A multi-stage utilization method of chromium residue

Abstract

The application provides a multistage utilization method of chromium slag, comprising the following steps: S1. detoxification of the chromium slag; S2. mixing the detoxified chromium slag with water, acid leaching, filtering to obtain filter residue one and filtrate one; S3. adjusting the pH of the filtrate one to 2-3 to make Fe 3+ in the filtrate one precipitate, solid-liquid separation to obtain iron hydroxide and filtrate two; S4. adjusting the pH of the filtrate two to 11-11.5, and obtaining filter residue three containing calcium hydroxide, magnesium hydroxide and chromium hydroxide and filtrate three after reaction; S5. adding soluble bicarbonate to the filtrate three to obtain aluminum hydroxide after reaction; S6. preparing the filter residue three into a mixed solution with a pH of 12-14, and obtaining a calcium hydroxide and magnesium hydroxide mixture and filtrate five after solid-liquid separation after reaction; and S7. adding sufficient boiling water to the filtrate five, standing, solid-liquid separation to obtain chromium hydroxide and lye. The method realizes multistage treatment of the chromium slag and efficient resource utilization of the chromium slag.

Description

Technical Field

[0001] This invention relates to the field of waste resource utilization technology, specifically to a multi-stage utilization method for chromium slag. Background Technology

[0002] Chromium slag refers to the solid waste generated during the production of metallic chromium and chromium salts, which poses certain hazards to human health. Currently, the discharge of industrial chromium slag is substantial, and its composition is complex. In addition to metallic elements such as chromium, iron, magnesium, and aluminum, it also contains the highly toxic heavy metal chromium (Cr(VI)), which can pollute soil, surface water, and groundwater, thereby impacting human health and the ecological environment. Therefore, the comprehensive utilization and treatment of chromium slag is of paramount importance.

[0003] Currently, the main treatment of chromium slag both domestically and internationally involves detoxification, converting hexavalent chromium into trivalent chromium and fixing it. Detoxification technologies include chemical reduction, chemical leaching, microbial remediation, and biomass pyrolysis. However, chemical reduction cannot completely convert hexavalent chromium into trivalent chromium, and the strong alkalinity of the chromium slag can cause the reducing agent to become ineffective. Chemical leaching has low detoxification efficiency and the potential for secondary pollution. Microbial remediation also suffers from low efficiency because microorganisms are highly susceptible to environmental influences and have difficulty growing and multiplying in chromium slag. Compared to these technologies, biomass pyrolysis is more environmentally friendly, economical, and readily available, showing promising application prospects.

[0004] After detoxification, chromium slag, due to its high melting point and hardness, is often used in the production of building materials, road materials, and refractory materials. However, these comprehensive utilization methods waste the rich metal resources contained in the chromium slag. Detoxified chromium slag mainly contains trivalent chromium, aluminum, magnesium, iron, calcium, and other metallic elements. While technologies exist for recovering these metallic elements from detoxified chromium slag, most studies only focus on recovering individual metallic elements, and systematic research on the comprehensive utilization of chromium slag is lacking. Summary of the Invention

[0005] To address the problems existing in the background technology, the present invention provides a multi-stage utilization method for chromium slag, which performs multi-stage treatment on chromium slag and realizes the efficient utilization of chromium slag resources.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0007] A method for multi-stage utilization of chromium slag includes the following steps:

[0008] S1. Detoxification of chromium slag;

[0009] S2. Mix the detoxified chromium slag with water to form a slurry, add acid for acid leaching, filter, and obtain filter residue 1 containing Mg. 2 + Ca2+ Al 3+ Fe 3+ and Cr 3+ Filtrate 1;

[0010] S3. Adjust the pH of filtrate one to 2-3, and react it at a certain temperature to reduce the Fe content. 3+ Precipitation, solid-liquid separation, yielding ferric hydroxide and Mg. 2+ Ca 2+ Al 3+ and Cr 3+ Filtrate 2;

[0011] S4. Adjust the pH of filtrate two to 11-11.5. After the reaction, filter residue three containing calcium hydroxide, magnesium hydroxide, and chromium hydroxide and residue three containing AlO2 are obtained. - The filtrate is three;

[0012] S5. Add soluble bicarbonate to filtrate three, react and filter to obtain aluminum hydroxide;

[0013] S6. Prepare a mixed solution with a pH of 12-14 from the filter residue. After the reaction, separate the solid and liquid components to obtain a mixture of calcium hydroxide and magnesium hydroxide, and a solution containing CrO2. - The filtrate is five;

[0014] S7. Add sufficient boiling water to filtrate five, let stand, and separate the solid and liquid to obtain chromium hydroxide and alkaline solution.

[0015] According to the above scheme, the chromium slag in step S1 is detoxified by biomass pyrolysis.

[0016] According to the above scheme, the biomass pyrolysis method is as follows: chromium slag is ground and mixed with straw, and then heated by a tubular furnace to detoxify the chromium slag.

[0017] Furthermore, the temperature of the tube furnace is 500℃~600℃, and the reaction time is 3~5h.

[0018] Furthermore, the particle size of the chromium slag after grinding is 50-100 mesh.

[0019] According to the above scheme, in step S2, the mass ratio of water to chromium slag is 1.5 to 2:1, the acid leaching temperature is 80 to 90°C, and the time is 12 to 36 hours.

[0020] According to the above scheme, the acid in step S2 is hydrochloric acid, and the concentration of the acid is 3-5 mol / L; based on the concentration of 3 mol / L hydrochloric acid, the mass ratio of hydrochloric acid to chromium slag is 3-4:1.

[0021] According to the above scheme, the reaction temperature in step S3 is 90-100℃ and the time is 3-4h.

[0022] According to the above scheme, the reaction time in step S4 is 5 to 8 hours.

[0023] According to the above scheme, in step S5, the mass ratio of soluble bicarbonate to chromium slag is 1:5-6, and the reaction time is 2-4 hours.

[0024] According to the above scheme, the alkali used to adjust the pH in steps S3, S4, and S6 is sodium hydroxide or potassium hydroxide, and the soluble carbonate in step S5 is sodium bicarbonate or potassium bicarbonate.

[0025] According to the above scheme, the alkaline solution obtained in step S7 is recycled in step S6 to adjust the pH value of filter residue three.

[0026] The beneficial effects of this invention are:

[0027] The inventors conducted a systematic study on chromium slag. Through in-depth analysis and long-term exploration, they finally obtained the multi-stage utilization method of chromium slag of this invention. This method realizes multi-stage treatment of chromium slag and successfully prepares four products using the valuable metals in the chromium slag: iron hydroxide, aluminum hydroxide, a mixture of calcium hydroxide and magnesium hydroxide, and chromium hydroxide. This multi-stage utilization of the metal elements in the chromium slag maximizes the utilization of metal resources in the chromium slag and solves the problem of chromium slag discharge, an industrial solid waste. Among the four products prepared, the utilization rates of valuable metals iron, aluminum, calcium and magnesium, and chromium in the chromium slag reach 86.2%, 62.7%, 79.3%, and 64.2%, respectively, improving the economic benefits of chromium salt enterprises and possessing good industrial utilization value.

[0028] The prepared ferric hydroxide can be used to prepare pigments and pharmaceuticals, and due to its excellent surface adsorption properties, it can also be used as a water purification agent. Aluminum hydroxide is widely used in the production of inorganic salts, polyaluminum chloride, flame-retardant fillers, and water purification agents. Especially in the field of flame retardants, aluminum hydroxide not only retards flames but also prevents smoke, dripping, and the production of toxic gases, thus gaining wide application. A mixture of calcium hydroxide and magnesium hydroxide is a good composite flame retardant with excellent triple functions of flame retardancy, smoke suppression, and filling, and it is non-toxic and harmless. Using it as a filler can improve the flame retardant performance of materials and reduce costs. Chromium hydroxide can be used to prepare trivalent chromium salts and chromium trioxide, and it can also be used in paints, pigments, wool processing, metallurgy, enamel, and other industries.

[0029] This method has a short process flow, simple equipment, and the by-products can be recycled without generating secondary pollutants, making it green and environmentally friendly, while also improving the efficiency of raw material utilization. Attached Figure Description

[0030] Figure 1 This is a flowchart of the multi-stage utilization method of chromium slag according to the present invention. Detailed Implementation

[0031] The principles and features of the present invention are described below with reference to the accompanying drawings and specific embodiments. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0032] It should be noted that, in the description of the embodiments of this application, the term "some specific embodiments" means that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same implementation or instance. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0033] Chromium slag is a solid waste generated during the production of metallic chromium and chromium salts. Its main components include chromium trioxide, sodium dichromate, silicon dioxide, aluminum oxide, magnesium oxide, and calcium oxide. Among them, hexavalent chromium is highly toxic. In this invention, the chromium slag is first detoxified to reduce the hexavalent chromium to trivalent chromium. Then, through a graded preparation method, the valuable metals are fully utilized to prepare iron hydroxide, aluminum hydroxide, a mixture of calcium hydroxide and magnesium hydroxide, and chromium hydroxide, thereby maximizing the utilization of chromium slag resources.

[0034] like Figure 1 As shown, the present invention provides a method for multi-stage utilization of chromium slag, comprising the following steps:

[0035] S1. Detoxification of chromium slag;

[0036] S2. Mix the detoxified chromium slag with water to form a slurry, add acid for acid leaching, filter, and obtain filter residue 1 containing Mg. 2 + Ca 2+ Al 3+ Fe 3+ and Cr 3+ Filtrate 1;

[0037] S3. Adjust the pH of filtrate one to 2-3, and react it at a certain temperature to reduce the Fe content. 3+ Precipitation, solid-liquid separation, yielding ferric hydroxide and Mg. 2+ Ca 2+ Al 3+ and Cr 3+ Filtrate 2;

[0038] S4. Adjust the pH of filtrate two to 11-11.5. After the reaction, filter residue three containing calcium hydroxide, magnesium hydroxide, and chromium hydroxide and residue three containing AlO2 are obtained. - The filtrate is three;

[0039] S5. Add soluble bicarbonate to filtrate three, react and filter to obtain aluminum hydroxide;

[0040] S6. Prepare a mixed solution with a pH of 12-14 from the filter residue. After the reaction, separate the solid and liquid components to obtain a mixture of calcium hydroxide and magnesium hydroxide, and a solution containing CrO2. - The filtrate is five;

[0041] S7. Add sufficient boiling water to filtrate five, let stand, and separate the solid and liquid to obtain chromium hydroxide and alkaline solution.

[0042] The filter residue obtained after acid leaching of the detoxified chromium slag in step S2 mainly contains silicon dioxide, while the filtrate contains Mg. 2+ Ca 2+ Al 3+ Fe 3+ and Cr 3+ By utilizing the difference in pH value between the metal ion precipitation sites in the filtrate, alkali was added to adjust the pH of the filtrate to 2-3. At this point, Fe... 3+ Ferric hydroxide precipitate (Product 1), while Mg... 2+ Ca 2+ Al 3+ and Cr 3+ The solution does not precipitate and enters filtrate two. Alkali is added to adjust the pH of filtrate two to 11–11.5. At this point, Mg… 2+ Ca 2+ and Cr 3+ The precipitate forms a filter residue containing magnesium hydroxide, calcium hydroxide, and chromium hydroxide. 3+ Aluminate (AlO2) is generated - The product enters filtrate three, where soluble bicarbonate is added. This bicarbonate reacts with aluminate to form aluminum hydroxide (product two). Alkali solution is added to residue three to adjust the pH to 12-14. The chromium hydroxide in residue three is an amphoteric hydroxide, which, under strongly alkaline conditions, forms chromite (CrO2). - The magnesium hydroxide and calcium hydroxide mixture (product three) in filtrate five do not react. The chromite ions in filtrate five react with boiling water to produce chromium hydroxide (product four) and alkaline solution.

[0043] The above-mentioned products, namely, ferric hydroxide (product 1), aluminum hydroxide (product 2), a mixture of magnesium hydroxide and calcium hydroxide (product 3), and ferric hydroxide (product 4), are precipitates obtained by washing, drying, and pulverizing after solid-liquid separation.

[0044] Ferric hydroxide can be used to prepare pigments and pharmaceuticals, and due to its excellent surface adsorption properties, it can also be used as a water purification agent. Aluminum hydroxide is widely used in the production of inorganic salts, polyaluminum chloride, flame-retardant fillers, and water purification agents. Especially in the field of flame retardants, aluminum hydroxide not only retards flames but also prevents smoke, dripping, and the production of toxic gases, thus gaining wide application. A mixture of calcium hydroxide and magnesium hydroxide is a good composite flame retardant with excellent triple functions of flame retardancy, smoke suppression, and filling, and it is non-toxic and harmless. Using it as a filler can improve the flame retardant performance of materials and reduce costs. Chromium hydroxide can be used to prepare trivalent chromium salts and chromium trioxide, and it can also be used in paints, pigments, wool processing, metallurgy, enamel, and other industries.

[0045] In some specific embodiments, the chromium slag in step S1 is detoxified using biomass pyrolysis, where reducing gases and biochar generated by the biomass are used to detoxify the chromium slag. The biomass can be straw, which not only solves the pollution problem of chromium slag but also realizes the recycling of crop straw, turning waste into treasure. Furthermore, using biomass pyrolysis to detoxify chromium slag is more environmentally friendly, readily available, and renewable.

[0046] Preferably, the biomass pyrolysis method is as follows: the chromium slag is ground and mixed with straw, and then heated in a tubular furnace to detoxify the chromium slag. Preferably, the temperature of the tubular furnace is 500℃~600℃ and the reaction time is 3~5h.

[0047] Preferably, the particle size of the chromium slag after grinding is 50-100 mesh.

[0048] In some specific embodiments, the ratio of chromium slag to water in step S2 is 1.5 to 2:1, the acid leaching temperature is 80 to 90°C, and the time is 12 to 36 hours.

[0049] In some specific embodiments, the acid in step S2 is hydrochloric acid, and the concentration of the acid is 3-5 mol / L; based on the concentration of 3 mol / L hydrochloric acid, the mass ratio of hydrochloric acid to chromium slag is 3-4:1. The filtrate obtained from the reaction contains magnesium chloride, calcium chloride, aluminum chloride, ferric chloride, and chromium chloride.

[0050] In some specific embodiments, the reaction temperature in step S3 is 90–100°C and the reaction time is 3–4 hours.

[0051] According to the above scheme, the reaction time in step S4 is 5 to 8 hours.

[0052] According to the above scheme, in step S5, the mass ratio of soluble bicarbonate to chromium slag is 1:5-6, and the reaction time is 2-4 hours.

[0053] According to the above scheme, the alkali used to adjust the pH in steps S3, S4, and S6 is sodium hydroxide or potassium hydroxide, and the soluble carbonate in step S5 is sodium bicarbonate or potassium bicarbonate.

[0054] When sodium hydroxide is used as the alkali to adjust the pH, the solute in filtrate three is sodium aluminate (NaAlO2), and the solute in filtrate five is sodium chromite (NaCrO2). When potassium hydroxide is used as the alkali, the solute in filtrate three is potassium aluminate (KAlO2), and the solute in filtrate five is potassium chromite (KCrO2).

[0055] In several of the following embodiments, sodium hydroxide is used as the alkali and sodium bicarbonate is used as the bicarbonate.

[0056] In some specific embodiments, the alkaline solution obtained in step S7 enters step S6 to adjust the pH value of filter residue three for recycling. This avoids secondary pollution and improves the efficiency of raw material utilization.

[0057] Based on the above embodiments, the present invention provides the following specific examples to further illustrate the invention. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following examples, unless otherwise specified, are generally performed according to the manufacturer's recommended conditions. Unless otherwise stated, percentages and parts are calculated by mass.

[0058] The general mass percentage of the main components of chromium slag is as follows: Fe2O3 40.0–50.0%, Al2O3 8.0–15.0%, CaO 5.0–10.0%, MgO 10.0–20.0%, Cr2O3 10.0–15.0%, SiO2 1.0–5.0%, Cr2O6 0.6–0.8%, and Na2Cr2O7 1.0–1.5%.

[0059] The main components of the chromium slag used in the following examples are as follows:

[0060] Content / wt% 48.59 9.10 6.21 14.68 12.29 1.72 0.67 1.36

[0061] Example 1

[0062] A method for multi-stage utilization of chromium slag includes the following steps:

[0063] 1. Grind 50g of chromium slag and straw separately. The main chemical components of the chromium slag include chromium trioxide, sodium dichromate, silicon dioxide, aluminum oxide, iron oxide, magnesium oxide, and calcium oxide. Grind the chromium slag to a particle size of 80 mesh. Mix the ground chromium slag and straw in a high-speed mixer at a mass ratio of 5:1. Detoxify the chromium slag by heating in a tubular furnace at a temperature of 500℃ for 5 hours.

[0064] 2. Mix the detoxified chromium slag with water to form a slurry. After stirring thoroughly, add 150g of 3mol / L hydrochloric acid. Heat in an 80℃ water bath for 24 hours and then filter to obtain filtrate one and filter residue one. Filter residue one mainly contains silicon dioxide, while filtrate one contains magnesium chloride, calcium chloride, aluminum chloride, ferric chloride, and chromium chloride.

[0065] 3. Heat filtrate one in a 90°C water bath while stirring, add sodium hydroxide to adjust the pH to 2, filter after the reaction is complete to obtain filtrate two and filter residue two. Filter residue two obtained by filtration is iron hydroxide, and filtrate two contains magnesium chloride, calcium chloride, aluminum chloride and chromium chloride.

[0066] 4. After washing, drying, and pulverizing the filter residue, product ferric hydroxide is obtained;

[0067] 5. Add 9g of sodium hydroxide to filtrate two and adjust the pH to 11. After reacting for 6 hours, filter to obtain filtrate three and residue three. Filtrate three is sodium aluminate solution, and residue three is calcium hydroxide, magnesium hydroxide and chromium hydroxide.

[0068] 6. Add 10g of sodium bicarbonate to filtrate three, mix and react for 4 hours, then filter to obtain filtrate four and residue four. Filtrate four is a sodium chloride solution and residue four is aluminum hydroxide.

[0069] 6. After washing, drying, and pulverizing the filter residue, aluminum hydroxide is obtained as the product.

[0070] 7. Mix filter residue three with water to form a slurry, add 4g of sodium hydroxide and adjust the pH to 12. After the reaction is complete, filter to obtain filter residue five and filtrate five. Filter residue five is a mixture of calcium hydroxide and magnesium hydroxide, and filtrate five is a sodium chromite solution.

[0071] 9. After washing, drying, and pulverizing the filter residue, product 3, a mixture of calcium hydroxide and magnesium hydroxide, is obtained;

[0072] 10. Add sufficient boiling water to filtrate five until no precipitate forms, let stand for 7 hours, filter to obtain filtrate six and filter residue six; wherein filter residue six is ​​chromium hydroxide and filtrate six is ​​sodium hydroxide.

[0073] 11. After washing, drying and crushing the filter residue 6, the product chromium tetrahydroxide is obtained; the filtrate 6 can be recycled in step 8.

[0074] Example 2

[0075] 1. Grind 75g of chromium slag and straw separately. The main chemical components of the chromium slag include chromium trioxide, sodium dichromate, silicon dioxide, aluminum oxide, iron oxide, magnesium oxide, and calcium oxide. Grind the chromium slag to a particle size of 100 mesh. Mix the ground chromium slag and straw in a high-speed mixer at a mass ratio of 5:1. Detoxify the chromium slag by heating in a tubular furnace at a temperature of 500℃ for 5 hours.

[0076] 2. Mix the detoxified chromium slag with water to form a slurry. After stirring thoroughly, add 230g of 3mol / L hydrochloric acid. Heat in an 80℃ water bath for 36 hours and then filter to obtain filtrate one and filter residue one. Filter residue one mainly contains silicon dioxide, while filtrate one contains magnesium chloride, calcium chloride, aluminum chloride, ferric chloride, and chromium chloride.

[0077] 3. Heat filtrate one in a 90°C water bath while stirring, add sodium hydroxide to adjust the pH to 2, filter after the reaction is complete to obtain filtrate two and filter residue two. Filter residue two obtained by filtration is iron hydroxide, and filtrate two contains magnesium chloride, calcium chloride, aluminum chloride and chromium chloride.

[0078] 4. After washing, drying, and pulverizing the filter residue, product ferric hydroxide is obtained;

[0079] 5. Add 12g of sodium hydroxide to filtrate two and adjust the pH to 11.5. After reacting for 6 hours, filter to obtain filtrate three and residue three. Filtrate three is sodium aluminate solution, and residue three is calcium hydroxide, magnesium hydroxide and chromium hydroxide.

[0080] 6. Add 15g of sodium bicarbonate to filtrate three, mix and react for 3 hours, then filter to obtain filtrate four and residue four. Filtrate four is a sodium chloride solution and residue four is aluminum hydroxide.

[0081] 7. After washing, drying, and pulverizing the filter residue, aluminum hydroxide product is obtained.

[0082] 8. Mix filter residue three with water to form a slurry, add 6g of sodium hydroxide and adjust the pH to 12. After the reaction is complete, filter to obtain filter residue five and filtrate five. Filter residue five is a mixture of calcium hydroxide and magnesium hydroxide, and filtrate five is a sodium chromite solution.

[0083] 9. After washing, drying, and pulverizing the filter residue, product 3, a mixture of calcium hydroxide and magnesium hydroxide, is obtained;

[0084] 10. Add sufficient boiling water to filtrate five until no precipitate is formed, let stand for 5 hours, filter to obtain filtrate six and filter residue six; wherein filter residue six is ​​chromium hydroxide and filtrate six is ​​sodium hydroxide.

[0085] 11. After washing, drying and crushing the filter residue 6, the product chromium tetrahydroxide is obtained; the filtrate 6 can be recycled in step 8.

[0086] Example 3

[0087] 1. Grind 100g of chromium slag and straw separately. The main chemical components of the chromium slag include chromium trioxide, sodium dichromate, silicon dioxide, aluminum oxide, iron oxide, magnesium oxide, and calcium oxide. Grind the chromium slag to a particle size of 100 mesh. Mix the ground chromium slag and straw in a high-speed mixer at a mass ratio of 5:1. Detoxify the chromium slag by heating in a tubular furnace at a temperature of 600℃ for 5 hours.

[0088] 2. Mix the detoxified chromium slag with water to form a slurry. After stirring thoroughly, add 300g of 3mol / L hydrochloric acid. Heat in an 80℃ water bath for 24 hours and then filter to obtain filtrate one and filter residue one. Filter residue one mainly contains silicon dioxide, while filtrate one contains magnesium chloride, calcium chloride, aluminum chloride, ferric chloride, and chromium chloride.

[0089] 3. Heat filtrate one in a 90°C water bath and stir. Add sodium hydroxide to adjust the pH to 3. After the reaction is complete, filter to obtain filtrate two and filter residue two. Filter residue two is iron hydroxide, and filtrate two contains magnesium chloride, calcium chloride, aluminum chloride and chromium chloride.

[0090] 4. After washing, drying, and pulverizing the filter residue, product ferric hydroxide is obtained;

[0091] 5. Add 15g of sodium hydroxide to filtrate two and adjust the pH to 11.5. After reacting for 7 hours, filter to obtain filtrate three and residue three. Filtrate three is sodium aluminate solution, and residue three is calcium hydroxide, magnesium hydroxide and chromium hydroxide.

[0092] 6. Add 20g of sodium bicarbonate to filtrate three, mix and react for 4 hours, then filter to obtain filtrate four and residue four. Filtrate four is a sodium chloride solution and residue four is aluminum hydroxide.

[0093] 7. After washing, drying, and pulverizing the filter residue, aluminum hydroxide product is obtained.

[0094] 8. Mix filter residue three with water to form a slurry, add 8g of sodium hydroxide to bring the pH to 13, filter after the reaction is complete to obtain filter residue five and filtrate five, wherein filter residue five is a mixture of calcium hydroxide and magnesium hydroxide, and filtrate five is a sodium chromite solution;

[0095] 9. After washing, drying, and pulverizing the filter residue, product 3, a mixture of calcium hydroxide and magnesium hydroxide, is obtained;

[0096] 10. Add sufficient boiling water to filtrate five until no precipitate is formed, let stand for 6 hours, filter to obtain filtrate six and filter residue six; wherein filter residue six is ​​chromium hydroxide and filtrate six is ​​sodium hydroxide;

[0097] 11. After washing, drying and crushing the filter residue 6, the product chromium tetrahydroxide is obtained; the filtrate 6 can be recycled in step 8.

[0098] X-ray diffraction was performed on the prepared products 1, 2, 3 and 4 respectively. The results showed that product 1 was iron hydroxide, product 2 was aluminum hydroxide, product 3 was a mixture of magnesium hydroxide and calcium hydroxide, and product 4 was chromium hydroxide.

[0099] The proportions of metal elements in the chromium slag of product 1 (ferric hydroxide), product 2 (aluminum hydroxide), product 3 (a mixture of calcium hydroxide and magnesium hydroxide), and product 4 (chromium hydroxide) in Examples 1-3 were determined to determine the utilization rate (η) of iron, aluminum, calcium, magnesium, and chromium elements in the multi-stage utilization method of the present invention. The results are shown in Table 1.

[0100]

[0101] Using the multi-stage utilization method of chromium slag of the present invention, four products were prepared: iron hydroxide, aluminum hydroxide, a mixture of calcium hydroxide and magnesium hydroxide, and chromium hydroxide. The utilization rates of valuable metals iron, aluminum, calcium, magnesium and chromium in the chromium slag reached more than 86.2%, 62.7%, 79.3% and 64.2% respectively. The comprehensive utilization rate of metal resources in chromium slag is high, and the utilization of metal resources in chromium slag is maximized.

[0102] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for multi-stage utilization of chromium slag, characterized in that, Includes the following steps: S1. Detoxification of chromium slag; S2. The detoxified chromium residue is mixed with water to form a slurry, acid is added for acid leaching, filtration is performed, and filter residue one and filter liquor one containing Mg 2+ , Ca 2 + , Al 3+ , Fe 3+ , and Cr 3+ are obtained; S3. Adjust the pH of filtrate one to 2-3, and react it at a certain temperature to reduce the Fe content. 3+ Precipitation, solid-liquid separation, yielding ferric hydroxide and Mg. 2+ Ca 2+ Al 3+ and Cr 3+ Filtrate 2; S4. Adjust the pH of filtrate two to 11-11.

5. After the reaction, filter residue three containing calcium hydroxide, magnesium hydroxide, and chromium hydroxide and filter residue three containing AlO2 are obtained. - The filtrate is three; S5. Add soluble bicarbonate to filtrate three, react and filter to obtain aluminum hydroxide; S6. Prepare a mixed solution with a pH of 12-14 from the filter residue. After the reaction, separate the solid and liquid components to obtain a mixture of calcium hydroxide and magnesium hydroxide, and a solution containing CrO2. - The filtrate is five; S7. Add sufficient boiling water to filtrate five, let stand, and separate the solid and liquid to obtain chromium hydroxide and alkaline solution.

2. The method for multi-stage utilization of chromium slag according to claim 1, characterized in that, In step S1, the chromium slag is detoxified using biomass pyrolysis.

3. The method for multi-stage utilization of chromium slag according to claim 2, characterized in that, The biomass pyrolysis method specifically involves grinding chromium slag and mixing it with straw, then heating it in a tubular furnace to detoxify the chromium slag.

4. The method for multi-stage utilization of chromium slag according to claim 1, characterized in that, In step S2, the mass ratio of water to chromium slag is 1.5~2:1, the acid leaching temperature is 80~90℃, and the time is 12~36h.

5. The method for multi-stage utilization of chromium slag according to claim 4, characterized in that, In step S2, the acid is hydrochloric acid with a concentration of 3-5 mol / L; based on a concentration of 3 mol / L hydrochloric acid, the mass ratio of hydrochloric acid to chromium slag is 3-4:

1.

6. The method for multi-stage utilization of chromium slag according to claim 1, characterized in that, The reaction temperature in step S3 is 90~100℃, and the reaction time is 3~4h.

7. The method for multi-stage utilization of chromium slag according to claim 1, characterized in that, The reaction time in step S4 is 5-8 hours.

8. The method for multi-stage utilization of chromium slag according to claim 1, characterized in that, In step S5, the mass ratio of soluble bicarbonate to chromium slag is 1:5~6, and the reaction time is 2~4 hours.

9. The method for multi-stage utilization of chromium slag according to any one of claims 1 to 8, characterized in that, In steps S3, S4, and S6, the alkali used to adjust the pH is sodium hydroxide or potassium hydroxide, and in step S5, the soluble carbonate is sodium bicarbonate or potassium bicarbonate.

10. The method for multi-stage utilization of chromium slag according to any one of claims 1 to 8, characterized in that, The alkaline solution obtained in step S7 is recycled in step S6 to adjust the pH value of filter residue three.

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