Treatment process for wastewater from hydrogen fluoride method for purifying graphite

Abstract

The application provides a hydrogen fluoride acid method purification graphite production wastewater treatment process and relates to the technical field of hydrogen fluoride acid method purification graphite, which comprises the following steps: after the first-stage water washing wastewater is concentrated, mixed concentrated acid and fresh water are obtained through separation; the mixed concentrated acid is adjusted to a predetermined concentration and then reused in a first-stage acid washing section of a hydrogen fluoride acid method purification graphite production line, or the mixed concentrated acid is directly reused in the first-stage acid washing section of the hydrogen fluoride acid method purification graphite production line; the fresh water is treated to reach a standard and then discharged. After the first-stage water washing wastewater is concentrated, the mixed concentrated acid and the fresh water are obtained through separation, and then the mixed concentrated acid can be reused as the first-stage acid washing acid in the first-stage acid washing section according to production requirements and on demand after the concentration of the mixed concentrated acid is adjusted, in the process, the amount of hydrochloric acid, nitric acid and hydrogen fluoride acid added to the first-stage water washing wastewater can be reduced, and the input cost of the acid in the first-stage acid washing section is saved.

Description

Technical Field

[0001] This invention relates to the field of graphite purification technology using hydrofluoric acid, and in particular to a process for treating wastewater from graphite purification using hydrofluoric acid. Background Technology

[0002] The main process for purifying graphite using hydrofluoric acid involves mixing graphite with a mixed acid (including hydrofluoric acid, hydrochloric acid, and nitric acid). The mixed acid reacts with impurities for a period of time to produce soluble substances or volatiles. After washing to remove impurities, the graphite is dehydrated and dried to obtain purified graphite. In this process, the graphite ore needs to go through several stages in sequence: primary acid washing (adding HF, HCl, and HNO3), primary water washing, secondary acid washing (adding H2SO4, HCl, and HNO3), and secondary water washing. The primary water washing stage generates primary water washing wastewater, and the secondary water washing stage generates secondary water washing wastewater.

[0003] Because the primary washing wastewater has a high acid content, it needs to be treated before it can be recycled or discharged in compliance with standards. To address this, the inventors have proposed a hydrofluoric acid method for treating graphite production wastewater. Summary of the Invention

[0004] In view of the above situation, the present invention provides a process for treating wastewater from graphite production using hydrofluoric acid, which can treat primary washing wastewater and then recycle or discharge it in compliance with standards.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] In a first aspect, the present invention provides a process for treating wastewater from graphite production using hydrofluoric acid, which mainly includes the following steps:

[0007] Collect primary washing wastewater;

[0008] After concentrating the primary washing wastewater, a mixture of concentrated acid and fresh water is obtained.

[0009] The mixed concentrated acid is adjusted to the predetermined concentration and then reused in the primary pickling section of the hydrofluoric acid purification graphite production line; the fresh water is treated to meet the standards before being discharged.

[0010] In some embodiments of the present invention, when concentrating primary washing wastewater, the primary washing wastewater is concentrated by passing it through an RO system and / or a DTRO system.

[0011] In some embodiments of the present invention, when fresh water is treated to meet the standards before being discharged, the fresh water is subjected to alkali precipitation, pressure filtration, advanced oxidation and biochemical treatment in sequence before being discharged.

[0012] Advanced oxidation processes include one or more of the following: Fenton, iron-carbon microelectrolysis, electrocatalytic oxidation, and catalytic ozone oxidation.

[0013] In some embodiments of the present invention, after the freshwater undergoes biochemical treatment, it is first subjected to coagulation sedimentation and / or resin adsorption, and then discharged after meeting the standards.

[0014] In some embodiments of the present invention, the biochemical treatment includes a sulfur autotrophic denitrification process and a conventional biochemical process, wherein the conventional biochemical process includes AO and A. 2 One or more of the following processes: O, SBR, and oxidation ditch.

[0015] In some embodiments of the present invention, the conventional biochemical process includes the AO process, with the sulfur autotrophic denitrification process serving as the A stage of the AO process.

[0016] In some embodiments of the present invention, before concentrating the primary washing wastewater, the monovalent salt and the high-valent salt in the primary washing wastewater are separated to obtain low-valent salt wastewater and high-valent salt wastewater.

[0017] Low-priced salt wastewater is concentrated and reused in the primary pickling process; high-priced salt wastewater is treated to meet standards before being discharged.

[0018] In some embodiments of the present invention, when high-priced salt wastewater is treated to meet the standards before being discharged, the high-priced salt wastewater is subjected to alkali precipitation, pressure filtration, advanced oxidation, biochemical treatment, coagulation sedimentation and resin adsorption in sequence, and then discharged after meeting the standards.

[0019] Secondly, the present invention provides a process for treating wastewater from graphite production using hydrofluoric acid, which further includes the following steps:

[0020] Collect secondary washing wastewater;

[0021] The secondary washing wastewater will be treated to meet discharge standards.

[0022] In some embodiments of the present invention, when the secondary washing wastewater is treated to meet the discharge standards, the secondary washing wastewater is subjected to alkali precipitation, pressure filtration, advanced oxidation, biochemical treatment, coagulation sedimentation and resin adsorption in sequence, and then discharged after meeting the standards.

[0023] The embodiments of the present invention have at least the following advantages or beneficial effects:

[0024] After concentration, the primary washing wastewater is separated into a mixed concentrated acid and fresh water. The mixed concentrated acid includes a large amount of hydrochloric acid, nitric acid, and hydrofluoric acid. The concentration of the mixed concentrated acid is adjusted according to production requirements and then reused as primary pickling acid in the primary pickling section. In this process, the amount of hydrochloric acid, nitric acid, and hydrofluoric acid added to the primary washing wastewater can be reduced, saving the acid input cost of the primary pickling section. When the primary washing wastewater can directly reach the required concentration after concentration, it is even unnecessary to add hydrochloric acid, nitric acid, and hydrofluoric acid to adjust the concentration.

[0025] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 A schematic diagram of the process for treating wastewater from the hydrofluoric acid method for purifying graphite. Detailed Implementation

[0028] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the embodiments of the invention.

[0029] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0030] Please refer to Figure 1 This embodiment provides a process for treating wastewater from graphite production using hydrofluoric acid, which mainly includes the following steps:

[0031] Primary and secondary washing wastewater are collected and treated separately. The primary washing wastewater is treated and reused in the primary pickling section of the hydrofluoric acid purification graphite production line, while the secondary washing wastewater is treated to meet discharge standards.

[0032] When treating secondary washing wastewater to meet discharge standards, the secondary washing wastewater is sent to the wastewater treatment and discharge system for further treatment (the wastewater treatment and discharge system will be described below) and discharged after meeting the standards.

[0033] The treatment of primary washing wastewater mainly includes the following steps:

[0034] Step S1: Separate the monovalent salt and the high-valent salt from the primary washing wastewater to obtain low-valent salt wastewater and high-valent salt wastewater;

[0035] The components of high-valent salt wastewater mainly come from graphite raw materials and mixed acid added in the primary pickling stage; high-valent salts include divalent and higher cations (such as ions corresponding to elements like Si, Fe, Al, Ca, and Mg) and anions (such as sulfate ions);

[0036] Low-valent salt wastewater contains monovalent salts, which include monovalent ions such as F.- Cl - NO 3- and Na + Plasma;

[0037] In step S1 of this embodiment, preferably, the primary washing wastewater is sent into a nanofiltration system to separate monovalent salts and hypervalent salts, resulting in low-valent salt wastewater and hypervalent salt wastewater.

[0038] Step S2: The low-priced salt wastewater is reused in the primary pickling section of the hydrofluoric acid method graphite purification production line; the high-priced salt wastewater is treated to meet the standards before being discharged.

[0039] In step S2, the low-cost salt wastewater is recycled to the primary pickling section of the hydrofluoric acid-based graphite purification production line, which mainly includes the following steps:

[0040] Step S21: After concentrating the low-priced salt wastewater, a mixed concentrated acid and fresh water are separated; the mixed concentrated acid contains a large amount of HCl, nitric acid and HF; the fresh water is relative to the mixed concentrated acid.

[0041] The above-mentioned concentration refers to increasing the concentration of the solution without adding solutes (i.e., HCl, nitric acid, and HF). Preferably, in this embodiment, when concentrating low-valent salt wastewater, the low-valent salt wastewater is passed through an RO system and a DTRO system in sequence for concentration, so that a large number of monovalent ions and a small number of high-valent ions are concentrated, thereby obtaining a separated mixed concentrated acid. In other embodiments, the low-valent salt wastewater can also be concentrated using only an RO system or a DTRO system.

[0042] Step S22: After adjusting the mixed concentrated acid to the predetermined concentration, it is reused in the primary pickling section of the hydrofluoric acid purification graphite production line; the fresh water is treated to meet the standards before being discharged.

[0043] In step S22, the freshwater is treated to meet the standards before being discharged. This mainly includes the following steps: sending the freshwater into a wastewater treatment and discharge system for treatment, and then discharging it after it meets the standards.

[0044] In step S2, when the high-priced salt wastewater is treated to meet the standards before being discharged, the high-priced salt wastewater is sent to the wastewater treatment and discharge system for treatment, and then discharged after meeting the standards.

[0045] It should be noted that when treating secondary washing wastewater, fresh water, and high-value salt wastewater, they can be treated through the same wastewater treatment and discharge system or through their respective independent wastewater treatment and discharge systems. In this embodiment, it is preferable to treat high-value salt wastewater and fresh water through the same wastewater treatment and discharge system to reduce equipment investment costs.

[0046] The aforementioned wastewater treatment and discharge system mainly includes, in sequence, an alkali addition and sedimentation section, a filter press section, an advanced oxidation section, a biochemical treatment section, a coagulation and sedimentation section, and a resin adsorption section. Secondary washing wastewater, fresh water, and high-valent salt wastewater are discharged in compliance with standards after passing through alkali addition and sedimentation, filter press, advanced oxidation, biochemical treatment, coagulation and sedimentation, and resin adsorption in sequence.

[0047] In the alkali precipitation section, calcium oxide and / or calcium hydroxide are added to neutralize and produce precipitates such as calcium fluoride and calcium sulfate.

[0048] The filter press section produces filter liquid and sludge formed from the above-mentioned sediments. The filter liquid enters the biological treatment section, and the sludge is sent for external treatment.

[0049] The advanced oxidation section employs advanced oxidation processes, including one or more of the following: Fenton oxidation, iron-carbon micro-electrolysis, electrocatalytic oxidation, and catalytic ozone oxidation.

[0050] In this embodiment, preferably, the biochemical treatment section includes a sulfur autotrophic denitrification process and a conventional biochemical process. The conventional biochemical process includes AO and A. 2 One or more of the following processes: O, SBR, and oxidation ditch. Sulfur autotrophic denitrification uses reduced sulfur sources such as sodium sulfide (Na₂S), sodium thiosulfate (Na₂S₂O₃), and elemental sulfur as electron donors, and inorganic carbon sources in water (CO₃⁻) as the carbon source. 2- HCO3 - This novel autotrophic denitrification technology uses CO2 as a carbon source to reduce NO3-N (nitrate nitrogen) to N2 in an oxygen-deficient environment. Compared with conventional biochemical processes, it can reduce the addition of carbon sources, thereby reducing operating costs by more than 50%.

[0051] In a specific implementation scenario, secondary washing wastewater, freshwater, and high-priced salt wastewater are first treated by an advanced oxidation process, and then by an AO process. In this process, sulfur autotrophic denitrification is used as the A stage of the AO process to degrade nitrate nitrogen and some COD. Then, some COD is degraded by a conventional aerobic aeration stage (i.e., the O stage in the AO process).

[0052] The reason for using advanced oxidation technology followed by conventional biological treatment in the wastewater treatment and discharge system is as follows: Although the COD in primary and secondary washing wastewater is low, it mainly consists of organic matter that is difficult to utilize by conventional biological treatment, resulting in poor effectiveness when using conventional biological treatment directly. If the COD in primary and secondary washing wastewater exceeds the standard (although the COD is low, it does not mean that the discharge standard has been met), in order to meet the corresponding discharge standard, the aforementioned advanced oxidation technology should be used first to degrade the organic matter that is difficult to utilize by biological treatment, and then the aforementioned conventional biological treatment should be used for further treatment, thereby ensuring the effectiveness of biological treatment.

[0053] The resin adsorption section generates desorption liquid, which is then returned to the alkali precipitation section.

[0054] Secondary washing wastewater, freshwater, and high-valent saline wastewater, after sequential alkali precipitation, pressure filtration, advanced oxidation, and biological treatment, can meet the discharge standard for fluoride levels not exceeding 10 mg / L; after treatment in the coagulation and sedimentation stage, the discharge standard for fluoride levels is lower than 3–5 mg / L; and after treatment in the resin adsorption stage, the discharge standard for fluoride levels is 0.5 mg / L–2 mg / L. Users can rationally select the stages included in the wastewater treatment and discharge system according to their actual needs.

[0055] In summary, this embodiment has at least the following beneficial effects:

[0056] First, the primary washing wastewater is concentrated and separated to obtain a mixed concentrated acid and fresh water. The mixed concentrated acid includes a large amount of hydrochloric acid, nitric acid and hydrofluoric acid. The concentration of the mixed concentrated acid is adjusted as needed according to production requirements and then it can be reused as acid for primary pickling in the primary pickling section. In this process, the amount of hydrochloric acid, nitric acid and hydrofluoric acid added to the primary washing wastewater can be reduced, saving the acid input cost of the primary pickling section. When the primary washing wastewater can directly reach the required concentration after concentration, it is even unnecessary to add hydrochloric acid, nitric acid and hydrofluoric acid to adjust the concentration.

[0057] II. Primary and secondary washing wastewater contain a significant amount of high-valent and monovalent salts. Specifically, due to the relatively stable raw materials and processes, the main high-valent cations in primary and secondary washing wastewater are ions corresponding to elements such as Si, Fe, Al, Ca, and Mg, while the main high-valent anions are sulfate ions, and the main monovalent ions are F. - Cl - NO 3- and Na + Plasma, and due to the order of the processes, the high valence anions and cations in the primary washing wastewater are much higher than those in the secondary washing wastewater; in addition, the acid content in both primary and secondary washing wastewater is high, and due to the order of the processes, the acid content in the primary washing wastewater is much higher than that in the secondary washing wastewater.

[0058] Since there is a significant difference in the content of high-valence salts and acids between primary and secondary washing wastewater, the method of collecting and treating primary and secondary washing wastewater separately in this embodiment is of great practical significance.

[0059] III. In this embodiment, the high-valent and monovalent salts in the primary washing wastewater are first separated to obtain low-valent salt wastewater, which is then concentrated. Specifically, after treatment by the nanofiltration system, the high-valent and monovalent salts in the primary washing wastewater are separated. The separated high-valent salts have multiple uses. The low-valent salt wastewater is then concentrated by passing it through an RO system and a DTRO system, which concentrates a large number of monovalent ions and a small amount of residual high-valent ions into a mixed concentrated acid, thereby recovering approximately 70% of the acid from the primary washing wastewater. Since the mixed concentrated acid has removed most of the high-valent salts, it meets the acid quality requirements of the primary pickling section. After concentration measurement and adjustment, the mixed concentrated acid can be reused in the primary pickling section, which reduces the acid consumption of the primary pickling section and saves a lot of costs.

[0060] Fourth, because a large amount of HF, hydrochloric acid, and nitric acid, as well as a small portion of sulfuric acid, are recovered, the amount of acid entering the alkali precipitation section of the wastewater treatment and discharge system is reduced. Therefore, the amount of alkali added for neutralization is reduced by approximately 60% or more, reducing alkali consumption. This, in turn, reduces the amount of sludge filtered out by the filter press section by approximately 50-60%, reducing the cost of sludge disposal and the labor intensity of workers transporting sludge. In summary, by reducing the amount of alkali added and reusing the aforementioned mixed concentrated acid, water treatment costs can be saved by approximately 20-30 yuan per ton, resulting in significant economic benefits.

[0061] Fifth, because the amount of alkali added in the alkali precipitation section is reduced by more than 60%, the amount of salt generated by the acid-base neutralization reaction in the alkali precipitation section can be reduced by more than half. As a result, less salt enters the biological treatment section, thus reducing the salinity of the biological treatment section (usually not exceeding 6000 mg / L). This greatly reduces the difficulty of biological treatment and improves the efficiency of biological treatment. On the other hand, it eliminates the need to add or cultivate salt-tolerant bacteria in the biological treatment section, reducing the construction and operation costs of the biological treatment section.

[0062] VI. Secondary washing wastewater, as well as freshwater and high-valent saline wastewater from primary washing wastewater, after sequential treatment including alkali precipitation, pressure filtration, advanced oxidation, and biological treatment, can meet the discharge standard for fluoride levels not exceeding 10 mg / L; after treatment in the coagulation and sedimentation stage, it can meet the discharge standard for fluoride levels below 3–5 mg / L; and after treatment in the resin adsorption stage, it can meet the discharge standard for fluoride levels between 0.5 mg / L and 2 mg / L. Users can rationally select the stages included in the wastewater treatment and discharge system according to their actual needs.

[0063] Finally, it should be noted that 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. Without conflict, the embodiments and features described in the embodiments of this application can be arbitrarily combined with each other. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for treating waste water produced in the purification of graphite by the hydrofluoric acid method, characterized by, The method comprises the following steps: Collecting primary water washing wastewater; After concentrating the primary water washing wastewater, mixed concentrated acid and fresh water are separated; The mixed concentrated acid is adjusted to a predetermined concentration and then reused in a primary acid washing section of a hydrogen fluoride method graphite purification production line, or the mixed concentrated acid is directly reused in the primary acid washing section of the hydrogen fluoride method graphite purification production line; the fresh water is treated and discharged after reaching a standard; When the primary water washing wastewater is concentrated, the primary water washing wastewater is concentrated through an RO system; Before the primary water washing wastewater is concentrated, monovalent salt and high-valence salt in the primary water washing wastewater are separated to obtain low-valence salt wastewater and high-valence salt wastewater; The low-valence salt wastewater is concentrated and then reused in the primary acid washing section; The high-valence salt wastewater is treated and discharged after reaching a standard; When the fresh water is treated and discharged after reaching a standard, the fresh water is sequentially subjected to alkali addition precipitation, filter pressing, advanced oxidation and biochemical treatment, and then discharged after reaching a standard; The advanced oxidation comprises one or more of Fenton, electro-catalytic oxidation and catalytic ozone oxidation processes; When the high-valence salt wastewater is treated and discharged after reaching a standard, the high-valence salt wastewater is sequentially subjected to alkali addition precipitation, filter pressing, advanced oxidation, biochemical treatment, coagulation precipitation and resin adsorption, and then discharged after reaching a standard; The method further comprises the following steps: Collecting secondary water washing wastewater; Treating and discharging the secondary water washing wastewater after reaching a standard.

2. The process for treating the wastewater from the production of hydrogen fluoride acid purified graphite according to claim 1, characterized in that, After the fresh water is subjected to the biochemical treatment, coagulation precipitation and / or resin adsorption are performed, and then the fresh water is discharged after reaching a standard.

3. The process for treating the hydrogen fluoride method purification of graphite production wastewater according to claim 1, characterized in that, When the secondary water washing wastewater is treated and discharged after reaching a standard, the secondary water washing wastewater is sequentially subjected to alkali addition precipitation, filter pressing, advanced oxidation, biochemical treatment, coagulation precipitation and resin adsorption, and then discharged after reaching a standard.

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