US 2769706 A
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Nov. 6, 1956 F. o. HERNERYD ET AL 2,769,706
SMELTING SULF'IDE ORES 2 Sheets-Sheet 1 Filed Sept. 29, 1952 lTl INVENTORS Nov. 6, 1956 F. o. HERNERYD ETAL 2,769,706
SMELTING SULFIDEI ORES 2 Sheets-Sheet 2 Filed Sept. 29, 1952 ,7 2 INVENTO 5 BY 51 Q4% w; m m M wan United States Patent SMELTING SULFIDE ORES Fritz O. Herneryd, Allan F. Norrii, and Erik 0. A. Sundstriim, Skelleftehamn, Sweden, assignors to Bolidens Gruvakfiebolag, Skelleftehamn, Sweden, a Swedish joint-stock company Application September 29, 1952, Serial No. 312,092 Claims priority, application Sweden June 4, 1948 5 Claims. (Cl. 7510) This application is a continuation-in-part of our prior co-pending application Serial No. 96,536, filed June 1, 1949, now abandoned.
The present invention relates to a method for the smelting of sulphide ores for producing a matte. While the invention can be applied to all kinds of sulphide ores it is especially applicable to sulphide ores containing at least one metal of the group consisting of copper, gold, silver, nickel and lead.
When carrying out the smelting process a matte is produced containing the above mentioned metal-s and a slag containing constituents of the ore such as iron and silica, which are without value in this connection. Said slag, however, always has a certain amount of the valuable constituents which thus are carried away by the slag when this is being removed from the matte and discharged. The content of the desired metals appears in the slag in the form of suspended matte particles, in the form of matte in physical-chemical solution and in the form of compounds of the metals in solution or suspension such as iron or silica compounds.
The possibilities of treating sulphide ores economically are to a great extent dependent upon the possibilities of maintaining low slag losses, that is a low content of valuable constituents such as copper, gold, silver, nickel and lead in the slag.
In the following specification, for the sake of simplicity, reference is made mostly to copper ores while it is to be understood that the invention also can be applied to other sulphide ores as mentioned above.
To reduce the slag losses it has previously been proposed to wash the slag of its copper content by distributing fluent washing ore over the surface of the slag, the ore being treated in a reverberatory furnace and the entire charge superheated. This method has, however, as far as the inventors know, not been successful in practice, apparently at least partly due to the fact that no precautions have been taken to prevent the rich matte formed from the normal ore to enrich the matte formed from the washing ore. Furthermore, a method of matte or pyritic smelting has been proposed, wherein the matte is treated by the converting or bessemerizing process, the slag formed in said process being caused to flow to a reverberatory forehearth where ore rich in sulphur is added. The low-grade matte formed in the forehearth flows back to the converting zone. In this proposal steps have not been taken effectively to prevent the high-grade matte from the converting zone from entering the forehearth and enriching the matte therein.
The present inventors have now discovered that it is possible in spite of the unsuccessful results when using the processes suggested above to obtain in practice an essential reduction of the copper content in the slag by following some important rules of which the most essential are the following:
1. The high-grade matte must not have any possibility essentially to enrich the low-grade matte.
2. There must be a controlled mixture of low-grade matte and slag flowing from any zone where high-grade matte is present.
3. The slag having been admixtured with the low-grade matte must not be withdrawn from the furnace until the matte prills contained in said slag have been given opportunity to settle.
Accordingly the process of this invention comprises the steps of charging and smelting in a first zone of an electrode furnace said sulphide ore containing material producing a matte having a higher grade of the said metal and charging and smelting in a second zone of the same furnace a material producing a matte having a lower grade of the said metal, the first mentioned zone being at a greater distance from the slag discharge point of the furnace than the second zone, and the second zone being at a greater distance from the matte discharge point than the first mentioned zone; causing the slag produced in the first mentioned zone to Flow through the second zone to the slag discharge point, while immersing at least one electrode into the slag in said second zone to a depth to cause a violent agitation of substantially all the slag entering the second zone and of matte of said second zone, said agitation causing mixing of said slag and said matte, the latter in form of prills, leaving the said mixture of slag and matte when then approaching the slag discharge point in a quiet condition, and controlling the rate of said slag-flow to cause substantially all the matte prills in suspension in the slag to have settled at least to a level lower than the slag discharge point before the slag reaches said point; substantially preventing the high-grade matte produced in the first mentioned zone from enriching the low-grade matte produced and present in the second zone, causing the matte produced in the second zone to flow into the matte in the first mentioned zone, and causing the matte of the first mentioned zone including the matte from the second zone to flow to the matte discharge point of the furnace.
Preferably the prevention of the high-grade matte of the first mentioned zone enriching low-grade matte of the second zone is obtained by using a threshold on the bottom of the furnace between said two zones and by maintaining the surface of the matte layer formed on the bottom of the first mentioned zone on a level lower than the lowest point of the upper surface of said threshold.
The objects, results and advantages of the invention will be understood by and apparent to those skilled in the art upon considering the following detailed description and explanation of a presently preferred embodiment of the invention and from the accompanying drawings, in which:
Figure 1 illustrates diagrammatically an electrode furnace suitable for the practice of the invention,
Figure 2 is a cross-section on the line 2-2 in Figure 1,
Figure 3 is a cross-section on the line 3-3 of Figure 1. In the drawings 10 designates a furnace, which in the usual manner is lined with refractory material.
The furnace is shown principally to have oblong, rectangular shape, which the inventors have found to be most suitable when carrying out the invention in practice. Through openings 11 in the roof of the furnace electrodes are introduced. The electrodes shown are of the so-called Soederberg-type and supplied with alternating current by variable transformers. The furnace is shown divided into two parts by a threshold principally designated 12. In the left part of the furnace (Figure 1), called zone 1, four electrode 1316 are arranged while two further electrodes 17 and 18 are placed in the right part, zone II, of the furnace.
The furnace is provided with one or several matte disadapted cooling medium, such as air or water.
charge openings 19 in the left (Figure 1) end wall, that is in zone I, and with one of several slag discharge openings 20 in the right end wall of the furnace, that is in zone II. To all the discharge openings chutes are connected in the usual manner. Outside the end walls diagrammatically shown conventional devices 21 and 22 are arranged for closing the matte and slag discharge openings. To the furnace conduits 23 and 24 are connected for withdrawing gases from the furnace. Furthermore charging devices are arranged which principaly have been designed 25 for zone I and 26 for zone Ii. Said charging devices are shown to comprise pockets from which pipes led through openings in the furnace roof (see especially Figure l and Figure 3).
The threshold, which generally has been designated 12, consists of an inverted arch as shown by Figure 2. Due to the high temperatures cooling pipes 27 preferably are arranged in the threshold, which pipes are fed with an In the drawing is shown a blast machine 28 for supplying cooling air to the pipes 27.
33 designates a floor arranged above the furnace for facilitating the operation thereof.
In operation material containing the sulphide ores to be smelted in the furnace are introduced from the charging pockets 25 into zone I, where the materials melt to form a slag layer 29 and a matte layer 30. The slag layer contains as stated above also matte in the form of matte prills and in form of matte in physical-chemical solution, the amount of the last-mentioned matte depending upon the grade of the matte in the under-laying matte layer 30. The slag discharge point of the furnace being in zone II, the slag will flow in direction thereof passing the threshold 12. When flowing in the direction of the threshold the matte prills suspended in the slag in zone I will settle towards the matte layer 39. By controlling the rate of the flow of the slag the inventors cause most of said matte prills to settle so that they are prevented to enter zone 11.
In zone II of the furnace the material charged is washing ore, that is material being poor in the metal or metals desired in the matte. in zone II will be formed a lowgrade matte and a slag, which when equilibrium is obtained will show a corresponding low content of valuable metals. The slag entering zone II from the zone I is thoroughly admixed with the slag produced in zone II to reduce the content of valuable metals. According to a feature of invention the immersion of the electrodes 17 and 18 is controlled to cause a violent agitation between the low-grade matte 32 and substantially all slag entering from zone I and as a result said entering rich slag will be brought into equilibrium with the low-grade matte 32 to reduce the content'of matte in physical-cheniical solution in the slag. When the slag leaves the electrode 18 on its way to the slag discharge opening 20 it still contains a certain amount of matte in form of matte prills. According to a special feature of the invention the rate of flow of said slag is controlled in relation to the distance between the electrode 18 and the slag discharge point as well as the agitation used to enable substantially all matte prills of the slag to settle to a level lower than the slag discharge opening, causing said prills to enter the matte layer 32.
In case the threshold shown in the drawings is used the level of the surface of the matte layer 30 should be maintained on a level lower than the lowest point of the upper surface of the threshold. The controlling of the level of the matte layer surface is dependent upon several factors such as how the matte is discharged through the discharge opening 19 and how much matte is being sup-' plied from the slag layer 29 of zone I and from zone II. Due 'to this fact it is important in operation to check the level of the surface of the matte layer 30. In practice this can be done by immersing an iron bar into the bath. The slag will adhere to the bar while substantially no material will adhere to the bar from the boundary between slag layer and matte layer which boundary has a range of about 1".
As stated above the inventors prefer to arrange a threshold on the bottom for dividing the furnace into the two zones I and II. It is, however, not absolutely necessary to arrange such a furnace provided that in another way it is arranged that high-grade matte 30 should not enrich low-grade matte 32. This can be made by arranging the whole bottom of zone II on a higher level than the surface of the high-grade matte layer 30. Furthermore it is possible to charge into zone II material containing such amounts of iron sulphur compounds to produce a pronounced flow of matte in direction from zone II to zone I as shown on the drawing.
It will be understood that several different factors influence the operation of the furnace and that said factors must be varied from case to case i. a. depending upon the materials disposed for charging the two zones 1 and II. It should however be stated that a proper control of said factors will give extraordinary good results, particularly when a threshold is used. The following Table I shows analysis results on slag and matte from a furnace which has been operated without a threshold and then with a threshold according to the invention. The analysis values are average values from operation of the furnace during two different weeks.
Table l Analysis of Analysis of slag matte Cu Ou SiO CaO Percent Percent Percent Percent Furnace Without threshold 35. 2 0.37 3S. 4 4. 6 Furnace with threshold 34. 9 O. 27 38. 5 3. 4
As will be seen by using a threshold it was possible to reduce the copper content of the slag from 0.37 to 0.27%, that is 27% improvement.
As stated above it is suitable to cause matte prills formed in zone I to settle to a level lower than the upper surface of the threshold 12 before the flow of slag passes said threshold. This result is obtained by controlling the rate of flow of the slag but also when building the furnace by placing the electrodes at a suitable distance from the threshold as well as in operation to charge in a suitable way as will be evident to anyone skilled in this art.
The charging of the material into zone It suitably can be carried out around the electrodes because in this way the material added will quickly smelt and come into intimate contact with material already molten.
As stated above it is important that the matte prills contained in the slag layer 31 of zone II should settle to a level lower than the slag discharge opening before the slag reaches said opening. This effect is obtained by controlling the rate of flow of the slag. When constructing the furnace this should be taken into account and in certain cases the distance between the last electrode and the slag discharge point may be considerable. To prevent the slag from freezing on its way from the electrode. to the slag discharge point it has been found suitable to heat the surface of the slag in any suitable manner such as by using a conventional oil burner or distributing carbon over the slag surface. It is also possible 7 to superheat the bath at the electrodes to prevent the temperature of the upper part of the slag layer to drop to a value where the slag freezes. Such a superheating is however not always suitable as it may cause a higher copper solubility of the slag.
On the drawing two electrodes 17 and 18 have been shown in zone II. It is however also possible to use in said one single immersible electrode and a bottom electrode. The shown system having two or more immersible electrodes is however most suitable in practice.
The Washing ore may preferably consist of iron pyrites or magnetic pyrites; but also other materials may be used.
Having now particularly described and ascertained the nature of our said invention and which manner the same is to be performed, we declare that what we claim is:
1. In smelting sulphide ores containing at least one metal of the group consisting of copper, gold, silver, nickel and lead for producing a matte; the steps of charging and smelting by means of electrodes in a first zone of an electrode furnace, said sulphide ore containing material producing a matte having a relatively high content of said metal and charging and smelting in a second zone of the same furnace by means of at least one further electrode a material producing a matte having a lower content of the said metal than the matte of the first mentioned zone, the first mentioned zone being established and maintained at a greater distance from the slag discharge point of the furnace than the second zone, and the second zone being established and maintained at a greater distance from the matte discharge point than the first mentioned zone; discharging slag from the furnace at the slag discharge point to cause the slag produced in the first mentioned zone to flow by gravity through the second zone to the slag discharge point, while immersing the said further electrode into the slag in said second zone to a depth such as to cause a violent agitation around said further electrode of substantially all the slag entering the second zone and of matte of said second zone, said agitation causing mixing of said slag and said matte in the form of prills around said further electrode; correlating the distance between the electrode nearest the slag discharge point and said slag discharge point and the rate of flow at which the slag leaves the furnace at said slag discharge point, such as to cause substantially all the matte prills in suspension in the slag to settle at least to a level lower than the slag discharge point before the slag reaches said point; discharging matte from the first mentioned Zone from the furnace at the matte discharge point, said matte discharge point being at a lower level than said slag discharge point and therefore causing the matte produced in the second zone to flow by gravity into the matte in the first mentioned zone, thereby substantially preventing the matte produced in the first mentioned zone from enriching the matte produced and present in the second zone.
2. A method as claimed in claim 1, comprising providing a threshold on the bottom of the furnace between said two zones and discharging matte from the furnace at said matte discharge point at a rate to maintain the surface of the matte layer in said first mentioned zone at a level lower than the level of the lowest point of the upper surface of said threshold, thereby preventing matte from said first mentioned zone from flowing into said second zone and enriching the matte of said second zone.
3. A method as claimed in claim 1, wherein the material smelt ed in the second zone is charged around at least one electrode in the second zone.
4. A method as claimed in claim 1, comprising corre lating the distance between the electrode of the first mentioned Zone nearest the second zone and said second zone and the rate of flow with which the slag leaves the furnace at said slag discharge point, such as to cause substantially all the matte prills formed from the material charged in the first mentioned zone to settle into the resulting matte layer on the bottom of the first mentioned zone before the slag reaches the second zone.
5. A method as claimed in claim 1, comprising correlating the rate of flow with which the matte is discharged from the furnace at the matte discharge point and the content of iron and sulphur of material charged to and melted in the second zone, and thereby the amount of matte produced in said second zone, to cause a pronounced flow of matte in the direction of the first mentioned zone.
References Cited in the file of this patent UNITED STATES PATENTS 596,991 Garretson Jan. 11, 1898 728,701 Garretson May 19, 1903 782,123 Garretson Feb. 7, 1905 981,850 Fleming Jan. 17, 1911 1,063,486 Wierum June 3, 1913 1,435,742 Saklatwalla Nov. 14, 1922 1,803,663 Carson May 5, 1931 1,873,800 Wejnarth Aug. 23, 1932 2,668,107 Gordon et a1. Feb. 2, 1954