Coal gasification coarse slag-based polyaluminum ferric chloride flocculant, preparation method and application thereof

Abstract

The application provides a preparation method of a polymeric aluminum ferric chloride flocculant based on coal gasification coarse slag and application thereof. 3+ and Fe 3+ Metal ions such as Al The two-step acid leaching method (hydrochloric acid-sulfuric acid) is used to leach Al The two-step acid leaching method (hydrochloric acid-sulfuric acid) is used to leach Al The hydrochloric acid leaching liquid and the sulfuric acid leaching liquid are mixed in a volume ratio of 1:1 to carry out a polymerization reaction under the condition that the pH value is 1, and finally, the coal gasification coarse slag-based polymeric aluminum ferric chloride flocculant is obtained through aging, drying and grinding. The application not only improves the high-value utilization rate of the coal gasification coarse slag, but also realizes effective treatment of the coal washing wastewater, and achieves the purpose of "waste treatment by waste".

Description

Technical Field

[0001] This invention relates to the technical field of flocculants, specifically to a coal gasification coarse slag-based polyaluminum ferric chloride flocculant, its preparation method, and its application. Background Technology

[0002] In recent years, the world has faced major challenges such as environmental pollution, ecological imbalance, and energy resource shortages. Against this backdrop, China has made environmental protection and sustainable development of resource utilization a core strategy. The Yulin region of Shaanxi Province is rich in coal resources, which has spurred the rapid rise of the coal chemical industry. However, due to its late start and the immaturity of some technologies, a large amount of coal gasification slag has not been effectively utilized and is usually disposed of through landfill or stockpiling. In the development of the coal industry, problems such as coal washing wastewater, coal slurry from coal preparation plants, and surface washing wastewater from coal-fired power plants have posed serious challenges to the ecological environment. Coal washing wastewater, due to its high turbidity, small particle size, and negative charge, is suspended in water; at the same time, affected by gravity and Brownian motion, it remains turbid. Especially after natural sedimentation, the supernatant of the coal washing wastewater still contains a large amount of black coal slurry suspended solids, including various chemical reagents added during the coal preparation process and harmful heavy metal components. If these wastewaters fail to meet discharge standards, they will not only severely pollute water sources but also potentially cause problems such as river blockage and coal slurry loss. Furthermore, if they cannot be properly recycled, they will exacerbate water shortages in the coal industry, reducing production efficiency and economic benefits. Therefore, the effective treatment of coal washing wastewater has become an important research topic for improving the environmental protection level and economic efficiency of the coal industry.

[0003] In addition to traditional methods, new treatment technologies have been incorporated into the treatment strategies for coal washing wastewater. These new methods mainly integrate various treatment resources, applying innovative techniques such as microbial treatment and microwave treatment to practice. The use of flocculants is a traditional chemical method. Common flocculants can be divided into inorganic and organic flocculants. Inorganic flocculants mainly include low-molecular-weight or high-molecular-weight iron and aluminum flocculants, as well as composite flocculants. This method involves adding flocculants to the coal washing wastewater, utilizing the dissociation and hydrolysis products of the flocculants to cause fine suspended particles and colloidal particles to aggregate into larger particles through collision, adsorption, adhesion, and bridging, thereby settling and purifying the wastewater. This method can effectively reduce the turbidity and color of wastewater and treat fine suspended solids and colloidal particles that are usually difficult to remove by natural sedimentation. The flocculation and sedimentation treatment process includes several parts such as dosing, mixing, reaction, and sedimentation separation. It can be used as an independent wastewater treatment method or combined with other wastewater treatment methods as a pretreatment, intermediate treatment or final treatment for coal washing wastewater.

[0004] In the coal washing process, the large amount of wastewater generated by coal washing plants needs to be recycled. However, this process typically requires the use of large amounts of flocculants. Market research shows that, under normal circumstances, processing one ton of clean coal requires 1 to 3 kilograms of flocculant. As the processing volume increases, the amount of flocculant used also increases significantly. This not only leads to increased costs for enterprises but may also have adverse effects on the aquatic environment. Therefore, designing a low-cost and high-performance flocculant is of great significance to the wastewater treatment market.

[0005] The gasification slag was sourced from Shaanxi Jingyi Chemical Group. Gasification slag is an important byproduct of coal gasification, possessing rich chemical components and potential for resource utilization. The gasifier used to generate this slag is a Texaco gasifier. Figure 1 As shown. Due to differences in gasification processes, operating conditions, and coal types, the morphology, moisture content, and residual carbon content of the coarse and fine slag also vary. For example... Figure 2 As shown, the fine slag has a black surface and its particles are finer than those of the coarse slag, with a dull and lackluster surface. The coarse slag has a grayish-black surface, with more distinct particles, some of which are glossy. The particle size of the coarse slag ranges from 450 to 1650 μm, accounting for 60% to 80% of the total slag discharge.

[0006] The carbon content of the gasification slag was analyzed according to the national standard method, as shown in Table 1. The residual carbon content of the coarse slag is around 15%, while that of the fine slag can be as high as 45%. However, the distribution of residual carbon is uneven, mainly due to the difference in particle size of the gasification slag, resulting in differences in pore structure. Specifically, the residual carbon content of the coarse slag decreases with increasing particle size. During gasification, the gasifying agent reacts with carbon, and the reaction rate is closely related to the diffusion rate affected by pore diffusion. The slag constituting the coarse slag has a longer residence time in the gasifier, resulting in a relatively complete gasification reaction, and the residual carbon can fully participate in the gasification reaction. In addition, the molten state of the slag allows its particles to reach the slag discharge port along the furnace wall, where the temperature decreases and larger particles are formed.

[0007] Table 1. Determination of Loss on Ignition of Coal Combustion Residue in Coal Gasification Slag

[0008]

[0009] The microstructure of coarse coal gasification slag is as follows Figure 3As shown, the morphological differences are mainly determined by their formation process. The coarse slag is obtained through a quenching and pulverizing process in a quenching tower. During quenching, the high-temperature product is rapidly cooled, forming larger inorganic particles. Subsequently, these particles are pulverized, forming a spherical particle structure with a broad and stable particle size distribution (B1). Simultaneously, a honeycomb-like porous structure (B2) may form between some particles, due to collisions between particles and structural reorganization under specific conditions during pulverization.

[0010] The main components of coal gasification slag are SiO2, Al2O3, CaO, Fe2O3, and residual carbon. Its chemical composition is significantly influenced by factors such as the origin of the raw coal and the type of gasifier. Although the chemical composition of coarse and fine slag differs, a high content of silicon, carbon, aluminum, and iron is a common and significant characteristic. XRF analysis of fine and coarse coal gasification slag yielded the results shown in Table 2. Regardless of whether it is coarse or fine slag, the main components remain SiO2, Al2O3, CaO, and Fe2O3, with the average content of these four oxides exceeding 88%. Notably, the content of alkaline oxides is higher than 40% of the total content, while the content of acidic oxides is lower than 35%. This finding reveals that variations in raw coal and gasification equipment can affect the chemical composition of coal gasification slag, but the high content of silicon, carbon, aluminum, and iron remains one of its significant characteristics.

[0011] Table 2. Oxide Composition Analysis of Fine and Coarse Coal Gasification Slag

[0012] Summary of the Invention

[0013] To address the aforementioned problems, this invention proposes a method for preparing a polyaluminum ferric chloride flocculant based on coal gasification coarse slag and its application. This flocculant not only effectively enhances the high-value utilization of coal gasification coarse slag but also efficiently treats coal washing wastewater, achieving waste reuse and thus realizing the goal of "treating waste with waste." Furthermore, the flocculant prepared by this invention has low production costs, significantly reducing wastewater treatment expenses.

[0014] In a first aspect, the present invention provides a method for preparing a polyaluminum ferric chloride flocculant based on coal gasification coarse slag, comprising the following steps:

[0015] (1) Hydrochloric acid leaching method: Add HCl solution and gasified crude residue into a container, place the container in a constant temperature water bath, heat and stir to carry out the reaction; let stand to separate the layers, take out the supernatant and place it in reagent bottle No. 1 for later use, put the remaining reactants into a centrifuge for solid-liquid separation, take out the liquid and place it in reagent bottle No. 1 for later use; wash the residue twice with deionized water, put the washed liquid in reagent bottle No. 1 to mix into HCl leaching solution, dry the residue and weigh it;

[0016] (2) Sulfuric acid leaching method: Add H2SO4 solution and gasification crude residue into a container, place the container in a constant temperature water bath, heat and stir to carry out the reaction; let stand to separate the layers, take out the supernatant and place it in reagent bottle No. 2 for later use, put the remaining reactants into a centrifuge for solid-liquid separation, take out the liquid and place it in reagent bottle No. 2 for later use; wash the residue twice with deionized water, put the washed liquid in reagent bottle No. 2 and mix to form H2SO4 leaching solution, dry the residue and weigh it;

[0017] (3) Polymerization: Mix HCl leachate with H2SO4 leachate, adjust pH value, mix, age, dry, synthesize flocculant, grind into powder for later use.

[0018] Preferably, in step (1), the molar concentration of the HCl solution is 7.5-8.5 mol / L.

[0019] Preferably, in step (1), the ratio of the volume of HCl solution added to the mass of the gasified crude residue is mL:g=(28-32):1.

[0020] Preferably, in step (1), the heating temperature is 75-85°C.

[0021] Preferably, in step (2), the molar concentration of the H2SO4 solution is 3.5-4.5 mol / L.

[0022] Preferably, in step (2), the ratio of the added volume of H2SO4 solution to the mass of gasified crude residue is mL:g=(38-42):1.

[0023] Preferably, in step (2), the heating temperature is 55-65°C.

[0024] Preferably, in step (3), the mass ratio of hydrochloric acid leachate to sulfuric acid leachate is (0.8-1.2):(0.8-1.2), the pH value is 0.8-1.2, and the aging time is 22-26h.

[0025] Preferably, the leaching efficiency of hydrochloric acid solution and sulfuric acid solution for metal ions in gasified crude slag is calculated using the following formula:

[0026]

[0027] In the formula:

[0028] d0 is the initial mass of the coarse slag from coal gasification, in grams;

[0029] d1 is the mass of the coarse coal gasification residue after acid leaching, in grams.

[0030] Secondly, the present invention provides a coal gasification coarse slag-based polyaluminum ferric chloride flocculant obtained by the preparation method described above.

[0031] Thirdly, this invention provides an application of the coal gasification coarse slag-based polyaluminum ferric chloride flocculant as described above in the treatment of coal washing wastewater.

[0032] In summary, this invention provides a coal gasification coarse slag-based polyaluminum ferric chloride flocculant, its preparation method, and its application. The beneficial effects of this invention are as follows:

[0033] This invention recovers Al from gasification crude residue through a two-stage process of hydrochloric acid impregnation and sulfuric acid impregnation. 3+ Fe 3+ By utilizing metal ions, a polyaluminum ferric chloride flocculant based on coal gasification coarse slag was successfully prepared. Through optimization of acid leaching conditions, adjusting the ratio of hydrochloric acid to sulfuric acid in the leachate to 1:1, and adjusting the pH to 1, a structurally stable amorphous polyionic flocculant was finally obtained. This invention not only enhances the high-value utilization of coal gasification coarse slag but also achieves efficient purification treatment of coal washing wastewater, thereby achieving the goal of "treating waste with waste" and significantly saving wastewater treatment costs.

[0034] Furthermore, the flocculant prepared under optimal conditions according to this invention achieved removal rates of 85.56% for chemical oxygen demand (COD) and 83.3% for ammonia nitrogen (NH3-N) in coal washing wastewater. When the flocculant dosage was 0.5 g·L... -1 After standing for 30 minutes, the removal efficiency of suspended solids (SS) reached 96.5%. Zeta potential analysis revealed that the flocculant carries a positive charge. Upon addition to the negatively charged coal washing wastewater, the interaction between the positive and negative charges neutralizes the charge, reducing the repulsive force between suspended solids and forming free flocs. Furthermore, the addition of the flocculant promotes the adsorption of colloidal particles, gradually transforming the flocculated structure from loose to dense. Adsorption bridging extends the branches, forming a long-chain network that extends the branches around other unadsorbed particles, causing them to aggregate and eventually form large aggregates. Finally, the trapping effect further promotes colloidal flocculation, achieving sedimentation of suspended solids. These results demonstrate that the flocculant has excellent decontamination capabilities for actual coal washing wastewater. Attached Figure Description

[0035] Figure 1 This is a demonstration diagram of the Texaco gasification system.

[0036] Figure 2 This is the original image of coal gasification slag.

[0037] Figure 3 This is a SEM image of the coal gasification slag.

[0038] Figure 4The figure shows the effects of hydrochloric acid solution concentration, the liquid-solid ratio of hydrochloric acid and gasified crude residue, acid leaching temperature, and acid leaching time on the leaching efficiency of metal ions.

[0039] Figure 5 The effects of the liquid-to-solid ratio of sulfuric acid solution and gasified crude residue, the concentration of sulfuric acid solution, the acid leaching time, and the acid leaching temperature on the leaching efficiency of metal ions were investigated.

[0040] Figure 6 This is the effect diagram of the optimal aggregation conditions.

[0041] Figure 7 This is a comparison chart of flocculation effects.

[0042] Figure 8 The image shows the results of the SS measurement.

[0043] Figure 9 XRD analysis diagrams of flocculants prepared with different volume ratios of hydrochloric acid leachate and sulfuric acid leachate.

[0044] Figure 10 Infrared spectroscopy images of flocculants prepared with different volume ratios of hydrochloric acid leachate and sulfuric acid leachate.

[0045] Figure 11 This is a flowchart of the flocculation mechanism.

[0046] Figure 12 This is a map showing the location of the Zeta points.

[0047] Figure 13 This is an image from an electron microscope analysis.

[0048] Figure 14 This is a SEM analysis image of the flocculant.

[0049] Figure 15 This is the energy spectrum of the flocculant. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0051] Example 1

[0052] A method for preparing a coal gasification coarse slag-based polyaluminum ferric chloride flocculant includes the following steps:

[0053] (1) Hydrochloric acid immersion method

[0054] A 4.0 mol / L HCl solution was used, and the HCl solution and the gasified crude residue were added to a flask at a liquid-to-solid ratio of mL:g = 10:1. The flask was placed in a constant temperature water bath for reaction at 40℃ for 2.0 h with a stirring speed of 200 rpm. After standing for 1 hour to allow for layering, the supernatant was aspirated with a syringe and placed in reagent bottle No. 1 for later use. The remaining reactants were placed in a centrifuge for solid-liquid separation, and the liquid was aspirated with a syringe and placed in reagent bottle No. 1 for later use. The residue was washed twice with 50 mL of deionized water (the washing solution was placed in reagent bottle No. 1 for later use), and the residue was dried and weighed.

[0055] (2) Sulfuric acid immersion method

[0056] A 2.0 mol / L H₂SO₄ solution was used, and the H₂SO₄ solution and the gasified crude residue were added to a flask at a liquid-to-solid ratio of mL:g = 20:1. The flask was placed in a constant temperature water bath for reaction at 40℃ for 1.0 h with a stirring speed of 200 rpm. After standing for 1 hour to allow for layering, the supernatant was aspirated with a syringe and placed in reagent bottle No. 2. The remaining reactants were placed in a centrifuge for solid-liquid separation, and the liquid was aspirated with a syringe and placed in reagent bottle No. 2 for later use. The residue was washed twice with 50 mL of deionized water (the washing solution was placed in reagent bottle No. 2 for later use), dried, and weighed.

[0057] (3) Aggregation

[0058] HCl leachate and H2SO4 leachate were mixed at a volume ratio of 3:1, and the pH was adjusted to 5.0 with NaOH solution. The mixture was stirred for 0.5 h. After the reaction was complete, the mixture was aged for 24 h and then dried in a constant temperature drying oven to obtain a flocculant, which was then ground into powder for later use.

[0059] Example 2

[0060] A method for preparing a coal gasification coarse slag-based polyaluminum ferric chloride flocculant includes the following steps:

[0061] (1) Hydrochloric acid immersion method

[0062] A 6.0 mol / L HCl solution was used, and the HCl solution and the gasified crude residue were added to a flask at a liquid-to-solid ratio of mL:g = 20:1. The flask was placed in a constant temperature water bath for reaction at 60℃ for 1.0 h with a stirring speed of 200 rpm. After standing for 1 hour to allow for layering, the supernatant was aspirated with a syringe and placed in reagent bottle No. 1 for later use. The remaining reactants were placed in a centrifuge for solid-liquid separation, and the liquid was aspirated with a syringe and placed in reagent bottle No. 1 for later use. The residue was washed twice with 50 mL of deionized water (the washing solution was placed in reagent bottle No. 1 for later use), dried, and weighed.

[0063] (2) Sulfuric acid immersion method

[0064] A 3.0 mol / L H₂SO₄ solution was used, and the H₂SO₄ solution and the gasified crude residue were added to a flask at a liquid-to-solid ratio of mL:g = 30:1. The flask was placed in a constant temperature water bath for reaction at 80℃ for 1.5 h with a stirring speed of 200 rpm. After standing for 1 hour to allow for layering, the supernatant was aspirated with a syringe and placed in reagent bottle No. 2. The remaining reactants were placed in a centrifuge for solid-liquid separation, and the liquid was aspirated with a syringe and placed in reagent bottle No. 2 for later use. The residue was washed twice with 50 mL of deionized water (the washing solution was placed in reagent bottle No. 2 for later use), dried, and weighed.

[0065] (3) Aggregation

[0066] HCl leachate and H2SO4 leachate were mixed at a volume ratio of 2:1, and the pH was adjusted to 4.0 with NaOH solution. The mixture was stirred for 0.5 h. After the reaction was complete, the mixture was aged for 24 h and then dried in a constant temperature drying oven to obtain a flocculant, which was then ground into powder for later use.

[0067] Example 3

[0068] A method for preparing a coal gasification coarse slag-based polyaluminum ferric chloride flocculant includes the following steps:

[0069] (1) Hydrochloric acid immersion method

[0070] An 8.0 mol / L HCl solution was used, and the HCl solution and the gasified crude residue were added to a flask at a liquid-to-solid ratio of mL:g = 30:1. The flask was placed in a constant temperature water bath for reaction at 80℃ for 1.5 h with a stirring speed of 200 rpm. After standing for 1 hour to allow for layering, the supernatant was aspirated with a syringe and placed in reagent bottle No. 1 for later use. The remaining reactants were placed in a centrifuge for solid-liquid separation, and the liquid was aspirated with a syringe and placed in reagent bottle No. 1 for later use. The residue was washed twice with 50 mL of deionized water (the washing solution was placed in reagent bottle No. 1 for later use), dried, and weighed.

[0071] (2) Sulfuric acid immersion method

[0072] A 4.0 mol / L H₂SO₄ solution was used, and the H₂SO₄ solution and the gasified crude residue were added to a flask at a liquid-to-solid ratio of mL:g = 40:1. The flask was placed in a constant temperature water bath for reaction at 60℃ for 2.0 h with a stirring speed of 200 rpm. After standing for 1 hour to allow for layering, the supernatant was aspirated with a syringe and placed in reagent bottle No. 2. The remaining reactants were placed in a centrifuge for solid-liquid separation, and the liquid was aspirated with a syringe and placed in reagent bottle No. 2 for later use. The residue was washed twice with 50 mL of deionized water (the washing solution was placed in reagent bottle No. 2 for later use), dried, and weighed.

[0073] (3) Aggregation

[0074] HCl leachate and H2SO4 leachate were mixed at a volume ratio of 1:1, and the pH was adjusted to 1.0 with NaOH solution. The mixture was stirred for 0.5 h. After the reaction was complete, the mixture was aged for 24 h and then dried in a constant temperature drying oven to obtain a flocculant, which was then ground into powder for later use.

[0075] Example 4

[0076] A method for preparing a coal gasification coarse slag-based polyaluminum ferric chloride flocculant includes the following steps:

[0077] (1) Hydrochloric acid immersion method

[0078] A 10.0 mol / L HCl solution was used, and the HCl solution and the gasified crude residue were added to a flask at a liquid-to-solid ratio of mL:g = 40:1. The flask was placed in a constant temperature water bath for reaction at 100℃ for 0.5 h with a stirring speed of 200 rpm. After standing for 1 hour to allow for layering, the supernatant was aspirated with a syringe and placed in reagent bottle No. 1 for later use. The remaining reactants were placed in a centrifuge for solid-liquid separation, and the liquid was aspirated with a syringe and placed in reagent bottle No. 1 for later use. The residue was washed twice with 50 mL of deionized water (the washing solution was placed in reagent bottle No. 1 for later use), dried, and weighed.

[0079] (2) Sulfuric acid immersion method

[0080] A 5.0 mol / L H₂SO₄ solution was used, and the H₂SO₄ solution and the gasified crude residue were added to a flask at a liquid-to-solid ratio of mL:g = 50:1. The flask was placed in a constant temperature water bath for reaction at 100℃ for 2.5 h with a stirring speed of 200 rpm. After standing for 1 hour to allow for layering, the supernatant was aspirated with a syringe and placed in reagent bottle No. 2. The remaining reactants were placed in a centrifuge for solid-liquid separation, and the liquid was aspirated with a syringe and placed in reagent bottle No. 2 for later use. The residue was washed twice with 50 mL of deionized water (the washing solution was placed in reagent bottle No. 2 for later use), dried, and weighed.

[0081] (3) Aggregation

[0082] HCl leachate and H2SO4 leachate were mixed at a volume ratio of 2:3, and the pH was adjusted to 2.0 with NaOH solution. The mixture was stirred for 0.5 h. After the reaction was complete, the mixture was aged for 24 h and then dried in a constant temperature drying oven to obtain a flocculant, which was then ground into powder for later use.

[0083] Example 5

[0084] A method for preparing a coal gasification coarse slag-based polyaluminum ferric chloride flocculant includes the following steps:

[0085] (1) Hydrochloric acid immersion method

[0086] An 8.0 mol / L HCl solution was used, and the HCl solution and the gasified crude residue were added to a flask at a liquid-to-solid ratio of mL:g = 30:1. The flask was placed in a constant temperature water bath for reaction at 80℃ for 1.5 h with a stirring speed of 200 rpm. After standing for 1 hour to allow for layering, the supernatant was aspirated with a syringe and placed in reagent bottle No. 1 for later use. The remaining reactants were placed in a centrifuge for solid-liquid separation, and the liquid was aspirated with a syringe and placed in reagent bottle No. 1 for later use. The residue was washed twice with 50 mL of deionized water (the washing solution was placed in reagent bottle No. 1 for later use), dried, and weighed.

[0087] (2) Sulfuric acid immersion method

[0088] A 4.0 mol / L H₂SO₄ solution was used, and the H₂SO₄ solution and the gasified crude residue were added to a flask at a liquid-to-solid ratio of mL:g = 40:1. The flask was placed in a constant temperature water bath for reaction at 60℃ for 2.0 h with a stirring speed of 200 rpm. After standing for 1 hour to allow for layering, the supernatant was aspirated with a syringe and placed in reagent bottle No. 2. The remaining reactants were placed in a centrifuge for solid-liquid separation, and the liquid was aspirated with a syringe and placed in reagent bottle No. 2 for later use. The residue was washed twice with 50 mL of deionized water (the washing solution was placed in reagent bottle No. 2 for later use), dried, and weighed.

[0089] (3) Aggregation

[0090] HCl leachate and H2SO4 leachate were mixed at a volume ratio of 3:2, and the pH was adjusted to 3.0 with NaOH solution. The mixture was stirred for 0.5 h. After the reaction was complete, the mixture was aged for 24 h and then dried in a constant temperature drying oven to obtain a flocculant, which was then ground into powder for later use.

[0091] The leaching efficiency of hydrochloric acid solution and sulfuric acid solution for metal ions in gasified crude slag in Examples 1 to 5 is calculated as follows:

[0092]

[0093] In the formula:

[0094] d0 is the initial mass of the coarse slag from coal gasification, in grams;

[0095] d1 is the mass of the coarse coal gasification residue after acid leaching, in grams.

[0096] Detection methods and results:

[0097] 1. Optimal immersion conditions

[0098] To illustrate the metal ion leaching behavior of hydrochloric acid solution during the impregnation of gasified coarse slag, the effects of hydrochloric acid solution concentration, the liquid-to-solid ratio of hydrochloric acid and gasified coarse slag, the acid leaching temperature, and the acid leaching time on the metal ion leaching efficiency were investigated. Figure 4 As shown.

[0099] (a) As the concentration of hydrochloric acid solution increases from 4 mol / L to 8 mol / L, Al 3+ and Fe 3+ The leaching efficiency is correspondingly improved, especially for Fe. 3+ A high concentration of hydrochloric acid solution can provide sufficient H+. + This facilitates the reaction with active sites on the gasification slag, thereby improving Al 3+ and Fe 3+ The leaching efficiency. At a hydrochloric acid solution concentration of 10 mol / L, Al... 3+ and Fe 3+ The leaching efficiency decreased slightly. Therefore, the optimal hydrochloric acid solution concentration was found to be 8 mol / L.

[0100] (b) In the liquid-solid ratio of hydrochloric acid solution and gasified crude residue, the leaching efficiency is the highest when the solution volume increases from 10 mL to 30 mL, and the leaching efficiency decreases when it increases to 40 mL. Therefore, the optimal liquid-solid ratio of hydrochloric acid solution is 30:1.

[0101] (c) At 40–80 °C, Fe 3+ The leaching efficiency increased from 35.78% to 55.59%. At 80–100℃, Fe... 3 + The leaching efficiency decreased from 55.59% to 33.76%. This may be attributed to the accelerated molecular motion and increased activity of the acid leaching process. Therefore, the leaching temperature was chosen to be 80℃ during the acid leaching process in hydrochloric acid solution.

[0102] (d) It is clear from the figure that the leaching efficiency of metal ions is the highest at 1.5h.

[0103] It can be known Figure 4 The chemical reaction that occurs in is:

[0104] Al₂O₃ + 6HCl = 2AlCl₃ + 3H₂O (1)

[0105] Fe₂O₃ + 6HCl = 2FeCl₃ + 3H₂O (2)

[0106] Both Al₂O₃ and Fe₂O₃ oxides are readily soluble in acids. During the above reaction, the solution gradually changes from colorless to yellowish-brown, indicating that Fe... 3+ After acid leaching, no significant color lightening occurred despite increases in leaching time, acid concentration, and leaching temperature. This indicates that during hydrochloric acid leaching, the primary leached component is Fe. 3+ And Al 3+ Only a portion was leached. This phenomenon may be due to Fe. 3+ It is more stable in hydrochloric acid solution, and even in high concentrations of H+. + and Cl - Under certain conditions, it is more easily dissolved and leached. In contrast, although Al 3+ It can dissolve under acidic conditions, but its solubility and leaching rate are relatively low, resulting in a low concentration in solution.

[0107] 2. Optimal sulfuric acid immersion conditions

[0108] To illustrate the leaching behavior of metal ions in the gasification slag leaching process using sulfuric acid solution, the effects of the liquid-to-solid ratio of sulfuric acid solution and gasification slag, sulfuric acid concentration, leaching time, and leaching temperature on the metal ion leaching efficiency were investigated. Figure 5 As shown.

[0109] (a) As the liquid-to-solid ratio of the sulfuric acid solution to the gasified crude slag increases, the leaching rate of metal ions also increases. This is especially true for Al. 3+ Considering overall economic benefits and energy consumption, a leaching liquid-to-solid ratio of 40:1 was selected.

[0110] (b) The results show that increasing the concentration of sulfuric acid solution is beneficial to Al 3+ The leaching of Al, and when the concentration of sulfuric acid solution increases from 40% to 50%, 3+ The overall leaching efficiency decreased slightly. Therefore, it is believed that the sulfuric acid solution has the greatest impact on the metal leaching efficiency when the concentration of sulfuric acid solution is controlled at 4 mol / L.

[0111] (c) The acid leaching time is relatively gradual overall, indicating that the acid leaching time has a relatively stable effect on Al. 3+ It doesn't have a significant impact; the optimal pickling time, as shown in the graph, is 2 hours.

[0112] (d) In the temperature range of 40–60℃, Al 3+ The leaching efficiency increased rapidly from 36.23% to 41.55% at a leaching temperature of 80℃. 3+The leaching efficiency decreased significantly, indicating that temperature changes have a certain influence on the leaching of metal ions. Therefore, the optimal leaching temperature is 60℃.

[0113] It can be known Figure 5 The chemical reaction that occurs in is:

[0114] Al2O3+3H2SO4=Al2(SO4)3+3H2O (3)

[0115] 2Fe2O3+3H2SO4=Fe2(SO4)3+3H2O (4)

[0116] During the sulfuric acid impregnation process, both Al2O3 and Fe2O3 will dissolve and leach out Al. 3+ and Fe 3+ However, during the impregnation process, although Al 3+ and Fe 3+ All were leached out, but the resulting solution was grayish-white and did not show any signs of Fe. 3+ The resulting yellowish-brown change indicates that Al 3+ These are the main leaching ions. As the concentration of H₂SO₄ increases, the grayish-white color of the solution intensifies, becoming more opaque. This is because... The increase in ion concentration makes Al 3+ More easily leached, while Fe 3+ Mostly related to H + The H2SO4 solution will combine with Fe under heating conditions. However, some of the H2SO4 solution will evaporate, reducing the amount of H2SO4 that can combine with Fe. 3+ Combined H + Concentration, only a small portion remains with The reaction. Therefore, Fe in the solution 3+ The content of [unspecified substance] is relatively low; the main component is Al. 3+ Furthermore, the grayish-white color of the leachate is mainly due to Al. 3+ The existence of [something] causes this.

[0117] 3. Optimal aggregation conditions

[0118] like Figure 6 As shown, (a) and (b) are the NH3-N determination results of coal washing wastewater. The bar chart represents the NH3-N determination, and the line graph represents the flocculation efficiency. The leftmost column is the control, which shows the NH3-N content of the coal washing wastewater used in the experiment. Figure (a) shows that the NH3-N value is lowest and the flocculation efficiency is highest when the pH of the flocculant is 1, and then increases sequentially, slightly decreasing at pH 4 before increasing again. Figure (b) indicates that the NH3-N value is lowest and the flocculation efficiency is highest when the volume ratio of hydrochloric acid leachate to sulfuric acid leachate is 1:1.

[0119] Figures (c) and (d) show the COD determination results. The bar chart represents the COD determination of coal washing wastewater, and the line graph represents the flocculation efficiency. The leftmost column represents the control, showing the COD content of the coal washing wastewater used in the experiment. Figure (c) shows that the COD value is lowest and the flocculation efficiency is highest when the pH value of the flocculant is 1, with subsequent values ​​increasing sequentially. Figure (d) shows that the COD value is lowest and the flocculation efficiency is highest when the ratio of hydrochloric acid leachate to sulfuric acid leachate is 1:1.

[0120] pH is one of the direct factors affecting the coagulation performance of flocculants, directly influencing their adsorption bridging and charge neutralization capabilities. Based on the results of two experiments, the optimal polymerization conditions are achieved when the volume ratio of hydrochloric acid leachate to sulfuric acid leachate is 1:1 and the pH of the flocculant is 1, resulting in COD and NH3-N removal rates of 85.56% and 83.3%, respectively. This also indicates that some acid-base neutralization reactions occur during the flocculation process.

[0121] Figure 6 The reaction is as follows: ferric chloride and aluminum sulfate hydrolyze to produce hydrogen ions, which then undergo a double hydrolysis reaction. The two acid leaching solutions are mixed in a certain proportion, and the removal efficiency of COD and NH3-N in coal washing wastewater is used to determine the Al2O3 concentration. 3+ and Fe 3+ The effect of different molar ratios on flocculation effect. The results show that Fe... 3+ The introduction of [a specific ingredient] can improve the coagulation performance of this invention, but Al 3+ and Fe 3+ Both excessively high and low molar ratios may be detrimental to improving coagulation performance, indicating that in the hydrolysis polymerization process of this invention, polyAl... 3+ and Fe 3+ There is a synergistic effect between them. Only in suitable Al... 3+ and Fe 3+ Only under specific molar ratios can stable products and excellent processing results be obtained.

[0122]

[0123] The two hydrolysis reactions are superimposed to obtain:

[0124] FeCl3+3H2O+Al2(SO4)3=Fe(OH)3+Al(OH)3↓+3HCl (7)

[0125] After aging for 24 hours, the polymerized solution turned a deep yellow color, indicating the presence of Fe in the solution. 3+ A white precipitate was also present. This is due to the instability of the system caused by the addition of an alkalizing agent for neutralization. 3+ With OH - The reaction, as the pH value increases, OH -The concentration also increased accordingly, breaking the Al 3+ The dissolution and precipitation equilibrium is reached, forming Al(OH)3 precipitate. To avoid excessive Al... 3+ With OH - The combination of precipitation and Al 3+ Loss and loss of Fe 3+ To maintain a balance and reduce the synergistic effect of the two ions, the pH value must be controlled to avoid being too high. Ultimately, the optimal pH value was determined to be 1 to ensure Fe... 3+ And Al 3+ It has an effective synergistic effect, while preventing the formation of excessive Al(OH)3 precipitate.

[0126] 4. Flocculation effect

[0127] 4.1 Comparison of flocculation effects

[0128] Figure 7 The image shows a comparison of five 200mL cups of the same batch of coal washing wastewater. From left to right, the images show the effects of adding (0.25, 0.5, 1.0, 1.5, and 2.0g) of flocculant with a pH of 1 to the coal washing wastewater and letting it stand for 20 minutes.

[0129] 4.2 Concentration of suspended solids (SS)

[0130] This invention uses quantitative filter paper to determine suspended solids (SS) according to national standards. Before filtration, the quantitative filter paper is weighed. Flocculant (0.25g, 0.5g, 1.0g, 1.5g, 2.0g) is added to 200mL of coal washing wastewater, stirred rapidly at 300rpm for 30s, then slowly stirred at 60rpm for 30s, and allowed to stand for 1min, 5min, 10min, 15min, 20min, 25min, and 30min respectively. 100mL of the supernatant is then collected for filtration. When the filter paper or filter is close to being released from vacuum (or pressure), the filter paper is carefully removed from the funnel on the filtration flask using tweezers and placed into a clean petri dish. The petri dish is then placed in an oven and dried at 80℃ for 10 hours. After drying, the filter paper is weighed and recorded.

[0131] The suspended solids content is expressed as mass concentration ρ, in mg / L, according to the formula:

[0132]

[0133] In the formula:

[0134] m — the numerical value of the mass of the filter paper after filtration, in mg;

[0135] m0 — The numerical value of the mass of the filter paper before filtration, in mg;

[0136] V – The numerical value of the volume of liquid filtered, in mL.

[0137] from Figure 8 The results show that the removal efficiency reaches 96.2% after a standing time of 20 minutes, and the changes are relatively gradual at 25 minutes and 30 minutes, but still showing an upward trend. When the flocculant dosage increases from 0.5 g / L... -1 Increased to 5.0 g·L -1 The SS removal efficiency reached 96.5%. Insufficient flocculant dosage failed to neutralize the negative charge of suspended solids in the coal washing wastewater, failing to destabilize them. However, with increased flocculant dosage, a colloidal state formed in the wastewater, where suspended solids remained, hindering sedimentation.

[0138] 5. Characterization of flocculants

[0139] 5.1 X-ray diffraction analysis

[0140] XRD is a technique that obtains information about the internal structure of materials by studying the diffraction phenomenon of X-rays in crystals. It can reveal the arrangement of atoms or molecules within a material, helping us to better understand its properties and characteristics. Figure 15 This invention relates to a material containing Fe 3+ Al 3+ and Ca 2+ The polyionic composite flocculant. The presence of Na comes from NaOH used to adjust the pH during the preparation process, and from Cl- in the reaction with HCl. - NaCl crystals were formed, which also... Figure 9 The XRD pattern shows that when the volume ratio is 3:1, only the NaCl diffraction peak is relatively obvious, indicating that the present invention may be an amorphous polymer. Furthermore, no diffraction peaks were detected for aluminum sulfate, ferrous sulfate, and ferric sulfate, indicating that they do not coexist in the complex forms of conventional metal sulfates. When the ratio changes from 2:3 to 3:2, the intensity of the diffraction peaks in the crystallization of the compound decreases significantly; when When the ratio reaches 1:1, the diffraction peaks of the compound crystallization completely disappear, revealing Al 3+ Further polymerization occurs in the solution, leading to an increase in the amount of polymerized material.

[0141] 5.2 Fourier Transform Infrared Analysis

[0142] FT-IR spectra of flocculants with different volume ratios were obtained by Figure 10 It can be seen that the flocculant at 3428cm -1 An absorption peak is observed at 1628 cm⁻¹, which, compared with the standard infrared spectrum, indicates the presence of -OH stretching vibrations, suggesting the presence of hydroxyl functional groups, meaning the flocculant contains hydroxyl functional groups; at 1628 cm⁻¹... -1The presence of an absorption peak at 1473 cm⁻¹ indicates the presence of C=O double bond vibrations, suggesting the presence of carbon-oxygen double bond functional groups, meaning the flocculant contains such functional groups. -1 The presence of an absorption peak at this location indicates the presence of a -CH3 stretching vibration, suggesting the presence of methyl functional groups, meaning the flocculant contains methyl functional groups; 1199 cm⁻¹ -1 The wavelength at that point is the tensile vibration of Fe-OH-Fe or Al-OH-Al, 607 cm⁻¹. -1 The band at that point represents the bending vibrations of Fe-OH and Al-OH.

[0143] 6. Analysis of the mechanism of action of flocculants in coal washing wastewater

[0144] like Figure 11 When a positively charged flocculant is added to negatively charged coal washing wastewater, the positive and negative charges neutralize each other through interaction, thereby reducing the repulsive force between them and forming chain-like flocs. The addition of the flocculant causes colloidal particles to be adsorbed, and the flocculation of the colloidal particles is promoted through adhesion and bridging.

[0145] 6.1 Charge neutralization

[0146] The charge neutralization effect, through the action of multiple forces, causes negatively charged colloidal particles to adsorb onto positively charged polymers, thereby reducing the charge, decreasing electrostatic repulsion, and promoting aggregation and precipitation. Cationic polymeric flocculants have abundant positive potential sites in their molecular structure. In water, they can hydrolyze to generate positive potential sites, which interact with emulsified oil droplets containing negative potential sites through electrostatic attraction, initiating a charge neutralization reaction.

[0147] like Figure 12 Flocculants hydrolyze and acquire a positive charge, which generates electrostatic attraction with the negative charge on the surface of colloidal particles. This lowers the surface potential of the colloidal particles, causing their cohesion to gradually destabilize under the influence of electrostatic attraction, ultimately leading to sedimentation. As the flocculant dosage increases, the Zeta potential gradually decreases, indicating that charge neutralization plays a role in the flocculation process. When 10 g·L⁻¹… -1 At that time, the optimal value was achieved, but considering both economic benefits and SS removal efficiency, the final decision was to select 5 g·L⁻¹. -1 suitable.

[0148] 6.2 Net trapping and settling

[0149] Figure 13 To add (0.5, 2.5, 5, 7.5, 10 g·L⁻¹) to the coal washing wastewater respectively -1The image shows an organic flocculant observed under an optical microscope. As shown, the organic flocculant forms a three-dimensional network structure through hydrophobic association, effectively capturing and sweeping away colloidal particles and suspended microparticles in the water, forming large flocs. This process mainly occurs in the later stage of flocculation. By adding flocculant to weakly alkaline oily wastewater and stirring, a series of large-volume network-like flocs are formed. These flocs move under the action of water flow, effectively sweeping away small particulate pollutants, which eventually settle at the bottom of the pool or float on the surface.

[0150] 6.3 Web Flocculation

[0151] High-molecular-weight organic flocculants are long-chain molecules with numerous active groups, effectively adsorbing surrounding particles and colloids. Through the linkage of these long chains, they can combine with other flocculant molecules to form large flocs. Even if the emulsified oil has not yet broken down, its oil droplets can be collected and removed from the water. For example... Figure 14 As shown, the spatial network cross-linking system formed by mutual links significantly enhances the adsorption bridging and sweeping capture capabilities, thereby improving the flocculation effect.

[0152] Figure 14 (a) It possesses a rich, dense, and complex gel network structure, which is beneficial for the adsorption and bridging of suspended matter. (b) It has a spiky net-like structure, which is beneficial for the net-trapping of suspended matter. (c) and (d) further reveal that the flocculant has a dense and complex gel network structure.

[0153] Figure 15 As reflected in the elemental mapping diagram, elements such as iron and aluminum are evenly distributed on the flocculant surface, which is conducive to the full combination of metal elements and pollutants during pure hydrolysis, thereby efficiently removing pollutants. In addition, the flocculant surface has more wrinkles, resulting in a larger surface roughness and spectral surface area than the other two types of shields, thus improving computational performance.

[0154] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing polyaluminum ferric chloride flocculant based on coal gasification coarse slag, characterized in that, It includes the following steps: (1) Hydrochloric acid impregnation method: Add HCl solution and gasified crude residue into a container, place the container in a constant temperature water bath, heat and stir to carry out the reaction; let stand and separate into layers, take out the supernatant and place it in reagent bottle No. 1 for later use, put the remaining reactants into a centrifuge for solid-liquid separation, take out the liquid and place it in reagent bottle No. 1 for later use; wash the residue twice with deionized water, put the washed liquid in reagent bottle No. 1 to mix into HCl leachate, dry the residue and weigh it; (2) Sulfuric acid leaching method: Add H2SO4 solution and gasification crude residue into a container, place the container in a constant temperature water bath, heat and stir to carry out the reaction; let stand to separate the layers, take out the supernatant and place it in reagent bottle No. 2 for later use, put the remaining reactants into a centrifuge for solid-liquid separation, take out the liquid and place it in reagent bottle No. 2 for later use; wash the residue twice with deionized water, put the washed liquid in reagent bottle No. 2 and mix to form H2SO4 leaching solution, dry the residue and weigh it; (3) Polymerization: Mix HCl leachate with H2SO4 leachate, adjust pH value, mix, age, dry, synthesize flocculant, and grind into powder for later use; In step (1), the ratio of the volume of HCl solution added to the mass of the gasified crude residue is mL:g = (28-32):1, the molar concentration of the HCl solution is 7.5-8.5 mol / L, and the heating temperature is 75-85℃; In step (2), the ratio of the added volume of H2SO4 solution to the added mass of gasified crude residue is mL:g = (38-42):1, the molar concentration of H2SO4 solution is 3.5-4.5 mol / L, and the heating temperature is 55-65℃; In step (3), the mass ratio of hydrochloric acid leachate to sulfuric acid leachate is (0.8-1.2):(0.8-1.2), the pH value is 0.8-1.2, and the aging time is 22-26h.

2. The preparation method of the coal gasification coarse slag-based polyaluminum ferric chloride flocculant according to claim 1, characterized in that, The leaching efficiency of hydrochloric acid solution and sulfuric acid solution for metal ions in gasified crude slag is calculated as follows: ； In the formula: d0 is the initial mass of the coarse slag from coal gasification, in grams; d1 is the mass of the coarse coal gasification residue after acid leaching, in grams.

3. A coal gasification slag-based polyaluminum ferric chloride flocculant obtained by the preparation method according to any one of claims 1 to 2.

4. The application of the coal gasification coarse slag-based polyaluminum ferric chloride flocculant as described in claim 3 in the treatment of coal washing wastewater.

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