A method for the recovery of wastes containing ferrochrome powders into value-added ferrochrome products

Abstract

The invention relates to a method for the recovery of ferrochrome products, wherein powdered wastes containing ferrochrome, obtained from waste recovery plants, are combined with at least one magnetizing agent to form a mixture and subjected to recovery processes in induction furnaces.

Description

[0001] A METHOD FOR THE RECOVERY OF WASTES CONTAINING FERROCHROME POWDERS INTO VALUE-ADDED FERROCHROME PRODUCTS

[0002] TECHNICAL FIELD

[0003] The invention relates to a method for obtaining value-added ferrochrome products, in particular from wastes of very small size containing ferrochrome powders.

[0004] PRIOR ART

[0005] Ferrochrome is an alloy of iron and chromium in varying ratios and usually contains carbon. The high ratio of chromium makes ferrochrome an essential component, especially in stainless steel production. Ferrochrome is obtained by reducing chromium from its oxide form to its metallic form and then alloying it with iron.

[0006] Obtaining ferrochrome is a metallurgical process based on alloying chromium metal with iron at high temperatures. The production is carried out using blast furnaces or electric arc furnaces.

[0007] Ferrochrome production is often an energy-intensive process, and its cost depends on many factors. These factors include the quality of the chromium ore, energy costs, the performance of the devices used and the time consumed.

[0008] Ferrochrome is generally considered to be an expensive component as it is included as a component to obtain steel, and its recovery from waste is important in terms of reducing these costs. As with the recycling of any material, the recycling of ferrochrome helps to reduce costs and the environmental impact of waste and to increase resource efficiency.

[0009] However, in the relevant technical field, the use of electric arc furnaces for metallurgical processes, especially for the recycling of waste containing powdered ferrochrome, does not meet the expectations of high-efficiency recovery. Electric arc furnaces are better suited for larger volumes and for obtaining block materials, however, they do not have sufficient performance for obtaining materials of small size that require precise heat control and fast processing.

[0010] For obtaining ferrochrome products from wastes containing ferrochrome, it is envisaged that the research and development of new methods will offer solutions and advantages for the relevant technical field due to reasons such as the inability to perform recovery processes from small-sized wastes, the inability to ensure precise heat control and homogeneous heating during the processes, and the long processing times.

[0011] BRIEF DESCRIPTION OF THE INVENTION

[0012] Ferrochrome is considered an expensive component as it is generally used for obtaining steels. Therefore, supporting ferrochrome production with waste recovery processes will help lower costs and reduce environmental impacts.

[0013] Although electric arc furnaces meet expectations in the metallurgical processes for ferrochrome production, they cannot offer efficient metallurgical recovery processes. It has been found that different recovery processes should be investigated and developed, especially in the recycling of wastes containing powdered ferrochrome due to inefficiency, poor precise heat control and long processing times. Accordingly, the present inventors provide a method for obtaining value-added ferrochrome products especially from wastes containing powdered ferrochrome.

[0014] Another object of the invention is to provide a method for the recovery of ferrochrome products from wastes containing ferrochrome, in which precise heat control is achieved and the process rate is increased.

[0015] DETAILED DESCRIPTION OF THE INVENTION

[0016] In this detailed description, the subject matter of the invention relates to a method for recovering ferrochrome products from wastes containing ferrochrome coming from waste recovery plants, and is described only by way of non-limiting examples for a better understanding of the subject matter. In the invention, the waste containing ferrochrome is a mixture of metal powders obtained from ferrochrome production plants. As it is a powdered mixture, the grain size of the components is very small. 80% of the components have grain sizes smaller than 300 pm.

[0017] In the relevant technical field, electric arc furnaces are generally used for obtaining ferrochrome. Metallurgical processes take place in the high temperature environment created by these furnaces, and ferrochrome can be obtained by alloying chromium ore and iron.

[0018] As is known in the relevant technical field, electric arc furnaces are not useful for the recovery processes of wastes with small grain sizes. The present inventors propose the use of induction melting technology in the metallurgical processes for recovering and obtaining ferrochrome products from said powdered wastes containing ferrochrome.

[0019] In the present invention, induction melting technology refers to a process in which the material is melted using the principle of induction heating. In this technology, a high- frequency alternating current is passed through an induction coil to generate heat in the material, thereby making melting possible.

[0020] In induction furnaces, the heating of the material is realized by induced Eddy currents and Joule heating resulting from the interaction of these currents with the electrical resistance of the material. The magnetic property of the material plays an important role in this process. However, the effectiveness of induction heating does not only depend on the magnetic properties of the material; the electrical conductivity of the material is also critical.

[0021] Therefore, the magnetic and electrical conductivity properties of the material to be heated in induction furnaces are expected to be at values suitable for this melting technology.

[0022] The object of the present invention is to obtain value-added ferrochrome products.

[0023] Accordingly, the intended ferrochrome products are expected to contain at least 60% by weight of chromium and no more than 0.05% by weight of sulfur. The intended ferrochrome product is shown in Table 1 .

[0024] Table 1. The chemical composition of the intended ferrochrome product as a result of recovery processes.

[0025] The metallurgical processes of the wastes containing ferrochrome according to the present invention are completed by chemical and physical conversions during the induction heating process. These wastes are intended to be melted and converted into the intended ferrochrome products in Table 1. With melting, wastes containing ferrochrome become liquid and the metallic components come together to form a homogeneous structure. Meanwhile, impurities rise to the surface and separate from the liquid due to the density difference. During melting, metallic elements such as iron and chromium in the wastes come together to form ferrochrome alloy.

[0026] In order for all these metallurgical processes to be realized in induction furnaces, it is necessary to ensure that the wastes containing ferrochrome have electrically conductive and magnetic properties. Therefore, in the invention, a mixture of wastes containing ferrochrome from waste recovery plants is obtained, and at least one magnetizing agent is also added to this mixture, which enables the processes to be carried out in induction furnaces.

[0027] The magnetizing agent referred to in the present invention must contain at least one component to provide magnetic properties.

[0028] The magnetizing agent may be at least one of the elements nickel, iron or cobalt.

[0029] The magnetizing agent may be a compound or alloy containing at least one of the elements nickel, iron or cobalt.

[0030] In a preferred embodiment, the magnetizing agent contains iron in certain weight ratios as the component providing magnetic properties. In the present invention, at least one from the group consisting of ferromanganese, ferrochrome, ferrosilicon, ferrovandium or ferronickel may be included as magnetizing agents, in particular containing an iron component.

[0031] In a preferred embodiment of the present invention, the magnetizing agent contains nickel in certain weight ratios as the component providing magnetic properties.

[0032] In the present invention, at least one from the group consisting of nickel ferrite, permalloy, nickel-aluminum, nickel-cobalt may be included as magnetizing agents, in particular containing a nickel component.

[0033] In a preferred embodiment of the present invention, the magnetizing agent contains cobalt in certain weight ratios as the component providing magnetic properties.

[0034] In the present invention, at least one from the group consisting of cobalt ferrite, samarium cobalt, aluminum-nickel-cobalt, cobalt-nickel may be included as magnetizing agents, in particular containing a cobalt component.

[0035] In addition to these compounds or alloys, complex compositions containing the component(s) providing magnetic properties can also be used as magnetizing agents. In accordance with this definition, at least one from the group consisting of ladle bottom metal, liquid metal, slags, steel scrap obtained from ferrochrome furnaces can be used as the magnetizing agent.

[0036] In the present invention, ladle bottom metal means the metal mixture obtained from the furnaces during the production of ferrochrome products and deposited at the bottom of the furnaces and usually removed during the casting or maintenance of the furnace. This mixture of metals is a raw material that should be utilized and recovered as a valuable resource. It contains more than 50% by weight of chromium, more than 20% by weight of iron and between 5 to 7% by weight of carbon.

[0037] In the present invention, liquid metal refers to the molten and liquid state during ferrochrome production. The liquid metal is subsequently cooled and solidified and is a mixture naturally containing chromium, iron and carbon. It contains more than 50% by weight of chromium, more than 20% by weight of iron and between 5 to 7% by weight of carbon.

[0038] As mentioned hereinbefore, the present invention relates to the recovery of powdered wastes of small grain sizes containing ferrochrome in induction furnaces after being supplied from waste recovery plants.

[0039] As can be expected, if powdered wastes of small grain sizes containing ferrochrome can be subjected to recovery processes with this method, it will be possible to recover wastes with higher grain sizes containing ferrochrome. In the present invention, it is possible to obtain the intended ferrochrome product by subjecting even powdered wastes with grain size of 1 mm and less to recovery processes.

[0040] The wastes containing ferrochrome are added to the induction furnaces, followed by at least one magnetizing agent. In a preferred embodiment, a mixture comprising waste containing ferrochrome and at least one magnetizing agent contains at least 10% by weight of the magnetizing agent. This is to ensure the magnetic property for the intended melting process.

[0041] In the present invention, all of these components added to induction furnaces can be referred to as the mixture. The mixture may also contain other auxiliary components to ensure that the intended ferrochrome product has the desired chemical composition in the furnace environment.

[0042] In a preferred embodiment of the method according to the present invention, induction furnaces are provided with a power capacity in the range of 50 to 500 kW. In the invention, the temperature of the induction furnace is in the range of 1700 to 1800 °C.

[0043] In the invention, at least one desulphurization agent is added to the induction furnace. The aim is to maintain the amount of sulfur in the mixture subjected to melting processes while reducing the amount in the final product to obtain the intended ferrochrome product. The intended ferrochrome product is expected to have a sulfur content of 0.05% by weight and less. In the present invention, at least one from the group consisting of calcium oxide, calcium hydroxide, magnesium oxide, sodium carbonate, fluorite or barite is used as the desulphurization agent.

[0044] The inventors have carried out a test to prove that the intended ferrochrome products can be obtained from wastes containing ferrochrome using induction melting technology as a method. In this test, the induction furnace has a power capacity of 50 kW. The chemical composition of the waste with a grain size of 1 mm and below from the waste recovery facility (abbreviated as AGK) is given in Table 2 and the chemical composition of the ladle bottom metal obtained from the ferrochrome electric arc furnaces used as a magnetizing agent is given in Table 3. The amount of AGK waste contains 20 kg and 5 kg of ladle bottom metal.

[0045] The product obtained by applying recovery processes is presented in Table 4.

[0046] Table 2. Chemical composition of waste from AGK used in the recovery processes.

[0047] Table 3. Chemical composition of ladle bottom metal used in the recovery processes.

[0048] Table 4. Ferrochrome product obtained in the recovery processes.

[0049] When the chemical composition of the ferrochrome product obtained after the recovery processes carried out in induction furnaces was examined, it was determined that the amount of chromium was above 60% by weight and the sulfur value was below 0.05% by weight and according to the results obtained, it was determined that the intended ferrochrome product in Table 1 was closely achieved. It has been proven through the studies that the recovery processes of wastes containing ferrochrome can be realized in induction furnaces. One of the innovative aspects of the present invention is the addition of at least one magnetizing agent to the induction furnaces to achieve this. The scope of protection of the invention is set out in the appended claims and cannot be limited to what is described in this detailed description for illustrative purposes in any way. Indeed, it is clear that a person skilled in the art can come up with similar embodiments in the light of the foregoing without departing from the main theme of the invention.

Claims

CLAIMS1. A method for the recovery of ferrochrome products, wherein powdered wastes containing ferrochrome, obtained from waste recovery plants, are combined with at least one magnetizing agent to form a mixture and subjected to recovery processes in induction furnaces.

2. A method according to claim 1 , characterized in that it comprises a magnetizing agent comprising at least one of the elements nickel, iron or cobalt as a component.

3. A method according to claim 1 , characterized in that it comprises at least one alloy or compound comprising nickel, iron or cobalt as a magnetizing agent.

4. A method according to claim 3, characterized in that the magnetizing agent is at least one from the group consisting of ferromanganese, ferrochrome, ferrosilicon, ferrovandium, ferronickel, nickel ferrite, permalloy, nickel-aluminum, nickel-cobalt, cobalt ferrite, samarium cobalt, aluminum-nickel-cobalt, cobalt-nickel, ladle bottom metal, liquid metal, slags, steel scrap.

5. A method according to one of the preceding claims, characterized in that the mixture subjected to recovery processes in induction furnaces contains at least 10% by weight of a magnetizing agent.

6. A method according to one of the preceding claims, characterized in that the temperature of the induction furnace is in the range of 1700 to 1800 °C.

7. A method according to one of the preceding claims, characterized in that the mixture subjected to recovery processes in induction furnaces contains at least one desulphurization agent.

8. A method according to claim 7, characterized in that said desulphurization agent is at least one from the group consisting of calcium oxide, calcium hydroxide, magnesium oxide, sodium carbonate, fluorite or barite.

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