Phosphorus gypsum as cement retarder

                                             Phosphorus gypsum as cement retarder

The main composition of phosphogypsum is CaSO4 ・ 2 h2o. Therefore, as long as have enough process conditions, phosphogypsum can instead of natural gypsum is used for cement production, but for a long time with the status of the phosphorus gypsum to produce cement retarder is not satisfactory. Are the main reasons why untreated phosphogypsum used in cement production are the following hazards: (1) the soluble P in phosphogypsum: O, the phosphorus gypsum acidic, this will accelerate the corrosion of equipment; Because of soluble P20, exist at the same time, the condensation rate of cement is not normal, caused the slow fast setting and condensation, phosphorus gypsum production equipment could also reduce the strength of cement; (2) the water content of phosphogypsum is commonly 20% one 30%, this will cause the bunker agglomerate, jams, etc.; (3) the phosphogypsum of phosphorus, fluorine, impurities such as organic matter, affect the physical properties of cement. Of phosphorus, the influence of fluorine is very big, can make the initial setting time of cement treads, strength decreased. Phosphorus gypsum in cement production, therefore, to get a great development, it needs to be modified.

Phosphogypsum modification can be used to add alkali lime milk and kinds of methods of reinforced material, phosphorus gypsum production line modification is mainly divided into the following several aspects: (1) to eliminate water soluble phosphorus in phosphogypsum and other impurities of cement condensation rate, adverse effect of the physical properties such as strength, its soluble P2O5, less than 0. 3%, soluble F less than 0. 05%; (2) sulfate content is constant, (3) phosphogypsum should not be acidic, modified phosphogypsum in pH 6. 5 to 7. It is advisable to 5; (4) of the modified phosphogypsum moisture content should be low, Ⅲ for cement production.

The method of phosphogypsum modification mainly include: (1) the water washing method; (2) calcination method; (3) legal; (4) the natural ageing process, etc. Phosphogypsum by the lime milk neutralization, calcination and recrystallization after modification, the water soluble phosphorus content, phase composition and the dissolving properties are changed. People enhance the seed material curing enhancement effect to the phosphogypsum, and as the cement hydration, the seed is beneficial to early strength cement.