CN120817687A - A method for quickly treating pulping wastewater - Google Patents

Abstract

The present invention provides a method for rapidly treating pulping wastewater, which belongs to the technical field of sewage treatment and comprises the following steps: (1) adjusting the pulping wastewater to a COD content of less than 20,000 mg/L, adding color stabilizer A and color stabilizer B, adding polyaluminum chloride and stirring, adding polyacrylamide, and achieving solid-liquid separation for the first time; (2) adding ferrous sulfate and hydrogen peroxide to the liquid treated in step (1), stirring for reaction, adding separation control agent A and separation control agent B, and adding polyacrylamide; achieving solid-liquid separation for the second time; (3) adding a flocculant to the liquid treated in step (2), achieving solid-liquid separation for the third time, and completing the treatment of the pulping wastewater. The advantages of the present invention are: 1. Low cost: The method of the present invention is simple to operate and requires almost no additional investment in equipment and technology. 2. Resource utilization: The solids produced in each step can be converted into high-value chemical products, achieving the dual goals of wastewater treatment and commercial value. 3. High versatility: Applicable to various pulping wastewaters.

Description

Method for rapidly treating pulping waste liquid

Technical Field

The invention belongs to the technical field of sewage treatment, and particularly relates to a method for rapidly treating pulping waste liquid.

Background

In the pulp and paper industry, small pulp mills are challenged, with sewage disposal problems being particularly acute. These small-sized pulp mills are generally limited in capital and are difficult to put into a large amount of capital to build perfect sewage treatment facilities, so that the production efficiency is low and the cost is high. The traditional sewage treatment method, such as flocculation precipitation and biochemical treatment, can reduce the pollution load of waste liquid to a certain extent, but the treated sludge brings new environmental protection problems. The sludge contains a large amount of pollutants such as heavy metals and organic matters, if the pollutants are not properly treated, the pollutants are treated at will, so that serious pollution is caused to the soil, the water body and other environments, the treatment difficulty is high, the cost is high, and the burden of enterprises is further increased.

In addition, the large amount of waste liquid, especially black liquid, generated in the pulping process contains rich chemical substances, such as lignin, polyphenol and the like, and the substances have potential economic value. However, most of the current small-sized pulp mills cannot effectively utilize the resources, and the resources are directly discharged or simply disposed of and then discarded, so that not only is the resources wasted greatly, but also environmental protection punishment is faced due to the fact that the discharge does not reach the standard, and the sustainable development of enterprises is seriously affected. Therefore, the development of the treatment method which is efficient, low in cost and capable of realizing high-valued waste liquid has extremely important significance for solving the sewage treatment problem of a small-sized pulping plant, improving the production efficiency and economic benefit, and protecting the environment.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a method for rapidly treating pulping waste liquid, which has the following technical scheme:

A method for rapidly treating pulping waste liquid, comprising the steps of:

(1) Adjusting the pulping waste liquid to be within 20000mg/L of COD, adding 1-6 g/L of a color stabilizer, stirring for 2-30 minutes, adding 3-10 g/L of polyaluminum chloride, stirring for 2-3 minutes, adding 5-50 g/L of polyacrylamide, stirring for 2-3 minutes, standing for 1-5 minutes, and realizing solid-liquid separation for the first time;

(2) Adding 0.5-1.0 g/L of ferrous sulfate and 0.6-1.2 g/L of hydrogen peroxide into the liquid treated in the step (1), stirring and reacting for 5-30 minutes, adding 1-3 g/L of a release control agent A and 2-8 g/L of a release control agent B, stirring and reacting for 5-120 minutes, adding 20-50 g/L of polyacrylamide, stirring for 2-3 minutes, standing for 1-5 minutes, and carrying out solid-liquid separation for the second time;

(3) And (3) adding 0.5-3 g/L of flocculant into the liquid treated in the step (2), stirring for 1-3 minutes, adding 3-20 g/L of polyacrylamide, stirring for 1-3 minutes, standing for 1-5 minutes, and carrying out solid-liquid separation for the third time to finish the treatment of pulping waste liquid.

In the step (1), the color stabilizer is a biological enzyme composite preparation, which comprises one or more than two of pectase, laccase or xylanase according to any proportion.

In the step (1), the polyaluminum chloride is 30% solution, and the polyacrylamide is 1% solution.

In the step (1), during the first solid-liquid separation, solid-liquid separation can occur in black liquor/waste liquor, solid matters enter a plate frame or a stacked filter press for press filtration to form mud, the liquid enters the next stage of treatment, after the treatment in the step (1), the COD/BOD/chromaticity of the liquid is reduced, the pH value is less than 7, and during the second solid-liquid separation, the solid matters enter the plate frame or the stacked filter press for press filtration to form mud, the COD/BOD of the liquid is continuously reduced, and the pH value is more than 8. In the third solid-liquid separation, the COD/BOD/chromaticity of the liquid reaches the discharge standard, namely the COD is less than 100mg/L, the BOD is less than 20mg/L, the chromaticity is less than 50 times, and the pH=6.5-7.5.

In the step (2), the ferrous sulfate is 65% of ferrous sulfate pentahydrate, the hydrogen peroxide is 27% hydrogen peroxide, and the mass ratio of ferrous sulfate to hydrogen peroxide is 1.0:1.2.

And the mass ratio of the release agent A to the release agent B is 3:8.

The ion control agent A and the ion control agent B are ion control agents, the ion control agent A is NaAlO ₂, and the ion control agent B is CaCl ₂.

The invention has the advantages that:

1. the method has the advantages of simple operation and almost no need of additional investment equipment and technology.

2. The solid matters generated in each step can be converted into high-value chemical products, so that the dual purposes of waste liquid treatment and commercial value are realized.

3. The universal pulp is suitable for various pulping waste liquid, including chemical pulp, semi-chemical pulp, wheat straw pulp, cow dung pulp and the like, and is particularly suitable for small pulping plants.

Detailed Description

The invention will be further described with reference to specific embodiments, and advantages and features of the invention will become apparent from the description. These examples are merely exemplary and do not limit the scope of the invention in any way. It will be understood by those skilled in the art that various changes and substitutions of details and forms of the technical solution of the present invention may be made without departing from the spirit and scope of the present invention, but these changes and substitutions fall within the scope of the present invention.

The invention provides a method for rapidly treating pulping waste liquid, which comprises the following three steps:

1. The color stabilization method is used for rapidly flocculating and separating soluble lignin and colloid in the waste liquid, 2, the Fenton separation control method is a Fenton method and an ultrahigh lime aluminum salt method, and low molecular organic matters, inorganic salts and chloride ions in the waste liquid are removed, 3, the flocculation method is solid-liquid separation.

The solid matters in each step can form corresponding high-value chemicals for use in the way, thereby realizing the treatment of waste liquid and creating commercial value.

The basic principle of the invention is as follows:

1. The color stabilizer is a composite chemical product for stabilizing/removing waste liquid/black liquid containing biological enzyme, wherein pectase is used for rapidly degrading polygalacturonic acid in the waste liquid/black liquid into galacturonic acid, and the galacturonic acid is chelated with inorganic metal ions such as Ca ²⁺,Al³⁺,Zn^{2 +},Fe²⁺ for sedimentation, and laccase, xylanase and other substances for rapidly polymerizing the waste liquid/black liquid polyphenol for sedimentation. Wherein the dosage of pectase is more than or equal to 5u/g solids, the dosage of laccase is more than or equal to 2u/g, and the dosage of xylanase is more than or equal to 5u/g. Under further flocculation of polyaluminum chloride and polyacrylamide, the layering is separated out, and the solid matters generally show a floating state.

The solid matter treated by the biological enzyme is lignin/polyphenol polymer, can be directly or after filter pressing used for filling surfaces or wet parts of corrugated paper, kraft paper, bobbin paper, gray board paper, maze paper and the like, and is used for replacing waste paper pulp or improving the strength and moisture resistance of paper. The paper is used for replacing waste paper fiber, and the ton paper consumption is recommended to be within 5 percent. For surface sizing, the ton paper dosage is recommended to be 3%.

The step designs the acidity of the waste liquid, neutralizes the alkalinity in the waste liquid and reserves the second step of Fenton.

2. Fenton off control method:

the Fenton method is essentially that a chain reaction between ferrous ions (Fe ²⁺) and hydrogen peroxide is catalyzed to generate hydroxyl free radicals, has strong oxidizing capability, can oxidize solid matters which are not precipitated in the waste liquid left in the first step into carbon dioxide and water, but has high cost due to large consumption, and can display efficiency under an acidic condition, and the treated Fe ²⁺,Fe³⁺ causes the color of a water body to be deep, such as black, brown and brown.

The method provides the precondition of the Fenton method in the first step, so that the design amount is low, the cost is low, and the Fenton method can not be executed in the second step according to the actual COD requirement.

Fe²⁺+H₂O₂->Fe³⁺+(OH)^-+OH·

3. The method is mainly used for controlling inorganic ions in waste liquid, and because polyaluminium chloride is used in sewage treatment, a large amount of aluminum ions and chloride ions are inevitably brought into the system, and are pollutants, the method is an upgrade of an ultrahigh lime aluminum salt method in fact, the lime alkalinity of the method can precipitate Fe ²⁺,Fe³⁺ generated by Fenton into Fe (OH) ₂,Fe(OH)₃ in advance, and the Fe ²⁺,Fe³⁺ is combined with chloride ions in the waste liquid to generate calcium aluminum chloride French salt (Ca ₄Al₂Cl₂(OH)₁₂), so that the inorganic ions and chloride ions added in the first step and the original waste liquid are removed from the system. The French salt is a layered and porous substance similar to hydrotalcite-like structure, is widely used in the fields of ion exchange, adsorption and catalysis, such as biodiesel catalysis, and can be widely used as paper filler for replacing titanium dioxide and improving the bulk, opacity and the like of paper. Or the surface micro-coating/surface sizing is used for replacing silicon dioxide and improving the drying speed of paper ink, and the paper can play an excellent printing effect in the fields of digital paper, thermal sublimation paper, flexography paper and the like.

The reaction involved in this step is:

2NaAlO₂+4H₂O→2Al(OH)₃+2NaOH

4Ca(OH)₂+2Al(OH)₃→Ca₄Al₂(OH)₁₄

Ca₄Al₂(OH)₁₄+2Cl^-→Ca₄Al₂Cl₂(OH)₁₂+2OH^-

CaCl₂+3Ca(OH)₂+2NaAlO₂+8H₂O→2Ca₂Al(OH)₆Cl·4H₂O↓+2NaOH

Fe³⁺+3OH^-＝Fe(OH)₃↓

4. Flocculation method:

The method adopts flocculant and polyacrylamide to remove the residual substances in the water body, and the mud obtained by filter pressing is a novel milky flocculant/chelating agent which is used as white water PCD (Poly Crystal Diamond) descending treating agent, white water conductivity chelating agent, papermaking filler, sewage treatment flocculant and the like.

Example 1:

APMP pulping waste liquid is taken from small multi-disc clear filtrate, COD 15000mg/L, pH 9.0 and chromaticity 3000 times;

Firstly, adding 1g/L of a color stabilizer, stirring for 3 minutes, changing waste liquid into milky white, adding 10g/L of 30% polyaluminium chloride, slightly stirring for 3 minutes, adding 25g/L of 0.1% polyacrylamide, slightly stirring for 1 minute, performing solid floating, then performing solid-liquid separation, and performing second-step treatment on the solid for later use, wherein COD (chemical oxygen demand) is 3500mg/L, pH is 6.0 and chromaticity is 500 times, wherein the color stabilizer is a biological enzyme composite preparation, and is formed by mixing one or more than two of pectase, laccase and xylanase according to any proportion.

In the second step, 0.5g/L of ferrous sulfate and 0.6g/L of 27% hydrogen peroxide are added, stirring and reacting are carried out for 10 minutes, 4g/L of a release control agent A1.5g/L of a release control agent B is added, stirring and reacting are carried out for 20 minutes, 50g/L of 0.1% polyacrylamide is added, slight stirring is carried out for 3 minutes, solid precipitation occurs, then solid and liquid are separated for later use, liquid enters the third step for treatment, COD is 500mg/L, pH is 9.0 and chromaticity is 300 times, the mass ratio of the release control agent A to the release control agent B is 3:8, the release control agent A is NaAlO ₂, and the release control agent B is CaCl ₂.

Thirdly, adding 1.5g/L of flocculant, slightly stirring for 1 minute, adding 5g/L of 0.1% polyacrylamide, slightly stirring for 1 minute, and carrying out solid floating, then carrying out solid-liquid separation, wherein the COD of the liquid is 35mg/L, the pH value is 7.0 and the chromaticity is 15 times, so that the national secondary emission standard is reached.

Example 2:

black liquor from small size pulp mill is taken from circulating black liquor pool, COD 60000mg/L, pH 14, chroma 5000 times and 4 times diluted post treatment.

The first step, adding 3g/L of a color stabilizer, stirring for 15 minutes, changing the waste liquid into brown, adding 10g/L of 30% polyaluminium chloride, slightly stirring for 3 minutes, adding 30g/L of 0.1% polyacrylamide, slightly stirring for 1 minute, performing solid floating, then performing solid-liquid separation, and performing second step treatment on the solid for later use, wherein COD (chemical oxygen demand) is 3000mg/L, pH is 6.3 and chromaticity is 600 times, wherein the color stabilizer is a biological enzyme composite preparation, and comprises one or more than two of pectase, laccase or xylanase according to any proportion.

Secondly, adding 1.0g/L of ferrous sulfate and 1.2g/L of 27% hydrogen peroxide, stirring and reacting for 10 minutes, adding 3g/L of a release control agent A, 8g/L of a release control agent B, stirring and reacting for 20 minutes, adding 100g/L of 0.1% polyacrylamide, slightly stirring for 3 minutes, and carrying out solid precipitation, then carrying out solid-liquid separation, standing the solid for later use, and carrying out third-step treatment on the liquid, wherein the COD is 700mg/L, the pH value is 9.5 and the chromaticity is 300 times. The mass ratio of the release agent A to the release agent B is 3:8, the release agent A is NaAlO ₂, and the release agent B is CaCl ₂.

Thirdly, adding 3g/L of flocculant, slightly stirring for 1 min, adding 10g/L of 0.1% polyacrylamide, slightly stirring for 1 min, floating solids, separating solid from liquid, and keeping the solid for later use, wherein the COD of the liquid is 50mg/L, the pH value is 7.0 and the chromaticity is 10 times. Reaching the standard of direct discharge or reuse.

Example 3:

the wheat straw pulp pulping waste liquid is taken from a black liquor storage tank, COD 80000mg/L, pH 14, chroma 6000 times and dilution 10 times.

The first step, adding 6g/L of a color stabilizer, stirring for 30 minutes, changing waste liquid into dark brown, adding 15g/L of 30% polyaluminium chloride, slightly stirring for 3 minutes, adding 50g/L of 0.1% polyacrylamide, slightly stirring for 1 minute, performing solid floating, then performing solid-liquid separation, and performing second step treatment on the liquid, wherein COD (chemical oxygen demand) is 2000mg/L, pH value is 6.0 and chromaticity is 300 times, wherein the color stabilizer is a biological enzyme composite preparation, and is formed by mixing one or more than two of pectase, laccase and xylanase according to any proportion.

Secondly, adding 0.5g/L of ferrous sulfate and 0.6g/L of 27% hydrogen peroxide, stirring and reacting for 10 minutes, adding 4g/L of a release control agent A1.5g/L of a release control agent B, stirring and reacting for 20 minutes, adding 60g/L of 0.1% polyacrylamide, slightly stirring for 3 minutes, carrying out solid precipitation, then carrying out solid-liquid separation, standing the solid for later use, and carrying out third-step treatment on the liquid, wherein COD is 200mg/L, pH is 8.0 and chromaticity is 300 times. The mass ratio of the release agent A to the release agent B is 3:8, the release agent A is NaAlO ₂, and the release agent B is CaCl ₂.

Thirdly, adding 1.0g/L of flocculant, slightly stirring for 1 minute, adding 3g/L of 0.1% polyacrylamide, slightly stirring for 1 minute, and carrying out solid floating, then carrying out solid-liquid separation, wherein the COD of the liquid is 30mg/L, the pH value is 7.0, and the chromaticity is 10 times, so that the national secondary emission standard is reached.

The description of the solids (chemical sludge) after each treatment step is as follows:

A first step solid-polyphenol polymer;

the second step solid-friedel salt/fries salt.

The composition of the Friedel salt is 3 CaO.Al ₂O₃·CaCl₂·10H₂ O (other forms are Ca ₄Al₂Cl₂(OH)₁₂,Ca₂Al(OH)₆Cl·2H₂ O and the like), and belongs to layered double hydroxides (Layered Double Hydroxides, LDHs) -hydrocalumite, wherein the main layer is [ Ca ₂Al(OH)₆]⁺,Al³⁺ is hexacoordinated, ca ²⁺ is heptacoordinated, and the middle layer is orderly arranged [ Cl.2H2 ₂O]^- ].

The friedel salt can exist stably in water with the pH value of 4-12, and the adsorbent is low in cost. Particle morphology and pore structure are key to regulating active sites of high performance adsorbent materials, while friedel salt as LDHs can easily regulate adsorption sites on an atomic scale. Friedel salts can remove different heavy metal cations and anionic contaminants from aqueous media by 3 different mechanisms, namely surface adsorption, interlayer anion exchange, reconstitution of memory effect (lamina cation exchange). The anion exchange capacity depends on many factors including the ratio of cationic metals, the stability of the interlayer anions, the molecular mass of the cations and anions present in LDHs, the anionic charge density, and the strength of the metal layer interactions, among others. At the same time, the properties of the charge, functionality, and solubility of the contaminant may also affect the adsorption capacity of the contaminant. The adsorption capacity of friedel salts varies for each contaminant, and some contaminants may damage the friedel salt structure and reduce the adsorption capacity. However, the Friedel salt has the characteristics of large specific surface area, high anion exchange capacity, good thermal stability and the like, and has great application potential in the aspects of treating heavy metal cations, oxygen-containing anions and the like.

The French salt is an ink drier with better effect than silicon dioxide, and the French salt generated by the APMP waste liquid in the Galaxy paper industry is one of key raw materials for producing thermal sublimation and digital paper.

Is also an excellent raw material for improving the APMP waste liquid anion garbage, which is irreplaceable by common chemical industry such as retention aids, fixing agents and the like.

According to the component characteristics of aluminum, calcium and chlorine of the Friedel salt, the polyaluminum chloride (PAC) can be recovered and manufactured.

PAC is an inorganic high-molecular water treatment agent, has high-charge polymer chains, has high electric neutralization and bridging effects on colloid and particles in water, and can effectively remove trace toxic substances and heavy metal ions.

At present, the aluminum-based coagulant has wide market application prospect due to the excellent coagulation property. Existing solid wastes such as fly ash, bauxite tailings, red mud and the like can be used as raw materials for preparing PAC, but the aluminum extraction of the materials is influenced by the aluminum content, high stability and other impurities. In contrast, friedel-crafts salt has much higher reactivity with acid than the above materials due to its own layered structure and strong acidity. Furthermore, friedel salts typically contain about 20wt% Al ₂O₃ and 5wt% Cl ^- are preferred starting materials for PAC production.

The LDHs of friedel salts have a double layer structure connected to a hydrogen bond network, with an intermediate layer filled with water molecules and Cl ^-. HCl molecules can enter the interlayer cavity to be fully contacted with the Friedel salt, so that the complete dissolution of the precipitate is realized. In conventional manufacturing processes, dissolution of the starting materials (e.g., al ₂O₃) produces aluminum species that tend to form higher molecular weight polymers, resulting in a decrease in the electrical neutralization capability of the resulting PAC. While the calcium-based framework in the friedel salt can be formed during leaching, which can surround and separate aluminum species to prevent further polymerization, thereby improving flocculation efficiency in water treatment. In addition, the calcium-based skeleton enhances the flocculation capability of the coagulant, and further lime is added to improve the alkalinity of PAC and prevent too small aluminum species from causing too high concentration of residual Al ³⁺ in the solution. The leaching experimental result of the PAC flocculant shows that 97.2% of Al ³⁺ can be extracted from the precipitate when the concentration of the fixed hydrochloric acid is 210g/L, the temperature is 353.15K and the leaching time is 180 min. Friedel salts are more suitable as raw materials for PAC production than other solid waste due to their calcium-based backbone. The PAC prepared from the Friedel salt has excellent coagulation performance equivalent to that of commercial products, so that the application of the Friedel salt is further expanded.

The friedel salt can be used as a heavy metal flocculation-adsorbent to realize the purification of the water body. Common heavy metals include copper, nickel, zinc, lead, chromium, cadmium, arsenic and the like, and are mainly derived from industries such as mining, smelting, forging, electroplating, tanning and the like. The inorganic polymeric flocculant generally has layered, three-dimensional net-shaped structures and the like, and can remove heavy metals through adsorption and bridging. The flaky structure and high ion exchange capacity of the Friedel salt lead the Friedel salt to have great application potential in the aspect of heavy metal removal. The residual quantity of heavy metal after treatment by utilizing the Friedel salt can be reduced below various heavy metal indexes of the emission standard of electroplating pollutants (GB 21900-2008).

Copper-containing wastewater is treated by utilizing Friedel salt with a micro/nano structure, and when the concentration of Cu ²⁺ is 4.41mg/L, the Friedel salt with the concentration of 0.45g/L is added, so that the removal rate of 99.17% can be obtained. During the flocculation precipitation of Cu ²⁺, a portion of the friedel salt reacts with CO ₂ in water to convert to calcite and amorphous alumina, and Cu ²⁺ forms hydroxide, which is adsorbed by the newly formed amorphous aluminum hydroxide and precipitates with entrapped calcite.

The method adopts the Friedel salt emulsion as an adsorption-flocculating agent to remove heavy metal cadmium in water, the result shows that the removal rate of the Friedel salt flocculation sedimentation Cd ²⁺ reaches 97.8 percent, the Friedel salt undergoes a dissolving-recrystallization process in water treatment, part of Cd ²⁺ in the water is adsorbed or coprecipitated on the surface of hexagonal columnar calcite, part of Cd ²⁺ can be adsorbed or coprecipitated by an amorphous aluminum hydroxide colloid formed by hydrolysis, and XRD spectrogram analysis shows that part of Cd ²⁺ is also like to replace calcium in calcite to enter a crystal lattice.

And removing Cd ²⁺ in the leaching solution by adopting Friedel salt, wherein when the adding amount of the Friedel salt is 0.45g/L, the removing rate of Cd ²⁺ reaches 89.17 percent. Co ²⁺ in the wastewater is removed by utilizing Friedel salt, and the result shows that the Friedel salt can effectively adsorb Co ²⁺ at the initial pH of 4.0-6.0, and the adsorption capacity is 3.682mmol/g. When the concentration of Co ²⁺ is 2.0-16.0 mmol/L, the Friedel salt can remove more than 99.98% of Co ²⁺ from the solution. The adsorption process follows a pseudo-second order model and follows Langmuir adsorption isotherms. The immobilization of Co ²⁺ is mainly determined by isomorphic substitution, thereby forming Ca-Co-Al LDHs. The leaching test shows that the Friedel salt adsorption Co ²⁺ has higher stability, and meanwhile, the Friedel salt has the advantage of high cost benefit in the aspects of the remediation of heavy metal contaminated soil and the wastewater treatment.

The removal of various metals by the friedel salt shows that the friedel salt is an effective treatment agent for various heavy metal oxyanions and heavy metal cations. The friedel salt treatment of heavy metal oxyanions belongs to an ion exchange mechanism, the removal of Zn ²⁺,Cd²⁺ cations belongs to a structure reconstruction mechanism, and the removal of Pb ²⁺,Cu²⁺ cations belongs to a surface adsorption mechanism.

The friedel salt emulsion synthesized by the oxide-salt decomposition precipitation method can be directly used for dynamic flocculation precipitation of heavy metal wastewater without changing the existing flocculation-sedimentation treatment process, and the precipitation separation is completed faster than the separation of the existing aluminum salt and ferric salt alum.

The friedel salt has a high adsorption capacity and adsorption rate for Pb ²⁺, and the adsorption isotherm does not conform to classical adsorption models Langmuir and Freundlich isothermal adsorption equations because friedel salt realizes binding of Pb ²⁺ by forming lead-containing compounds 6 PbO.PbCl ₂ and Pb ₂ OCl (OH), and Pb ₂ OCl (OH) phase tends to be generated under the condition of high initial concentration of Pb ²⁺. From infrared analysis, it was found that, as the initial concentration of Pb ²⁺ increased and the Al-O bond was broken, pb ²⁺ entered the Friedel salt, and the structure was changed.

It should be noted that when the friedel salt removes heavy metals, cl ^- may be released again into the water, so that the Cl ^- concentration in the wastewater increases, but this is related to the heavy metal content and the friedel salt dosage, so that the related research is less and further research is needed.

Redox-sensitive metallic elements often enter the aqueous environment in the form of oxidation states. The oxygen-containing anionic pollutants have the characteristics of toxicity, non-biodegradability, high solubility and the like, are easy to accumulate in the environment and are difficult to remove, so that the oxygen-containing anionic pollutants are harmful to human health. How to effectively remove oxyanion-containing contaminants from aqueous environments has become a critical issue in protecting natural environments and public health. Among the methods for treating and removing oxyanions, the adsorption method is favored because of the advantages of high removal efficiency, easy treatment, low running cost, etc., while the friedel salt is a good adsorption material as a layered double hydroxide, and has great application value in water treatment.

The Friedel salt is utilized to remove antimony, so that the removal rate exceeding 97% can be obtained in neutral and alkaline areas, and the phenomenon of 'anion absorption edge' existing in conventional various antimony removing adsorbents is broken. The concentration of antimony in the waste water of the east peak antimony ore pit can be reduced to 32 mug/L by using the Friedel salt alone, and the concentration of antimony in the waste water of the pit can be reduced to 24.4 mug/L by using the Friedel salt and the polyaluminum ferric chloride flocculant in combination. The principle of Friedel salt antimony removal is that most of antimony in a water body exists in a form of Sb (OH) ₆ ^- with negative charges, and the antimony is fixed after ion exchange with Cl ^-·2H₂ O and CO ₃ ^2- in the Friedel salt interlayer structure. The Friedel salt is used for removing antimony, so that the concentration of the residual antimony in the pit wastewater is far lower than the emission standard of industrial pollutant emission standard of tin, antimony and mercury (GB 30770-2014). The friedel salt is thus a potential flocculation-adsorbent for removing antimony from wastewater.

The adsorption performance of the friedel salt on nitrate in landfill leachate is found that Cl ^- in the friedel salt can enhance the adsorption capacity of the friedel salt, while sulfate, PO ₄ ^3- and organic matters can inhibit adsorption, and the optimal pH value is 9.0.

The application of the friedel salt in removing arsenate (AsO ₄ ^3-) in alkali liquor, the characterization of the friedel salt after adsorption analyzes the removal mechanism of arsenate in alkali liquor, and the result shows that anion exchange exists, and the friedel salt decomposition product Ca ₃Al₂(OH)₁₂ also has larger adsorption capacity for arsenate, because AsO ₄ ^3- reacts with-OH bonds of Ca ₃Al₂(OH)₁₂. Zhang et al ^[65] utilized the synthesized Friedel salt as the arsenate adsorbent, and the adsorption process was quickly promoted in the first 12 hours to reach equilibrium in 48 hours, and at pH 4 and 7, the adsorption capacities for arsenate reached 11.85 and 7.80mg/g, respectively.

Studies have shown that the presence of the Friedel salt phase in the chloride-containing alunite [ Ca ₂Al(OH)₆Cl(H₂O)₂·mH₂ O ] can rapidly adsorb large amounts of selenate (up to 1.37 mmol/g) by anion exchange to remove SeO ₄ ^2-. The alunite adsorbed with SeO ₄ ^2- can exist stably in water with pH value of 4-13, which shows that selenate has strong fixation effect in the phase. The intercalated selenate in the Friedel salt crystal phase can be desorbed and recovered by NaCl solution, so that the used adsorbent can be regenerated and recovered.

The method utilizes the friedel salt of the calpain dechlorination product to remove the dichromate ions (CrO ₄ ^2-), and the removal rate can reach 96 percent. The release of Cl ^- was accompanied by the removal of CrO ₄ ^2-, indicating that removal of CrO ₄ ^2- was achieved by Cl ^- ion exchange.

The friedel salt can remove up to 95% of the silica from the sodium aluminate solution.

The Friedel salt has higher adsorption capacity and higher adsorption rate to vanadate (VO ₄ ^3-), the adsorption isotherm accords with a Langmuir isothermal adsorption model, the theoretical adsorption capacity is 72.40mg/g, and the mechanism of Friedel salt treatment of oxyanions comprises ion exchange and surface adsorption.

The main components in the incinerator bottom ash comprise CaO, al ₂O₃ and Friedel salt consisting of high-concentration Cl ^-. The bottom ash was washed with distilled water and compared to acetic acid wash. It was found that when CO ₂ microbubbles were introduced, cl ^- elution increased to 53.9% -61.1% and CO ₂ decomposed friedel salts as shown in the equation:

3CaO·Al₂O₃·CaCl₂·10H₂O+3CO₂→3CaCO₃+2Al(OH)₃+CaCl₂+7H₂O Lowering the pH to 2.8 facilitates the decomposition of the friedel salt, which upon washing with acetic acid yields calcium acetate and at 400 ℃ decomposes to CaCO ₃, see the following formulas:

2CH₃CO₂H+CaO→Ca(CH₃COO)₂+H₂O

Ca (CH) at 400 DEG C ₃COO)₂→CaCO₃+CH₃COCH₃

When the bottom ash of the incinerator is washed by acetic acid (1.5 mol/L) combined with CO ₂ micro-bubbles, the concentration of Cl ^- in the incineration ash is reduced to 1.70g/kg, the elution efficiency of chlorine reaches 87.78%, and the obtained product can be used as a raw material for manufacturing cement.

For the purpose of dissolving a large amount of chemical sludge containing Friedel salt generated in the treatment of high-chlorine wastewater by an ultrahigh lime aluminum method, zhou Zhen subject group ^[37] also proposes to utilize the sludge to enhance urban sludge dehydration. The Friedel salt has a layered structure and a larger specific surface area, so that the Friedel salt can be used as an adsorption material ^[70] in the sludge conditioning process. The research shows that the uniformly dispersed mesoporous structure is formed in the sludge treated by ferric chloride, which is favorable for releasing the water in cells to dewater. And after the Friedel salt is added, the adsorption of extracellular polymers can be improved, and the dehydration performance of the sludge is further improved.

Chemical precipitation chlorine removal methods have been widely studied, however, expensive chemical agents such as silver nitrate, mercury nitrate, cuprous oxide, bismuth oxide and the like, and secondary pollution generated limit the wide use of these chlorine removal agents. The Fred salt precipitation dechlorination method has the advantages of wide raw material sources and low cost, and can obtain chemical sludge containing Fred salt. However, the chemical sludge is large in production amount, low in friedel salt purity and various in impurity types, and is difficult to be absorbed, so that the existing ultra-high lime aluminum method, calcium aluminum stone method for removing chlorine and the like are difficult to apply on a large scale. Therefore, finding out the market application requirements of friedel's salt is extremely important for the popularization of friedel's salt precipitation dechlorination. The application state of the Friedel salt is summarized on the basis of introducing the Friedel salt characteristics and the obtaining method, and a reference is provided for further high-value recycling of the Friedel salt. The dosage of the medicament (CaO and NaAlO ₂) is large in the ultra-high lime aluminum method dechlorination process, a large amount of Na ⁺ is introduced into the wastewater, and the purity of the mayenite in the medicament is low and the activity is poor (the specific surface area is small) in the mayenite method dechlorination process, so that the problems all cause excessive dosage of the medicament and huge production of dechlorination product sludge. In order to overcome the defects of the ultra-high lime aluminum method, the calcium-aluminum stone method for chlorine removal and the like, on the basis of conventional elements such as calcium, aluminum and the like, a calcium-aluminum-based chlorine removal agent with higher purity and stronger activity needs to be developed, and a chlorine removal reaction mechanism is studied and expanded deeply, so that the chlorine removal efficiency is improved, the production amount of a rear-end chlorine removal product is reduced, the purity of Friedel salt is improved, and more reliable guarantee is provided for recycling Friedel salt. The current application of the Friedel salt not only comprises the preparation of a coagulant and the removal of various anionic and cationic pollutants, but also can be introduced with CO ₂ for chlorine elution to be used as a cement raw material or directly used as a regulator for urban sludge dehydration and the like. Friedel salts have been reported for the treatment of a wide variety of heavy metal cations and oxyanions, but related market applications have yet to be fully investigated and demonstrated. For the massive consumption of friedel salt, the process and mechanism for preparing coagulant are worth more intensive study. Besides the reported applications, the catalyst can be used as an adsorbent, a catalyst and the like of various waste gases so as to widen the required market of Friedel salt, exert the maximum economic benefit and realize the change of waste into valuable.

And a third step of solid-flocculant for adjusting white water PCD or sewage treatment flocculant.

The foregoing is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art, who is within the scope of the present invention, should make equivalent substitutions or modifications according to the technical scheme of the present invention and the inventive concept thereof, and should be covered by the scope of the present invention.

Claims (7)

1. A method for rapidly treating pulping wastewater, comprising the following steps: (1) The pulping wastewater is adjusted to a COD of less than 20,000 mg/L, 1 to 6 g/L of color stabilizer is added, stirred for 2 to 30 minutes, 3 to 10 g/L of polyaluminum chloride is added, stirred for 2 to 3 minutes, 5 to 50 g/L of polyacrylamide is added, stirred for 2 to 3 minutes, and allowed to stand for 1 to 5 minutes to achieve solid-liquid separation for the first time; (2) adding 0.5-1.0 g/L of ferrous sulfate and 0.6-1.2 g/L of hydrogen peroxide to the liquid treated in step (1), stirring and reacting for 5-30 minutes, adding 1-3 g/L of separation control agent A and 2-8 g/L of separation control agent B, stirring and reacting for 5-120 minutes, adding 20-50 g/L of polyacrylamide, stirring for 2-3 minutes, standing for 1-5 minutes, and performing solid-liquid separation for the second time; (3) Add 0.5-3 g/L of flocculant to the liquid treated in step (2), stir for 1-3 minutes, add 3-20 g/L of polyacrylamide, stir for 1-3 minutes, let stand for 1-5 minutes, and achieve solid-liquid separation for the third time to complete the treatment of the pulping waste liquid. 2. The method for rapidly treating pulping wastewater according to claim 1, characterized in that, in the step (1), the color stabilizer is a biological enzyme composite preparation, comprising one or more of pectinase, laccase or xylanase mixed in any proportion. 3. The method for rapidly treating pulping wastewater according to claim 1 or 2, characterized in that, in the step (1), the polyaluminium chloride is a 30% solution and the polyacrylamide is a 1% solution. 4. The method for rapidly treating pulping wastewater according to claim 1, characterized in that, in said step (1), during the first solid-liquid separation, the black liquor/wastewater undergoes solid-liquid separation, the solids enter a plate-and-frame or stacked filter press to form mud, and the liquid enters the next stage of treatment. After the treatment in step (1), the liquid COD/BOD/color decreases, and the pH is less than 7; during the second solid-liquid separation, the solids enter a plate-and-frame or stacked filter press to form mud, and the liquid COD/BOD continues to decrease, and the pH is greater than 8. During the third solid-liquid separation, the liquid COD/BOD/color meets the discharge standard, i.e., COD < 100 mg/L, BOD < 20 mg/L, color < 50 times, and pH = 6.5 to 7.5. 5. The method for rapidly treating pulping wastewater according to claim 4, characterized in that, in the step (2), the ferrous sulfate is 65% ferrous sulfate pentahydrate, the hydrogen peroxide is 27% hydrogen peroxide, and the mass ratio of ferrous sulfate to hydrogen peroxide is 1.0:1.2. 6 . The method for rapidly treating pulping wastewater according to claim 5 , wherein the mass ratio of the separation control agent A to the separation control agent B is 3:8. 7 . The method for rapidly treating pulping wastewater according to claim 6 , wherein the ion control agent A and the ion control agent B are ion quantity control agents, the ion control agent A is NaAlO ₂ , and the ion control agent B is CaCl ₂ .