Research Of Flue Gas Desulphurization Gypsum As A Retarder In Cement

As industrial by-product gypsum,flue-gas-desulfurization is considered as the new building materials which offer very high potential for exploitation in the 21 century.With more and more requirement of sulfur dioxide reduction,desulfurization project is increasing and the flue gas desulfurization gypsum as the by-product increases rapidly.So researching the application of FGD gypsum and making the new material which can meet the requirements of the project has important significance.This paper focuses on the properties of FGD gypsum using as cement retarder, according to the high moisture which effecs cement production, reasearching the effect of heat treatment temperature and dosage on thesetting time and mechanical properties of cement. Reasearching the properties of clotty material through making the gypsum into a ball ,then used in cement production. Besides, study the effect of FGD gypsum mixed with natural as retarder and the method of dislodging impurities of FGD gypsum.The results are as follows:①FGD gypsum can completely replace the natural gypsum as the cement retarder, and the setting time becomes longer. When it was used in portland cement as retarder, adding 6% of FGD gypsum which was processed at 50℃, the setting time is longest, it reaches 4:16 (h:min). When it is added into ordinary cement as retarder, adding 5% of FGD gypsum processed at 50℃, the setting time is longest, it reaches 4:51(h:min).②When adding 5% of FGD gypsum which was processed at 110℃, the strength of cement achieves maximum.③Taking the method through adding active mineral into FGD gypsum to cement into a ball, the best treatment method is: the content of slag and fly ash is 25%, lime content (percentage of the amount of slag and fly ash ) is 1%, the proportion of slag and fly ash is1:1,curing temperature is 40℃. The clotty material can be cemented into the ball and the strength can achieve the transport requirements.④Removing soluble salt impurities through washing FGD gypsum, the setting time extends 4.5%,9.8%,2.8% than the untreated gypsum. Through adding 1% oxyful to oxygenize the calcium sulfite, when the dosage of FGD gypsum is 5% ,compared with the gypsum without oxyful, initial setting time prolongs 5.9%, final setting time prolongs 12.5%.⑤Natural gypsum mixed with FGD gypsum as retarder, the retarding effect is good, when the total percentage of the two kinds of gypsum is 5%, the proportion is 1:1, final setting time achieves to 3:58(h:min),which can meet the engineering need. In the premise of the percentage is 1:1 , the total content of the two kinds of gypsum is 7%,compared with the content is 5% and 6%, mechanical properties of cement is better, compressive strength respectively improve 2.1% and 4.3%.