Mainly used for metal etching and sewage treatment. Among them, the etching includes the etching of copper, stainless steel, aluminum and other materials. It has the advantages of good effect and low price for the treatment of low-oil raw water, but it brings the disadvantage of yellowing of the water. It is also used for printing and dyeing cylinder engraving, electronic industrial circuit board and fluorescent digital tube production, etc. The construction industry is used to prepare concrete to enhance its strength, corrosion resistance and water resistance. It can also be formulated with ferrous chloride, calcium chloride, aluminum chloride, aluminum sulfate, hydrochloric acid, etc. to be a water-repellent agent for clay, and used in the inorganic industry to produce other iron salts and inks. In the dye industry, it is used as an oxidizing agent in dyeing with Yindixin dyes. Used as a mordant in the printing and dyeing industry. The metallurgical industry is used as a chlorinated ingress agent for extracting gold and silver. The organic industry is used as a catalyst, oxidant and chlorinating agent. The glass industry is used as a hot coloring agent for glassware. The soap industry is used as a coagulant for the recovery of glycerin from soap waste liquid.