Method for preparing calcium fluoride and lithium phosphate by synergistically treating waste cathode and carbon residue

Abstract

The present application relates to a kind of waste cathode and carbon residue preparation calcium fluoride and lithium phosphate method for collaborative treatment, comprising the following steps: step 1) pre-calcination: waste cathode is pre-calcined after mixing, grinding, flotation with carbon residue, carbon powder and product P1 are obtained;Step 2) subsection calcination: product P1 obtained in step 1) is calcined after one stage, product P2 is obtained;The product P2 is calcined after two stages, product P3 is obtained;Step 3) acid leaching impurity removal: product P3 is immersed in water, solid-liquid separation, product P4 and filtrate are obtained;The product P4 adds inorganic acid and removes impurities, after washing and drying, calcium fluoride is obtained;Step 4) precipitation lithium extraction: the filtrate obtained in step 3) is added with sodium phosphate and sodium hydroxide, white precipitate is obtained after sufficient reaction, solid-liquid separation, washing and drying, lithium phosphate is obtained.The present application has the advantages that flotation process is used to separate fluoride and carbon powder, and three-stage calcination process is used to realize the collaborative recovery of fluorine, lithium and carbon elements.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization technology of hazardous waste from the electrolytic aluminum industry, and in particular to a method for the co-processing of waste cathodes and carbon slag to prepare calcium fluoride and lithium phosphate. Background Technology

[0002] Aluminum electrolysis waste carbon materials are mainly divided into anode carbon slag and waste cathode carbon blocks. Besides carbon, their main components include valuable substances such as aluminum fluoride, sodium fluoride, calcium fluoride, cryolite, and alumina. The fluoride content of the carbon slag is approximately 60%-70%, and the fluoride content of the waste cathode is approximately 25%-30%. The lithium content of both carbon slag and waste cathode is approximately 0.5%-2.5%, all of which are renewable resources. Statistics show that approximately 20-30 kg of aluminum electrolysis waste carbon materials are generated for every ton of electrolytic aluminum produced. In 2018, global electrolytic aluminum production reached 64.34 million tons, generating over 1.2 million tons of aluminum electrolysis waste carbon materials (calculated at 20 kg of waste carbon materials per ton of primary aluminum), a huge quantity. Recycling aluminum electrolysis waste carbon materials not only benefits the sustainable development of the electrolytic aluminum industry but also achieves significant economic benefits.

[0003] Invention patent CN109179457B discloses a method for extracting lithium from electrolytic aluminum waste residue, comprising: (1) reacting electrolytic aluminum waste residue with concentrated sulfuric acid to obtain mixture A; (2) dissolving mixture A in water and filtering to obtain filtrate B, slowly adding calcium oxide to filtrate B, filtering the resulting solution to obtain filter residue C and filtrate D; (3) heating and evaporating filtrate D to concentrate it, filtering it and further evaporating and concentrating the filtrate to obtain filtrate E, maintaining filtrate E under heating; (4) saturating filtrate E with sodium carbonate solution to obtain suspension F, filtering suspension F to obtain filter cake, washing and drying the filter cake to obtain lithium carbonate product.

[0004] Patent application CN115959689A discloses a method for enriching and extracting lithium salts from overhaul slag and carbon slag. The method includes: (1) after slurrying the overhaul slag, it is subjected to pressure alkaline leaching and cyanide removal treatment in sequence, and the overhaul slag alkaline leachate and overhaul slag alkaline leachate residue are obtained by solid-liquid separation; (2) after slurrying the carbon slag, aluminum salt leaching is performed, and the carbon slag leachate and carbon slag leachate residue are obtained by solid-liquid separation; (3) the overhaul slag alkaline leachate and the carbon slag leachate are mixed, neutralized and precipitated, and the supernatant is obtained by solid-liquid separation; (4) the supernatant is subjected to iron removal and desiliconization treatment, and the permeate and concentrate are obtained by concentration separation; (5) the overhaul slag and carbon slag are slurryed using the permeate, and steps (1) to (4) are repeated. When the lithium element in the permeate is enriched to a certain concentration, lithium salt is extracted.

[0005] None of the above technical solutions can achieve the synergistic recovery of fluorine, lithium, and carbon elements when processing waste cathodes and carbon slag. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for the co-processing of waste cathode and carbon slag to prepare calcium fluoride and lithium phosphate. The method aims to separate fluorides and carbon powder using a flotation process, and simultaneously achieve the synergistic recovery and utilization of fluorine, lithium and carbon elements through a three-stage roasting process, thereby realizing the purpose of resource conversion.

[0007] This invention is achieved through the following technical solution: On one hand, it provides a method for the co-processing of waste cathodes and carbon slag to prepare calcium fluoride and lithium phosphate, comprising the following steps:

[0008] Step 1) Pre-baking: After pre-baking, the waste cathode is mixed with carbon slag, ground, and floated to obtain carbon powder and fluoride 1;

[0009] Step 2) Segmented roasting: Fluoride 1 obtained in step 1) is roasted in one stage to obtain fluoride 2; Fluoride 2 is roasted in two stages to obtain calcium fluoride clinker;

[0010] Step 3) Acid leaching to remove impurities: The clinker is leached in water and separated into solid and liquid to obtain crude calcium fluoride and filtrate; the crude calcium fluoride is added with inorganic acid to remove impurities, and after washing and drying, calcium fluoride is obtained;

[0011] Step 4) Precipitation and lithium extraction: Add sodium phosphate and sodium hydroxide to the filtrate obtained in step 3). After the reaction is complete, a white precipitate is obtained. After solid-liquid separation, washing and drying, lithium phosphate is obtained.

[0012] Preferably, the fluoride 1 is composed of cryolite, sodium fluoride, a small amount of carbon, and aluminum oxide;

[0013] The composition of fluoride 2 is cryolite, sodium fluoride, and a small amount of aluminum oxide;

[0014] The calcium fluoride clinker consists of calcium fluoride, soluble sodium / lithium salts, and a small amount of aluminum oxide.

[0015] The crude calcium fluoride consists of calcium fluoride and a small amount of aluminum oxide.

[0016] The purpose of the above technical solution is to remove cyanide, nitride, and carbide from the waste cathode;

[0017] The purpose of the first roasting step is to remove the residual carbon in fluoride 1 and obtain carbon-free fluoride 2;

[0018] The purpose of the second-stage roasting is to transform cryolite and sodium fluoride in fluoride 2 into calcium fluoride, while obtaining soluble sodium salt and lithium salt, thereby achieving the separation of fluorine and lithium elements.

[0019] The purpose of acid leaching is to remove aluminum oxide from crude calcium fluoride and obtain pure calcium fluoride.

[0020] The purpose of lithium precipitation is to convert lithium salts in the filtrate into lithium phosphate precipitate, thereby achieving the separation of lithium salts from sodium salts.

[0021] Further, in step 1), the amount of carbon slag added accounts for 5 wt% to 95 wt% of the total weight of the roasted waste cathode.

[0022] Furthermore, in step 2), an auxiliary agent 1 is added during the calcination stage, and the amount of auxiliary agent 1 added accounts for 5 wt% to 20 wt% of the total weight of the fluoride 1.

[0023] Through the above technical solution, additive 1 has CH2 and CO functional groups, low ignition point, no irritating odor, no pollution, and does not contaminate the product; additive 1 can promote the rapid oxidation of C in fluoride 1 to CO2, and avoid the inclusion of C element in subsequent products.

[0024] Furthermore, the auxiliary agent 1 is selected from at least one of glycerol, citric acid, and stearic acid.

[0025] Through the above technical solution, the additive 1 is preferentially burned, which drives the rapid combustion of C in the fluoride 1, which helps to shorten the calcination time. Under the same temperature conditions, the calcination time is shortened by about 30%.

[0026] Furthermore, in step 2), an auxiliary agent 2 is added during the second-stage roasting process, and the amount of the auxiliary agent 2 added is 0.8 to 1.2 times the total weight of the fluoride 2.

[0027] Preferably, the auxiliary agent 2 is selected from at least one of calcium chloride, calcium nitrate, calcium sulfate, calcium acetate, calcium oxalate, and calcium citrate.

[0028] Through the above technical solution, additive 2 can separate fluorine and lithium elements, converting fluorine into calcium fluoride and entering the solid phase, and converting lithium into soluble lithium salt and entering the solution. Additive 2 preferably uses calcium chloride, calcium acetate and calcium nitrate, which have wide sources of raw materials, and the excessive amount of the agent will not contaminate the calcium fluoride product.

[0029] Furthermore, in step 2), the calcination conditions are as follows: calcination temperature is 600–700°C, and calcination time is 60–120 min. If the calcination temperature is too high, it can easily lead to the volatilization loss of fluorides; if the calcination temperature is too low, the combustion of C will be incomplete.

[0030] Furthermore, in step 2), the two-stage calcination conditions are: a calcination temperature of 700–900°C and a calcination time of 60–180 min. These selected calcination conditions effectively disrupt the cryolite structure, rapidly converting fluorine into calcium fluoride. Compared to existing technologies, this method facilitates the separation of fluorine and lithium elements and improves the conversion rate of fluorine.

[0031] Furthermore, the calcination transformation reaction described in step 3) is (taking calcium chloride as an example):

[0032] 3CaCl2+2Na3AlF6=3CaF2+6NaCl+2AlF3 (1.1)

[0033] 3CaCl2+2LiNa2AlF6=3CaF2+4NaCl+2AlF3+2LiCl (1.2)

[0034] 3CaCl2+2Li2NaAlF6=3CaF2+2NaCl+2AlF3+4LiCl (1.3)

[0035] CaCl₂ + 2NaF = CaF₂ + 2NaCl (1.4)

[0036] 3CaCl2+2AlF3=3CaF2+2AlCl3 (1.4)

[0037] Further, in step 3), the amount of inorganic acid added is three times the molar amount of alumina in the crude calcium fluoride. The purpose of adding the inorganic acid is to remove alumina from the calcium fluoride product and further improve the purity of the calcium fluoride. The inorganic acid is any one of hydrochloric acid, sulfuric acid, and nitric acid.

[0038] Furthermore, the impurity removal reaction described in step 3) is (taking sulfuric acid as an example):

[0039] Al2O3+3H2SO4=Al2(SO4)3+3H2O(1.5)

[0040] Furthermore, the amount of sodium phosphate added is 8 to 12 times the weight of lithium in the filtrate; the amount of sodium hydroxide added is 5 wt% to 10 wt% of the weight of sodium phosphate. The purpose of adding sodium phosphate is to convert soluble lithium salt into insoluble lithium phosphate, thereby achieving effective separation of lithium salt and sodium salt.

[0041] In addition, the precipitation lithium extraction reaction described in step 4) is (taking lithium sulfate as an example):

[0042] 2Na3PO4+3Li2SO4=2Li3PO4+3Na2SO4(1.6)

[0043] Beneficial effects

[0044] 1) Flotation can separate fluorides and carbon powder, recover carbon, and avoid CO2 emissions from subsequent roasting processes, thus significantly reducing carbon emissions.

[0045] 2) Rationally design a three-stage roasting process: The purpose of pre-roasting is to decompose cyanide and aluminum nitride / aluminum carbide in the waste cathode to avoid the release of toxic and harmful gases in the subsequent flotation process; the purpose of the first stage roasting is to remove the residual carbon in fluoride 1; the purpose of the second stage roasting is to react cryolite / sodium fluoride in fluoride 2 with calcium salts to convert fluorine and lithium elements into calcium fluoride and soluble lithium salts, thereby achieving the purpose of separating fluorine and lithium elements.

[0046] 3) The role of additive 1 is to promote the rapid oxidation of residual carbon in fluoride 1 to obtain carbon-free fluoride 2, avoid carbon contamination of subsequent products, and help improve the purity of calcium fluoride products. Attached Figure Description

[0047] Figure 1 This is a process flow diagram of the present invention;

[0048] Figure 2 This invention presents the XRD pattern of calcium fluoride;

[0049] Figure 3 This invention presents the XRD pattern of lithium phosphate. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0051] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise stated, all percentages, ratios, proportions, or parts are by weight.

[0052] Unless otherwise specified, the reagents and raw materials used in the embodiments and comparative examples of this invention are commercially available.

[0053] Example 1

[0054] A method for the co-processing of waste cathodes and carbon slag to prepare calcium fluoride and lithium phosphate, such as... Figure 1 As shown, it includes the following steps:

[0055] 1) Select waste cathodes and carbon slag from a company in Shandong, crush and grind them to below 2mm, pre-calcine the waste cathodes to obtain calcined waste cathodes; mix the calcined waste cathodes and carbon slags at a ratio of 100:5, grind the mixture to below 200 mesh, and obtain carbon powder and fluoride 1 after flotation; the main components of fluoride 1 are cryolite, sodium fluoride, a small amount of alumina and carbon;

[0056] 2) Fluoride 1 and stearic acid were mixed and ground at a mass ratio of 100:5 and calcined at 600℃ for 120 min to obtain fluoride 2; wherein, the main components of fluoride 2 are cryolite, sodium fluoride and a small amount of alumina.

[0057] 3) Fluoride 2 and calcium chloride are mixed and ground at a mass ratio of 1:0.8, and then calcined at 700℃ for 180 min to obtain calcium fluoride clinker; wherein, the main components of calcium fluoride clinker are calcium fluoride, sodium chloride, lithium chloride, and a small amount of alumina;

[0058] 4) The clinker was soaked in water and the solid-liquid separation was performed to obtain crude calcium fluoride and filtrate. Hydrochloric acid was added to the crude calcium fluoride to remove impurities, and after washing and drying, calcium fluoride was obtained (see...). Figure 2 The calcium fluoride meets the requirements of GB / T27804-2011; the main components of crude calcium fluoride are calcium fluoride and a small amount of aluminum oxide.

[0059] 5) Add sodium phosphate and a small amount of sodium hydroxide to the filtrate. The amount of sodium phosphate added is 8 times the mass of lithium in the filtrate, and the amount of sodium hydroxide added is 5% of the mass of sodium phosphate. After the reaction is complete, a white precipitate is obtained. After solid-liquid separation, washing and drying, lithium phosphate is obtained (see...). Figure 3 The product meets the requirements of YS / T637-2022.

[0060] Comparative Example 1

[0061] A method for co-processing waste cathodes and carbon slag to prepare calcium fluoride and lithium phosphate includes the following steps:

[0062] 1) Select waste cathodes and carbon slag from a company in Shandong, crush and grind them to below 2mm, pre-calcine the waste cathodes to obtain calcined waste cathodes; mix the calcined waste cathodes and carbon slags at a ratio of 100:5, grind the mixture to below 200 mesh, and obtain carbon powder and fluoride 1 after flotation; the main components of fluoride 1 are cryolite, sodium fluoride, a small amount of alumina and carbon;

[0063] 2) After grinding fluoride 1, calcined at 600°C for 155 min to obtain fluoride 2; the main components of fluoride 2 are cryolite, sodium fluoride, and a small amount of alumina; other operating conditions are the same as in Example 1.

[0064] A comparison between Example 1 and Comparative Example 1 shows that the roasting time of Example 1 is shortened by 35 minutes, indicating that the addition of stearic acid significantly shortens the roasting time, which is beneficial for energy conservation and carbon reduction.

[0065] Example 2

[0066] A method for co-processing waste cathodes and carbon slag to prepare calcium fluoride and lithium phosphate includes the following steps:

[0067] 1) Select waste cathodes and carbon slag from a company in Guangxi, grind them to less than 2 mm, and pre-calcine the waste cathodes after grinding to obtain calcined waste cathodes; mix the calcined waste cathodes and carbon slags at a ratio of 100:50, grind them to less than 200 mesh, and obtain carbon powder and fluoride 1 (composition as above) after flotation.

[0068] 2) Fluoride 1 and citric acid were mixed and ground at a mass ratio of 100:10, and then calcined at 700℃ for 90 min to obtain fluoride 2 (with the same composition as above);

[0069] 3) Fluoride 2 and calcium sulfate are mixed and ground at a mass ratio of 1:1, and then calcined at 800℃ for 120 min to obtain calcium fluoride clinker; wherein, the main components of calcium fluoride clinker are calcium fluoride, sodium sulfate, lithium sulfate, and a small amount of alumina;

[0070] 4) The clinker is soaked in water and subjected to solid-liquid separation to obtain crude calcium fluoride (composition as above) and filtrate. Sulfuric acid is added to the crude calcium fluoride to remove impurities. After washing and drying, pure calcium fluoride is obtained (see...). Figure 2 The product meets the requirements of GB / T27804-2011;

[0071] 5) Add sodium phosphate and a small amount of sodium hydroxide to the filtrate. The amount of sodium phosphate added is 10 times the mass of lithium in the filtrate, and the amount of sodium hydroxide added is 7% of the sodium phosphate. After the reaction is complete, a white precipitate is obtained. After solid-liquid separation, washing and drying, lithium phosphate is obtained (see...). Figure 3 The product meets the requirements of YS / T637-2022.

[0072] Comparative Example 2

[0073] A method for co-processing waste cathodes and carbon slag to prepare calcium fluoride and lithium phosphate includes the following steps:

[0074] 1) Select waste cathodes and carbon slag from a company in Guangxi, grind them to less than 2 mm, and pre-calcine the waste cathodes after grinding to obtain calcined waste cathodes; mix the calcined waste cathodes and carbon slags at a ratio of 100:50, grind them to less than 200 mesh, and obtain carbon powder and fluoride 1 (composition as above) after flotation.

[0075] 2) After grinding fluoride 1, calcined it at 700°C for 120 min to obtain fluoride 2 (with the same composition as above); other operating conditions are the same as in Example 2.

[0076] Comparing Example 2 and Comparative Example 2, it can be seen that the roasting time of Example 2 is shortened by 30 minutes, that is, the roasting time with the addition of citric acid is shortened by 30 minutes.

[0077] Example 3

[0078] A method for co-processing waste cathodes and carbon slag to prepare calcium fluoride and lithium phosphate includes the following steps:

[0079] 1) Select waste cathodes and carbon slag from a company in Xinjiang, grind them to less than 2 mm, and pre-calcine the waste cathodes after grinding to obtain calcined waste cathodes; mix the calcined waste cathodes and carbon slags in a ratio of 100:95, grind the mixture to less than 200 mesh, and obtain carbon powder and fluoride 1 (composition as above) after flotation.

[0080] 2) Mix and grind fluoride 1 with glycerol at a mass ratio of 100:20, and calcine at 800℃ for 60 min to obtain fluoride 2 (with the same composition as above);

[0081] 3) Mix and grind fluoride 2 and calcium nitrate at a mass ratio of 1:1.2, and calcine at 900℃ for 60 min to obtain a clinker containing calcium fluoride (composed of calcium fluoride, sodium nitrate, lithium nitrate, and a small amount of alumina).

[0082] 4) The clinker is soaked in water and subjected to solid-liquid separation to obtain crude calcium fluoride (composition as above) and filtrate. Nitric acid is added to the crude calcium fluoride (composition as above) to remove impurities. After washing and drying, pure calcium fluoride is obtained (see...). Figure 2 The product meets the requirements of GB / T27804-2011;

[0083] 5) Add sodium phosphate and a small amount of sodium hydroxide to the filtrate. The amount of sodium phosphate added is 12 times the mass of lithium in the filtrate, and the amount of sodium hydroxide added is 10% of the amount of sodium phosphate. After the reaction is complete, a white precipitate is obtained. After solid-liquid separation, washing and drying, lithium phosphate is obtained (see...). Figure 3 The product meets the requirements of YS / T637-2022.

[0084] Comparative Example 3

[0085] A method for co-processing waste cathodes and carbon slag to prepare calcium fluoride and lithium phosphate includes the following steps:

[0086] 1) Select waste cathodes and carbon slag from a company in Xinjiang, grind them to less than 2 mm, and pre-calcine the waste cathodes after grinding to obtain calcined waste cathodes; mix the calcined waste cathodes and carbon slags in a ratio of 100:95, grind the mixture to less than 200 mesh, and obtain carbon powder and fluoride 1 (composition as above) after flotation.

[0087] 2) After grinding fluoride 1, calcined it at 800°C for 80 min to obtain fluoride 2 (with the same composition as above); other operating conditions are the same as in Example 3.

[0088] A comparison between Example 3 and Comparative Example 3 shows that the calcination time of Example 3 is shortened by 20 minutes. Adding glycerol can significantly shorten the calcination time, which is beneficial for energy saving and carbon reduction.

[0089] Example 4

[0090] A method for co-processing waste cathodes and carbon slag to prepare calcium fluoride and lithium phosphate includes the following steps:

[0091] 1) Select waste cathodes and carbon slag from a company in Ningxia, grind them to below 2mm, and pre-calcine the waste cathodes after grinding to obtain calcined waste cathodes; mix the calcined waste cathodes and carbon slags in a ratio of 100:20, grind the mixture to below 200 mesh, and obtain carbon powder and fluoride 1 after flotation.

[0092] 2) Fluoride 1 and stearic acid were mixed and ground at a mass ratio of 100:7, and then calcined at 650℃ for 105 min to obtain fluoride 2.

[0093] 3) Mix and grind fluoride 2 and calcium acetate at a mass ratio of 1:1.1, and calcine at 750℃ for 160 min to obtain a clinker containing calcium fluoride (composed of calcium fluoride, sodium acetate, lithium acetate, and a small amount of alumina).

[0094] 4) The clinker was soaked in water and the solid-liquid mixture was separated to obtain crude calcium fluoride and filtrate. Hydrochloric acid was added to the crude calcium fluoride to remove impurities, and after washing and drying, calcium fluoride was obtained (see...). Figure 2 The product meets the requirements of GB / T27804-2011;

[0095] 5) Add sodium phosphate and a small amount of sodium hydroxide to the filtrate. The amount of sodium phosphate added is 9 times the mass of lithium in the filtrate, and the amount of sodium hydroxide added is 6% of the mass of sodium phosphate. After the reaction is complete, a white precipitate is obtained. After solid-liquid separation, washing and drying, lithium phosphate is obtained (see...). Figure 3 The product meets the requirements of YS / T637-2022.

[0096] Comparative Example 4

[0097] A method for co-processing waste cathodes and carbon slag to prepare calcium fluoride and lithium phosphate includes the following steps:

[0098] 1) Select waste cathodes and carbon slag from a company in Ningxia, grind them to below 2mm, and pre-calcine the waste cathodes after grinding to obtain calcined waste cathodes; mix the calcined waste cathodes and carbon slags in a ratio of 100:20, grind the mixture to below 200 mesh, and obtain carbon powder and fluoride 1 after flotation.

[0099] 2) Fluoride 1 and stearic acid were mixed and ground at a mass ratio of 100:7, and then calcined at 650℃ for 105 min to obtain fluoride 2.

[0100] 3) Mix and grind fluoride 2 and calcium acetate at a mass ratio of 1:0.9, and calcine at 750°C for 160 min to obtain calcium fluoride clinker (components include calcium fluoride, sodium acetate, lithium acetate, a small amount of alumina, and a small amount of cryolite); other operating conditions are the same as in Example 4.

[0101] A comparison between Example 4 and Comparative Example 4 shows that the calcium acetate addition in Comparative Example 4 was too low, resulting in incomplete cryolite conversion and cryolite residue in the product.

[0102] Example 5

[0103] A method for co-processing waste cathodes and carbon slag to prepare calcium fluoride and lithium phosphate includes the following steps:

[0104] 1) Select waste cathodes and carbon slag from a company in Yunnan, grind them to less than 2 mm, and pre-calcine the waste cathodes after grinding to obtain calcined waste cathodes; mix the calcined waste cathodes and carbon slags in a ratio of 100:60, grind the mixture to less than 200 mesh, and obtain carbon powder and fluoride 1 after flotation.

[0105] 2) Fluoride 1 and citric acid were mixed and ground at a mass ratio of 100:10, and then calcined at 750℃ for 75 min to obtain fluoride 2;

[0106] 3) Mix and grind fluoride 2 and calcium oxalate at a mass ratio of 1:0.9, and calcine at 850℃ for 100 min to obtain calcium fluoride clinker (components: calcium fluoride, sodium oxalate, lithium oxalate, and a small amount of alumina).

[0107] 4) The clinker was soaked in water and the solid-liquid mixture was separated to obtain calcium fluoride 1 and filtrate. Calcium fluoride 1 was treated with sulfuric acid to remove impurities, and after washing and drying, calcium fluoride was obtained (see...). Figure 2 The product meets the requirements of GB / T27804-2011;

[0108] 5) Add sodium phosphate and a small amount of sodium hydroxide to the filtrate. The amount of sodium phosphate added is 11 times the mass of lithium in the filtrate, and the amount of sodium hydroxide added is 8% of the mass of sodium phosphate. After the reaction is complete, a white precipitate is obtained. After solid-liquid separation, washing and drying, lithium phosphate is obtained (see...). Figure 3 The product meets the requirements of YS / T637-2022.

[0109] Comparative Example 5

[0110] A method for co-processing waste cathodes and carbon slag to prepare calcium fluoride and lithium phosphate includes the following steps:

[0111] 1) The raw materials are waste cathodes and carbon slag from a certain enterprise in Yunnan. They are ground to less than 2 mm. After grinding, the waste cathodes are pre-roasted to obtain roasted waste cathodes. The roasted waste cathodes and carbon slags are mixed in a ratio of 100:60. The mixture is ground to less than 200 mesh and then floated to obtain carbon powder and fluoride 1.

[0112] 2) Fluoride 1 and citric acid were mixed and ground at a mass ratio of 10:1, and then calcined at 750℃ for 75 min to obtain fluoride 2;

[0113] 3) Fluoride 2 and calcium oxalate were mixed and ground at a mass ratio of 1:1.3, and then calcined at 850°C for 100 min to obtain a calcium fluoride-containing clinker (composed of calcium fluoride, sodium oxalate, lithium oxalate, a small amount of alumina, and a small amount of calcium carbonate / calcium oxide); other operating conditions were the same as in Example 5.

[0114] A comparison between Example 5 and Comparative Example 5 shows that Comparative Example 5 had an excessive amount of calcium oxalate added. The excess calcium oxalate was converted into calcium carbonate during the calcination process, and then decomposed into calcium oxide. A small amount of calcium carbonate / calcium oxide residue was found in the product.

[0115] Comparative Example 6

[0116] A method for co-processing waste cathodes and carbon slag to prepare calcium fluoride and lithium phosphate includes the following steps:

[0117] 1) The raw materials are waste cathodes and carbon slag from a company in Qinghai. They are ground to less than 2 mm. After grinding, the waste cathodes are pre-roasted to obtain roasted waste cathodes. The roasted waste cathodes and carbon slags are mixed in a ratio of 100:75. The mixture is ground to less than 200 mesh and then floated to obtain carbon powder and fluoride 1.

[0118] 2) Fluoride 1 and glycerol were mixed and ground at a mass ratio of 10:2, and then calcined at 800℃ for 60 min to obtain fluoride 2;

[0119] 3) Fluoride 2 and calcium citrate were mixed and ground at a mass ratio of 1:3.6 and calcined at 900°C for 60 min to obtain a clinker containing calcium fluoride (composed of calcium fluoride, sodium citrate, lithium citrate, and a small amount of alumina); other operating conditions were the same as in Example 3.

[0120] By comparing Example 3 with Comparative Example 6, it can be seen that the ratio of calcium citrate to calcium nitrate increases from 1:1.2 to 1:3.6, resulting in a 2-fold increase in consumption. Based on the principle of conservation, calcium nitrate is preferred.

[0121] In summary, this invention can separate fluorides and carbon powder and recover carbon through flotation, while avoiding CO2 emissions in subsequent roasting processes, thus significantly reducing carbon emissions. Through a rationally designed three-stage roasting process: pre-roasting aims to decompose cyanide and aluminum nitride / aluminum carbide in the waste cathode, preventing the release of toxic and harmful gases in subsequent flotation processes; the first-stage roasting aims to remove residual carbon from fluoride 1; the second-stage roasting aims to react cryolite / sodium fluoride in fluoride 2 with calcium salts, converting fluorine and lithium elements into calcium fluoride and soluble lithium salts, achieving the separation of fluorine and lithium elements. Furthermore, the role of additive 1 is to promote the rapid oxidation of residual carbon in fluoride 1, obtaining carbon-free fluoride 2, avoiding carbon contamination of subsequent products, and improving the purity of calcium fluoride products.

[0122] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. 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 preparing calcium fluoride and lithium phosphate through co-processing of waste cathode and carbon slag, characterized in that, Includes the following steps: Step 1) Pre-baking: The waste cathode is pre-baked and then mixed with carbon slag, ground, and floated to obtain carbon powder and fluoride 1; Step 2) Segmented roasting: Fluoride 1 obtained in step 1) is roasted in one stage to obtain fluoride 2; Fluoride 2 is roasted in two stages to obtain clinker containing calcium fluoride; Step 3) Acid leaching to remove impurities: The clinker is leached in water and separated into solid and liquid components to obtain crude calcium fluoride and filtrate; the crude calcium fluoride is then treated with inorganic acid to remove impurities, washed and dried to obtain calcium fluoride. Step 4) Lithium precipitation: Add sodium phosphate and sodium hydroxide to the filtrate obtained in step 3), and after sufficient reaction, a white precipitate is obtained. After solid-liquid separation, washing, and drying, lithium phosphate is obtained; wherein, In step 2), an auxiliary agent 1 is added during the roasting process. The auxiliary agent 1 is selected from at least one of glycerol, citric acid, and stearic acid. The amount of the auxiliary agent 1 added is 5 wt% to 20 wt% of the total weight of the fluoride 1. The second-stage roasting process includes an additive 2, which is selected from at least one of calcium chloride, calcium nitrate, calcium sulfate, calcium acetate, calcium oxalate, and calcium citrate. The amount of additive 2 added is 0.8 to 1.2 times the total weight of the fluoride 2.

2. The method for preparing calcium fluoride and lithium phosphate by co-processing waste cathode and carbon slag according to claim 1, characterized in that, In step 1), the amount of carbon slag added accounts for 5 wt% to 95 wt% of the total weight of the roasted waste cathode.

3. The method for preparing calcium fluoride and lithium phosphate by co-processing waste cathode and carbon slag according to claim 1, characterized in that, In step 2), the roasting conditions are as follows: the roasting temperature is 600-800℃ and the roasting time is 60-120min.

4. The method for preparing calcium fluoride and lithium phosphate by co-processing waste cathode and carbon slag according to claim 1, characterized in that, In step 2), the two-stage roasting conditions are: roasting temperature of 700-900℃ and roasting time of 60-180min.

5. The method for preparing calcium fluoride and lithium phosphate by co-processing waste cathode and carbon slag according to claim 1, characterized in that, In step 3), the amount of inorganic acid added is three times the number of moles of alumina in the crude calcium fluoride.

6. The method for preparing calcium fluoride and lithium phosphate by co-processing waste cathode and carbon slag according to claim 1, characterized in that, The amount of sodium phosphate added is 8 to 12 times the weight of lithium in the filtrate; the amount of sodium hydroxide added is 5 wt% to 10 wt% of the weight of sodium phosphate.

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