A method for preparing high-activity polyaluminum sulfate flocculants from secondary aluminum dross and products thereof

Abstract

The application discloses a method for preparing high-activity polymeric aluminum sulfate flocculants from secondary aluminum ash, which comprises the following steps: mixing a phosphoric acid solution and a sulfuric acid solution, adding secondary aluminum ash, stirring, drying, calcining, adding water, stirring, solid-liquid separation, adding a sodium hydroxide solution into the liquid to adjust pH, low-temperature plasma irradiation, and drying to obtain the high-activity polymeric aluminum sulfate flocculants. The high-activity polymeric aluminum sulfate flocculants are prepared from the secondary aluminum ash through acid leaching, calcining and low-temperature plasma irradiation, the effective resource utilization of the secondary aluminum ash is realized, and compared with the existing polymeric aluminum sulfate and polymeric aluminum chloride, the high-activity polymeric aluminum sulfate flocculants have more excellent flocculation performance and can more efficiently remove total phosphorus, ammonia nitrogen, COD and heavy metal pollutants in polluted water bodies.

Description

Technical Field

[0001] This invention relates to a method for preparing highly active polyaluminum sulfate flocculant using secondary aluminum ash and the product thereof, belonging to the field of hazardous waste resource utilization. Background Technology

[0002] Aluminum ash is a byproduct of aluminum smelting or processing. It exhibits significant reactivity and poses environmental hazards. Stockpiling aluminum ash occupies land resources, and when it comes into contact with water, it releases methane, ammonia, hydrogen, and other gases, affecting air quality. Untreated and indiscriminate discharge of aluminum ash can also disrupt the lives of nearby residents and increase safety risks. Furthermore, aluminum ash, when exposed to water, not only makes the soil alkaline, disrupting its pH balance, but also releases toxic and harmful substances into the soil and groundwater systems, causing long-term pollution to the ecological environment. Given these environmental risks, aluminum ash has been included in the "National Hazardous Waste List" and is managed and disposed of as hazardous waste.

[0003] Aluminum ash is divided into primary aluminum ash and secondary aluminum ash. Primary aluminum ash, also known as quicklime, is the residue directly left from the electrolytic aluminum production process, or the residue from aluminum smelting without the addition of salts. Its main components are metallic aluminum and its oxides. Primary aluminum ash is mainly used for recovering metallic aluminum, and its metallic aluminum content is relatively high, usually between 15% and 70%. Secondary aluminum ash, on the other hand, is the residue produced after resource extraction and recovery of primary aluminum ash and the addition of salts for aluminum smelting. It is mainly composed of aluminum, aluminum oxides, nitrides, molten salts, and other substances. Therefore, the composition of secondary aluminum ash is relatively complex. In addition to metallic aluminum, it also contains a large amount of salt flux, oxides, and aluminum nitrides. This results in more impurities needing to be processed during the resource utilization of secondary aluminum ash, increasing the technical difficulty.

[0004] Secondary aluminum ash can be used as a raw material to prepare products such as aluminum sulfate, polyaluminum sulfate, desulfurizers, and refractory materials. However, these methods for the comprehensive resource utilization of secondary aluminum ash are still not effective enough, the preparation process is too long, and the performance of the obtained target products is poor, making production and promotion difficult. Therefore, the resource utilization technology of secondary aluminum ash still needs further research and development.

[0005] Although the patent (application number: 2023112005185) discloses a method for preparing polymeric flocculants using secondary aluminum ash, this method involves mixing tar and secondary aluminum ash, obtaining aluminum chloride slurry through a fluidized bed chlorination furnace, dust collection, and washing tower processes, adjusting the pH with hydrochloric acid, and then filtering and drying to obtain the polymeric flocculant. This method uses aluminum chloride and other dust impurities generated in the fluidized bed chlorination furnace for polymeric flocculant preparation, failing to maximize the activation of the secondary aluminum ash itself, nor deeply stimulating and maximizing the aluminum release and polymeric aluminum hydrolysis polymerization processes. Therefore, the performance of the prepared flocculant still has room for improvement, and new technologies need to be developed. Summary of the Invention

[0006] Purpose of the invention: The technical problem to be solved by the present invention is to provide a method and product for preparing a highly active polyaluminum sulfate flocculant that can more efficiently remove total phosphorus, ammonia nitrogen, COD and heavy metal pollutants from polluted water using secondary aluminum ash.

[0007] Technical Solution: To solve the above-mentioned technical problems, this invention provides a method for preparing highly active polyaluminum sulfate flocculant using secondary aluminum ash, comprising the following steps:

[0008] (1) Mix phosphoric acid solution and sulfuric acid solution to obtain phosphorus-doped sulfuric acid solution;

[0009] (2) Mix the phosphorus-doped sulfuric acid solution and secondary aluminum ash described in step (1), stir, and obtain phosphorus-sulfuric acid degassing aluminum ash slurry;

[0010] (3) Dry the phosphorus-sulfuric acid gas-releasing aluminum slurry described in step (2) and calcine it to obtain the calcined activated material;

[0011] (4) Mix water and the calcined activated material described in step (3), stir, separate solid and liquid, add sodium hydroxide solution to the liquid to adjust pH, irradiate with low temperature plasma, and dry to obtain high-activity polyaluminum sulfate flocculant.

[0012] In step (1), the molar mass ratio of phosphoric acid solution to sulfuric acid solution is 4-16:100.

[0013] The concentration of the sulfuric acid solution mentioned in step (1) is 2.5 to 7.5 M.

[0014] In step (2), the liquid-to-solid ratio of the phosphorus-doped sulfuric acid solution and the secondary aluminum ash is 0.4–1.2:1 mL / g.

[0015] In step (2), the stirring time is 1 to 5 hours and the stirring speed is 30 to 180 rpm.

[0016] The calcination temperature in step (3) is 300–600°C.

[0017] The calcination time in step (3) is 0.5 to 4.5 hours.

[0018] The drying temperature in step (3) is 50 to 150°C.

[0019] The time for low-temperature plasma irradiation in step (4) is 0.5 to 4.5 hours.

[0020] In step (4), the liquid-solid ratio of water and calcined activated material is 1-3:1 mL / g.

[0021] In step (4), the pH is 3 to 6.

[0022] The stirring time in step (4) is 1 to 5 hours and the stirring speed is 30 to 180 rpm.

[0023] In step (4), the concentration of the sodium hydroxide solution is 2.5–5 M.

[0024] In step (4), the voltage of the low-temperature plasma irradiation is 5 to 75 kV.

[0025] The present invention also provides a highly active polyaluminum sulfate flocculant prepared by the method described above.

[0026] Reaction Mechanism: When a phosphorus-doped sulfuric acid solution is mixed with secondary aluminum ash, the sulfuric acid and phosphoric acid promote the dissolution of aluminum nitride, aluminum carbide, and elemental aluminum, releasing ammonia, methane, and hydrogen gases, and forming aluminum sulfate and aluminum phosphate gels. During calcination, the aluminum phosphate gel selectively binds to elements such as calcium, magnesium, silicon, and titanium in the secondary aluminum ash, forming insoluble impurity precipitates and molten agglomerates. Simultaneously, during calcination, sulfate ions further penetrate into the aluminum ash particles, forming aluminum sulfate with more aluminum. When water and calcination activators are mixed, the aluminum sulfate dissolves in the water during stirring, while the impurity precipitates and molten agglomerates have very low solubility and are separated during solid-liquid separation, thus achieving the purification of aluminum sulfate. Adding sodium hydroxide solution to aluminum-rich liquid and subjecting the aluminum-rich slurry to low-temperature plasma irradiation promotes the hydrolysis and polymerization of aluminum sulfate in the slurry through the synergistic effect of hydroxide ions, oxygen radicals, and hydroxide radicals. Simultaneously, oxygen radicals and hydroxide radicals oxidize residual trace amounts of iron and titanium in the aluminum sulfate, forming a polyaluminum sulfate flocculant containing multivalent iron and titanium substances. The ultrasound, microwaves, and free radicals released during the low-temperature plasma irradiation process also significantly alter the microstructure of the polyaluminum sulfate flocculant, thus preparing a highly active polyaluminum sulfate flocculant.

[0027] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The present invention prepares a highly active polyaluminum sulfate flocculant from secondary aluminum ash through acid leaching, calcination and low-temperature plasma irradiation, realizing the effective resource utilization of secondary aluminum ash. Compared with existing polyaluminum sulfate and polyaluminum chloride, it has better flocculation performance and can remove total phosphorus, ammonia nitrogen, COD and heavy metal pollutants from polluted water more efficiently. Attached Figure Description

[0028] Figure 1 This is a flowchart of the processing method of the present invention. Detailed Implementation

[0029] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0030] Secondary aluminum ash: The secondary aluminum ash was obtained from Xinchang Aerospace Machine Tool Equipment Co., Ltd. It is flue ash generated during the aluminum smelting and casting process. It was sealed with a waterproof belt and used as a test sample. It mainly includes: 72.24% Al2O3, 3.32% SiO2, 7.48% MgO, 1.24% CaO, 3.01% Na2O, 0.86% K2O, 2.43% Fe2O3, 1.52% F, 5.37% Cl and other components (unavoidable impurities and loss on ignition).

[0031] Sampling, Concentration, and Basic Properties of Municipal Solid Waste Leachate: The leachate used in the experiment was taken from the Qingchengshan Municipal Solid Waste Sanitary Landfill in Haizhou District, Lianyungang City. This batch of municipal solid waste leachate was heated and concentrated to 0.2 times its original volume. The resulting leachate concentrate had a COD concentration of 5789 mg / L, a total phosphorus concentration of 893 mg / L, and an ammonia nitrogen concentration of 3897 mg / L. Soluble mercury ions were added to the leachate concentrate to achieve a mercury ion concentration of 200 mg / L.

[0032] Example 1: Effect of the molar ratio of phosphoric acid and sulfuric acid on the performance of the prepared highly active polyaluminum sulfate flocculant

[0033] Phosphoric acid and sulfuric acid solutions were mixed at molar ratios of 1:100, 2:100, 3:100, 4:100, 12:100, 16:100, 18:100, 20:100, and 22:100 respectively to obtain phosphorus-doped sulfuric acid solutions, with a sulfuric acid concentration of 2.5M. The phosphorus-doped sulfuric acid solutions were mixed with secondary aluminum ash at a liquid-to-solid ratio of 0.4:1 mL / g and stirred for 1 hour to obtain phosphorus-sulfuric acid-releasing aluminum slurry, with a stirring speed of 30 rpm. The phosphorus-sulfuric acid-releasing aluminum slurry was dried at 50℃ to obtain phosphorus-sulfuric acid-releasing aluminum powder. The phosphorus-sulfuric acid-releasing aluminum powder was calcined in a calcining furnace for 0.5 hours to obtain calcined activated material, with a calcination temperature of 300℃. Water and calcined activated material were mixed at a liquid-to-solid ratio of 1:1 mL / g and stirred for 1 hour, followed by solid-liquid separation. The resulting liquid portion was aluminum-rich liquid, with a stirring speed of 30 rpm. Sodium hydroxide solution was added to the aluminum-rich liquid to adjust the pH to 3, resulting in an aluminum-rich slurry with a sodium hydroxide solution concentration of 2.5 M. The aluminum-rich slurry was then subjected to low-temperature plasma irradiation for 0.5 hours to obtain a plasma-activated aluminum-rich slurry, with an irradiation voltage of 5 kV. The plasma-activated aluminum-rich slurry was then sprayed into a drum drying oven, yielding dried particles that were highly active polyaluminum sulfate flocculants.

[0034] Landfill leachate concentrate purification test: Weigh 1g of high-activity polyaluminum sulfate flocculant and add it to 1L of landfill leachate concentrate. Stir continuously for 30min, centrifuge, and obtain the treated landfill leachate concentrate.

[0035] COD Concentration Detection and COD Adsorption Capacity Calculation: The chemical oxygen demand (COD) concentration of the leachate was determined according to the national standard "Determination of Chemical Oxygen Demand in Water - Dichromate Method" (HJ 828-2017). The COD adsorption capacity was calculated according to formula (1), where Q... COD COD adsorption capacity (mg / g), c0 and c t The values ​​represent the COD concentration (mg / L) of the leachate concentrate before and after treatment, respectively. V represents the volume of the leachate concentrate (1L), and m represents the mass of the highly active polyaluminum sulfate flocculant (1g).

[0036]

[0037] Total phosphorus concentration detection and total phosphorus adsorption capacity calculation: The total phosphorus concentration of the leachate was determined according to the standard "Determination of Phosphate and Total Phosphorus in Water - Continuous Flow-Ammonium Molybdate Spectrophotometric Method" (HJ 670-2013). The total phosphorus adsorption capacity was calculated according to formula (2), where Q... TP The total phosphorus adsorption capacity (mg / g) is c TP0 and c TPt The values ​​represent the total phosphorus concentration (mg / L) of the leachate concentrate before and after treatment, respectively; V represents the volume of the leachate concentrate (1L); and m represents the mass of the highly active polyaluminum sulfate flocculant (1g).

[0038]

[0039] Ammonia nitrogen concentration detection and ammonia nitrogen adsorption capacity calculation: The ammonia nitrogen concentration in the leachate was determined according to the "Determination of Ammonia Nitrogen in Water Quality - Salicylic Acid Spectrophotometric Method" (HJ 536-2009). The ammonia nitrogen adsorption capacity was calculated according to formula (3), where Qx is the ammonia nitrogen adsorption capacity (mg / g), and c N0 To determine the initial concentration (mg / L) of ammonia nitrogen in the leachate concentrate before treatment, c Nt V represents the residual ammonia nitrogen concentration (mg / L) in the treated leachate concentrate, V represents the volume of the landfill leachate concentrate (1L), and m represents the mass of the highly active polyaluminum sulfate flocculant (1g).

[0040]

[0041] Mercury ion concentration detection and adsorption capacity calculation: The mercury ion concentration in the leachate was determined according to the standard "Determination of Mercury, Arsenic, Selenium, Bismuth and Antimony in Water by Atomic Fluorescence Method" (HJ 694-2014). The mercury ion adsorption capacity was calculated according to formula (4), where Q... H c is the mercury ion adsorption capacity (mg / g). H0 To determine the initial concentration (mg / L) of mercury ions in the pretreatment leachate concentrate, c HtV represents the mercury ion concentration (mg / L) in the treated leachate concentrate, V represents the volume of the landfill leachate concentrate (1L), and m represents the mass of the highly active polyaluminum sulfate flocculant (1g).

[0042]

[0043] The adsorption capacities for COD, total phosphorus, ammonia nitrogen, and mercury ions are shown in Table 1.

[0044] Table 1. Effect of the molar ratio of phosphoric acid and sulfuric acid on the performance of the prepared high-activity polyaluminum sulfate flocculant.

[0045]

[0046] As shown in Table 1, when the molar ratio of phosphoric acid to sulfuric acid is less than 4:100 (as shown in Table 1, when the molar ratio of phosphoric acid to sulfuric acid is 3:100, 2:100, 1:100, and even lower ratios not listed in Table 1), less phosphoric acid is added, and the synergistic effect of phosphoric acid and sulfuric acid is weakened. This results in a significant decrease in the adsorption capacity of pollutants COD, total phosphorus, ammonia nitrogen, and mercury ions in the prepared flocculant as the molar ratio of phosphoric acid to sulfuric acid decreases. When the molar ratio of phosphoric acid to sulfuric acid is equal to 4–16:100 (as shown in Table 1, when the molar ratio of phosphoric acid to sulfuric acid is 4:100, 12:100, and 16:100), when the phosphoric acid-doped sulfuric acid solution is mixed with secondary aluminum ash, during stirring, sulfuric acid and phosphoric acid can promote the dissolution of aluminum nitride, aluminum carbide, and elemental aluminum, releasing ammonia, methane, and hydrogen, and forming aluminum sulfate and aluminum phosphate gels. Ultimately, the prepared flocculants exhibited COD adsorption capacities greater than 1265 mg / g, total phosphorus adsorption capacities greater than 167 mg / g, ammonia nitrogen adsorption capacities greater than 587 mg / g, and mercury ion adsorption capacities greater than 32 mg / g. When the molar ratio of phosphoric acid to sulfuric acid was greater than 16:100 (as shown in Table 1, where the molar ratios were 18:100, 20:100, 22:100, and higher ratios not listed in Table 1), excessive phosphoric acid addition weakened the synergistic effect of phosphoric acid and sulfuric acid. Consequently, the adsorption capacities of pollutants COD, total phosphorus, ammonia nitrogen, and mercury ions in the prepared flocculants significantly decreased with further increases in the molar ratio of phosphoric acid to sulfuric acid. Therefore, considering both benefits and costs, a molar ratio of phosphoric acid to sulfuric acid between 4 and 16:100 is most favorable for improving the adsorption performance of the prepared highly active polyaluminum sulfate flocculants.

[0047] Example 2: Effect of calcination temperature on the performance of the prepared high-activity polyaluminum sulfate flocculant

[0048] A phosphoric acid solution and a sulfuric acid solution were mixed at a molar ratio of 16:100 to obtain a phosphorus-doped sulfuric acid solution, wherein the concentration of the sulfuric acid solution was 5M. The phosphorus-doped sulfuric acid solution was mixed with secondary aluminum ash at a liquid-to-solid ratio of 0.8:1 mL / g and stirred for 3 hours to obtain a phosphorus-sulfuric acid-released aluminum ash slurry, wherein the stirring speed was 105 rpm. The phosphorus-sulfuric acid-released aluminum ash slurry was dried at 100℃ to obtain phosphorus-sulfuric acid-released aluminum powder. The phosphorus-sulfuric acid-released aluminum powder was placed in a calcining furnace and calcined for 2.5 hours to obtain calcined activated material, wherein the calcination temperatures were 225℃, 250℃, 275℃, 300℃, 450℃, 600℃, 650℃, 700℃, and 750℃. Water and the calcined activated material were mixed at a liquid-to-solid ratio of 2:1 mL / g and stirred for 3 hours, followed by solid-liquid separation. The resulting liquid portion was an aluminum-rich liquid, wherein the stirring speed was 105 rpm. Sodium hydroxide solution was added to the aluminum-rich liquid to adjust the pH to 4.5, resulting in an aluminum-rich slurry with a sodium hydroxide solution concentration of 3.75 M. The aluminum-rich slurry was then subjected to low-temperature plasma irradiation for 2.5 hours to obtain a plasma-activated aluminum-rich slurry, with an irradiation voltage of 40 kV. The plasma-activated aluminum-rich slurry was then sprayed into a drum drying oven, yielding dried particles that were highly active polyaluminum sulfate flocculants.

[0049] The purification test of landfill leachate concentrate, the detection of COD concentration and the calculation of COD adsorption capacity, the detection of total phosphorus concentration and the calculation of total phosphorus adsorption capacity, the detection of ammonia nitrogen concentration and the calculation of ammonia nitrogen adsorption capacity, and the detection of mercury ion concentration and the calculation of adsorption capacity are all the same as in Example 1.

[0050] The adsorption capacity results for COD, total phosphorus, ammonia nitrogen, and mercury ions are shown in Table 2.

[0051] Table 2. Effect of calcination temperature on the performance of the prepared high-activity polyaluminum sulfate flocculant

[0052]

[0053]

[0054] As shown in Table 2, when the calcination temperature is below 300℃ (as shown in Table 2, calcination temperatures = 275℃, 250℃, 225℃, and even lower values ​​not listed in Table 2), the calcination temperature is low, resulting in insufficient material reaction. Consequently, the adsorption capacity of pollutants COD, total phosphorus, ammonia nitrogen, and mercury ions in the prepared flocculant decreases significantly with decreasing calcination temperature. When the calcination temperature is between 300℃ and 600℃ (as shown in Table 2, calcination temperatures = 300℃, 450℃, and 600℃), during the calcination process, aluminum phosphate gel can selectively bind elements such as calcium, magnesium, silicon, and titanium in the secondary aluminum ash, forming insoluble impurity precipitates and molten agglomerates. Simultaneously, during the calcination process, sulfate ions further penetrate into the aluminum ash particles, forming aluminum sulfate with more aluminum. Ultimately, the prepared flocculants exhibited adsorption capacities greater than 1344 mg / g for COD, greater than 184 mg / g for total phosphorus, greater than 626 mg / g for ammonia nitrogen, and greater than 35 mg / g for mercury ions. When the calcination temperature exceeded 600℃ (as shown in Table 2, calcination temperatures of 650℃, 700℃, 750℃, and higher values ​​not listed in Table 2), the excessively high calcination temperature led to over-burning of the material, resulting in a significant decrease in the adsorption capacities of COD, total phosphorus, ammonia nitrogen, and mercury ions in the prepared flocculants with further increases in calcination temperature. Therefore, considering both efficiency and cost, a calcination temperature between 300 and 600℃ is most favorable for improving the adsorption performance of the prepared highly active polyaluminum sulfate flocculant.

[0055] Example 3: Effect of Low-Temperature Plasma Irradiation Time on the Performance of the Prepared Highly Active Polyaluminum Sulfate Flocculant

[0056] A phosphoric acid solution and a sulfuric acid solution were mixed at a molar ratio of 16:100 to obtain a phosphorus-doped sulfuric acid solution, wherein the concentration of the sulfuric acid solution was 7.5M. The phosphorus-doped sulfuric acid solution was mixed with secondary aluminum ash at a liquid-to-solid ratio of 1.2:1 mL / g and stirred for 5 hours to obtain a phosphorus-sulfuric acid-released aluminum ash slurry, wherein the stirring speed was 180 rpm. The phosphorus-sulfuric acid-released aluminum ash slurry was dried at 150℃ to obtain phosphorus-sulfuric acid-released aluminum powder. The phosphorus-sulfuric acid-released aluminum powder was calcined in a calcining furnace for 4.5 hours to obtain a calcined activated material, wherein the calcination temperature was 600℃. Water and the calcined activated material were mixed at a liquid-to-solid ratio of 3:1 mL / g and stirred for 5 hours, followed by solid-liquid separation. The resulting liquid portion was an aluminum-rich liquid, wherein the stirring speed was 180 rpm. Sodium hydroxide solution was added to the aluminum-rich liquid to adjust the pH to 6, thereby obtaining an aluminum-rich slurry, wherein the concentration of the sodium hydroxide solution was 5M. Aluminum-rich slurry was subjected to low-temperature plasma irradiation for 0.25 hours, 0.3 hours, 0.4 hours, 0.5 hours, 2.5 hours, 4.5 hours, 5 hours, 5.5 hours, and 6 hours to obtain plasma-activated aluminum-rich slurry, wherein the low-temperature plasma irradiation voltage was 75 kV. The plasma-activated aluminum-rich slurry was sprayed into a drum drying oven, and the resulting dried particles were highly active polyaluminum sulfate flocculants.

[0057] The purification test of landfill leachate concentrate, the detection of COD concentration and the calculation of COD adsorption capacity, the detection of total phosphorus concentration and the calculation of total phosphorus adsorption capacity, the detection of ammonia nitrogen concentration and the calculation of ammonia nitrogen adsorption capacity, and the detection of mercury ion concentration and the calculation of adsorption capacity are all the same as in Example 1.

[0058] The adsorption capacities for COD, total phosphorus, ammonia nitrogen, and mercury ions are shown in Table 3.

[0059] Table 3. Effect of low-temperature plasma irradiation time on the performance of the prepared high-activity polyaluminum sulfate flocculant.

[0060]

[0061] As shown in Table 3, when the low-temperature plasma irradiation time is less than 0.5 hours (as shown in Table 3, when the low-temperature plasma irradiation time = 0.4 hours, 0.3 hours, 0.25 hours, and even lower values ​​not listed in Table 3), the low-temperature plasma irradiation time is short, the hydrolysis and polymerization of aluminum sulfate in the aluminum-rich slurry are weakened, the oxidation of iron and titanium is insufficient, and the microstructure of the polyaluminum sulfate flocculant is not significantly changed. As a result, the adsorption capacity of pollutants COD, total phosphorus, ammonia nitrogen, and mercury ions in the prepared flocculant decreases significantly with the decrease of low-temperature plasma irradiation time. When the low-temperature plasma irradiation time is equal to 0.5–4.5 hours (as shown in Table 3, low-temperature plasma irradiation time = 0.5 hours, 2.5 hours, and 4.5 hours), sodium hydroxide solution is added to the aluminum-rich liquid, and the aluminum-rich slurry is subjected to low-temperature plasma irradiation. Hydroxide ions, in conjunction with oxygen free radicals and hydroxyl free radicals, promote the hydrolysis and polymerization of aluminum sulfate in the aluminum-rich slurry. At the same time, oxygen free radicals and hydroxyl free radicals can oxidize the small amount of residual iron and titanium elements in aluminum sulfate, forming a polyaluminum sulfate flocculant mixed with multivalent iron and titanium substances. The ultrasound, microwaves, and free radicals released during the low-temperature plasma irradiation process can also simultaneously and significantly change the microstructure of the polyaluminum sulfate flocculant, thereby preparing a highly active polyaluminum sulfate flocculant. Finally, the prepared flocculant has a COD adsorption capacity greater than 1386 mg / g, a total phosphorus adsorption capacity greater than 188 mg / g, an ammonia nitrogen adsorption capacity greater than 640 mg / g, and a mercury ion adsorption capacity greater than 38 mg / g. When the low-temperature plasma irradiation time exceeds 4.5 hours (as shown in Table 3, where the irradiation time is 5 hours, 5.5 hours, 6 hours, and higher values ​​not listed in Table 3), the excessively long irradiation time leads to excessive agglomeration and potential neutralization of the flocculant. Consequently, the adsorption capacity of the prepared flocculant for pollutants such as COD, total phosphorus, ammonia nitrogen, and mercury ions significantly decreases with further increases in the low-temperature plasma irradiation time. Therefore, considering both benefits and costs, a low-temperature plasma irradiation time of 0.5–4.5 hours is most advantageous for improving the adsorption performance of the prepared highly active polyaluminum sulfate flocculant.

[0062] The effect of different processes on the performance of the prepared high-activity polyaluminum sulfate flocculant

[0063] The process of this invention is as follows: Phosphoric acid solution and sulfuric acid solution are mixed at a molar ratio of 16:100 to obtain a phosphorus-doped sulfuric acid solution, wherein the concentration of the sulfuric acid solution is 7.5M. The phosphorus-doped sulfuric acid solution is mixed with secondary aluminum ash at a liquid-to-solid ratio of 1.2:1 mL / g and stirred for 5 hours to obtain a phosphorus-sulfuric acid-released aluminum ash slurry, wherein the stirring speed is 180 rpm. The phosphorus-sulfuric acid-released aluminum ash slurry is dried at 150℃ to obtain phosphorus-sulfuric acid-released aluminum powder. The phosphorus-sulfuric acid-released aluminum powder is placed in a calcining furnace and calcined for 4.5 hours to obtain a calcined material, wherein the calcination temperature is 600℃. Water and the calcined material are mixed at a liquid-to-solid ratio of 3:1 mL / g and stirred for 5 hours, followed by solid-liquid separation. The resulting liquid portion is an aluminum-rich liquid, wherein the stirring speed is 180 rpm. Sodium hydroxide solution is added to the aluminum-rich liquid to make the pH of the aluminum-rich liquid 6, thereby obtaining an aluminum-rich slurry, wherein the concentration of the sodium hydroxide solution is 5M. Aluminum-rich slurry was subjected to low-temperature plasma irradiation for 4.5 hours to obtain plasma-activated aluminum-rich slurry, wherein the low-temperature plasma irradiation voltage was 75kV. The plasma-activated aluminum-rich slurry was sprayed into a drum drying oven, and the resulting dried particles were highly active polyaluminum sulfate flocculants.

[0064] Comparative Process 1: A diluted sulfuric acid solution with a concentration of 7.5M was obtained by mixing water and sulfuric acid solution at a molar mass ratio of 16:100. The diluted sulfuric acid solution was then mixed with secondary aluminum ash at a liquid-to-solid ratio of 1.2:1 mL / g and stirred for 5 hours to obtain sulfuric acid-released aluminum ash slurry at a stirring speed of 180 rpm. The sulfuric acid-released aluminum ash slurry was dried at 150℃ to obtain sulfuric acid-released aluminum powder. The sulfuric acid-released aluminum powder was calcined in a calcining furnace for 4.5 hours to obtain calcined activated material at a calcination temperature of 600℃. Water and calcined activated material were then mixed at a liquid-to-solid ratio of 3:1 mL / g and stirred for 5 hours to separate the solid and liquid components. The resulting liquid portion was an aluminum-rich liquid, with a stirring speed of 180 rpm. Sodium hydroxide solution was added to the aluminum-rich liquid to adjust the pH to 6, resulting in an aluminum-rich slurry with a sodium hydroxide solution concentration of 5M. Aluminum-rich slurry was subjected to low-temperature plasma irradiation for 4.5 hours to obtain plasma-activated aluminum-rich slurry, wherein the low-temperature plasma irradiation voltage was 75kV. The plasma-activated aluminum-rich slurry was sprayed into a drum drying oven, and the resulting dried particles were highly active polyaluminum sulfate flocculants.

[0065] Comparative Process 2: A phosphoric acid solution and a sulfuric acid solution were mixed at a molar ratio of 16:100 to obtain a phosphorus-doped sulfuric acid solution, with a sulfuric acid concentration of 7.5M. The phosphorus-doped sulfuric acid solution was mixed with secondary aluminum ash at a liquid-to-solid ratio of 1.2:1 mL / g and stirred for 5 hours to obtain a phosphorus-sulfuric acid-released aluminum ash slurry, with a stirring speed of 180 rpm. The phosphorus-sulfuric acid-released aluminum ash slurry was dried at 150℃ to obtain phosphorus-sulfuric acid-released aluminum powder. Water and phosphorus-sulfuric acid-released aluminum powder were mixed at a liquid-to-solid ratio of 3:1 mL / g and stirred for 5 hours, followed by solid-liquid separation. The resulting liquid portion was an aluminum-rich liquid, with a stirring speed of 180 rpm. Sodium hydroxide solution was added to the aluminum-rich liquid to adjust the pH to 6, obtaining an aluminum-rich slurry with a sodium hydroxide solution concentration of 5M. The aluminum-rich slurry was subjected to low-temperature plasma irradiation for 4.5 hours to obtain a plasma-activated aluminum-rich slurry, with a low-temperature plasma irradiation voltage of 75 kV. The plasma-activated aluminum-rich slurry was sprayed into a drum drying oven, and the resulting dried particles were high-activity polyaluminum sulfate flocculants.

[0066] Comparative Process 3: A phosphoric acid solution and a sulfuric acid solution were mixed at a molar ratio of 16:100 to obtain a phosphorus-doped sulfuric acid solution, with a sulfuric acid concentration of 7.5M. The phosphorus-doped sulfuric acid solution was mixed with secondary aluminum ash at a liquid-to-solid ratio of 1.2:1 mL / g and stirred for 5 hours to obtain a phosphorus-sulfuric acid-released aluminum ash slurry, with a stirring speed of 180 rpm. The phosphorus-sulfuric acid-released aluminum ash slurry was dried at 150℃ to obtain phosphorus-sulfuric acid-released aluminum powder. The phosphorus-sulfuric acid-released aluminum powder was calcined in a calcining furnace for 4.5 hours to obtain a calcined activated material, with a calcination temperature of 600℃. Water and the calcined activated material were mixed at a liquid-to-solid ratio of 3:1 mL / g and stirred for 5 hours, followed by solid-liquid separation. The resulting liquid portion was an aluminum-rich liquid, with a stirring speed of 180 rpm. Sodium hydroxide solution was added to the aluminum-rich liquid to adjust the pH to 6, obtaining an aluminum-rich slurry with a sodium hydroxide solution concentration of 5M. The aluminum-rich slurry is sprayed into a drum drying oven, and the resulting dried particles are highly active polyaluminum sulfate flocculants.

[0067] The purification test of landfill leachate concentrate, the detection of COD concentration and the calculation of COD adsorption capacity, the detection of total phosphorus concentration and the calculation of total phosphorus adsorption capacity, the detection of ammonia nitrogen concentration and the calculation of ammonia nitrogen adsorption capacity, and the detection of mercury ion concentration and the calculation of adsorption capacity are all the same as in Example 1.

[0068] The adsorption capacities for COD, total phosphorus, ammonia nitrogen, and mercury ions are shown in Table 4.

[0069] Table 4. Effects of different processes on the performance of the prepared high-activity polyaluminum sulfate flocculant.

[0070]

[0071]

[0072] As shown in Table 4, the COD, total phosphorus, ammonia nitrogen and mercury ion adsorption capacity of the high-activity polyaluminum sulfate flocculant prepared by the process of the present invention are significantly higher than those of comparative process 1, comparative process 2 and comparative process 3.

Claims

1. A method for preparing highly active polyaluminum sulfate flocculant using secondary aluminum ash, characterized in that, Includes the following steps: (1) Mix phosphoric acid solution and sulfuric acid solution to obtain phosphorus-doped sulfuric acid solution; the molar mass ratio of the phosphoric acid solution and sulfuric acid solution is 4~16:100; (2) Mix the phosphorus-doped sulfuric acid solution and secondary aluminum ash described in step (1), stir, and obtain phosphorus-sulfuric acid degassing aluminum ash slurry; (3) The phosphorus-sulfuric acid degassing aluminum slurry described in step (2) is dried and calcined to obtain calcined activated material; the calcination temperature is 300~600℃; (4) Mix water and the calcined activated material described in step (3), stir, separate solid and liquid, add sodium hydroxide solution to the liquid to adjust pH, irradiate with low-temperature plasma, and dry to obtain high-activity polyaluminum sulfate flocculant; the low-temperature plasma irradiation time is 0.5~4.5 hours.

2. The method according to claim 1, characterized in that, The concentration of the sulfuric acid solution mentioned in step (1) is 2.5~7.5M.

3. The method according to claim 1, characterized in that, The liquid-to-solid ratio of the phosphorus-doped sulfuric acid solution and the secondary aluminum ash mentioned in step (2) is 0.4~1.2:1mL / g.

4. The method according to claim 1, characterized in that, The calcination time in step (3) is 0.5 to 4.5 hours.

5. The method according to claim 1, characterized in that, The liquid-solid ratio of water and calcined activated material in step (4) is 1~3:1mL / g.

6. The method according to claim 1, characterized in that, The pH value mentioned in step (4) is 3 to 6.

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