CN101519853B - Treatment method of alkaline pulping black liquor in papermaking process - Google Patents

Abstract

A method for treating alkaline pulping black liquor in a papermaking process belongs to the technical field of chemical industry and environmental protection. Acidifying pulping black liquor by using acid wastewater generated by producing activated clay until the pH value is 3-4, layering, separating out precipitate, and separating out clear liquid; the activated clay wastewater is wastewater with pH of 1-2 generated by preparing activated clay by acidifying bentonite with inorganic acid. The separated clear liquid is reused for pulping process or discharged after biochemical treatment. And carrying out filter pressing and drying on the separated precipitate, and then extracting lignin. The present invention uses the waste water produced by producing activated clay to acidify pulping black liquor, and makes substitution reaction with alkali lignin in the black liquor to make flocculation separation so as to attain the goal of separation, and can treat pollution and change waste into benefit.

Description

Treatment method of alkaline pulping black liquor in papermaking process

field of invention

The invention belongs to the technical field of chemical industry and environmental protection, and relates to the treatment technology of alkaline pulping wastewater, in particular to the treatment method of alkaline pulping black liquor in the papermaking process.

technical background

In the field of papermaking, alkaline pulping is the pulping method with the greatest development prospect at home and abroad, the widest application range, and the majority of its pulp output.

Pulping and cooking black liquor is high-concentration, high-alkaline organic wastewater. Among the three waste waters of black liquor, mid-stage water and white water produced by papermaking, black liquor has the largest pollution load, accounting for 90% of the pollution load of the entire papermaking industry. COD, BOD ₅ , chroma, and suspended solids in the water are high, and contain a large amount of inorganic substances. Salt. Papermaking wastewater accounts for more than 1/10 of the total wastewater discharged by various industries in the country; the wastewater has a high content of organic pollutants, accounting for more than 1/4 of the country's total.

About 70% of the wastewater is organic matter, about 30% is inorganic sodium salt, COD _Cr is generally about 15,000-40,000 mg/L, pH 10-13, and COD _Cr exceeds 50 times the discharge standard. And it is difficult to decolorize.

The pollutants in the black liquor are mainly the products of the raw materials under the condition of high temperature and strong alkali, and more than 50% of the substances in the raw materials are dissolved into the cooking liquor after chemical reaction. Lignin accounts for a high proportion in the cooking liquor. It is a three-dimensional network polymer with an aromatic structure, which is a difficult biodegradable compound. For aerobic and anaerobic processes, lignin is difficult to remove. Moreover, because the current industrialization of comprehensive utilization technology for black liquor resources is not perfect enough, the produced lignin by-products are often unable to be sold or utilized because the purity does not meet the requirements, so most of them still pollute the environment in the form of solid waste.

If these high-concentration and large-volume wastewater is discharged directly without treatment, it will not only cause great harm to the production and life of people near the papermaking enterprise and the surrounding environment, but will also spread to distant rivers and lakes.

Due to the presence of refractory substances such as high concentrations of lignin, the treatment of cooking black liquor is extremely difficult. People have done a lot of work on black liquor treatment, but it is difficult to achieve the desired effect due to various factors.

Patent CN 101234833A discloses a process for treating waste water in the mid-stage of wheat straw cleaning pulping and papermaking or sulfite pulping and papermaking. A calcium-containing precipitant is selected and added to the mid-stage wastewater before the biochemical treatment of the mid-stage wastewater to remove sulfite ions in the wastewater to reduce the content of sulfite ions in the wastewater, and then perform biochemical treatment. However, since black liquor wastewater is generally highly alkaline, it is generally difficult to carry out biochemical treatment without neutralization treatment.

Patent CN 1920170A discloses a method for extracting lignin from papermaking black liquor by biological acidification-flocculation precipitation. Using solid organic matter to establish a biological acidification fermentation system, the organic matter in the solid organic matter is fermented under the action of microorganisms to produce acid, which is used as the initial starting acid source for the acidification and neutralization of black liquor, and lignin is extracted from the neutralized black liquor through the flocculation and sedimentation process. However, the amount of biological acid production is limited, which cannot well meet the needs of black liquor treatment.

Contents of the invention

The purpose of the present invention is to provide a relatively low-cost, easy-to-use method for processing black liquor from papermaking alkaline pulping.

According to the method for treating black liquor from alkaline pulping in the papermaking process of the present invention, the pH of the black liquor is 10-13.

The acidic waste water produced by the production of activated clay is used to acidify the pulping black liquor to pH 3-4, layered, precipitated, and the clear liquid is separated; the activated clay wastewater is produced by acidifying bentonite with inorganic acid to prepare activated clay. Wastewater with a pH of 1-3.

The above-mentioned separated supernatant is reused in the pulping process, or discharged after biochemical treatment. After the above-mentioned precipitation is filtered and dried, the lignin is extracted.

The invention adopts the acidification pulping black liquor produced by the production of active clay, and undergoes a substitution reaction with the alkali lignin in the black liquor to flocculate and separate out to achieve the purpose of separation. Pulping wastewater is acidified by activated clay acid wastewater, and lignin is extracted to turn waste into profit.

The production of activated clay is to acidify bentonite with inorganic acid, and replace the cations such as calcium, sodium, magnesium, and iron between the crystal layers of bentonite with hydrogen ions of inorganic acid. The pores of the unit cell are enlarged, the specific surface area is increased, and countless active acid points are formed.

After the acidification treatment, it is necessary to wash out the residual acid with a large amount of water, and the production of 1 ton of activated clay will produce about 50 tons of waste water. The waste water also contains a large amount of acid, and the pH value of the waste water is 1-3. The conventional wastewater treatment method is to neutralize the wastewater with alkali and then discharge it. A large amount of alkali is required and the cost is very high, which is the main factor restricting the production of activated clay.

The invention utilizes the waste water produced by active clay production to acidify pulping black liquor, extracts lignin, treats sewage with sewage, turns waste into profit, saves pollution control expenses, has high environmental protection value, and social and economic benefits.

Each ton of pulping black liquor contains about 25kg of cellulose, hemicellulose and lignin, which account for 85% of the chroma components and 75% of the CODcr components, and are the main pollutants. The rest are suspended small fibers and parenchyma cells. The CODCr of black liquor is generally about 15000-40000mg/L, SS1000mg/L-2500mg/L, and pH10-13. These substances are difficult to precipitate and handle under alkaline conditions. Adjust the pH value to acidic, and the alkaline lignin will be precipitated.

Alkaline lignin is the main pollutant in pulping black liquor. Use activated clay wastewater to acidify papermaking black liquor and adjust the pH value. Alkaline lignin will undergo substitution reaction under acidic conditions and flocculate and precipitate to achieve the purpose of separation. And further extract lignin.

The activated clay wastewater also neutralizes the alkaline substances in the black liquor, which include: sodium hydroxide, sodium sulfide, sodium carbonate, sodium lignin, sodium formate, sodium acetate, sodium sulfite, sodium silicate, etc. Meet emission standards.

Description of drawings

Figure 1 is a flow chart of pulping black liquor acidification treatment using waste water generated from the production of activated clay.

The treatment effect of activated clay wastewater on pulping black liquor is as follows:

Table 1 Separation phenomenon of black liquor under different pH conditions

pH 5.5 4.5 3 Effect Produces microflocculation, slightly sinks, and the layering is not obvious The flocs are larger, the particles sink obviously, and a small amount floats up The flocs increase, the sinking is obvious, more substances float up, and the middle water is clear

Table 2 CODcr treatment effect

Detailed ways

The specific implementation steps of the present invention are as follows:

1) The pulp mill builds multiple black liquor pools to meet the needs of continuous production, and the papermaking black liquor is stored in the black liquor pools for standby.

2) Activated clay wastewater is precipitated and filtered to remove residual activated clay particles, and the upper clarified liquid is taken as the acidified black liquor.

3) Add activated clay wastewater to pulping black liquor, mix thoroughly, and stop adding activated clay wastewater to pH 3-4.

4) After the pulping black liquor is acidified, it is separated into layers. The supernatant is separated and reused for pulping or further biochemical treatment.

5) The precipitated substance is the floc after acidification of alkali lignin, which is filtered and dried to further extract lignin.

Example 1

Take 10 tons of caustic soda anthraquinone process wood pulp black liquor, pH value is 10.6, CODcr value is 29546mg/L, SS 1538mg/L, add about 100kg activated clay wastewater, adjust pH to 3.5, black liquor precipitates, take clear night for detection The CODcr value is 8513mg/L, and the CODcr removal rate is 71.2%. The lignin was further extracted from the precipitate to obtain 67kg of lignin.

Example 2

Take 30 tons of alkaline sulfite wheat straw pulp black liquor, pH value is 11, CODcr value is 35754mg/L, SS 1936mg/L, add about 450kg activated clay wastewater, adjust pH to 3.5, black liquor precipitates, take clear night The detected CODcr value was 12756mg/L, and the CODcr removal rate was 64.3%. The lignin was further extracted from the precipitate to obtain 159 kg of lignin.

Claims (3)

1. the processing method of alkaline pulping black liquor in papermaking technology, its pH of described black liquor is 10-13, it is characterized in that: adopt the acid waste water acidification treatment pulping black liquor that produces activated clay, to pH 3- 4. Layering, precipitation, and separation of clear liquid; the activated clay wastewater is wastewater with a pH of 1-3 produced by acidifying bentonite with inorganic acids to prepare activated clay. 2. The method for processing black liquor from alkaline pulping in the papermaking process according to claim 1, characterized in that: the separated clear liquid is reused in the pulping process, or discharged after biochemical treatment. 3. The processing method of alkaline pulping black liquor in the papermaking process as claimed in claim 1, characterized in that: after the precipitates are press-filtered and dried, lignin is extracted.

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