Hydrometallurgy for rare metals
For example, when smelting tungsten, scheelite (calcium tungstate) is first mixed with sodium carbonate and roasted in the air (800℃ ~ 900℃) to generate sodium tungstate.
CaWO4+Na2CO3=Na2WO4+CaO+CO2↑
Immersing the sintered block in water at 90℃ to dissolve sodium tungstate, adding hydrochloric acid for acidification, filtering out precipitated tungstic acid, and then heating to generate tungsten oxide.
Na2WO4+2HCl=H2WO4↓+2NaCl
H2WO4=WO3+H2O↑
Finally, tungsten oxide is roasted in hydrogen flow to obtain metallic tungsten.
WO3+3H2=W+3H2O
(2) used in organic synthesis
For example, at the temperature of 180℃ ~ 200℃, using mercury salt (such as HgCl2) as catalyst, the addition reaction of hydrogen chloride and acetylene generates vinyl chloride, and then it is polymerized into polyvinyl chloride under the action of initiator.
(3) Used in bleaching and dyeing industry
For example, cotton should be washed with hydrochloric acid after bleaching, and residual alkali should be neutralized with hydrochloric acid after mercerized cotton. In the process of printing and dyeing, some dyes are insoluble in water and need to be treated with hydrochloric acid to make them soluble in hydrochloric acid before they can be used.
④ Used for metal processing.
For example, in the pretreatment of steel parts before electroplating, caustic soda solution is used to wash away oil stains, and then hydrochloric acid is used to soak them; Before metal welding, it is necessary to apply a little hydrochloric acid to the joint. All of them use the property that hydrochloric acid can dissolve metal oxides to remove rust. In this way, the metal surface can be electroplated firmly and welded firmly.
(5) Used in food industry.
For example, when making chemical soy sauce, raw materials such as cooked bean cakes are soaked in a solution containing a certain amount of hydrochloric acid and kept at a certain temperature. Hydrochloric acid can catalyze the hydrolysis of complex protein. After a certain period of time, amino acids with delicate flavor are generated, and then neutralized with caustic soda (or soda ash) to obtain amino acid sodium. The production principle of monosodium glutamate is similar to this.
(6) Used for producing inorganic drugs and organic drugs.
Hydrochloric acid is a strong acid, which can react with some metals, metal oxides, metal hydroxides and most metal salts (such as carbonate and sulfite) to form hydrochloride. Therefore, hydrochloric acid is used in the production of many inorganic drugs.
In medicine, many organic drugs, such as novocaine and thiamine hydrochloride (a preparation of vitamin B 1), are also made from hydrochloric acid.
The above are just some examples of the application of hydrochloric acid in industrial production. In fact, hydrochloric acid has many uses. In daily life, we sometimes use it, such as insufficient stomach acid and indigestion. The doctor gave us a certain amount of dilute hydrochloric acid to make up for the deficiency of gastric acid. Hydrochloric acid is widely used in chemical experiments and scientific research.