Phosphogypsum Modification And Applied Research, As Cement Retarder

Phosphogypsum is by-product which the wet process produces the phosphoric acid. The analyze show that the chemical composition of phosphogypsum is CaSQ₄ ? 2H₂O mostly similar to natural gypsum. Phosphogypsum can replace natural gypsum as cement retarder. There are many deleterious impurities such as soluble P₂O₅, F, and organic substance etc in phosphogypsum because of phosphorite and the reaction in producing phosphogypsum process. It is difficult that the phosphogypsum is used to cement widely because of his characteristics such as high water ratio, acidic property and etc.The effect on setting time and strength of cement are obvious when untreated raw phosphogypsum is used as retarder. In this paper, different content, different habitat, different ageing time of phosphogypsum were comprehensively studied. The result shows that when phosphogypsum was added, cement setting time was delayed and cement early strength was decreased compare to natural gypsum. In the same time manufacturing facility trend to be corroded and blanking silo trend to be jammed, result in cement production is difficult to control and fluctuation of cement quality increase. Because the process of cement production is continuous mode and the raw phosphogypsum can't be added in cement continuously and steadily, the raw phosphogypsum can't be utilized widespread in producing cement. In order to use phosphogypsum continuously and steadily in cement production, the raw phosphogypsum must be modified.The theory of modify is based on the properties of soluble impurities and invert them to insoluble calcium phosphate through the neutralization reaction by adding alkali calcareous materials, the effect of impurities and the damage to cement will be decreased. This study used phosphogypsum as cement retarder which added lime, fly ash and modified agent, then modified by mixed and extrude forming or disk sphericity, and dry.The result show that modified phosphogypsum improves cement performance as retarding agent in stead of the natural gypsum. The setting time and strength of...