US2209331A

US2209331A - Roasting process

Info

Publication number: US2209331A
Application number: US171177A
Authority: US
Inventors: Haglund Ture Robert
Original assignee: Individual
Current assignee: Individual
Priority date: 1936-11-12
Filing date: 1937-10-26
Publication date: 1940-07-30
Anticipated expiration: 1957-07-30

Description

July 30, 1940.

T. R. HAGLUND ROASTING:v PROGESS Filed Oct. 26, 1937 @ecol/ffy lgf.

Patented July 30, 1940 PATENT vOFFICE `v 2,209,331 VaoAs'rIfNc. raocass Ture Robert Haglund,` Stockholm, Sweden Application october ze, 1937, serial No. 171,177

' In Sweden November 12, 1936 14 Claims.

The present invention relates to processes for roasting or roasting and smelting of materials containing sulphides, such as sulphides and sulphide-ores. AThe processes are particularly adapted to the winning of the sulphur content of these materials in the form of free sulphur or as acomponent of a gas having a high content of sulphur dioxide.

In the present processes for the roasting of sulphides and sulphide-ores a high content of nely divided particles will easily vcause a sintering of the sulphide material to form lumps, which makes a control of the roasting procedure highly dilcult. When sulphide-ores are treated -in shaft-furnacesvit has also been difficult to use a charge having larger percentages of nely divided sulphide. These circumstances must naturally be regarded as a drawback in view of the fact, that the tendency is to employ flotation 2o -processes to an increasing degree for the working up of sulphide-ores, which processes as a.

and smelting of other finely divided or finely' comminuted sulphides, mattes, and sulphideores.

According to the present invention the roasting of the sulphide material is effected by dispersing the iinely divided sulphide material in an oxidizing stream of gas preferably consisting of oxygen or air enriched with oxygen. After the roasting, the material is either collected in a solid state or in the form of a molten bath. The amount of free oxygen supplied by the oxidizing gas may be so adjusted that the free oxygen is consumed without oxidizing more than part of the sulphur content of the sulphide material into SO2. The temperature is, according to one embodiment of the invention, raised to such a level that the sulphide of iron melts while in suspension. As soon as the free oxygen has been consumed by the formation of SO2, the iron sulphide reacts to a considerable degree with the SO2 under formation of free sulphur and oxide of iron. The oxidized particles may be separated from the gas in the form of a molten bath. In .3 order to facilitate this separation the velocity of (Cl. I5-9) v the gas is kept very low by employing an oxidizing gas with a considerably higher content of oxygen than that contained in ordinary air. 'I'his also means a more intensified evolution of heat, which is necessary to produce fusion of the dilcultly melting oxide particles. The amount of the oxidizing gas may be adjusted so that only part of the sulphur content is converted into SO2, but in certain cases the amount of oxygen may, for the purpose of intensifying the development of heat, be increased so that all or nearly all the sulphur in the resulting gas is obtained aS S02.

By an adjustment of the temperature conditions during the roasting in the described manner the advantage is i. a. obtained that a more complete oxidation will be effected in shorter time than otherwise is possible, even when working with a deficiency or only a slight excess of the oxidizing agent. It is in this way possible to obtain a gas which is richer in SO2 than that which is usually obtained, for which' reason the utilization of the gas e.` g. for thev recovery ofvsulphur may be made more economical. It has further been discovered that at temperatures higher than that at which melting of iron sulphide occurs, an oxidation of iron sulphide by SO2 with the formation of oxide of iron and free gaseous sulphur will take place. It is thus possible, by using a suitably adjusted amount of oxygen in the reaction, tocause the reaction to proceed in such a direction that SO2 which is rst formed will, at least partly, react with iron sulphide to form free sulphur. 'I'his oxidation may, if desired, also be carried out by means of extra supplied SOz.

In order to obtain the high temperature which is characteristic for the reaction process according to the invention, it is advisable toupreheat the gas to be used for the oxidation. The sulphide material may also be subjected to a preheating prior to its dispersing in the gas stream. The temperature may likewise be regulated by supplying and burning one or several additional combustible substances such as powdered coal, fuel oil, sulphur, carbon monoxide gas, etc. The supply of such additional combustibles is in many cases of great importance for attaining the temperature which is necessary for an initiating of the reaction process between the oxidizing gas and the sulphide material. The composition of the employed oxidizing gas is of particular importance for the reaction process. Although this gas, in certain cases when the products of oxidation are not separated in form of a molten bath,

A this showing,

may consist of air, use is preferably made of oxygen gas or air enriched with omen, in which latter case a high enrichment of the omen as a rule is preferable. By the use of oxygen or air highly enriched with oxygen instead of ordinary air, the following advantages are i. a.. obtained. The temperature at which the sulphide material will begin to oxidize will be lower than if air is used. Heat liberated in the oxidation process will not, or at least only to considerably less dearee be used for the heating of nitrogen, which constitutes the major part of ordinary air, and may therefore be better utilized for producing the desired temperature of the components taking part in the reaction processes, as well as of the products formed. The temperature conditions may e. g. in this way be easily controlled in such directicm that a complete melting of the material under treatment will take place. Since, furthermore, the volume of gas may be kept at only a fraction of that which is obtained when the oxidation is made by means of air, it is possible to separate at least a considerable part of the molten particles from the gas stream and to collect them in the form of a molten bath. It is possible to obtain a gas in the roasting having a very high content of S02, which thus i. a. may be used to great advantage for the production of free sulphur by a reduction of S02, e. g. ac cording to processes known per se. It is also possible to control the oxidation process when roasting sulphides of iron in such a manner that at least a considerable percentage of the sulphur content of the sulphides will be directly recovered as free .sulphur and as a component of a gas having a high content of sulphur.

My invention can be described in more detail by reference to the accompanying drawing which shows, in the form of now sheets, two embodiments of my process, wherein a sulphide ore is roasted with the production of free sulphur. In

Fig. l represents a reaction in which a suspension of a sulphide ore moves downwardly through three reaction zones and in parallel with a flow of oxidizing gases, while Fig. 2 represents a process in which the suspended particles of sulphide ore move downwardly in a tower in counter-current to a stream of gases which ascend the tower.

The two gures are provided with descriptive legends which are believed to make the respective processes represented therein immediately evident. In Fig. 1 the ore is introduced into Stage A in the form of a suspension at the top of the figure, together with oxygen or enriched air. An auxiliary fuel may be introduced to initiate the reaction or to supply additional heat, as indicated by the 'dotted lines which represent an optional procedure. Recycled SO: may also be introduced in Stage A. In this stage partial roasting takes place, the sulphide ore reacting with the oxygen with the formation of SO2. In Stage B which is shown just below Stage A, the temperature reaches the point at which the suspended particles of ore fuse and these molten particles react with the SO2 present to form sulphur and metal oxide. The suspended particles and gases then enter the Stage C where the reaction is completed, this stage being cooled, if desired, by the introduction of a cooling medium which may be molten sulfur or water, for example, as indicated by the dotted lines. If a. cooling medium is employed, the metal oxide formed in the process is collected as a solid and may be passed directly to a metal recovery operation. In another embodiment, indicated on the flow sheet in dotted lines, the temperature in Stage C is maintained above the fusion point of the metal oxide which then falls to the bottom and is collected in the form of a molten bath. The molten bath may be passed to a purification step for the removal of sulphide impurities. The gases recovered in Stage C are passed to a sulphur recovery step and from this step SC may be recycled to Stage A, as indicated in dotted lines.

The reactions which occur in the process represented in Fig. 2 arethe same as those which have -been already described. But in this process the suspended ore passes downwardly through a tower in counter-current iiow to SO2-containing gases which are introduced at the bottom of the tower, as shown. In this process oxygen is introduced into the tower, preferably between Stages A and B, passing upwardly and 'serving to produce SO2 by reaction with the ore. The SO: and sulphur formed in the process passes out at the top of the tower to a sulphur recovery step from which point SO: is passed to a recovery step, part being recycled to the bottom of the tower,

as indicated in the figure. The metal oxide which falls to the bottom of the tower is passed to a metal recovery step.

- The invention will be more fully described in thefollowing with` reference to some examples o f applications thereof.

First those forms of the invention will be described in which the sulphide material is led in parallel flow with the oxidizing gas. and for the sake of simplicity it is at first assumed that the sulphide material only contains sulphide of iron, e. g. pyrites or pyrrhotites. When the sulphide material is not present in a pulverulent state, it should first be finely ground. Fiotationmaterials (e. g. fines) may as a rule be used without further comminution, but if a very rapid and complete oxidation is desired, a further crushing of4 at least coarser particles in the flotation material may be advisable. If the sulphide material contains an appreciable amount of moisture, it should be dried before The distribution of the sulphide material in the oxidizing gas stream may be eected by mechanical or pneumatical means, the latter method being generally preferred. The whole or part of the oxidizing gas is preferably employed as a means of obtaining the pneumatic action and the distribution is effected in substantially the same manner as in the case of heating with pulverized fuel. In

order to effect or promote the initiation of the oxidation process some other more inflammable substance, such as fuel oil, powdered coal, sul-- phur, producer or natural gas, gas containing carbon monoxide, etc., may be injected together with the sulphide material into the gas stream, so as to produce suiilcient heat, after ignition, to start the oxidation process proper. When using oxygen of air highly enriched with oxygen, the additional combustibles will generate a higher temperature than would otherwise be the case.

At the same time the advantage is obtained, that such gas richer in oxygen will cause the oxidation of the sulphide material to begin at a lower temperature than when the oxidation is carried out by means of air.f A strong preheating of all or part of the oxidation gas as well as of the sulphide material will facilitate the starting of the oxidation process.

The stream of gas is now, by aforesaid means, given a temperature at least corresponding to I ing of the oxidized sulphide material.

As mentioned above, the roasting may be carried out in such a way that a melting of the metallic oxides formed will take place during the oxidation process. In connection therewith, the molten particles present in the gas stream are, according to one mode of procedure of the -inventlon, completely or partly separated from this in the form of a molten bath. In the oxidation of materials wholly or substantially consisting of sulphides of iron, these particles will, besides a possibly remaining content of sulphide, wholly or substantially consist of oxides of iron. l,Since the oxides of iron have a comparatively high melting point, it is, in the case of such a mode of procedure of the invention, important to impart such a high temperature to the gas stream that it will have a melting and not coolingaction on unmelted iron oxide. It is therefore preferred to use oxygen or air highly enriched with oxygen as al means of oxidation. In this way it is possible t0 obtain a low velocity of the gas stream, which is important for the separation of the particles in the form of a molten bath. The process may be carried out in a reverberatory furnace, "ash roaster or the like to which the sulphide material is supplied -by the a-id of oxygen through jet burners, in which case an easily igniting material which is supplied for a starting up of the combustion, e. g. powdered coal, may be supplied through the same burner. Part of the oxygen may if desired be supplied outside the burner. After ignition, the sulphide particles will rapidly become heated to such a temperature that a reaction takes place between these and the oxygen. If the sulphide consists of pyrites, SO2 is first formed, which diiuses in the gas and causes its temperature to rise rapidly, while the particles of pyrite, owing to the sulphur which evaporates from their interior will become heated somewl t slower. If the sulphide consists of FeS, a simu.- taneous formation of SO2 and iron oxide will chiefly take place. As soon as the iron sulphide begins to melt, the SO2 will also be able to a large extent to react with the iron sulphide with the formation of oxide of iron and free gaseous sulphur. By regulating the supply of oxygen, it is thus possible according to the result desired, to carry out the oxidation process under such conditions that either all or practically a-ll sulphur will be 'transformed into SO2, or else so that at least a considerable percentage of the sulphur originally combined as sulphides will be recovered in the form of free sulphur. If the process is to be carried out in such a way that a high sulphur content is obtained in the resultant gas, an extra supply of heat is generally required to accomplish the reaction; in such cases a larger quantity of additional combusti-bles in the form of powdered coal, oil or the like, is therefore supplied, than when the chief aim of these additions is simply the starting up of the oxidation process. A preheating of the oxidation gas and the pyrites is also in such cases to be recommended. Oxygen should furthermore in this case be used as oxidation gas.

As already mentioned the separation of the oxidized sulphide particles in the form of a molten bath may be facilitated by the simultaneous use of a gas rich in oxygen and by a combustion to SO2.,l of sulphur liberated from the sulphide material by means of a/regulation of the oxygen supply, instead of 'recovering the sulphur in a free s-tate. The oxygen content of the supplied oxidizing gas should in such cases be at least twice that of ordinary air and preferably still higher. When a high melting temperature is required or when-\the sulphide material has a high content of gangue, practically pure oxygen gas is preferably employed as oxidizing gas. Excess of oxidizing gas should as a rule be avoided. The

quantity of free Aoxygen added should preferably `be adjusted in such manner," that it will be completely or practically completely consumed. This will make the amount of gas smaller and formation of S03 will be avoided. In certain cases. particularly when as complete an oxidation of the sulphur in .the sulphide material as possible is desired, it is advisable to supply an excess of oxygen; in this case the content of free oxygen in the exit gas, however, should preferably not be allowed to rise higher than to correspond to less than half the content of SO2 in the exit gas computed on a volume base. and the oxygen content of the supplied gas stream are generally adjusted so that the SO2-content of the exit gas will exceed 1A, 4by volume of the gas; the Soz-content preferably being kept between 50 and 100 per cent by volume. It is however possible, particularly if the suspended particles are of not too small grain size,v to permit the SO2-content of the waste gases to sink to 25'per cent by volume. It is suitable, also in such cases when the roasting is conducted in such a manner, that a considerable formation of free sulphur takes place, to adjust the percentage of oxygen in the oxidizing gas in such manner that the exit gas, after the sulphur has been separated off, will contain at least 25 per cent by volume of SO2. If it is desired to conduct the oxidation process in such a way that a particularly high con-tent of S02 is obtained in the exit gas, e. g. 'T5-100 per cent, and if by using oxygen or air highly enriched with oxygen the reaction temperature obtained will become higher than would be desirable, it is possible, instead of using air less rich in oxygen, thus obtaining a lower SO2-content than desired, to dilute the oxidizing gas by returning part of the exit gas or SO2 recovered from this gas. Y

The richer the employed oxygen containing gas is, the smaller will be the volume of gas and the easier the precipitation of the oxidized sulphide particles in the form of a molten bath at the bottom of the furnace. To facilitate the separation, the jet burners are preferably directed downwards obliquely or at right angles to the molten bath. Such measures should as a rule be taken that the particles will have to travel a comparatively long distance before striking the molten bath; it is also advisable to let the gas stream with its suspended particles make a fairly sharp turn in the furnace. It is e. g. possible to direct the gas stream containing the particles, towards a rear wall of the furnace or against the molten bath near this rear wall, and to let the gas stream turn and sweep over the surface of the molten bath, and then remove it from the furnace on the same side as the burners are located, e. g. at some point below these latter. The molten iron oxide bath is preferably tapped at certain intervals. It is in this case advisable to subject it, directly from its state of fusion, to a granulation, e. g. by means of air, to effect The oxidation process* an oxidation of iron sulphide which may be mechanically mixed with or dissolved in the bath. As an alternative or inc'onnection herewith, the bath may, after cooling, besubiected to a sintering. If, on the other hand, the iron noxide bath also contains more valuable sulphides. e. g. of copper or nickel, it is advisable to let the bath slowly solidify and, after crushing to a finely divided state, subject it to notation. If the sulphide material contains a considerable amount of gangue, the molten bath will, besides oxide of iron, also contain a considerable amount of other constituents such as silica. Since for this reason, it will be less suited asa raw material for the production of iron, it is as a rule advisable in such cases to disregard its use for this purpose and instead to adjust the composition of the slag by means of slag-producing additions, so that unreacted (non-oxidized) sulphide is more easily separated out in the form of matte. In many cases, when a material with a high content of sulphide is used, it is also advisable to reduce the melting-point of the slag by means of slagproducing additions. This is i. af made in order to overcome the difiiculty of obtaining a refractory lining in the furnace which is not strongly attacked by slag rich in iron oxide. It is also possible to considerably reducejhe heat losses due to radiation if the melting-point of the slag is lowered. 'I'he slag-producing additions may consist of quartz, lime, iluorspar, etc., and may be directly added to the molten bath or else wholly or in part supplied in powder form disum, owing to the formation of silicate. is dis-- placed in favour of the formation of sulphur. If the sulphidic material besides sulphides of iron, also contains a considerable amount of sulphides of other metals such as copper or nickel, it is advisable to adjust the process of roasting in such a way that an incomplete oxidation of iron sulphide will take place, in which case these other sulphides will chieily enter as constituents in a matte which collects below the slag bath. When an incomplete oxidation of the sulphide material is desired, the length of the path which the sulphide material has to travel to reach the molten bath may be made shorter than in other cases. When this matte has a comparatively high content of iron sulphide, an enrichment of the more valuable components such as copper, nickel and precious metals, may be obtained by crushing the matte and subjecting it in above described manner to an incomplete roasting in combination with smelting. The main part of its content of iron sulphide will by this treatment become oxidized and. together with possibly supplied slag-producing additions enter into the slag, whereas the remaining sulphides will i'orm a matte.

If at a given reaction temperature, a reaction is possible between metallic sulphide and metallic oxide, formed by the oxidation of the former, with lthe formation of metal and SO2, the process may be adjusted in such a way, that the roasting will take place with the formation of metal. This will e. g. be the case when roasting materials containing copper sulphide. By regulating the supply of oxygen it is thus according to process possible to recover copper matte in the form of molten copper. In this case the oxidizing gas consists of engen or highly oxygen-enriched air and the quantity of oxygen should preferably be adjusted, so that it will be sufficient to convert the whole quantity of sulphur combined with the copper to SO2. Mattes which. in addition to copper. contain other metals may also be roasted according to the process with the formation of free copper. Materials rich in lead sulphide, such as galena, may according to the invention be treated similarly to copper sulphide in such a manner that lead is liberated and separated in a molten state.

If the sulphide material at the same time contains sulphides which are comparatively diiilcult to volatilize, e. g. sulphides of iron, copper, nickel, and components which are or, during oxidation, will give rise to more volatile products, such as compounds of arsenic, the process may be carried out in such a way that the non-gaseous oxidation products of the sulphides difficult to volatilize are, at least to a large extent, separated in the form of a molten bath, while the more volatile products will be separated from the gas during a later stage. If, according to modes of procedure described below, the non-gaseous oxidation products of the sulphides are separated in a pulverulent state instead of in the form of a molten bath, it is advisable to separate at least the major part of the pulverulent oxidation products from the gas at such a high temperature, that the compounds of arsenic will still remain in a gaseous state. If the gas contains a considerable amount of free sulphur the compounds of arsenic will be obtained in the form of sulphide upon separation from the gas. If a sufficient amount of oxygen is present in the gas arsenic oxide will, however, form.

Instead of separating particles from the gas stream at such a high temperature that a molten bath is formed, it is according to a mode of procedure of the invention, possible to separate the roasted particles in a pulverulent state. In this case the temperature conditions are preferably regulated during the roasting in such a way, that no melting of the oxides of iron formed during the roasting will take place. This procedure may preferably be carried out in such a way, that the sulphide material and the oxidizing gas are supplied in the upper part of a high tower, e. g.

.by means of jet burners, and allowed to move downwardly in parallel ow, the oxidation process being started by means of easily lgniting fuel additions. Alternatively, use may be made of an upward movement of the gas and the sulphide material, in which case the sectional area of the tower should be adjusted, in relation to the desired total amount of gas per unit of time, in such a manner that the velocity of the gas will suiiice for carrying with it the sulphide particles. Coarser particles, in the case of an otherwise upward directed iiow, may, if desired, be introduced at the top of the tower and be allowed to sink through the stream and are in this case withdrawn from the base of the tower. If these particles have not been completely roasted during their downward movement, an after-roasting pletely or chiey consisting of sulphides of iron, aq'ueous solutions, it is possible, by adjusting the suitable to employ the last mentioned process for 'the roasting in a vertical tower in combination with such a mode of roasting that at least a considerable amount of the sulphur will separate out in the form of free sulphur. It has, in fact, been found that, apart from the use of an extremely high temperature, the most favourable temperature range for a reaction between SO2 and iron sulphide with the formation of iron oxide and free sulphur is precisely limited, downwards by the melting point of iron sulphide and upwards by the melting of iron oxide. this temperature range yields of more than 90 per cent of the sulphur from the sulphide have been obtained in the form of free sulphur, whereas immediately below the melting point of iron sulphide only a slight formation of free sulphur has been ',demonstrated. Enriched air with a high oxygen content is preferably used as an oxidation gas, since this i. e. has the advantage that the particles, after the treatment in the tower, may be more easily separated and the condensation of the sulphur highly facilitated. In certain cases it is however possible to use a gas poorer in Oxygen, or an oxygen gas diluted with water vapour or SO2. To regulate the temperature it is thus possible to inject water or introduce SO2-gas into those parts of the tower where the temperature has a tendency to become too high. In lthose parts of the tower where the reaction has proceeded to such extent that no free oxygen is avallable, the temperature will show a tendency to sink; by supplying oxygen to these parts it is possible again to increase or maintain the temperature. If desired, the temperature may, at the beginning of the reaction process, be allowed to exceedthe melting point of the iron oxides, but should in this case, after the free oxygen has been consumed, be reduced below said temperature. When employing such a treatment in a tower it is as an alternative also possible to conduct the process in such a manner that the sulphur of the sulphides will completely or chiey become oxidized to SO2.

A rapid cooling of the gas stream with the* particles suspended in it, from a temperature exceeding the melting point-of iron sulphide down to such a temperature that a re-forming of sulphide by a reaction between sulphur and iron oxide is as far as possible prevented, is advisable in such cases, when it is desired to recover sulphur in a free state. If desired 'the particles may as an alternative, wholly or in part, be separated from the gas stream, e. g. in settling chambers, before the temperature of the gas stream has reached a level below the melting point of the iron sulphide. A rapid cooling may be effected by injection of solid or uid sulphur or by means of water. The cooling is preferably not accomplished until the gas stream has left the tower. When the gas and the sulphide material are supplied at the top of the tower and move downwardly, the cooling may, as an alternative, 4oe effected by injecting the cooling media into the lower part of the tower. If water is used as a cooling medium, the quantity of water may be adjusted so that the sulphur contained in the gas will also condense and be removed with the water or with the water vapour formed, in which latter case it is recovered by a condensation of this latter. If the sulphur is removed with the water together with the roasted sulphide material, it is, if necessary, possible to separate it by a flotation process. If the cooling is effected by means of Within quantity of solution, to utilize the sensible heat of the gas stream and its particles, for concentrating the solution by vaporization. Sea water may e. g. be evaporated by ald of waste heat of this kind for the recovery of salts dissolved in the water.

If the cooling is effected by sulphur or a quantity of water adjusted in such a way, that the gas still contains all or a substantial part of the sulphur in the form of vapour, the solid particles are separated from the gas, e. g. in settling chambers or by Cottrell precipitation, before the gaseous sulphur is condensed. The sulphur is then condensed out, the heat of condensation preferably being utilized for the production of steam. It is in this case suitable to employ coolers in -which the production of steam is effected at such \a pressure that the temperature of the cooling tubes is kept either below 160 C., e. g. at about 125 C., or else above 250 C., for the purpose of preventing the separation of sulphur in a viscous form. Particularly in such cases where the gas is cooled to a temperature above that at which condensation begins by means of sulphur injected in the gas in solid or fluid form, it is advisable to eifect the condensation step-Wise, e. g. in two or three stages in each of which the sulphur is partially condensed. y In the case of a three procedure itis suitable to collect the first condensed sulphur, containing the largest quantity of impurities, separately, and to subject it toga special purifying process. The subsequently separated fraction is utilized for cooling the gas, whereas the third fraction as a rule is of a marketable quality without any further treatment.

When copper sulphide forms par-t of the material which contains iron sulphide, and this material is subjected to a roasting in a tower according to the procedure described, for the purpose of recovering free sulphur, the roasted material will still contain the copper in the form of sulphide. The copper may therefore be recovered from the particles separated from the gas by means of a :dotation process. This also applies for' some other sulphides, such as nickel sulphide. Magnetic nickel sulphide ores and concentrates may therefore, especially if the nickel is present in the form of free pentlandite grains, after being roasted for the recovery of sulphur according to the described procedure, with advantage be subjected to a treatment for the recovery of nickel and copper. This may e. g. be done by flotation or chlorination, e. g. with gaseous chlorine, of the nickel sulphide and a following leaching. The chlorination process is to be preferred to a otation in the case of ores in which the nickel sullphide minerals are intimately associated with the magnetic sulphide minerals Roasting in connection with the separation of the solid particles in a pulverulent state may, if it is desired to obtain copper, nickel etc., also be effected in such a manner, that a certain amount of iron sulphide will also be contained in the roasted material, which latter may then be subjected to a smelting in a reverberatory furnace for a recovery of the more valuable metals in the form of components of a matte.

According to a further mode of procedure of the invention, it is possible to recover sulphur by the roasting of materials containing sulphide of iron, while'these in a finely dividedr state are falling counter-currently to the oxidizing gas in a tower. From a thermal point of view such a procedure offers great advantages. The procedure is particularly applicable to the treatment of sulphide materials with not too high a content of extremely nely divided particles. 'Ihe preheating and, in the case of pyrites, also the driving oil. of sulphur takes place in the upper part of the tower. If this preheating and driving oif of sulphur should be effected exclusively by means of the sensible heat ofthe gas stream, this would necessitate the use of a very large quantity of gas, which, in turn. would result in a 10W-sulphur content in the exit gases. Supplemental heat is therefore preferably supplied to the upper parts of the tower by combustion, e. g. by introducing oxygen at one or more points in the upper part of the tower for the combustion of sulphur, or by supplying combustible substances either separately or in combination with an oxygen containing gas, which substances will produce heat by reaction with the SO2 present in the upper part of the tower or with the oxygen supplied. Such combustible substances may e. g. consist of powdered coal, fuel-oil, gas containing carbon monoxide, hydrocarbons, producer or natural gas, hydrogen, etc. If powdered coal is used, this should preferably be so flnely divided that it will not sink in the gas stream to any appreciable degree. It is also possible as an alternative to add powdered coal of such a grain size that the grains will sing in the gas stream, but the powder should in such cases preferably be supplied from the uppermost part of the tower, e. g. in admixture with the powdered sulphide material. This latter material is mechanically or pneumatically dispersed into the gas stream. In the latter case the dispersing may be effected by means of a gas which contains e. g. carbon monoxide, and which may be utilized for convert- -ing the SO2, forming part of the exit gas, to sulphur, or else by returning part of the escaping gas, preferably after the sulphur has been removed by condensation. For the purpose of temperature control in the furnace, the major part of the oxygen is preferably introduced at di'erent levels of the middle sections of the tower, whereas SO2-gas, with or without admixture of free oxygen, is preferably introduced at the base of the tower. The SO2-gas is heated by the hot particles and will, after having attained a suillciently high temperature, react with the iron sulphide remaining in the grains. A content of free oxygen in the SO2-gas will contribute to make the oxidation process more complete. A preheating of the SO2-gas will also help this to more rapidly attain the temperature necessary for the reaction. A supply of SO2-gas at the base of the tower will also contribute to a displacing of the equilibrium in the upper part of the tower in favour of the formation of sulphur. Instead of adding SO2, or simultaneously with such addition, it is possible to supply water vapour, e. g. by spraying water on the particles which have collected in the lower part of the tower. A mixture of water vapour and oxygen may also be used to advantage. Instead of oxygen it is possible to use either air enriched with oxygen or ordinary air, although this will make it more diiiicult to recover sulphur and SO2 from the waste gases. Part of the sulphide material may instead of being introduced at the top be introduced at lower levels of the tower.

'I'he roasted sulphide material withdrawn from the base of the tower may be converted by sintering to a form suitable for its use as iron ore. If the roasted sulphide material contains sulphides of copper, nickel, etc., it may be worked up for recovery of these metals, e. g. in substantially the same manner as already described.

'I'he gasesl escaping from the tower are freed from entrained particles, e. g. in settling chambers. Volatile compounds of arsenic which may possibly be present in the gas are condensed out and preferably separated od, before the condensation of sulphur takes place. The cooling of the gas stream and separation of the sulphur content of the gas may be effected in substantially the same manner as described above. As, however, it is not necessary in the case of this procedure, to cool the gas extremely rapidly. it is in this case possible as an alternativeto carry out the ilrst part of the cooling with a view to utilizing the heat for the productionof steam. After the sulphur has been condensed out, all or part of the residual gas may, if desired, be returned directly to the base of the tower in the form of an SO:- containing gas. It is however, as a rule. advisable to remove other constituents, e. g. a possible nitrogen content, from that part of the gas which is to be re-circulated in the process, before the gas is returned to the tower. 'I'his may be done by dissolving SO2 in water or other solvent and then expelling it from this. Even in cases, when the SO2-content of the gas is not, either wholly or in part, returned to the process, it is advisable to subject it to a purification, before utilizing it for the production of sulphur according to known methods or for other purposes. Reducing agents for the SO2 may, if desired, be supplied to the gas immediately after it has left the tower and before it has been cooled down.

In certain cases it is advisable to divide the sulphide material into different grain classes and to treat each of these separately, the most ilnely divided particles being preferably treated in a parallel ilow.

I claim:

1. A process for the production of sulphur from a sulphide of iron-containing-material, comprising bringing said material in the form of ne particles in suspension in an SO: containing gas and regulating the composition of the gas and the temperature, so that the suspended fine particles fuse and at least a considerable amount of sulphur is formed by the reaction, in the absence of free oxygen, between the suspended molten sulphide and the SO2.

2. A process for the production of sulphur from a sulphide of iron-containing-material, comprising oxidizing line particles of said material while in suspension in a stream of a gas originally containing free oxygen, regulating the amount of said oxygen in said gas in such manner that only a part of the sulphur content of the sul"` phide material is oxidized to SO2, and, in order to produce sulphur, continuing the oxidation of sulphide of iron by means of SO2 at a temperature at which suspended sulphide particles are at least partly in a molten condition.

3.V A process for the production of sulphur from a sulphide of iron-containing-material, comprising suspending and oxidizing fine particles of the sulphide material in a stream of a gas, which originally contains at least a considerably higher percentage of free oxygen than ordinary air, reg-I ulating the amount of oxygen in said gas in such manner that said oxygen is suillcient to oxidize a part only of the sulphur content of the sulphide material to SO2, and, in order to produce sulphur, continuing the oxidation of the suspended sulphide of iron by means of SO2 at a temperature at which the suspended particles contain sulphide of iron in a molten state.

4. A process for the production of sulphur from a sulphide of iron-containing-material, comprising suspending and oxidizing ne particles of the sulphide material in a stream of a gas, originally containing at least a considerably higher content of free oxygen than that of ordinary air, initiating the oxidation by burning in the gas of a material which ignites easier than the sulphide material, regulating the amount of free oxygen in said gas in such manner that said oxygen is sufficient to oxidize a part only of the sulphur content of the sulphide material to SO2, and producing free gaseous sulphur by continuing the oxidation of the suspended sulphide of iron by means of SO2 at a temperature at which at least part of the iron sulphide content of the suspended particles is in a molten state.

5 A process for the production of sulphur comprising suspending and oxidizing ne particles of.

a pyrite material in a stream of a gas, which originally at least mainly consists of free oxygen, regulating the oxidation, so that the free oxygen is consumed when only part of the sulphur content of the pyrite is oxidized to SO2, continuing the oxidation by means of SO2 at a temperature at which at least part of the remaining suspended sulphide is in a molten condition, and regulating both steps of the oxidation so that gaseous sulphur is formed during this latter oxidation in a quantity exceeding half the original sulphur content of the pyrite.

6. A process for the roasting and smelting of ne particles rich in sulphide of iron, comprising suspending and roasting the sulphide material in a gas containing free oxygen, regulating the amount of free oxygen so that only part ofthe sulphide of iron is oxidized to form SO2 and regulating the temperature so that the oxidation continues by reaction between SO2 and sulphide of iron converted to a molten state under formation of gaseous sulphur and oxide of iron, at least partly separating the oxidized product from the gas while in a molten condition under the formation of a molten bath, said bath being at least partly in the form of an oxide slag mainly consisting of oxide of iron and also containing sulphides as impurities, tapping said oxide slag and granulating the slag while in a fluid condition by treatment with an oxidizing gas, for the purpose of lowering the sulphur content of the slag.

7. A process for treating materials containing sulphide of iron and a sulphide of at least one of the metals copper and nickel, comprising suspending the sulphide material in form of 'fine particles in an oxidizing gas originally containing free oxygen in amount substantially greater than that contained in air, and submitting the sulphide material while in suspension to an incomplete roasting while regulating the temperature so that the roasted particles will melt, and collecting at least part of the oxide and the sulphide-containing particles while still in a molten condition into a molten bath, and regulating the slag forming components of the suspended material so that the oxide component of the roasted particles collected in the bath will be rich in oxide of iron, the volume of gas employed being substantially less than that required when air is used in the process, whereby collection of the roasted particles is facilitated.

8. A process for roasting of sulphide material, mainly consisting of a sulphide of at least one of the metals copper and lead, for the purpose of recovering the corresponding metals, comprising suspending and oxidizing the sulphide material in a nely divided form-in a stream oi a gas, obtained by mixing a gas at least mainly consisting of free oxygen with part of the resulting SO2-containing roasting gas, regulating the oxidation so that formation of SO2 and molten metal takes place, and collecting at least part oi the suspended material while in a molten condition in the form of a molten bath.

9. A process for producing sulphur from sulphide of iron-containing-material, comprising suspending the sulphide material in the form of iine particles in a stream of an oxidizing gas, which originally has a considerably higher content of free oxygen than that of air, regulating the amount of free oxygen and the development of heat so that the free oxygen will be consumed to form SO2 while producing an incomplete oxidation of the sulphide material, continuing the oxidation of sulphide of iron by means of SO2 to form elementary gaseous sulphur at a temperature maintained sufficiently high to keep the iron sulphide in a molten state but below the melting point of oxide of iron.

10. A process for producing sulphur, comprising suspending ne particles of a sulphide of iron-containing-material in a stream of a gas originally containing free oxygen, roasting the suspended material while at least mainly conducting the gas and the sulphide particles in parallel ow, regulating the total amount of free oxygen and the development of heat so that the oxygen is consumed to form SO2 while only incompletely oxidizing the sulphide material, and so that oxidation of sulphide of iron will continue by means of SO2 at a temperature at which said sulphide is in a molten condition; and thereafter lsuddenly cooling to such a temperature, that no considerable :je-formation of sulphide of iron will occur.

11. A process for producing sulphur, comprising suspending ne particles of a sulphide of iron-containing-material in a stream of a gas originally containing free oxygen, roasting the suspended material While at least mainly conducting the gas, and the sulphide particles in parallel ilow, regulating the total amount of free oxygen and the development of heat so that the oxygen is consumed to form SO2 in an incomplete oxidation of the sulphide material; continuing the oxidation of sulphide of iron by means of SO2 at a temperature at which said sulphide is in a molten state, and thereafter cooling the resulting gases by contact with sulphur.

12. A process for producing sulphur, comprising suspending fine particles of a sulphide of iron-containing-material in a stream of a gas originally containing free oxygen, roasting the suspended material while at least mainly conducting the gas and the sulphide particles in parallel ilow, regulating the total amount of free oxygen and the development of heat so that the oxygen is consumed to form SO2 while only incompletely oxidizing the sulphide material; and continuing oxidation of the sulphide of iron by means of SO2 at a temperature at which said sulphide is in a molten state, and thereafter cooling directly by contact with water.

13. A process for roasting sulphide of ironcontaining-materials comprising heating and oxidizing the sulphide material while in the form of line particles falling in a tower against an upwardly directed ow of a gas, introducing a stream of a gas rich in SO: in the lower part of the tower and mixing said gas, at least at one level of the tower, with a gas mainly consisting of free oxygen, the temperature in at least one part of said tower being maintained above the melting point of iron sulphide.

14. A process for roasting and smelting comprising suspending ilnely divided particles of an iron sulphide-containing ore in a gas originally containing free oxygen in amount substantially 10 greater than that contained in air, heating the