Recycling and harmless treatment method for overhaul slag

Abstract

The invention discloses a resourceful and harmless treatment method for overhaul slag, which realizes dangerous component decomposition and resource recovery through a closed-loop process of crushing, ball-milling, flotation and separation, sulfating, roasting and drying, three-section countercurrent leaching, neutralization and impurity removal, lithium precipitation and purification and evaporative crystallization. Wherein the dust is collected and treated by a closed system; the flotation section adopts a'two-roughing, one-scavenging and two-refining 'process to recover carbon powder, cyanide is completely decomposed through sulfating roasting drying, fluoride enters a gas phase through sulfating roasting drying decomposition and completely enters gypsum slag, the leaching section extracts lithium and silicon components step by step through pH subsection control, leaching liquid is subjected to two-stage impurity removal, sodium carbonate is added into purified liquid in a lithium precipitation tank to precipitate lithium, and the purified liquid is subjected to secondary purification. Washing the wet product by a rinsing tank, and drying by a flash dryer to obtain lithium carbonate; evaporating the lithium precipitation mother liquor to recover sodium sulfate salt. According to the method, the carbon powder, the lithium carbonate and the machine-made silica sand are synchronously recovered, the whole process is closed, secondary pollution is avoided, and the problems of high cyanogen and fluorine residues and low resource recovery rate of a traditional process are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hazardous waste treatment, in particular to a resource and harmless treatment method of overhaul slag. BACKGROUND

[0002] With the vigorous development of the electrolytic aluminum industry, the environmental risks brought by the hazardous waste such as overhaul slag, carbon slag, aluminum ash and the like generated in the production process of electrolytic aluminum in China are increasingly prominent. 30 kg of carbon slag is generated per ton of electrolytic aluminum produced. According to this estimate, 1.335 million tons of carbon slag are generated annually in the country, of which 891,000 tons are generated annually in the northwest (Xinjiang, Gansu, Inner Mongolia, Ningxia, Qinghai, Shanxi and Shaanxi).

[0003] Overhaul slag is the inevitable product of the lining material in the electrolytic cell under the action of high-temperature chemical corrosion (fluorine / sodium penetration) + physical stress (thermal shock / erosion) + electrochemistry, and its danger is directly related to residual fluoride and cyanide. About 10-30 kg of overhaul slag is generated per ton of primary aluminum produced, and the amount of overhaul slag generated by individual enterprises with poor control conditions will be higher. Overhaul slag contains about 30-50% carbon material, 20-40% refractory material and a small amount of fluoride salt, metal oxide and cyanide. Because of its complex composition, containing harmful components such as heavy metals, cyanide and fluoride to varying degrees, overhaul slag is listed as 321-023-48 waste in the National Hazardous Waste List. SUMMARY

[0004] The present application provides a resource and harmless treatment technology for overhaul slag, which is simple to produce and has less impact on the environment.

[0005] To achieve the above purpose, the technical solution adopted by the present application is as follows: A resource and harmless treatment method of overhaul slag, comprising the following steps: Step one, crushing and ball milling: the overhaul slag is crushed to 0.3-5 mm by a crusher, and then sent to a ball mill for dry ball milling to 150-250 mesh, and then the aluminum blocks are separated by a screening machine, and the remaining material is transported to a de-cyanide and fluoride removal process; Step two, flotation: the slurry is pumped into a flotation machine for "two roughing, one scavenging and two cleaning" flotation to separate carbon fine powder and tailings; the carbon fine powder contains 70-80% carbon, and the tailings are dewatered by a plate and frame filter and then enter a rotary kiln sulfurization roasting and drying process; Step three, sulfurization drying: The tailings from the flotation are mixed with sodium carbonate and 20% sulfuric acid and fed into a rotary kiln for sulfurization drying. The ratio of sodium carbonate, 10% sulfuric acid, and the material after flotation is 1:2:10. The flue gas generated by the sulfurization drying in the rotary kiln is first fed into a bag filter for dust removal treatment, and then into a lye absorption tower for removal of fluorides. The treated flue gas is discharged from a 45m chimney. The dried tailings are fed into a slurry tank, and the dust collected by the bag filter is also fed into the slurry tank. The gypsum slag generated by the lye absorption tower is disposed as solid waste; Step four, three-stage leaching: A 10% sulfuric acid is added to the leaching tank, the pH is controlled at 2-3, and the solid-liquid ratio is 1.5. The leaching time is 2 hours. The leaching solution is filtered by a plate and frame filter. The leaching solution is fed into a neutralization and impurity removal tank. The leaching residue is fed into a second leaching tank. The second leaching tank receives the first leaching residue. The pH of the leaching is controlled at 3.5-4.5 using the third leaching filtrate, and the solid-liquid ratio is 1.5. The leaching time is 2 hours. The leaching solution is filtered by a plate and frame filter. The leaching solution is returned to the slurry tank. The second leaching residue is fed into a third leaching tank. The third leaching tank receives the second leaching residue. The pH of the leaching is controlled at 4.5-5.5 using the rinsing liquid, and the solid-liquid ratio is 1.5. The leaching time is 2 hours. The leaching solution is filtered by a plate and frame filter. The leaching solution is returned to the second leaching tank. The third leaching residue is dried by a flash dryer to produce machine-made silica sand. The tail gas from the flash dryer is treated by a bag filter and discharged from a 15m exhaust pipe. The dust collected by the bag filter is mixed into the machine-made sand as a product for sale. Step five, neutralization and impurity removal: The filtrate from the plate and frame filter is pumped into a neutralization and impurity removal tank. Lime is added to adjust the pH to 7-8. The reaction time is 1 hour to precipitate calcium fluoride. Then the slurry is pumped into a purification reaction tank. Sodium hydroxide is added to adjust the pH to 11. The temperature is controlled at 60°C for 30 minutes to precipitate iron and magnesium hydroxides. Finally, the purified liquid and impurity-containing residue with 30% water are separated by a plate and frame filter. The purified liquid is fed into a lithium precipitation tank. The residue is classified and disposed according to GB34330-2017. Step six, lithium precipitation: The purified liquid and evaporation mother liquor are mixed in the lithium precipitation tank. An excess of 5% sodium carbonate solution is pumped at a flow rate. The temperature is controlled at >95°C for 3 hours. After the reaction, the slurry is fed into a pH adjustment tank to adjust the pH to 7-9. The slurry after pH adjustment is separated by a centrifugal filter to obtain lithium carbonate wet product with 5% water and lithium precipitation mother liquor. Step seven, lithium carbonate washing: The wet product is added to the rinsing tank with 10 times the mass of evaporation condensate water. The temperature is controlled at >95°C for washing. After washing, the slurry is separated by a centrifugal filter twice to obtain washed wet product with 5% water. The filtrate is returned to the third leaching tank. Step eight, drying and packaging: The washed wet product is fed into a flash dryer to dry to a water content of ≤0.4%. The dried product is loaded into ton bags by a pneumatic conveying machine. The exhaust gas from the flash dryer is treated by a bag filter and discharged from a 15m exhaust pipe. The dust collected by the bag filter is mixed into the lithium carbonate as a product for sale. Step nine, evaporation: the filtrate produced by the centrifugal filter enters the flash dryer to condense the moisture stream back to the ball milling process and lithium precipitation process; the evaporation residue is a salt containing sodium sulfate and potassium sulfate, which is sold as a product; the waste gas produced by the flash dryer is discharged by a 15m exhaust pipe after being treated by a bag dust collector, and the dust collected by the bag dust collector is mixed into sodium sulfate and sold as a product; Product index: the calorific value of the carbon powder in step three is 18.85MJ / kg -20.05MJ / kg ; The purity of lithium carbonate in step eight is 98.5%-99.5%. The soluble F content in the silica sand prepared in step four is <100mg / L, and the cyanide content is <5mg / L.

[0006] Preferably, the water content of the tailings after dehydration in step three is ≤30%.

[0007] Preferably, the neutralization and impurity removal filter residue in step five is washed three times in countercurrent, and is classified and disposed after identification according to GB34330-2017.

[0008] Preferably, the lithium precipitation temperature in step six is >95℃, and the reaction time is 3 hours.

[0009] Preferably, the washing water temperature in step 7 is >95℃.

[0010] Preferably, the sodium sulfate salt obtained by evaporation in step nine is sold as a product.

[0011] Preferably, the carbon powder, lithium carbonate and machine-made silica sand meet the relevant standard requirements in "Commercial Coal Quality - Pulverized Coal for Power Generation Coal Boiler" GB / T7562-2018, "Lithium Carbonate" GB / T11075-2013 and "Sand for Silicate Building Products" JC / T622-2009.

[0012] Preferably, the "two roughing, one scavenging and two cleaning" flotation process in step three is as follows: first roughing: add collector kerosene 180-220g / t, stirring time 3-5min; second roughing: add collector kerosene 60-100g / t, stirring time 2-3min; scavenging: add frother 2# oil 20-40g / t, stirring time 1-2min; first cleaning: add modifier water glass 300-400g / t, stirring time 4-6min; second cleaning: add modifier CMC 100-150g / t, stirring time 3-4min.

[0013] Compared with the prior art, the present application has the following advantages: (1) The present application completely decomposes toxic substances in the overhaul slag through hierarchical leaching and impurity removal mechanism. Cyanide is oxidized by calcium hypochlorite to remove to a concentration of less than 0.1 mg / L, and fluoride is stably solidified to 1 mg / L or less by calcium salt precipitation. The whole process is carried out in a closed device, dust is captured by a bag dust removal system, the amount of final solid waste is reduced by more than 50% compared with the traditional process, and the hazardous components are essentially harmless.

[0014] (2) The present application converts the overhaul slag into three types of high-value products. The carbon powder extracted from the flotation section has a heat value of more than 18.85 MJ / kg, meeting the relevant standards in “Commercial Coal Quality for Coal for Pulverized Coal Boiler” (GB / T7562-2018); lithium elements are leached by three-stage countercurrent leaching and deep purification, and finally recovered in the form of lithium carbonate with a purity of 98.5%-99.5% (GB / T 11075-2013); silicon-aluminum components are leached by controlled acid leaching and flash drying mechanism to form silica sand, which meets the relevant requirements in “Sand for Silicate Building Products” (JC / T622-2009) and can be used as building material raw material.

[0015] (3) The present application adopts closed loop closed processing in the whole process, which maximally reduces the processing cost and environmental load. The lithium removal mother liquor and washing water are neutralized and evaporated to extract sodium sulfate, 60% of the condensate water is used for ball milling and slurry preparation, and 40% is used for lithium carbonate washing, achieving a process water reuse rate of 100%; the impurity removal residue is landfilled as general solid waste, and the total amount is only 25%-30% of the raw material. The energy consumption per ton of slag treatment is reduced by 40% compared with the wet process, and a small amount of waste gas is discharged (mainly dust), and no waste water is discharged, solving the problem of secondary pollution. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is the process flow diagram of the present application; Figure 2 is the process flow diagram of the present application; DETAILED DESCRIPTION

[0017] The present application will be further described in detail below with specific examples.

[0018] Example 1 Raw material: overhaul slag of a certain electrolytic aluminum plant in Gansu Province, composition as shown in the table below:

[0019] Step one, crushing and ball milling: the overhaul slag is crushed to 2 mm by a crusher (1), dry ball milled to 200 mesh by a ball mill (2), and the aluminum blocks are separated by a screening machine (3) and sold; Step two, flotation: first roughing: add 200 g / t of kerosene to the flotation machine (5) and stir for 4 min; Second coarse selection: Add 80g / t of kerosene and stir for 2.5min; Sweeping: Add 30g / t of No. 2 oil and stir for 1.5 minutes; First selection: Add 350g / t of water glass and stir for 5 minutes; Second selection: Add 120g / t of CMC and stir for 3.5 minutes; After the roughing foam is scavenged, it enters the fine selection section. The tailings are dewatered by the plate and frame filter (8) (water content 28%), the carbon concentrate yield is 60.66%, and the calorific value of the carbon concentrate is 19.25 MJ / kg.

[0020] Step 3, Sulfation and Drying: The tailings produced by flotation are mixed with sodium carbonate and 20% sulfuric acid and fed into a rotary kiln (6) for sulfation and drying. The ratio of sodium carbonate, 10% sulfuric acid, and the flotation material is 1:2:10. The flue gas generated by the sulfation and drying in the rotary kiln first enters a bag filter (7) for dust removal, and then enters an alkaline absorption tower (8) for fluoride removal. The treated flue gas is discharged through a 45m chimney. The dried tailings enter a slurry mixing tank (9). The dust collected by the bag filter (7) and the dried tailings enter the slurry mixing tank (9) together. The gypsum slag generated by the alkaline absorption tower (8) is disposed of as solid waste.

[0021] Step 4, Three-stage leaching: Add 10% sulfuric acid (pH 2.5, solid-liquid ratio 1:1.5, 2h) to a soaking tank (10), and filter the filtrate through a plate and frame filter (11) to remove impurities; The second immersion tank (12) is leached with the filtrate from the third immersion tank (pH 4.0, 2h), and the filtrate is returned to the first immersion tank; The three-stage leaching tank (15) was used to leach the filter residue with rinsing solution (pH 5.0, 2h), and the filter residue was dried by flash drying (17) to obtain silica sand (SiO2 92.5%). Step 5: Neutralization and impurity removal: Add lime to neutralization and impurity removal tank (13) to adjust pH to 7.5 (react for 1 hour); Add NaOH to the impurity tank to adjust the pH to 11 (let stand at 60℃ for 30 min), and use a plate and frame filter (20) to obtain purified liquid and filter residue. The purified liquid enters the lithium precipitation tank (21), and the filter residue is identified and classified according to GB34330-2017. Step 6, Lithium precipitation: The purified liquid and the evaporation mother liquor are mixed in the lithium precipitation tank (21), and an excess of 5% sodium carbonate solution is pumped in at a certain flow rate. The temperature is controlled to be >95℃ and the reaction is carried out for 3 hours. After the reaction, the slurry enters the pH adjustment tank (22) to adjust the pH value to 7~9. The pH-adjusted slurry is separated by a centrifugal filter (23) to obtain a wet lithium carbonate product with a water content of 5% and a lithium precipitation mother liquor. Step seven, washing: rinse the tank (27) with 10 times of condensed water (>95°C) for washing, and separate the secondary centrifugal filter (28); Step eight, drying: flash dryer (29) drying to 0.35% moisture content, air conveyor ton bag packaging; Step nine, evaporation: 60% of the condensed water is returned to the ball mill, and 40% is returned to the sink lithium, and the evaporation residue is a salt containing 90-95% sodium sulfate, which is sold as a product; Product index: carbon powder: heat value 19.25MJ / kg (GB / T 15224.1-2018) Lithium carbonate: purity 99.1% (GB / T 11075-2013) Silica sand: SiO268% (JC / T 622-2009) Solid waste rate: 6.81%.

[0022] Example 2 Raw materials: overhaul slag of a certain electrolytic aluminum plant in Xinjiang, composition as shown in the table below: Component F（%） C（%） Li (%) Cyanide (mg / kg) Content 11.04 68.83 1.08 Not detected Treatment process: Step one, crushing and ball milling: crushed to 0.3mm by crusher (1), and milled to 150 mesh by ball mill (2), and separated by screening machine (3); Step two, flotation: first roughing: kerosene 180g / t, stirring for 3min; Second roughing: kerosene 60g / t, stirring for 2min; Scavenging: 2# oil 20g / t, stirring for 1min; First cleaning: water glass 300g / t, stirring for 4min; Second cleaning: CMC 100g / t, stirring for 3min; Carbon powder yield 63.32%, carbon powder heat value 19.55MJ / kg.

[0023] Step three, sulfurization and drying: The tailings produced by flotation are mixed with sodium carbonate and 20% sulfuric acid into the rotary kiln (6) for sulfurization and drying, and the ratio of sodium carbonate, 10% sulfuric acid and the material after flotation is 1:2:10. The flue gas generated by the rotary kiln sulfurization and drying is first treated by the bag dust collector (7), and then enters the alkali absorption tower (8) for removal of fluorides. The treated flue gas is discharged by a 45m chimney. The tailings after drying enter the slurry tank (9), the dust collected by the bag dust collector (7) is mixed with the tailings after drying into the slurry tank (9), and the gypsum slag produced by the alkali absorption tower (8) is treated as solid waste.

[0024] Step four, three-stage leaching: One leaching tank (10) is added with 10% sulfuric acid (pH 3.0, solid-liquid ratio 1:1.5, 2h); The second leaching tank (12) is leached with the third leaching filtrate (pH 4.5, 2h); The third leaching tank (15) is leached with the rinsing liquid (pH 5.5, 2h), and the filter residue is fed into a flash dryer (17) to obtain silica sand (SiO290.8%); Step five, neutralization and impurity removal: The neutralization and impurity removal tank (13) is added with lime to adjust the pH to 8.0 (reaction for 1h); The impurity removal tank is added with NaOH to adjust the pH to 11 (60°C for 30min), and a plate and frame filter (20) is used to obtain a purified liquid and impurity removal residue containing 30% water, and the purified liquid is fed into a lithium precipitation tank (21), and the filter residue is classified and disposed according to GB34330-2017; Step six, lithium precipitation: an excess of 5% sodium carbonate is added to the lithium precipitation tank (21) (95°C, 3h), and a centrifugal filter (23) is used to obtain a wet product (containing 5% water, Li2CO399.2%); Step seven, washing: a rinsing tank (27) is added with 10 times of condensed water (95°C) for washing, and a secondary centrifugal filter (28) is used for separation; Step eight, drying: a flash dryer (29) is used for drying until the water content is 0.38%; Step nine, evaporation: 50% of the condensed water is returned to the ball mill, and 50% is returned to the lithium precipitation, and the evaporation residue is a salt containing 90-95% sodium sulfate, which is sold as a product; Product index: carbon powder: heat value 19.55MJ / kg (GB / T 15224.1-2018) Lithium carbonate: purity 98.9% (GB / T 11075-2013) Silica sand: SiO270% (JC / T 622-2009) Solid waste rate: 7.26%.

[0025] Example 3 Raw material: overhaul slag of an electrolytic aluminum plant in Ningxia, composition as shown in the following table: Component F（%） C（%） Li (%) Cyanide (mg / kg) Content 8.60 78.62 0.18 Not detected Treatment process: Step one, crushing and ball milling: crushed to 5mm by a crusher (1), and milled to 250 mesh by a ball mill (2), and aluminum blocks are separated by a screening machine (3); Step two, flotation: first roughing: kerosene 220g / t, stirring for 5min; Second roughing: kerosene 100g / t, stirring for 3min; Scavenging: 2# oil 40g / t, stirring for 2min; First cleaning: water glass 400g / t, stirring for 6min; Second cleaning: CMC 150 g / t, stirring for 4 min; Carbon powder yield 72.33%, carbon powder calorific value 20.21 MJ / kg.

[0026] Step three, sulfuric acid drying: The tailings from the flotation are mixed with sodium carbonate and 20% sulfuric acid and fed into a rotary kiln (6) for sulfuric acid drying. The ratio of sodium carbonate, 10% sulfuric acid, and the material after flotation is 1:2:10. The flue gas generated by the sulfuric acid drying in the rotary kiln is first treated by a bag dust collector (7) for dust removal, and then enters an alkali liquor absorption tower (8) for removal of fluorides. The treated flue gas is discharged through a 45m chimney. The dried tailings enter a slurry tank (9), and the dust collected by the bag dust collector (7) is mixed with the dried tailings and fed into the slurry tank (9). The gypsum slag generated by the alkali liquor absorption tower (8) is disposed as solid waste.

[0027] Step four, three-stage leaching: One leaching tank (10) adds 10% sulfuric acid (pH 2.0, solid-liquid ratio 1:1.5, 2h); Two leaching tank (12) uses three leaching filtrate for leaching (pH 3.5, 2h); Three leaching tank (15) uses rinsing liquid for leaching (pH 4.5, 2h), and the filter residue is fed into a flash dryer (17) to obtain silica sand (SiO2 94.2%); Step five, neutralization and impurity removal: The neutralization and impurity removal tank (13) adds lime to adjust the pH to 7.0 (reaction for 1h); The impurity removal tank adds NaOH to adjust the pH to 11 (60°C for 30min), and a plate and frame filter (20) is used to obtain purified liquid and impurity removal residue containing 30% water. The purified liquid is fed into a lithium precipitation tank (21), and the filter residue is classified and disposed according to GB34330-2017; Step six, lithium precipitation: The lithium precipitation tank (21) adds an excess of 5% sodium carbonate (98°C, 3h), and a centrifugal filter (23) is used to obtain a wet product (containing 5% water, Li2CO3 99.6%); Step seven, washing: The rinsing tank (27) adds 10 times of condensed water (98°C) for washing, and a secondary centrifugal filter (28) is used for separation; Step eight, drying: The flash dryer (29) is used for drying until the moisture content is 0.30%; Step nine, evaporation: 70% of the condensed water is returned to the ball mill, and 30% is returned to the lithium precipitation. The evaporation residue is a salt containing 90-95% sodium sulfate, which is sold as a product; Product index: Carbon powder: calorific value 20.21 MJ / kg (GB / T 15224.1-2018) Lithium carbonate: purity 98.5% (GB / T 11075-2013) Silica sand: SiO2 69% (JC / T 622-2009) Solid waste rate: 8.56%.

[0028] The product yield and analysis results are shown in Table 1.

[0029] Table 1 Product yield and analysis results No. Charcoal powder calorific value (MJ / kg) Charcoal powder yield (%) Lithium carbonate purity (%) Silica sand Si02content (%) Solid waste rate (%) Example 1 19.25 60.66 99.10 68 6.81 Example 2 19.55 63.32 98.9 70 7.26 Example 3 20.21 72.33 98.5 69 8.56 From the data in Table 1, it can be concluded that based on the process data verification of Examples 1-3, the processing method has the following advantages compared to the traditional method: 1) High resource recovery efficiency: The calorific value of carbon powder (19.25-20.21 MJ / kg) is much higher than the standard (≥18.85 MJ / kg), and the yield of 60.66-72.33% is positively correlated with the carbon content of the raw material (65.93-78.62%); The purity of lithium carbonate (98.5-99.1%) is higher than the national standard (GB / T 11075-2013); The SiO2 content of silica sand (68-70%) meets the standard for building material sand (JC / T 622-2009), and the cyanide / fluorine residual amount (not detected) meets the harmless requirements.

[0030] 2) Significant solid waste reduction effect: The solid waste rate of the whole process is only 6.81-8.56% (traditional process > 50%). The main sources are as follows: The countercurrent process of leaching section (three leaching filtrate circulation) reduces acid consumption; 100% of the evaporation condensate is used for ball milling / washing, and the lithium precipitation mother liquor is recovered for sodium sulfate salt; The dust is all incorporated into the product (silica sand / lithium carbonate).

[0031] This method realizes the high-value recovery of carbon powder, lithium carbonate, and silica sand (all meeting the national standard) through the core design of "staged leaching-closed loop recovery", and the solid waste rate is <9%, solving the problem of cyanide and fluorine residues, and having the dual benefits of resource utilization and harmlessness.

Claims

1. A method for the resource-based and harmless treatment of overhaul slag, characterized in that, Includes the following steps: Step 1, Crushing and Ball Milling: The overhaul slag is crushed to 0.3-5mm by the crusher (1), and then fed into the ball mill (2) for dry ball milling to 150-250 mesh. The aluminum blocks are then separated by the screening machine (3), and the remaining material is transported to the decyanation and fluorine fixation process. Step 2, flotation: The slurry is pumped into the flotation machine (5) for "two roughing, one scavenging and two cleaning" flotation to separate carbon concentrate and tailings; the carbon concentrate has a carbon content of 70-80%, and the tailings are dewatered by the plate and frame filter and then enter the rotary kiln (6) for sulfation roasting and drying process. Step 3, Sulfation and Drying: The tailings produced by flotation are mixed with sodium carbonate and 20% sulfuric acid and fed into a rotary kiln (6) for sulfation and drying. The ratio of sodium carbonate, 10% sulfuric acid and flotation material is 1:2:

10. The flue gas generated by the sulfation drying of the rotary kiln first enters the bag filter (7) for dust removal, and then enters the alkaline absorption tower (8) for fluoride removal. The treated flue gas is discharged from the 45m chimney. The dried tailings enter the slurry mixing tank (9), and the dust collected by the bag filter (7) enters the slurry mixing tank (9) together with the dried tailings. The gypsum residue produced by the alkaline absorption tower (8) is disposed of as solid waste. Step 4, Three-stage leaching: 10% sulfuric acid is added to the first leaching tank (10), the pH is controlled at 2-3 and the solid-liquid ratio is 1.5, and leaching is carried out for 2 hours. The leachate is filtered through a plate and frame filter (11) and then enters the neutralization and impurity removal tank (13). The first leaching filter residue enters the second leaching tank (12). The second leaching tank (12) receives the first leaching residue and leaches it with the third leaching filtrate (pH 3.5-4.5, solid-liquid ratio 1.5, 2 hours). The leaching filtrate passes through a plate and frame filter (14) and is returned to the slurry preparation tank (9). The second leaching residue enters the third leaching tank (15). The triple leaching tank (15) receives the residue from the second leaching and leaches it with rinsing solution (pH 4.5-5.5, solid-liquid ratio 1.5, 2 hours). The leachate passes through a plate and frame filter (16) and is returned to the second leaching tank (12). The residue from the triple leaching is processed into machine-made silica sand by a flash dryer (17). The exhaust gas from the flash dryer (17) is treated by a bag filter (19) and discharged through a 15m exhaust stack. The dust collected is incorporated into the machine-made sand and sold as a product. Step 5, Neutralization and Impurity Removal: The filtrate produced by the plate and frame filter (11) is pumped into the neutralization and impurity removal tank (13), and lime is added to adjust the pH to 7-8. The reaction is carried out for 1 hour to precipitate calcium fluoride. The slurry is then pumped into the purification reaction tank, and sodium hydroxide is added to adjust the pH to 11. The temperature is controlled at 60℃ and the mixture is left to stand for 30 minutes to precipitate iron and magnesium hydroxides. Finally, the purified liquid and impurity removal residue with 30% water content are separated by the plate and frame filter (20). The purified liquid enters the lithium precipitation tank (21), and the filter residue is classified and disposed of according to GB34330-2017. Step 6, Lithium precipitation: The purified liquid and the evaporation mother liquor are mixed in the lithium precipitation tank (21), and an excess of 5% sodium carbonate solution is pumped in at a flow rate. The temperature is controlled to be >95℃ and the reaction is carried out for 3 hours. After the reaction, the slurry enters the pH adjustment tank (22) to adjust the pH value to 7~9. The slurry after pH adjustment is separated by a centrifugal filter (23) to obtain a wet lithium carbonate product with 5% water content and lithium precipitation mother liquor. Step 7, Lithium carbonate washing: Add 10 times the mass of evaporated condensate to the rinsing tank (27) and wash at a temperature >95℃; after washing, the slurry is separated twice by a centrifugal filter (28) to obtain a washed wet product with a water content of 5%, and the filtrate is returned to the third dipping tank (15). Step 8, Drying and Packaging: The washed wet products are dried in a flash dryer (29) until the water content is ≤0.4%, and then loaded into ton bags by a pneumatic conveyor. The exhaust gas generated by the flash dryer (29) is treated by a bag filter (31) and then discharged through a 15m exhaust stack. The dust collected by the bag filter (31) is incorporated into lithium carbonate and sold as a product. Step 9, Evaporation: The filtrate produced by the centrifugal filter (23) enters the flash dryer (24), and the condensate is diverted back to the ball milling process and the lithium precipitation process; the evaporation residue is a salt containing sodium sulfate and potassium sulfate, which is sold as a product; the exhaust gas produced by the flash dryer (24) is treated by the bag filter (25) and then discharged through a 15m exhaust stack. The dust collected by the bag filter (25) is incorporated into the sodium sulfate and sold as a product. Product specifications: The calorific value of the carbon concentrate in step three is 18.85 MJ / kg - 20.05 MJ / kg; In step eight, the purity of lithium carbonate is 98.5% - 99.5%; Step four yields silica sand with a soluble F content of <100 mg / L and a cyanide content of <5 mg / L.

2. The method for resource-based and harmless treatment of overhaul slag according to claim 1, characterized in that, The moisture content of the flotation tailings after dewatering in step three is ≤30%.

3. The method for resource-based and harmless treatment of overhaul slag according to claim 2, characterized in that, The neutralized and impurity-removed filter residue described in step five is washed three times in countercurrent and then classified and disposed of according to GB34330-2017.

4. The method for resource-based and harmless treatment of overhaul slag according to claim 3, characterized in that, Step 6: Lithium precipitation temperature > 95℃, reaction time 3 hours.

5. The method for resource-based and harmless treatment of overhaul slag according to claim 4, characterized in that, Step (7) Washing water temperature > 95℃.

6. The method for resource-based and harmless treatment of overhaul slag according to claim 5, characterized in that, The sodium sulfate obtained from the evaporation in step nine is sold as a product.

7. The method for resource-based and harmless treatment of overhaul slag according to claim 6, characterized in that, The carbon concentrate, lithium carbonate, and manufactured silica sand meet the relevant standard requirements in "Commercial Coal Quality for Pulverized Coal Boilers for Power Generation" (GB / T7562-2018), "Lithium Carbonate" (GB / T11075-2013), and "Sand for Silicate Building Products" (JC / T622-2009), respectively.

8. The method for resource-based and harmless treatment of overhaul slag according to claim 7, characterized in that, The "two roughing, one scavenging, and two cleaning" flotation process in step three is specifically as follows: First roughing: Add 180-220g / t of collector kerosene and stir for 3-5 minutes; Second roughing: Add 60-100g / t of collector kerosene and stir for 2-3 minutes; Sweeping: Add 20-40g / t of foaming agent #2 oil and stir for 1-2 minutes; First selection: Add 300-400g / t of water glass as a modifier, and stir for 4-6 minutes; Second selection: Add 100-150g / t of CMC modifier and stir for 3-4 minutes.

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