What Is Gypsum Recycling?

This is an industrial waste residue based on calcium sulfate. Waste gypsum is powdery, the main component is calcium sulfate, the content is above 80%, and the other components are silicon, aluminum, iron, magnesium, sodium, potassium, phosphorus, sulfur, titanium, manganese, cerium, carbon, fluorine and other elements Of oxides.

Approximately 5 tons of phosphogypsum are discharged for each ton of phosphoric acid produced. The emissions of phosphogypsum in many countries exceed the extraction of natural gypsum. For example, the emissions of phosphogypsum in the Soviet Union in 1975 were 14 million tons, and the emissions in Japan in 1978 were 2.488 million tons, which are both greater than the natural gypsum extraction. If the waste gypsum is not used, it will occupy a large area of land and pollute the soil and water systems. For example, fluorogypsum has a fluorine content of 3.07%, of which 2.05% is water-soluble. Improper handling will endanger humans and animals (see the impact of fluorine pollution on health). ^[1]

Japan is the country with the highest utilization of waste gypsum. For example, in 1956, the trial of using phosphogypsum as a cement retarder has been widely used. China also has rich experience in using waste gypsum as a cement retarder. Phosphogypsum contains water-soluble phosphorus pentoxide and fluorine, which will adversely affect the hydration reaction of the cement, causing the cement to set too slowly and reducing the early strength. Therefore, phosphogypsum used as a retarder can be washed with water or lime milk to neutralize these impurities. The performance of fluorogypsum, soda gypsum and titanium gypsum as cement retarder is better than phosphogypsum, and its application is relatively simple. There are two main processing methods for producing building materials products from waste gypsum. One is to produce -hemihydrate gypsum by the baking method represented by Japan, and the other method is to produce -hemihydrate high-strength gypsum by the autoclave method represented by the Federal Republic of Germany. The main building material product is gypsum board. China also develops gypsum boards using waste gypsum as raw materials, mainly phosphogypsum hollow slabs, fluorogypsum hollow slabs, fluorogypsum paper gypsum boards, salt gypsum fiber gypsum boards, and various boards have good technical performance. In addition, the production of -semi-water high-strength gypsum by liquid-phase conversion autoclave method and the simultaneous production of sulfuric acid and cement from waste gypsum have certain development prospects. ^[1]