Method for treating waste glass powder in cooperation with carbon residue of electrolytic aluminum

Abstract

The present application relates to solid waste resource utilization technical field, disclose a kind of method for electrolytic aluminium carbon residue and waste glass powder are handled in conjunction, comprising: electrolytic aluminium carbon residue and waste glass powder are mixed according to SiO2 and Na3ALF6 molar ratio 3.15:2 to 3.45:2, calcination is carried out at 850 to 1050 DEG C high temperature, make fluorine with SiF4 gas form migration to gas phase;SiF4 containing flue gas is obtained by alkali absorption NaF and Na2SiO3 mixed solution, after separation, respectively NaF product and liquid water glass product are obtained;Solid-phase product NaALO2 is obtained after dissolution, precipitation, calcination AL2O3 product.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization technology, and more specifically, to a method for co-processing waste glass powder with electrolytic aluminum carbon slag. Background Technology

[0002] The electrolytic aluminum production process inevitably generates a large amount of carbon slag solid waste, the main components of which are sodium hexafluoroaluminate (Na3ALF6, mass fraction 40% to 50%) and carbon powder (mass fraction 40% to 50%). Fluorides in the carbon slag are highly susceptible to leaching into the soil and groundwater if not properly disposed of, and have been classified as hazardous waste.

[0003] Existing carbon slag treatment technologies mainly include three categories: flotation, pyrometallurgical treatment, and wet leaching. Flotation is complex, consumes large amounts of reagents, and is ineffective at separating fine-grained carbon slag. In pyrometallurgical treatment, fluorides escape in a disorderly gaseous state, making flue gas absorption and control difficult and prone to secondary pollution. Wet leaching has a long process route, generates large volumes of waste liquid, and is difficult to separate fluorine and aluminum. All of these methods only treat carbon slag as a single solid waste, failing to utilize the chemical synergistic effects between different solid wastes.

[0004] Meanwhile, waste glass powder, mainly composed of SiO2, is largely disposed of through landfill due to its high remelting energy consumption and complex impurities, failing to achieve high-value utilization of silicon resources. Existing technologies lack a synergistic treatment method for the directional gas-phase transfer of fluorine from Na3ALF6, simultaneous recovery of aluminum resources, and value-added utilization of waste glass powder. This results in the inability to fundamentally eliminate the environmental risks of fluorides in carbon slag, and the failure to recover and utilize aluminum, fluorine, and silicon in product form. Summary of the Invention

[0005] This invention provides a method for co-processing waste glass powder with electrolytic aluminum carbon slag, solving the technical problems in related technologies where electrolytic aluminum carbon slag and waste glass powder cannot be utilized in a resource-based and synergistic manner, and where fluoride pollution is difficult to control effectively.

[0006] This invention discloses a method for co-processing waste glass powder with electrolytic aluminum carbon slag, comprising the following steps: Electrolytic aluminum carbon slag is crushed, ground, and dried to obtain dried carbon slag; waste glass is crushed, ground, and dried to obtain waste glass powder. The dried carbon slag and waste glass powder were mixed and formulated at a molar ratio of SiO2 to Na3ALF6 of 3.15:2 to 3.45:2 to obtain a homogeneous mixture. The homogeneous mixture is calcined at 850 to 1050 °C for 2 to 4 hours. Na3ALF6 reacts with SiO2 in a solid phase to generate NaALO2 and releases SiF4 gas, resulting in calcined solid products and flue gas containing SiF4. The flue gas containing SiF4 is cooled after dust removal and sent to an alkaline spray absorption system. SiF4 is absorbed by NaOH aqueous solution to obtain a mixed absorbent containing NaF and Na2SiO3. The mixed absorbent is then evaporated, concentrated, crystallized, and separated to obtain NaF product and sodium silicate solution. The calcined solid product was dissolved in water to obtain a sodium aluminate solution. The sodium aluminate solution was then precipitated and separated to obtain AL(OH)3, which was then calcined to obtain the AL2O3 product.

[0007] Furthermore, the particle size of the dried carbon slag is less than 0.15 mm, and the particle size of the waste glass powder is less than 0.075 mm; the mass fraction of Na3ALF6 in the dried carbon slag is 40% to 50%, and the mass fraction of carbon powder is 40% to 50%.

[0008] Furthermore, the calcination temperature is 900 to 1000°C; air is introduced during the calcination process to control the volume ratio of CO2 to CO in the furnace to be maintained between 2:1 and 5:1, so that the carbon powder in the mixture is burned in a controlled manner to supplement the heat of the reaction system.

[0009] Furthermore, in the alkaline spray absorption system, the initial mass fraction of NaOH is 10% to 20%, the liquid-to-gas ratio is controlled at 3 to 8 L / m³, and the pH value of the circulating alkaline solution is maintained between 8 and 12; the actual amount of NaOH used is 20% to 30% more than the theoretical requirement.

[0010] Further, the evaporation, concentration, crystallization, and separation process includes: evaporating and concentrating NaF at 80 to 90°C to crystallize it out, cooling it to 20 to 30°C to promote further crystallization, with the cooling rate controlled at 0.5 to 2°C / min, and centrifuging to separate the NaF solid from the mother liquor; the mother liquor is then concentrated to a SiO2 to Na2O molar ratio of 2.0:1 to 3.5:1 and a Baume degree of 35 to 50°Bé to obtain a liquid water glass product.

[0011] Furthermore, the precipitation separation of the sodium aluminate solution is carried out by carbonation decomposition or acid precipitation. The carbonation decomposition method involves introducing CO2 gas into the sodium aluminate solution to lower the pH to 9 to 10. The acid precipitation method involves adding 10% to 15% by mass of dilute hydrochloric acid or dilute sulfuric acid into the sodium aluminate solution to lower the pH to 7 to 9. The resulting Al(OH)3 precipitate is washed, dried, and then calcined at 1100 to 1200°C for 2 to 3 hours to obtain the Al2O3 product.

[0012] Furthermore, before the mixing of ingredients, the process includes an ultrasonic spray freeze-drying step of treating the dried carbon slag and waste glass powder: the dried carbon slag and waste glass powder are dispersed in anhydrous ethanol, ultrasonically treated for 30 to 60 minutes at an ultrasonic frequency of 20 to 40 kHz and a power density of 50 to 150 W / L, and then mixed. The mixed suspension is sprayed into a liquid nitrogen freezing chamber with a droplet size of 20 to 80 μm through an ultrasonic spraying device for instant solidification, and then freeze-dried for 8 to 16 hours at a temperature below -40°C and a vacuum degree below 50 Pa to obtain porous microsphere powder.

[0013] Furthermore, the method also includes a step of carbothermic activation of the porous microsphere powder under nitrogen protection: under a high-purity nitrogen protective atmosphere, the temperature is increased to 900 to 1100°C at a heating rate of 10 to 15°C / min, and the temperature is held for 30 to 60 minutes for carbothermic activation. After cooling, activated powder is obtained.

[0014] Furthermore, the method also includes a step of paraffin coating and granulation of the activated powder: based on 100 parts by mass of activated powder, 5 to 12 parts by mass of low-melting-point paraffin with a melting point of 50 to 60°C are added, heated to 65 to 75°C to melt the paraffin, stirred and coated, cooled and solidified, and then 3 to 6 parts by mass of bentonite and 8 to 12 parts by mass of anhydrous ethanol are added for granulation to obtain dense spherical material with a particle size of 3 to 8 mm and a bulk density of 0.6 to 1.0 g / cm³; the dense spherical material is continuously fed into a rotary kiln, and successively passes through a preheating section at 250 to 400°C to remove paraffin, a reaction section at 600 to 800°C for defluorination reaction, and a cooling section to cool down before discharging the solid product.

[0015] Furthermore, the temperature of the rotary kiln reaction section is 650 to 750°C, the residence time of the material in the reaction section is 1.5 to 3 hours, and the oxygen content in the reaction section is 5% to 12%.

[0016] The beneficial effects of this invention are as follows: This invention utilizes the solid-phase chemical reaction between SiO2 in waste glass powder and Na3ALF6 in electrolytic aluminum slag under high-temperature conditions to allow fluorine to migrate directionally from the solid phase to the gas phase in the form of SiF4 gas. This solves the technical problems of disordered volatilization and difficulty in directional capture of fluorides in the prior art, and achieves the technical effect of complete separation of fluorine and aluminum at the solid phase level, simplifying the subsequent flue gas treatment process.

[0017] Through alkaline absorption and separation processes, fluorine is recovered as solid NaF, silicon as liquid Na2SiO3, and aluminum as Al2O3. This solves the technical problem that aluminum, fluorine, and silicon cannot be simultaneously utilized as resources in existing technologies, and achieves the technical effect of synergistically converting two solid wastes into three industrial products.

[0018] The controlled combustion of carbon powder in the charcoal slag during calcination replenishes the main reaction system with the released heat, achieving the technical effect of reducing the need for external energy supply. The reduced residual fluoride content in the solid products eliminates the environmental risk of fluoride leakage from electrolytic aluminum charcoal slag. Attached Figure Description

[0019] Figure 1 This is a process flow diagram of the preparation of waste glass powder for co-processing electrolytic aluminum carbon slag provided in an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the effect of the excess SiO2 ratio on the conversion rate of Na3AlF6 and the concentration of fluoride ions leached from the solid product, as provided in the embodiments of the present invention. Figure 3 This is a schematic diagram illustrating the effect of calcination temperature on the conversion rate of Na3AlF6 and the concentration of fluoride ions leached from the solid product (Example 1 route) provided in the embodiments of the present invention. Figure 4 This is a schematic diagram illustrating the effect of the carbothermic activation step provided in this embodiment of the invention on the defluorination performance of the route in Example 2; Figure 5 This is a schematic diagram comparing the bulk density of activated powder and dense spherical material provided in the embodiments of the present invention (Example 2 route); Figure 6 This is a schematic diagram of the XRD diffraction pattern of the electrolytic aluminum carbon slag raw material provided in the embodiments of the present invention; Figure 7 This is a schematic diagram of the SEM microstructure of the calcined solid product provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of the FTIR infrared absorption spectrum of the Al2O3 product provided in an embodiment of the present invention. Detailed Implementation

[0020] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, some features described in the examples may be combined in other examples.

[0021] At least one embodiment of the present invention discloses a method for co-processing waste glass powder with electrolytic aluminum carbon slag, which solves the following technical problems in the prior art: The electrolytic aluminum industry inevitably generates a large amount of carbon slag solid waste during production, mainly composed of sodium hexafluoroaluminate (Na3ALF6, mass fraction 40% to 50%) and carbon powder (C, mass fraction 40% to 50%). Fluorides in the carbon slag, if not properly disposed of, can easily leach into the soil and groundwater, and have been classified as hazardous waste. Existing treatment technologies have the following shortcomings: flotation processes are complex, consume large amounts of reagents, and are ineffective at separating fine-grained carbon slag; fluorides escape in a disorderly gaseous state during pyrometallurgical treatment, making flue gas absorption and control difficult and prone to secondary pollution; wet leaching processes are lengthy, involve large volumes of waste liquid, and are difficult to separate fluoride and aluminum. The above methods only address the treatment of carbon slag as a single solid waste, failing to utilize the chemical synergistic effects between different solid wastes. Meanwhile, waste glass powder, mainly composed of silicon dioxide (SiO2), is largely disposed of through landfill due to high remelting energy consumption and complex impurities, failing to achieve high-value utilization of silicon resources. Existing technologies lack a synergistic treatment method for the directional gas-phase transfer of fluorine in Na3ALF6, simultaneous recovery of aluminum resources, and value-added utilization of waste glass powder. Example 1

[0022] This invention discloses a method for co-processing waste glass powder with electrolytic aluminum carbon slag, comprising: Step 1, raw material pretreatment.

[0023] The collected electrolytic aluminum carbon slag is initially crushed in a crushing device, then ground and sieved in a ball mill to obtain electrolytic aluminum carbon slag with a particle size of less than 0.15 mm. If the moisture content of the electrolytic aluminum carbon slag exceeds 3 wt%, it is dried at 80 to 100℃ for 2 to 4 hours to obtain dried carbon slag for later use. The chemical composition of the electrolytic aluminum carbon slag used should meet the following requirements: Na3ALF6 mass fraction of 40% to 50%, carbon powder mass fraction of 40% to 50%, and the remainder being impurity minerals such as CaF2 and MgF2, with a total impurity content not exceeding 15 wt%. The actual mass fraction of Na3ALF6 in the dried carbon slag is quantitatively determined by X-ray fluorescence spectrometry or chemical titration, and the obtained value is recorded as w1 for subsequent batching calculations.

[0024] After waste glass is sorted to remove impurities such as metal and plastic, it is sent to crushing equipment for crushing, then ground in a ball mill, and sieved to a particle size of less than 0.075mm (D). 90 ≤75μm, where D 90 The waste glass powder (corresponding to the particle size of 90% of the particles in the cumulative particle size distribution) is dried at 100 to 120°C for 1 to 2 hours for later use. The actual mass fraction of SiO2 in the waste glass powder is quantitatively determined by X-ray fluorescence spectroscopy or chemical analysis, and the obtained value is recorded as w2 for subsequent batching calculations.

[0025] It should be noted that grinding the two raw materials to the aforementioned particle size requirements aims to increase the solid-phase contact area between Na3ALF6 and SiO2, thereby improving the reaction conversion rate in the subsequent high-temperature calcination stage. The combination of dried carbon slag with a particle size of less than 0.15 mm and waste glass powder with a particle size of less than 0.075 mm is an optimal particle size matching scheme determined based on the differences in hardness and grindability of the two materials. Due to its greater brittleness, waste glass powder is easier to grind finely; using a finer particle size helps to fully expose the reaction interface of waste glass powder as a SiO2 donor in the solid-phase reaction.

[0026] Furthermore, the dust generated during ball milling in the raw material pretreatment process must be handled in a closed environment or equipped with a dust removal device to prevent the spread of fluorine-containing dust; operators must wear dust masks and goggles.

[0027] Step 2: Mix the ingredients.

[0028] Based on w1 and w2 measured in step 1, calculate the theoretical amount of waste glass powder m (unit: g) required per kilogram of dried carbon slag using the following formula: In the formula, m is the theoretical mass of waste glass powder required per kilogram of dried carbon slag, in g; w1 is the mass fraction of Na3ALF6 in the dried carbon slag, substituted as a decimal; w2 is the mass fraction of SiO2 in the waste glass powder, substituted as a decimal; M1 is the molar mass of Na3ALF6, taken as 209.94 g / mol; M2 is the molar mass of SiO2, taken as 60.09 g / mol. This formula is derived based on the stoichiometric relationship of the main reaction in the high-temperature calcination stage, i.e., the molar ratio of Na3ALF6 to SiO2 is 2:3.

[0029] In actual batching, the actual amount of waste glass powder used is 5% to 15% (molar) more than the theoretical amount, that is, the actual molar ratio of SiO2 to Na3ALF6 is controlled between 3.15:2 and 3.45:2, with the preferred molar ratio being 3.24:2 to 3.36:2 (corresponding to an excess of 8% to 12%), in order to ensure the full conversion of Na3ALF6 in the dried carbon slag.

[0030] It should be noted that when the SiO2 excess is less than 5%, some Na3ALF6 may not react completely due to uneven local proportions, resulting in a high residual fluoride content in the solid product; when the SiO2 excess exceeds 15%, the excess SiO2 will enter the subsequent sodium aluminate dissolution process along with the calcined solid product, increasing the burden of filtration and impurity removal.

[0031] Weigh the dried carbon slag and waste glass powder according to the above calculated proportions, and place them in a mixer for dry mixing. The speed should be controlled between 15 and 30 r / min, and the mixing time should not be less than 30 min. The uniformity of mixing is considered acceptable if the relative standard deviation of the mass ratio of SiO2 to Na3ALF6 in the sample test does not exceed 5%, resulting in a homogeneous mixture.

[0032] Step 3, high-temperature calcination.

[0033] The homogeneous mixture obtained in step 2 is loaded into a calcining apparatus and heated according to the following heating procedure: First, the temperature is increased from room temperature to 300°C at a heating rate of 5 to 10°C / min, and held for 20 to 30 minutes to allow the free moisture in the material to fully evaporate; then, the temperature is increased to the target calcination temperature of 850 to 1050°C at a heating rate of 5 to 8°C / min, preferably 900 to 1000°C, and held for 2 to 4 hours to allow the high-temperature solid-phase reaction between Na3ALF6 and SiO2 to proceed fully. The main reaction equation is as follows: It should be noted that within the preferred temperature range of 900 to 1000℃, the solid-state reaction rate between Na3ALF6 and SiO2 achieves a good match with the SiF4 gas escape rate. Below 850℃, the solid-state reaction kinetics are insufficient, and the conversion rate of Na3ALF6 decreases significantly; above 1050℃, the material tends to sinter and agglomerate, which is not conducive to the smooth escape of SiF4 gas.

[0034] During calcination, the carbon powder in the homogeneous mixture undergoes a combustion reaction under aerobic conditions, replenishing the system with heat and helping to reduce external energy consumption. By adjusting the air intake of the calcination equipment, the volume ratio of CO2 to CO in the furnace is maintained between 2:1 and 5:1 to control the carbon powder combustion rate and prevent a sudden rise in furnace temperature that could lead to localized overburning of the material.

[0035] Furthermore, air is introduced during the calcination process as an oxygen supply atmosphere. The amount of air introduced is controlled based on maintaining the CO2 to CO volume ratio in the furnace within the range of 2:1 to 5:1. The composition of the atmosphere in the furnace is monitored in real time by an online gas analyzer, and the opening of the air inlet valve is adjusted accordingly.

[0036] Furthermore, the SiF4 produced during the calcination process is a toxic and corrosive gas. The calcination equipment must be kept sealed during operation, and the operating area must be equipped with a ventilation and exhaust system and a fluorine gas leak alarm device. Operators must wear gas masks and acid and alkali resistant protective gloves.

[0037] The method for determining the calcination endpoint is as follows: when the concentration of SiF4 in the exhaust gas is detected by an online infrared gas analyzer to drop to less than 5% of the initial peak concentration and remain there for more than 10 minutes, the reaction is considered complete; or when X-ray diffraction analysis is performed on the taken solid and it is confirmed that the characteristic diffraction peaks of Na3ALF6 have basically disappeared and the main phase is NaALO2, the reaction is considered complete.

[0038] Furthermore, the conversion rate of Na3ALF6 was determined by quantitative analysis using X-ray diffraction. Based on the intensity of the characteristic diffraction peaks of Na3ALF6 in the dried charcoal slag before calcination, the residual Na3ALF6 content in the solid product after calcination was calculated, and the conversion rate η was calculated using the following formula: In the formula, η is the conversion rate of Na3ALF6; n o n represents the amount of Na3ALF6 in the material before calcination, expressed in mol. r This represents the amount of residual Na3ALF6 in the solid product after calcination, expressed in mol.

[0039] After the reaction is complete, the furnace is cooled to below 200°C, and the solid product is removed. This solid product, with NaAlO2 as its main component, is designated as the calcined solid product and stored in a sealed container for later use. The high-temperature flue gas containing SiF4 generated during the calcination process is introduced into the subsequent flue gas treatment system through a tail gas outlet pipe.

[0040] Furthermore, the atmosphere pressure inside the calcination equipment is maintained at atmospheric pressure during operation, and the furnace body sealing must ensure that the negative pressure inside the furnace does not exceed 500 Pa at the calcination temperature to prevent the disorderly leakage of fluorine-containing flue gas.

[0041] Step 4, flue gas treatment.

[0042] The high-temperature flue gas containing SiF4 generated in step 3 is introduced into a cyclone dust collector through a high-temperature resistant pipe to remove solid dust particles carried in the flue gas. After dust removal, the flue gas is cooled to 150 to 200°C by a heat exchanger and then enters the alkaline solution spray absorption system.

[0043] The alkaline spray absorption system uses sodium hydroxide (NaOH) aqueous solution as the absorption medium, with an initial NaOH mass fraction of 10% to 20%. The liquid-to-gas ratio is controlled at 3 to 8 L / m³ (the ratio of liquid volume to flue gas volume). During the absorption process, the pH value of the circulating alkaline solution should be maintained between 8 and 12. When the pH of the circulating solution falls below 8, NaOH solution should be added promptly. SiF4 reacts with the NaOH solution in the following absorption reaction: The flue gas also contains CO2 (originating from carbon powder combustion). CO2 reacts with NaOH solution to form sodium carbonate (Na2CO3), which consumes some NaOH and interferes with the subsequent separation of sodium fluoride (NaF) and sodium silicate (Na2SiO3). The actual amount of NaOH used should comprehensively consider the total amount of SiF4 and CO2 in the flue gas, and should be 20% to 30% (molar) in excess of the theoretical requirement. If necessary, an appropriate amount of calcium hydroxide (Ca(OH)2) can be added to the absorbent to allow Na2CO3 to react with Ca(OH)2 to form calcium carbonate (CaCO3), which can then be removed by filtration. The amount of Ca(OH)2 added should be such that the molar ratio of Na2CO3 to Ca(OH)2 in the absorbent is 1:1 to 1:1.2. An online pH meter and fluoride detector are installed at the outlet of the absorption tower to ensure that the fluoride concentration in the emitted flue gas meets the relevant environmental protection standards.

[0044] Furthermore, when adding Ca(OH)2 to the absorbent, it must be done under alkaline conditions with a pH higher than 9 to prevent the formation of calcium fluoride (CaF2) precipitate in the absorbent under locally over-acidic conditions, which would entrain NaF and lead to its loss. Ca(OH)2 should be added slowly in suspension form, with the addition rate preferably such that the pH of the absorbent changes by no more than 0.3 units per minute. The stirring speed should be controlled at 100 to 200 r / min. After the addition is complete, continue stirring for 15 to 30 minutes, filter to remove the CaCO3 precipitate, and return the filtrate to the absorption circulation system.

[0045] Furthermore, NaOH is a highly alkaline and corrosive substance. When preparing and using NaOH solutions, operators must wear alkali-resistant protective gloves and goggles; eyewash stations and showers must be installed around the alkaline solution spray absorption system.

[0046] After the above absorption reaction, a mixed absorption liquid containing NaF and Na2SiO3 is obtained, which is used for product separation in step 5.

[0047] Furthermore, the operating temperature of the alkaline spray absorption system is controlled between 40 and 60°C to maintain the absorption efficiency of the NaOH solution for SiF4; the residence time of the flue gas in the absorption tower is not less than 3 seconds to ensure that the absorption reaction is fully completed.

[0048] Furthermore, the fluorine-containing solid dust collected by the cyclone dust collector is hazardous waste and must be collected separately and disposed of by a professional hazardous waste treatment agency. It must not be directly discharged or mixed with general solid waste.

[0049] Step 5: Separation of sodium fluoride and sodium silicate.

[0050] The mixed absorbent obtained in step 4 is fed into an evaporation crystallization apparatus and concentrated at 80 to 90°C, so that the NaF concentration in the mixed absorbent exceeds its solubility at that temperature (the solubility of NaF in water is approximately 4.0 to 4.3 g / 100 mL, with a small variation with temperature), causing NaF to precipitate in solid crystal form. The concentrated solution is then cooled to 20 to 30°C to promote further NaF crystallization, with the cooling rate controlled at 0.5 to 2°C / min, resulting in a suspension containing NaF crystals.

[0051] The suspension containing NaF crystals was centrifuged at 1500 to 3000 r / min for 10 to 20 min to separate the NaF solid from the mother liquor containing Na2SiO3. The obtained NaF solid was washed 1 to 2 times with a small amount of cold pure water, and the wash water was added to the mother liquor. The NaF solid was dried in an oven at 80 to 100 °C for 2 to 3 h to obtain the NaF product.

[0052] Furthermore, the purity of the NaF product was determined using ion chromatography, with F... - and Na + The mass fraction of NaF was calculated from the chromatographic peak area.

[0053] Furthermore, NaF is a toxic substance. When handling solid NaF, protective gloves and dust masks must be worn to avoid inhaling dust or ingesting it through skin contact. NaF products must be stored in sealed containers with a toxic warning label.

[0054] It should be noted that the above separation process utilizes the significant difference in solubility between NaF and Na2SiO3 in water: NaF has low solubility in water and its solubility changes little with temperature, while Na2SiO3 has high solubility. During the evaporation and concentration process, NaF preferentially crystallizes out, thereby achieving effective separation of the two.

[0055] The separated mother liquor is a sodium silicate solution rich in Na2SiO3. After filtration to remove trace suspended solids, it can be used directly as a liquid sodium silicate product, or it can be further evaporated and concentrated to a SiO2 to Na2O molar ratio of 2.0:1 to 3.5:1 and a Baume degree of 35 to 50°Bé, and then used as a liquid water glass product.

[0056] Furthermore, the molar ratio of SiO2 to Na2O in the liquid water glass product was determined by chemical titration, and the Baumé degree was determined by a Baumé hydrometer at 20°C.

[0057] Furthermore, the fluoride-containing washing wastewater generated during the evaporation, crystallization, and centrifugation processes must be collected and returned to the absorption and recycling system for reuse, and must not be directly discharged.

[0058] Step 6: Dissolution of sodium aluminate and preparation of alumina.

[0059] The calcined solid product obtained in step 3 is added to pure water at a liquid-to-solid ratio of 5:1 to 10:1 (mL:g). The mixture is stirred at 50 to 80°C for 30 to 60 minutes at a stirring speed of 200 to 400 r / min to dissolve NaAlO2 in the calcined solid product, forming a sodium aluminate solution. The pH of the solution is typically between 12 and 14. The solution is then filtered to remove insoluble solid impurities such as CaF2, yielding the sodium aluminate solution.

[0060] Furthermore, the CaF2-containing insoluble solid impurities removed by filtration are fluorine-containing solid wastes, which must be collected separately and disposed of by a professional hazardous waste treatment agency.

[0061] The aluminum component in sodium aluminate solution can be recovered by precipitation using one of the following two methods.

[0062] One method is carbonation decomposition: CO2 gas is introduced into the sodium aluminate solution, and the rate of CO2 introduction is controlled to gradually reduce the pH of the sodium aluminate solution from above 12 to 9 to 10, resulting in a large amount of AL(OH)3 precipitating out.

[0063] Furthermore, during the carbonation decomposition process, the CO2 introduction rate was controlled at 0.1 to 0.5 L / (min·L solution), the solution temperature was maintained at 40 to 60℃, and the pH was monitored in real time using an online pH meter. When the pH dropped to 9 to 10, the CO2 introduction was stopped.

[0064] The second method is acid precipitation: Slowly add 10% to 15% (w / w) dilute hydrochloric acid or 10% to 15% (w / w) dilute sulfuric acid to the sodium aluminate solution while stirring. Gradually lower the pH of the sodium aluminate solution to 7 to 9, causing Al(OH)3 to precipitate. During the acid addition process, the pH must be strictly controlled to not fall below 4 to prevent Al(OH)3 from dissolving due to excessive acidity. The volume ratio of dilute hydrochloric acid or dilute sulfuric acid to the sodium aluminate solution is 1:5 to 1:20.

[0065] Furthermore, during the acid precipitation process, dilute hydrochloric acid or dilute sulfuric acid is slowly added dropwise to the sodium aluminate solution, rather than adding the sodium aluminate solution directly to the acid, to avoid local over-acidity that could lead to the dissolution of Al(OH)3; the stirring speed is controlled at 150 to 300 r / min, the acid addition rate is preferably such that the pH of the sodium aluminate solution decreases by no more than 0.5 units per minute, the solution temperature is maintained at 20 to 40℃, and the pH is monitored in real time using an online pH meter.

[0066] Furthermore, dilute hydrochloric acid and dilute sulfuric acid are corrosive acidic reagents, and acid-resistant protective gloves and goggles must be worn during operation, and the operation must be carried out in a well-ventilated environment.

[0067] The precipitate of Al(OH)3 was collected by filtration, washed with pure water until the conductivity of the washing solution was below 200 μS / cm, dried in an oven at 105℃ to constant weight, and then calcined at 1100 to 1200℃ for 2 to 3 hours to completely dehydrate and decompose the Al(OH)3. After cooling, the AL2O3 product is obtained.

[0068] Furthermore, the purity of the AL2O3 product was determined by X-ray fluorescence spectroscopy, and the product quality was characterized by the mass fraction of AL2O3.

[0069] Furthermore, to improve the purity of the AL2O3 product, a deep purification step can be added after filtration of the sodium aluminate solution: Sodium sulfide (Na2S) solution is added to the sodium aluminate solution, with the amount of Na2S solution added being 0.1% to 0.5% of the volume of the sodium aluminate solution, and the mass fraction of Na2S being 5% to 10%. The stirring speed is controlled at 150 to 300 r / min, and stirring is performed for 30 min to remove trace heavy metal ions (such as Fe) from the sodium aluminate solution. 3+ Cu 2+ (etc.) precipitate as sulfide precipitates, which are then removed by filtration and followed by carbonation decomposition or acid precipitation.

[0070] Furthermore, the Na2S solution must be added under alkaline conditions (pH above 10) to prevent Na2S from decomposing and producing toxic hydrogen sulfide (H2S) gas under slightly acidic conditions. This step must be carried out in a well-ventilated, closed operating environment, and operators must wear respirators and protective gloves. Residual sulfides in the waste liquid must be oxidized (by adding an appropriate amount of hydrogen peroxide (H2O2) until the sulfide concentration is below 0.5 mg / L) before being discharged.

[0071] Furthermore, the heavy metal sulfide precipitates removed by the deep impurity removal process are hazardous waste and must be collected separately in sealed containers and disposed of by a professional hazardous waste treatment facility.

[0072] Furthermore, the alkaline waste liquid containing sodium chloride or sodium sulfate generated by the acid precipitation method can be discharged into the sewage treatment system as industrial wastewater after neutralization and pH adjustment to 6 to 9; the sodium carbonate-containing waste liquid generated by the carbonation decomposition method can be recycled or neutralized before being discharged. Example 2

[0073] Based on the synergistic processing method described in Example 1, this example further provides solutions to the following engineering implementation problems: In conventional mechanical mixing processes, the dry carbon slag and waste glass powder particles only have micron-level contact, resulting in a limited solid-phase reaction interface, requiring a higher calcination temperature to achieve a full reaction; the low-density powder obtained after activation has insufficient effective processing capacity in continuous production equipment due to its low bulk density, and the powder is easily lifted by airflow, causing material loss; in traditional water-addition granulation methods, the capillary action of water will destroy the uniform dispersion structure inside the powder, reducing the reactivity.

[0074] This embodiment achieves nanoscale uniform mixing of dried carbon slag and waste glass powder through ultrasonic spray freeze-drying process, combined with temporary densification granulation of low melting point paraffin wax, and continuously feeds the resulting dense spherical material into a rotary kiln for carbothermal activation and defluorination reaction. While solving the problem of low-density activated powder being difficult to continuously feed into the kiln, the carbothermal activation temperature is controlled at 900 to 1100°C, and efficient continuous defluorination is achieved in the temperature range of 600 to 800°C.

[0075] Step 1, raw material pretreatment.

[0076] The electrolytic aluminum carbon slag is crushed and ground to a particle size of less than 0.075 mm. If the moisture content of the electrolytic aluminum carbon slag exceeds 3 wt%, it is dried at 80 to 100 °C for 2 to 4 hours to obtain dried carbon slag for later use. The chemical composition of the dried carbon slag is required to be the same as in Example 1, that is, the mass fraction of Na3ALF6 is 40% to 50%, the mass fraction of carbon powder is 40% to 50%, and the total impurity content does not exceed 15 wt%. The actual mass fraction of Na3ALF6 in the dried carbon slag is determined by X-ray fluorescence spectrometry or chemical titration and recorded as w1.

[0077] Waste glass is sorted to remove impurities such as metal and plastic, then crushed and ground to a particle size of less than 0.075 mm. It is then dried at 100-120℃ for 1-2 hours to obtain waste glass powder for later use. The actual mass fraction of SiO2 in the waste glass powder is determined using X-ray fluorescence spectroscopy or chemical analysis, and denoted as w2.

[0078] Step 2, ultrasonic dispersion and suspension preparation.

[0079] Based on 100 parts by weight of dried carbon slag, the dried carbon slag was dispersed in anhydrous ethanol (analytical grade, purity ≥99.5%, water content ≤0.1%) and a suspension of dried carbon slag was prepared at a liquid-solid ratio of 10:1 to 20:1 (mL:g). The suspension was placed in an ultrasonic dispersion device and ultrasonically treated for 30 to 60 minutes at an ultrasonic frequency of 20 to 40 kHz and a power density of 50 to 150 W / L to fully deagglomerate the dried carbon slag particles.

[0080] Based on w1 and w2, calculate the theoretical amount of waste glass powder according to the formula described in step 2 of Example 1, controlling the actual molar ratio of SiO2 to Na3ALF6 to be 3.15:2 to 3.45:2. The required amount of waste glass powder is 80 to 140 parts by mass (based on 100 parts by mass of dried carbon residue). Disperse the waste glass powder in anhydrous ethanol using the same method, prepare a waste glass powder suspension at a liquid-to-solid ratio of 10:1 to 20:1 (mL:g), and sonicate for 30 to 60 minutes.

[0081] The dried carbon slag suspension and the waste glass powder suspension are transferred to a mixing container and stirred for 15 to 30 minutes at a stirring speed of 200 to 400 r / min to obtain a mixed suspension.

[0082] It should be noted that anhydrous ethanol is used as the dispersion medium instead of water because Na3ALF6 is only slightly soluble in water. Using water as a dispersion medium might cause partial dissolution of Na3ALF6, which could then segregate during the subsequent drying process, disrupting the mixing homogeneity. Anhydrous ethanol is insoluble in both Na3ALF6 and SiO2, thus maintaining the uniformity of the solid particles' dispersion.

[0083] Furthermore, anhydrous ethanol is a flammable liquid (flash point 13°C). Ultrasonic dispersion and suspension preparation operations must be carried out in a fume hood or explosion-proof ventilation environment, away from open flames and heat sources; the operation area must be equipped with explosion-proof electrical equipment and dry powder fire extinguishers; operators must wear anti-static work clothes.

[0084] Step 3: Ultrasonic spray freeze drying.

[0085] The mixed suspension obtained in step 2 was sprayed into a liquid nitrogen freezing chamber using an ultrasonic spraying device (nozzle frequency 1.5 to 2.5 MHz) with droplet diameters of 20 to 80 μm. The mixed suspension droplets instantly solidified into frozen microspheres. The frozen microspheres were collected and placed in a freeze-drying device and dried for 8 to 16 hours at a temperature below -40°C and a vacuum degree below 50 Pa. Anhydrous ethanol was removed by sublimation to obtain porous microsphere powder that maintained a uniform nanoscale mixing state.

[0086] Furthermore, the ethanol vapor recovered during the ultrasonic spray freeze-drying process is condensed and collected, and the purity of the recovered ethanol is detected by gas chromatography. When the water content in the recovered ethanol does not exceed 0.5 wt%, it can be recycled for the preparation of the suspension in step 2 to reduce solvent consumption.

[0087] Furthermore, cryogenic protective gloves and goggles must be worn during liquid nitrogen freezing operations to prevent frostbite caused by liquid nitrogen splashes; ethanol vapor recovered during freeze-drying must be introduced into a condensation recovery device through a closed pipeline and is prohibited from being directly discharged into the atmosphere.

[0088] It should be noted that the ultrasonic spray freeze-drying step fixes the spatial distribution of particles in the mixed suspension by instantaneous freezing, avoiding particle migration and aggregation caused by solvent evaporation during conventional evaporation drying. This results in porous microsphere powder with Na3ALF6 and SiO2 particles uniformly mixed at the nanoscale. This uniform mixing significantly increases the reaction interface area in the subsequent carbothermal activation stage, which is beneficial for reducing the activation temperature.

[0089] Step 4: Carbothermic activation under nitrogen protection.

[0090] The porous microsphere powder obtained in step 3 is placed in an atmosphere furnace, and high-purity nitrogen (purity ≥99.99%) is introduced as a protective atmosphere. The nitrogen flow rate is controlled at 0.5 to 2.0 L / min (per 100g of porous microsphere powder). The temperature is increased to 900 to 1100℃ at a heating rate of 10 to 15℃ / min, preferably 950 to 1050℃, and held for 30 to 60 min, preferably 40 to 50 min, for carbothermic activation.

[0091] Furthermore, before starting carbothermal activation, high-purity nitrogen must be introduced into the atmosphere furnace to replace the air inside the furnace for at least 10 minutes. The heating process can only begin after confirming that the oxygen content inside the furnace is below 100 ppm, in order to prevent premature oxidation and consumption of the carbon powder during the heating process.

[0092] It should be noted that carbothermal activation utilizes the partial reduction of SiO2 surface by carbon powder in porous microspheres under a high-temperature nitrogen protective atmosphere, creating oxygen vacancy defects on the SiO2 lattice surface, thereby reducing the activation energy required for the reaction between SiO2 and Na3ALF6 in the subsequent defluorination stage. The role of the high-purity nitrogen protective atmosphere is to prevent the carbon powder from being oxidized and consumed during this stage.

[0093] Furthermore, the exhaust gas emitted from the atmosphere furnace during the carbothermic activation process may contain trace amounts of carbon monoxide (CO), which must be introduced into the ventilation and exhaust system through the exhaust gas pipeline or treated by the catalytic combustion device before being discharged. The operating area must be equipped with a CO concentration detection alarm.

[0094] After activation, the powder is cooled to room temperature in the furnace at a rate not exceeding 10°C / min. During the cooling process, high-purity nitrogen is continuously introduced to maintain a protective atmosphere until the furnace temperature drops below 200°C. The activated powder is then removed and stored in a sealed container for later use. The bulk density of the activated powder is typically 0.1 to 0.3 g / cm³, classifying it as an ultralight powder.

[0095] Step 5: Paraffin coating and granulation.

[0096] The activated powder obtained in step 4 is placed in a sealed mixer, and 5 to 12 parts by mass of low-melting-point paraffin are added based on 100 parts by mass of activated powder. The low-melting-point paraffin used is a mixture of n-alkanes with a melting point of 50 to 60°C, a kinematic viscosity (at 100°C) of 3 to 6 mm² / s, and a carbon number distribution of C0.05. 20 To C 35 Heat to 65 to 75°C until the low-melting-point paraffin is completely melted, then stir at a low speed of 15 to 30 r / min for 10 to 20 minutes to ensure the molten low-melting-point paraffin uniformly coats the outer surface of the activated powder particles to form a thin film. Stop heating and allow to cool naturally to room temperature. After the low-melting-point paraffin solidifies, it binds the activated powder particles into dense granules.

[0097] Add 3 to 6 parts by weight of bentonite (sodium bentonite, montmorillonite content ≥85%, blue absorption ≥30 g / 100g) and 8 to 12 parts by weight of anhydrous ethanol (based on 100 parts by weight of activated powder) to dense agglomerates, and granulate in a granulator at a speed of 20 to 40 r / min for 10 to 20 min to obtain spherical particles with a particle size of 3 to 8 mm. After drying in an oven at 40 to 60 °C for 1 to 2 h to evaporate the anhydrous ethanol, a dense spherical material with a bulk density of 0.6 to 1.0 g / cm³ is obtained.

[0098] It should be noted that low-melting-point paraffin wax is used as a temporary binder instead of the traditional water-based granulation method because it coats the particle surface as a non-polar film, without generating capillary forces. This prevents the uniformly dispersed Na3ALF6 and SiO2 particles from migrating and agglomerating due to liquid bridging. The low-melting-point paraffin wax can be completely pyrolyzed and vaporized in the subsequent rotary kiln preheating section (250 to 400°C), restoring the porous structure within the particles while maintaining the original nanoscale mixing uniformity. The addition of bentonite provides inorganic skeletal support for the particles, preventing their collapse after the pyrolysis of the low-melting-point paraffin wax.

[0099] Furthermore, anhydrous ethanol is a flammable liquid used in the granulation process, and the operation must be carried out in a well-ventilated environment, away from open flames and high-temperature heat sources; the ethanol vapors volatilized during oven drying must be led outdoors through exhaust pipes or treated by activated carbon adsorption devices before being discharged.

[0100] Step 6: Continuous defluorination in the rotary kiln.

[0101] The dense spherical material obtained in step 5 is continuously fed into the rotary kiln at a feed rate of 30 to 150 kg / h. The rotational speed of the rotary kiln is controlled at 1 to 3 r / min, and the tilt angle is 2 to 4°. The rotary kiln is divided into the following three sections along its length: Step 6.1, Preheating Section: The temperature is controlled between 250 and 400℃, accounting for 20% to 25% of the kiln length. During the residence of dense spherical materials in the preheating section, the low-melting-point paraffin wax is removed through pyrolysis and gasification, the porous structure inside the particles is restored, and the shape is maintained by the bentonite skeleton. The material exiting the preheating section should be in a loose, porous spherical particle state. The criterion for judging the completion of low-melting-point paraffin wax pyrolysis is that the mass loss of the sampled particles after burning at 500℃ does not exceed 0.5wt%.

[0102] Furthermore, the atmosphere in the preheating section is air, and the ventilation volume is controlled at 20 to 50 m³ / h (per ton of material) to ensure the smooth discharge of low-melting-point paraffin pyrolysis products. The flue gas at the outlet of the preheating section is led to the exhaust gas treatment system through an independent pipeline.

[0103] Furthermore, the organic waste gas generated by the pyrolysis of paraffin in the preheating section must be treated by a catalytic combustion device or an activated carbon adsorption device in the tail gas treatment system before it can be discharged, and the emission concentration must meet the requirements of the volatile organic compound emission standards.

[0104] Step 6.2, Reaction Section: The temperature is controlled at 600 to 800℃, preferably 650 to 750℃, accounting for 55% to 65% of the kiln length. The material residence time in this section is 1.5 to 3 hours. Air is introduced into the reaction section, controlling the oxygen content within the reaction section to be 5% to 12% (volume fraction). After the loose porous spherical particles discharged from the preheating section enter the reaction section, Na3ALF6 reacts with carbothermally activated SiO2 to undergo a defluorination reaction. The main reaction is the same as described in Step 3 of Example 1, and the generated SiF4 gas continuously escapes from the gaps between the particles. The residual carbon powder burns under aerobic conditions to provide supplementary heat for the reaction.

[0105] Furthermore, the air in the reaction section is introduced through multiple air inlets evenly arranged along the length of the kiln, with the distance between the air inlets being 10% to 15% of the kiln length. This ensures that the oxygen content in the reaction section is evenly distributed within the range of 5% to 12% (volume fraction), avoiding localized oxygen deficiency or over-oxygenation.

[0106] Furthermore, the SiF4-containing flue gas generated in the reaction section must be promptly discharged to the flue gas treatment system through a closed pipeline. The sealing of the rotary kiln head and kiln tail must be checked regularly to prevent the leakage of fluorine-containing flue gas into the operating environment.

[0107] It should be noted that the reaction temperature in this embodiment (600 to 800°C) is about 200 to 250°C lower than the calcination temperature (850 to 1050°C) in Example 1. This is because after ultrasonic spray freeze-drying in step 3 and carbothermal activation in step 4, the solid-phase contact area between Na3ALF6 and SiO2 increases significantly and the surface activity of SiO2 is enhanced, which reduces the starting temperature and completion temperature of the defluorination reaction accordingly.

[0108] Step 6.3, Cooling Section: This section comprises 15% to 20% of the kiln length. The material cools naturally in this section and is discharged from the kiln tail, yielding the rotary kiln solid product. The outlet temperature of the material in the cooling section should not exceed 200℃. The rotary kiln solid product is primarily composed of NaAlO2. X-ray diffraction analysis confirms the near disappearance of the characteristic diffraction peaks of Na3ALF6, indicating the defluorination reaction is complete.

[0109] Furthermore, the conversion rate of Na3ALF6 was determined by quantitative analysis using X-ray diffraction, and the calculation method was the same as described in step 3 of Example 1.

[0110] Step 7, flue gas treatment.

[0111] The SiF4-containing flue gas generated in step 6 is treated by a cyclone dust collector to remove dust particles, then cooled to 150-200°C by a heat exchanger before entering the alkaline spray absorption system. The alkaline spray absorption system uses NaOH aqueous solution as the absorption medium, with an initial NaOH mass fraction of 10%-20%, a liquid-to-gas ratio controlled at 3-8 L / m³, and the pH of the circulating alkaline solution maintained between 8 and 12. The absorption reaction is the same as described in step 4 of Example 1. The treatment of NaOH consumption and Na2CO3 interference by CO2 in the flue gas is the same as in step 4 of Example 1, including adding 20%-30% excess NaOH (molar amount) based on the theoretical requirement and, if necessary, supplementing with Ca(OH)2. The addition of Ca(OH)2 must be carried out under conditions where the pH of the circulating alkaline solution is higher than 9, and the operation method is the same as described in step 4 of Example 1. After absorption treatment, a mixed absorbent containing NaF and Na2SiO3 is obtained.

[0112] Furthermore, the operating temperature of the alkaline spray absorption system is controlled between 40 and 60°C, and the residence time of the flue gas in the absorption tower is no less than 3 seconds to ensure that the absorption reaction is fully completed.

[0113] Furthermore, the fluorine-containing solid dust collected by the cyclone dust collector must be collected separately and disposed of by a professional hazardous waste treatment agency.

[0114] Step 8: Dissolution of solid product and preparation of alumina.

[0115] The solid product discharged from the cooling section in step 6 is crushed to a particle size of less than 5 mm, and then added to pure water at a liquid-to-solid ratio of 8:1 to 12:1 (mL:g). The mixture is stirred at 60 to 80°C for 40 to 60 minutes at a stirring speed of 200 to 400 r / min to dissolve the NaAlO2 in the solid product, forming a sodium aluminate solution. The insoluble solid residue containing bentonite is removed by filtration to obtain the sodium aluminate solution.

[0116] Furthermore, trace amounts of fluoride may remain in the filter residue containing bentonite-insoluble solids removed by filtration. It is necessary to confirm whether it belongs to hazardous waste through leaching toxicity testing. If the concentration of fluoride ions in the leachate exceeds the standard, it must be disposed of by a professional hazardous waste treatment agency.

[0117] CO2 gas is introduced into the sodium aluminate solution, and the rate of CO2 introduction is controlled to gradually reduce the pH of the sodium aluminate solution from above 12 to 9 to 10, causing Al(OH)3 to precipitate out.

[0118] Furthermore, during the carbonation decomposition process, the CO2 introduction rate was controlled at 0.1 to 0.5 L / (min·L solution), the solution temperature was maintained at 40 to 60℃, and the pH was monitored in real time using an online pH meter. When the pH dropped to 9 to 10, the CO2 introduction was stopped.

[0119] The AL(OH)3 precipitate was collected by filtration, washed with pure water until the conductivity of the washing solution was below 200 μS / cm, dried in an oven at 105°C to constant weight, and then calcined at 1100 to 1200°C for 2 to 3 hours. After cooling, the AL2O3 product was obtained. The calcination dehydration reaction was the same as described in step 6 of Example 1.

[0120] Furthermore, the purity of the AL2O3 product was determined by X-ray fluorescence spectroscopy, and the product quality was characterized by the mass fraction of AL2O3.

[0121] Step 9: Separation of sodium fluoride and sodium silicate.

[0122] The mixed absorbent obtained in step 7 was separated according to the method described in step 5 of Example 1: NaF was crystallized and concentrated by evaporation at 80 to 90°C, and then cooled to 20 to 30°C to promote further crystallization at a cooling rate of 0.5 to 2°C / min. The NaF solid and mother liquor were separated by centrifugation at 1500 to 3000 r / min for 10 to 20 min. The NaF solid was washed 1 to 2 times with cold pure water and then dried in an oven at 80 to 100°C for 2 to 3 h to obtain the NaF product. The mother liquor was filtered and then evaporated and concentrated to a SiO2 to Na2O molar ratio of 2.0:1 to 3.5:1 and a Baume degree of 35 to 50°Bé to obtain the liquid water glass product.

[0123] Furthermore, the purity of the NaF product was determined using ion chromatography, with F... - and Na + The mass fraction of NaF was calculated from the chromatographic peak area; the molar ratio of SiO2 to Na2O in the liquid water glass product was determined by chemical titration, and the Baumé degree was determined by a Baumé hydrometer at 20℃.

[0124] Furthermore, the fluoride-containing washing wastewater generated during the evaporation, crystallization, and centrifugation processes must be collected and returned to the absorption and recycling system for reuse, and must not be directly discharged.

[0125] This invention utilizes the synergistic high-temperature calcination of electrolytic aluminum slag and waste glass powder. The solid-phase chemical reaction between SiO2 in the waste glass powder and Na3ALF6 in the dried slag under high-temperature conditions causes fluorine to migrate directionally from the solid phase to the gas phase in the form of SiF4 gas, achieving complete separation of fluorine and aluminum at the solid-phase level. Because fluorine is transferred in a single gaseous form of SiF4, unlike existing technologies where fluorides are randomly volatilized in multiple forms such as HF, subsequent flue gas treatment only requires alkaline absorption of SiF4, simplifying the process control path.

[0126] In the calcination process, the carbon powder in the dried charcoal slag undergoes controlled combustion. By adjusting the air intake, the volume ratio of CO2 to CO in the furnace is maintained within the range of 2:1 to 5:1. The heat released from the combustion of carbon powder is supplemented to the main reaction system, reducing the need for external energy supply. After SiO2 in the waste glass powder participates in the solid-phase reaction, it enters the liquid phase as Na2SiO3. After separation and concentration, liquid water glass is obtained, transforming waste glass powder from landfill waste into industrial raw materials.

[0127] Through alkaline absorption and separation processes, fluorine is recovered as solid NaF, silicon as liquid Na2SiO3, and aluminum as Al2O3, with each element producing independent output products. This method requires no large amounts of external chemical reagents and generates relatively little waste liquid. By controlling the calcination temperature to 850–1050℃, the SiO2 excess to 5%–15% (molar), and maintaining the alkaline solution pH at 8–12, Na3ALF6 in the dried carbon slag is fully converted, reducing the residual fluoride content in the solid products and eliminating the environmental risk of fluoride leakage from the electrolytic aluminum carbon slag.

[0128] Furthermore, the overall process of this invention generates relatively little waste liquid. The alkaline absorption system operates in a recycling mode, and all fluoride-containing washing wastewater is returned to the system for reuse. Fluoride-containing dust and heavy metal sulfide precipitates in the solid waste are disposed of by specialized institutions. The waste gas meets emission standards after alkaline absorption, achieving effective control of the three wastes. Simultaneously, this invention uses two types of solid waste as raw materials for synergistic treatment. The heat from carbon powder combustion is used to supplement reaction energy consumption, and waste glass powder is converted into liquid water glass. The overall process has high raw material utilization and low external reagent consumption, demonstrating the environmental advantages of synergistic resource utilization of solid waste.

[0129] In Example 2, ultrasonic spray freeze-drying was used to improve the uniformity of solid-phase contact between Na3ALF6 and SiO2 to the nanoscale. Subsequent carbothermic activation created oxygen vacancy defects on the SiO2 surface, lowering the activation energy and consequently reducing the onset and completion temperatures of the solid-phase reaction. The defluorination reaction temperature range decreased from 850-1050℃ to 600-800℃. Temporary densification granulation with low-melting-point paraffin increased the bulk density of the activated powder from 0.1-0.3 g / cm³ to 0.6-1.0 g / cm³, solving the problem of continuously feeding low-density activated powder into the rotary kiln and providing a feasible engineering path for the continuous production of this co-processing method.

[0130] Furthermore, the anhydrous ethanol used in Example 2 was recycled after freeze-drying and condensation recovery, which significantly reduced solvent consumption; the temperature of the reaction section was reduced by about 200 to 250°C, which reduced the energy consumption per unit product and further demonstrated the environmental advantages of energy saving and emission reduction.

[0131] Example 1 The route of Example 1 was adopted, operating with the minimum endpoint parameter set. Electrolytic aluminum slag with a moisture content of 4.2 wt% was dried at 80°C for 2 hours, then ground in a ball mill and sieved to a particle size less than 0.15 mm to obtain dried slag. X-ray fluorescence spectroscopy analysis showed that the dried slag contained Na3AlF6 with a mass fraction w1 = 0.40%, carbon powder with a mass fraction of 40%, and the remainder consisted of impurity minerals such as CaF2 and MgF2, with a total impurity content not exceeding 15 wt%. Waste glass was sorted, crushed, and ball-milled to D... 90 ≤75μm, dried at 100℃ for 1h, yielded waste glass powder. X-ray fluorescence spectrometry determined the SiO2 mass fraction w2 in the waste glass powder to be 0.72.

[0132] According to the formula Where m is the theoretical amount of waste glass powder required per kilogram of dried carbon slag (g), W1 is the mass fraction of Na3ALF6 in the dried carbon slag, w2 is the mass fraction of SiO2 in the waste glass powder, M1 is the molar mass of Na3ALF6 (209.94 g / mol), and M2 is the molar mass of SiO2 (60.09 g / mol). Calculate the theoretical amount of waste glass powder required per kilogram of dried carbon slag: The actual molar ratio of SiO2 to Na3ALF6 was set to 3.15:2 (5% excess), and the actual amount of waste glass powder used was 249.7 g / kg of dry carbon residue. 1000 g of dry carbon residue and 249.7 g of waste glass powder were dry-mixed in a mixer at 15 r / min for 30 min. A sample was taken to test the relative standard deviation of the mass ratio of SiO2 to Na3ALF6, which was 3.8%, less than 5%, indicating uniform mixing.

[0133] The homogeneous mixture was loaded into a muffle furnace and heated from room temperature to 300°C at a rate of 5°C / min, holding at that temperature for 20 min. Then, the temperature was increased to 850°C at a rate of 5°C / min and held for 2 h. During calcination, the air intake was adjusted to maintain a CO2 to CO volume ratio of 2:1. After calcination, heating was stopped when the concentration of SiF4 in the exhaust gas detected by an online infrared gas analyzer dropped below 5% of the initial peak value and remained there for 10 min. The temperature was then lowered to below 200°C, and the calcined solid product was removed. Quantitative X-ray diffraction analysis showed that the conversion rate of Na3ALF6 was η = 91.2%.

[0134] High-temperature flue gas containing SiF4 is precipitated by a cyclone separator, cooled to 150°C, and then enters an alkaline solution spray absorption system. The initial NaOH mass fraction is 10%, the liquid-to-gas ratio is 3 L / m³, the pH of the circulating alkaline solution is maintained between 8 and 12, the operating temperature is 40°C, and the NaOH dosage is 20% excess (molarly) based on the theoretical requirement. After absorption, a Ca(OH)2 suspension is added to the absorbent at a Na2CO3 to Ca(OH)2 molar ratio of 1:1, with stirring at 100 r / min. Stirring continues for 15 min, and the CaCO3 precipitate is removed by filtration, yielding a mixed absorbent containing NaF and Na2SiO3.

[0135] The mixed absorbent was evaporated and concentrated at 80℃ until NaF precipitated. It was then cooled to 20℃ at a rate of 0.5℃ / min, and the NaF solid was separated by centrifugation at 1500 r / min for 10 min. After washing twice with cold pure water, it was dried at 80℃ for 2 h to obtain the NaF product, with a purity of 97.3% determined by ion chromatography. The mother liquor was evaporated and concentrated to a SiO2 to Na2O molar ratio of 2.0:1 and a Baume degree of 35°Bé to obtain the liquid water glass product.

[0136] The calcined solid product was added to pure water at a liquid-to-solid ratio of 5:1 (mL:g), and stirred at 200 r / min for 30 min at 50℃ to dissolve. The solution was then filtered to remove insoluble solid impurities, yielding a sodium aluminate solution (pH approximately 13.2). 0.1% (by volume) Na₂S solution (5% by mass) was added to the sodium aluminate solution, and the mixture was stirred at 150 r / min for 30 min. The solution was then filtered to remove heavy metal sulfide precipitates. Following the acid precipitation route: 10% (by mass) dilute hydrochloric acid was slowly added dropwise to the sodium aluminate solution at a volume ratio of 1:5, while stirring at 150 r / min. The solution temperature was maintained at 20℃, and acid addition was stopped when the pH dropped to 9. The Al(OH)₃ precipitate was collected by filtration, washed with pure water until the conductivity of the washing solution was below 200 μS / cm, dried at 105℃ to constant weight, and calcined at 1100℃ for 2 h to obtain the Al₂O₃ product. The purity was determined to be 97.1% by X-ray fluorescence spectrometry.

[0137] Example 2 The route of Example 1 was followed, operating with the maximum endpoint parameter group. Electrolytic aluminum carbon slag with a moisture content of 3.5 wt% was taken, dried at 100°C for 4 hours, ground in a ball mill, and sieved to a particle size of less than 0.15 mm to obtain dried carbon slag. X-ray fluorescence spectrometry determined W1=0.50, indicating a carbon powder mass fraction of 50%. Waste glass fragments were ball-milled to D90≤75μm, dried at 120°C for 2 hours, and X-ray fluorescence spectrometry determined W2=0.72 (from the same batch of waste glass powder as in Example 1).

[0138] Theoretical amount of waste glass powder required per kilogram of dried carbon residue: The actual molar ratio of SiO2 to Na3ALF6 was set to 3.45:2 (15% excess), and the actual amount of waste glass powder used was 342.0 g / kg of dry carbon residue. 1000 g of dry carbon residue and 342.0 g of waste glass powder were mixed dry in a mixer at 30 r / min for 30 min. The relative standard deviation of the sample was 2.9%, indicating that the mixture was uniform.

[0139] The homogeneous mixture was loaded into a muffle furnace and heated to 300°C at a rate of 10°C / min, held for 30 min, then heated to 1050°C at a rate of 8°C / min, and held for 4 h. The volume ratio of CO2 to CO in the furnace was maintained at 5:1. The conversion rate of Na3ALF6 was η = 98.7%.

[0140] After the flue gas is cooled to 200℃, it enters the alkaline solution spray absorption system. The initial mass fraction of NaOH is 20%, the liquid-to-gas ratio is 8 L / m³, the operating temperature is 60℃, and the excess NaOH is 30% (molar). Ca(OH)₂ is added at a molar ratio of Na₂CO₃ to Ca(OH)₂ of 1:1.2, with stirring at 200 r / min. Stirring is continued for 30 min, and the mixed absorption liquid is obtained after filtration.

[0141] The mixed absorbent was evaporated and concentrated at 90℃, cooled to 30℃ at a cooling rate of 2℃ / min, and the NaF solid was separated by centrifugation at 3000 r / min for 20 min. The NaF product was dried at 100℃ for 3 h, with a purity of 98.1%. The mother liquor was concentrated to a SiO2 to Na2O molar ratio of 3.5:1 and a Baume degree of 50°Bé to obtain liquid water glass product.

[0142] The calcined solid product was added to pure water at a liquid-to-solid ratio of 10:1 (mL:g), and stirred at 400 r / min for 60 min at 80℃ to dissolve. After filtration, 0.5% (by volume) of Na₂S solution (10% by mass) was added to the sodium aluminate solution, and the mixture was stirred at 300 r / min for 30 min. Impurities were removed by filtration. Following the carbonation decomposition route: CO₂ was bubbled into the sodium aluminate solution at a rate of 0.5 L / (min·L), with the solution temperature at 60℃, and the process was stopped when the pH dropped to 10. The Al(OH)₃ precipitate was collected by filtration, washed until the conductivity was below 200 μS / cm, dried at 105℃, and calcined at 1200℃ for 3 h to obtain the Al₂O₃ product with a purity of 98.5%.

[0143] Example 3 The procedure of Example 1 was followed, using intermediate and preferred parameter sets. Electrolytic aluminum slag was dried at 90°C for 3 hours, then ground and sieved until the particle size was less than 0.15 mm, yielding dried slag. X-ray fluorescence spectrometry determined W1 = 0.45, indicating a carbon powder mass fraction of 45%. Waste glass powder was dried at 110°C for 1.5 hours, and W2 was determined to be 0.72.

[0144] Theoretical amount of waste glass powder required per kilogram of dried carbon residue: The actual molar ratio of SiO2 to Na3ALF6 was set to 3.30:2 (10% excess), and the actual amount of waste glass powder used was 294.3 g / kg of dry carbon residue. 1000 g of dry carbon residue and 294.3 g of waste glass powder were taken and dry-mixed in a mixer at 22 r / min for 30 min, with a relative standard deviation of 3.2%, and the mixture was homogeneous.

[0145] The homogeneous mixture was loaded into a muffle furnace and heated to 300℃ at a rate of 7.5℃ / min, held for 25 min, then heated to 950℃ at a rate of 6.5℃ / min, and held for 3 h. The volume ratio of CO2 to CO in the furnace was maintained at 3.5:1. The conversion rate of Na3ALF6 was η = 96.4%.

[0146] After the flue gas is cooled to 175℃, it enters the alkaline solution spray absorption system. The initial NaOH mass fraction is 15%, the liquid-to-gas ratio is 5.5 L / m³, the operating temperature is 50℃, and the NaOH excess is 25% (molar). Ca(OH)₂ is added at a Na₂CO₃ to Ca(OH)₂ molar ratio of 1:1.1, with stirring at 150 r / min. Stirring is continued for 22 min, and the mixed absorption solution is obtained after filtration.

[0147] The mixed absorbent was evaporated and concentrated at 85℃, cooled to 25℃ at a cooling rate of 1℃ / min, and the NaF solid was separated by centrifugation at 2250 r / min for 15 min. The NaF product was then dried at 90℃ for 2.5 h, yielding a purity of 98.0%. The mother liquor was concentrated to a SiO2 to Na2O molar ratio of 2.75:1 and a Baume degree of 42°Bé to obtain liquid water glass.

[0148] The calcined solid product was added to pure water at a liquid-to-solid ratio of 7.5:1 (mL:g), and stirred at 300 r / min for 45 min at 65 °C. After filtration, 0.3% (by volume) Na₂S solution (7.5% by mass) of sodium aluminate solution was added to the sodium aluminate solution, and stirred at 225 r / min for 30 min. The mixture was then filtered to remove impurities. Following the carbonation decomposition route, CO₂ was introduced at a rate of 0.3 L / (min·L), the solution temperature was 50 °C, and the process was stopped when the pH dropped to 9.5. The Al(OH)₃ precipitate was collected by filtration, washed until the conductivity was below 200 μS / cm, dried at 105 °C, and calcined at 1150 °C for 2.5 h to obtain the Al₂O₃ product with a purity of 98.3%.

[0149] Example 4 The route of Example 2 was adopted, with the minimum endpoint parameter group used. The pretreatment conditions for carbon slag and waste glass powder were the same as in Example 1: the carbon slag was dried at 80°C for 2 hours and ground to a particle size of less than 0.075 mm, W1=0.40; the waste glass powder was dried at 100°C for 1 hour, W2=0.72.

[0150] Based on 100 parts by mass of dried carbon slag, the dried carbon slag was dispersed in anhydrous ethanol (purity ≥99.5%, water content ≤0.1%) at a liquid-to-solid ratio of 10:1 (mL:g), and ultrasonically treated for 30 min at an ultrasonic frequency of 20 kHz and a power density of 50 W / L. The theoretical amount of waste glass powder was calculated according to the formula in Example 1, and the actual molar ratio of SiO2 to Na3ALF6 was controlled at 3.15:2, requiring 87.5 parts by mass of waste glass powder. The waste glass powder was ultrasonically dispersed in anhydrous ethanol in the same manner (liquid-to-solid ratio 10:1, ultrasonic treatment for 30 min), combined with the carbon slag suspension, and stirred at 200 r / min for 15 min to obtain a mixed suspension.

[0151] The mixed suspension was sprayed into the liquid nitrogen freezing chamber through an ultrasonic nozzle (frequency 1.5MHz) with a droplet size of 20μm. After freezing, the microspheres were collected and freeze-dried for 8 hours at a temperature below -40℃ and a vacuum degree below 50Pa to obtain porous microsphere powder.

[0152] Porous microsphere powder was placed in an atmosphere furnace. High-purity nitrogen (≥99.99%) was first introduced to replace the air in the furnace until the oxygen content was below 100 ppm. The nitrogen flow rate was 0.5 L / min (per 100g powder). The temperature was increased to the carbothermic activation temperature of 900℃ at a rate of 10℃ / min and held for 30 min. The powder was then cooled to room temperature in the furnace at a rate not exceeding 10℃ / min, with nitrogen continuously introduced during the cooling process until the furnace temperature was below 200℃. The activated powder was then removed, with a bulk density of 0.14 g / cm³.

[0153] Based on 100 parts by mass of activated powder, 5 parts by mass of low-melting-point paraffin (melting point 50℃, kinematic viscosity 3 mm² / s at 100℃) were added. The mixture was heated to 65℃ and completely melted, then stirred at a low speed of 15 r / min for 10 min and cooled to room temperature. Subsequently, 3 parts by mass of bentonite (montmorillonite content ≥85%) and 8 parts by mass of anhydrous ethanol were added. The mixture was granulated in a granulator at 20 r / min for 10 min to obtain spherical particles with a particle size of approximately 3 mm. After drying at 40℃ for 1 h, dense spherical material with a bulk density of 0.63 g / cm³ was obtained.

[0154] Dense spherical material is continuously fed into the rotary kiln at a feed rate of 30 kg / h (rotation speed 1 r / min, tilt angle 2°). The preheating section, occupying 20% ​​of the kiln length and with a ventilation rate of 20 m³ / h (per ton of material), completely pyrolyzes the paraffin. The reaction section, occupying 55% of the kiln length and with a material residence time of 1.5 h and an oxygen content of 5% (volume fraction), undergoes a defluorination reaction of Na₃ALF₆. The cooling section, occupying 15% of the kiln length, has an outlet material temperature below 200℃. Quantitative X-ray diffraction analysis shows a Na₃ALF₆ conversion rate η = 88.5%.

[0155] The SiF4-containing flue gas in the reaction section, after being cyclone dust collector and cooled to 150°C by heat exchange, enters the alkaline solution spray absorption system. The initial NaOH mass fraction is 10%, the liquid-to-gas ratio is 3 L / m³, the operating temperature is 40°C, and the NaOH excess is 20% (molar). Ca(OH)2 is added at a Na2CO3 to Ca(OH)2 molar ratio of 1:1, with stirring at 100 r / min for 15 min. After filtration, a mixed absorbent is obtained. The parameters for subsequent NaF and water glass separation and Al2O3 preparation steps are the same as in Example 1: the mixed absorbent is evaporated and concentrated at 80°C, cooled to 20°C at 0.5°C / min, centrifuged at 1500 r / min for 10 min, and the NaF product is dried at 80°C for 2 h with a purity of 97.0%. The mother liquor is concentrated to a SiO2 to Na2O molar ratio of 2.0:1 and a Baume degree of 35°Bé to obtain liquid water glass. The solid product from the rotary kiln was crushed to a particle size of less than 5 mm. Pure water was added at a liquid-to-solid ratio of 8:1 (mL:g), and the mixture was stirred and dissolved at 60°C for 40 min. After filtration, CO2 was introduced at a rate of 0.1 L / (min·L) while maintaining the solution temperature at 40°C. The process was stopped when the pH dropped to 9. The Al(OH)3 was collected by filtration, washed, dried at 105°C, and calcined at 1100°C for 2 h to obtain the Al2O3 product with a purity of 97.5%.

[0156] Example 5 The route of Example 2 was adopted, and the operation was performed with the maximum endpoint parameter group. The pretreatment conditions for carbon slag and waste glass powder were the same as in Example 2: the carbon slag was dried at 100°C for 4 hours and ground to a particle size of less than 0.075 mm, W1=0.50; the waste glass powder was dried at 120°C for 2 hours, W2=0.72.

[0157] Based on 100 parts by weight of dried carbon slag, the dried carbon slag was dispersed in anhydrous ethanol at a liquid-to-solid ratio of 20:1 (mL:g) and ultrasonically treated for 60 min at an ultrasonic frequency of 40 kHz and a power density of 150 W / L. The actual molar ratio of SiO2 to Na3ALF6 in waste glass powder was controlled at 3.45:2, requiring 121.1 parts by weight. The waste glass powder was also ultrasonically treated for 60 min at a liquid-to-solid ratio of 20:1. The mixtures were then stirred at 400 r / min for 30 min to obtain a mixed suspension.

[0158] The mixed suspension was sprayed into the liquid nitrogen freezing chamber through an ultrasonic nozzle (frequency 2.5MHz) with a droplet size of 80μm, and the freeze-drying time was 16h to obtain porous microsphere powder.

[0159] The porous microsphere powder was heated to 1100℃ at a nitrogen flow rate of 2.0 L / min (per 100g powder) and held at that temperature for 60min. The powder was then cooled in the furnace and the activated powder was removed. The bulk density was 0.26 g / cm³.

[0160] Based on 100 parts by mass of activated powder, 12 parts by mass of low-melting-point paraffin (melting point 60℃, kinematic viscosity 6 mm² / s at 100℃) were added. The mixture was heated to 75℃ to melt, stirred at 30 r / min for 20 min, and then cooled to room temperature. Subsequently, 6 parts by mass of bentonite and 12 parts by mass of anhydrous ethanol were added, and the mixture was granulated in a granulator at 40 r / min for 20 min to obtain spherical particles with a particle size of approximately 8 mm. These particles were then dried at 60℃ for 2 h, resulting in a bulk density of 0.95 g / cm³.

[0161] Dense spherical material is fed into the rotary kiln at a feed rate of 150 kg / h (rotation speed 3 r / min, tilt angle 4°). The preheating section has a temperature of 400℃, occupies 25% of the kiln length, and has a ventilation volume of 50 m³ / h; the reaction section has a temperature of 800℃, occupies 65% of the kiln length, has a material residence time of 3 h, and an oxygen content of 12% (volume fraction); the cooling section occupies 20% of the kiln length. The Na₃ALF₆ conversion rate η = 97.8%.

[0162] The SiF4-containing flue gas, after being cooled to 200°C by a cyclone dust collector, enters the alkaline solution spray absorption system. The initial NaOH mass fraction is 20%, the liquid-to-gas ratio is 8 L / m³, the operating temperature is 60°C, and the NaOH excess is 30% (molar). Ca(OH)2 is added at a Na2CO3 to Ca(OH)2 molar ratio of 1:1.2, with stirring at 200 r / min for 30 min. The mixture is then filtered to obtain the mixed absorption solution. The subsequent NaF and water glass separation and Al2O3 preparation parameters are the same as in Example 2: NaF product purity is 97.8%; the liquid water glass SiO2 to Na2O molar ratio is 3.5:1, and the Baume degree is 50°Bé. The solid product from the rotary kiln was dissolved at a liquid-to-solid ratio of 12:1 (mL:g) at 80℃ with stirring for 60 min. CO2 was then introduced at a rate of 0.5 L / (min·L) while the solution temperature remained at 60℃. The solution was stopped when the pH dropped to 10. The product was then calcined at 1200℃ for 3 h to obtain Al2O3 with a purity of 98.6%.

[0163] Example 6 The route of Example 2 was adopted, and the operation was carried out with intermediate and preferred parameter sets. The pretreatment conditions for carbon slag and waste glass powder were the same as those in Example 3: the carbon slag was dried at 90°C for 3 hours and ground to a particle size of less than 0.075 mm, W1=0.45; the waste glass powder was dried at 110°C for 1.5 hours, W2=0.72.

[0164] Based on 100 parts by weight of dried carbon slag, the dried carbon slag was dispersed in anhydrous ethanol at a liquid-to-solid ratio of 15:1 (mL:g) and ultrasonically treated for 45 min at an ultrasonic frequency of 30 kHz and a power density of 100 W / L. The actual molar ratio of SiO2 to Na3ALF6 was controlled at 3.30:2, and the required amount of waste glass powder was 103.8 parts by weight. The powder was ultrasonically treated for 45 min in the same way. The mixtures were then stirred at 300 r / min for 22 min to obtain a mixed suspension.

[0165] The mixed suspension was sprayed into the liquid nitrogen freezing chamber through an ultrasonic nozzle (frequency 2.0MHz) with a droplet size of 50μm, and the freeze-drying time was 12h to obtain porous microsphere powder.

[0166] The porous microsphere powder was heated to the carbothermic activation temperature of 1000℃ at a nitrogen flow rate of 1.2 L / min (per 100g powder) and a heating rate of 12.5℃ / min, held at that temperature for 45min, cooled in the furnace, and the activated powder was taken out with a bulk density of 0.19 g / cm³.

[0167] Based on 100 parts by weight of activated powder, 8 parts by weight of low-melting-point paraffin (melting point 55℃, kinematic viscosity 4.5 mm² / s at 100℃) were added. The mixture was heated to 70℃ to melt, stirred at 22 r / min for 15 min, and then cooled to room temperature. Subsequently, 4.5 parts by weight of bentonite and 10 parts by weight of anhydrous ethanol were added, and the mixture was granulated in a granulator at 30 r / min for 15 min to obtain spherical particles with a particle size of approximately 5.5 mm. These particles were dried at 50℃ for 1.5 h, with a bulk density of 0.82 g / cm³.

[0168] Dense spherical material is fed into the rotary kiln at a feed rate of 90 kg / h (rotation speed 2 r / min, tilt angle 3°). The preheating section has a temperature of 325℃, accounting for 22% of the kiln length, with a ventilation volume of 35 m³ / h; the reaction section has a temperature of 700℃, accounting for 60% of the kiln length, with a material residence time of 2.25 h and an oxygen content of 8.5% (volume fraction); the cooling section accounts for 17% of the kiln length. The Na₃ALF₆ conversion rate η = 96.1%.

[0169] The SiF4-containing flue gas, after being cooled to 175°C by a cyclone dust collector, enters the alkaline solution spray absorption system. The initial NaOH mass fraction is 15%, the liquid-to-gas ratio is 5.5 L / m³, the operating temperature is 50°C, and the NaOH excess is 25% (molar). Ca(OH)2 is added at a Na2CO3 to Ca(OH)2 molar ratio of 1:1.1 under stirring at 150 r / min for 22 min. After filtration, a mixed absorption liquid is obtained. The subsequent separation of NaF and water glass and the Al2O3 preparation parameters are the same as in Example 3: NaF product purity is 98.2%; the molar ratio of SiO2 to Na2O in the liquid water glass is 2.75:1, and the Baume degree is 42°Bé. The solid product from the rotary kiln was stirred and dissolved at 70℃ for 50 min at a liquid-to-solid ratio of 10:1 (mL:g). CO2 was then introduced at a rate of 0.3 L / (min·L). The solution temperature was maintained at 50℃, and the solution was stopped when the pH dropped to 9.5. The product was then calcined at 1150℃ for 2.5 h to obtain Al2O3 product with a purity of 98.4%.

[0170] Comparative Example 1 The route of Example 1 was adopted, except that the parameters were exactly the same as those in Example 3, except for the molar ratio of SiO2 to Na3ALF6. In this comparative example, the actual molar ratio of SiO2 to Na3ALF6 was set to a stoichiometric ratio of 3.00:2 (without excess), that is, the amount of waste glass powder used per kilogram of dried carbon slag (w1=0.45, w2=0.72) was 267.5g (only the theoretical amount, without excess). The remaining steps, including raw material pretreatment (carbon slag dried at 90℃ for 3h, waste glass powder dried at 110℃ for 1.5h), mixing (22 r / min, 30min), high-temperature calcination (950℃, 3h, CO2 to CO volume ratio 3.5:1), flue gas treatment, separation of NaF and water glass, and preparation of Al2O3, were all consistent with those in Example 3.

[0171] Comparative Example 2 The route of Example 1 was adopted, and all parameters were exactly the same as in Example 3 except for the calcination temperature. In this comparative example, the target calcination temperature for the high-temperature calcination stage was set at 800℃ (lower than the minimum endpoint of 850℃). The remaining steps, including raw material pretreatment (carbon slag dried at 90℃ for 3h, waste glass powder dried at 110℃ for 1.5h, w1=0.45, w2=0.72), mixing (actual molar ratio of SiO2 to Na3ALF6 3.30:2, 22 r / min, 30min), the first stage of heating (heating to 300℃ at 7.5℃ / min and holding for 25min), the second stage of heating to 800℃ at 6.5℃ / min and holding for 3h, CO2 to CO volume ratio of 3.5:1, as well as subsequent flue gas treatment, separation of NaF and water glass, and preparation of Al2O3, were all consistent with those in Example 3.

[0172] Comparative Example 3 The route of Example 2 was adopted, omitting the carbothermal activation step, while the remaining parameters were exactly the same as in Example 6. Specifically, the porous microsphere powder (bulk density of approximately 0.19 g / cm³) obtained by ultrasonic spray freeze-drying was directly fed into paraffin coating granulation without carbothermal activation in a nitrogen-protected atmosphere furnace. The granulation parameters were the same as in Example 6: 8 parts by mass of low-melting-point paraffin (melting point 55℃, kinematic viscosity 4.5 mm² / s at 100℃) were added, melted at 70℃, stirred at 22 r / min for 15 min, 4.5 parts by mass of bentonite and 10 parts by mass of anhydrous ethanol were added, granulated at 30 r / min for 15 min, and dried at 50℃ for 1.5 h. The resulting dense spherical material was also fed into a rotary kiln at a feed rate of 90 kg / h. The temperature parameters of each section of the rotary kiln were exactly the same as in Example 6 (preheating section 325℃, reaction section 700℃, cooling section natural cooling), and the parameters for subsequent flue gas treatment, NaF and water glass separation, and Al₂O₃ preparation were also consistent with those in Example 6.

[0173] Experimental objective: Experimental objective 1: To investigate the effect of the excess SiO2 ratio (in molar) in Example 1 on the conversion rate of Na3ALF6 and the residual fluoride content of the solid product in the dried carbon slag, and to verify the necessity of controlling the actual SiO2 molar ratio within the range of 3.15:2 to 3.45:2 (a control experiment between Examples 1, 2, and 3 and Comparative Example 1).

[0174] Objective 2: To investigate the effect of high-temperature calcination temperature on the conversion rate of Na3ALF6 and the quality of the final product in the route of Example 1, and to verify the technical requirement that the calcination temperature must not be lower than 850℃ (a control experiment between Example 3 and Comparative Example 2).

[0175] Objective 3: To investigate the contribution of the carbothermic activation step in Example 2 to the defluorination reaction efficiency, and to verify the necessity of this step for achieving efficient defluorination in the lower temperature range of 600 to 800 °C (a control experiment between Example 6 and Comparative Example 3).

[0176] Experimental sample preparation: The sample preparation in Examples 1 to 3 followed the route of Example 1, using the same batch of electrolytic aluminum carbon slag and waste glass powder as raw materials. w1 varied with different values ​​set in the examples (0.40, 0.50, and 0.45, respectively), while w2 was uniformly 0.72. The three sets of examples independently completed all steps under their respective parameter combinations, and each set prepared one batch of calcined solid product and one batch of three types of products (NaF, liquid water glass, and Al2O3).

[0177] The sample preparation of Examples 4 to 6 followed the route of Example 2. After pretreatment of the raw materials, they were ground to a particle size of less than 0.075 mm, and activated powder was prepared by ultrasonic spray freeze drying and carbothermal activation. After paraffin granulation, the powder was continuously fed into a rotary kiln and completed independently under their respective parameter combinations. Each group prepared a batch of rotary kiln solid products and a batch of three types of product samples.

[0178] Comparative Examples 1 and 2 both followed the route of Example 1, with all raw materials from the same batch as in Example 3, only the molar ratio (Comparative Example 1) or calcination temperature (Comparative Example 2) was changed. Comparative Example 3 followed the route of Example 2, with all raw materials from the same batch as in Example 6, only the carbothermal activation step was omitted.

[0179] Experimental conditions: All examples and comparative examples were conducted on a laboratory scale, with each batch of dried charcoal slag fed in 1000g (Example 1 route) or based on 100 parts by weight (approximately 500g) of activated powder (Example 2 route). The calcination equipment consisted of a tubular muffle furnace (Example 1 route) and an atmosphere-controlled tubular furnace (Example 2 carbothermic activation). The rotary kiln test section (Example 2 route) had an effective kiln length of 5m and an inner diameter of 0.2m, with each parameter set independently. Analytical instruments included an X-ray fluorescence spectrometer (for determining the purity of Al₂O₃ and the composition of each raw material), an X-ray diffractometer (for determining the conversion rate of Na₃AlF₆), an ion chromatograph (for determining the purity of NaF), an online infrared gas analyzer (for monitoring the concentration of SiF₄ in flue gas), a Baumé hydrometer (for determining the Baumé degree of water glass), and a chemical titration apparatus (for determining the molar ratio of SiO₂ to Na₂O).

[0180] Experimental steps: Step 1, Raw material composition determination: w1 is determined for each batch of dried carbon slag using X-ray fluorescence spectroscopy, and w2 is determined for waste glass powder. The measured values ​​are used as inputs for subsequent batching calculations.

[0181] Step 2, Ingredient Calculation and Mixing: According to the formula Calculate the theoretical dosage, weigh according to the actual molar ratio set in each embodiment or comparative example, and the mixing uniformity is considered qualified if the relative standard deviation of the sampling does not exceed 5%.

[0182] Step 3, high-temperature calcination or rotary kiln reaction: carried out according to the temperature program and atmosphere conditions set in each embodiment or comparative example. The concentration of SiF4 in the exhaust gas is monitored in real time by an online infrared gas analyzer. The reaction is considered complete when the concentration of SiF4 drops to below 5% of the initial peak value and remains there for 10 minutes.

[0183] Step 4, Na3ALF6 conversion determination: The solid product was taken out and quantitatively analyzed by X-ray diffraction, according to... Calculate the conversion rate, where η is the conversion rate of Na3ALF6, n0 is the molar amount of Na3ALF6 before the reaction, and n r The value represents the molar amount of residual Na3ALF6 in the solid product after the reaction. Simultaneously, a water leaching test was performed on the solid product, and the fluoride ion concentration in the leachate was measured to characterize the residual fluoride content in the solid product (expressed as leached fluoride ion concentration in mg / L).

[0184] Step 5, flue gas treatment: The flue gas containing SiF4 is cyclone dust removal and heat exchange cooling before entering the alkaline solution spray absorption system. The absorption effect is monitored by an online pH meter and fluoride detector. The resulting mixed absorption liquid enters the subsequent separation steps.

[0185] Step 6, Product Separation and Preparation: The mixed absorption liquid is evaporated, crystallized, and centrifuged to obtain NaF product, and its purity is determined by ion chromatography; the mother liquor is evaporated and concentrated, and the molar ratio of SiO2 to Na2O is determined by chemical titration, and the Baumé degree is determined at 20℃ using a Baumé hydrometer to obtain liquid water glass product; the sodium aluminate solution is decomposed by carbonation or precipitated by acid precipitation, and the obtained AL(OH)3 is dried and calcined to obtain AL2O3 product, and its purity is determined by X-ray fluorescence spectrometry.

[0186] Step 7, Data Recording and Comparison: For the samples obtained in Examples 1 to 6 and Comparative Examples 1 to 3, record the Na3ALF6 conversion rate, solid product leaching fluoride ion concentration, NaF purity, AL2O3 purity, and bulk density of dense spherical materials (Example 2 route), and compile and list them for comparison.

[0187] The experimental or test results are shown in the table below and Figures 2-8 As shown: Table 1. Comparison of main process parameters and core performance indicators of Examples 1 to 3 and Comparative Examples 1 and 2 (Example 1 route) As shown in Table 1, under the conditions of SiO2 to Na3ALF6 actual molar ratio of 3.15:2 to 3.45:2 and calcination temperature of 850 to 1050℃ in Examples 1 to 3, the conversion rate of Na3ALF6 was above 91%, the fluoride ion concentration of the leached solid product was below 30 mg / L, the purity of AL2O3 was above 97%, and the purity of NaF was above 97%, showing good performance in all aspects.

[0188] Comparative Example 1 used a stoichiometric ratio of SiO2 to Na3ALF6 of 3.00:2 (not excessive). Compared to Example 3, the conversion rate of Na3ALF6 decreased from 96.4% to 83.6%, a reduction of 12.8 percentage points; the fluoride ion concentration leached from the solid product increased from 9.8 mg / L to 67.3 mg / L, an increase of approximately 5.9 times; and the purity of Al2O3 also decreased by 2.5 percentage points accordingly. These results indicate that when SiO2 is not excessive, local uneven proportions lead to insufficient reaction of some Na3ALF6, resulting in a significantly higher residual fluoride content in the solid product. This verifies the necessity of requiring a 5% to 15% (molar) excess of SiO2 in this invention.

[0189] Comparative Example 2 reduced the calcination temperature to 800℃. Compared with Example 3, the Na3ALF6 conversion rate decreased from 96.4% to 71.4%, a reduction of 25 percentage points; the fluoride ion concentration leached from the solid product increased sharply from 9.8 mg / L to 112.6 mg / L, an increase of approximately 10.5 times. These results indicate that when the calcination temperature is below 850℃, the solid-phase reaction kinetics are significantly insufficient, resulting in a large amount of residual Na3ALF6 and excessive fluoride content in the solid product. This verifies the technical rationale for requiring a calcination temperature of not less than 850℃ in this invention.

[0190] Table 2 Comparison of main process parameters and core performance indicators of Examples 4 to 6 and Comparative Example 3 (Example 2 route) As shown in Table 2, under the conditions of carbothermic activation temperature of 900-1100℃ and rotary kiln reaction section temperature of 600-800℃ in Examples 4 to 6, the conversion rate of Na3ALF6 was above 88%, the fluoride ion concentration of the leached solid product was below 35 mg / L, and the purity of Al2O3 was above 97%, all indicators showing good performance. Meanwhile, the bulk density of the activated powder increased from 0.14-0.26 g / cm³ to 0.63-0.95 g / cm³ after paraffin granulation, an increase of 3.6 to 4.5 times, meeting the engineering requirements for continuous feeding in the rotary kiln.

[0191] Comparative Example 3, which omits the carbothermal activation step, has a similar bulk density of dense spherical material (0.81 g / cm³) to Example 6 (0.82 g / cm³), indicating that the granulation operation itself is not significantly affected by whether or not carbothermal activation is performed. However, under the same rotary kiln reaction section temperature of 700°C and material residence time of 2.25 h, the Na₃ALF₆ conversion rate of Comparative Example 3 is only 74.2%, a decrease of 21.9 percentage points compared to 96.1% in Example 6; the fluoride ion concentration leached from the solid product increases from 8.7 mg / L to 89.5 mg / L, an increase of approximately 9.3 times; and the AL₂O₃ purity also decreases from 98.4% to 95.3%. The above results show that at a reaction temperature of 700℃, if the SiO2 surface is not activated by carbothermal activation to generate oxygen vacancy defects and reduce the activation energy, the defluorination reaction kinetics are significantly insufficient, and a large amount of Na3ALF6 remains. This proves that the carbothermal activation step is the key to achieving efficient defluorination in the lower temperature range of 600 to 800℃ in the route of Example 2.

[0192] Table 3. Comprehensive performance comparison of the optimal parameter groups for routes in Example 1 and Example 2 As shown in Table 3, the conversion rate of Na3ALF6 in Example 2 (Example 6) at a reaction temperature of 700℃ (96.1%) is comparable to that in Example 1 (Example 1) at 950℃ (96.4%), while the calcination temperature is reduced by 250℃. This results in a corresponding reduction in the external heat demand per unit product, demonstrating the effectiveness of the ultrasonic spray freeze-drying combined with carbothermal activation process in lowering the reaction temperature. Furthermore, the dense spherical material obtained in Example 2 has a bulk density of 0.82 g / cm³, meeting the engineering requirements for continuous feeding in a rotary kiln, a constraint not present in the batch muffle furnace operation of Example 1. The purity of Al2O3 and NaF obtained from both routes is above 98%, indicating comparable product quality.

[0193] Based on the above experimental results, the technical effectiveness of the method for co-processing waste glass powder with electrolytic aluminum carbon slag described in this invention is verified as follows.

[0194] Firstly, an excess of 5% to 15% (molar) of SiO2 is a necessary condition to ensure the full conversion of Na3ALF6. In Comparative Example 1, after removing the excess SiO2, the conversion rate decreased by 12.8 percentage points, and the concentration of fluoride ions leached from the solid product increased by approximately 5.9 times. In contrast, Examples 1 to 3 all had conversion rates exceeding 91% within the aforementioned excess range, and the concentration of fluoride ions leached from the solid product remained at a low level. This demonstrates that the excess design effectively eliminated the problem of high residual fluoride levels caused by uneven local proportioning.

[0195] Secondly, the route in Example 1 requires a calcination temperature of not less than 850°C. Comparative Example 2, when operated at 800°C, had a conversion rate of only 71.4% and a leached fluoride ion concentration exceeding 110 mg / L, indicating insufficient solid-phase reaction kinetics; while Examples 1 to 3 all had conversion rates exceeding 91% in the range of 850 to 1050°C, proving the rationality of the lower limit of this temperature.

[0196] Thirdly, the carbothermal activation step is key to achieving efficient defluorination in the 600-800℃ range of Example 2. In Comparative Example 3, omitting carbothermal activation, under the same reaction temperature of 700℃ and residence time of 2.25h, the conversion rate decreased by 21.9 percentage points, and the leached fluoride ion concentration increased by approximately 9.3 times. In contrast, Example 6, after carbothermal activation, achieved a conversion rate of 96.1%, comparable to the 950℃ condition of Example 1. This verifies the actual effect of carbothermal activation in reducing the activation energy of the solid-phase reaction between SiO2 and Na3ALF6, and its contribution to reducing the defluorination reaction temperature range from 850-1050℃ to 600-800℃.

[0197] Fourth, the temporary densification granulation of low-melting-point paraffin increases the bulk density of activated powder from 0.14 to 0.26 g / cm³ to 0.63 to 0.95 g / cm³, an increase of 3.6 to 4.5 times. This solves the engineering problem that low-density activated powder cannot be continuously fed into the rotary kiln, providing feasible conditions for continuous production in the route of Example 2. Moreover, the quality of AL2O3 and NaF products obtained in each example is not affected by the granulation operation.

[0198] The embodiments of the present invention have been described above. However, the embodiments are not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make more equivalent embodiments under the guidance of the present embodiments, and all of them are within the protection scope of the present embodiments.

Claims

1. A method for co-processing waste glass powder with electrolytic aluminum carbon slag, characterized in that, Includes the following steps: Electrolytic aluminum carbon slag is crushed, ground, and dried to obtain dried carbon slag; waste glass is crushed, ground, and dried to obtain waste glass powder. The dried carbon slag and waste glass powder were mixed and formulated at a molar ratio of SiO2 to Na3ALF6 of 3.15:2 to 3.45:2 to obtain a homogeneous mixture. The uniform mixture is calcined at 850 to 1050℃ for 2 to 4 hours. Na3ALF6 reacts with SiO2 in a solid phase to generate NaALO and releases SiF4 gas, resulting in calcined solid products and flue gas containing SiF4. The flue gas containing SiF4 is cooled after dust removal and sent to an alkaline spray absorption system to absorb SiF4 with NaOH aqueous solution, resulting in a mixed absorption liquid containing NaF and Na2SiO. The mixed absorbent was evaporated, concentrated, crystallized, and separated to obtain NaF product and sodium silicate solution; The calcined solid product was dissolved in water to obtain a sodium aluminate solution. The sodium aluminate solution was then precipitated and separated to obtain AL(OH)3. After calcination, the AL2O3 product was obtained.

2. The method according to claim 1, characterized in that, The dried carbon slag has a particle size of less than 0.15 mm, and the waste glass powder has a particle size of less than 0.075 mm; the dried carbon slag contains 40% to 50% Na3ALF6 by mass and 40% to 50% carbon powder by mass.

3. The method according to claim 1, characterized in that, The calcination temperature is 900 to 1000°C; air is introduced during the calcination process to control the volume ratio of CO2 to CO in the furnace to be maintained between 2:1 and 5:1, so that the carbon powder in the mixture is burned in a controlled manner to supplement the heat of the reaction system.

4. The method according to claim 1, characterized in that, The initial mass fraction of NaOH in the alkaline spray absorption system is 10% to 20%, the liquid-to-gas ratio is controlled at 3 to 8 L / m³, and the pH value of the circulating alkaline solution is maintained between 8 and 12; the actual amount of NaOH used is 20% to 30% more than the theoretical requirement.

5. The method according to claim 1, characterized in that, The evaporation, concentration, crystallization, and separation process includes: evaporating and concentrating NaF at 80 to 90°C to crystallize it out; cooling the temperature to 20 to 30°C to promote further crystallization; controlling the cooling rate at 0.5 to 2°C / min; centrifuging to separate the NaF solid from the mother liquor; and concentrating the mother liquor to a SiO2 to Na2O molar ratio of 2.0:1 to 3.5:1 and a Baume degree of 35 to 50°Bé to obtain a liquid water glass product.

6. The method according to claim 1, characterized in that, The precipitation separation of sodium aluminate solution is carried out by carbonation decomposition or acid precipitation. Carbonation decomposition involves introducing CO2 gas into the sodium aluminate solution to lower the pH to 9 to 10. Acid precipitation involves adding 10% to 15% dilute hydrochloric acid or dilute sulfuric acid to the sodium aluminate solution to lower the pH to 7 to 9. The resulting Al(OH)3 precipitate is washed, dried, and then calcined at 1100 to 1200°C for 2 to 3 hours to obtain Al2O3 product.

7. The method according to claim 1, characterized in that, Before the mixing of ingredients, the process includes an ultrasonic spray freeze-drying step of treating the dried carbon slag and waste glass powder: the dried carbon slag and waste glass powder are dispersed in anhydrous ethanol, ultrasonically treated for 30 to 60 minutes at an ultrasonic frequency of 20 to 40 kHz and a power density of 50 to 150 W / L, and then mixed. The mixed suspension is sprayed into a liquid nitrogen freezing chamber with a droplet size of 20 to 80 μm through an ultrasonic spraying device for instant solidification, and then freeze-dried for 8 to 16 hours at a temperature below -40°C and a vacuum degree below 50 Pa to obtain porous microsphere powder.

8. The method according to claim 7, characterized in that, The process also includes a step of carbothermic activation of the porous microsphere powder under nitrogen protection: under a high-purity nitrogen protective atmosphere, the temperature is increased to 900 to 1100°C at a heating rate of 10 to 15°C / min, and the temperature is held for 30 to 60 minutes for carbothermic activation. After cooling, activated powder is obtained.

9. The method according to claim 8, characterized in that, The method also includes a step of paraffin coating and granulation of the activated powder: based on 100 parts by mass of activated powder, 5 to 12 parts by mass of low-melting-point paraffin with a melting point of 50 to 60°C are added, heated to 65 to 75°C to melt the paraffin, stirred and coated, cooled and solidified, and then 3 to 6 parts by mass of bentonite and 8 to 12 parts by mass of anhydrous ethanol are added for granulation to obtain dense spherical material with a particle size of 3 to 8 mm and a bulk density of 0.6 to 1.0 g / cm³; the dense spherical material is continuously fed into a rotary kiln, and successively passes through a preheating section at 250 to 400°C to remove paraffin, a reaction section at 600 to 800°C for defluorination reaction, and a cooling section to cool down before discharging the solid product.

10. The method according to claim 9, characterized in that, The temperature of the rotary kiln reaction section is 650 to 750°C, the residence time of the material in the reaction section is 1.5 to 3 hours, and the oxygen content in the reaction section is 5% to 12%.

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