NO330140B1 - Process for the preparation of a manganese alloy - Google Patents

Abstract

The invention relates to a process for preparing a manganese alloy, the process comprising the steps of: heating at least iron oxide and manganese oxide together with carbon in a furnace (1), extracting a manganese alloy from the furnace, furnace gas generated in the furnace (1) is purified in a wet scrubber (9) to form pure furnace gas and a manganese-containing material, that acid is added to the manganese-containing material to form a mixture of pH 2-6, that a precipitant is added to the mixture for at least partially precipitating zinc from the mixture, separating the undissolved particles, including at least a proportion of the precipitated zinc, from said mixture to form a liquid solution containing dissolved manganese, a proportion of the manganese content of the liquid solution is passed as a manganese source to an oven (1) to be heated together with at least iron oxide and carbon to form a manganese alloy.

Description

Technical area.

The present invention relates to a method for producing a manganese alloy.

Technical background

Manganese, in the form of manganese alloys, is often used in the production of, for example, iron and steel, as a result of its deoxidizing and alloying properties. Such manganese alloys are mainly produced from ore and coke at high temperatures. During the production of manganese alloys, process gases containing metals are formed. Before these gases are released, they are usually cleaned by bringing them into contact with water in a wet scrubber. During the purification of the process gases, a sludge is formed which contains metal particles. Today, such sludge is placed in landfills at high costs. The handling and storage of the sludge can create additional work and environmental problems

GB patent 1 371 113 describes a method for using manganese which is present in sludge generated by purifying the process gases which are diverted from the smelting furnace. However, this method is considered inefficient in terms of economic and environmental considerations.

Summary of the invention.

It is an object of the present invention to overcome the disadvantages described above, and to produce an improved method for the production of manganese alloys.

These and other purposes, which will become clear from the following summary and description, are achieved by means of a method for producing a manganese alloy, which method is characterized by the fact that it mentions the following steps: that iron oxide and manganese oxide are heated together at least with carbon in a furnace; that a manganese alloy is withdrawn from the furnace; that furnace gas generated in the furnace is cleaned in a wet scrubber to form clean furnace gas and a manganese-containing material; adding acid to the manganese-containing material to form a mixture with a pH of 2-6; that a precipitant is added to the mixture to, at least partially, precipitate zinc from the mixture; separating undissolved particles, including at least one portion of the precipitated zinc, from said mixture to form a liquid solution containing dissolved manganese; that at least a portion of the manganese content of the liquid solution is directed as a source of manganese to a furnace to be heated together with at least iron oxide and carbon to form a manganese alloy.

A method has therefore been developed for the production of a manganese alloy which makes it possible to recover valuable metals in the furnace gas. By treating the furnace gas originating from the production of manganese alloy in this way, it becomes possible to recover a large proportion of the manganese content in the furnace gas, and still avoid that zinc accumulates in the system. The recovered manganese is used as raw material during the production of a manganese alloy, which means that the amount of necessary added raw material, for example manganese ore, can be reduced. In known processes, the presence of high zinc levels will prevent the reuse of sludge as a manganese source during the manufacture of manganese alloys. The removal of zinc therefore makes it possible to recover valuable manganese in the furnace gas. A cost-effective method for the production of a manganese alloy has therefore been developed. Moreover, the method is advantageous from an environmental point of view, since the natural resources are used in a more efficient way. Consequently, less waste is generated compared to known methods for producing manganese alloys, where sludge generated from the gas purification is removed and placed in a waste depot where it is considered an environmental problem in many areas.

According to one embodiment, the method comprises a step where, after the step where acid is added to the manganese-containing material and before the step where a precipitating agent is added for precipitating zinc, undissolved particles are separated from the mixture with a pH of 2-6. The separated material, for example in the form of a filter cake, can be fed to a furnace as a source of silicon during the production of silicomanganese. An advantage of this design is that the reuse level of metals in the furnace gas is further improved. In addition, the amount of waste produced during the process is further reduced.

According to one embodiment, the method comprises, after the step of separating undissolved particles, comprising at least a proportion of precipitated zinc, from the mixture to form a liquid containing dissolved manganese, a step of adding a manganese precipitant to precipitate, at least in part, manganese from the liquid solution, and a step where the precipitated manganese is separated from the liquid solution, which step where at least a proportion of the manganese content in the liquid solution is supplied as a manganese source to a furnace for further heating together with at least iron oxide and carbon, comprises the use of said precipitated manganese as a manganese source. More preferably, said manganese precipitant comprises a carbonate and/or a hydroxide-containing or hydroxide-generating compound. An advantage of this design is that less water is added to the oven, which increases the oven's energy efficiency.

During the step where acid is added to the manganese-containing compound to form a mixture of pH 2-6, the added acid preferably comprises sulfuric acid. It has been shown that by choosing sulfuric acid, the manganese-containing compound is dissolved in a cost-effective manner.

In the step where acid is added to the manganese-containing compound to form a mixture with pH 2-6, according to one embodiment, the added acid may comprise hydrochloric acid.

In the step where acid is added to the manganese-containing compound, the acid is preferably added in such an amount that a mixture is formed with a pH of 3.0-5.0, and more preferably with a pH of 3.5-4.5, to dissolve metal particles in the mud acid in an even more efficient way. Preferably, the acid is added in such an amount that a mixture with a pH of 3.8-4.2 is formed.

In the step where a precipitating agent is added to the mixture, in order to at least partially precipitate zinc from the mixture, the precipitating agent preferably comprises a sulfur-containing compound. An advantage of adding a sulfur-containing compound is that the sulfides form complexes with many metals, including zinc.

In the step where a precipitant is added to the mixture, to at least partially precipitate zinc from the mixture, the precipitant may be an alkaline compound.

Further advantages of the invention will be apparent from the following description and patent claims.

Brief description of the figures.

The present invention will now be described in more detail with reference to the accompanying schematic figures which show an embodiment of the invention, and in which: Figure 1 shows a method for producing a manganese alloy according to an embodiment of the present invention.

Figure 2 shows selected steps of the procedure shown in Figure 1.

Technical description.

As used in this description, the term "ferroalloys" means various per se known alloys of iron with a high proportion of one or more other elements, for example manganese or silicon. For example, ferromanganese is a ferroalloy with a high manganese content, while silicomanganese is a ferroalloy with a high content of manganese and silicon. Ferromanganese and silicon manganese are also referred to as manganese alloys. As a result of their deoxidation and/or alloying properties, manganese alloys are used, for example, in the production of steel.

Ferromanganese is produced by heating a mixture of manganese oxide Mn02 and iron oxide Fe203 with carbon, such as coal, in a furnace, for example a blast furnace or an electric arc furnace. Usually, iron oxide is used in the form of iron ore, manganese oxide in the form of manganese ore and carbon in the form of coke.

The metallurgical process for producing manganese alloy in a furnace is known per se, see for example GB - 2,255,350. In order to clean the furnace gases generated during the production of a manganese alloy, before they are released, they are subjected to a normal gas cleaning in a wet scrubber and this process is also known in and of itself.

In what follows, with reference to Figure 1, which schematically shows the method, a method for producing a manganese alloy, in this case ferromanganese, according to a preferred embodiment of the present invention, and to Figure 2, which illustrates the specific steps, will be described S1 to S8 in the procedure. As indicated above, the steps for heating the raw materials, extracting a manganese alloy and purifying the process gases are known in and of themselves, and will therefore only be briefly described.

In step S1, a mixture of iron oxide Fe 2 O 3 and manganese oxide Mn 0 2 together with carbon is heated in a furnace 1, such as a blast furnace or an electric arc furnace. For this purpose, the raw materials are supplied e.g. the ores containing manganese, and iron and coke to the furnace 1 as indicated by arrow A, through an opening 3 which is arranged in the upper part of the furnace 1. The main source of manganese is often a manganese-containing ore, also referred to as manganese ore, as a such ore also contains iron. In addition, manganese is supplied in the form of a manganese-containing liquid solution and/or in the form of a solid manganese salt, such as manganese carbonate MnCO-3, as will be explained later.

In step S2, the ferromanganese FeMn in the form of a molten metal is extracted from the furnace by means of conventional metallurgical processes. It should be understood that the mixture inside the furnace 1 is fused together with coke at a high temperature, for example 1400 °C. The molten metal is drained off as indicated by the arrow B through a drain hole 5 which is arranged in the lower part of the furnace 1. As a by-product it forms slag. Molten slag is removed from the furnace 1, as indicated by arrow C through another drain hole 7 in the lower part of the furnace 1. This melting of the materials in the furnace 1 generates a hot process gas, also referred to as a furnace gas, which contains various metals in the form of metal particles. The furnace gas is fed to a wet scrubber 9 via a gas line 10. The wet scrubber 9 comprises a tower 11, nozzles 13 for distributing a scrubber solution 12 in the tower 11, and a pipe 15 for recycling the scrubber solution 12. The scrubber solution 12 is recycled using a pump 17 which is arranged in the recirculation pipe 15. The wet scrubber 9 also comprises a pipe for the supply of fresh water, and possibly a pipe for the supply of an absorbent, such as NaOH, but for the sake of clarity, none of these are shown in figure 1.

In step S3, the furnace gas is cleaned in the wet scrubber 9 to form a clean furnace gas and a manganese-containing material, which is also referred to as a sludge.

The clean furnace gas is led further to a chimney 19 via a gas pipe 21 and is led out to the atmosphere. A portion of the scrubbing solution 12 flowing through the recirculation pipe 15 is directed to a conventional water treatment unit 23 via a pipe 25 which is connected to the high pressure side of the recirculation pipe 15. The water treatment unit 23 includes, for example, means 27, such as a series of tanks with agitators, for regulating the pH and /or flocculation, and a sedimentation device 29, such as a sedimentation tank or a lamellar separator. In the water treatment unit 23, the scrubber solution is thus treated in a series of successive steps to form purified water, as shown by arrow D, and a manganese-containing sludge. The purified water can be discharged into a recipient.

Optionally, the water treatment unit 23 may comprise a sludge dewatering unit 31, where the water is removed from the sludge by, for example, filtration where a filter press or a press of the "bucher" type is used to form solid filter cakes. Alternatively, the water in the sludge dewatering unit 31 can be removed by sedimentation or centrifugation.

In the gas cleaning step S3, metal particles in the furnace gas are captured in the wet scrubber 9 in the circulating scrubber solution 12, and are then precipitated and separated as a manganese-containing material in the water treatment unit. The separated sludge generally contains elements such as Mn, Si, Fe, Al, Ca, Mg, Zn, C, Pb and water. The composition of the sludge generated in the gas purification step S3 can vary as a result of, for example, variations in the raw material and the process conditions. At least some of the mentioned elements in the sludge are generally present as oxides and/or carbonates.

Consequently, the manganese-containing sludge that is withdrawn from the sedimentation device 29 can optionally be dewatered using the sludge dewatering device 31, the resulting filter cakes being taken out of the sludge dewatering device 31 to be further processed as indicated by arrow E.

Optionally, the manganese-containing sludge can be dewatered using the sludge dewatering device 31 and taken to a waste landfill 33, as indicated by arrow F, for further treatment on a later occasion, as indicated by arrow G.

The produced sludge and/or filter cakes are led to a tank 35, as indicated by the arrow H. In the case illustrated in figure 1, the sludge is led directly from the sedimentation device 29 and to the tank 35.

In step S4, acid, in this case sulfuric acid (arrow I) and water, (arrow J) are added to the sludge which is received in the tank 35. Accordingly, the sludge 37 is diluted, and its content of metal salts, such as oxides and carbonates as indicated above, is at least partially dissolved as a result of the sludge's 37 pH value being reduced. In order to dissolve the desired types and/or a sufficient amount of particles, the acid must be added in such a quantity that the sludge 37 pH value is reduced to a pH of 2-6. The lower the pH value, the more particles are dissolved. It is preferred to reduce the solution's pH value to typically around 4. The mixture of sludge, water and acid is stirred to accelerate the dissolution of the particles.

In step S5, the particles that are not dissolved in step S4 are separated from the liquid to form filter cakes, using e.g. filtration, sedimentation or centrifugation, using a suitable separation device 38, such as a filter press or a belt filter, the filter cakes being removed from the device 38 as shown by arrow K. When separating undissolved particles, a liquid solution 39 is produced which contains dissolved manganese and zinc, and this is led to a second tank 41 via a pipe 40. The filter cakes produced in step S5, which are removed in the separation device 38 shown by arrow 38, mainly comprise silicon dioxide and can possibly be used as a source of silicon during the production of silicon manganese.

In step S6, a sulphide solution is added as indicated by the arrow L, to the liquid 39 in the tank 41, in order to precipitate zinc. A molar ratio between sulphide and zinc of 1.1 -1.2 to 1 is preferred to effectively precipitate zinc present in the liquid solution 39. The mixture of liquid solution and sulphide solution is preferably stirred to accelerate zinc precipitation. By adding, for example, disodium sulphide Na2S, dissolved zinc is precipitated from the liquid solution 39 in the form of solid zinc sulphide ZnS.

In step S7, the precipitated zinc in step S6 is separated by, for example, filtration, sedimentation, or centrifugation, in a suitable separation device 42, such as a filter press or belt filter, to form filter cakes which are removed from the separation device 42, as indicated by the arrow M, to form a liquid solution containing dissolved manganese. In step S7, a manganese-rich liquid solution is thus produced which is mainly free of zinc.

In step S8, the manganese content of the liquid solution produced in step S7 is fed as a manganese source to the production of a manganese alloy. In this case, the liquid solution is passed on without further treatment to a furnace 1, as indicated by the arrow N, to be heated together with manganese ore, iron ore and coke.

Alternatively, the liquid produced in step S7 can be directed to a tank 43 via a pipe 44 to precipitate solid manganese carbonate MnC03 by adding a carbonate solution, such as sodium carbonate Na2C03, as indicated by the arrow O. The solid manganese carbonate MnC03 is then separated by, for example a separation device 45, such as a filter press, a belt filter, a centrifuge, a sieve, and is passed on to the furnace 1, as indicated by the arrow P. In this case, step S8 comprises that MnC03 is precipitated and separated from the liquid solution leaving the separation device in S7. It is an advantage of this design that less water is led to the furnace 1, which increases its energy efficiency. As an alternative to adding a carbonate-containing compound, such as Na2CO3, it is also possible to add a hydroxide-containing compound, such as NaOH, to precipitate the manganese in the form of manganese hydroxide Mn(OH)2.

A more detailed embodiment of the present invention will now be described, with reference to the following example.

Example 1.

According to a first example, a manganese-containing sludge was produced in accordance with steps S2, S2 and S3 described above. In the first example, 0.5 kg of the produced sludge, with a chemical composition as shown in Table 1, was mixed with 216.5 grams of water. Sulfuric acid with a concentration of 96% by weight was added in step S4 to reduce the pH value of the sample. A total of 235.4 grams of sulfuric acid was added. The sample was then subjected to intense stirring for 2 hours at approximately 100 °C. When the sample's pH value dropped below a pH value of 6, the sample started to foam. A defoamer of the polyethylene oxide-polypropylene oxide-modified fatty acid type was then added. The sample's pH value was reduced to 4.1.

Then undissolved particles were removed from the sample by filtration in step S5. Of the total amount of manganese and zinc in the original sludge, 8% of the manganese and 10.5% of the zinc were removed by this filtration. The total weight of the removed particles was 77.7 grams. The filter cake was washed with water to clean out remaining dissolved manganese. After separation of the undissolved particles, the sample contained 947 grams of liquid solution containing 9.4% manganese and 2.3% zinc.

In step S6, 53.1 g of Na2S solution with a concentration of 60% by weight, corresponding to 1.2 mol of sulfur to 1 mol of zinc, was added to the liquid solution. Zinc sulfide ZnS was formed and removed in step S7 by a second filtration of the sample. After this second filtration, the remaining liquid sample had a weight of 884g, and contained 10.4% Manganese and 0.004% Zinc. The remaining liquid thus contained as much as 90% of the amount of manganese in the original sludge, but very little of the zinc. The total amount of zinc removed from the original sludge that precipitated ZnS was 21.9 grams. Consequently, as demonstrated, most of the manganese leaving the furnace with the furnace gas can be returned to the furnace, after treatment according to an embodiment of the present invention, while avoiding zinc accumulation in the system.

A method according to an embodiment of the present invention can be regarded as a method with a closed loop (closed-loop) since manganese that is recovered from the furnace gas is reused for the production of manganese alloy.

It should be understood that the described embodiment of the invention can be modified and varied by a person skilled in the field, without deviating from the inventive idea as defined in the claims.

It should thus be understood that the manganese content in the liquid solution produced in S7, not necessarily in step S8, needs to be passed on to the furnace in step S1, i.e. the furnace from which the furnace gas that is treated in step S3 originates. Recovered manganese, e.g. in the form of a liquid solution containing dissolved manganese or solid manganese in the form of MnC03 precipitated therefrom, can thus be led to an optional furnace to be heated together with at least iron oxide and carbon to produce a manganese alloy.

It should also be understood that furnace gas from a number of furnaces can be introduced into a wet scrubber for further treatment, or that the furnace gas from a furnace can be distributed between several wet scrubbers.

Moreover, it should be understood that it is possible to lead manganese which is recovered from the production of a first manganese alloy, e.g. ferromanganese or silicon manganese, for the production of a second manganese alloy, e.g. ferromanganese or silicon manganese, where the second manganese alloy is the same or of a different type to the first manganese alloy. As an example, manganese recovered from the production of ferromanganese can be passed on to a furnace for and further heated together with iron oxide, manganese oxide, silica (SiO 2 ) and carbon to produce silicon manganese (SiMn).

In step S6, a sulphide solution containing disodium sulphide is added to precipitate zinc. It should be understood that other water-soluble sulphide salts, such as dipotassium sulphide, can be used as an alternative to disodium sulphide. As an alternative to inorganic sulfide salts, it is also possible to use organo-sulfide-containing compounds, such as trimercapto-s-triazine trisodium salt, dithiocarbamate, or sodium trithiocarbonate to precipitate zinc.

As mentioned above, the sludge and/or filter cakes produced from the gas washing step S3 can, for shorter or longer periods, be removed and placed in a waste depot 33 before it is processed further in step S4.1 in this case the circuit is closed when the filter cakes are brought back and processed further in accordance with steps S4, S6, S7 and S8 according to an embodiment of the method. Accordingly, sludge that has been removed several years ago in a wastewater treatment plant 23, and then transported to a waste landfill 33 to be stored for many years, such as 2-20 years, may very well be according to an embodiment of the present invention , is used to produce manganese, so that the manganese circuit is closed.

As mentioned above, the main source of the manganese used to produce the manganese alloy according to an embodiment of the present invention is a manganese-containing ore. However, in a shorter period of time it is possible to use recovered manganese as the main source, or even as the only source of manganese.

Claims (9)

1. Process for producing a manganese alloy characterized by the steps: that at least iron oxide and manganese oxide are heated together with carbon in a furnace (1); that a manganese alloy is withdrawn from the furnace; that furnace gas generated in the furnace (1) is cleaned in a wet scrubber (9) to form pure furnace gas and a manganese-containing material, that acid is added to the manganese-containing material to form a mixture with a pH of 2-6, that it is added a precipitant to the mixture to, at least partially, precipitate zinc from the mixture, that undissolved particles, including at least a portion of the precipitated zinc, are separated from said mixture to form a liquid solution containing dissolved manganese, and that in at least a portion of the manganese content of the liquid solution is fed as a manganese source to a furnace (1) to be heated together with at least iron oxide and carbon to form a manganese alloy. 2. Method in accordance with claim 1, characterized in that it further comprises that after the step where acid is added to the manganese-containing material and before the step where a precipitating agent is added for precipitating zinc, a step is carried out where undissolved particles are separated from the mixture with a pH 2-6. 3. Method according to one of the preceding claims, characterized in that it further comprises that, after the step of separating undissolved particles, including a proportion of the precipitated zinc, from the mixture to form a liquid solution containing dissolved manganese, a step is carried out where a manganese precipitating agent is added for at least partial precipitation of manganese from the liquid solution, and a step where the precipitated manganese is separated from the liquid solution, which step where at least a proportion of the manganese content in the liquid solution is supplied as a manganese source to a furnace (1) to be heated together with at least iron oxide and carbon where said precipitated manganese is used as a manganese source. 4. Method in accordance with claim 3, characterized in that the manganese precipitating agent comprises a carbonate and/or a hydroxide-containing or hydroxide-generating compound. 5. Method in accordance with one of the preceding claims, characterized in that in the step where acid is added to the manganese-containing material to form a mixture with pH 2-6, the added acid is sulfuric acid. 6. Method in accordance with one of the preceding claims, characterized in that in the step where acid is added to the manganese-containing material to form a mixture with pH 2-6, the added acid is hydrochloric acid. 7. Method in accordance with one of the preceding claims, characterized in that in the step where acid is added to the manganese-containing material, the acid is added in such an amount that a mixture with a pH of 3.0 - 5.0 is formed, 8. Method according to one of the preceding claims, characterized in that in the step where a precipitating agent is added to the mixture, in order to at least partially precipitate zinc from the mixture, the precipitating agent is preferably a sulfur-containing compound. 9. Method according to one of the preceding claims, characterized in that in the step where a precipitating agent is added to the mixture, in order to at least partially precipitate zinc from the mixture, the precipitating agent is an alkaline compound.