Method for preparing chromium-silicon-iron alloy by co-reduction of hazardous waste chromium residue and siderite under magnetic field strengthening

Abstract

The application discloses a method for preparing chromium-silicon-iron alloy by co-reducing hazardous waste chromium residue and siderite under the action of a magnetic field. First, the chromium residue and the siderite are ground into powder, and then mixed with a special biomass reducing agent and a binder at a certain ratio to form pellets. After drying, the mixed pellets are put into a heating furnace for co-reduction roasting. Then, the reaction products are separated by screening and magnetic separation to obtain the chromium-silicon-iron alloy required by steel smelting enterprises, and at the same time, the high-MgO tailings which can be used as non-ferrous magnesium refining raw materials are separated. The industrial solid waste, low-grade iron ore and crop straw are used cooperatively, which can not only reduce the co-reduction temperature and avoid the use of carbonaceous reducing agent, but also realize the synchronous extraction of Fe, Cr and Si and the enrichment of MgO in the tailings. In addition, according to the good magnetic properties of the raw materials and the alloy products, the static magnetic field characteristics are utilized to promote the aggregation and growth of the chromium-silicon-iron alloy and improve the yield.

Description

Technical Field

[0001] This invention relates to the field of industrial solid waste resource utilization technology, and more specifically to a method for preparing chromium-silicon-ferroalloy by co-reduction of hazardous waste chromium slag and siderite using magnetic field enhancement. Background Technology

[0002] Chromium slag is a solid waste discharged during the production processes of ferrochrome alloy and chromium salt enterprises. Hexavalent chromium ions in chromium slag are highly toxic. Currently, there are three main methods for treating chromium slag in my country: the first is to use seepage-proof and waterproof landfills; the second is to add reducing agents to the slag to reduce hexavalent chromium to trivalent chromium; and the third is to detoxify and render the slag harmless before comprehensive utilization. These methods are difficult to industrialize and also present several problems, including potential secondary pollution, failure to recover valuable elements, and incomplete detoxification.

[0003] Siderite is one of the most representative complex and difficult-to-process iron ore resources in my country. Its main component is ferrous carbonate, and it often occurs in isomorphous associations with silicon and magnesium, resulting in low iron grade and making large-scale development and utilization difficult. It is a typical low-grade and difficult-to-process iron ore resource. my country is rich in siderite resources, with proven reserves of nearly 2 billion tons, but less than 10% of the total reserves have been utilized. It is mainly used for steelmaking, with virtually no applications in other areas. Therefore, how to achieve efficient development and utilization of my country's difficult-to-process iron ore resources is of significant strategic importance.

[0004] Furthermore, existing methods for recycling valuable metals from solid waste mainly rely on carbonaceous reducing agents and electrically heated high-temperature furnaces. These processes are time-consuming, generate significant amounts of greenhouse gases, are energy-intensive and costly, and result in low overall resource utilization rates for solid waste. Moreover, my country generates substantial amounts of crop straw during agricultural production and processing, as well as in daily life; this solid waste has not been effectively utilized. Summary of the Invention

[0005] In view of this, the present invention addresses the aforementioned problems and, considering the characteristics of hazardous waste chromium slag, siderite, and crop straw resources, aims to provide a method for the co-reduction preparation of chromium-silicon-ferroalloy using hazardous waste chromium slag and siderite in a magnetic field-enhanced manner, thereby achieving the synergistic and comprehensive resource utilization of multiple solid waste resources. This method fully utilizes the magnetization and decomposition of siderite by the magnetic field and the migration, aggregation, and growth of the chromium-silicon-ferroalloy. Under the influence of reducing gases and biochar generated by the pyrolysis of a specially formulated biomass reducing agent, the simultaneous extraction of Fe, Cr, and Si elements from the hazardous waste chromium slag and siderite, as well as the separation of high-MgO tailings, are achieved. This results in the comprehensive resource utilization and high-value-added utilization of various solid wastes and low-grade iron ore.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing chromium-silicon-ferroalloys by co-reduction of hazardous chromium slag and siderite using magnetic field enhancement specifically includes the following steps:

[0008] (1) Grind chromium slag and siderite into powder of 200 mesh or higher, then add a certain amount of reducing agent and binder, mix them thoroughly in proportion, and press them into pellets with a diameter of 30 mm.

[0009] (2) The mixed pellets obtained in step (1) are placed in a drying oven and dried to constant weight;

[0010] (3) Place the dried pellets obtained in step (2) into a heating furnace. First, keep them at 500-600℃ for 40-60 minutes, then continue to heat them at 1150-1250℃ for 90-120 minutes. During the heating process, argon gas is continuously introduced into the furnace so that the reaction is completed in an inert atmosphere. During the heat preservation stage, the static magnetic field is turned on. After the reaction is completed, the furnace is naturally cooled to room temperature to obtain the co-reduced product.

[0011] (4) The co-reduction product obtained in step (3) is screened to obtain chromium-silicon-iron alloy particles with a particle size greater than 1.0 mm, and particles smaller than 1 mm are crushed, ground, magnetically separated and dried to obtain chromium-silicon-iron alloy powder.

[0012] Preferably, the mass ratio of the chromium slag, siderite, and special reducing agent is 5:2 to 3:6 to 8.

[0013] Preferably, the binder is industrial waste syrup, and the amount added is 8-10 wt% of the total mass of chromium slag, siderite, and special reducing agent.

[0014] Preferably, the main raw material of the reducing agent is crop straw with a fixed carbon content of 15% or more, which can be one or a mixture of several types such as rice straw, wheat straw, and corn straw. The crop straw needs to be crushed to a particle size of less than 150 mesh. First, a mixed solution of Na2CO3 and K2CO3 with a Na / K molar ratio of 1:1 is prepared, and the total solute concentration is 0.12 mol / L. Then, the crop straw powder is thoroughly stirred and mixed with the Na2CO3 and K2CO3 mixed solution for more than 3 hours, with a mass ratio of 1:5. The mixture is then placed in a drying oven at 90°C and kept at constant weight to obtain the specially prepared reducing agent.

[0015] Preferably, the moisture content of the dried pellets in step (2) is less than 3 wt%, and the drum strength of the dried pellets (+6.3 mm) (%) is ≥85%.

[0016] Among them, (+6.3mm)(%)≥85% means that after the pellet sample is sieved by the standard drum test, the proportion of the part larger than 6.3mm is ≥85%.

[0017] Preferably, the heating process involves first holding the temperature at 500–600°C for 40–60 minutes, then continuing to heat the temperature at 1150–1250°C for 90–120 minutes, with argon gas protection throughout the process. After the high-temperature reduction is completed, the product is cooled to room temperature in the furnace to obtain the reduction product.

[0018] Preferably, in step (3), an electrostatic electromagnet is installed at the position where the sample is placed in the heating furnace. The electromagnet generates a horizontal magnetic field with adjustable intensity and is turned on during the heat preservation process. The static magnetic field strength is 0.7 to 0.8 T in the low temperature stage (500 to 600°C) and 0.9 to 1.0 T in the high temperature stage (1150 to 1250°C).

[0019] Preferably, the chromium-silicon-iron alloy obtained in step (4) contains 70-74 wt% iron, 10-14 wt% chromium, and 12-16 wt% silicon by mass. The iron recovery rate reaches over 82%, the chromium recovery rate reaches over 83%, and the silicon recovery rate reaches over 85%. The tailings remaining after magnetic separation contain over 75% MgO by mass.

[0020] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0021] Compared with existing technologies, this invention provides a method for preparing chromium-silicon-ferroalloy by co-reduction of hazardous waste chromium slag and siderite using magnetic field enhancement. Using hazardous waste chromium slag, siderite, and crop straw as main raw materials, this method fully utilizes the magnetic field's magnetization and decomposition of siderite, as well as the migration, aggregation, and growth of the chromium-silicon-ferroalloy. Simultaneously, a specially formulated reducing agent efficiently generates reducing gases and biochar during high-temperature pyrolysis, achieving efficient simultaneous extraction of Fe, Cr, and Si elements from the hazardous waste chromium slag and siderite, and separation of high-MgO tailings. This achieves full resource utilization and high-value-added utilization of various solid wastes. It has advantages such as large solid waste absorption capacity, low energy consumption, and low carbon footprint. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0023] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1

[0026] (1) Thoroughly mix chromium slag, siderite, special reducing agent, and binder, and press them into pellets with a diameter of 30 mm. The mass ratio of chromium slag, siderite, and special reducing agent is 5:3:8. The chromium slag and siderite are crushed to a particle size of less than 200 mesh. The binder is industrial waste syrup, and the amount added is 10 wt% of the total mass of chromium slag, siderite, and special reducing agent. The raw material for the special reducing agent is 150 mesh rice straw.

[0027] Main raw material composition: Chromium slag: Cr₂O₃ 13.42%, SiO₂ 5.76%, Al₂O₃ 6.14%, Fe₂O₃ 43.97%, MgO 20.72%, CaO 2.05%, TiO₂ 1.21%, Na₂O 2.88%, MnO 0.33%, others 3.52%. Siderite: TFe 39.57%, FeO 30.92%, SiO₂ 28.47%, Al₂O₃ 4.28%, MgO 5.35%, CaO 1.16%, MnO 1.04%, others 13.26%. Rice straw industrial analysis: fixed carbon 15.31%, volatile matter 63.69%, ash 13.66%, moisture 7.34%.

[0028] (2) Place the mixed pellets from step (1) in a drying oven to dry them thoroughly, ensuring that the moisture content is below 3 wt% and the drum strength of the dried pellets (+6.3 mm) (%) is ≥85%.

[0029] (3) Place the dried mixed pellets from step (2) into a high-temperature furnace. First, hold the mixture at 500℃ for 60 minutes, then continue heating to 1150℃ for 120 minutes, with a heating rate of 10℃ / min. Argon gas is used for protection throughout the process, with a gas flow rate of 300 ml / min. The static magnetic field is fully activated during the holding phase. The static magnetic field strength is 0.7T during the 500℃ holding phase and 0.9T during the 1150℃ calcination phase.

[0030] (4) The co-reduction product obtained by cooling with the furnace in step (3) is first separated by sieving to obtain chromium-silicon-iron alloy particles with a particle size greater than 1.0 mm, and particles smaller than 1.0 mm are separated by crushing, grinding and wet magnetic separation to obtain chromium-silicon-iron alloy powder.

[0031] (5) The chromium-silicon-iron alloy prepared in this embodiment contains 72.16 wt% iron, 11.51 wt% chromium, 15.02 wt% silicon, and 1.31 wt% other components. The iron recovery rate reaches 83.26%, the chromium recovery rate reaches 83.94%, and the silicon recovery rate reaches over 86.75%. The tailings remaining after magnetic separation contain 76.34% MgO.

[0032] Example 2

[0033] (1) Thoroughly mix chromium slag, siderite, special reducing agent, and binder, and press them into pellets with a diameter of 30 mm. The mass ratio of chromium slag, siderite, and special reducing agent is 5:2:6. The chromium slag and siderite are crushed to a particle size of less than 200 mesh. The binder is industrial waste syrup, and the amount added is 8 wt% of the total mass of chromium slag, siderite, and special reducing agent. The raw materials for the special reducing agent are 150-mesh wheat straw and corn straw, with a mass ratio of 1:1.

[0034] Main raw material composition: Chromium slag: Cr₂O₃ 14.06%, SiO₂ 4.95%, Al₂O₃ 5.88%, Fe₂O₃ 42.86%, MgO 21.43%, CaO 2.23%, TiO₂ 1.18%, Na₂O 2.17%, MnO 0.41%, others 4.83%. Siderite: TFe 39.68%, FeO 32.46%, SiO₂ 27.82%, Al₂O₃ 4.66%, MgO 6.24%, CaO 1.43%, MnO 1.21%, others 11.75%. Wheat straw industrial analysis: fixed carbon 15.39%, volatile matter 67.94%, ash 8.34%, moisture 8.33%. Corn straw industrial analysis: fixed carbon 16.02%, volatile matter 64.38%, ash 13.04%, moisture 6.56%.

[0035] (2) Place the mixed pellets from step (1) in a drying oven to dry them thoroughly, ensuring that the moisture content is below 3 wt% and the drum strength of the dried pellets (+6.3 mm) (%) is ≥85%.

[0036] (3) Place the dried mixed pellets from step (2) into a high-temperature furnace. First, hold the mixture at 600℃ for 40 minutes, then continue heating to 1250℃ for 90 minutes, with a heating rate of 10℃ / min. Argon gas is used for protection throughout the process, with a gas flow rate of 300 ml / min. The static magnetic field is fully activated during the holding phase. The static magnetic field strength is 0.8T during the 600℃ holding phase and 1.0T during the 1250℃ calcination phase.

[0037] (4) The co-reduction product obtained by cooling with the furnace in step (3) is first separated by sieving to obtain chromium-silicon-iron alloy particles with a particle size greater than 1.0 mm, and particles smaller than 1.0 mm are separated by crushing, grinding and wet magnetic separation to obtain chromium-silicon-iron alloy powder.

[0038] (5) The chromium-silicon-iron alloy prepared in this embodiment contains 71.68 wt% iron, 13.15 wt% chromium, 13.93 wt% silicon, and 1.24 wt% other components. The iron recovery rate reaches 82.45%, the chromium recovery rate reaches 84.21%, and the silicon recovery rate reaches over 85.92%. The tailings remaining after magnetic separation contain 77.83% MgO.

[0039] Effect Analysis

[0040] Compared with Example 1, under the same raw materials and process conditions, no special reducing agent or static magnetic field was used. The comparative analysis of the reduction products is shown in Table 1 below:

[0041] Table 1

[0042]

[0043] Compared with Example 2, under the same raw materials and process conditions, no special reducing agent or static magnetic field was used. The comparative analysis of the reduction products is shown in Table 2 below:

[0044] Table 2

[0045]

[0046] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0047] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing chromium-silicon-ferroalloy by co-reduction of hazardous waste chromium slag and siderite using magnetic field enhancement, characterized in that, Includes the following steps: (1) Grind chromium slag and siderite into powder, then add reducing agent and binder, mix thoroughly and press into pellets; wherein, the preparation process of the reducing agent is as follows: first, prepare a mixed solution of Na2CO3 and K2CO3 with a Na / K molar ratio of 1:1 and a total solute molar concentration of 0.12mol / L, then crush crop straw powder with a fixed carbon content of more than 15wt% to more than 150 mesh, and mix it thoroughly with the mixed solution of Na2CO3 and K2CO3 for more than 3 hours, with a mass ratio of 1:5, place the mixture in a drying oven at 90℃ and keep it at constant weight, and then obtain the reducing agent; (2) Dry the pellets obtained in step (1) to constant weight to obtain dried pellets; (3) The dried pellets obtained in step (2) are first kept at 500~600 ℃ for 40~60 min, and then the temperature is raised to 1150~1250 ℃ for 90~120 min. During the holding at 500~600 ℃, the static magnetic field is turned on with a static magnetic field strength of 0.7~0.8T. During the holding at 1150~1250 ℃, the static magnetic field is turned on again with a static magnetic field strength of 0.9~1.0T. At the same time, inert gas is continuously introduced into the furnace during the heating process so that the reaction is completed in an inert atmosphere. The static magnetic field is turned on during the holding stage. After the reaction is completed, the furnace is naturally cooled to room temperature to obtain the co-reduction product. (4) The co-reduction product obtained in step (3) is screened to obtain chromium-silicon-iron alloy particles with a particle size greater than 1.0 mm, and particles smaller than 1.0 mm are crushed, ground, magnetically separated and dried to obtain chromium-silicon-iron alloy powder.

2. The method for preparing chromium-silicon-ferroalloy by co-reduction of hazardous waste chromium slag and siderite using magnetic field enhancement according to claim 1, characterized in that, In step (1), the chromium slag and siderite are ground into powders of 200 mesh or finer; the pellets have a particle size of 30 mm.

3. The method for preparing chromium-silicon-ferroalloy by co-reduction of hazardous waste chromium slag and siderite using magnetic field enhancement according to claim 1, characterized in that, The mass ratio of chromium slag, siderite, and reducing agent in step (1) is 5:2~3:6~8.

4. The method for preparing chromium-silicon-ferroalloy by co-reduction of hazardous waste chromium slag and siderite using magnetic field enhancement according to claim 1, characterized in that, The binder is industrial waste syrup, and the amount added is 8-10 wt% of the total mass of chromium slag, siderite and special reducing agent.

5. The method for preparing chromium-silicon-ferroalloy by co-reduction of hazardous waste chromium slag and siderite using magnetic field enhancement according to claim 1, characterized in that, The moisture content of the dried pellets in step (2) is less than 3 wt%, and the drum strength of the dried pellets is such that the mass percentage of the pellets with a diameter greater than 6.3 mm is ≥ 85%.

6. The method for preparing chromium-silicon-ferroalloy by co-reduction of hazardous waste chromium slag and siderite using magnetic field enhancement according to claim 1, characterized in that, The chromium-silicon-iron alloy obtained in step (4) contains 70-74 wt% iron, 10-14 wt% chromium, and 12-16 wt% silicon. The iron recovery rate is above 82%, the chromium recovery rate is above 83%, the silicon recovery rate is above 85%, and the MgO content in the tailings remaining after magnetic separation is above 75%.

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