A method for detoxifying chromium slag and extracting ferrochromium concentrate as a resource and its application

Abstract

The present invention discloses a method for detoxifying chromium slag and extracting ferrochromium concentrate as a resource, and its application, and belongs to the technical field of chromium slag treatment. The method for detoxifying chromium slag and extracting ferrochromium concentrate as a resource comprises the following steps: (1) crushing the chromium slag, adding it into water for soaking, stirring, and obtaining a chromium slag slurry; (2) adding an iron-containing reducing agent into the chromium slag slurry, adjusting the pH value of the system to 8-14, and obtaining a pre-reaction mixture; (3) subjecting the pre-reaction mixture to a hydrothermal reaction to obtain a hydrothermal reaction product; (4) cooling the hydrothermal reaction product to room temperature, filtering, and obtaining a chromium-containing residue and a filtrate; (5) subjecting the chromium-containing residue to magnetic separation to obtain ferrochromium concentrate and non-magnetic residue. The method of the present invention not only realizes efficient and thorough detoxification of chromium slag, but also makes the detoxified chromium slag stable and difficult to be reoxidized, and the ferrochromium resources can be recycled through magnetic separation, and the obtained ferrochromium concentrate can be used in the steel industry.

Description

Technical Field

[0001] The invention belongs to the technical field of chromium slag treatment, and specifically relates to a method for detoxifying chromium slag and extracting ferrochromium concentrate as a resource, and an application thereof. Background Art

[0002] Chromium slag is industrial waste residue generated in the process of producing metallic chromium and chromium salts. Due to the extensive use of chromium resources in various industries, China ranks first in the world in the production and stockpiling of chromium slag. Among them, the chromium slag produced by the chromium salt process has the largest amount of chromium slag, with an annual emission of about 750,000 tons and a historical stockpile of millions of tons. Chromium slag contains a large amount of water-soluble and acid-soluble hexavalent chromium. With natural weathering or rain and snow, the hexavalent chromium, a strong carcinogenic substance contained in it, is dissolved and seeps into groundwater or enters rivers and lakes, seriously threatening the safety of humans and the environment.

[0003] At present, the main treatment method for chromium slag is to render it harmless, specifically to reduce highly toxic hexavalent chromium to low-toxic trivalent chromium. High-temperature roasting, solidification method, hydrothermal method and reduction method using reducing agents such as FeSO4, nZVI, alkali metal sulfides and organic reducing agents are commonly used for the treatment of chromium slag. Chinese patent ZL201510214047.2, a method for integrated detoxification and solidification of chromium slag, proposes to mix blast furnace slag, chromium slag, reducing agent and activator together for integrated detoxification and solidification treatment. This method is economical, practical and easy to operate, but the detoxification is usually not thorough, and the chromium resources therein are also wasted. Chinese patent application CN201810720230.3 proposes a method for efficient hydrothermal detoxification of chromium slag by cellulose. This method can thoroughly detoxify the chromium slag, but the final generated chromium hydroxide will also have the risk of yellowing, and further resource utilization of the chromium slag after treatment is not considered.

[0004] At present, there are three main bottlenecks in the treatment technology of chromium slag: First, due to the presence of micro-nano minerals in chromium slag, hexavalent chromium is in the state of interface adsorption, aggregation and lattice doping. The entrapment of chromium by coexisting minerals will make it difficult for chromium to fully contact the reducing agent and difficult to release from the interface or lattice. Second, the trivalent chromium in the chromium slag after treatment generally exists in the form of chromium sulfate, chromium hydroxide or chromium trioxide, which is easily oxidized to hexavalent chromium by natural oxidants (such as manganese oxide) or air, making the chromium slag after treatment easily become toxic and harmful waste again, resulting in the yellowing phenomenon of chromium slag. Third, the ferrochromium resources in chromium slag are not fully utilized, and the consumption of high energy, large amounts of reducing agents and acid-base reagents makes the current utilization of chromium slag uneconomical and incomplete. Therefore, it is necessary to develop an effective, stable and low-cost resource utilization method to treat chromium slag.

[0005] Ferrochrome spinel (FeCr2O4) is the most stable chromium mineral phase in nature, and its formation requires hundreds of years of hydrothermal mineralization on Earth. Therefore, converting hexavalent chromium into ferrochrome spinel by mimicking the formation of natural chromite is an ideal strategy for long-term stabilization of hexavalent chromium. However, the use of hydrothermal reaction to detoxify unstable hexavalent chromium in chromium slag, convert it into stable ferrochrome spinel, and further magnetic separation to recover ferrochrome resources has not been reported so far. Summary of the invention

[0006] In view of the shortcomings and deficiencies of the above prior art, the primary purpose of the present invention is to provide a method for detoxifying chromium slag and extracting ferrochromium concentrate as a resource. The method of the present invention mixes chromium slag with an aqueous solution to obtain a chromium slag slurry, and then mixes the chromium slag slurry with an iron-containing reducing agent and then performs a hydrothermal reaction. The residue after hydrothermal reaction is subjected to magnetic separation to obtain ferrochromium concentrate, thereby achieving the purpose of detoxification and resource extraction of chromium slag. The present invention realizes efficient detoxification of chromium slag, and the chromium slag is stable and difficult to reoxidize after reduction. At the same time, ferrochromium resources are recycled as a resource, and has the advantages of simple process, low management cost, no secondary pollution, and short detoxification cycle.

[0007] The second object of the present invention is to provide an application of the above-mentioned method for detoxifying chromium slag and extracting ferrochromium concentrate as a resource.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A method for detoxifying chromium slag and extracting ferrochromium concentrate by recycling it, comprising the following steps:

[0010] (1) crushing the chromium slag, adding the crushed chromium slag into water, soaking the crushed chromium slag in water, and stirring the crushed chromium slag to obtain a chromium slag slurry;

[0011] (2) adding an iron-containing reducing agent to the chromium slag slurry, adjusting the pH value of the system to 8 to 14, and obtaining a pre-reaction mixture;

[0012] (3) subjecting the pre-reaction mixture to a hydrothermal reaction to obtain a hydrothermal reaction product;

[0013] (4) cooling the hydrothermal reaction product to room temperature and filtering it to obtain a chromium-containing residue and a filtrate;

[0014] (5) The chromium-containing residue is subjected to magnetic separation to obtain ferrochromium concentrate and non-magnetic residue.

[0015] In step (1), the chromium slag and water are preferably calculated at a mass (g) to volume (mL) ratio of 2:35 to 45; more preferably 2:40.

[0016] In step (1), the stirring conditions are preferably: stirring and mixing at a speed of 200 to 1000 rpm at room temperature for 5 to 24 hours; more preferably: stirring and mixing at a speed of 200 rpm at room temperature for 18 hours.

[0017] The normal temperature mentioned here refers to room temperature.

[0018] In step (2), the iron-containing reducing agent is preferably at least one of ferrous sulfate, ferrous sulfide and ferrous nitrate.

[0019] In step (2), the chromium slag and the iron-containing reducing agent are preferably calculated at a mass ratio (g / g) of 2:0.1-1.5; more preferably, at a mass ratio (g / g) of 2:0.15-1.0.

[0020] In step (2), the pH value of the regulating system is adjusted to 12.

[0021] In step (2), the reagent for adjusting the pH value of the system is preferably a sodium hydroxide solution; more preferably a 0.5-6.0 mol / L sodium hydroxide solution; more preferably a 0.5 mol / L sodium hydroxide solution.

[0022] In step (2), the system refers to a system consisting of chromium slag slurry, an iron-containing reducing agent and a reagent for adjusting the pH value of the system.

[0023] In step (3), the hydrothermal reaction time is preferably 0.5 to 24 hours.

[0024] In step (3), the temperature of the hydrothermal reaction is preferably 100-200°C.

[0025] In step (3), the standing time is preferably 0.5 to 24 hours, and more preferably 12 hours.

[0026] In step (5), the magnetic field strength of the magnetic separation is preferably 12000-20000 Oe, and more preferably 18000 Oe.

[0027] The above method for detoxifying chromium slag and extracting ferrochromium concentrate as a resource is applied in the steel industry.

[0028] The inventors unexpectedly discovered that in order to promote the reduction of hexavalent chromium in chromium slag and the formation of ferrochrome spinel (i.e., the main phase of chromium in chromium-containing residues; the same below), a hydrothermal method can be used to treat the chromium slag, which is a method that is conducive to the release of hexavalent chromium in the chromium slag and the growth of crystals. In addition, a ferrous iron reducing agent is indispensable in the formation process of ferrochrome spinel (i.e., the main phase of chromium in chromium-containing residues). The ferrous iron reducing agent can not only reduce hexavalent chromium in the hydrothermal reaction, but also promote the formation of a magnetic spinel complex containing ferrochrome spinel, so that non-magnetic and highly toxic hexavalent chromium is converted into strongly magnetic and non-toxic ferrochrome spinel, and further the extraction of ferrochrome resources is achieved through magnetic separation.

[0029] The principle of the present invention is as follows:

[0030] The hydrothermal environment promotes the release of unstable hexavalent chromium in the chromium slag that causes toxicity into the solution. The released chromate ions further undergo redox reactions with the iron-containing reducing agent, reducing the hexavalent chromium to trivalent chromium. Trivalent chromium and iron ions undergo mineralization reactions under alkaline hydrothermal conditions to generate magnetic ferrochrome spinel (the main phase of chromium in the chromium-containing residue), which can be further extracted through magnetic separation to produce ferrochrome concentrate that can be used in the steel industry.

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] (1) The present invention uses hydrothermal mineralization technology to reduce hexavalent chromium in chromium slag to trivalent chromium and fix it in ferrochrome spinel (i.e., the main phase of chromium in chromium-containing residue). The total chromium leaching concentration in the chromium-containing residue after treatment is lower than the total chromium leaching concentration threshold of 15 mg / L in the "Identification of Hazardous Waste Identification Standard Leaching Toxicity Identification" (GB 5085.3-2007), and the total chromium concentration in the filtrate produced after treatment is lower than the maximum allowable discharge concentration of total chromium of 1.5 mg / L in the Comprehensive Sewage Discharge Standard (GB8978-1996). Not only does the chromium slag achieve efficient and thorough detoxification, but the detoxified chromium slag is also stable and difficult to be reoxidized. In addition, the ferrochrome resources can be recycled through magnetic separation, and the obtained ferrochrome concentrate can be used in the steel industry.

[0033] (2) The preparation process of the method of the present invention is simple, no secondary pollution such as toxic and harmful waste residues and wastewater is generated, the treatment cost is low, the detoxification cycle is short, and it has significant economic and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The process flow chart of the method for detoxifying chromium slag and extracting ferrochromium concentrate for resource utilization.

[0035] Figure 2 This is a graph showing the total iron and total chromium contents in the chromium slag raw material, chromium-containing residue and ferrochromium concentrate in the method described in Example 1.

[0036] Figure 3 This is a graph showing the total chromium leaching concentration in the chromium-containing residue obtained after different hydrothermal treatment times in Example 2.

[0037] Figure 4 This is a graph showing the total chromium leaching concentration in the chromium-containing residue obtained after treatment at different hydrothermal reaction temperatures in Example 3.

[0038] Figure 5 This is a graph showing the total chromium leaching concentration in the chromium-containing residue obtained after treatment with different amounts of ferrous sulfate added in Example 5. DETAILED DESCRIPTION

[0039] The present invention is further described in detail below in conjunction with embodiments, comparative examples and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0040] The process flow chart of the method for detoxifying chromium slag and extracting ferrochromium concentrate according to the present invention is as follows: Figure 1 shown.

[0041] The composition of the chromium slag raw material used in the following examples and comparative examples is shown in Table 1.

[0042] Table 1: Chemical composition of chromium slag raw materials

[0043]

[0044] Embodiment 1:

[0045] A method for detoxifying chromium slag and extracting ferrochromium concentrate as a resource, the process flow chart of which is as follows: Figure 1 As shown, the specific steps include:

[0046] (1) 2 g of chromium slag was crushed and added into 40 mL of water for immersion, and the mixture was stirred and mixed at a speed of 200 rpm for 18 h at room temperature to obtain a chromium slag slurry;

[0047] (2) transferring the chromium slag slurry to a polytetrafluoroethylene liner, adding 0.15 g of ferrous sulfate, and adjusting the pH value of the mixed system to 12 with a 0.5 mol / L sodium hydroxide solution at room temperature to obtain a pre-reaction mixture;

[0048] (3) subjecting the pre-reaction mixture to a hydrothermal reaction in a hydrothermal reactor at a temperature of 180° C. for 8 h to obtain a hydrothermal reaction product;

[0049] (4) The hydrothermal reaction product is allowed to stand and cool to room temperature for 12 hours, and after cooling, the reaction product is filtered for solid-liquid separation to obtain chromium-containing residue and filtrate. The total chromium concentration in the filtrate is less than 1.5 mg / L, which meets the requirements for total chromium in the Integrated Wastewater Discharge Standard (GB8978-1996);

[0050] (5) The chromium-containing residue was magnetically separated using a magnetic separator at a magnetic field strength of 18000 Oe, and the products were dried and weighed to obtain 1.8 g of ferrochromium concentrate and 0.1 g of non-magnetic residue.

[0051] The results are as follows Figure 2 As shown in the figure, the total iron and total chromium contents in the chromium slag raw material, chromium-containing residue and ferrochrome concentrate are not the same after testing. Among them, the total iron and total chromium contents in ferrochrome concentrate are significantly higher, with the total iron content (mass fraction, the same below) in ferrochrome concentrate being 53.5% and the total chromium content being 12.6%.

[0052] The total chromium leaching concentration in the above-mentioned chromium slag raw materials and chromium-containing residues was tested in accordance with HJ / T299-2007 "Toxicity leaching method for solid waste - sulfuric acid and nitric acid method".

[0053] The total chromium leaching concentration in the chromium slag raw material is 109.28 mg / L. The total chromium leaching concentration in the chromium-containing residue is 0.23 mg / L, which meets the requirements for total chromium in the "Identification Standard for Hazardous Wastes - Identification of Leaching Toxicity" (GB 5085.3-2007).

[0054] Embodiment 2:

[0055] A method for detoxifying chromium slag and extracting ferrochromium concentrate by recycling it, specifically comprising the following steps:

[0056] (1) 2 g of chromium slag was crushed and added into 40 mL of water for immersion, and the mixture was stirred and mixed at a speed of 200 rpm for 18 h at room temperature to obtain a chromium slag slurry;

[0057] (2) transferring the chromium slag slurry to a polytetrafluoroethylene liner, adding 0.15 g of ferrous sulfate, and adjusting the pH value of the mixed system to 12 with a 0.5 mol / L sodium hydroxide solution at room temperature to obtain a pre-reaction mixture;

[0058] (3) subjecting the pre-reaction mixture to a hydrothermal reaction in a hydrothermal reactor, wherein the temperature of the hydrothermal reaction is 180° C., and the time of the hydrothermal reaction is 0.5 h, 1 h, 2 h, 4 h, 6 h, 8 h, 12 h, 16 h, and 24 h, respectively, to obtain a hydrothermal reaction product;

[0059] (4) The hydrothermal reaction product is allowed to stand and cool to room temperature for 12 hours, and after cooling, the reaction product is filtered for solid-liquid separation to obtain chromium-containing residue and filtrate. The total chromium concentration in the filtrate is less than 1.5 mg / L, which meets the requirements for total chromium in the Integrated Wastewater Discharge Standard (GB8978-1996);

[0060] (5) The chromium-containing residue is magnetically separated by a magnetic separator at a magnetic field strength of 18000 Oe, and the products are dried and weighed respectively to obtain ferrochromium concentrate and non-magnetic residue.

[0061] According to HJ / T299-2007 "Toxicity leaching method of solid waste - sulfuric acid and nitric acid method", the total chromium leaching concentration in the above-mentioned chromium slag raw materials and the chromium-containing residues obtained after treatment with different hydrothermal times (0.5h, 1h, 2h, 4h, 6h, 8h, 12h, 16h, 24h) was tested.

[0062] The total chromium leaching concentration in the chromium slag raw material is 109.28 mg / L. The total chromium leaching concentration in the chromium-containing residue obtained after different hydrothermal treatment times is as follows Figure 3As shown. When the hydrothermal reaction time is 0.5 to 2 hours, the total chromium leaching concentration of the chromium-containing residue decreases rapidly. As the hydrothermal reaction time continues to increase, the total chromium leaching concentration of the chromium-containing residue is 0.23 mg / L at 8 hours. Subsequently, the total chromium leaching concentration of the chromium-containing residue remains basically stable, which meets the requirements for total chromium in the "Hazardous Waste Identification Standard Leaching Toxicity Identification" (GB 5085.3-2007), indicating that the increase in hydrothermal time is conducive to the detoxification of chromium slag and the extraction of ferrochromium concentrate.

[0063] Embodiment 3:

[0064] A method for detoxifying chromium slag and extracting ferrochromium concentrate by recycling it, specifically comprising the following steps:

[0065] (1) 2 g of chromium slag was crushed and added into 40 mL of water for immersion, and the mixture was stirred and mixed at a speed of 200 rpm for 18 h at room temperature to obtain a chromium slag slurry;

[0066] (2) transferring the chromium slag slurry to a polytetrafluoroethylene liner, adding 0.15 g of ferrous sulfate, and adjusting the pH value of the mixed system to 12 with a 0.5 mol / L sodium hydroxide solution at room temperature to obtain a pre-reaction mixture;

[0067] (3) subjecting the pre-reaction mixture to a hydrothermal reaction in a hydrothermal reactor, wherein the hydrothermal reaction temperatures are 100° C., 120° C., 140° C., 160° C., 180° C., and 200° C., respectively, and the hydrothermal reaction time is 8 h, to obtain a hydrothermal reaction product;

[0068] (4) The hydrothermal reaction product is allowed to stand and cool to room temperature for 12 hours, and after cooling, the reaction product is filtered for solid-liquid separation to obtain chromium-containing residue and filtrate. The total chromium concentration in the filtrate is less than 1.5 mg / L, which meets the requirements for total chromium in the Integrated Wastewater Discharge Standard (GB8978-1996);

[0069] (5) The chromium-containing residue is magnetically separated by a magnetic separator at a magnetic field strength of 18000 Oe, and the products are dried and weighed respectively to obtain ferrochromium concentrate and non-magnetic residue.

[0070] According to HJ / T299-2007 "Solid Waste Leaching Toxicity Leaching Method Sulfuric Acid and Nitric Acid Method" the total chromium leaching concentration in the chromium-containing residue obtained after the above-mentioned chromium slag raw materials and treatment at different hydrothermal reaction temperatures (100°C, 120°C, 140°C, 160°C, 180°C, 200°C) was tested.

[0071] The total chromium leaching concentration in the chromium slag raw material is 109.28 mg / L. The total chromium leaching concentration in the chromium-containing residue obtained after treatment at different hydrothermal reaction temperatures is as follows Figure 4As shown. When the hydrothermal reaction temperature increases from 100°C to 180°C, the total chromium leaching concentration of the chromium-containing residue decreases to the lowest point, which is 0.23 mg / L, indicating that the increase in hydrothermal temperature is conducive to the detoxification of chromium slag and the extraction of ferrochromium concentrate; when the reaction temperature continues to increase to 200°C, due to the excessively high hydrothermal temperature, the reaction rate is too fast, and the reaction time is limited, causing part of the hexavalent chromium in the chromium slag raw material to fail to be completely reduced and stabilized, and the total chromium leaching concentration of the chromium-containing residue increases instead, but all meet the requirements for total chromium in the "Identification Standard for Hazardous Waste Leaching Toxicity Identification" (GB 5085.3-2007).

[0072] Embodiment 4:

[0073] A method for detoxifying chromium slag and extracting ferrochromium concentrate by recycling it, specifically comprising the following steps:

[0074] (1) 2 g of chromium slag was crushed and added into 40 mL of water for immersion, and the mixture was stirred and mixed at a speed of 200 rpm for 18 h at room temperature to obtain a chromium slag slurry;

[0075] (2) transferring the chromium slag slurry to a polytetrafluoroethylene liner, adding 0.15 g of ferrous sulfate, and adjusting the pH value of the mixed system to 12 with a 0.5 mol / L sodium hydroxide solution at room temperature to obtain a pre-reaction mixture;

[0076] (3) subjecting the pre-reaction mixture to a hydrothermal reaction in a hydrothermal reactor at a temperature of 160° C. for 8 h to obtain a hydrothermal reaction product;

[0077] (4) The hydrothermal reaction product is allowed to stand and cool to room temperature for 12 hours, and after cooling, the reaction product is filtered to separate the solid and liquid to obtain a chromium-containing residue and a filtrate. The total chromium concentration in the filtrate is less than 1.5 mg / L, which meets the requirements for total chromium in the Integrated Wastewater Discharge Standard (GB8978-1996).

[0078] (5) The chromium-containing residue was magnetically separated using a magnetic separator at a magnetic field strength of 18000 Oe, and the products were dried and weighed to obtain 1.7 g of ferrochromium concentrate and 0.1 g of non-magnetic residue.

[0079] After testing, the total iron content in the ferrochromium concentrate was 50.5%, and the total chromium content was 10.1%.

[0080] The total chromium leaching concentration in the above-mentioned chromium slag raw materials and chromium-containing residues was tested in accordance with HJ / T299-2007 "Toxicity leaching method for solid waste - sulfuric acid and nitric acid method".

[0081] The total chromium leaching concentration in the chromium slag raw material is 109.28 mg / L. The total chromium leaching concentration in the chromium-containing residue is 0.26 mg / L, which meets the requirements for total chromium in the "Identification Standard for Hazardous Wastes - Identification of Leaching Toxicity" (GB 5085.3-2007).

[0082] Embodiment 5:

[0083] A method for detoxifying chromium slag and extracting ferrochromium concentrate by recycling it, the specific steps are as follows:

[0084] (1) 2 g of chromium slag was crushed and added into 40 mL of water for immersion, and the mixture was stirred and mixed at a speed of 200 rpm for 18 h at room temperature to obtain a chromium slag slurry;

[0085] (2) transferring the chromium slag slurry to a polytetrafluoroethylene liner, adding 0.15 g, 0.2 g, 0.5 g, 0.8 g, and 1.0 g of ferrous sulfate, respectively, and adjusting the pH value of the mixed system to 12 with a 0.5 mol / L sodium hydroxide solution at room temperature to obtain a pre-reaction mixture;

[0086] (3) subjecting the pre-reaction mixture to a hydrothermal reaction in a hydrothermal reactor at a temperature of 180° C. for 8 h to obtain a hydrothermal reaction product;

[0087] (4) The hydrothermal reaction product is allowed to stand and cool to room temperature for 12 hours, and after cooling, the reaction product is filtered to separate the solid and liquid to obtain a chromium-containing residue and a filtrate. The total chromium concentration in the filtrate is less than 1.5 mg / L, which meets the requirements for total chromium in the Integrated Wastewater Discharge Standard (GB8978-1996).

[0088] (5) The chromium-containing residue is magnetically separated by a magnetic separator at a magnetic field strength of 18000 Oe, and the products are dried and weighed respectively to obtain ferrochromium concentrate and non-magnetic residue.

[0089] According to HJ / T299-2007 "Toxicity leaching method of solid waste - sulfuric acid and nitric acid method", the total chromium leaching concentration in the above-mentioned chromium slag raw material and the chromium-containing residue obtained under different ferrous sulfate addition conditions (0.15g, 0.2g, 0.5g, 0.8g, 1.0g) was tested.

[0090] The total chromium leaching concentration in the chromium slag raw material is 109.28 mg / L. The total chromium leaching concentration in the chromium-containing residue obtained after treatment with different amounts of ferrous sulfate is as follows: Figure 5 As shown, from Figure 5It can be seen that when the addition amount of ferrous sulfate is 0.15g, the total chromium leaching concentration of the chromium-containing residue is reduced to 0.23mg / L, which meets the requirements for total chromium in the "Hazardous Waste Identification Standard Leaching Toxicity Identification" (GB5085.3-2007); when the addition amount of ferrous sulfate is further increased, the total chromium leaching concentration of the chromium-containing residue remains stable, indicating that the increase in the addition amount of ferrous sulfate is beneficial to the detoxification of the chromium slag raw material and the extraction of ferrochromium concentrate.

[0091] Embodiment 6:

[0092] A method for detoxifying chromium slag and extracting ferrochromium concentrate by recycling it, specifically comprising the following steps:

[0093] (1) 2 g of chromium slag was crushed and added into 40 mL of water for immersion, and the mixture was stirred and mixed at a speed of 200 rpm for 18 h at room temperature to obtain a chromium slag slurry;

[0094] (2) transferring the chromium slag slurry to a polytetrafluoroethylene liner, adding 0.8 g of ferrous sulfate, and adjusting the pH value of the mixed system to 12 with a 0.5 mol / L sodium hydroxide solution at room temperature to obtain a pre-reaction mixture;

[0095] (3) subjecting the pre-reaction mixture to a hydrothermal reaction in a hydrothermal reactor at a temperature of 180° C. for 8 h to obtain a hydrothermal reaction product;

[0096] (4) The hydrothermal reaction product is allowed to stand and cool to room temperature for 12 hours, and after cooling, the reaction product is filtered for solid-liquid separation to obtain chromium-containing residue and filtrate. The total chromium concentration in the filtrate is less than 1.5 mg / L, which meets the requirements for total chromium in the Integrated Wastewater Discharge Standard (GB8978-1996);

[0097] (5) The chromium-containing residue was magnetically separated using a magnetic separator at a magnetic field strength of 18000 Oe, and the products were dried and weighed to obtain 1.5 g of ferrochromium concentrate and 0.3 g of non-magnetic residue.

[0098] After testing, the total iron content in the ferrochromium concentrate was 52.2% and the total chromium content was 10.9%.

[0099] The total chromium leaching concentration in the above-mentioned chromium slag raw materials and chromium-containing residues was tested in accordance with HJ / T299-2007 "Toxicity leaching method for solid waste - sulfuric acid and nitric acid method".

[0100] The total chromium leaching concentration in the chromium slag raw material is 109.28 mg / L. The total chromium leaching concentration in the chromium-containing residue is 0.24 mg / L, which meets the requirements for total chromium in the "Identification Standard for Hazardous Wastes - Identification of Leaching Toxicity" (GB 5085.3-2007).

[0101] Comparative Example 1:

[0102] A method for detoxifying chromium slag and extracting ferrochromium concentrate by recycling it, the specific steps are as follows:

[0103] (1) 2 g of chromium slag was crushed and added into 40 mL of water for immersion, and the mixture was stirred and mixed at a speed of 200 rpm for 18 h at room temperature to obtain a chromium slag slurry;

[0104] (2) transferring the chromium slag slurry to a polytetrafluoroethylene liner, adding 0.02 g of ferrous sulfate, and adjusting the pH value of the mixed system to 12 with a 0.5 mol / L sodium hydroxide solution at room temperature to obtain a pre-reaction mixture;

[0105] (3) subjecting the pre-reaction mixture to a hydrothermal reaction in a hydrothermal reactor at a temperature of 180° C. for 8 h to obtain a hydrothermal reaction product;

[0106] (4) The hydrothermal reaction product was allowed to stand and cool to room temperature for 12 hours, and after cooling, the reaction product was filtered for solid-liquid separation to obtain chromium-containing residue and filtrate. The total chromium concentration in the filtrate was 26.41 mg / L, which was higher than the maximum allowable discharge concentration of total chromium of 1.5 mg / L in the Comprehensive Wastewater Discharge Standard (GB8978-1996);

[0107] (5) The chromium-containing residue was magnetically separated using a magnetic separator at a magnetic field strength of 18000 Oe, and the products were dried and weighed to obtain 1.5 g of ferrochromium concentrate and 0.4 g of non-magnetic residue.

[0108] According to the test, the total iron content of the ferrochromium concentrate is 49.0%, and the total chromium content is 9.8%.

[0109] The total chromium leaching concentration in the above-mentioned chromium slag raw materials and chromium-containing residues was tested in accordance with HJ / T299-2007 "Toxicity leaching method for solid waste - sulfuric acid and nitric acid method".

[0110] The total chromium leaching concentration in the chromium slag raw material is 109.28 mg / L. The total chromium leaching concentration in the chromium-containing residue is 1.47 mg / L, which is lower than the total chromium leaching toxicity identification standard value of 15 mg / L in the "Identification Standard for Hazardous Wastes - Identification of Leaching Toxicity" (GB 5085.3-2007).

[0111] The above results show that when the amount of ferrous sulfate added is insufficient, the hexavalent chromium in the chromium slag raw material is difficult to be reduced and stabilized in hydrothermal treatment, resulting in a large amount of hexavalent chromium being released into the solution after hydrothermal treatment. Experiments have found that in the method for detoxifying chromium slag and resource-based extraction of ferrochromium concentrate described in the present invention, the chromium slag and the iron-containing reducing agent are preferably treated in a mass ratio (g / g) of 2:0.15-1.0 for better results.

[0112] Comparative Example 2:

[0113] A method for detoxifying chromium slag and extracting ferrochromium concentrate by recycling it, the specific steps are as follows:

[0114] (1) 2 g of chromium slag was crushed and added into 40 mL of water for immersion, and the mixture was stirred and mixed at a speed of 200 rpm for 18 h at room temperature to obtain a chromium slag slurry;

[0115] (2) transferring the chromium slag slurry to a polytetrafluoroethylene liner, adding 0.15 g of ascorbic acid, and adjusting the pH value of the mixed system to 12 with a 0.5 mol / L sodium hydroxide solution at room temperature to obtain a pre-reaction mixture;

[0116] (3) subjecting the pre-reaction mixture to a hydrothermal reaction in a hydrothermal reactor at a temperature of 180° C. for 8 h to obtain a hydrothermal reaction product;

[0117] (4) The hydrothermal reaction product was allowed to stand and cool to room temperature for 12 hours, and after cooling, the reaction product was filtered for solid-liquid separation to obtain chromium-containing residue and filtrate. The total chromium concentration in the filtrate was 5.24 mg / L, which was higher than the maximum allowable discharge concentration of total chromium of 1.5 mg / L in the Comprehensive Wastewater Discharge Standard (GB8978-1996);

[0118] (5) using a magnetic separator to magnetically separate the chromium-containing residue at a magnetic field strength of 18000 Oe, and drying and weighing the products to obtain 1.4 g of ferrochromium concentrate and 0.5 g of non-magnetic residue;

[0119] After testing, the total iron content in the ferrochromium concentrate was 48.9% and the total chromium content was 9.5%.

[0120] The total chromium leaching concentration in the above-mentioned chromium slag raw materials and chromium-containing residues was tested in accordance with HJ / T299-2007 "Toxicity leaching method for solid waste - sulfuric acid and nitric acid method".

[0121] The total chromium leaching concentration in the chromium slag raw material is 109.28 mg / L. The total chromium leaching concentration in the chromium-containing residue is 19.24 mg / L, which is much higher than the total chromium leaching toxicity identification standard value of 15 mg / L in the "Hazardous Waste Identification Standard Leaching Toxicity Identification" (GB 5085.3-2007).

[0122] The above results show that, compared with ferrous sulfate, ascorbic acid is not as good in the detoxification and stabilization effect of chromium slag and the total iron and total chromium content of extracted ferro-chromium concentrate. Experiments have found that the method for detoxifying chromium slag and extracting ferro-chromium concentrate according to the present invention is more suitable for treatment with an iron-containing reducing agent.

[0123] Comparative Example 3:

[0124] A method for detoxifying chromium slag and extracting ferrochromium concentrate by recycling it, the specific steps are as follows:

[0125] (1) 2 g of chromium slag was crushed and added into 40 mL of water for immersion, and the mixture was stirred and mixed at a speed of 200 rpm for 18 h at room temperature to obtain a chromium slag slurry;

[0126] (2) transferring the chromium slag slurry to a polytetrafluoroethylene liner, adding 0.15 g of ferrous sulfate, and adjusting the pH value of the mixed system to 12 with a 0.5 mol / L sodium hydroxide solution at room temperature to obtain a pre-reaction mixture;

[0127] (3) subjecting the pre-reaction mixture to a hydrothermal reaction in a hydrothermal reactor at a temperature of 60° C. for 8 h to obtain a hydrothermal reaction product;

[0128] (4) The hydrothermal reaction product was allowed to stand and cool to room temperature for 12 hours, and after cooling, the reaction product was filtered for solid-liquid separation to obtain chromium-containing residue and filtrate. The total chromium concentration in the filtrate was 2.31 mg / L, which was higher than the maximum allowable discharge concentration of total chromium of 1.5 mg / L in the Integrated Wastewater Discharge Standard (GB8978-1996).

[0129] (5) The chromium-containing residue was magnetically separated using a magnetic separator at a magnetic field strength of 18000 Oe, and the products were dried and weighed to obtain 1.5 g of ferrochromium concentrate and 0.4 g of non-magnetic residue.

[0130] After testing, the total iron content in the ferrochromium concentrate was 50.7% and the total chromium content was 10.2%.

[0131] The total chromium leaching concentration in the above-mentioned chromium slag raw materials and chromium-containing residues was tested in accordance with HJ / T299-2007 "Toxicity leaching method for solid waste - sulfuric acid and nitric acid method".

[0132] The total chromium leaching concentration in the chromium slag raw material is 109.28 mg / L. The total chromium leaching concentration in the chromium-containing residue is 1.18 mg / L, which is lower than the total chromium leaching toxicity identification standard value of 15 mg / L in the "Hazardous Waste Identification Standard Leaching Toxicity Identification" (GB 5085.3-2007).

[0133] The above results indicate that when the hydrothermal temperature is too low, hexavalent chromium is difficult to be stabilized in the ferrochromium spinel after being reduced during the hydrothermal process of the chromium slag, resulting in a higher concentration of chromium ions in the solution after hydrothermal treatment. Experiments have shown that in the method for detoxifying chromium slag and extracting ferrochromium concentrate according to the present invention, the temperature of the hydrothermal reaction is preferably 100-200°C for better results.

[0134] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for detoxifying chromium slag and extracting ferrochromium concentrate by recycling, characterized in that: The steps include: (1) crushing the chromium slag, adding it into water, soaking it, and stirring it to obtain a chromium slag slurry; (2) adding an iron-containing reducing agent to the chromium slag slurry, adjusting the pH value of the system to 8 to 14, and obtaining a pre-reaction mixture; (3) subjecting the pre-reaction mixture to a hydrothermal reaction to obtain a hydrothermal reaction product; (4) cooling the hydrothermal reaction product to room temperature, filtering it, and obtaining a chromium-containing residue and a filtrate; (5) subjecting the chromium-containing residue to magnetic separation to obtain ferrochromium concentrate and non-magnetic residue; In step (1), the chromium slag and water are calculated at a mass volume ratio of 2 g:35-45 mL; In step (2), the chromium slag and the iron-containing reducing agent are calculated in a mass ratio of 2 g:0.15-1.0 g; In step (2), the iron-containing reducing agent is at least one of ferrous sulfate, ferrous sulfide and ferrous nitrate; In step (3), the temperature of the hydrothermal reaction is 100-200°C.

2. The method according to claim 1, characterized in that In step (3), the hydrothermal reaction time is 0.5 to 24 h.

3. The method according to claim 1, characterized in that In step (1), the stirring conditions are: stirring and mixing at a speed of 200 to 1000 rpm for 5 to 24 hours at room temperature.

4. The method according to claim 3, characterized in that In step (1), the chromium slag and water are calculated in a mass / volume ratio of 2:

40. In step (1), the stirring conditions are: stirring and mixing at 200 rpm at room temperature for 18 h.

5. The method according to claim 1, characterized in that In step (2), the reagent for adjusting the pH value of the system is a sodium hydroxide solution; In step (2), the pH value of the regulating system is adjusted to 12; In step (3), the standing time is 0.5 to 24 h; In step (5), the magnetic field strength of the magnetic separation is 12000 to 20000 Oe.

6. The method according to claim 5, characterized in that In step (2), the reagent for adjusting the pH value of the system is a 0.5-6.0 mol / L sodium hydroxide solution; In step (3), the standing time is 12 h; In step (5), the magnetic field strength of the magnetic separation is 18000 Oe.

7. Application of the method for detoxifying chromium slag and extracting ferrochromium concentrate as claimed in any one of claims 1 to 6 in the steel industry.

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