US2803532A - Method of agglomerating and sintering granular lead sulphide - Google Patents

Description

United States Patent I METHOD OF AGGLOMERATING AND SINTERING GRANULAR LEAD SULPHIDE Bjiirn Erik Anders Berglund, Bromma, and Karl Giiran Gtirling, Nils Berti] Lindvall, and Sven Johan Wallden, Skelleftchamn, Sweden, assignors to Bclidens Grnvaktieboiag, Skelleftehamn, Sweden, a joint-stock company limited of Sweden No Drawing. Application February 6, 1956, Serial No. 563,452 Claims priorit application Sweden June 20, 1951 11 Claims. (Cl. 75-5) This is a continuation-in-part of our application Serial No. 293,213 of June 12, 1952 now abandoned.

The present invention relates to a process of sintering and agglomerating high-grade concentrates of lead sulphide minerals, containing the lead substantially combined as sulphide.

The raw material generally used for the production of lead in the lead plants, is galena. Ore in the form of large pieces is seldom used but is instead crushed and concentrated at the mine. By the modern flotation concentration methods now in use, it is possible to exceed the content of 50 60% lead and sometimes reach a value of about 80%. At this value the product comprises a substantially pure galena, the composition of which is 13.4% sulphur and 86.6% lead. A great part of the ore, which is now treated by the lead plants, is highly concentrated product with lead contents exceeding about 55%. In order to produce lead from the concentrates it is usually necessary to convert the fine granular materials into a sintered or agglomerated form, viz. subject the materials to a heat treatment in the presence of oxygen on a grate, while simultaneously removing a substantial portion of the sulphur contained in the product in the form of S02.

In Trans. A. I. M. E., vol. 159 (1944) p. 81, Some experiments on sintering lead sulphate products it is stated that a material subjected to sintering, having the usual gangue components and containing more than about 50% lead, tends to fuse during the sintering operation with the result that the grates and the charge are clogged. The result of this is that the air does not come into sufliciently good contact with the sulphides at the roasting temperatures so that the removal of sulphur is thereby small. For the lead concentrates mentioned above, containing about 55-80% Pb, it would be necessary to add diluents thereto and thus decrease the content of lead to about 50% or less. Although in the article this method is stated to result in economical disadvantages and is therefore not an ideal one, the method is used all over the world.

The most important disadvantages are:

1. The expense of providing barren diluents. 2. The diluents lower the blast furnace capacity. 3. Increased slag losses.

Moreover the heat consumption for smelting increases.

In the article it is also stated that experiments conducted in order to desulphun'ze high-grade lead concentrates by means of methods difierent fromsintering do not appear to be successful. Thus, it is stated that flash roasting converts most of the lead sulphide into lead to the diificulties in effecting sintering. These difliiculties tend to rise very rapidly above a lead content of 55%.

The reason for this is that when sintering by the present sintering methods, i. e., in which the charge is prepared by mixing the different components to a fine granular mass having a suitable content of water and with lead sulphide material charges having contents of lead ex; ceeding the value of about 55 large amounts of lowmelting phases are formed which render it difiicult to perform the sintering operation technically. As little as about 50% Pb in the charge will cause considerable difliculties in the sintering operation. The most important difiiculty is that low-melting products deriving from easily fusible phases will flow down to the lower parts of the charge and between the bars of the grate and will also adhere to said bars, whereby the flow of the air through the charge subjected to the sintering is obstructed. This results in additional work, i. e. to clean the bars and collect the molten material flowing down through the spaces between the bars. As mentioned above it will also result in unsatisfactory air passage so that an insufiiciently desulphurized agglomerate is obtained.

The reason for the formation of such great amounts of lead when sintering high-grade lead concentrates will be clear when studying the equilibrium investigations of the system ib-S-O, such as disclosed by Schenk, Metall und Erz 1926, number 15, pages 407420: Experimentelle und theoretische Untersuchungen uber die Rostgleichgcwichte beim Blei. A constitutional diagram of the Pb-SO-compounds in which the temperature and SOz-pressure are varied shows that it is necessary to reach the temperature of 300 C. or more in order to eliect the utmost possible desulphurization. To avoid a precipitation of lead at such high temperature the S02- pressure should be higher than about mm. Hg. In sintering it is possible to recirculate the waste gas to increase the SOz-pressure. However, by such a step it is not possible to obtain the said necessary minimum pressure.

Heretofore it has not been technically possible to perform a sintering of very lead-rich charges. It has been necessary to mix such concentrates with lead-poor or inert materials so that the lead contents of the sinter charge are appreciably below 50%. The reason is that the low-melting Pb-O-S-phases, which are formed, clog the charge and the grates and make the gas-passage more diiiicult. Owing to the high local temperature of the combustion zone and the low SOz-pressure, lead in considerable amounts is formed. This metal may trickle through the charge and solidify in contact with the grates or may drip down to the wind boxes. Such diificulties make the process impossible. The main object ofthe sintering is to bring down the sulphur content of the agglomerate to proportions suitable for the reactions between PbS and PbSOt+PbO, with respect to the sidereactions. Preferably the content of the sulphur combined as sulphate should be as low as possible. It has been established that the reactions between PbS and oxygen cannot be performed in solid state with desirable reaction speed and desirable result. At temperatures below 790 C. basic lead sulphates are the final products (see diagram by Schenk). If the temperatureis increased above this point, a range is reached in which low-melting eutectics exist. Consequently it is necessary to learn to control these difiiculties. At temperatures around or above 800 C. the roast reactions lead to :PbO and Pb (see Schenk). First at temperatures around ESQ-900 C. the speed of the reactions resulting in Pb is appreciable. Therefore it is not advisable to heat the reacting charge to temperatures above 850. C. forextendedperiods of,time. The controlling of the temperature is facilitated by the partial melting, starting at about 800 r C. Therefore it'is of deciding importance to find a method to control the inevitable melting process. Sintering is industrially performed today in such a way that the lead compounds are diluted with slag components of high melting point, said components forming a highmelting skeleton, which prevents low-melting phases to run together. Since it is intended to prepare a charge having a lead content of appreciably more than 50% and it is not desirable to dilute the lead-rich charge with material poor in lead, there is no other diluent available than return sinter and dust from the process. In finely divided state these materials will react with the lead sulphide. Coarser return sinter particles, however, will only react on the surface and the core remains intact. Ifit were possible to apply the concentrate and other fine-grained materials on the surface of such coarse particles, the sintering reactions should take place in a thin surface layer and it might be possible to solidify the partially molten reaction products by air-cooling before they drip from the core.

The object of the present invention is to provide a process by which it isv possible to remove sulphur from the high grade lead concentrates containing at least about 55% lead to a value preferably not exceeding about A second object of the invention is to provide a desulphurization process, Without easily fusible products including elementary lead being formed and flowing downwardly through the charge or adhering to the bars of the grate, and thereby diminishing the supply of air.

In addition to lead, the concentrates that are to be used according to the present invention, contain sulphur as a second main component. The sulphides act as a source of fuel in the sintering operation. In the concentrates that may be present a gangue consisting of quartz, silicic acid, silicates, aluminium oxide, oxides of alkaline metals and alkaline rare earth metals, metal sulphides, such as zinc sulphide, iron sulphide, pyrite, etc., may be present. Examples of concentrates, which may be used according to the invention, are revealed in the examples stated below. The concentrates that are to be used according to the present invention are in a very fine granular form, by which is meant that the particle size is generally below about 0.1 mm. More preferably the particle size distribution of the concentrates is such that at least 90% of the material will pass a screen of 240 mesh. For the ball rolling step it is of importance that the lead sulphide material is in a fine granular state. Thus the ball rolling is favoured by employing as fine a granular material as possible.

In its broadest form the invention resides in that particles of inert lead oxide containing material, preferably derived from a preceding sintering or agglomeration step and showing an average particle size of substantially above about 5 mm. but not more than about 30 mm. particularly not more than about mm. are provided with a coating of the lead sulphide material, viz. the high-concentrated fine granular lead sulphide material, so as to form a ball structure charge. The coating of the particles or pieces is effected in such a way that the balls will consist of an inner core of lead oxide containing material, particularly desulphurized, agglomerated material, and a shell of said fine granular lead sulphide materialin a layer of thickness of preferably about 1-3 mm. surrounding said core. Said layer should be thin so as to allow oxidizing gas to come into excellent contact with said sulphide material of the shell.

The use of such thin shells of the lead sulphide material to be treated enables a rapid desulphurization of said shells. By employing such shells there will not be liberation of sufiicient heat to bring the core of the balls to fusing temperatures. Since the core does not contain any substantial amount of sulphides it is not necessary to heat said core to a desulphurizing temperature.

The SOz-containing gas formed in the sintering reaction h diffuses through said shell, causing high local SOz-pressure.

Due to the thin shell the risk that easily fusible phases including lead, formed within the shell, will flow together and trickle down, clogging the charge is diminished. Owing to the suggested measure the core of such a ball will. have a. cooling effect on the shell during the reaction between the lead sulphide and the oxygen, whereby the oxidation of the lead sulphide of the shell will be substantially finished before the core consisting of oxidic material has become completely heated through and the head part of the core has reached fusing temperature.

In the preparation of the balls, devices well-known in the art are suitably used, c. g. rotating drums, cylinders, discs, etc. The oxidic material used for the core is placed in said device and the fine granular lead sulphide material is added thereto in portions or continuously while simultaneously moistening the mass. The conditions are controlled so as to form round balls in a manner known to everybody skilled in the art. In order to cause the lead sulphide material to adhere to the surface of the pieces of lead oxide and to effect the ball rolling it is necessary to add moisture or water in operation. Of course, the amount of water must not exceed that amount at which the fine granular material forms balls per se. The addition of water is about 5% calculated on the whole charge. The amount of lead sulphide material, which is added to the lead oxide containing material, is dependent on the content of lead in the lead sulphide material and on the gangue therein. For a lead sulphide material, containing about 55% Pb, viz. the lower limit for the material used in the present invention, an amount of oxidic material of about 30% calculated on the whole charge is used. For increasing the content of lead in the lead sulphide material the amount of lead oxide containing material must be increased in view of the fact that the lead sulphide material containing higher lead content will more readily form low melting phases and precipitate lead during the sintering. For a content of lead in the lead sulphide material of about lead it is suitable to use a content of lead oxide material of about 60%. Material of higher lead oxide content may also be used, if the impurities are particularly capable of forming low-melting phases easily. A man skilled in the art is capable of estimating how much lead oxide containing material should be used in the charge within the stated limits of about 35-60% in order to control the formation of easily fusing material and elementary lead being formed in a subsequent sintering operation.

According to a special embodiment of the present invention it has appeared to be particularly suitable to coat the pieces of lead oxide containing material with a thin layer of calcium carbonate or lime rock dust, or a d'lfierent heat consuming material, e. g. other carbonates such as magnesium carbonate, or dolomite, hydrates, crystal Water containing salts or similar compounds, prior to applying the shell of lead sulphide material. This step is recommended particularly for high lead content in the lead sulphide material, e. g. about 7080% Pb. The advantage of using such a heat consuming layer, preferably consisting of calcium carbonate, resides in that more concentrate can be applied to the pieces of lead oxide ma terial without any risk that the formation of low melting phases cannot be controlled. This discovery is particularly surprising and enables further economical advantages in performing the process according to the invention.

It is also within the scope of this invention to apply a material, containing lead oxide, e. g. lead oxide dust derived from filter devices, such as finely dispersed lead oxide and lead sulphates of the kind precipitated by electrostatic filters and fines from crushing the sinter as well as slimes, skimmings, etc.,to particles or pieces of lead oxide materials; Preferably such a layer is applied to the oxidic particles prior to applying the layer of lime rock dust.

According to the invention the balls consisting of an inner oxidic core having a surrounding shell of lead sulphide material and obtained by ball rolling in the described manner are spread on a grate of a suit-able sinter apparatus. Such an apparatus comprises an endless belt forming a web composed of a number of grate bars, on which web the material to be agglomerated is placed in form of a layer. This layer may have a thickness of about -30 cm. preferably not more than aboutSO cm. and not below about 5 cm. After having spread out the material to be sintered on the grate the upper surface of the same is ignited, i. e. by means of a burner fed with oil, gas or coal powder. A stream of air is suctioned through the charge, causing the high temperature combustion layer to proceed downwardly against the grates. The combustion gases formed preheat the underlying charge and the combustion air is preheated by the already sintered layer, while simultaneously cooling the layer. In the sintering operation it is an object to provide such conditions as will not cause any harmful fusing. If harmful amounts of low melting phases are formed on the surface of the balls this will result in the flowing of low melting products downwardly through the charge to adhere to the grate bars. As a result the supply of air for the desulphurizing will be decreased.

Generally sintering machines of the type Dwight Lloyd are used. Such machines are well-known to everyone skilled in this art. They consist of a number of flat pans having a bar grate at the bottom and which are combined to a forwardly travelling belt. The charge is fed continuously from a hopper to the grate, on which the surface is ignited by means of a flame. One or more wind boxes beneath the pan-s are connected with a fan capable of causing a sufiicient stream of air to be suctioned through the charge. At the outlet end of the sintering machine the sintered product, if not adhering to the grates, is thrown off automatically and if desired sprayed with water for cooling and then delivered to a crusher over a screen, in which the return material is separated. Another suitable apparatus for sintering is Rolfsens sintering machine according to the U. S. Pat. No. 2,193,698 (1940) and 2,493,421 (1950) with the watercooled grates arranged in form of a truncated con-e. Other suitable apparatus are large flat pans, in which the charging, combustion and throwing ofr occur discontinuously (Greenawalt etc). According to the invention the prepared char-ge consists of balls of oxidic material surrounded by -a shell of lead sulphide is applied to such a sintering apparatus. Air is then caused to pass through the same, after the charge has been ignited by means of a flame. After the ignition the surface of the balls will reach the necessary reaction temperature of 800 C. and more very rapidly and the reaction will proceed towards the core of the balls while simultaneously desulphurizing the outer layers of the shells. Due to the thinness of the layers the reaction will proceed very rapidly and will be finished before the core has been heated through. Said core will thus have a cooling effect on the shell and will consume a portion of the heat thus formed in the reaction. Moreover, the lead forming reactions will not have sufiicient time to proceed during the sintering due to the rapid oxidation reaction. Inasmuch as the charge has become porous because of the special method of preparation, it is not difiicult to control the amount of air passing therethrough. If there are any signs of the formation of low melting phases the amount of air passing the sinter charge is increased, so that a cooling of the surface layerof the balls is effected. If, on the other hand, the sintering temperature tends to become too low, so that the'desulphurizing effect ceases, the amount of air passing through the sinter charge on thegrate is decreased. On

investigation of the sinter it has been found that the precipitation oflead and low melti-ngaphases is very low aso sae and is generally below about 1% of the sinter. The in:

vention involves rapidly bringing the surface of the balls to the necessary reaction temperature of at least about 800 C., allowing the reaction to proceed through the thin layers of the balls very rapidly and cooling the balls very rapidly. Due to the ball structure of the charge material the oxidizing gas, viz. normally the air, can pass said charge very easily at a large velocity and simultaneously imp-art a cooling effect to the charge. The spaces between the balls oifer passages, through which the air can pass easily without too much power being consumed. The layer of lead sulphide on the surface of the lead oxide material is moreover relatively thin so that the penetration of oxygen into the interior of the shell and the diffusion of the sulphur dioxide formed will be improved. It is substantially the above mentioned factors thatwill be responsible for the particular advantages in carrying out the sintering operation.

According to the invention a portion of the sintered product is recycled and used for subsequent sintering operations. According to a suitable embodiment of the present invention the sintering is carried out by suctioning air through the charge. In this process it is suitable to arrange a number of wind boxes beneath the sintering belt and control the pressure of said wind boxes so as to maintain the suitable stream of air according to the temperature of the charge and according to signs of beginning formation of low melting phases. In the present process it is generally suitable to increase the flow of gas through the charge towards the end of the sintering.

According to the present invention it is possible to produce a sinter product, containing about 70-80% Pb and about 2-5% S. This value includes the contents of sulphur combined as sulphate as well as an amount of sulphur combined as sulphide. Such a material can be smelted according to conventional methods in a shaft furnace.

As stated above the invention also relates to a new method for preparing lead from high grade lead concentrates. According to this feature of the invention a sinter obtained according to the method described above is smelted. When smelting said sinter the proportion of the lead sulphide to the oxygen containing lead compounds should substantially correspond to the stoichiometric proportions for reacting to metallic lead.

Lead forming reactions, which occur in such a smelting procedure, can be stated by the formulas PbS+2PbO=3Pb+SOz-5S.6 kilogram calories 1) PbS+PbSO4=-2Pb+2SOz -94.4 kilogram calories In case the material to be smelted consists of the sinter in accordance with the present invention the smelting reaction will predominently occur-in accordance with the Formula 1 above. Said formulas show that a reaction according to (2) requires about 2.5 times as much energy per unit of lead as the reaction according to (1) and that it involves three times as great an amount of waste gases per unit of lead. By smelting the sinter obtained in accordance with the present invention i. a. the following advantages are therefore obtained in comparison with the conventional blast furnace process.

1. The energy consumption per unit of lead for smelting is considerably lower and the smelting capacity increases.

2. The amounts of waste gases produced are lower, which involves lower losses of dust.

3. The lead losses with the smelting furnace slag are decreased.

The following advantages are obtained in comparison "7 carryout .a converter blowing after the smelting operation. i

- 3. The circulating dust quantity can be kept very low.

4. The amount of gas from the smelting furnace decreases.

The following advantages are obtained in comparison with the Newman hearth smelting process.

1. Higher direct lead output.

2. No slag treatment necessary.

3. Lower dust amount.

In certain cases it canbe suitable to reduce the sulphur contents of the sinter to a lower value than required for carrying 'out the lead formation according to the reactions stated aboveinithe Formulas l and 2. A sinter having'such a low sulphur content can be obtained according to the present invention. The lead oxide excess can be reduced in the furnace, e. g. by using carbon or lead concentrate.

Any small amounts of sulphur, arsenic, antimony, tin, a. s. 0. present in the'molten lead discharged from the furnace can easily be removed by blowing in oxygen or oxygen enriched air, or air eventually preheated. When using pure oxygen gas very small waste gas amounts are obtained and substantially no dust losses occur. The blowing with oxygen can e. g. be carried out directly in the ladle, into which the lead is discharged from the furnace, or in a well connected to the discharging spout, continuously during the discharging.

The invention will now be described With the'following examples.

' Example 1 A sinter charge having the following composition was prepared:

Parts Sintered material returned from a previous sintering step and having a particle size of about 3-40 mm 45.5 Lead dust 5.4 Lime stone powder 3.5 Lead concentrate 45.5

This lead concentrate had a particle size less than 0.1 mm. and the following analytic composition: 78.4% lead, 12.6% sulphur, 0.5% zinc, 0.5% iron, 5.3% SiOz, 0.4% A1203, 0.2% MgO and 0.2% CaO. The sintered material recovered from a previous sintering step was moistened in a rotating drum with sufiicient water to dampen the surface (approximately 4.0 parts), and the lead dust was then added to the rotating drum, to form a basic lead sulphate coating on the sintered particles. The lead dust consists substantially of lead oxide and lead sulphate substantially below 200 mesh recovered from an electrostatic filter. The lime stone powder of air swept quality was then added while adding a further amount of water by spraying, to form a further coating on the particles. Finally the lead concentrates were added, forming an exterior coating on the moistened balls. The product thus obtained was of ball structure, and formed a charge particularly permeable to gas. The charge was thus very suitable forcarrying out the subsequent sintering. For the purpose of sintering said charge material was fed to a relatively small Dwight Lloyd machine having four wind boxes and an effective suction area of one square metre. The grate was first coated with a 30 mm. layer of sintered material in a manner well-known in the art. The total height of the charge applied to the machine was 250 mm. The vacuumconditions were controlled in such a way thata'vacuum of 50-80 mm. water gauge was maintained in the ignition wind box, No. 1. In the wind boxNo; 2 the vacuum was 150-200 mm. water gauge. In wind box No. 3 the vacuum was about 450 mmLwater gauge. In the last wind box No. 4, the vacuum was 400 mm. Water gauge. Under these circumstances it was possible to sinter the material without any formation of low melting phases which would flow downwardly, clogging the charge and adhering to the bars.

More air was passed through the sinter cake in the last stage than in earlier stages of the sintering to cool the hottest part of the sinter cake next to the grates. At the top temperature of about 800900 C. there appeared to be some melting of the surface coating, but said melting was not so remarkable as to cause any phases to flow down to the bars. The inner portion of the balls did not have sufi'icient time within which to be warmed to the fusing temperature The composition of the resulting product after sintering showed 5% total sulphur, 1.5% of which was present as sulphide, 20-25 tons per day of lead concentrates may Parts Sinter 93 Lime (calculated as CaO) 4 Coke breeze 3 240 kg. slag, containing 3% Pb, were obtained per ton of lead.

Example 2 The sintering process of Example I was carried out with I the following charge:

, Percent Returned sinter (particle size 4-12 mm.) 54.5 Lead dust 4.5 Lime stone powder 3 Lead concentrates 38 The composition of the lead sulphide material was as follows: 79.1% lead, 12.8% sulphur, 0.6% zinc, 0.4% iron, 4.9% SiOz (gangue), 0.3% A1203, 0.2% MgO and 0.1% CaO.

The sintered product analyzed 75% lead and 2.2% total sulphur of which 0.9% was present as sulphate. In this case from 18 to 20 tons of lead concentrate was sintered per day per square meter of effective sintering area. As shown in Example 1 above, the lead separation was very small. In Example 2, the particle size of the return sinter was kept considerably smaller than the particle size of the product charged in Example 1 above. This increased the surface area of the charge and decreased the thickness of the sulphide layer on the cores which is believed to be responsible for the decrease in total sulphur content.

Having now particularly described and ascertained the nature of our said invention and in which manner the same is to be performed, we declarethat what we claim is:

1. In a method ofagglomerating and sintering a fine granular lead sulphide material containing at least about 55% lead, while simultaneously desulphurizing the material and forming an oxide containing product, the improvement which comprises coating particles of lead oxide containing material derived from a sintering operation carried out previously and having an average particle size within the range of about 5-30 mm. with a thin layer of said lead sulphide material by ball rolling, said ball rolling being controlled so as to form balls having a shell of said lead sulphide material of a thickness within the range of about 1-3 mm. said oxidic material being present in an amount of at least about 30% and not more than about applying the material prepared by said ball rolling consisting of inner oxidic cores and surrounding shells of said lead sulphide material on a sintering grate in the form of a charge layer permeable to well gas, igniting said charge, causing oxygen containing gas to pass through said charge so as to effect the sintering without allowing easily fusible products to flow down through the charge and cooling said charge rapidly subsequent to said sintermg.

2. A method as claimed in claim 1 characterized by effecting the sintering while controlling the flow of air through the charge in such a way that no easily fusible products flow down through the charge.

3. A method as claimed in claim 2 characterized by, at signs of beginning flow of easily fusible phases through a portion of the charge, increasing the flow of air through said portion of charge.

4. A method as claimed in claim 2, characterized by decreasing the flow of air through a portion of the charge when the temperature of said charge tends to fall below the temperature necessary for effecting desulphurization.

5. A method as claimed in claim 1, characterized by effecting the sintering while controlling the contents of heat liberating and heat consuming components of the individual balls.

6. In a method for agglomerating and sintering a fine granular lead sulphide material containing at least about 55% lead, while simultaneously desu-lphurizing the material and forming an oxide containing product, the improvement which comprises coating particles of lead oxide containing material derived from a sintering operation carried out previously and having an average particle size within the range of about 5-30 mm. with a thin layer of said lead sulphide material by ball rolling, said ball rolling being controlled so as to form balls having a shell of said lead sulphide material of a thickness within the range of about 1-3 mm., said oxidic material being present in an amount of at least about 30% and not more than about 65 applying the material prepared by said ball rolling consisting of inner oxidic cores and surrounding shells of said lead sulphide material on a sintering grate in the form of a charge layer permeable to well gas, igniting said charge on the surface, causing oxygen containing gas to pass through said charge so as to effect the sintering without allowing easily fusible products to flow down through the charge by controlling the contents of heat consuming and heat liberating components of the individual balls and cooling the charge rapidly subsequent to said sintering.

7. A method as claimed in claim 6, characterized by at signs of formation of easily fusible products in the charge decreasing the shell thickness of the balls fed to the sintering grate.

8. In a method for agglomerating and sintering a fine granular lead sulphide material containing at least about 55% lead, while simultaneously desulphurizing the material and forming an oxide containing product, the improvement which comprises coating particles of lead oxide containing material derived from a sintering operation carried out previously and having an average particle size within the range of about 5-30 mm. with a thin layer of heat consuming material and subsequently with a thin layer of said lead sulphide material, both of said shells being applied by ball rolling, the last ball rolling being controlled so as to form balls having a sulphide shell of said lead sulphide material and a thickness within the range of about 1-3 mm., said lead oxide material being present in an amount of at least about 30% and not more than about 65%, applying the material prepared by said ball rolling, consisting of inner oxidic cores and surrounding shells of said lead sulphide material on a sintering grate in the form of a charge layer permeable to well gas, igniting said charge on the surface, causing oxygen containing gas to pass through said charge without allowing easily fusible products to flow down through the charge and cooling said charge rapidly subsequent to said sintering.

9. A method as claimed in claim 8, characterized in that the heat consuming material is selected from the group which consists of carbonates, crystal water containing salts and hydrates.

10. In a method for agglomerating and sintering a fine granular lead sulphide material containing at least about lead, while simultaneously desulphurizing the material and forming an oxide containing product, the improvement which comprises coating particles of lead oxide containing material derived from a sintering operation carried out previously and having an average particle size within the range of about 5-30 mm. with a thin layer of oxygen containing lead compounds such as obtained in metallurgical plants, in form of dusts, fines from crushing operations, slimes and skimmings, as well as a thin layer of said lead sulphide material by ball rolling, said ball rolling being controlled so as to form balls having a shell of said lead sulphide material of a thickness within the range of about 1-3 mm., said oxidic material being present in an amount of at least about 30% and not more than about applying the material prepared by said ball rolling consisting of inner oxidic cores and shells and surrounding shell of said lead sulphide material on a sintering grate in the form of a charge layer permeable to well gas, igniting said charge, causing oxygen contain ing gas to pass through said charge so as to efiect the sintering without allowing easily fusible products to flow down through the charge and cooling said charge rapidly subsequent to said sintering.

11. A method as claimed in claim 10, characterized by applying a shell of heat consuming material between said layer of oxygen containing lead compounds and said layer of lead sulphide material.

No references cited.

Claims (1)

1. IN A METHOD OF AGGLOMERATING AND SINTERING A FINE GRANULAR LEAD SULPHIDE MATERIAL CONTAINING AT LEAST ABOUT 55%LEAD, WHILE SIMULTANEOUSLY DESULPHURIZING THE MATERIAL AND FORMING AN OXIDE CONTAINING PRODUCT, THE IMPROVEMENT WHICH COMPRISES COATING PARTICLES OF LEAD OXIDE CONTAINING MATERIAL DERIVED FROM A SINTERING OPERATION CARRIED OUT PREVIOUSLY AND HAVING AN AVERAGE PARTICLE SIZE WITHIN THE RANGE OF ABOUT 5-30 MM. WITH A THIN LAYER OF SAID LEAD SULPHIDE MATERIAL BY BALL ROLLING, SAID BALL ROLLING BEING CONTROLLED SO AS TO FORM BALLS HAVING A SHELL OF SAID LEAD SULPHIDE MATERIAL OF A THICKNESS WITHIN THE RANGE OF ABOUT 1-3 MM. SAID OXIDIC MATERIAL BEING PRESENT IN AN AMOUNT OF AT LEAST ABOUT 30% AND NOT MORE THAN ABOUT 65%, APPLYING THE MATERIAL PREPARED BY SAID BALL ROLLING CONSISTING OF INNER OXIDIC CORES AND SURROUNDING SHELLS OF SAID LEAD SULPHIDE MATERIAL ON A SINTERING GRATE IN THE FORM OF A CHARGE LAYER PERMEABLE TO WELL GAS, IGNITING SAID CHARGE, CAUSING OXYGEN CONTAINING GAS TO PASS THROUGH SAID CHARGE SO AS TO EFFECT THE SINTERING WITHOUT ALLOWING EASILY FUSIBLE PRODUCTS TO FLOW DOWN THROUGH THE CHARGE AND COOLING SAID CHARGE RAPIDLY SUBSEQUENT TO SAID SINTERING.