Combined melting of molten slag and residues from stainless steel and ferrochrome plants

Abstract

The present invention relates to a method for dissolving metals and metal oxides, including intermediate distillates such as slags and waste products produced in stainless steel and ferrochrome plants. The treatment method of the present invention is a dissolution process for all intermediate distillates and residues from the above mentioned industries. The distillates are treated mainly in the liquid phase to save energy.

Description

Technical Field

[0001] The present invention relates to a method for dissolving metal and metal oxide-containing intermediate distillates such as slag and waste generated in stainless steel and ferrochrome factories. The treatment method of the present invention is a dissolution process for all intermediate distillates and residues from the above industries. The distillates are mainly treated in the liquid phase for energy conservation.

Summary of the Invention

Problems to be Solved by the Invention

[0002] In the steel industry using electric arc furnaces, a substantial amount of metal oxide-containing dust is produced. This dust contains a large amount of metals that cannot be discarded at landfills, resulting in waste problems. In addition, waste metals mean economic losses. In addition to dust, some waste distillates containing metals are generated in the industry, and these distillates present opportunities for metal recovery and reduction of environmental impacts.

[0003] In the early 1970s, the Enviroplas process was developed in South Africa to treat slag and dust from the metallurgical industry. A typical process includes a direct current arc furnace into which dust from a stainless steel plant, anthracite coal, a solvent, and a basic agent are charged. The products are, for example, alloys containing more than 90% of the introduced Cr and Ni, and disposable slag.

[0004] European Patent No. 1641946B discloses a method for producing a metal alloy melt in a plurality of subsequent steps, whereby dust and slag are reused in this process for recovering Cr and Ni.

[0005] Currently, intermediate distillates from stainless steel and ferrochrome production are processed separately in various designated processes. Slag is processed in a cooled form in metal recovery plants, while metal oxide waste, such as bag filter dust, mill scale, and sludge, is generally processed in separate waste dissolution plants or waste treatment facilities. Although some amount of metal oxide is always present in the production of intermediate distillates, it is generally not beneficial to remelt these distillates to improve reduction results. Residual metals from slag distillates are conventionally recovered by mechanical metal recovery equipment, and some metals remain in the slag after processing.

[0006] There is no modern method for processing liquid slag from stainless steel manufacturing and ferrochrome manufacturing using the same processing equipment.

[0007] [Table 1]

[0008] definition In the context of this invention, stainless steel slag refers to slag produced in the manufacturing of stainless steel during scrap melting, AOD / VOD conversion, and ladle processing processes.

[0009] [Table 2]

[0010] In the context of this invention, ferrochrome slag refers to slag produced by the ferrochrome dissolution process from chromium ore. Table 2 shows a typical composition range for ferrochrome slag.

[0011] The present invention is defined by what is disclosed in the independent claims. Preferred embodiments are described in the dependent claims.

[0012] According to the present invention, metal oxide waste such as filter dust, mill scale, and sludge is melted together with liquid slag from stainless steel and ferrochrome production in an electric arc furnace or conversion furnace. A notable feature is that the slag input material is supplied to the liquid phase, thus significantly reducing the energy requirements for melting and reduction.

[0013] Details of the invention Metal oxides from slag distillates and metal oxide waste distillates are already reduced to metals by dry metallurgy in the molten phase to save energy, thereby improving the efficiency of the dissolution process.

[0014] All slag distillates related to the present invention are slags from stainless steel and ferrochrome manufacturing vessels (electric arc furnaces, conversion furnaces, ladle processing), as well as other metal or metal oxide-containing intermediate distillates from the aforementioned metal manufacturing facilities, such as refractories after use. The metal oxide-containing intermediate distillates related to this technological innovation are metal oxides, sulfates, or hydroxide-containing gas purification dust, scale, and sludge from stainless steel and ferrochrome manufacturing (e.g., melting, molten, grinding, hot and cold rolling, and acid regeneration facilities).

[0015] The present invention combines the dissolution of metal oxide waste with the input material of molten slag. Therefore, separate processing equipment is not required for the metal oxide waste distillate. This combined process also eliminates the need for conventional mechanical separation of metal residues in the slag. Current processing methods produce pure metal alloys and metal-free slag as products.

[0016] Melting (energy input of molten distillate and reduction of metal oxides) can be carried out in an AC or DC electric arc furnace. Alternatively, if a conversion furnace vessel is preferred, chemical energy can be used.

[0017] The reduction of metal oxides is carried out with reducing agents. Examples of useful reducing agents include coke, anthracite, graphite, methane, plastics, and rubber. Other carbon sources can also be used. Furthermore, silicon and aluminum-based reducing agents can be used.

[0018] The dust in this context may also contain ZnO. The distillate for use in the method according to the present invention may include dust and particulate matter from a waste steel plant with a maximum dimension of 100 mm.

[0019] When the method according to the present invention is used, the recovery of chromium, iron, and nickel as metals is typically over 90%.

[0020] According to the present invention, the optimal slag basicity for Cr2O3 reduction is achieved by mixing molten stainless steel slag (acting as a lime source) and ferrochrome slag. Therefore, additional lime addition and melting are unnecessary, saving natural resources and energy.

[0021] According to the present invention, a method for producing a ferrochrome alloy is provided, comprising a series of sequential and synchronized method steps, preferably including Cr, Ni, and Mo. In the first step of the method, the molten stainless steel slag and molten ferrochrome slag are transferred from the stainless steel and ferrochrome manufacturing facility to the molten slag processing plant. The molten slag is fed into an electric arc furnace or a conversion furnace, and subsequently the liquid stainless steel slag and ferrochrome slag are naturally mixed. In the second method step, the reduction energy is supplied to the molten material in the form of electricity or chemical energy, in embodiments utilizing a conversion furnace. Additionally, since the slag is slightly cooled during transfer, extra energy is required to reach the desired melting temperature. In the third step of the process, a metal oxide waste distillate and a reducing agent, preferably anthracite, are introduced into the molten material, and the reduction of the metal oxides in the slag is carried out at an optimal temperature. · In the fourth method step, the reduced metal droplets in the slag are made to sink into the metal heel. After the metal reduction and sinking, the slag and the metal are withdrawn from the reduction furnace or vessel. · In the fifth method step, the withdrawn metal and slag are cooled into the form of aggregates or granulated into droplet-like particles. The metal alloy can also be immediately used as a liquid within a stainless steel manufacturing facility for energy savings. The produced metal alloy may be further used in the metal industry, and the produced slag may be further used mainly in various slag product applications in geotechnics.

Brief Description of the Drawings

[0022] The present invention is illustrated in more detail with reference to the accompanying drawings. [Figure 1] FIG. 1 shows the principle of the combined treatment of metal and metal oxide-containing residues from stainless steel and ferrochrome facilities.

Modes for Carrying Out the Invention

[0023] Figure 1 shows how molten slag is transferred from a metal manufacturing facility to a melting facility using a container. Liquid slag is fed into the melting furnace in phases equivalent to the amount of slag produced. In addition, solid slag and solid metal oxide waste distillates are fed into the furnace from a silo via an input chute. Excess energy is provided by electrodes to achieve the desired reduction temperature (1500°C to 1600°C for metal and 1600°C to 1700°C for slag). A carbon-based reducing agent is added to reduce the metal oxides from the slag layer to metal heel. The settling rate of the reduced metal droplets or other metallurgical parameters can be modified by slag additives, such as quartz and lime. After the reduction and settling of the produced metal alloy, the furnace is withdrawn. The metal alloy is used as a liquid in stainless steel manufacturing or granulated into metal granules for use in the metal industry. The slag produced from the melting furnace is granulated into slag products by air, water, or gas for different applications. Additionally, air cooling may be used to produce the slag aggregate. Since the produced slag does not contain metal, further metal separation is not necessary.

Claims

1. A method for producing ferrochrome alloy, - A step that allows for the mixing of molten stainless steel slag and molten ferrochrome slag as slag distillates in an electric arc furnace or a conversion furnace, - A step of supplying electrical energy to the molten material in the electric arc furnace, or chemical energy to the molten material in the conversion furnace, - A step of supplying at least one particulate matter containing metal oxide waste distillate and at least one reducing agent to the molten material in the electric arc furnace or the conversion furnace, - A step that enables the reduction of the slag distillate and the metal oxide waste distillate, forms a metal alloy, and allows the metal alloy to settle, A method comprising the step of recovering a metal alloy and slag from the electric arc furnace or the conversion furnace.

2. The method according to claim 1, wherein the particulate matter is dust from an electric arc furnace.

3. The method according to claim 1, wherein the particulate matter comprises at least one metal sulfate, sulfide, or hydroxide.

4. The method according to claim 1, wherein the particulate matter is flue gas dust, scale, precipitate, or sludge generated from a metallurgical process.

5. The method according to claim 1, wherein the at least one reducing agent includes anthracite.

6. The method according to claim 1, wherein a basic substance is not added to the electric arc furnace or the conversion furnace.

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