CN110451679B - Method for recovering sodium sulfate and removing potassium chloride ions from alkali ash separation filtrate - Google Patents

Abstract

The invention provides a method for recovering sodium sulfate and removing potassium chloride ions from alkali ash analysis filtrate, comprising the following steps: a. constant temperature crystallization: carrying out constant temperature crystallization of alkali ash analysis filtrate at -10-15°C, and then Carry out solid-liquid separation at this temperature to obtain sodium sulfate decahydrate crystals and crystallization mother liquor; b. adjust the pH value of the crystallization mother liquor obtained in step a, and adjust the pH value to 3‑8; Use activated carbon to absorb the COD in the crystalline mother liquor; d. Send the crystalline mother liquor treated in step c to the nanofiltration membrane system for nanofiltration and concentration, and the nanofiltration concentrated solution enters the alkali ash analysis filtrate for recycling. In the method for recovering sodium sulfate and removing potassium chloride ions from alkali ash analysis filtrate provided by the present invention, the recovery rate of sulfate ions is more than 90%, and the process conditions are simple and stable, and the obtained high-purity sodium sulfate can be recovered, realizing waste water The utilization of resources removes the organic matter that may be enriched in the wastewater, making wastewater treatment sustainable.

Description

A kind of alkali ash analysis filtrate reclaims the method for sodium sulfate and removes potassium chloride ion

technical field

The invention belongs to the field of water treatment, and relates to a method for recovering sodium sulfate and removing potassium chloride ions from alkali ash analysis filtrate.

Background technique

As one of the important industries of my country's national economic development, the paper industry has developed rapidly in recent years. Alkali recovery is widely used as the main way of papermaking waste liquid treatment and energy recovery. Soda ash, one of the combustion products of black liquor in the alkali recovery furnace, is mainly composed of inorganic salts such as sodium, potassium, sulfate, chloride, and carbonate. Among them, chloride ions and potassium ions will reduce the melting temperature of accumulated ash, cause pipeline blockage, shorten the operating cycle of the alkali furnace, and have a corrosive effect on the metal materials of the alkali furnace. The soda ash is generally treated by the analysis and filtration method, that is, the soda ash is dissolved in hot water to make the solution saturated, and the sodium sulfate in the soda ash is recovered by using the principle of low solubility of sodium sulfate, and potassium chloride ions are removed. The solution is the alkali ash analysis filtrate. However, some sodium sulfate is still contained in the soda ash analysis filtrate, which leads to low recovery efficiency of sodium sulfate in the analysis and filtration process, and a large amount of sodium sulfate is discarded.

Contents of the invention

1. Technical problems to be solved:

The existing analysis and filtration method processes soda ash, and the finally obtained soda ash analysis filtrate still contains part of sodium sulfate, which leads to low recovery efficiency of sodium sulfate in the analysis and filtration process, and a large amount of sodium sulfate is discarded.

2. Technical solution:

In order to solve the above problems, the present invention provides a method for recovering sodium sulfate and removing potassium chloride ions from alkali ash analysis filtrate, comprising the following steps: a. constant temperature crystallization: carrying out alkali ash analysis filtrate at -10-15°C constant temperature crystallization, and then carry out solid-liquid separation at this temperature to obtain sodium sulfate decahydrate crystals and crystallization mother liquor, and the sodium sulfate decahydrate obtained by drying the sodium sulfate decahydrate crystals is recovered; b. the pH of the crystallization mother liquor obtained in step a Adjust the pH value to 3-8; c. Activated carbon adsorption, use activated carbon to adsorb the COD in the crystallization mother liquor after adjusting the pH value; d. Send the crystallization mother liquor treated in step c into the nanofiltration membrane system for Concentrated by nanofiltration, the concentrated liquid on the concentrated side enters the alkali ash analysis filtrate for recycling, returns to step a to continue to participate in constant temperature crystallization, and the permeate is recovered as the electrolyte in the electrolysis industry.

In step b, the pH value of the crystallization mother liquor is adjusted by hydrochloric acid or sulfuric acid.

The activated carbon used in step c is wood activated carbon, fruit shell activated carbon or coal-based activated carbon.

In step d, the nanofiltration membrane is an organic membrane with an average pore size of 0.5-5 nm, and the membrane element is a roll membrane or a flat membrane.

In step d, the permeate is a mixed solution of sodium chloride and potassium chloride.

3. Beneficial effects:

In the method for recovering sodium sulfate and removing potassium chloride ions from the alkali ash analysis filtrate provided by the present invention, the recovery rate of sulfate ions is more than 90%, and the process conditions are simple and stable, which is convenient for industrialization and can recycle the obtained high-purity sodium sulfate , Realize the resource utilization of wastewater, remove the organic matter that may be enriched in the wastewater, and make the wastewater treatment sustainable.

Description of drawings

Fig. 1 is the process flow chart of invention.

Detailed ways

The present invention will be described in detail below by way of examples.

Example 1

The used alkali ash analysis filtrate composition is as follows:

Element Na⁺ K⁺ CO₃^2- SO₄^2- Cl^- COD Concentration g/L 100-130 30-60 15-30 150-250 20-50 0.3-0.6

After the soda ash analysis filtrate was crystallized at -10 ℃, Na ⁺ in the crystallization mother liquor was 32.1 g/L, SO ₄ ^2- was 35.9 g/L, CO ₃ ^2- was 44.1 g/L, Cl ^- was 67.3 g/L, K ⁺ is 61.6 g/L, and the volume fraction is reduced to 34%. Adjust the pH value of the crystallization mother liquor to 3 with concentrated hydrochloric acid. After adjusting the pH of the solution, activated carbon was used to absorb COD, and the COD was reduced to 54mg/L. After activated carbon adsorption, the liquid enters the nanofiltration concentration system for treatment. The nanofiltration system adopts a flat organic membrane with an average pore size of 1-5nm, and the permeation liquid fraction is 44%, of which SO ₄ ^2- is 0.2 g/L, and Cl ^- is 66.4 g /L, Na ⁺ is 31.5 g/L, K ⁺ is 62.1 g/L, COD is 20mg/L, it can be used as raw material for electrolysis industry. The concentrated side volume fraction is 22%, among which SO ₄ ^2- is 37.5 g/L, Cl ^- is 59.1 g/L, Na ⁺ is 33.7 g/L, and K ⁺ is 62.8 g/L. The concentrated liquid on the concentrated side is directly returned to the soda ash analysis filtrate, and continues to participate in the constant temperature crystallization process. After the above steps, the recovery rate of SO ₄ ^2- in the soda ash analysis filtrate was 93%, and the obtained anhydrous Na ₂ SO ₄ met the standard of GB/T6009-2014 Industrial Anhydrous Sodium Sulfate Class I First-Class Product.

Example 2

The used alkali ash analysis filtrate composition is the same as embodiment 1.

After the alkali ash analysis filtrate was crystallized at -5 °C, the Na ⁺ in the crystallization mother liquor was 46.3 g/L, the SO ₄ ^2- was 44.1 g/L, the CO ₃ ^2- was 42.3 g/L, and the Cl ^- was 63.7 g/L. K ⁺ is 57.2 g/L, and the volume fraction is reduced to 41%. Adjust the pH value of the crystallization mother liquor to 5 with concentrated sulfuric acid. Activated carbon was used to absorb COD in the pH-adjusted solution, and the COD was reduced to 83 mg/L. After activated carbon adsorption, the liquid enters the nanofiltration concentration system for treatment. The nanofiltration system adopts a roll-type organic membrane with an average pore size of 1-5nm, and the permeation liquid fraction is 47%, of which SO ₄ ^2- is 0.5 g/L, Cl ^- is 62.1 g/L, Na ⁺ is 46.1 g/L, K ⁺ is 58.6 g/L, COD is 17 mg/L, it can be used as raw material for electrolysis industry. The volume fraction of the concentrated side is 12%, of which SO ₄ ^2- is 57.6g/L, Cl ^- is 54.8 g/L, Na ⁺ is 47.5 g/L, and K ⁺ is 57.0g/L. The concentrated liquid on the concentrated side is directly returned to the soda ash analysis filtrate, and continues to participate in the constant temperature crystallization process. After the above steps, the recovery rate of SO ₄ ^2- in the soda ash analysis filtrate was 92%, and the obtained anhydrous Na ₂ SO ₄ complied with the standard of GB/T6009-2014 Industrial Anhydrous Sodium Sulfate Class I First Class.

Example 3

The used alkali ash analysis filtrate composition is the same as embodiment 1.

After the alkali ash analysis filtrate was crystallized at 10°C, Na ⁺ in the crystallization mother liquor was 58.2 g/L, SO ₄ ^2- was 50.8 g/L, CO ₃ ^2- was 38.2 g/L, Cl ^- was 56.3 g/L, K ⁺ is 50.6 g/L, and the volume fraction is reduced to 50%. The pH value of the crystallization mother liquor was adjusted to 7 with concentrated hydrochloric acid. After adjusting the pH of the solution, activated carbon was used to absorb COD, and the COD was reduced to 47 mg/L. After activated carbon adsorption, the liquid enters the nanofiltration concentration system for treatment. The nanofiltration system adopts a roll-type organic membrane with an average pore size of 1-5nm, and the permeation liquid fraction is 40%, of which SO ₄ ^2- is 0.6 g/L, Cl ^- is 53.4 g/L, Na ⁺ is 57.1 g/L, K ⁺ is 47.3 g/L, and COD is 24 mg/L, which can be used as raw materials for electrolysis industry. The volume fraction of the concentrated side is 10%, of which SO ₄ ^2- is 58.6 g/L, Cl ^- is 58.1 g/L, Na ⁺ is 56.1 g/L, and K ⁺ is 54.2 g/L. The concentrated liquid on the concentrated side is directly returned to the soda ash analysis filtrate, and continues to participate in the constant temperature crystallization process. After the above steps, the recovery rate of SO ₄ ^2- in the soda ash analysis filtrate is 90%, and the obtained anhydrous Na ₂ SO ₄ meets the standard of GB/T6009-2014 Industrial Anhydrous Sodium Sulfate Class I First-Class.

Although the present invention has been disclosed as above with preferred embodiments, they are not intended to limit the present invention. Any skilled person can make various changes or modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be defined by the protection scope of the claims of the present application.

Claims (3)

1. a kind of method that alkali ash analyzes filtrate and reclaims sodium sulfate and removes potassium chloride ion, and described alkali ash analyzes filtrate is in the papermaking industry, and the alkali ash that black liquor produces after alkali recovery furnace burns is through dissolving and analysis filtration method The solution after recovering sodium sulfate, the Na ⁺ concentration in the alkali ash analysis filtrate is 100-130 g/L, the K ⁺ concentration is 30-60 g/L, the CO ₃ ^2- concentration is 15-30 g/L, SO ₄ ^2- The concentration is 150-250 g/L, the Cl ^- concentration is 20-50 g/L, and the COD concentration is 0.3-0.6 g/L; The method comprises the steps of: a. Constant temperature crystallization: carry out constant temperature crystallization at -10-15°C for the alkali ash analysis filtrate, and then carry out solid-liquid separation at this temperature to obtain sodium sulfate decahydrate crystals and crystallization mother liquor, and the sodium sulfate decahydrate crystals are dried Gained anhydrous sodium sulfate reclaims; b. adjust the pH value of the crystallization mother liquor obtained in step a by hydrochloric acid or sulfuric acid, and adjust the pH value to 3-8; c. Activated carbon adsorption, use activated carbon to adsorb the COD in the crystallization mother liquor after adjusting the pH value; d. Send the crystallization mother liquor treated in step c into the nanofiltration membrane system for nanofiltration concentration, the concentrated liquid on the concentrated side enters the alkali ash analysis filtrate for recycling, returns to step a to continue to participate in constant temperature crystallization, and the permeate is used as electrolysis in the electrolysis industry Liquid recovery, the permeate is sodium chloride, potassium chloride mixed solution. 2. the method that alkali ash analyzes filtrate as claimed in claim 1 reclaims sodium sulfate and removes potassium chloride ion, it is characterized in that: the activated carbon used in step c is woody activated carbon, or fruit shell activated carbon, or coal-based activated carbon . 3. the method that alkali ash analyzes filtrate as claimed in claim 1 reclaims sodium sulfate and removes potassium chloride ion, it is characterized in that: the nanofiltration membrane described in step d is an organic membrane, and average aperture is 0.5-5nm, membrane The element is a roll film or a flat film.

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