Process for recovering iron, nickel and chromium elements from stainless steel smelting slag

Abstract

This invention provides a process for recovering iron, nickel, and chromium from stainless steel smelting slag. It combines dry grinding and dry separation with wet grinding and wet separation, and integrates magnetic separation with gravity separation. This process can effectively recover mixed slag from 300-series and 400-series stainless steel smelting. The recovered products include not only large, medium, and small slag steel particles in metallic form, but also nickel-chromium-iron concentrate in the form of metal oxides. The total recovered product content reaches over 6%, and the total iron, nickel, and chromium content in the recovered slag steel is greater than 80%, ensuring thorough recovery. Furthermore, the recovered tailings have a fine particle size and are free of metallic substances, making them a relatively good raw material for building materials. Compared to traditional processes, this invention offers significantly greater economic benefits and solves the environmental problems caused by long-term stockpiling of stainless steel slag.

Description

Technical Field

[0001] This invention belongs to the field of mineral processing technology and relates to a process for recovering iron, nickel, and chromium elements from stainless steel smelting slag. Background Technology

[0002] Stainless steel smelting slag is a solid waste generated during the stainless steel smelting process, accounting for approximately 30% of the crude stainless steel production. Its main chemical components, besides common elements like silicon, magnesium, and calcium, also include valuable metals such as iron, nickel, chromium, and manganese. When stored in the open or landfilled, it contains toxic substances such as chromium (Cr). 6+ and Ni 2+ It is relatively easy to leach out, which is harmful to the environment and human safety. In other words, stainless steel smelting slag has the dual characteristics of secondary resource and environmental pollution. Piling it up not only wastes resources, but also leads to serious heavy metal pollution problems.

[0003] Overseas, the utilization rate of stainless steel smelting slag is relatively high, reaching 100% in some cases, while in China it is only around 20%, with most still stored in open-air piles. There are two main reasons for this: firstly, a weaker environmental awareness; and secondly, limitations in storage space, leading to the mixed storage of smelting slag from various stainless steel products, which makes recycling difficult. With the implementation of national environmental protection laws and increasingly fierce competition in the stainless steel industry, the resource utilization of stainless steel smelting slag will be a key factor determining the survival of stainless steel enterprises. Therefore, finding a process to maximize the recovery and utilization of iron, nickel, and chromium metal elements from stainless steel smelting slag is of great significance, as it can not only effectively reduce the cost of stainless steel products but also broaden the avenues for utilizing the recovered tailings. Summary of the Invention

[0004] The purpose of this invention is to address the problems existing in the prior art by providing a process for recovering iron, nickel, and chromium elements from stainless steel smelting slag. This process can effectively recover metal components from both magnetic 400 series smelting slag and non-magnetic 300 series smelting slag.

[0005] Therefore, the present invention adopts the following technical solution:

[0006] A process for recovering iron, nickel, and chromium from stainless steel smelting slag includes the following steps:

[0007] Step 1: Dry grinding, screening, and dry magnetic separation: Stainless steel smelting slag smaller than 200mm is fed into a dry rod mill. After grinding, it is fed into a flat vibrating screen, which separates it into oversize and undersize products. The oversize product has a particle size greater than 15mm. The oversize product is transported to a conveyor belt, where a magnetic separator is installed. The magnetic separator selects out the magnetic product, which is medium-sized slag steel. The non-magnetic product is returned to the dry rod mill for further grinding. The undersize product enters a dry magnetic separator to separate the oversize product, resulting in dry magnetic concentrate and dry magnetic tailings.

[0008] Step 2, two-stage dry grinding and dry magnetic separation: The dry magnetic separation concentrate obtained in Step 1 is fed into a two-stage dry rod mill, and after grinding, it is fed into a two-stage dry magnetic separation to obtain a two-stage dry magnetic separation concentrate and a two-stage dry magnetic separation tailings.

[0009] Step 3: Dry magnetic separation concentrate wet grinding, screening, and magnetic separation: The two-stage dry magnetic separation concentrate obtained in step 2 is fed into the first wet ball mill (1). After grinding, it is screened by a cylindrical screen. The product on the screen with a diameter greater than 0.2mm is small slag steel, and the product under the screen with a diameter less than 0.2mm is separated by a wet magnetic separator to obtain nickel-chromium iron concentrate and wet magnetic separation tailings.

[0010] Step 4: Dry magnetic separation tailings wet grinding and spiral chute tailings disposal: The dry magnetic separation tailings from the first and second stages are combined and fed into the second wet ball mill (2). After grinding, they pass through a cylindrical screen. The cylindrical screen and the second wet ball mill (2) form a closed grinding circuit. The product under the cylindrical screen with a particle size of less than 0.2 mm enters the spiral chute for pre-disposal of tailings to obtain non-magnetic coarse concentrate and tailings.

[0011] Step 5: Regrinding and Shaking Table Separation of Non-Magnetic Coarse Concentrate: The non-magnetic coarse concentrate obtained in Step 4 is regrinded in the third wet ball mill (3) and forms a closed grinding circuit with the hydrocyclone. After the -200 mesh content in the hydrocyclone overflow reaches 90%, it enters the shaking table for separation. The finished product selected by the shaking table is ferrochrome powder. The tailings selected by the shaking table and the tailings of the wet magnetic separation are both qualified tailings.

[0012] Furthermore, the stainless steel smelting slag in step 1 includes various mixed slags from the smelting processes of 300 series and 400 series stainless steel. The mixed slag contains 6%-10% iron, 1%-5% chromium, less than 3% nickel, 40-46% CaO, 7-10% MgO, 23-30% SiO2, 2-5% Al2O3, with the remainder being unavoidable impurities. The particle size of all of these impurities is less than 200mm.

[0013] Furthermore, the total nickel-chromium-iron content in the medium-grained slag steel obtained in step 1 is above 75%.

[0014] Furthermore, the total nickel-chromium-iron content in the small-particle slag steel obtained in step 3 is above 80%, and the total nickel-chromium-iron content in the nickel-chromium-iron concentrate is above 60%.

[0015] Furthermore, the total nickel-chromium-iron content in the ferrochrome powder obtained in step 5 is more than 50%.

[0016] The beneficial effects of this invention are as follows:

[0017] Stainless steel smelting slag includes 200 series, 300 series, and 400 series slag. 200 series and 400 series slag are magnetic, while 300 series slag is non-magnetic. Currently, 300 series and 400 series slag are the main types. This invention uses a combination of magnetic separation and gravity separation processes to recover valuable elements such as iron, nickel, and chromium from stainless steel slag to a large extent. The recovered tailings can be used as high-performance building material raw materials. Therefore, it has important practical significance from both resource utilization and environmental protection perspectives.

[0018] Specifically:

[0019] ① This invention achieves thorough recovery of valuable elements such as iron, nickel, and chromium, resulting in good economic benefits and easy utilization of tailings, thus solving the problems of long-term storage of stainless steel slag occupying space and causing environmental pollution.

[0020] Current stainless steel smelting slag recycling typically only recovers large and medium-sized pieces of slag steel. The recycling methods mostly involve manual sorting, with a small portion using simple crushing and screening. This recycling method is inefficient, recovering less than 0.5% of the slag steel, and the total iron, nickel, and chromium content in the recovered slag steel is less than 70%. The recovered tailings cannot meet the requirements for building material raw materials due to their particle size and quality, and can only be stockpiled. Most of the valuable metals, nickel, chromium, and iron, remain in the tailings, causing not only resource waste but also environmental pollution.

[0021] This invention combines dry grinding and dry separation with wet grinding and wet separation, and integrates magnetic separation and gravity separation processes. It can effectively recover mixed slag from the smelting of 300-series and 400-series stainless steel. The recovered products include not only large, medium, and small slag steel particles in metallic form, but also nickel-chromium-iron concentrate in the form of metal oxides. The total recovered product content reaches over 6%, and the total iron, nickel, and chromium content in the recovered slag steel is greater than 80%, ensuring thorough recovery. The recovered tailings have a fine particle size and are free of metallic substances, making them excellent raw materials for building materials. Compared with traditional processes, this process offers significant economic benefits and solves the environmental problems caused by the long-term stockpiling of stainless steel slag.

[0022] ②The process setup of this invention is reasonable and flexible, applicable to various stainless steel slags, and has good promotional value.

[0023] Stainless steel slag can be classified by process into converter slag, electric furnace slag, continuous casting ladle residue slag, and dephosphorization slag. It can also be classified by product into 300 series austenitic steel slag and 400 series ferritic steel slag. Different processes result in different particle sizes, mineral phases, and selectivity of stainless steel slag. Domestic stainless steel slag recycling processes typically target only one type of slag; there are no mature recycling processes for mixed slags.

[0024] The process setup of this invention is reasonable and flexible, and can be adjusted in a timely manner according to the characteristics of stainless steel slag, ensuring that various slags are effectively recovered without increasing costs. Specifically, the mixed slag adopts the whole process; the 400 series slag adopts the magnetic separation process, that is, the part after the second wet ball mill (2) is stopped; the 300 series slag adopts the gravity separation process, that is, the part after the two-stage dry rod mill shown in the attached figure is stopped. Therefore, this invention has a wide range of applications, mature technology, and good promotion value. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0026] The technical solution of the present invention will be described below with reference to the accompanying drawings and implementation methods.

[0027] Example 1

[0028] like Figure 1 As shown, a process for recovering iron, nickel, and chromium elements from stainless steel smelting slag, applicable to mixed slag in stainless steel smelting, includes the following steps:

[0029] Step 1: Dry grinding, screening, and dry magnetic separation: Stainless steel smelting mixed slag smaller than 200mm is fed into a dry rod mill. After grinding, it is fed into a flat vibrating screen, separating into oversize and undersize products. The oversize product has a particle size greater than 15mm. An iron remover is installed above the conveyor belt. The iron remover selects the magnetic product as medium-grained slag steel; specifically, the total iron, nickel, and chromium content in the medium-grained slag steel is 78%.

[0030] The non-magnetic product is returned to a dry rod mill for further grinding, and the screened product is sent to a dry magnetic separator for separation to obtain a dry magnetic concentrate and a dry magnetic tailings.

[0031] Step 2, two-stage dry grinding and dry magnetic separation: The dry magnetic separation concentrate obtained in Step 1 enters the two-stage dry rod mill, and after grinding, it enters the two-stage dry magnetic separation to obtain the two-stage dry magnetic separation concentrate and the two-stage dry magnetic separation tailings.

[0032] Step 3: Dry magnetic separation concentrate wet grinding, screening, and magnetic separation: The two-stage dry magnetic separation concentrate obtained in Step 2 is fed into the first wet ball mill (1). After grinding, it is screened by a cylindrical screen. The product on the screen larger than 0.2mm is small slag steel; specifically, the total iron, nickel, and chromium content in the small slag steel is 83%. The product under the screen smaller than 0.2mm is separated by a wet magnetic separator to obtain nickel-chromium iron concentrate and wet magnetic separation tailings; specifically, the total iron, nickel, and chromium content in the nickel-chromium iron concentrate is 57%, and the total iron, nickel, and chromium content in the magnetic separation tailings is 6%.

[0033] Step 4: Dry magnetic separation tailings wet grinding and spiral chute tailings disposal: The dry magnetic separation tailings from the first and second stages are combined and fed into the second wet ball mill (2). After grinding, they pass through a cylindrical screen. The cylindrical screen and the second wet ball mill (2) form a closed grinding circuit. The product under the cylindrical screen with a particle size of less than 0.2 mm enters the spiral chute for pre-disposal of tailings to obtain non-magnetic coarse concentrate and tailings.

[0034] Step 5: Regrinding and shaking table separation of non-magnetic rough concentrate: The non-magnetic rough concentrate obtained in step 4 is regrinded in the third wet ball mill (3) and forms a closed grinding circuit with the hydrocyclone. After the content of -200 mesh in the overflow of the hydrocyclone reaches 90%, it enters the shaking table for separation. The finished product selected by the shaking table is ferrochrome powder; specifically, the total content of nickel, chromium and iron in the ferrochrome powder is 50%.

[0035] Both the tailings separated by the shaking table and the tailings separated by wet magnetic separation are qualified tailings, which are then dewatered and used as raw materials for building materials.

[0036] Example 2

[0037] A process for recovering iron, nickel, and chromium from stainless steel smelting slag, applicable to 400 series stainless steel smelting slag, includes the following steps:

[0038] Step 1: Dry grinding, screening, and dry magnetic separation: Stainless steel 400 series smelting slag smaller than 200mm is fed into a dry rod mill. After grinding, it is fed into a flat vibrating screen, which separates it into oversize and undersize products. The oversize product has a particle size greater than 15mm. An iron remover is installed above the conveyor belt. The iron remover selects the magnetic product as medium-grained slag steel. Specifically, the total iron, nickel, and chromium content in the medium-grained slag steel is 75%. The non-magnetic product is returned to the dry rod mill for further grinding. The undersize product enters the dry magnetic separator for separation, resulting in dry magnetic concentrate and dry magnetic tailings.

[0039] Step 2, two-stage dry grinding and dry magnetic separation: The dry magnetic separation concentrate obtained in Step 1 enters the two-stage dry rod mill, and after grinding, it enters the two-stage dry magnetic separation to obtain the two-stage dry magnetic separation concentrate and the two-stage dry magnetic separation tailings.

[0040] Step 3: Dry magnetic separation concentrate wet grinding, screening, and magnetic separation: The two-stage dry magnetic separation concentrate obtained in step 2 is fed into the first wet ball mill (1). After grinding, it is screened by a cylindrical screen. The product on the screen with a diameter greater than 0.2mm is small slag steel. Specifically, the total iron, nickel, and chromium content in the small slag steel is 80%. The product under the screen with a diameter less than 0.2mm is separated by a wet magnetic separator to obtain nickel-chromium iron concentrate and wet magnetic separation tailings. Specifically, the total iron, nickel, and chromium content in the nickel-chromium iron concentrate is 60%, and the total iron, nickel, and chromium content in the magnetic separation tailings is 5%.

[0041] Tailings from first-stage and second-stage dry magnetic separation, as well as wet magnetic separation, can be mixed or stacked separately as building material raw materials, depending on the requirements.

[0042] Example 3

[0043] A process for recovering iron, nickel, and chromium from stainless steel smelting slag, applicable to 300 series stainless steel smelting slag, includes the following steps:

[0044] Step 1: First-stage dry grinding, screening, and dry magnetic separation: Smelting 300 series stainless steel smelting slag smaller than 200mm is fed into a first-stage dry rod mill. After grinding, it is fed into a flat vibrating screen, separating into oversize and undersize products. The oversize product has a particle size greater than 15mm. An iron remover is installed above the conveyor belt. The iron remover selects the magnetic product as medium-grained slag steel, specifically, the total iron, nickel, and chromium content in the medium-grained slag steel is 70%. The non-magnetic product is returned to the first-stage dry rod mill for further grinding. The undersize product enters a first-stage dry magnetic separator for separation, obtaining first-stage dry magnetic separator concentrate and first-stage dry magnetic separator tailings. Specifically, the total iron, nickel, and chromium content in the first-stage dry magnetic separator concentrate is 50%.

[0045] Step 2: Dry magnetic separation tailings wet grinding and spiral chute tailings disposal: The dry magnetic separation tailings enter the second wet ball mill (2), and after grinding, they pass through a cylindrical screen. The cylindrical screen and the second wet ball mill (2) form a closed grinding circuit. The product under the cylindrical screen with a particle size of less than 0.2 mm enters the spiral chute for pre-disposal of tailings to obtain non-magnetic coarse concentrate and tailings.

[0046] Step 3, Non-magnetic rough concentrate regrinding and shaking table separation: The non-magnetic rough concentrate obtained in step 2 enters the third wet ball mill (3) for regrinding, forming a closed grinding circuit with the hydrocyclone. After the -200 mesh content in the hydrocyclone overflow reaches 90%, it enters the shaking table for separation. The finished product selected by the shaking table is ferrochrome powder. The tailings selected by the shaking table and the tailings of the wet magnetic separation are both qualified tailings. Specifically, the total iron, nickel and chromium content in the ferrochrome powder is 52%.

[0047] Tailings from spiral chute tailings and shaking table selection can be used as building material raw materials, and can be mixed or stacked separately according to needs.

Claims

1. A process for recovering iron, nickel and chromium elements from stainless steel smelting slag, characterized by, Includes the following steps: Step 1: Dry grinding, screening, and dry magnetic separation: Stainless steel smelting mixed slag smaller than 200mm is fed into a dry rod mill. After grinding, it is fed into a flat vibrating screen and separated into oversize and undersize products. The oversize product has a particle size greater than 15mm. The oversize product is transported to a conveyor belt. An iron remover is installed above the conveyor belt. The iron remover selects the magnetic product as medium-sized slag steel. The non-magnetic product is returned to the dry rod mill for further grinding. The undersize product enters a dry magnetic separator to separate, resulting in dry magnetic concentrate and dry magnetic tailings. The stainless steel smelting slag in step 1 includes various mixed slags from the smelting processes of 300 series and 400 series stainless steel. The mixed slag contains 6%-10% iron, 1%-5% chromium, less than 3% nickel, 40-46% CaO, 7-10% MgO, 23-30% SiO2, and 2-5% Al2O3, with the remainder being unavoidable impurities. The particle size of the mixed slag is less than 200mm. Step 2, two-stage dry grinding and dry magnetic separation: the concentrate obtained from the first-stage dry magnetic separation in step 1 is fed into a second-stage dry rod mill, and after grinding, it is fed into a second-stage dry magnetic separation to obtain a second-stage dry magnetic separation concentrate and a second-stage dry magnetic separation tailings. Step 3: Dry magnetic separation concentrate wet grinding, screening, and magnetic separation: The two-stage dry magnetic separation concentrate obtained in step 2 is fed into the first wet ball mill (1). After grinding, it is screened by a cylindrical screen. The product on the screen with a diameter greater than 0.2mm is small slag steel, and the product under the screen with a diameter less than 0.2mm is separated by a wet magnetic separator to obtain nickel-chromium iron concentrate and wet magnetic separation tailings. Step 4: Dry magnetic separation tailings wet grinding and spiral chute tailings disposal: The dry magnetic separation tailings from the first and second stages are combined and fed into the second wet ball mill (2). After grinding, they pass through a cylindrical screen. The cylindrical screen and the second wet ball mill (2) form a closed grinding circuit. The product under the cylindrical screen with a particle size of less than 0.2 mm enters the spiral chute for pre-disposal of tailings to obtain non-magnetic coarse concentrate and tailings. Step 5: Regrinding and Shaking Table Separation of Non-Magnetic Coarse Concentrate: The non-magnetic coarse concentrate obtained in Step 4 is regrinded in the third wet ball mill (3) and forms a closed grinding circuit with the hydrocyclone. After the -200 mesh content in the hydrocyclone overflow reaches 90%, it enters the shaking table for separation. The finished product selected by the shaking table is ferrochrome powder. The tailings selected by the shaking table and the tailings of the wet magnetic separation are both qualified tailings.

2. The process for recovering iron, nickel, and chromium elements from stainless steel smelting slag according to claim 1, characterized in that, The total nickel-chromium-iron content in the medium-grained slag steel obtained in step 1 is above 75%.

3. The process for recovering iron, nickel, and chromium elements from stainless steel smelting slag according to claim 1, characterized in that, The total nickel-chromium-iron content in the small slag steel obtained in step 3 is above 80%, and the total nickel-chromium-iron content in the nickel-chromium-iron concentrate is above 60%.

4. The process for recovering iron, nickel, and chromium elements from stainless steel smelting slag according to claim 1, characterized in that, The total nickel-chromium-iron content in the ferrochrome powder obtained in step 5 is more than 50%.

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