Combined smelting of molten slags and residuals from stainless steel and ferrochromium works

Abstract

To provide a method for smelting metals and metal oxides including side streams such as slags and wastes generated at stainless steel and ferrochromium works.SOLUTION: The processing method of the present invention is a smelting process for all side streams and residuals from the mentioned fields of industry. The streams are treated mainly in liquid phase for energy saving.SELECTED DRAWING: Figure 1

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.

Background Art

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

[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, a solvent, and a basic agent are charged. The products are, for example, alloys containing over 90% of the Cr and Ni charged, and disposable slag.

[0004] European Patent No. 1641946B discloses a method of 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, the intermediate distillates from stainless steel production and ferrochrome production are processed separately in various specified processes. The slag is processed in a cooled form in a metal recovery plant, and metal oxide-based wastes such as bag filter dust, mill scale, and sludge are generally processed in separate waste melting plants or landfills. Although there is always some amount of metal oxide present in the production of intermediate distillates, it is generally not beneficial to remelt these distillates in order to improve the reduction results. Residual metals from the slag distillates have conventionally been recovered by mechanical metal recovery devices, and some metals remain in the processed slag.

[0006] There is no current method for processing the liquid slag from stainless steel production and ferrochrome production in the same processing device.

[0007] [Table 1]

[0008] Definitions In the context of the present invention, stainless steel slag refers to the slag generated in the processes of scrap melting, AOD / VOD conversion, and ladle treatment in stainless steel production.

[0009] [Table 2]

[0010] In the context of the present invention, ferrochrome slag refers to the slag generated in the ferrochrome melting operation from chromite ore. The typical composition range of ferrochrome slag is presented in Table 2. [Summary of the Invention]

[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-based wastes such as filter dust, mill scale, and sludge are melted together with liquid slag from the production of stainless steel and ferrochrome in an electric arc furnace or a converter. A significant feature is the supply of the slag feedstock to the liquid phase, thus significantly reducing the energy requirements for melting and reduction.

Embodiments for Carrying Out the Invention

[0013] Metal oxides from slag distillates and metal oxide-based waste distillates are reduced to metals by dry metallurgy already in the molten phase for energy savings, thereby improving the benefits of dissolution.

[0014] All slag distillates related to the present invention are slags from stainless steel and ferrochrome production vessels (electric arc furnaces, converters, ladle treatment), and also other metal or metal oxide-containing intermediate distillates from the aforementioned metal production facilities, such as used refractories. 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 production (e.g., melting, fusing, grinding, hot and cold rolling, and acid regeneration facilities).

[0015] The treatment method of the present invention combines the dissolution of metal oxide-based wastes with a molten slag feedstock. Therefore, a separate treatment device is not required for metal oxide-based waste distillates. This combined process also eliminates the need for conventional mechanical separation of metal residues in the slag. Current treatment methods produce pure metal alloys and slag free of metals as products.

[0016] Dissolution (energy input of the molten distillate and reduction of metal oxides) can be carried out in an alternating or direct current electric arc furnace. Also, chemical energy can be used if a converter vessel is preferred.

[0017] The reduction of metal oxides is carried out with a reducing agent. Examples of useful reducing agents are coke, anthracite, graphite, methane, plastics, and rubber. Also, other carbon sources can be used. Further, 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 invention may contain dust and particulate matter from a scrap steel plant with a maximum dimension of 100 mm.

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

[0020] According to the invention, the optimal slag basicity for Cr2O3 reduction is achieved by mixing molten stainless steel slag (acting as a lime source) and ferrochrome slag. Thus, there is no need for additional lime input and melting, which saves natural resources and energy.

[0021] According to the invention, a method for producing a ferrochrome alloy is provided in a plurality of consecutive and synchronized method steps, preferably including Cr, Ni, and Mo. · In the first method step, the molten stainless steel slag and the molten ferrochrome slag are transferred from the stainless steel and ferrochrome production facilities to a molten slag treatment plant. The molten slag is charged into an electric arc furnace or a converter, and subsequently, the liquid stainless steel slag and the ferrochrome slag are naturally mixed. · In the second method step, in an embodiment using a converter, the reduction energy is supplied to the melt in the form of electrical or chemical energy. Also, since the slag is slightly cooled during transfer, additional energy is also required to reach the desired melting temperature. In the third method step, a metal oxide-based waste distillate and a reducing agent, preferably anthracite, are introduced into the melt, 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 submerged into the metal heel. After the metal reduction and submergence, the slag and the metal are withdrawn from the reduction furnace or container. · In the fifth method step, the withdrawn metal and slag are cooled into the form of aggregates or granulated into droplet-shaped particles. The metal alloy can also be immediately used as a liquid within a stainless steel manufacturing facility for energy conservation. 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

[0023] Figure 1 shows how molten slag is transferred from a metal manufacturing facility to a melting facility using a container. The liquid slag is charged into the melting furnace in an amount corresponding to the slag production volume. In addition, solid slag and solid metal oxide-based waste distillates are charged into the furnace from the silo via the charging chute. Excess energy is provided by the electrodes to achieve the desired reduction temperature (1500 °C - 1600 °C for the metal and 1600 °C - 1700 °C for the slag). A carbon-based reducing agent is added to reduce the metal oxides from the slag layer to the metal heel. The sedimentation rate of the reduced metal droplets or other metallurgical parameters can be changed by slag additives such as quartz and lime. After the reduction and sedimentation 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. Also, air cooling may be used to produce slag aggregates. Since the produced slag does not contain metal, no further metal separation is required.

Claims

[Claim 1] 1. A method for producing a ferrochromium alloy, comprising the steps of: - charging an electric arc furnace or a converter furnace with molten stainless steel slag and molten ferrochrome slag to allow the slags to mix; - supplying electrical energy to the melt in the electric arc furnace or chemical energy to the melt in the converter furnace; - feeding the melt in the electric arc furnace or the converter furnace with at least one particulate material comprising a metal salt and at least one reducing agent; - allowing the reduction of said metal oxide to form a metal alloy and allowing said metal alloy to settle; - recovering metal alloy and slag from said electric arc furnace or said converter furnace.

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