Method for preparing high-nickel-chromium ferroalloy by adding waste tire as reducing agent to treat stainless steel refining dust

Abstract

The application discloses a method for preparing high-nickel chromium ferroalloy by adding waste and old tires as reducing agents to treat stainless steel refining dust, and relates to the technical field of metallurgical solid waste resource collaborative comprehensive utilization. The method comprises the following steps: uniformly mixing the stainless steel refining dust, the waste and old tires and the coking coal, hot-pressing and forming to obtain mixed briquettes; high-temperature carbon thermal reduction of the mixed briquettes; cooling of the high-temperature carbon thermal reduction products under inert gas protection, crushing and magnetic separation to obtain high-nickel chromium ferroalloy and harmless slag. By adding the waste and old tires as the binder and the reducing agent and combining with the stainless steel refining dust, a large amount of C contained in the waste and old tires is used to replace part of the coking coal and reduce Fe, Cr, Ni and other metal components in the stainless steel refining dust, so that the purpose of turning waste into treasure is achieved, and the method does not need to add fluxes, binders and the like, can realize collaborative utilization of solid wastes in different fields, reduce energy consumption, and provides a new idea for collaborative treatment of various industrial solid wastes.

Description

Technical Field

[0001] This invention relates to the field of collaborative and comprehensive utilization technology of metallurgical solid waste resources, specifically to a method for preparing high-nickel ferrochromium alloy by adding waste tires as a reducing agent to treat stainless steel refining dust. Background Technology

[0002] With the continuous development of the steel industry, stainless steel has become an indispensable material in various modern industries. However, stainless steel production generates a large amount of stainless steel refining dust; approximately 20-30 kg of this dust is produced for every ton of stainless steel produced. This dust contains large amounts of metallic elements such as Fe, Cr, and Ni. While it has high recycling value if properly handled, improper handling can lead to negative consequences. The most obvious negative impact is pollution of our environment. For example, Cr in the dust is extremely unstable after long-term storage and is easily oxidized to form toxic Cr. 6+ Stainless steel refining dust pollutes soil and groundwater, endangering human health. Therefore, efficient recycling of stainless steel refining dust can not only alleviate environmental pollution from metallic elements but also reduce the supply of raw materials needed for stainless steel production, alleviating dependence on imported ore and saving costs while minimizing environmental pollution. Thus, how to efficiently and harmlessly recycle valuable metals from stainless steel refining dust and enhance its secondary resource value is a crucial research issue. Meanwhile, waste tires are an unavoidable solid waste generated during rubber industry production. Waste tires mainly contain elements such as carbon, and waste rubber is mostly infusible or refractory high-molecular-weight elastic materials with high chemical stability and resistance to degradation, as well as high toughness and elasticity, making it difficult to treat using either chemical or physical methods.

[0003] At present, there are many methods for treating stainless steel refining dust, but these methods often have the following problems: (1) A large amount of binder, additives, slag-forming agents and other components need to be added during the preparation of reaction raw materials. The raw material preparation process is complicated and requires a large amount of heat energy; (2) Some methods require the addition of nearly half or more coking coal, which consumes a large amount of coking coal and does not conform to the development goal of energy conservation and emission reduction; (3) Some methods use other carbon-containing reducing agents to reduce stainless steel refining dust to prepare ferroalloys, but the metal recovery rate is low and the metal grade in the alloy is low. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a method for preparing high-nickel ferrochromium alloys by adding waste tires as a reducing agent to treat stainless steel refining dust. This method reduces energy consumption, improves resource utilization, and embodies the concept of turning waste into treasure. By combining stainless steel refining dust with waste tires, the large amount of carbon contained in the waste tires is used to efficiently reduce the Fe, Cr, Ni, and other metallic elements in the stainless steel refining dust, thereby achieving the effect of turning waste into treasure. Moreover, this process does not require the addition of fluxes or binders, and while realizing the synergistic utilization of solid waste resources, it can also reduce energy consumption and improve the utilization rate of metallurgical solid waste and rubber-related solid waste.

[0005] This invention provides a method for preparing high-nickel ferrochromium alloy by adding waste tires as a reducing agent to treat stainless steel refining dust, comprising: Stainless steel refining dust, waste tires and coking coal are mixed evenly and then hot-pressed to form mixed briquettes; The mixed briquettes were subjected to high-temperature carbothermal reduction to obtain high-temperature carbothermal reduction products. The high-temperature carbothermic reduction product was cooled to room temperature under inert gas protection, and then crushed and magnetically separated to obtain a high-nickel ferrochromium alloy.

[0006] Furthermore, the mass ratio of the stainless steel refining dust, the waste tires, and the coking coal is (70-85):(15-30):(5-10), and the mass ratio of the waste tires to the coking coal is not greater than 4.

[0007] Furthermore, in the stainless steel refining dust, the total iron mass fraction is not less than 31%, the chromium mass fraction is not less than 8%, and the nickel mass fraction is not less than 2%.

[0008] Furthermore, the waste tires contain a carbon mass fraction of not less than 29% and an ash mass fraction of not more than 7%.

[0009] Furthermore, the coking coal has a carbon mass fraction of not less than 60%, an ash mass fraction of not more than 10%, a volatile matter mass fraction of not more than 30%, and a plastic layer index of not less than 12 mm.

[0010] Furthermore, the method also includes pretreatment of the raw materials: The stainless steel refining dust is dried, crushed, and passed through a 200-mesh sieve; The waste tires are dried, crushed with an angle grinder, and passed through an 80-mesh sieve. The coking coal is dried, crushed, and passed through a 200-mesh sieve; After processing, mix the three materials thoroughly.

[0011] Furthermore, in the hot pressing process, the hot pressing pressure is 30MPa-40MPa, the hot pressing temperature is 300℃-400℃, and the holding time is 0.5min-4min.

[0012] Furthermore, in the high-temperature carbothermic reduction, the reduction temperature is 1400℃-1500℃, the reduction time is 30min-60min, and the CO2 partial pressure does not exceed 10%.

[0013] Furthermore, the cooling process controls the cooling rate to be between 18°C / min and 23°C / min.

[0014] Furthermore, the magnetic separation yields a magnetic high-nickel ferrochrome alloy and a harmless slag containing non-magnetic materials; wherein the high-nickel ferrochrome alloy contains an Fe mass fraction of not less than 58%, a Cr mass fraction of not less than 11%, and a Ni mass fraction of not less than 4%.

[0015] Furthermore, the Fe recovery rate in the stainless steel refining dust is not less than 89%, the Cr recovery rate is not less than 87%, and the Ni recovery rate is not less than 89%.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: This invention provides a method for preparing high-nickel ferrochrome alloy by adding waste tires as a reducing agent to treat stainless steel refining dust. Using solid waste stainless steel refining dust, waste tires, and coking coal in relatively small amounts as raw materials, a high-temperature carbothermal reduction process is employed to obtain a high-nickel ferrochrome alloy with a high metal grade. The synergistic reduction effect of waste tires and solid waste stainless steel refining dust significantly improves the reduction efficiency of the entire preparation process. Furthermore, no flux or binder is required; the alloy particles and harmless slag are obtained by crushing and magnetic separation after cooling to room temperature in an inert atmosphere, reducing energy consumption and production costs. Moreover, this method for preparing high-nickel ferrochrome alloy by adding waste tires as a reducing agent uses a small amount of coking coal, resulting in less volatile matter and ash during the reduction process, leading to relatively less environmental pollution. The harmless slag obtained is free of metals such as Ni, Cr, and Fe, further reducing environmental pollution. Meanwhile, the present invention provides a method for preparing high-nickel ferrochromium alloy by adding waste tires as a reducing agent to treat stainless steel refining dust. The process is simple, the requirements for reaction temperature and other process conditions are low, it can save resources, reduce emissions and protect the environment, and has high economic benefits, and has broad industrial application prospects. Detailed Implementation

[0017] To better understand the above technical solutions, the technical solutions of the embodiments of this application will be described in detail below through specific embodiments. It should be understood that the embodiments of this application and the specific features in the embodiments are detailed descriptions of the technical solutions of the embodiments of this application, rather than limitations on the technical solutions of this application. In the absence of conflict, the embodiments of this application and the technical features in the embodiments can be combined with each other.

[0018] This invention provides a method for preparing high-nickel ferrochromium alloy by adding waste tires as a reducing agent to treat stainless steel refining dust, comprising: Stainless steel refining dust, waste tires and coking coal are mixed evenly and then hot-pressed to form mixed briquettes; The mixed briquettes were subjected to high-temperature carbothermic reduction to obtain high-temperature carbothermic reduction products; The high-temperature carbothermic reduction product was cooled to room temperature under inert gas protection, and then crushed and magnetically separated to obtain a high-nickel ferrochromium alloy.

[0019] Understandably, the carbon contained in waste tires can replace coking coal as a reducing agent, reducing the amount of externally added coking coal. With the increasing demand for stainless steel leading to a year-on-year increase in stainless steel production, the consumption of coking coal has increased significantly. This invention, based on the concept of reducing energy consumption, improving resource utilization, and turning waste into treasure, combines stainless steel refining dust with waste tires. The abundant carbon in the waste tires is used to efficiently reduce the Fe, Cr, Ni, and other metallic elements in the stainless steel refining dust, thus achieving the effect of turning waste into treasure. Furthermore, this process does not require the addition of fluxes or binders, achieving the synergistic utilization of solid waste resources while reducing energy consumption.

[0020] This invention provides a method for preparing high-nickel ferrochrome alloy by adding waste tires as a reducing agent to treat stainless steel refining dust. Using solid waste stainless steel refining dust, waste tires, and coking coal in relatively low amounts as raw materials, a high-nickel ferrochrome alloy with high metal grade is obtained through a high-temperature carbothermal reduction process. The synergistic reduction effect of waste tires and solid waste stainless steel refining dust significantly improves the reduction efficiency of the entire preparation process. No flux or binder needs to be added; after cooling to room temperature in an inert atmosphere, crushing and magnetic separation are sufficient to obtain the reduced alloy particles and harmless slag, reducing energy consumption and production costs. The resulting high-nickel ferrochrome alloy has an Fe mass fraction of not less than 58%, a Cr mass fraction of not less than 11%, and a Ni mass fraction of not less than 4%. The Fe recovery rate in the stainless steel refining dust is not less than 89%, the Cr recovery rate is not less than 87%, and the Ni recovery rate is not less than 89%. Meanwhile, the present invention provides a method for preparing high-nickel ferrochromium alloy by adding waste tires as a reducing agent to treat stainless steel refining dust. The process is simple, the requirements for reaction temperature and other process conditions are low, it can save resources, reduce emissions and protect the environment, and has high economic benefits, and has broad industrial application prospects.

[0021] In some embodiments, the stainless steel refining dust contains a total iron content of not less than 31%, a chromium content of not less than 8%, and a nickel content of not less than 2%. Waste tires contain a carbon content of not less than 29% and an ash content of not more than 7%. Coking coal contains a carbon content of not less than 60%, an ash content of not more than 10%, a volatile matter content of not more than 30%, and a gum layer index of not less than 12 mm.

[0022] In some embodiments, the mass ratio of stainless steel refining dust, waste tires and coking coal is (70-85):(15-30):(5-10), and the mass ratio of waste tires to coking coal is not greater than 4.

[0023] Specifically, the present invention provides a method for preparing high-nickel ferrochrome alloy by adding waste tires as a reducing agent to treat stainless steel refining dust. This method uses a small amount of coking coal, produces less volatile matter and ash during the reduction process, resulting in relatively less environmental pollution. Furthermore, the harmless slag obtained contains no metals such as Ni, Cr, and Fe, further reducing environmental pollution.

[0024] In some embodiments, the above method further includes pretreatment of the raw materials: Stainless steel refining dust is dried, crushed, and passed through a 200-mesh sieve; waste tires are dried, crushed by an angle grinder, and passed through an 80-mesh sieve; coking coal is dried, crushed, and passed through a 200-mesh sieve; after processing, the three materials are mixed evenly.

[0025] Specifically, pretreatment removes moisture to prevent vaporization during subsequent hot pressing or high-temperature reduction processes, which could affect the strength of the molded blocks and operational safety. Drying also improves the stability of the prepared samples in subsequent processes. Controlling particle size increases the specific surface area, promotes uniform mixing, and ensures a more complete reduction reaction, thereby improving the utilization rate of raw materials.

[0026] In some embodiments, during hot pressing, the hot pressing pressure is 30MPa-40MPa, the hot pressing temperature is 300℃-400℃, and the holding time is 0.5min-4min.

[0027] Specifically, the hot pressing parameters need to be comprehensively optimized: a pressure of 30MPa-40MPa aims to form internally compounded carbon blocks with suitable porosity and high strength. Too high a pressure will increase energy consumption, while too low a pressure will not meet the strength requirements for entering the rotary hearth furnace; a temperature of 300℃-400℃ allows the rubber to fully pyrolyze and produce a gel. Too high a temperature will lead to excessive decomposition of the binder components, while too low a temperature will not reach the pyrolysis temperature of waste tires, resulting in a loose block structure; a holding time of 0.5min-4min ensures that the internal structure of the pellets is dense. Too long a time will reduce efficiency, while too short a time will result in high porosity and low strength in the pellets.

[0028] In some embodiments, in high-temperature carbothermic reduction, the reduction temperature is 1400℃-1500℃, the reduction time is 30min-60min, and the CO2 partial pressure does not exceed 10%.

[0029] Specifically, a temperature of 1400℃-1500℃ ensures sufficient reduction of Cr oxides, guaranteeing metal recovery; a time of 30-60 minutes allows the reaction to proceed completely; and a low CO2 partial pressure not exceeding 10% maintains a strong reducing atmosphere to prevent metal re-oxidation. Inappropriate parameters will lead to decreased recovery, increased energy consumption, or reduced product purity.

[0030] In some embodiments, cooling is performed, with the cooling rate controlled at 18°C / min to 23°C / min.

[0031] Specifically, controlling the cooling rate to 18℃ / min-23℃ / min helps to balance the microstructure of the product during the cooling process and obtain a more ideal microstructure.

[0032] In the embodiments and comparative examples of this invention, the stainless steel refining dust comes from a domestic stainless steel production enterprise; the waste tires come from a domestic rubber production enterprise; and the coking coal comes from a domestic steel production enterprise. Specifically, the stainless steel refining dust contains at least 31% total iron, at least 8% chromium, and at least 2% nickel. The waste tires contain at least 29% carbon and at least 7% ash. The coking coal contains at least 60% carbon, at least 10% ash, at least 30% volatile matter, and at least 12 mm of gum layer. In the embodiments and comparative examples of this invention, nitrogen is used as the inert gas.

[0033] Example 1: A method for preparing high-nickel ferrochromium alloy by treating stainless steel refining dust with waste tires as a reducing agent. Includes the following steps: Stainless steel refining dust, waste tires, and coking coal in a mass ratio of 70:30:10 were thoroughly dried. The stainless steel refining dust and coking coal were crushed and sieved through a 200-mesh sieve, while the waste tires were crushed by an angle grinder and sieved through an 80-mesh sieve. After being mixed evenly, the mixture was pressed into a mixed briquette under hot pressing conditions of 30 MPa, 400℃, and 1 min to obtain a mixed briquette.

[0034] A crucible containing the mixed briquettes was placed in a high-temperature furnace. Under inert gas protection throughout the process, it underwent a high-temperature carbothermal reduction and cooling process. After cooling to room temperature, magnetic and non-magnetic materials were separated to obtain a high-nickel ferrochrome alloy and harmless slag, respectively. The high-temperature reduction temperature was 1400℃, the reduction time was 40 min, the CO2 partial pressure during high-temperature carbothermal reduction did not exceed 10%, and the cooling rate was 20℃ / min. The resulting high-grade ferrochrome alloy contained 58% Fe, 12% Cr, and 4% Ni by mass, with harmful components P and S both less than 0.05% by mass. The metal recovery rates of Fe, Cr, and Ni in stainless steel refining dust were 90%, 89%, and 91%, respectively.

[0035] Example 2: A method for preparing high-nickel ferrochromium alloy by treating stainless steel refining dust with waste tires as a reducing agent. Includes the following steps: Stainless steel refining dust, waste tires, and coking coal in a mass ratio of 80:20:5 were thoroughly dried. The stainless steel refining dust and coking coal were crushed and sieved through a 200-mesh sieve, while the waste tires were crushed by an angle grinder and sieved through an 80-mesh sieve. After being mixed evenly, the mixture was pressed into a mixed briquette under hot pressing conditions of 35 MPa, 400℃, and 1 min to obtain a mixed briquette.

[0036] A crucible containing the mixed briquettes was placed in a high-temperature furnace. Under inert gas protection throughout the process, it underwent a high-temperature carbothermal reduction and cooling process. After cooling to room temperature, magnetic and non-magnetic materials were separated to obtain a high-nickel ferrochrome alloy and harmless slag, respectively. The high-temperature reduction temperature was 1450℃, the reduction time was 45 min, the CO2 partial pressure during high-temperature carbothermal reduction did not exceed 10%, and the cooling rate was 20℃ / min. The resulting high-grade ferrochrome alloy contained 59% Fe, 12% Cr, and 4% Ni by mass, with harmful components P and S both less than 0.05% by mass. The metal recovery rates of Fe, Cr, and Ni in the stainless steel refining dust were 90%, 89%, and 90%, respectively.

[0037] Example 3: A method for preparing high-nickel ferrochromium alloy by treating stainless steel refining dust with waste tires as a reducing agent. Includes the following steps: Stainless steel refining dust, waste tires, and coking coal in a mass ratio of 85:15:5 were thoroughly dried. The stainless steel refining dust and coking coal were crushed and sieved through a 200-mesh sieve, while the waste tires were crushed by an angle grinder and sieved through an 80-mesh sieve. After being mixed evenly, the mixture was pressed into a block under hot pressing conditions of 35 MPa, 400℃, and 1 min to obtain a mixed block.

[0038] A crucible containing the mixed briquettes was placed in a high-temperature furnace. Under inert gas protection throughout the process, it underwent a high-temperature carbothermal reduction and cooling process. After cooling to room temperature, magnetic and non-magnetic materials were separated to obtain a high-nickel ferrochrome alloy and harmless slag, respectively. The high-temperature reduction temperature was 1450℃, the reduction time was 50 min, the CO2 partial pressure during high-temperature carbothermal reduction did not exceed 10%, and the cooling rate was 20℃ / min. The resulting high-grade ferrochrome alloy contained 59% Fe, 11% Cr, and 4% Ni by mass, with harmful components P and S both less than 0.05% by mass. The metal recovery rates of Fe, Cr, and Ni in stainless steel refining dust were 89%, 87%, and 89%, respectively.

[0039] Example 4: A method for preparing high-nickel ferrochromium alloy by treating stainless steel refining dust with waste tires as a reducing agent. Includes the following steps: Stainless steel refining dust, waste tires, and coking coal in a mass ratio of 85:15:5 were thoroughly dried. The stainless steel refining dust and coking coal were crushed and sieved through a 200-mesh sieve, while the waste tires were crushed by an angle grinder and sieved through an 80-mesh sieve. After being mixed evenly, the mixture was pressed into a mixed briquette under hot pressing conditions of 40 MPa, 400℃, and 2 min to obtain a mixed briquette.

[0040] A crucible containing the mixed briquettes was placed in a high-temperature furnace. Under inert gas protection throughout the process, it underwent a high-temperature carbothermal reduction and cooling process. After cooling to room temperature, magnetic and non-magnetic materials were separated to obtain a high-nickel ferrochrome alloy and harmless slag, respectively. The high-temperature reduction temperature was 1450℃, the reduction time was 55 min, the CO2 partial pressure during high-temperature carbothermal reduction did not exceed 10%, and the cooling rate was 20℃ / min. The resulting high-grade ferrochrome alloy contained 58% Fe, 12% Cr, and 5% Ni by mass, with harmful components P and S both less than 0.05% by mass. The metal recovery rates of Fe, Cr, and Ni in stainless steel refining dust were 89%, 88%, and 90%, respectively.

[0041] Example 5: A method for preparing high-nickel ferrochromium alloy by treating stainless steel refining dust with waste tires as a reducing agent. Includes the following steps: Stainless steel refining dust, waste tires, and coking coal in a mass ratio of 80:20:10 were thoroughly dried. The stainless steel refining dust and coking coal were crushed and sieved through a 200-mesh sieve, while the waste tires were crushed by an angle grinder and sieved through an 80-mesh sieve. After being mixed evenly, the mixture was pressed into a mixed briquette under hot pressing conditions of 40 MPa, 400℃, and 3 min to obtain a mixed briquette.

[0042] A crucible containing the mixed briquettes was placed in a high-temperature furnace. Under inert gas protection throughout the process, it underwent a high-temperature carbothermal reduction and cooling process. After cooling to room temperature, magnetic and non-magnetic materials were separated to obtain a high-nickel ferrochrome alloy and harmless slag, respectively. The high-temperature reduction temperature was 1500℃, the reduction time was 40 min, the CO2 partial pressure during high-temperature carbothermal reduction did not exceed 10%, and the cooling rate was 20℃ / min. The resulting high-grade ferrochrome alloy contained 59% Fe, 11% Cr, and 4% Ni by mass, with harmful components P and S both less than 0.05% by mass. The metal recovery rates of Fe, Cr, and Ni in the stainless steel refining dust were 90%, 87%, and 90%, respectively.

[0043] Comparative Example 1 The difference from Example 1 is that waste tires are not used, and the mass ratio of stainless steel refining dust to coking coal is 100:10.

[0044] Stainless steel refining dust and coking coal with a mass ratio of 100:10 are thoroughly dried. Waste tires are not used. The stainless steel refining dust and coking coal are crushed and sieved through a 200-mesh sieve. After being mixed evenly, they are pressed into shape under the conditions of hot pressing pressure of 30MPa, hot pressing temperature of 400℃ and holding time of 1min to obtain mixed briquettes.

[0045] A crucible containing the mixed briquettes was placed in a high-temperature furnace. Under inert gas protection throughout the process, it underwent a high-temperature carbothermal reduction and cooling process. After cooling to room temperature, a mixed reduction product of high-nickel ferrochromium alloy and harmless slag was obtained. The high-temperature reduction temperature was 1400℃, the reduction time was 40 min, the CO2 partial pressure during the high-temperature carbothermal reduction did not exceed 10%, and the cooling rate was 20℃ / min. The efficiency of the obtained reduction product was reduced by separating magnetic and non-magnetic materials. The metal recovery rates of Fe, Cr, and Ni in stainless steel refining dust were 81%, 80%, and 83%, respectively.

[0046] Comparative Example 2 The difference from Example 2 is that the mass ratio of stainless steel refining dust to waste tires is 90:10.

[0047] Stainless steel refining dust, waste tires, and coking coal in a mass ratio of 90:10:5 were thoroughly dried. The stainless steel refining dust and coking coal were crushed and sieved through a 200-mesh sieve, while the waste tires were crushed by an angle grinder and sieved through an 80-mesh sieve. After being mixed evenly, the mixture was pressed into a mixed briquette under hot pressing conditions of 35 MPa, 400℃, and 1 min to obtain a mixed briquette.

[0048] A crucible containing the mixed briquettes was placed in a high-temperature furnace. Under inert gas protection throughout the process, it underwent a high-temperature carbothermal reduction and cooling process. After cooling to room temperature, magnetic and non-magnetic materials were separated to obtain a high-nickel ferrochrome alloy and harmless slag, respectively. The high-temperature reduction temperature was 1450℃, the reduction time was 45 min, the CO2 partial pressure during high-temperature carbothermal reduction did not exceed 10%, and the cooling rate was 20℃ / min. The resulting high-grade ferrochrome alloy contained 57% Fe, 11% Cr, and 3% Ni by mass, with harmful components P and S both less than 0.05% by mass. The metal recovery rates of Fe, Cr, and Ni in stainless steel refining dust were 86%, 85%, and 84%, respectively.

[0049] Comparative Example 3 The difference from Example 3 is that the mass ratio of stainless steel refining dust to waste tires is 70:30.

[0050] Stainless steel refining dust and coking coal with a mass ratio of 70:30:5 were crushed and screened through a 200-mesh sieve. Meanwhile, waste tires were crushed by an angle grinder and screened through an 80-mesh sieve. After being mixed evenly, the mixture was pressed into a block under hot pressing conditions of 35 MPa, 400℃, and 1 min to obtain a mixed block.

[0051] A crucible containing the mixed briquettes was placed in a high-temperature furnace. Under inert gas protection throughout the process, it underwent a high-temperature carbothermal reduction and cooling process. After cooling to room temperature, magnetic and non-magnetic materials were separated to obtain a high-nickel ferrochrome alloy and harmless slag, respectively. The high-temperature reduction temperature was 1450℃, the reduction time was 50 min, the CO2 partial pressure during high-temperature carbothermal reduction did not exceed 10%, and the cooling rate was 20℃ / min. The resulting high-grade ferrochrome alloy contained 57% Fe, 11% Cr, and 3% Ni by mass, with harmful components P and S both less than 0.05% by mass. The metal recovery rates of Fe, Cr, and Ni in stainless steel refining dust were 86%, 84%, and 88%, respectively.

[0052] Comparative Example 4 The difference from Example 4 is that the cooling rate under inert gas protection is 15°C / min.

[0053] Stainless steel refining dust and coking coal with a mass ratio of 85:15:5 were crushed and screened through a 200-mesh sieve. Meanwhile, waste tires were crushed by an angle grinder and screened through an 80-mesh sieve. After being mixed evenly, the mixture was pressed into a mixed briquette under the conditions of hot pressing pressure of 40MPa, hot pressing temperature of 400℃, and holding time of 2min.

[0054] A crucible containing the mixed briquettes was placed in a high-temperature furnace. Under inert gas protection throughout the process, it underwent a high-temperature carbothermal reduction and cooling process. After cooling to room temperature, magnetic and non-magnetic materials were separated to obtain a high-nickel ferrochrome alloy and harmless slag, respectively. The high-temperature reduction temperature was 1450℃, the reduction time was 55 min, the CO2 partial pressure during high-temperature carbothermal reduction did not exceed 10%, and the cooling rate was 15℃ / min. The resulting high-grade ferrochrome alloy contained 60% Fe, 12% Cr, and 5% Ni by mass, with harmful components P and S both less than 0.05% by mass. The metal recovery rates of Fe, Cr, and Ni in the stainless steel refining dust were 90%, 89%, and 90%, respectively.

[0055] Comparative Example 5 The difference from Example 5 is that the cooling rate under inert gas protection is 25°C / min.

[0056] Stainless steel refining dust and coking coal with a mass ratio of 80:20:10 were crushed and screened through a 200-mesh sieve. Meanwhile, waste tires were crushed by an angle grinder and screened through an 80-mesh sieve. After being mixed evenly, the mixture was pressed into a mixed briquette under the conditions of hot pressing pressure of 40MPa, hot pressing temperature of 400℃, and holding time of 3min.

[0057] A crucible containing the mixed briquettes was placed in a high-temperature furnace. Under inert gas protection throughout the process, it underwent a high-temperature carbothermal reduction and cooling process. After cooling to room temperature, magnetic and non-magnetic materials were separated to obtain a high-nickel ferrochrome alloy and harmless slag, respectively. The high-temperature reduction temperature was 1500℃, the reduction time was 40 min, the CO2 partial pressure during high-temperature carbothermal reduction did not exceed 10%, and the cooling rate was 25℃ / min. The resulting high-grade ferrochrome alloy contained 56% Fe, 11% Cr, and 4% Ni by mass, with harmful components P and S both less than 0.05% by mass. The metal recovery rates of Fe, Cr, and Ni in stainless steel refining dust were 88%, 88%, and 87%, respectively.

[0058] Table 1 Comparison of key parameters between Examples 1-5 and Comparative Examples 1-5

[0059] Table 2. Recovery rates of Fe, Cr, and Ni in Examples 1-5 and Comparative Examples 1-5

[0060] As can be seen from Tables 1 and 2: 1) The only difference between Comparative Example 1 and Example 1 is that waste tires are not used. In this case, the separation efficiency of high-grade nickel-chromium-iron alloy and slag phase in Comparative Example 1 is reduced. This is because the addition of waste tires can change the reduction characteristics of the mixed briquettes, improve the metal aggregation effect in the high-temperature carbothermic reduction process, and improve the crushing and magnetic separation effect of the reduction products. When waste tires are not used, the metal recovery rates of Fe, Cr and Ni decrease from 90%, 89% and 91% to 81%, 80% and 83%, respectively.

[0061] 2) The only difference between Comparative Example 2 and Example 2 is that the mass ratio of stainless steel refining dust to waste tires changed from 80:20 to 90:10. The metal recovery rates of Fe, Cr and Ni decreased from 90%, 89% and 90% to 86%, 85% and 84%, respectively.

[0062] 3) The only difference between Comparative Example 3 and Example 3 is that the mass ratio of stainless steel refining dust to waste tires changed from 85:15 to 70:30. The metal recovery rates of Fe, Cr and Ni decreased from 89%, 87% and 89% to 86%, 84% and 88%, respectively.

[0063] 4) The only difference between Comparative Example 4 and Example 4 is that the cooling rate was reduced from 20°C / min to 15°C / min. Although the metal recovery rate of Comparative Example 4 was also slightly higher than that of Example 4, the cooling rate of Comparative Example 4 was too low, which made the recovery process too time-consuming and energy-intensive, thus losing the purpose of recovery.

[0064] 5) The only difference between Comparative Example 5 and Example 5 is that the cooling rate was increased from 20°C / min to 25°C / min, and the metal recovery rates of Fe, Cr and Ni decreased from 90%, 87% and 90% to 88%, 88% and 87%, respectively.

[0065] It will be readily understood by those skilled in the art that the above-described advantageous methods can be freely combined and superimposed without conflict. The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application. The above are merely preferred embodiments of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this application, and these improvements and modifications should also be considered within the protection scope of this application.

Claims

1. A method for preparing high-nickel ferrochromium alloy by adding waste tires as a reducing agent to treat stainless steel refining dust, characterized in that, include: Stainless steel refining dust, waste tires and coking coal are mixed evenly and then hot-pressed to form mixed briquettes; The mixed briquettes were subjected to high-temperature carbothermal reduction to obtain high-temperature carbothermal reduction products. The high-temperature carbothermic reduction product was cooled to room temperature under inert gas protection, and then crushed and magnetically separated to obtain a high-nickel ferrochromium alloy.

2. The method according to claim 1, characterized in that, The mass ratio of the stainless steel refining dust, the waste tires, and the coking coal is (70-85):(15-30):(5-10), and the mass ratio of the waste tires to the coking coal is not greater than 4.

3. The method according to claim 1 or 2, characterized in that, The stainless steel refining dust contains a total iron content of not less than 31%, a chromium content of not less than 8%, and a nickel content of not less than 2%.

4. The method according to claim 1 or 2, characterized in that, The waste tires contain no less than 29% carbon by mass and no more than 7% ash by mass.

5. The method according to claim 1 or 2, characterized in that, The coking coal shall have a carbon content of not less than 60%, an ash content of not more than 10%, a volatile matter content of not more than 30%, and a plastic layer index of not less than 12 mm.

6. The method according to claim 1 or 2, characterized in that, The method further includes pretreatment of the raw materials: The stainless steel refining dust is dried, crushed, and passed through a 200-mesh sieve; The waste tires are dried, crushed with an angle grinder, and passed through an 80-mesh sieve. The coking coal is dried, crushed, and passed through a 200-mesh sieve; After processing, mix the three materials thoroughly.

7. The method according to claim 1 or 2, characterized in that, In the hot pressing process, the hot pressing pressure is 30MPa-40MPa, the hot pressing temperature is 300℃-400℃, and the holding time is 0.5min-4min.

8. The method according to claim 1 or 2, characterized in that, In the high-temperature carbothermic reduction, the reduction temperature is 1400℃-1500℃, the reduction time is 30min-60min, and the CO2 partial pressure does not exceed 10%.

9. The method according to claim 1 or 2, characterized in that, The cooling process controls the cooling rate to be between 18°C / min and 23°C / min.

10. The method according to claim 1 or 2, characterized in that, The magnetic separation yields a magnetic high-nickel ferrochrome alloy and a harmless slag containing non-magnetic materials; wherein the high-nickel ferrochrome alloy contains at least 58% Fe by mass, at least 11% Cr by mass, and at least 4% Ni by mass. The recovery rate of Fe in the stainless steel refining dust is not less than 89%, the recovery rate of Cr is not less than 87%, and the recovery rate of Ni is not less than 89%.

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