensed in the second named portion and thereby rendered capable of separation. In the practice of that process, the entire body of ore subjected to the action of heat is ordinarily of substantially uniform quality and after the heating process is completed, the upper layer, which has been freed of the lead and cadmium compounds. and from which the sulphur has been driven off, is separated by a scraping device which removes the purified ore and leaves the remaining ore. containing the impurities, for subsequent treatment,

While that process of said prior application has been found to be very satisfactory in commeicial use, it has been discovered that the purification of the zinc ore may be carried on more efciently and more quickly by the improvement of the present invention according to which different grades of ore are superimposed upon each other in the purifying apparatus and simultaneously subjected to the action of heat in such a manner that the better grade or grades of ore are puried more quickly than the residue and may be separated from the remaining layer or layers of ore for use in manufacturing zinc of the highest quality.

Many zinc companies, particularly those operating zinc rolling mills, use different grades of spelter, depending upon the purpose for which the rolled zinc is intended, and four different grades of spelter are commonly specified. namely,

"high grade", intermediate, brass special and prime western. The last two mentioned grades of spelter may be readily produced in a zinc smelter but the first two mentioned grades must be produced by the electrolytic process, the redistillation process, or by the retort process, us-

ing the purified zinc ore produced by the process of my said prior application. The zinc smelters are ordinarily supplied with different grades of ore which are known as high grade, prime western and floatation ores", which differ in the amount of impurities contained therein. It is generally understood that a high grade ore is one which contains less than one-tenth of one per cent of lead and that a low grade or prime western ore is an ore which contains more than one-tenth of one per cent of lead, Without regard to the percentages of other impurities which may be contained in the ore. By the process of the present invention, these different grades of ore may be treated simultaneously in sintering apparatus, similar to that employed in the sintering of iron ores, whereby a zinc ore of a high grade of purity is more quickly and efficiently obtained than is possible by the invention of said application. Y

According to the present invention, the zinc ore to be treated is divided into portions of high grade and low grade quality and the pans of the sintering machine are partially filled in succession with the low'grade ore and then a layer 80 of the high grade ore is progressively filled into the pans above the low grade ore. Both grades of ore have preliminarily been crushed to a considerable degree of fmeness, for example, that which would enable them to pass through a tenmesh screen, and they are preferably subjected to a preliminary roasting before being placed in the sintering machine in order that the major portion of the sulphur, about ninety per cent, maybe driven off before the ore is subjected to the action of heat. The zinc ore introduced 'into the sintering machine will have been converted by the roasting operation, which is ordinarily carried on at a temperature of from 1600 degrees Fahrenheit to 1800 degrees Fahrenheit, from zinc sulphide (ZnS) into zinc oxide (ZnO) and this zinc ore is fed into the sintering machine through hoppers so that the different grades of ore are automatically superimposed upon each other as the pans of the sintering machine move along their endless path of travel. Some sulphur, usually about three per cent, will remain in the ore when it is introduced into the sintering machine anda quantity of coal, coke or anthracite is also preferably mixed thoroughly with the ore before it is introduced into the hoppers so that process. The heating of the ore is effected, as in the prior process, by moving the sintering pans beneath a sintering hood equipped with gas burners or other burners capable of producing a high temperature therein sufficient to ignite the coal or sulphur contained in the material to be4 sintered, preferably a temperature of between 2600 degrees Fahrenheit and 2800 degrees Fahrenheit. A number of burners are preferably provided in this hood, the rst ones being fed with air or oil and gas to produce an oxidizing ame while the later ones of the'series are fed byv steam or oil and gas to form a reducing fiame and to cause the production of free vhydrogen which is made use of in freeing the zinc ore of the cadmium oxide contained therein. To facilitate the purification of the ore, a small quan- `tity of common salt (NaCl) is mixed with the top layer of high grade ore. This salt is vaporized by the heat and the vapors passing through the ore convert the lead oxide (PbO) into lead chloride (PbClz) which is more readily driven off from the top layer of ore and condensed in the lower layer as the sintering pans continue their travel.

The heat produced by the burners and the burning of the coal mixed with the ore, causes the upper top layer of high grade ore to be'substantially freed of both lead and cadmium compounds. The lead is driven out of the upper layer of ore and collects partly in the low grade ore beneath the same in the form of sulphate or chloride (while a part escapes as such through the fan and stack to the air). The cadmium is likewise driven out of the upper layer of high grade ore and collects partly in the lower layer of low grade ore in the form of sulphate and sulphide, while a part thereof escapes. The zinc oxide in the upper layer of ore is not driven out during the limited time in-which the ore is exposed to the flame. It appears that the lead and cadmium compounds in the upper layer of high grade ore are reduced and then volatilized so that they recombine in the vaporized state with sulphur and oxygen to form the sulphates and sulphides which are condensed in the lower layer of low grade ore. In this way, the upper layer of high grade ore is substantially freed of cadmium and lead compounds and due to the high guality of this layer at the commencement of the operation, the purification of the upper layer may be effected very rapidly while the lower layer, from which the upper puried layer is separated, may be subjected to further treatment or use in the manufacture of zinc of low quality. The upper purified layer of zinc is separated from the other and subsequently distilled in a retort with carbon to obtain free zinc.

Although various forms of apparatus might be employed in carrying on the process described above, there is illustrated in the accompanying drawings an improved sintering apparatus, similar to that employed in the sintering of iron ore, except that certain improvements have been added for the purpose of adapting it to the practice of the present process. In the drawings,

Fig. 1 shows a side elevation of the improved sintering machine;

Fig. 2 shows a partial longitudinal section through the upper row of sintering pans showing the method of depositing the different layers of ore in these pans and the means for breaking up these layers and separating the upper layer from the lower layer;

Fig. 3 shows a detail vertical section, on an enlarged scale, taken on the line 3 3 of Fig. 1, showing the construction and mounting of the sintering pans and the means for drawing oil` the gases from beneath these pans, and

. Fig. 4 is a detail section on the line 4-4 of Fig. 2, showing the device by which the upper layer of ore is broken up after heating in preparation for its separation from the lower layer.

As illustrated in the accompanying drawings, the sintering machine 10 comprises a plurality of sintering pans 11 which are mounted to follow an endless path of travel and which form a substantially continuous series so that, along the upper stretch of their path of travel, each pan is located closely adjacent to the next leading and following `pans of the series. Since the pans are provided with bottom walls and side walls, but are Without end walls, it will be understood that the side walls and bottom walls, joining onto each other, form a continuous movable trough, successive portions ofl which are progressively filled as the pans move beneath the feeding hoppers. The sintering pans 11 are supported by a frame 14 comprising a plurality of vertical frame members l5 and a number of transverse longitudinal frame members 16. The frame 14 serves as a support for certain track members which are provided to coact with rollers 17 mounted to revolve on trunnions 18 projecting laterally from opposite sides of the sintering pans 11, as shown in Fig. 3, there being two rows at each side of each pan. In the upper horizontal portion of the path of travel of the sintering pans 11, the rollers coact with horizontal trackways 19 having depending anges 19a which are secured to brackets 20 attached to the longitudinal side frame members 21. At the discharge end of the machine, the track members 19 are curved downwardly in semicircular fashion, as shown at 19h, and are arranged to cooperate with the upturned semicircular eX- tremities 22b of the lower track members 22 which are attached to the vertical frame members 15, thus forming a semicircular slot at the discharge end of the machine through which the rollers 17 travel as the sintering pans move downwardly and are reversed in position. The lower track members 22 are inclined downwardly towardy the forward end of the machine and are thence curved upwardly in a semicircle as shown at 22c, thus guiding the sintering pans in their upward movements at the forward end of the machine. Each roller 17 has an annular flange 17a which projects over the edges of the adjacent track members 19 and 22 so that lateral displacement of the sintering pans is prevented. The movement of the sintering pans 1l on the trackways 19 and 22 is effected by a pair of driving wheels 24 mounted on a transverse shaft 25 and journaled in bearings 26 which are secured to the longitudinal frame members 27 adjacent the forward end of the machine. The driving wheels 24 are provided with teeth 24a arranged in pairs, the teeth of one pair ,being spaced apart from those of the nextadjacent pair in such a manner that the teeth of each pair will move downwardly over one of the rollers 17 on a sintering pan l1 when this sintering pan has moved by gravity along the lower inclined tracks 22 from the rear end of the machine to the forward end thereof. As the rollers of the sintering pans are engaged by the teeth 24a of the wheels 24, While these pans are in their reversed positions, they are then moved by the wheels 24 around the curved portion 22c of the lower trackways and brought into their upright positions where the rollers 17 pass onto the upper horizontal trackways 19. The pans on the trackways 19 are then moved rearwardly by the engagement therewith of the next following pans 11 which are continuously elevated by the driving wheels 24 and moved onto the trackways 19 at the forward end of the machine. The driving wheels 24 are actuated by a series of reducing gears 28 which are mounted on a shaft journaled in suitable bearings carried by the frame of the machine and in turn driven by a pinion 29 fixed on the shaft of an electric motor 3D. The reducing gears serve to actuate the driving wheels 24 at a relatively low speed so that' the sintering pans 11 have a relatively slow travel in a rearward direction on the upper horizontal trackways 19.

When a sintering pan 11 reaches the rear end of its path of travel on the horizontal portions of the trackways 19, it falls by gravity around the semicircular track members 19b and 22b and a gap 3l is preferably provided between adjacent pans at the beginning of this downward movement so that the initial movement of each pan and the engagement therewith at the bottom of the gap with the next lower pan produces a jar suiicient to discharge the materials contained therein.

The extent of the gap 31 and the maintenance of a continuous series of pans 1l along the upper horizontal portions of the trackways 19 is insured by a pair of controlling wheels 32 mounted some distance forwardly from the rear end of the machine and provided with teeth 32a which engage the rollers 17 of the pans 11 on both their upper and lower paths of travel. The wheels 32 are mounted on a shaft 33 journaled in bearing blocks 34 which are adjustable in slides 35 and controlled through levers 36 by suspended Weights 36a. The wheels 32 are thus rotated by the advancing pans 1l along the upper trackways 19 and as they rotate, they automatically vdischarge successive pans in inverted position which are engaged by the lower portions of the wheels so that a predetermined number of pans ll are retained in position around the curved trackways 19b and 22b with a predetermined gap 3l through which the pans fall successively from their positions on the upper horizontal trackways 19.

The sintering pans 11 are provided with upwardly extending side walls 11a connected by transverse bars 11b and these side walls 11a have ledges, as shown in Fig. 3, upon which are mounted the ends of the grates 11c onto which the crushed ore is loaded. As before stated, the sintering pans/ are open at their ends so that when they are located in close spaced relation on the upper trackways 19, as shown in Fig. 1, they form a continuous trough for the reception of the crushed ore. In the region beneath the sintering pans which are mounted upon the upper trackways 19, there is located a casing 37 which forms a vacuum chamber 38. The upper edges of the walls of the casing 37 are connected to a rectangular frame 39 which is seated on and secured to the inturned flanges 21a of the side frame members 21 and which forms a funnel for directing materials downwardly into the chamber 38. The chamber 38 has pipes 40 leading from the side thereof and connected to a suction pump or other suitable apparatus adapted for maintaining a partial vacuum in the chamber 38 so that the sulphur dioxide and other gases which are liberated in the ore, and not condensed or deposited therein, are drawn inwardly into the chamber 38 and thence outwardly through the pipes 40. In order to form a seal between the vacuum chamber and the sintering pans while these pans are in the upper part of their path of travel, a sealing plate 4l, of somewhat flexible construction, is mounted along each lateral edge of the frame 39, being held in position by clamping members 42 engaging the threaded studs 43 which are secured to the opposite sides of the frame 39. By adjusting the clamping members 42, the upper edges of the sealing plates 41 may be caused to engage in the desired manner the grooves 44 which are formed in the side members of the sintering pans on the under sides thereof so that the grooves in successive pans align accurately with each other. A seal is thus formed so that the gases from the sintering pans may be drawn down into the vacuum pan 38 without actual loss.

The crushed and wetted ores which are to be sintered in the machine l0 are fed to the sintering pans 11 through hoppers positioned adjacent the front end of the machine. The low grade of crushed ore 45 is fed from a hopper 46 and the high gradev of ore v47 is fed from a hopper 48. The hopper 46 has its mouth positioned some distance below the upper edges of the side walls 11a of the sintering pans so that as these pans travel beneath the hopper 46a layer 45a of low grade ore is deposited in the pans with its upper surface located some distance below the upper edges of the pans. The pans which are thus partially filled then pass beneath the hopper 48 which has its mouth so located that it discharges into the pans an upper layer 47@l of high grade ore having its upper surface located substantially fiush with the upper edges of the side walls 11a of the pans. The pans which are thus filled then pass successively beneath the burner hood 49 which, as above described, is preferably provided with two series of burners so that the desired action is obtained upon the ore through the application of heat. As the ore is heated, the lead and cadmium compounds are driven out of the upper layer 47a and condensed in the lower layer 45a and the sulphur is driven off and drawn downwardly by the vacuum chamber 38. The heating of the upper layer of ore and the combustion of the fuel mixed therewith, brings about a hard or crusted condition thereof and, to facilitate the separation of the upper purified layer from the lower layer, means are provided for breaking up the upper layer of ore at a point adjacent to the discharge end of the machine. This breaking action is effected by a sca'rier 50 which comprises a drum 51 mounted on a shaft 52 which-is journaled in brackets 53 extending upwardly from the side frame members of the machine.` The drum 51 lcarries a number of scarifying blades 54 each of which extends radially outward from the drum 51 with a laterally turned extremity 54a adapted to move in `a cylindrical path concentric with the axis of the drum. The radial portions of these blades are mounted in slots 55 formed in the drum and are secured in adjusted position by inclined set screws 56. By this arrangement, the blades are adjustable to cause the portions 54a to move in cylindrical paths of different diameter so that they may be caused to break up upper layers 47a of different thickness. The shaft 52 of the'drum 5l is actuated by suitable driving mechanism from the motor 30 and is preferably. driven in the direction indicated by the arrow 57. After the crusted ore 47a has been broken up by the scarier 50, it is removed from the lower layer 45a by a bucket elevator 58 comprising endless chains 59 mounted to travel around gears 60 and having buckets 61 mounted thereon to engage and pick up portions of the upper layer 4'?a of ore as they move in the direction of the arrow 62 in the lower portion of their path of travel. After the upper purified layer of ore has been separated from the lower layer 45, the latter layer is broken up by a breaking roll 63 which is provided with a plurality of longitudinal flutes or teeth 63a adapted to dig into the lower layer of ore 45a as the roll is driven in the direction of the arrow 64. This roll is mounted on a shaft 65 journaled in suitable bearings at the side of the machine and is adapted to be driven by operating connections extending preferably from the motor 30. The lower layer 45a which vis thus broken up is then in readiness to be discharged from the sintering pans as these pans move through the gap 3l and pass around the curved trackways 19b and 22h. The bucket elevator 58 is preferably located ina housing 66 having a discharge'mouth 67 through which the ore picked 'up by the buckets 61 is discharged. Similarly,

the portion of the trackways over which the pans travel during the discharge of the lower layer 45a is preferably enclosed in a housing 68 which is open at its lower end so that the sintered ore may be discharged therethrough as it falls from the pans 1l. The entire bucket elevator 58 is preferably adjustable vertically so that the buckets 61.may be employed for removing upper layers 47a of different thickness. For this purpose, the frame members 69 by which this bucket elevator is carried are preferably mounted upon adjustable supports.

Although one example of the improved apparatus has been illustrated and described in 1 connection with the explanation of one example of the improved process of purifying zinc ore, it

will be understood that the process may be practiced in various forms of apparatus all coming within the scope of the appended claims.

I claim:

1. A process of purifying zinc ores which consists in separately crushing and wetting a high grade oie and a low grade ore, thensuperimposing the high grade ore upon the low grade ore in a traveling conveyor, subjecting said ores during their travel to the action of heat applied directly to said high grade ore at a temperature and pressure sufficient to free said high grade ore of lead and cadmium compounds, condensing the vaporized lead and cadmium compounds in said low grade ore, breaking up the upper layer of said ore, and then continuously separating said upper layer of ore from said lower layer during their travel.

2. The process of purifying zinc ores which consists in separately crushing and wetting quantities of high grade ore and low grade ore, mixing fuel with said ores, superimposing a layer of said high grade ore upon a layer of said low grade ore, heating said layers of ore by the application of heat to said upper layerat a temperature suflicient to vaporize lead and cadmium compounds in said `upper layer while maintainconsists in separately crushing and wetting quantities of high grade ore and low grade ore, mixing fuel with said ores, mixing a small quantity of sodium chloride with said high grade ore, superimposing a layer of said high grade ore upon a layer of said low grade ore, heating said layers of ore by the application of heat to said upper layer sufficient to vaporize the lead and cadmium compounds in said upper layer while maintaining said lower layer at a lower temperature to condense the lead and cadmium compounds vaporized from said upper layer, drawing oi the liberated gases from said ores, and then separating the upper layer of high grade ore from said lower layer.

4. The process of freeing zinc ores from lead and cadmium contained therein which comprises the operations of superimposing a layer of high grade ore upon a layer of` low grade ore, subjecting the upper layer of high grade ore to a temperature and atmosphere at which lead and cadmium vaporize while maintaining said lower layer of low grade ore at a substantially lower temperature kwhereby lead and cadmium are volatilized from said upper layer and condensed in said lower layer, and then separating the upper and lower layers.

5. A process of purifying zinc ores which consists in superimposing a high grade ore upon a low grade ore, heating said ores by the application ofheat to said high grade ore to vaporize the lead and cadmium compounds therein while maintaining said low grade ore at a lower temperature to condense therein the vapors from said upper layer, and then separating said high grade ore from said low grade ore.

6. A process of purifying zinc ores which consists in superimposing a layer of high grade ore upon a layer of low grade ore, continuously mov- /ing said layers of ore and applying heat thereto during their travel suicient to vaporize the lead and cadmium compounds in said high grade ore while maintaining said low grade ore at a lower temperature than said high grade ore to condense in said low grade ore the vapors of lead and cadmium liberated from said high grade ore, and then separating said high grade ore from said low grade ore during 'their movement.

7. A process of purifying zinc ores which contheir travel to the action of heat applied direct- 136 1y to said high grade ore -suflicient toA vaporize the lead and cadmium compounds in said high grade ore, maintaining said low grade ore at a lower temperature than said high grade ore to condense therein the lead and cadmium vapors liberated from said high grade ore, and continuously removing said high grade ore from said layer of low grade ore during their travel.

8. The process of purifying zinc ore which ccnsists in placing a layer of high grade ore upon a layer of low grade ore in a conveyor, subjecting said ore to the action of heat while moving, in a conveyor to vaporize the lead and cadmium compounds in said upper layer, subjecting said heated ore to the action of suction and causing the lead and cadmium vapors to be condensed in said lower layer, continuously removing said upper layer from the moving lower layer of ore, and then separately treating the separated layers.

9. The process of purifying zinc ores which consists in separately crushing and wetting a high grade ore and a low grade ore, superimposing a layer of said high grade ore upon a layer of said low grade ore in a conveyor, causing said ore to pass beneath a heating means whereby lead and cadmium compounds in said high grade layer are vaporized, then subjecting the ore to the action of suction means located beneath the moving body of ore to cause the lead and cadmium CERTIFICATE OF CORRECTION.

Patent No. l, 921, 743.

August 8, 1933..

OSCAR GERLACH.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 4, lines 69, 70 and j claim 2,v strike out the words "and condensing the vaporized lead and cadmium compounds in said layer of"; and line 72, after "ores" insert the words and condensing the vaporized lead and cadmium compounds in said layer of ore'. and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in. the Patent Office.

- Signed and sealed this 14th day'of November, A. D. 1933.

(Seal) F. M. Hopkins Acting Commissioner of Patenti.

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