Method for acid leaching of fluorine and lithium in cathode alkaline leaching residues and combined treatment of alkaline leaching waste liquid

Abstract

The invention relates to a method for acid leaching of fluorine and lithium in cathode alkaline leaching residues and combined treatment of alkaline leaching waste liquid, and belongs to the technical field of aluminum electrolysis waste cathode recycling. The method comprises the steps that the alkaline leaching residues of aluminum electrolysis waste cathodes are added into an AlCl3 solution for ultrasonic leaching, hydrochloric acid is used for adjusting the leaching pH value, and after leaching, solid-liquid separation is conducted to obtain primary carbon powder and first filtrate; returning the first filtrate to a system for recycling to obtain a final leachate with relatively saturated electrolyte content; washing the primary carbon powder with deionized water to obtain high-purity carbon powder; and the final leaching solution and the waste cathode alkali leaching solution are mixed and precipitated to obtain lithium-containing cryolite and a precipitation solution, and the precipitation solution can be returned to an alkali leaching system to be used for preparing alkali liquor. According to the method, valuable substances in the alkaline leaching residues and the alkaline leaching waste liquid in the aluminum electrolysis waste cathodes are effectively recycled, meanwhile, harmless treatment of the waste cathodes is achieved, and the recycling process of the valuable substances in the alkaline leaching residues and the alkaline leaching waste liquid in the aluminum electrolysis waste cathodes is greatly simplified.

Description

Technical Field

[0001] The invention belongs to the technical field of recycling waste cathodes from aluminum electrolysis, and in particular relates to a method for acid leaching cathodes to remove fluorine and lithium from alkaline leaching residues and jointly treating alkaline leaching waste liquid. Background Art

[0002] Waste cathode is one of the solid wastes generated by the electrolytic aluminum industry. According to statistics, every ton of aluminum metal produced consumes 50 kg of electrolyte and produces 30-50 kg of waste cathode materials. Waste cathode is a mixture of multiple elements and multiple substances and is classified as hazardous waste. At the same time, because the carbon, sodium fluoride, cryolite, lithium fluoride, etc. contained in it have high recycling value, it can be regarded as a concentrate with high recycling value.

[0003] At present, there are mainly physical methods, high-temperature pyrolysis and wet treatment methods for the treatment of waste cathodes. Through these treatment methods, the purpose of harmless treatment of waste cathodes and partial resource recovery can be achieved. There are two goals for the treatment of waste cathodes: (1) Harmless treatment: mainly for toxic substances in waste cathodes, so that waste cathodes become a harmless solid after treatment. (2) Recycling of valuable substances: mainly for the recovery of various valuable components in waste cathodes, such as carbon, fluorine, sodium, lithium, etc. Wet treatment can well take into account these two goals.

[0004] Wet treatment mainly separates and purifies the substances in the waste cathode by their different solubility in the solution and their different chemical properties. The wet treatment mainly includes oxidation, water leaching and alkaline leaching, among which alkaline leaching is a commonly used method. After alkaline leaching of the waste cathode, some fluoride, lithium ions and alkali still remain in the leached residue. The alkaline concentration of the leachate is too high to be handled, and the leached residue and leachate need to be treated secondary. Summary of the invention

[0005] In view of the problems raised by the background technology, the present invention provides a method for acid leaching fluorine and lithium in alkaline leaching residue of the cathode and jointly treating the alkaline leaching waste liquid. The alkaline leaching residue of the waste cathode of aluminum electrolysis is ultrasonically acid-leached with an aluminum chloride solution, and hydrochloric acid is added during the acid leaching process to adjust the pH value, so that the fluorine and lithium in the waste cathode can be effectively leached; the acid leaching solution is jointly treated with the alkaline leaching residue of the waste cathode of aluminum electrolysis to directly generate cryolite, effectively realizing the recovery of valuable substances in the alkaline leaching residue and alkaline leaching waste liquid of the waste cathode of aluminum electrolysis, and at the same time realizing the harmless treatment of the waste cathode To achieve the above object, the present invention is implemented through the following technical solutions: The method for acid leaching fluorine and lithium in cathode alkali leaching residue and jointly treating alkali leaching waste liquid comprises the following steps: (1) Crushing the waste cathode alkaline leaching residue; (2) Leaching the crushed waste cathode alkaline leaching residue with AlCl3 solution under ultrasonic conditions, and adding hydrochloric acid to adjust the pH value of the AlCl3 solution; (3) Liquid-solid separation to obtain primary carbon powder and leachate; (4) The leaching solution is added dropwise to the alkaline leaching waste liquid of the spent cathode to produce cryolite.

[0006] Furthermore, in step (2), the concentration of the AlCl3 solution is 0.2-1.2 mol / L, and the pH value is 0-1.7.

[0007] Furthermore, the pH value at the reaction end point of step (4) is 13.6-9.

[0008] Furthermore, the solid-liquid ratio of the leaching in step (2) is 1:3-8 g / mL, the leaching temperature is 50-70° C., and the leaching time is 20-120 min.

[0009] Furthermore, the leaching solution of step (3) is returned to step (2) for recycling, and after the electrolyte in the leaching solution is relatively saturated, it is added dropwise as the final leaching solution to the alkaline leaching waste liquid of the waste cathode in step (4).

[0010] Furthermore, the alkali leaching residue of step (1) is crushed to a particle size of 200-800 mesh, and the material accounts for 90-100wt.%.

[0011] Furthermore, the primary carbon powder obtained in step (3) is washed with deionized water, separated into solid and liquid, and recovered after drying; and the washing liquid is used to prepare the AlCl3 solution.

[0012] Furthermore, the solid-liquid ratio of the primary carbon powder to deionized water is 1:1 to 3 g:mL, and the water immersion washing time is 5 to 10 min.

[0013] Beneficial effects of the present invention: 1. The present invention uses aluminum chloride solution to leach the alkaline leaching residue of the aluminum electrolysis waste cathode under ultrasonic conditions, and adds hydrochloric acid to adjust the leaching pH value, thereby achieving a high leaching rate of fluorine and lithium in the alkaline leaching residue of the aluminum electrolysis waste cathode.

[0014] 2. When leaching the alkaline leaching residue of the aluminum electrolysis waste cathode, the aluminum chloride added enters the leaching solution, and when the final leaching solution is added to the alkaline leaching waste liquid in the subsequent sequence, it reacts with the fluoride and lithium ions in the alkaline leaching waste liquid to generate cryolite containing lithium fluoride. While realizing the leaching of fluorine and lithium in the alkaline leaching residue, the recovery of fluoride and lithium ions in the alkaline leaching waste liquid is realized, which greatly simplifies the recovery process of valuables in the alkaline leaching residue and alkaline leaching waste liquid of the aluminum electrolysis waste cathode.

[0015] 3. The present invention can not only improve the leaching effect of fluoride and lithium ion by recycling the leaching solution, but also save the amount of AlCl3 solution, and when the final acid leaching solution is used to react with the alkaline leaching waste liquid, the fluoride in the alkaline leaching waste liquid can be fully reacted.

[0016] 4. The present invention leach the alkaline leaching residue of the waste cathode of aluminum electrolysis under ultrasonic conditions, and utilizes the three major effects of ultrasound, namely cavitation effect, mechanical effect, and thermal effect, to synergistically strengthen the leaching, which can accelerate the reaction, shorten the leaching time, and improve the leaching effect of the electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a process flow chart of the present invention; Figure 2 This is the XRD comparison diagram of the waste cathode alkaline leaching residue before and after the reaction in Example 1; Figure 3 This is a SEM comparison of the waste cathode alkaline leaching residue in Example 1 before and after the reaction. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and beneficial effects of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0019] In the following examples, waste cathode slag from aluminum electrolysis (hereinafter referred to as cathode alkaline leaching slag) and alkaline leaching waste liquid (hereinafter referred to as alkaline leaching waste liquid) after alkaline leaching in a certain factory were taken. The main element contents (wt.%) in the cathode alkaline leaching slag were: C 73.89%, Na2.04%, F 2.66%, Al 3.84%, O 4.36%, and Li 0.25%; the main element concentrations in the alkaline leaching waste liquid were: F 19.35 g / L, Li265.8 mg / L. Example 1

[0020] A method for acid leaching fluorine and lithium in cathode alkaline leaching residue and jointly treating alkaline leaching waste liquid, the specific steps are as follows: (1) drying the cathode alkaline leaching residue and crushing it to a particle size of 200-800 mesh, wherein the material accounts for 95wt.%, to obtain cathode alkaline leaching residue particles; (2) Prepare 0.4 mol / L AlCl3 solution, adjust the pH value of AlCl3 solution to 1.7 with hydrochloric acid (concentration of 3 mol / L), and add cathode alkaline leaching residue particles to the leaching solution to start the ultrasonic enhanced leaching process. The solid-liquid ratio of cathode alkaline leaching residue to leaching solution is 5:1 g:mL, the ultrasonic power is 250W, the leaching temperature is 70°C, and the time is 40min. Solid-liquid separation obtains primary carbon powder and the first filtrate; (3) The first filtrate is returned to step (2) to circulate and leach new cathode alkaline leaching residue, and the circulated leaching is repeated 5 times to obtain a final filtrate; (4) The primary carbon powder is washed with deionized water, solid-liquid separated, and vacuum dried to obtain high-purity carbon powder. The washing liquid is used to prepare AlCl3 solution. The solid-liquid ratio of the primary carbon powder to deionized water is 1:2 g:mL, and the water washing time is 3-5 min.

[0021] (5) The final filtrate is slowly dripped into the alkaline leaching waste liquid for reaction. The reaction end point pH value is 10. After the reaction, the solid and liquid are separated. The solid phase is vacuum dried to obtain cryolite containing lithium fluoride. The lithium-containing cryolite is returned to the aluminum electrolysis system for use, and the filtrate is returned to the alkaline leaching system of the waste cathode for the preparation of alkaline solution.

[0022] The X-ray diffraction pattern of the cathode alkaline leaching residue and high-purity carbon powder in this embodiment is shown in FIG. Figure 2 (The left picture shows cathode alkaline leaching residue, and the right picture shows high-purity carbon powder). Figure 2 It can be seen that after leaching, calcium fluoride, cone cryolite (NaF 11 O 17 ) and other substances have disappeared; The scanning electron microscope images of the cathode alkali leaching residue before and after the reaction, that is, the cathode alkali leaching residue and the high-purity carbon powder are shown in Figure 3 (The left picture shows cathode alkaline leaching residue, and the right picture shows high-purity carbon powder). Figure 3 It can be seen from the figure before the reaction that the structure of the carbon material is tight before leaching, and some bright spot substances are embedded in the carbon material, mainly fluorides, and agglomerated into spheres. After detection, the spherical fluorides are mainly calcium fluoride insoluble in alkali; from the figure after leaching, it can be seen that after ultrasonic-assisted leaching, the structure of the carbon material is tighter, and the carbon material mainly presents a layered structure. Its morphology has changed significantly compared with before leaching. Because before leaching, most of the electrolyte in the cathode alkaline leaching residue is wrapped by the carbon layer, the cavitation effect and high-speed vibration during ultrasonic leaching will open the carbon layer so that the electrolyte in it can contact the AlCl3 solution.

[0023] The fluoride content in the high-purity carbon powder of this embodiment is 1.05%, the lithium ion content is 0.06%, and the purity of the carbon powder is 97.56wt.%; the fluoride concentration in the filtrate is 0.79g / L, and the lithium ion concentration is 24.3 mg / L.

[0024] Comparative Example 1

[0025] The difference between this comparative example and Example 1 is that: ultrasound is not introduced in step (2) and step (3);

[0026] The fluoride content in the high-purity carbon powder of this comparative example is 1.36%, the lithium ion content is 0.13%, and the purity of the carbon powder is 88.35wt.%; the fluoride concentration in the filtrate is 1.33g / L, and the lithium ion concentration is 56.1mg / L. Example 2

[0027] A method for acid leaching fluorine and lithium in cathode alkaline leaching residue and jointly treating alkaline leaching waste liquid, the specific steps are as follows: (1) drying the cathode alkali leaching residue and crushing the alkali leaching residue particles until the particle size of the alkali leaching residue particles is 200-800 mesh, accounting for 95wt.%, to obtain cathode alkali leaching residue particles; (2) Prepare an AlCl3 solution with a concentration of 0.6 mol / L, and use hydrochloric acid (concentration of 3 mol / L) to adjust the pH value of the AlCl3 solution to 1. After the solution is prepared, add the cathode alkaline leaching residue particles to the AlCl3 solution to start the ultrasonic enhanced leaching process. The solid-liquid ratio of the cathode alkaline leaching residue to the leaching solution is 6:1 g:mL, the ultrasonic power is 250 W, the leaching temperature is 60 °C, and the time is 40 min. Solid-liquid separation obtains primary carbon powder and the first filtrate; (3) The first filtrate returns to step (2) and continues to leach new cathode alkaline leaching residue into the electrolyte in the leaching solution for 5 times to obtain a final filtrate; (4) The primary carbon powder is washed with deionized water, solid-liquid separated, and vacuum dried to obtain high-purity carbon powder. The washing liquid is returned to the system and used to prepare AlCl3 solution. The solid-liquid ratio of the primary carbon powder to deionized water is 1:2 g:mL, and the water washing time is 3-5 min; (5) The final filtrate is slowly dripped into the alkaline leaching waste liquid to adjust the pH value to 10. After mixed precipitation, the solid and liquid are separated. The solid phase is vacuum dried to obtain cryolite containing lithium fluoride, which is returned to the aluminum electrolysis system for use. The filtrate is returned to the alkaline leaching system of the waste cathode for the preparation of alkaline solution.

[0028] The fluoride content in the high-purity carbon powder of this embodiment is 0.76%, the lithium ion content is 0.05%, and the purity of the carbon powder is 98.33wt.%; the fluoride concentration in the filtrate is 0.11g / L, and the lithium ion concentration is 25mg / L. Example 3

[0029] A method for acid leaching fluorine and lithium in cathode alkaline leaching residue and jointly treating alkaline leaching waste liquid, the specific steps are as follows: (1) drying the cathode alkali leaching residue and crushing the cathode alkali leaching residue particles until the particles with a diameter of 200-800 mesh account for 95 wt.%, thereby obtaining cathode alkali leaching residue particles; (2) Prepare an AlCl3 solution with a concentration of 0.8 mol / L, and use hydrochloric acid (concentration of 3 mol / L) to adjust the pH value of the AlCl3 solution to 1. After the solution is prepared, add the cathode alkaline leaching residue particles to the AlCl3 solution to start the ultrasonic enhanced leaching process. The solid-liquid ratio of the cathode alkaline leaching residue to the leaching solution is 5:1 g:mL, the ultrasonic power is 250 W, the leaching temperature is 60 °C, and the time is 60 min. Solid-liquid separation obtains primary carbon powder and the first filtrate; (3) The first filtrate returns to step (2) and continues to leach new cathode alkaline leaching residue into the electrolyte in the leaching solution for 5 times to obtain a final filtrate; (4) The primary carbon powder is washed with deionized water, solid-liquid separated, and vacuum dried to obtain high-purity carbon powder. The washing liquid is returned to the system and used to prepare AlCl3 solution. The solid-liquid ratio of the primary carbon powder to deionized water is 1:2 g:mL, and the water washing time is 3-5 min; (5) The final filtrate is slowly dripped into the alkali leaching waste liquid to adjust the pH value to 10. After mixed precipitation, the solid and liquid are separated. The solid phase is vacuum dried to obtain cryolite containing lithium fluoride, which is returned to the aluminum electrolysis system for use. The filtrate is returned to the alkali leaching system for the preparation of alkali solution.

[0030] The fluoride content in the high-purity carbon powder of this embodiment is 0.45%, the lithium ion content is 0.03%, and the purity of the carbon powder is 99.17wt.%; the fluoride concentration in the filtrate is 0.28g / L, and the lithium ion concentration is 0.82mg / L. Example 4

[0031] A method for acid leaching fluorine and lithium in cathode alkaline leaching residue and jointly treating alkaline leaching waste liquid, the specific steps are as follows: (1) drying the cathode alkali leaching residue and crushing the cathode alkali leaching residue particles until the particles with a diameter of 200-800 mesh account for 95 wt.%, thereby obtaining cathode alkali leaching residue particles; (2) Prepare an AlCl3 solution with a concentration of 1 mol / L, and adjust the pH value of the AlCl3 solution to 0.8 with hydrochloric acid (concentration of 3 mol / L). After the solution is prepared, add the cathode alkaline leaching residue particles to the AlCl3 solution to start the ultrasonic enhanced leaching process. The solid-liquid ratio of the cathode alkaline leaching residue to the leaching solution is 7:1 g:mL, the ultrasonic power is 250 W, the leaching temperature is 60 °C, and the time is 90 min. Solid-liquid separation obtains primary carbon powder and the first filtrate; (3) The first filtrate returns to step (2) and continues to leach new cathode alkaline leaching residue into the electrolyte in the leaching solution for 5 times to obtain a final filtrate; (4) The primary carbon powder is washed with deionized water, solid-liquid separated, and vacuum dried to obtain high-purity carbon powder. The washing liquid is returned to the system and used to prepare AlCl3 solution. The solid-liquid ratio of the primary carbon powder to deionized water is 1:2 g:mL, and the water washing time is 3-5 min; (5) The final filtrate is slowly dripped into the alkali leaching waste liquid to adjust the pH value to 10. After mixed precipitation, the solid and liquid are separated. The solid phase is vacuum dried to obtain cryolite containing lithium fluoride, which is returned to the aluminum electrolysis system for use. The filtrate is returned to the alkali leaching system for the preparation of alkali solution.

[0032] The fluoride content in the high-purity carbon powder of this embodiment is 0.38%, the lithium ion content is 0.03%, and the purity of the carbon powder is 99.42wt.%; the fluoride concentration in the filtrate is 0.024g / L, and the lithium ion concentration is 0.14mg / L.

[0033] Comparative Example 2: No aluminum chloride solution was added during leaching The method of acid leaching of cathode alkaline leaching residue has the following specific steps: (1) drying the cathode alkali leaching residue and crushing the cathode alkali leaching residue particles until the particles with a diameter of 200-800 mesh account for 95 wt.%, thereby obtaining cathode alkali leaching residue particles; (2) Use hydrochloric acid (concentration of 3 mol / L) to prepare a solution with a pH value of 0.8, and add the cathode alkaline leaching residue particles into the hydrochloric acid to start the ultrasonic enhanced leaching process. The solid-liquid ratio of the cathode alkaline leaching residue to the leaching solution is 7:1 g:mL, the ultrasonic power is 250W, the leaching temperature is 60°C, and the leaching time is 90min. Solid-liquid separation obtains primary carbon powder and the first filtrate; (3) The first filtrate returns to step (2) and continues to leach new cathode alkaline leaching residue into the electrolyte in the leaching solution for 5 times to obtain a final filtrate; (4) The primary carbon powder is washed with deionized water, solid-liquid separated, and vacuum dried to obtain carbon powder.

[0034] (5) The final filtrate is slowly dripped into the alkaline leaching waste liquid to adjust the pH value to 10, and the solid-liquid separation is carried out after mixed precipitation.

[0035] The fluoride content in the carbon powder of this comparative example is 1.13%, the lithium ion content is 0.06%, and the purity of the carbon powder is 98.14wt.%; the fluoride concentration in the filtrate is 3g / L, and the lithium ion concentration is 147.5mg / L, and a large amount of fluoride and lithium ions cannot be precipitated.

[0036] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A method for acid leaching fluorine and lithium in cathode alkali leaching residue and jointly treating alkali leaching waste liquid, characterized in that: The following steps are involved: (1) Crushing the waste cathode alkaline leaching residue; (2) Leaching the crushed waste cathode alkaline leaching residue with AlCl3 solution under ultrasonic conditions, and adding hydrochloric acid to adjust the pH value of the AlCl3 solution; (3) Liquid-solid separation to obtain primary carbon powder and leachate; (4) The leaching solution is added dropwise to the alkaline leaching waste liquid of the spent cathode to produce cryolite.

2. The method for removing fluorine and lithium from acid leaching cathode alkali leaching residue and jointly treating alkali leaching waste liquid according to claim 1, characterized in that: In step (2), the concentration of the AlCl3 solution is 0.2-1.2 mol / L, and the pH value is 0-1.

7.

3. The method for removing fluorine and lithium from acid leaching cathode alkali leaching residue and jointly treating alkali leaching waste liquid according to claim 1, characterized in that: The pH value at the reaction end point of step (4) is 13.6-9.

4. The method for acid leaching fluorine and lithium in cathode alkali leaching residue and jointly treating alkali leaching waste liquid according to any one of claims 1 to 3, characterized in that: The solid-liquid ratio of step (2) leaching is 1:3-8 g / mL, the leaching temperature is 50-70° C., and the leaching time is 20-120 min.

5. The method for acid leaching fluorine and lithium in cathode alkali leaching residue and combined treatment of alkali leaching waste liquid according to claim 1, characterized in that: The leaching solution of step (3) is returned to step (2) for recycling. After the electrolyte in the leaching solution is relatively saturated, it is added dropwise as the final leaching solution to the alkaline leaching waste liquid of the waste cathode in step (4).

6. The method for acid leaching fluorine and lithium in cathode alkali leaching residue and combined treatment of alkali leaching waste liquid according to claim 1, characterized in that: The alkali leaching residue in step (1) is crushed to a particle size of 200-800 mesh, accounting for 90-100wt.%.

7. The method for acid leaching of fluorine and lithium in cathode alkali leaching residue and combined treatment of alkali leaching waste liquid according to claim 1, characterized in that: The primary carbon powder obtained in step (3) is washed with deionized water, separated into solid and liquid, and recovered after drying; the washing liquid is used to prepare the AlCl3 solution.

8. The method for acid leaching of fluorine and lithium in cathode alkali leaching residue and combined treatment of alkali leaching waste liquid according to claim 7, characterized in that: The solid-liquid ratio of primary carbon powder to deionized water is 1:1~3 g:mL, and the water immersion washing time is 5~10min.

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