1. Application and use of sodium sulfite in paper industry

The paper industry consumes the most sodium sulfite products. Cooking plant fiber raw materials with sodium sulfite cooking solution at a certain temperature and pressure is one of the important pulping methods in the paper industry, especially suitable for non-wood materials. The advantages of this pulping method are that the color of the pulp is light, the consumption of bleach and other chemicals is low, and the waste liquid can be recycled to produce a variety of by-products. When sodium sulfite is used in alkaline wheat straw cooking, the pulp yield is significantly improved, the pulp has less foam, good water filtration, easy washing, water saving and power consumption reduction. The beating degree of the pulp is reduced, the fiber strength is good, and it is easy to make paper. The color of the pulp is light, easy to bleach, and the chlorine consumption is reduced. 20% (mass) sodium sulfite has a very good delignification effect on bagasse and the ability to separate fiber at 160 ℃, and the delignification rate reaches more than 48% after 30 minutes.

With the continuous development of the paper industry, secondary fiber recycling has been highly valued by the paper industry. It can not only save the cost of paper making, but also save forest resources, reduce energy consumption, and benefit environmental protection. Sodium sulfite is a good deinking agent. Its role in deinking is to prevent the pulp from yellowing, while sodium sulfite deinking under weak alkaline conditions is more beneficial for ink removal. In the absence of surfactant, it has obvious effect to add 2% sodium sulfite in 10% pulp concentration. Neutral sodium sulfite is used for deinking old newspapers. The amount of sodium sulfite is 3%~4%, which can achieve good deinking effect, reduce the pollution load of wastewater, and is conducive to the later treatment of wastewater.

2. Application and use of sodium sulfite in water treatment industry

In order to prevent the corrosion of dissolved oxygen in water to the boiler, most of the boiler water needs to be deoxidized. Sodium sulfite is the first chemical deoxidizer used to remove dissolved oxygen in water. It is widely used because of its advantages such as good quality, cheap price, convenient source, non-toxic, and rapid reaction with oxygen. The combination of sodium sulfite with stabilizer and catalyst can improve the stability of sodium sulfite and reduce the operating cost.

The sodium sulfite reduction treatment method is one of the most environmentally friendly and energy-saving methods in the current chromium-containing wastewater treatment process. It can not only ensure that the effluent quality can meet the discharge standard, but also recover and utilize chromium hydroxide. The equipment and operation are also relatively simple, saving money and floor space.

3. Application and use of sodium sulfite in chemical industry

As a raw material or assistant, sodium sulfite is widely used in the chemical industry. Boiling reaction of sodium sulfite with sulfur is one of the main methods of producing sodium thiosulfate. In the production process of sodium hydroxide removal of brackish water, the residual free chlorine can be removed by adding Na2SO3 under alkaline conditions. Sodium sulfite process is one of the internationally recognized mature and reliable refining methods for TNT industrialization. As a sulfonating agent, sodium sulfite is widely used in the synthesis of fine chemicals. Sodium 4-methylbenzenesulfonate is an important intermediate in the synthesis of a new herbicide methazochlor, which is obtained by reduction of 4-methylbenzenesulfonyl chloride with sodium sulfite. Fluorocarbon surfactant is a kind of surfactant with the highest surface activity so far. Fluorocarbon alkyl succinate sulfonate surfactant can be prepared from octafluoropentanol, maleic anhydride and sodium sulfite through esterification and sulfonation steps. The combination of sodium sulfite and other corrosion inhibitors can greatly improve the corrosion inhibition effect.

4. Application and use of sodium sulfite in food industry

Sodium sulfite is a widely used food additive permitted by the state and can be used as a bleaching agent, preservative, loosening agent, antioxidant, color protection agent and preservative in food processing. Sodium sulfite is a polyphenol oxidase (PPO) activity inhibitor, which can effectively protect the browning of fruits and vegetables and improve their added value.

Cauliflower is one of the most important vegetables in China, but it is prone to browning during storage, which reduces the edible value. Using 0.15% ascorbic acid, 0.35% citric acid, 0.5% sodium sulfite and 0.35% sodium pyrosulfite composite aqueous solution to treat cauliflower has good anti-browning effect, and the texture of cauliflower remains soft during storage. The color, taste and flavor of sterilized bracken soft cans remained unchanged at room temperature for 6 months after blanching with 400mg/kg zinc gluconate solution, 200mg/kg Na2SO3 solution and hardening with 0.4% CaCl2 solution.

Using red Fuji apple as raw material, under the conditions of sodium sulfite concentration of 0.3%, sulfurizing time of 80 min, drying temperature of 75 ℃ and drying time of 2.5 h, the golden apple dry product with uniform color, sweet and sour taste and apple fragrance can be obtained.

The application of sodium sulfite in the food industry has a long history. With the gradual deepening of research, the toxicity of sodium sulfite has been increasingly concerned. The scope of use, the maximum amount of use and the residual amount of sodium sulfite are clearly specified in the national standard.

5. Application and application of sodium sulfite in metallurgical industry

Sodium sulfite is widely used in mineral processing as an inhibitor. Luo Chaoyan et al. studied the effect of cyanide-free reagent or combination reagent on the floatability of jamesonite and marmatite. Zinc sulfate+sodium sulfite (molar ratio 1:1) is a highly effective inhibitor of marmatite, which can successfully and effectively separate lead and zinc minerals and obtain ideal lead concentrate indicators, and can reduce pollution and protect the ecological environment. The copper-lead mixed concentrate uses potassium dichromate and sodium sulfite as the inhibitor, and the copper concentrate grade is 24.99%, the lead content is 5.48%, and the lead concentrate grade is 34.34%, the copper content is 6.56%, and the copper and lead can be separated, which points out a new research direction to solve the separation problem of copper and lead.

6. Application and application of sodium sulfite in printing and dyeing industry

Sodium sulfite is used as a deoxidizer and bleach in the printing and dyeing industry for the cooking of various cotton fabrics, which can prevent the local oxidation of cotton fibers under high temperature and alkali conditions from affecting the fiber strength, and improve the whiteness of the cooked fabrics; It can make lignin form alkali-soluble derivatives and be removed. It can decompose impurities such as protein and pectin and dissolve them in alkaline solution, especially for low-grade cotton with more impurities.

7. Application and application of sodium sulfite in leather industry

Sodium sulfite is an important auxiliary in the leather industry. It can make leather soft, plump and tough when used in leather processing, and has the properties of water resistance, folding resistance and wear resistance. At the same time, it can also be used in the manufacture of leather fatliquor.

8. Application and use of sodium sulfite in medicine

It can be used for the synthesis of crude drugs. Taurine can be prepared from ethanolamine, sulfuric acid and sodium sulfite as the main raw materials through two steps of cooling-up and sulfonation, and then extracted and separated by hydrochloric acid and alcohol.

9. Others: sodium sulfite is an indispensable developer and fixer in the photographic industry; It is used as common analytical reagent and photoresist material.