A method for extracting sodium sulfide using electrolytic aluminum hazardous waste residue

Abstract

The present invention discloses a method for extracting sodium sulfide from hazardous waste residues of electrolytic aluminum. The method comprises the following steps: (1) subjecting the hazardous waste residues of electrolytic aluminum to aluminum salt leaching, to neutralization and precipitation, and to solid-liquid separation, to obtain a precipitate and a filtrate; (2) subjecting the filtrate obtained in step (1) to nanofiltration concentration and freeze crystallization to prepare Na2SO4·10H2O; (3) subjecting the Na2SO4·10H2O obtained in step (2) to reverse dissolution, evaporation and crystallization, removal of crystal water, and drying to obtain anhydrous sodium sulfate; and (4) calcining the anhydrous sodium sulfate obtained in step (3) using the carbonaceous slag leached from the aluminum salt as fuel and reducing agent to produce sodium sulfide. The method for extracting sodium sulfide from hazardous waste residues of electrolytic aluminum according to the present invention can significantly improve the level of resource recycling of hazardous waste residues of electrolytic aluminum, reduce the production cost of electrolytic aluminum, and improve the economic benefits of enterprises.

Description

Technical Field

[0001] The present invention relates to the technical field of comprehensive utilization of hazardous waste slag resources from electrolytic aluminum, and in particular to a method for extracting sodium sulfide from hazardous waste slag from electrolytic aluminum. Background Art

[0002] The existing comprehensive utilization process of hazardous waste slag resources from electrolytic aluminum still needs to be improved. Summary of the Invention

[0003] The present invention aims to solve, at least to a certain extent, one of the technical problems in the related art. To this end, one object of the present invention is to provide a method for extracting sodium sulfide from hazardous waste slag from electrolytic aluminum. The method of extracting sodium sulfide from hazardous waste slag from electrolytic aluminum is used to comprehensively utilize hazardous waste slag resources, thereby recovering resources such as Al and F while extracting valuable sodium resources, thereby improving the level of resource recycling, reducing the cost of electrolytic aluminum production, and improving the economic benefits of the enterprise.

[0004] In order to achieve the above object, the present invention provides a method for extracting sodium sulfide using hazardous waste slag from electrolytic aluminum. According to an embodiment of the present invention, the method comprises:

[0005] (1) The leachate obtained after leaching aluminum salt from electrolytic aluminum hazardous waste slag is neutralized and precipitated, and the precipitate and filtrate are obtained after solid-liquid separation;

[0006] (2) The filtrate obtained in step (1) is concentrated by nanofiltration and then freeze-crystallized to prepare Na2SO4·10H2O;

[0007] (3) Re-dissolving the Na2SO4·10H2O obtained in step (2) and performing evaporation crystallization to remove crystal water, and drying to obtain anhydrous sodium sulfate;

[0008] (4) The anhydrous sodium sulfate obtained in step (3) is calcined to produce sodium sulfide using the carbon-containing slag leached after aluminum salt leaching as fuel and reducing agent.

[0009] According to the method for extracting sodium sulfide from hazardous waste slag from electrolytic aluminum according to an embodiment of the present invention, sodium sulfide can be produced. Compared to existing methods for comprehensive utilization of hazardous waste slag from electrolytic aluminum, the method of the present invention can simultaneously recover resources such as Al and F while extracting valuable sodium resources. Therefore, the method of extracting sodium sulfide from hazardous waste slag from electrolytic aluminum according to the present invention can significantly improve the level of recycling and utilization of hazardous waste slag from electrolytic aluminum, reduce the cost of electrolytic aluminum production, and improve the economic benefits of the enterprise.

[0010] In addition, the method for extracting sodium sulfide from hazardous waste slag of electrolytic aluminum according to the above embodiment of the present invention may also have the following additional technical features:

[0011] In some embodiments of the present invention, in step (1), the electrolytic aluminum hazardous waste slag includes at least one of overhaul slag, carbon slag and aluminum ash, and the obtained precipitate is washed and then calcined, thereby recovering resources such as Al element and F element.

[0012] In some embodiments of the present invention, in step (1), the neutralization precipitation comprises: adding NaOH solution and adding fluoride salt as seed crystals, the concentration of the NaOH solution is 2-4 mol / L, the addition rate of the NaOH solution is 3-9 ml / min, and the amount of the fluoride salt added is 5-10% of the mass of the precipitate, thereby making AlF2 + Al2F 3.24 (OH) 2.76 · The precipitation in the form of H2O is complete.

[0013] In some embodiments of the present invention, in step (1), the concentration of Na2SO4 in the filtrate is 26-52 g / L, and the concentration of NaOH in the filtrate is 4-8 mg / L.

[0014] In some embodiments of the present invention, step (2) further comprises: recycling the filtrate obtained in step (1) back to the leaching system, regularly opening a circuit to remove at least part of the leachate and repeating step (1), and the filtrate obtained after repeating step (1) is concentrated by nanofiltration and then freeze-crystallized to prepare Na2SO4·10H2O. Since the sodium ions in the cryolite and the sulfate ions in the aluminum sulfate leachate will be circulated and enriched in the leaching system during the leaching process, the main component of the leachate is sodium sulfate, and it is necessary to regularly open the circuit to realize the circulation of the leachate in the leaching system. Considering the solubility of sodium sulfate, the filtrate obtained after filtration and precipitation can be recycled back to the leaching system. When the sodium sulfate in the leaching system is enriched to a certain concentration, freeze-crystallization is used to produce the by-product Glauber's salt (Na2SO4·10H2O). This can further improve the level of resource recycling of hazardous waste slag from electrolytic aluminum, reduce the production cost of electrolytic aluminum, and improve the economic benefits of the enterprise.

[0015] In some embodiments of the present invention, in step (2), the leachate is concentrated by nanofiltration to obtain a saturated Na2SO4 solution, thereby reducing the processing volume of the subsequent freeze crystallization.

[0016] In some embodiments of the present invention, the freeze crystallization includes: using a continuous crystallization method, reducing the Na2SO4 solution to -5~0℃ through two-stage freezing for crystallization, the two-stage freezing includes primary freezing and secondary freezing, the primary freezing temperature is 0~5℃, and the secondary freezing temperature is -5~0℃, the Na2SO4·10H2O obtained after freeze crystallization has a water content of ≤10% after centrifugal separation, and the mother liquor after freezing is returned to the leaching system, thereby further improving the level of recycling of electrolytic aluminum hazardous waste slag resources, reducing the production cost of electrolytic aluminum, and improving the economic benefits of the enterprise.

[0017] In some embodiments of the present invention, in step (3), the liquid used for the reverse dissolution is from the mother liquor of the evaporation crystallization, the mass ratio of the liquid used for the reverse dissolution to Na2SO4·10H2O is (0.5-0.7):1, the evaporation crystallization temperature is 80-90°C, the water content of the anhydrous sodium sulfate obtained after the evaporation crystallization is ≤10%, the drying temperature is 100-120°C, the drying time is 1-3h, and the water content of the anhydrous sodium sulfate obtained after drying is ≤0.35%.

[0018] In some embodiments of the present invention, in step (4), the mass ratio of anhydrous sodium sulfate to carbon-containing slag leaching residue is 100:(24~30), thereby effectively utilizing the carbon-containing slag leaching residue, thereby improving the level of recycling and utilization of electrolytic aluminum hazardous waste slag resources, reducing the production cost of electrolytic aluminum, and improving the economic benefits of the enterprise.

[0019] In some embodiments of the present invention, in step (4), the calcination temperature is 1050°C to 1150°C, and the calcination residence time is 15 to 20 minutes, thereby further improving the yield of sodium sulfide, thereby improving the level of recycling and utilization of electrolytic aluminum hazardous waste slag resources, reducing the production cost of electrolytic aluminum, and improving the economic benefits of the enterprise.

[0020] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments with reference to the following drawings, in which:

[0022] Figure 1 The present invention is a flowchart of a method for extracting sodium sulfide using hazardous waste slag from electrolytic aluminum according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0024] In one aspect of the present invention, a method for extracting sodium sulfide from hazardous waste residues of electrolytic aluminum is provided. The method for extracting sodium sulfide from hazardous waste residues of electrolytic aluminum according to an embodiment of the present invention is further described below in detail.

[0025] Hazardous waste residues from electrolytic aluminum, such as overhaul slag, aluminum ash, and carbon slag, contain large amounts of sodium resources. The inventors discovered that during the aluminum salt leaching process, sodium ions in cryolite and sulfate ions in the aluminum sulfate leachate circulate and accumulate in the leaching system. As a result, the leachate is primarily composed of sodium sulfate, allowing the extraction of valuable sodium resources. In light of this, the present invention proposes a method for extracting sodium sulfide from hazardous waste residues from electrolytic aluminum. The method comprises: neutralizing and precipitating the leachate obtained from aluminum salt leaching of hazardous waste residues from electrolytic aluminum, subjecting the slag to solid-liquid separation to obtain a precipitate and a filtrate. The filtrate is then concentrated by nanofiltration and freeze-crystallized to produce Na2SO4·10H2O. The Na2SO4·10H2O is then reverse-dissolved, evaporated, crystallized, and the crystallization water removed. The filtrate is then dried to produce anhydrous sodium sulfate. Finally, the dried anhydrous sodium sulfate is calcined using the carbon slag-containing leachate from aluminum salt leaching as fuel and a reducing agent to produce sodium sulfide.

[0026] Reference below Figure 1 The method for extracting sodium sulfide using hazardous waste slag from electrolytic aluminum in the above embodiment of the present invention is described in detail.

[0027] S100: The leachate obtained after aluminum salt leaching from electrolytic aluminum hazardous waste slag is neutralized and precipitated and solid-liquid separation is performed

[0028] According to a specific embodiment of the present invention, by leaching the electrolytic aluminum hazardous waste slag with aluminum salt, the valuable Al element and F element can be converted into AlF3 products required for electrolysis, and the Na element can be converted into Na2SO4. The chemical reaction formula of the aluminum salt leaching process is as follows:

[0029] Al2(SO4)3+2Na3AlF6=3Na2SO4+4AlF3

[0030] According to a specific embodiment of the present invention, NaOH solution is added during the neutralization and precipitation process, and fluoride salt is added as a seed crystal, wherein the concentration of the NaOH solution can be 2-4 mol / L, the addition rate of the NaOH solution is 3-9 ml / min, and the amount of fluoride salt added can be 5-10% of the mass of the precipitate. The inventors found that if the concentration of the NaOH solution is too low, a large amount needs to be added, affecting the liquid-solid ratio, while if the concentration of the NaOH solution is too high, impurities such as cryolite will be formed; if the addition rate of the NaOH solution is too low, the production efficiency will be reduced, while if the addition rate of the NaOH solution is too high, impurities such as cryolite will be formed; in the present invention, by controlling the concentration and rate of the added NaOH solution, the pH of the leachate can be controlled to not exceed 6, reducing the formation of impurities such as cryolite, and making AlF2 + Al2F 3.24 (OH) 2.76 The inventors found that if the amount of fluoride salt added is too small, it cannot be a fluorinated aluminum precursor (Al2F3.24 (OH) 2.76 ·H2O) provides sufficient effective nuclei for the growth of fluoroaluminum precursor nuclei, affecting their growth. If too much fluoride salt is added, more effective nuclei are provided for the growth of fluoroaluminum precursor nuclei, resulting in a finer particle size of the fluoroaluminum precursor, which affects its use in electrolytic production. In the present invention, by controlling the amount of fluoride salt added, suitable effective nuclei are provided for the growth of fluoroaluminum precursor nuclei, forming a fluoroaluminum precursor with a moderate particle size. The chemical reaction principle of the above neutralization precipitation process is as follows:

[0031] 0.76Al 3+ +3.24AlF2 + + 2H + +7.52NaOH→2Al2F 3.24 (OH) 2.76 ·H2O↓ + 7.52Na +

[0032] Al(OH)4 - +1.24F - + AlF2 + + 1.24H + → Al2F 3.24 (OH) 2.76 ·H2O↓ + 0.24H2O

[0033] According to a specific embodiment of the present invention, the leaching solution is neutralized and precipitated and the solid-liquid separation is performed, and the precipitate obtained is washed and then calcined, thereby further recovering resources such as Al and F elements.

[0034] According to a specific embodiment of the present invention, the concentration of Na2SO4 in the filtrate obtained by neutralizing, precipitating and solid-liquid separation of the above-mentioned leachate is 26~52g / L, and the concentration of NaOH in the above-mentioned filtrate is 4~8mg / L, thereby converting the Na element into Na2SO4, which is further beneficial to the recovery and utilization of valuable Na resources in the hazardous waste slag of electrolytic aluminum.

[0035] S200: The filtrate obtained in step S100 is concentrated by nanofiltration and then freeze-crystallized to prepare Na2SO4·10H2O

[0036] According to a specific embodiment of the present invention, the filtrate obtained by neutralizing, precipitating, and performing solid-liquid separation on the leachate can be recycled back to the leaching system. At least a portion of the leachate can be periodically removed to repeat step S100. The filtrate obtained after repeating step S100 is concentrated by nanofiltration and then freeze-crystallized to produce Na2SO4·10H2O. Since the sodium ions in the cryolite and the sulfate ions in the aluminum sulfate leachate will circulate and enrich in the leaching system during the leaching process, and the main component of the leachate is sodium sulfate, it is necessary to periodically open the circuit to achieve leachate circulation in the leaching system. Considering the solubility of sodium sulfate, the filtrate obtained after filtration and precipitation can be recycled back to the leaching system. When the sodium sulfate in the leaching system is enriched to a certain concentration, freeze-crystallization is used to produce the by-product Glauber's salt (Na2SO4·10H2O). This can further improve the level of resource recycling of hazardous waste slag from electrolytic aluminum, reduce the cost of electrolytic aluminum production, and improve the economic benefits of the enterprise. The main reaction equations of the freeze-crystallization process are as follows:

[0037] 2Na + +SO4 2- +10H2O→Na2SO4·10H2O

[0038] According to a specific embodiment of the present invention, the above-mentioned leachate is concentrated by nanofiltration to obtain a saturated Na2SO4 solution, thereby increasing the Na2SO4 concentration in the filtrate after neutralization and precipitation, reducing the processing volume of the subsequent freeze crystallization, and the clean fresh water obtained in this process can be used as new water for countercurrent washing.

[0039] According to a specific embodiment of the present invention, the above-mentioned freeze crystallization includes: using a continuous crystallization method, reducing the Na2SO4 solution to -5~0℃ through two-stage freezing for crystallization. In this process, the Na2SO4 solution can use a 25℃ Na2SO4 solution, and the two-stage freezing includes primary freezing and secondary freezing. The primary freezing temperature can be 0~5℃, and the secondary freezing temperature can be -5~0℃. The Na2SO4·10H2O obtained after freeze crystallization has a water content of ≤10% after centrifugal separation, and the mother liquor after freezing is returned to the leaching system, thereby further improving the level of recycling of electrolytic aluminum hazardous waste slag resources, reducing the production cost of electrolytic aluminum, and improving the economic benefits of the enterprise.

[0040] S300: The Na2SO4·10H2O obtained in step S200 is reversely dissolved, evaporated, crystallized and dried to obtain anhydrous sodium sulfate

[0041] According to a specific embodiment of the present invention, in this process, no new water is required for the reverse dissolution. The liquid used for the reverse dissolution is derived from the mother liquor of the evaporation crystallization. The mass ratio of the liquid used for the reverse dissolution to Na2SO4·10H2O can be (0.5-0.7):1. The inventors have found that if the mass ratio of the liquid used for the reverse dissolution to Na2SO4·10H2O is too low, the concentration of Na2SO4·10H2O is high, and the nanofiltration process will affect the service life of the nanofiltration membrane. If the mass ratio of the liquid used for the reverse dissolution to Na2SO4·10H2O is too high, the production efficiency of the nanofiltration system will be reduced, and the mother liquor input and production costs will increase. The evaporation crystallization temperature can be 80-90°C. After evaporation crystallization, the crystal water is evaporated and the resulting anhydrous sodium sulfate has a moisture content of ≤10%. The drying temperature can be 100-120°C, and the drying time can be 1-3 hours. The anhydrous sodium sulfate obtained after drying has a moisture content of ≤0.35%. The main reaction equation of this process is as follows:

[0042] Na2SO4·10H2O→Na2SO4+10H2O

[0043] S400: calcining the anhydrous sodium sulfate obtained in step S300 to produce sodium sulfide

[0044] According to a specific embodiment of the present invention, in this process, the anhydrous sodium sulfate obtained in step S300 can be fed into a short converter using the carbon-containing slag leached after aluminum salt leaching as fuel and reducing agent to reduce and produce sodium sulfide slag. The main chemical reaction principles of this process are as follows:

[0045] Na2SO4 + 2C → Na2S + 2CO2

[0046] Na2SO4 + 4C → Na2S + 4CO

[0047] Na2SO4 + 4CO →Na2S + 4CO2

[0048] According to a specific embodiment of the present invention, the mass ratio of anhydrous sodium sulfate to carbon-containing slag leaching residue can be 100: (24-30), thereby effectively utilizing the carbon-containing slag leaching residue, thereby improving the level of recycling and utilization of electrolytic aluminum hazardous waste slag resources, reducing the production cost of electrolytic aluminum, and improving the economic benefits of the enterprise.

[0049] According to a specific embodiment of the present invention, the calcination temperature can be 1050°C to 1150°C, and the calcination residence time can be 15 to 20 minutes. The inventors have found that if the calcination temperature is too low or the residence time is too short, the reaction is insufficient and the impurity content is high; if the calcination temperature is too high or the residence time is too long, energy consumption is high and production costs are high. In the present invention, by controlling the above-mentioned calcination conditions, the yield of sodium sulfide can be further increased, thereby improving the level of recycling and utilization of electrolytic aluminum hazardous waste slag resources, reducing electrolytic aluminum production costs, and improving the economic benefits of the enterprise.

[0050] Thus, according to the method for extracting sodium sulfide from hazardous waste slag from electrolytic aluminum according to an embodiment of the present invention, sodium sulfide can be produced. Furthermore, compared to existing methods for comprehensive utilization of hazardous waste slag from electrolytic aluminum, the method of the present invention can simultaneously recover resources such as Al and F while extracting valuable sodium resources. Therefore, the method of extracting sodium sulfide from hazardous waste slag from electrolytic aluminum according to the present invention can significantly improve the level of recycling and utilization of hazardous waste slag from electrolytic aluminum, reduce the cost of electrolytic aluminum production, and improve the economic benefits of the enterprise.

[0051] The present invention is described below with reference to specific examples. It should be noted that these examples are merely illustrative and do not limit the present invention in any way.

[0052] Example 1

[0053] The leachate obtained after the electrolytic aluminum hazardous waste slag is leached with aluminum salt is neutralized and precipitated. During the neutralization and precipitation process, a 2 mol / L NaOH solution is added at a rate of 9 ml / min, and a fluoride salt is added as a seed crystal to make AlF2 +The precipitation is complete, and a precipitate and a filtrate are obtained after solid-liquid separation. The amount of fluoride salt added is 5% of the mass of the obtained precipitate. The obtained precipitate is washed and sent to the fluoride salt calcination process. The concentration of Na2SO4 in the obtained filtrate is 52g / L, and the concentration of NaOH in the obtained filtrate is 8mg / L. The obtained filtrate is concentrated by nanofiltration and then sent to a freeze crystallization system to prepare Na2SO4·10H2O. The freeze crystallization system adopts a continuous crystallization method, and is cooled to -5~0℃ through two-stage freezing (first stage 0~5℃, second stage -5~0℃) to crystallize. The crystallized Na2SO4·10H2O is centrifuged to obtain a water content of ≤10%. The mother liquor after freezing is returned to the aluminum salt leaching system; the obtained Na2S After the sodium sulfate is reversely dissolved with Na2SO4·10H2O, evaporation and crystallization are performed. The reverse liquid is derived from the mother liquor of the evaporation and crystallization, and the mass ratio of the liquid used for the reverse dissolution to Na2SO4·10H2O is 0.5:1. The evaporation and crystallization temperature is 80°C. The moisture content of the anhydrous sodium sulfate after evaporation and crystallization is ≤10%. The sodium sulfate is then dried at 120°C for 1 hour, and the moisture content of the dried anhydrous sodium sulfate is ≤0.35%. The anhydrous sodium sulfate obtained after drying is mixed with the carbonaceous slag leached with aluminum salt and dried in a mass ratio of 100:24, and calcined at 1050°C for 15 minutes to obtain industrial sodium sulfide with a sodium sulfide content greater than 60%.

[0054] Example 2

[0055] The filtrate obtained from the neutralization and precipitation process of Example 1 was recycled back to the leaching system for the leaching process of the overhaul slag. At least part of the leachate was periodically opened for neutralization and precipitation. During the neutralization and precipitation process, a 3 mol / L NaOH solution was added at a rate of 6 ml / min, and a fluoride salt was added as a seed crystal to make AlF2 +The precipitation is complete, and a precipitate and a filtrate are obtained after solid-liquid separation. The amount of fluoride salt added is 7% of the mass of the obtained precipitate. The obtained precipitate is washed and sent to the fluoride salt calcination process. The concentration of Na2SO4 in the obtained filtrate is 52g / L, and the concentration of NaOH in the obtained filtrate is 8mg / L. The obtained filtrate is concentrated by nanofiltration and then sent to a freeze crystallization system to prepare Na2SO4·10H2O. The freeze crystallization system adopts a continuous crystallization method, and is crystallized by two-stage freezing (first stage 0~5℃, second stage -5~0℃) to -5~0℃. The crystallized Na2SO4·10H2O is centrifuged to obtain a water content of ≤10%. The mother liquor after freezing is returned to the aluminum salt leaching system; the obtained Na2S After the sodium sulfate is reversely dissolved with sodium iodide·10H2O, evaporation and crystallization are performed. The reverse solution liquid comes from the mother liquor of the evaporation and crystallization, and the mass ratio of the liquid used for the reverse dissolution to Na2SO4·10H2O is 0.6:1. The evaporation and crystallization temperature is 90°C. The moisture content of the anhydrous sodium sulfate after evaporation and crystallization is ≤10%. The sodium sulfate is then dried at 100°C for 3 hours, and the moisture content of the dried anhydrous sodium sulfate is ≤0.35%. The anhydrous sodium sulfate obtained after drying is mixed with the carbon-containing slag leached with aluminum salt and dried in a mass ratio of 100:26, and calcined at 1050°C for 20 minutes to obtain industrial sodium sulfide with a sodium sulfide content greater than 60%.

[0056] Example 3

[0057] The leachate obtained after the electrolytic aluminum hazardous waste slag is leached with aluminum salt is neutralized and precipitated. During the neutralization and precipitation process, a 4 mol / L NaOH solution is added at a rate of 3 ml / min, and a fluoride salt is added as a seed crystal to make AlF2 +The precipitation is complete, and after solid-liquid separation, a precipitate and a filtrate are obtained. The amount of fluoride salt added is 10% of the mass of the obtained precipitate. The obtained precipitate is washed and sent to the fluoride salt calcination process. The concentration of Na2SO4 in the obtained filtrate is 39g / L, and the concentration of NaOH in the obtained filtrate is 6mg / L. The obtained filtrate is concentrated by nanofiltration and then sent to the freeze crystallization system to prepare Na2SO4·10H2O. The freeze crystallization system adopts a continuous crystallization method, and is crystallized by two-stage freezing (first stage 0~5℃, second stage -5~0℃) to -5~0℃. The crystallized Na2SO4·10H2O is separated by centrifugation to a water content of ≤10%. The mother liquor after freezing is returned to the aluminum salt leaching system; the obtained Na2 SO4·10H2O is reversely dissolved and then evaporated and crystallized. Except for crystallization water, the reverse solution liquid comes from the mother liquor of evaporation and crystallization. The mass ratio of the liquid used for reverse dissolution to Na2SO4·10H2O is 0.7:1. The evaporation and crystallization temperature is 85°C. The moisture content of the anhydrous sodium sulfate after evaporation and crystallization is ≤10%. The sodium sulfate is then dried at 110°C for 2 hours. The moisture content of the dried anhydrous sodium sulfate is ≤0.35%. The anhydrous sodium sulfate obtained after drying is mixed with the carbon-containing slag leached with aluminum salt and dried in a mass ratio of 100:27. The mixture is calcined at 1150°C for 20 minutes to obtain industrial sodium sulfide with a sodium sulfide content greater than 60%.

[0058] Example 4

[0059] The leachate obtained after the electrolytic aluminum hazardous waste slag is leached with aluminum salt is neutralized and precipitated. During the neutralization and precipitation process, a 2 mol / L NaOH solution is added at a rate of 3 ml / min, and a fluoride salt is added as a seed crystal to make AlF2 +The precipitation is complete, and a precipitate and a filtrate are obtained after solid-liquid separation. The amount of fluoride salt added is 5% of the mass of the obtained precipitate. The obtained precipitate is washed and sent to the fluoride salt calcination process. The concentration of Na2SO4 in the obtained filtrate is 26g / L, and the concentration of NaOH in the obtained filtrate is 4mg / L. The obtained filtrate is concentrated by nanofiltration and then sent to a freeze crystallization system to prepare Na2SO4·10H2O. The freeze crystallization system adopts a continuous crystallization method, and is crystallized by two-stage freezing (first stage 0~5℃, second stage -5~0℃) to -5~0℃. The crystallized Na2SO4·10H2O is centrifuged to obtain a water content of ≤10%. The mother liquor after freezing is returned to the aluminum salt leaching system; the obtained Na2S After the sodium sulfate is reversely dissolved with sodium sulfate (Na2SO4·10H2O), evaporation and crystallization are performed. The reversed solution is derived from the mother liquor of the evaporation and crystallization, and the mass ratio of the liquid used for the reversed solution to Na2SO4·10H2O is 0.5:1. The evaporation and crystallization temperature is 90°C. The moisture content of the anhydrous sodium sulfate after evaporation and crystallization is ≤10%. The sodium sulfate is then dried at 120°C for 3 hours, and the moisture content of the dried anhydrous sodium sulfate is ≤0.35%. The anhydrous sodium sulfate obtained after drying is mixed with the carbonaceous slag leached with aluminum salt and dried in a mass ratio of 100:30, and calcined at 1150°C for 15 minutes to obtain industrial sodium sulfide with a sodium sulfide content greater than 60%.

[0060] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0061] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for extracting sodium sulfide from hazardous waste residues of electrolytic aluminum, characterized in that: include: (1) neutralizing and precipitating the leachate obtained after leaching aluminum salt from electrolytic aluminum hazardous waste slag, and obtaining a precipitate and a filtrate after solid-liquid separation; (2) the filtrate obtained in step (1) is concentrated by nanofiltration and then freeze-crystallized to prepare Na2SO4·10H2O; (3) Re-dissolving the Na2SO4·10H2O obtained in step (2) and performing evaporative crystallization to remove crystal water, and drying to obtain anhydrous sodium sulfate; (4) calcining the anhydrous sodium sulfate obtained in step (3) to produce sodium sulfide using the carbon-containing slag leached after aluminum salt leaching as fuel and reducing agent, In step (1), the neutralization precipitation comprises: adding NaOH solution and adding fluoride salt as seed crystals to make AlF2 + The precipitation is complete, the concentration of the NaOH solution is 2-4 mol / L, the addition rate of the NaOH solution is 3-9 ml / min, and the amount of the fluoride salt added is 5-10% of the mass of the precipitate. The filtrate obtained in step (1) is circulated back to the leaching system, and at least part of the leaching solution is periodically opened to repeat step (1). The filtrate obtained after repeating step (1) is concentrated by nanofiltration and then freeze-crystallized to prepare Na2SO4·10H2O.

2. The method according to claim 1, characterized in that In step (1), the electrolytic aluminum hazardous waste slag includes at least one of overhaul slag, carbon slag and aluminum ash, and the obtained precipitate is washed and then calcined.

3. The method according to claim 1, characterized in that In step (1), the concentration of Na2SO4 in the filtrate is 26-52 g / L, and the concentration of NaOH in the filtrate is 4-8 mg / L.

4. The method according to claim 1, wherein In step (2), the leachate is concentrated by nanofiltration to obtain a saturated Na2SO4 solution.

5. The method according to claim 4, characterized in that The freeze crystallization includes: using a continuous crystallization method to reduce the Na2SO4 solution to -5~0℃ through two-stage freezing for crystallization, the two-stage freezing includes primary freezing and secondary freezing, the primary freezing temperature is 0~5℃, and the secondary freezing temperature is -5~0℃.

6. The method according to claim 1, characterized in that In step (3), the liquid used for the reverse dissolution is from the mother liquor of the evaporation crystallization, the mass ratio of the liquid used for the reverse dissolution to Na2SO4·10H2O is (0.5-0.7):1, the evaporation crystallization temperature is 80-90°C, the drying temperature is 100-120°C, and the drying time is 1-3h.

7. The method according to claim 1, characterized in that In step (4), the mass ratio of anhydrous sodium sulfate to carbon-containing slag leaching residue is 100:(24-30).

8. The method according to claim 1, characterized in that In step (4), the calcination temperature is 1050° C. to 1150° C., and the calcination residence time is 15 to 20 minutes.

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