Method and system for removing chlorine from high-chlorine coal washing waste water by using feng's salt precipitation method and preparing pac

Abstract

The application discloses a method and system for removing chlorine from high-chlorine coal washing wastewater by using a Fehling salt precipitation method and preparing PAC (polyaluminum chloride) by recycling resources, the method adopts two-stage step-by-step Fehling salt precipitation reaction on the high-chlorine coal washing wastewater, realizes deep removal of chlorine ions in the high-chlorine coal washing wastewater, and has a high chlorine ion removal rate; meanwhile, byproduct Fehling salt sludge generated in the reaction is acidified and polymerized to prepare polyaluminum chloride coagulant, and is returned to the Fehling salt precipitation reaction, so that the precipitation effect is strengthened, and the recycling and utilization of the hazardous byproduct is realized, and remarkable economic benefits and environmental benefits are achieved.

Description

Technical Field

[0001] This invention belongs to the field of high-chlorine wastewater treatment technology. Specifically, this invention relates to a method and system for dechlorinating high-chlorine coal washing wastewater using the Freund's salt precipitation method and for the resource-based preparation of PAC. Background Technology

[0002] Coal washing is one of the main methods for treating high-chlorine coal, and it is widely used due to its simple operation and wide adaptability. However, this process generates a large amount of washing wastewater with high salt, high chlorine, and high suspended solids. If discharged directly without effective treatment, it will pose a serious threat to the receiving water bodies and soil ecosystem. Therefore, developing economical and efficient high-chlorine wastewater treatment technologies has become one of the key issues for environmental protection and sustainable development in the coal washing industry. Currently, the main technologies for treating high-chlorine wastewater include membrane desalination, evaporation crystallization, ion exchange, and chemical precipitation. However, evaporation crystallization has excessively high energy consumption and high operating costs; ion exchange resin is easily saturated, requires frequent regeneration, and generates secondary waste liquid; membrane separation is prone to fouling and has high investment costs, making it difficult to meet the large-scale, low-cost treatment needs of the coal washing industry. The Fraunhofer salt precipitation method has become the preferred process for treating chlorinated wastewater due to its advantages of mild reaction conditions, low reagent costs, and considerable chlorine removal efficiency. However, the traditional Fraunhofer salt dechlorination process has problems such as unreasonable calcium and aluminum addition ratio, insufficient reaction, and incomplete removal of chloride ions. Moreover, the Fraunhofer salt sludge generated by the reaction is mostly disposed of as solid waste, which not only wastes resources such as aluminum and calcium, but also increases the cost of sludge disposal.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a method and system for dechlorinating high-chlorine coal washing wastewater using Freund's salt precipitation and for the resource-based preparation of PAC.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, embodiments of the present invention provide a method for dechlorinating and resource-based preparing of PAC from high-chlorine coal washing wastewater using the Fracker salt precipitation method, comprising the following steps: (1) Homogenize and adjust the water quality and quantity of high-chlorine coal washing wastewater; (2) Add some calcium source agent and aluminum source agent to the adjusted wastewater to carry out the first Freund's salt precipitation reaction; (3) The first reaction product obtained in step (2) is subjected to a first solid-liquid separation to obtain a first supernatant and a first Freund's salt sludge. (4) Add the remaining calcium source and aluminum source to the first supernatant to carry out the second Freund's salt precipitation reaction; (5) The second reaction product obtained in step (4) is subjected to a second solid-liquid separation to obtain a second supernatant and a second Freund's salt sludge. (6) After deep filtration of the second supernatant, hydrochloric acid is added to adjust the pH to 6-8 to obtain clear water, which is then recycled. (7) The first Freund's salt sludge and the second Freund's salt sludge are first concentrated by gravity and then dewatered to obtain Freund's salt sludge residue; (8) The Freund's salt sludge is acidified, dissolved, polymerized and matured in sequence to obtain polyaluminum chloride. The polyaluminum chloride is reused in the first Freund's salt precipitation reaction in step (2) and the second Freund's salt precipitation reaction in step (4).

[0007] The method for treating high-chlorine coal washing wastewater in this invention significantly improves the removal efficiency of chloride ions and the stability of system operation by employing a two-stage reaction process and optimizing the calcium-aluminum dosage ratio and reaction conditions. Furthermore, this invention further utilizes the generated Freund's salt sludge to prepare polyaluminum chloride (PAC) coagulant, widely used in water treatment, and reuses it in wastewater treatment processes. This achieves resource conversion of waste, reduces treatment costs and environmental burden, and demonstrates good environmental and economic benefits, embodying the green concept of "treating waste with waste" and resource recycling.

[0008] In some embodiments, in steps (2) and / or (4), the calcium source agent includes at least one of CaO, Ca(OH)2, CaCl2, and Ca(HCO3)2, and the aluminum source agent includes at least one of NaAlO2, Al(OH)3, and Al2O3.

[0009] In some embodiments, the total amount of calcium source agent added in step (2) and step (4), the total amount of aluminum source agent added, and the molar ratio of Cl element in the high-chlorine coal washing wastewater are (6~10):(3~4):1.

[0010] In some embodiments, in step (2), the reaction temperature of the first Freund's salt precipitation reaction is 20~30℃, the pH is 10~12, and the reaction time is 1~2h.

[0011] In some embodiments, in step (4), the reaction temperature of the second Freund's salt precipitation reaction is 20~30℃, the pH is 10~12, and the reaction time is 1~2h.

[0012] In some embodiments, in step (7), the moisture content of the Freund's salt sludge is ≤45%.

[0013] In some embodiments, in step (8), the Freund's salt sludge is acidified and dissolved to a pH of 3.5 to 4.0, and the polymerization and maturation time is 2 to 6 hours.

[0014] In some embodiments, in step (8), the polyaluminum chloride has an Al2O3 content ≥10% and a basicity ≥35%.

[0015] Secondly, embodiments of the present invention also propose a system for dechlorination and resource-based preparation of PAC from high-chlorine coal washing wastewater using the Freund's salt precipitation method. The system is used to implement the method described in the first aspect and includes: a wastewater collection tank, a first reaction tank, a first clarification tank, a second reaction tank, a second clarification tank, a V-type filter, a clear water tank, a calcium source dosing device, an aluminum source dosing device, a hydrochloric acid dosing device, a sludge thickening tank, a centrifugal dewatering machine, a PAC preparation device, and a PAC dosing device; the wastewater collection tank, the first reaction tank, the first clarification tank, the second reaction tank, the second clarification tank, the V-type filter, and the clear water tank are sequentially connected along the wastewater treatment direction. The calcium source dosing ports of the first reaction tank and the second reaction tank are both connected to the calcium source dosing device, and the aluminum source dosing ports of the first reaction tank and the second reaction tank are both connected to the aluminum source dosing device. The effluent pipe of the V-type filter is connected to the hydrochloric acid dosing device. The sludge discharge ports of the first clarifier and the second clarifier are both connected to the inlet of the sludge thickening tank. The outlet of the sludge thickening tank is sequentially connected to the inlet of the centrifugal dewatering machine, the PAC preparation device, and the PAC dosing device. The outlet of the PAC dosing device is connected to the PAC inlet of the first reaction tank and the PAC inlet of the second reaction tank, respectively.

[0016] In some embodiments, the first reaction tank is provided with a first stirring device, and the second reaction tank is provided with a second stirring device.

[0017] The advantages and beneficial effects of the embodiments of the present invention are as follows: (1) High dechlorination efficiency and stable effluent quality: The embodiment of this invention adopts a two-stage graded reaction process, combined with an optimized calcium-aluminum-chlorine molar ratio, to achieve the synergistic effect of "primary precipitation + deep removal" of chloride ions in high-chlorine coal washing wastewater. The chloride ion removal rate can reach more than 80%, and the effluent chloride ion concentration meets the coal washing wastewater reuse standard, effectively solving the technical difficulties of high-chlorine wastewater treatment.

[0018] (2) Sludge resource utilization to achieve zero discharge: In this embodiment of the invention, PAC coagulant is prepared by acidification and polymerization of Freund's salt sludge, realizing the resource conversion of hazardous waste, achieving zero discharge of sludge, greatly reducing sludge disposal costs, and saving the purchase cost of PAC, resulting in significant cost reduction and efficiency improvement.

[0019] (3) Strong process adaptability and good resistance to water quality fluctuations: The two-stage reaction in the embodiment of the present invention can effectively buffer water quality fluctuations. The system can flexibly adjust the reagent ratio and reaction parameters according to the chloride ion concentration and water quality characteristics of the influent to adapt to the treatment of high-chlorine coal washing wastewater under different working conditions. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the system for dechlorination and resource-based preparation of PAC from high-chlorine coal washing wastewater using the Freund's salt precipitation method, as described in an embodiment of the present invention.

[0021] Attached reference numerals: 1-Wastewater collection tank, 2-First reaction tank, 3-First clarification tank, 4-Second reaction tank, 5-Second clarification tank, 6-V-type filter, 7-Clear water tank, 8-Calcium source dosing device, 9-Aluminum source dosing device, 10-Hydrochloric acid dosing device, 11-Sludge thickening tank, 12-Centrifuge dewatering machine, 13-PAC preparation device, 14-PAC dosing device. Detailed Implementation

[0022] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0023] In this invention, when a value is described as a range, it should be understood that such disclosure includes disclosure of all possible subranges within that range, as well as specific numerical values ​​falling within that range, regardless of whether specific numerical values ​​or specific subranges are explicitly specified.

[0024] In this invention, the terms “comprising” and “including” and their various variations mean that other elements or wholes may be included but are not specifically described.

[0025] In this invention, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0026] In a first aspect, embodiments of the present invention provide a method for dechlorinating and resource-based preparing of PAC from high-chlorine coal washing wastewater using the Fracker salt precipitation method, comprising the following steps: (1) Homogenize and adjust the water quality and quantity of high-chlorine coal washing wastewater; (2) Add some calcium source agent and aluminum source agent to the adjusted wastewater to carry out the first Freund's salt precipitation reaction; (3) The first reaction product obtained in step (2) is subjected to a first solid-liquid separation to obtain a first supernatant and a first Freund's salt sludge. (4) Add the remaining calcium source and aluminum source to the first supernatant to carry out the second Freund's salt precipitation reaction; (5) The second reaction product obtained in step (4) is subjected to a second solid-liquid separation to obtain a second supernatant and a second Freund's salt sludge. (6) After deep filtration of the second supernatant, hydrochloric acid is added to adjust the pH to 6-8 to obtain clear water, which is then recycled. (7) The first Freund's salt sludge and the second Freund's salt sludge are first concentrated by gravity and then dewatered to obtain Freund's salt sludge residue; (8) The Freund's salt sludge is acidified, dissolved, polymerized and matured in sequence to obtain polyaluminum chloride. The polyaluminum chloride is reused in the first Freund's salt precipitation reaction in step (2) and the second Freund's salt precipitation reaction in step (4).

[0027] In some embodiments, in steps (2) and / or (4), the calcium source agent includes at least one of CaO, Ca(OH)2, CaCl2, and Ca(HCO3)2, and the aluminum source agent includes at least one of NaAlO2, Al(OH)3, and Al2O3.

[0028] In some embodiments, the total amount of calcium source agent added in step (2) and step (4) (calculated as calcium), the total amount of aluminum source agent added (calculated as aluminum), and the molar ratio of Cl element in the high-chlorine coal washing wastewater are (6~10):(3~4):1.

[0029] In some embodiments, in step (2), the reaction temperature of the first Freund's salt precipitation reaction is 20~30℃, the pH is 10~12, and the reaction time is 1~2h.

[0030] In some embodiments, in step (4), the reaction temperature of the second Freund's salt precipitation reaction is 20~30℃, the pH is 10~12, and the reaction time is 1~2h.

[0031] It should be noted that in the method of this embodiment, the calcium source agent and the aluminum source agent are added to the water sample in two separate steps. In step (2), the calcium source agent and the aluminum source agent added account for 60% or more of the total calcium source agent and the total aluminum source agent, respectively, so that most of the chloride ions in the wastewater react with calcium and aluminum ions to form Freund's salt precipitate. In step (4), the remaining (≤40% of the total calcium source agent and aluminum source agent) calcium source agent and aluminum source agent are added to further remove residual chloride ions in the wastewater.

[0032] After treatment by the two-stage graded reaction method of this invention, the removal rate of chloride ions in high-chlorine coal washing wastewater can reach ≥80%, the removal rate of hardness can reach ≥90%, the effluent quality can be stably up to standard, fully meet the reuse requirements of high-chlorine coal washing workshop, and realize the recycling of water resources.

[0033] In some embodiments, in step (7), the moisture content of the Freund's salt sludge is ≤45%.

[0034] In some embodiments, in step (8), the Freund's salt sludge is acidified and dissolved to a pH of 3.5 to 4.0, and the polymerization and maturation time is 2 to 6 hours.

[0035] In some embodiments, in step (8), the polyaluminum chloride (PAC) has an Al2O3 content ≥10% and a basicity ≥35%. By using Fraunhofer sludge to prepare PAC, not only can 100% resource utilization of Fraunhofer sludge be achieved with no hazardous waste discharge and reduced sludge disposal costs, but the self-made PAC can also completely replace commercially available PAC products, saving the cost of purchasing commercially available coagulants. The coagulant can be reused in the Fraunhofer salt precipitation reaction in steps (2) and (4), which can enhance the Fraunhofer salt precipitation effect and realize the resource recycling of by-products.

[0036] Secondly, such as Figure 1 As shown in the figure, this invention also proposes a system for dechlorination and resource-based preparation of PAC from high-chlorine coal washing wastewater using the Freund's salt precipitation method. The system is used to implement the method described in the first aspect and includes: a wastewater collection tank 1, a first reaction tank 2, a first clarification tank 3, a second reaction tank 4, a second clarification tank 5, a V-type filter 6, a clear water tank 7, a calcium source dosing device 8, an aluminum source dosing device 9, a hydrochloric acid dosing device 10, a sludge thickening tank 11, a centrifugal dewatering machine 12, a PAC preparation device 13, and a PAC dosing device 14; the wastewater collection tank 1, the first reaction tank 2, the first clarification tank 3, the second reaction tank 4, the second clarification tank 5, the V-type filter 6, and the clear water tank 7 are connected sequentially along the wastewater treatment direction. The calcium source dosing ports of the first reaction tank 2 and the second reaction tank 4 are both connected to the calcium source dosing device 8. The aluminum source dosing ports of the first reaction tank 2 and the second reaction tank 4 are both connected to the aluminum source dosing device 9. The effluent pipe of the V-type filter 6 is connected to the hydrochloric acid dosing device 10. The sludge discharge ports of the first clarifier 3 and the second clarifier 5 are both connected to the inlet of the sludge thickening tank 11. The outlet of the sludge thickening tank 11 is sequentially connected to the inlet of the centrifugal dewatering machine 12, the PAC preparation device 13, and the PAC dosing device 14. The outlet of the PAC dosing device 14 is connected to the PAC inlet of the first reaction tank 2 and the PAC inlet of the second reaction tank 4, respectively.

[0037] In some embodiments, the first reaction tank 2 is provided with a first stirring device (not shown in the figure), and the second reaction tank 4 is provided with a second stirring device (not shown in the figure).

[0038] The working process of the system for dechlorination and resource-based preparation of PAC from high-chlorine coal washing wastewater by Fracker salt precipitation in this embodiment of the invention is as follows: Wastewater from the high-chloride coal washing workshop first enters wastewater collection tank 1, where it is homogenized in terms of both quantity and quality to ensure stable subsequent treatment. The effluent from wastewater collection tank 1 enters the first reaction tank 2, where a portion of calcium source reagent (≥60% total calcium source reagent) and a portion of aluminum source reagent (≥60% total aluminum source reagent) are added via calcium source dosing device 8 and aluminum source dosing device 9 to initiate the first Freund's salt precipitation reaction. This reaction causes most of the chloride ions in the wastewater to react with calcium and aluminum ions to form Freund's salt precipitate. The effluent from the first reaction tank 2 enters the first clarification tank 3, where gravity sedimentation achieves the first solid-liquid separation. The resulting first supernatant enters the second reaction tank 4, where the first Freund's salt precipitate is removed from the bottom. The sludge is discharged into the sludge thickening tank 11; then, the remaining ≤40% of calcium and aluminum source agents are added to the second reaction tank 4 for a second Freund's salt precipitation reaction to further remove residual chloride ions from the first supernatant; the effluent from the second reaction tank 4 enters the second clarification tank 5, where gravity sedimentation achieves a second solid-liquid separation, and the bottom second Freund's salt sludge is discharged into the sludge thickening tank 11. The resulting second supernatant enters the V-type filter tank 6 for deep filtration to remove residual suspended solids and fine particles; the effluent from the V-type filter tank 6 is adjusted to pH 6-8 by the hydrochloric acid dosing device 10 to obtain clarified water, which enters the clear water tank 7 and is reused in the high-chlorine coal washing workshop to achieve water resource recycling.

[0039] The first and second Freund's salt sludge discharged from the first clarifier 3 and the second clarifier 5 enter the sludge thickening tank 11. After gravity thickening, they are sent to the centrifugal dewatering machine 12 for dewatering treatment to obtain Freund's salt sludge with low water content. Then, the Freund's salt sludge is sent to the PAC preparation device 13. Through acidification, dissolution and polymerization maturation, the aluminum element in the Freund's salt sludge is converted into polyaluminum chloride (PAC). The prepared PAC enters the PAC dosing device 14 and is added to the first reaction tank 2 and the second reaction tank 4 respectively as a coagulant to enhance the precipitation effect of Freund's salt and realize the resource recycling of by-products.

[0040] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. The raw materials used in the embodiments are all commercially available products. The experimental methods not specified in the embodiments are conventional methods and conditions well known in the field.

[0041] Example 1 This embodiment describes the treatment of high-chloride coal washing wastewater from a coal mine. The wastewater has the following characteristics: chloride ion concentration 1660 mg / L, conductivity 5940 µS / cm, pH 6.38, total hardness 886 mg / L (calculated as calcium carbonate), and suspended solids content 120 mg / L. The method of this invention is used for treatment, and the specific steps are as follows: (1) Homogenize and adjust the water quality and quantity of high-chlorine coal washing wastewater; (2) Add 60wt% of the total amount of Ca(OH)2 and 60wt% of the total amount of NaAlO2 to the adjusted wastewater, and carry out the first Freund's salt precipitation reaction at 20℃, pH 10.9 and stirring speed of 250r / min. After 1.5h of reaction, the first reaction product is obtained. Among them, Ca(OH)2 is measured as Ca element, NaAlO2 is measured as Al element, and wastewater is measured as Cl element, and the total molar ratio is controlled as Ca:Al:Cl=8:3.5:1. (3) The first reaction product was subjected to a first solid-liquid separation to obtain the first supernatant and the first Freund's salt sludge, respectively; (4) Add the remaining 40wt% of the total amount of Ca(OH)2 and 40wt% of the total amount of NaAlO2 to the first supernatant, and carry out the second Freund's salt precipitation reaction at 20℃, pH 10.9 and stirring speed of 250r / min. After 1.5h of reaction, the second reaction product is obtained. (5) The second reaction product is subjected to a second solid-liquid separation to obtain the second supernatant and the second Freund's salt sludge; (6) After deep filtration of the second supernatant, hydrochloric acid is added to adjust the pH to 7 to obtain clear water, which is then recycled. (7) The first and second Freund's salt sludge were first concentrated by gravity, and after 3 hours of concentration, they were dewatered to obtain Freund's salt sludge residue with a water content of less than 45%. (8) The Freund's salt sludge is acidified and dissolved under a pH of 3.5 to 4.0, and then polymerized and matured for 4 hours to obtain polyaluminum chloride (PAC). The polyaluminum chloride is reused in the first Freund's salt precipitation reaction in step (2) and the second Freund's salt precipitation reaction in step (4).

[0042] After treatment by the method of this embodiment, the chloride ion concentration in the clarified water obtained in step (6) is reduced to 270 mg / L, the chloride ion removal rate reaches 83.73%, the suspended solids concentration is reduced to below 10 mg / L, the effluent hardness is 85 mg / L, the hardness removal rate reaches 90.40%, and the pH value is 7.3, which meets the reuse requirements of the high-chlorine coal washing workshop. In addition, the effective Al2O3 content in the PAC product prepared in step (8) reaches 12.3%, and the basicity reaches 40.5%, which meets the standards for use of water treatment coagulants and can be reused in the two Freund's salt precipitation reactions.

[0043] Example 2 This embodiment addresses the treatment of another high-chloride coal washing wastewater, with the following characteristics: chloride ion concentration 3940 mg / L, conductivity 11250 µS / cm, pH 6.70, total hardness 1800 mg / L (calculated as calcium carbonate), and suspended solids content 194 mg / L. The method of this invention is used for treatment, and the specific steps are as follows: (1) Homogenize and adjust the water quality and quantity of high-chlorine coal washing wastewater; (2) Add 60wt% of total calcium source agent and 60wt% of total aluminum source agent to the adjusted wastewater, and carry out the first Freund's salt precipitation reaction at 25℃, pH 11.5 and stirring speed of 250r / min. After 2h of reaction, the first reaction product is obtained. Among them, the calcium source agent is a mixture of CaO and CaCl2 with a mass ratio of 1:1, which can balance reaction efficiency and agent cost. The aluminum source agent is Al(OH)3, and the total molar ratio is controlled by elemental measurement to be Ca:Al:Cl=10:4:1, which is suitable for the treatment of high concentration chloride ion wastewater.

[0044] (3) The first reaction product was subjected to a first solid-liquid separation to obtain the first supernatant and the first Freund's salt sludge, respectively; (4) Add the remaining 40wt% of the total amount of Ca(OH)2 and 40wt% of the total amount of NaAlO2 to the first supernatant, and carry out the second Freund's salt precipitation reaction at 25℃, pH 11.5 and stirring speed of 250r / min. After 2h of reaction, the second reaction product is obtained. (5) The second reaction product is subjected to a second solid-liquid separation to obtain the second supernatant and the second Freund's salt sludge; (6) After deep filtration of the second supernatant, hydrochloric acid is added to adjust the pH to 7.5 to obtain clear water, which is then recycled. (7) The first and second Freund's salt sludge were first concentrated by gravity, and after 3 hours of concentration, they were dewatered to obtain Freund's salt sludge residue with a water content of less than 45%. (8) The Freund's salt sludge is acidified and dissolved under a pH of 3.5 to 4.0, and then polymerized and matured for 4 hours to obtain polyaluminum chloride (PAC). The polyaluminum chloride is reused in the first Freund's salt precipitation reaction in step (2) and the second Freund's salt precipitation reaction in step (4).

[0045] After treatment by the method of this embodiment, the chloride ion concentration in the clarified water obtained in step (6) is reduced to 462 mg / L, the chloride ion removal rate reaches 88.27%, the turbidity is less than 5 NTU, the effluent hardness is 125 mg / L, the hardness removal rate reaches 93.06%, and the effluent quality is stable and meets the standards, and can be reused in the high-chlorine coal washing workshop. In addition, the PAC product prepared in step (8) has an effective Al2O3 content of 15% and a basicity of 43%, which meets the standards for use as a water treatment coagulant and can be reused in the two Freund's salt precipitation reactions.

[0046] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0047] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0048] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0049] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0050] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0051] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for removing chlorine from high-chlorine coal washing waste water by ferric sulfate precipitation and preparing PAC, characterized in that, Includes the following steps: (1) Homogenize and adjust the water quality and quantity of high-chlorine coal washing wastewater; (2) Add some calcium source agent and aluminum source agent to the adjusted wastewater to carry out the first Freund's salt precipitation reaction; (3) The first reaction product obtained in step (2) is subjected to a first solid-liquid separation to obtain a first supernatant and a first Freund's salt sludge. (4) Add the remaining calcium source and aluminum source to the first supernatant to carry out the second Freund's salt precipitation reaction; (5) The second reaction product obtained in step (4) is subjected to a second solid-liquid separation to obtain a second supernatant and a second Freund's salt sludge. (6) After deep filtration of the second supernatant, hydrochloric acid is added to adjust the pH to 6-8 to obtain clear water, which is then recycled. (7) The first Freund's salt sludge and the second Freund's salt sludge are first concentrated by gravity and then dewatered to obtain Freund's salt sludge residue; (8) The Freund's salt sludge is acidified, dissolved, polymerized and matured in sequence to obtain polyaluminum chloride. The polyaluminum chloride is reused in the first Freund's salt precipitation reaction in step (2) and the second Freund's salt precipitation reaction in step (4).

2. The method for removing chlorine and preparing PAC from high-chlorine coal washery waste water by the method of Frenaud salt precipitation according to claim 1, characterized in that, In steps (2) and / or (4), the calcium source agent includes at least one of CaO, Ca(OH)2, CaCl2, and Ca(HCO3)2, and the aluminum source agent includes at least one of NaAlO2, Al(OH)3, and Al2O3.

3. The method for removing chlorine and preparing PAC from high-chlorine coal washery waste water by using the Fenton's salt precipitation method according to claim 1, characterized in that, The total amount of calcium source agent added in step (2) and step (4), the total amount of aluminum source agent added, and the molar ratio of Cl element in the high-chlorine coal washing wastewater are (6~10):(3~4):

1.

4. The method for removing chlorine and preparing PAC from high-chlorine coal washery waste water by using the Fenton's salt precipitation method according to claim 1, characterized in that, In step (2), the reaction temperature of the first Freund's salt precipitation reaction is 20~30℃, the pH is 10~12, and the reaction time is 1~2h.

5. The method for removing chlorine and preparing PAC from high-chlorine coal washery waste water by using the Fenton's salt precipitation method according to claim 1, characterized in that, In step (4), the reaction temperature of the second Freund's salt precipitation reaction is 20~30℃, the pH is 10~12, and the reaction time is 1~2h.

6. The method for removing chlorine and preparing PAC from high-chlorine coal washery waste water by using the Fenton's salt precipitation method according to claim 1, characterized in that, In step (7), the moisture content of the Freund's salt sludge is ≤45%.

7. The method for dechlorination and resource-based preparation of PAC from high-chlorine coal washing wastewater by Fracker salt precipitation according to claim 1, characterized in that, In step (8), the Freund's salt sludge is acidified and dissolved to a pH of 3.5-4.0, and the polymerization and maturation time is 2-6 hours.

8. The method for dechlorination and resource-based preparation of PAC from high-chlorine coal washing wastewater by Fracker salt precipitation according to claim 1, characterized in that, In step (8), the polyaluminum chloride has an Al2O3 content ≥10% and a basicity ≥35%.

9. A system for dechlorinating and resource-based preparation of PAC from high-chlorine coal washing wastewater using the Fraunhofer salt precipitation method, characterized in that, The system is used to implement the method according to any one of claims 1-8, comprising: a wastewater collection tank, a first reaction tank, a first clarification tank, a second reaction tank, a second clarification tank, a V-type filter, a clear water tank, a calcium source dosing device, an aluminum source dosing device, a hydrochloric acid dosing device, a sludge thickening tank, a centrifugal dewatering machine, a PAC preparation device, and a PAC dosing device; the wastewater collection tank, the first reaction tank, the first clarification tank, the second reaction tank, the second clarification tank, the V-type filter, and the clear water tank are sequentially connected along the wastewater treatment direction; the calcium source in the first reaction tank and the second reaction tank... All dosing ports are connected to the calcium source dosing device. The aluminum source dosing ports of the first reaction tank and the second reaction tank are all connected to the aluminum source dosing device. The effluent pipe of the V-type filter is connected to the hydrochloric acid dosing device. The sludge discharge ports of the first clarifier and the second clarifier are all connected to the inlet of the sludge thickening tank. The outlet of the sludge thickening tank is sequentially connected to the inlet of the centrifugal dewatering machine, the PAC preparation device, and the PAC dosing device. The outlet of the PAC dosing device is connected to the PAC inlet of the first reaction tank and the PAC inlet of the second reaction tank, respectively.

10. The system for dechlorination and resource-based preparation of PAC from high-chlorine coal washing wastewater by Fracker salt precipitation according to claim 9, characterized in that, The first reaction tank is equipped with a first stirring device, and the second reaction tank is equipped with a second stirring device.

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