Method for recycling cobalt and chromium from cobalt-chromium alloy waste step by step

Abstract

The invention belongs to the field of hydrometallurgy, and provides a method for recycling cobalt and chromium from cobalt-chromium alloy waste step by step. The method comprises the steps of crushing and ball-milling, wet-process pressurized oxygen hydrochloric acid leaching, separation of cobalt and chromium from a sodium hypochlorite solution, and reduction and acid leaching for extraction of cobalt. According to the method, the cobalt-chromium alloy powder is treated in a pressurized oxygen leaching mode, and compared with the mode that high-temperature oxidation is conducted firstly and then wet leaching treatment is conducted in the prior art, the energy consumption is reduced, the technological process is saved, and the brought environmental problems are avoided. Meanwhile, the sodium hypochlorite solution generated in the cobalt electrodeposition process of the chlorination system is reused in the cobalt-chromium separation process, step-by-step recycling of cobalt and chromium is well achieved, and the method has great significance in reducing the production cost and optimizing the process configuration.

Description

Technical Field

[0001] The invention belongs to the field of hydrometallurgy and provides a method for recovering cobalt and chromium from cobalt-chromium alloy waste in steps. Background Art

[0002] Cobalt is an important raw material for the production of heat-resistant alloys, cemented carbides, anti-corrosion alloys, magnetic alloys and various cobalt salts. In the face of the urgent demand for cobalt resources, recovering cobalt from waste materials recovered from various sources has become an important breakthrough in alleviating the shortage of cobalt raw materials. Among the cobalt-containing waste materials, waste cemented carbides account for a large proportion, such as various brands of used tungsten-cobalt alloys, alloy mixtures, alloy chips, etc.

[0003] The existing methods for recovering cobalt-containing cemented carbide waste mainly include high-temperature oxidation, mechanical crushing, electrolysis, alkali leaching, acid leaching, sodium roasting, zinc melting, and high-pressure oxygen-enriched leaching with ammonia or ammonium solution. Among them, since the process technology of high-temperature oxidation has been relatively mature, it has a strong pertinence for separating the main elements tungsten and cobalt in cemented carbide. Therefore, high-temperature oxidation is generally used to separate and recover the cobalt and tungsten elements in waste cemented carbide. However, the high-temperature oxidation method also has the disadvantages of high energy consumption and certain pollution to the environment. In addition, for cemented carbide waste with chromium metal added, when recovering cobalt, Co and Cr need to be separated, which brings certain processing difficulties. Chinese patent CN 113430378 A uses high-temperature oxidation to oxidize the metal of cemented carbide into oxides, and then uses high-pressure alkali boiling to recover the tungsten therein, and then adds hydrogen peroxide and alkali to the alkali boiling slag to adjust the pH value again to achieve the separation of cobalt and chromium. This method has high energy consumption and also requires additional hydrogen peroxide and alkali, which is costly.

[0004] In addition, during the production of electrolytic cobalt, some manufacturers use the chlorination system insoluble anode electrowinning process. The large amount of chlorine produced in the process is treated by liquid alkali absorption. The main components of the liquid after alkali absorption are sodium hypochlorite and sodium hydroxide, which have a certain alkalinity. It is mainly used or exported in the form of by-product sodium hypochlorite solution, and the rest is discharged to the wastewater system for treatment. Recycling it through multiple channels is very critical to reducing production costs. If the sodium hypochlorite liquid produced by the chlorination system electrowinning can be reused in the treatment of cobalt-chromium alloy waste, it will be of great significance to reducing production costs and optimizing process configuration. Summary of the invention

[0005] The object of the present invention is to provide a method for recovering cobalt and chromium from cobalt-chromium alloy waste in steps, aiming to solve the problems existing in the prior art in the above-mentioned background technology.

[0006] To this end, the present invention provides the following technical solutions: The method for recovering cobalt and chromium from cobalt-chromium alloy waste in steps of the present invention comprises the following steps: (1) The cobalt-chromium alloy waste is crushed into powder by a crushing ball mill; the cobalt-chromium alloy powder contains 10-60% cobalt and 5-30% chromium.

[0007] (2) Add cobalt-chromium alloy powder into a pressure autoclave, add pure water, stir, and slurry. The leaching temperature is set to 140-180°C, and the temperature begins to rise. When the temperature reaches the set temperature, the pressure in the autoclave is 0.6-1.2 MPa, oxygen is introduced into the autoclave, and hydrochloric acid is added; the oxygen partial pressure is controlled to be 0.6-1.5 MPa, the total pressure is 1.2-2.7 MPa, and the heat preservation reaction time is 2-4 hours. After the reaction is completed, the leached slurry is separated into solid and liquid to obtain cobalt-chromium leaching solution and leaching residue; the solid-liquid mass ratio of cobalt-chromium alloy powder to pure water is 1:5-10; the amount of hydrochloric acid added is based on controlling the pH value of the reaction end point to be 1-1.5.

[0008] (3) Under stirring conditions, add sodium hypochlorite solution to the cobalt-chromium leaching solution, and use sodium hydroxide to supplement and adjust the system pH to 12-13, react at 60-80°C for 2-5 hours, and after the reaction is completed, separate the solid and liquid to obtain chromium-free cobalt hydroxide slag and chromium-containing solution; the cobalt hydroxide slag is washed twice with water. The sodium hypochlorite solution is the sodium hypochlorite solution produced by electrowinning cobalt in the chlorination system, and its ClO − The concentration is 12-20%, and the pH value is 11-13. The chromium content in the obtained cobalt hydroxide slag is less than 0.001%, and the cobalt content in the chromium-containing solution is less than 0.0001 g / L, which can be used in the downstream process to prepare various chromium salt products.

[0009] After adding sodium hypochlorite solution to the cobalt-chromium leaching solution, sodium hydroxide is used to adjust the system pH to 12-13, and the reaction is carried out at 60-80°C for 2-5 hours. During this reaction, cobalt remains in the slag in the form of hydroxide, while Cr 3+ Oxidized to CrO4 2- The chromium and cobalt are retained in the solution in the form of ions, thereby fully realizing the separation of cobalt and chromium. The reaction formula is: Cr 3+ +3OH − =Cr(OH)3(s)↓ 2Cr(OH)3+8ClO − +3OH − →2CrO4 2− +8Cl − +5H2O 2Co 2+ +4OH − +ClO − =2Co(OH)3↓+Cl − (4) Add acid and reducing agent to the cobalt hydroxide slag for leaching, and obtain a cobalt salt solution after solid-liquid separation. The acid is sulfuric acid or hydrochloric acid; the reducing agent is sodium sulfite or sodium pyrosulfite; the leaching temperature is 60~80℃, and the leaching time is 4~8h. The obtained cobalt salt solution can be used as a raw material for downstream processes such as the production of cobalt sulfate crystals, cobalt chloride crystals, etc.

[0010] The beneficial effects of the present invention are as follows: (1) The cobalt-chromium alloy powder is treated by pressurized oxygen leaching, which reduces energy consumption, saves process flow and avoids environmental problems compared with the prior art method of first high-temperature oxidation and then wet leaching. (2) The sodium hypochlorite solution produced by the electrolytic deposition of the chlorination system is reused in the cobalt-chromium separation process, which better realizes the step-by-step recycling of cobalt and chromium, and is of great significance for reducing production costs and optimizing process configuration. DETAILED DESCRIPTION

[0011] The present invention will be further described below through specific implementation modes.

[0012] Example 1 (1) The cobalt-chromium alloy waste was crushed into powder using a crushing ball mill. Sample analysis showed that the cobalt content was 56.4% and the chromium content was 25.6%.

[0013] (2) 500 g of cobalt-chromium alloy powder was added into a pressure autoclave, and 4 L of pure water was added, stirred, and slurried. The heating temperature was set to 180°C, and the temperature was started to rise. When the temperature reached 180°C, the pressure in the pressure autoclave was 1.17 MPa, oxygen was introduced, and the oxygen partial pressure was controlled to 0.7 MPa, and the total pressure was 1.87 MPa. The total pressure in the pressure autoclave was maintained unchanged, hydrochloric acid was added, and the reaction was continued for 3 hours. After the reaction was completed, the leached slurry was subjected to solid-liquid separation to obtain a cobalt-chromium leaching solution and a leaching residue. The cobalt-chromium content in the leaching residue was detected, which was 0.08% cobalt and 0.077% chromium, and the cobalt-chromium leaching rate was greater than 99%.

[0014] (3) Add sodium hypochlorite solution to the cobalt-chromium leaching solution at 80°C under stirring conditions (sodium hypochlorite solution is the sodium hypochlorite solution produced by electrolytic cobalt in the chlorination system, and its ClO − The concentration is 14.5% and the pH value is 12.8. ), and sodium hydroxide is used to supplement the system pH to 12-13. After reacting for 2 hours, solid-liquid separation is performed to obtain cobalt hydroxide slag and chromium-containing solution; the cobalt content of the chromium-containing solution is less than 0.0001g / L. The cobalt hydroxide slag is washed twice with water and the chromium content is less than 0.001g / L.

[0015] (4) Sulfuric acid and reducing agent sodium metabisulfite are added to the cobalt hydroxide slag and leached at 60°C for 6 hours, and a cobalt salt solution is obtained after solid-liquid separation, which can be used as a raw material for downstream processes such as the production of cobalt sulfate crystals, cobalt chloride crystals, etc.

[0016] Example 2 (1) The cobalt-chromium alloy waste was crushed into powder using a crushing ball mill. Sample analysis showed that the cobalt content was 36.2% and the chromium content was 18.3%.

[0017] (2) 500 g of cobalt-chromium alloy powder was added into a pressure autoclave, and 2.5 L of pure water was added, stirred, and slurried. The heating temperature was set to 160° C., and the temperature began to rise. When the temperature reached 160° C., the pressure in the pressure autoclave was 0.9 MPa, oxygen was introduced, and the oxygen partial pressure was controlled to 0.5 MPa, and the total pressure was 1.4 MPa. The total pressure in the pressure autoclave was maintained unchanged, hydrochloric acid was added, and the reaction was continued for 3 h. After the reaction was completed, the leached slurry was subjected to solid-liquid separation to obtain a cobalt-chromium leaching solution and a leaching residue. The cobalt-chromium content in the leaching residue was detected, which was 0.045% cobalt and 0.033% chromium, and the cobalt-chromium leaching rate was greater than 99%.

[0018] (3) Add sodium hypochlorite solution (sodium hypochlorite solution is the sodium hypochlorite solution produced by electrolytic cobalt deposition in a chlorination system, wherein ClO − The concentration is 16.9% and the pH value is 11.5. ), and sodium hydroxide is used to supplement the system pH to 12-13. After reacting for 2 hours, solid-liquid separation is performed to obtain cobalt hydroxide slag and chromium-containing solution; the cobalt content of the chromium-containing solution is less than 0.0001g / L. The cobalt hydroxide slag is washed twice with water and the chromium content is less than 0.001g / L.

[0019] (4) Add hydrochloric acid and reducing agent sodium metabisulfite to the cobalt hydroxide slag and leach at 80°C for 5 hours, and obtain a cobalt salt solution after solid-liquid separation, which can be used as a raw material for downstream processes such as the production of cobalt sulfate crystals, cobalt chloride crystals, etc.

[0020] In summary, the present invention provides a method for recycling cobalt and chromium from cobalt-chromium alloy waste in steps. The method uses pressurized oxygen leaching to treat cobalt-chromium alloy powder. Compared with the prior art method of first high-temperature oxidation and then wet leaching, it reduces energy consumption, saves process flow and avoids environmental problems. (2) The sodium hypochlorite solution produced by the electrolytic deposition of the chlorination system is reused in the cobalt-chromium separation process, which better realizes the step-by-step recycling of cobalt and chromium, and has great significance for reducing production costs and optimizing process configuration.

[0021] The above are preferred embodiments of the present invention. Any simple modification, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for recovering cobalt and chromium from cobalt-chromium alloy waste in steps, characterized in that: The following steps are involved: (1) The cobalt-chromium alloy waste is crushed into powder using a crushing ball mill; (2) Add cobalt-chromium alloy powder into a pressure autoclave, add pure water, stir, and slurry. Set the leaching temperature to 140-180°C, and start heating. When the temperature reaches the set temperature, the pressure in the autoclave is 0.6-1.2MPa, oxygen is introduced into the autoclave, and hydrochloric acid is added. The oxygen partial pressure is controlled to be 0.6-1.5MPa, the total pressure is 1.2-2.7MPa, and the heat preservation reaction time is 2-4 hours. After the reaction is completed, the leached slurry is subjected to solid-liquid separation to obtain cobalt-chromium leaching solution and leaching residue. (3) Under stirring conditions, adding sodium hypochlorite solution to the cobalt-chromium leaching solution, and using sodium hydroxide to supplement and adjust the pH of the system to 12-13, reacting at 60-80° C. for 2-5 hours. After the reaction is completed, solid-liquid separation is performed to obtain chromium-free cobalt hydroxide slag and chromium-containing solution; the cobalt hydroxide slag is washed twice with water; (4) Acid and a reducing agent are added to the cobalt hydroxide slag for leaching, and a cobalt salt solution is obtained after solid-liquid separation.

2. The method for recovering cobalt and chromium from cobalt-chromium alloy waste in steps according to claim 1, characterized in that: In step (1), the cobalt-chromium alloy powder contains 10-60% cobalt and 5-30% chromium.

3. The method for recovering cobalt and chromium from cobalt-chromium alloy waste in steps according to claim 1, characterized in that: In step (2), the solid-liquid mass ratio of the cobalt-chromium alloy powder and pure water is 1:5-10; the amount of hydrochloric acid added is based on controlling the pH value of the reaction end point to be 1-1.

5.

4. The method for recovering cobalt and chromium from cobalt-chromium alloy waste in steps according to claim 1, characterized in that: In step (3), the sodium hypochlorite solution is a sodium hypochlorite solution produced by electrowinning cobalt in a chlorination system, wherein ClO − The mass concentration is 12~20% and the pH value is 11~13.

5. The method for recovering cobalt and chromium from cobalt-chromium alloy waste in steps according to claim 1, characterized in that: In step (3), the cobalt content in the chromium-containing solution is less than 0.0001 g / L; and the chromium content in the cobalt hydroxide slag is less than 0.001%.

6. The method for recovering cobalt and chromium from cobalt-chromium alloy waste in steps according to claim 1, characterized in that: In step (4), the acid is sulfuric acid or hydrochloric acid; the reducing agent is sodium sulfite or sodium metabisulfite; the leaching temperature is 60-80° C., and the leaching time is 4-8 hours.