Experimental Study On Preparation Of High-strength Desulfurized Gypsum Products By Compression Molding

Desulfurized gypsum is one of the hardened cementitious materials.The composition of gypsum ore phase is changed from calcium sulfate dihydrate(CaSO4·2H2O)to calcium sulfate hemihydrate(CaSO4·0.5H2O)when it heated,which will continue to be transformed into anhydrous calcium sulfate(CaSO4).Anhydrite meets water and the ore phase consists of calcium sulfate(CaSO4)to calcium sulfate dihydrate(CaSO4·2H2O).Desulfurized gypsum exerts its gelation effect during phase change.This paper proposes to study the dehydration characteristics of desulfurized gypsum using a thermogravimetric analyzer,and then proposes a method for preparing a desulfurized gypsum products during the dehydration phase transition of calcium sulfate dihydrate(CaSO4·2H2O),and also proposes a method for the anhydrous calcium sulfate(CaSO4).The method for preparing the desulfurized gypsum products during the water absorption phase change process.(1)The thermal dehydration characteristics of FGD gypsum were investigated by thermal gravimetric analyzer(TGA)under different heating rates and different final temperatures for a period of time.The results showed that as the heating rate increased,desulfurization gypsum water began to end weightlessness and weightlessness temperature was higher,desulfurization gypsum crystal water loss faster;final temperature was 80?85?90?95?100?105?110?115 and 120? conditions under the constant temperature of 60 min desulfurization gypsum crystal thermal characteristics,final temperature higher desulfurization gypsum crystallization water began to weightlessness time is bigger and the end of weightlessness in less time,final temperature higher desulfurization gypsum water loss rate is greater.When the final temperature was 1000?,the desulfurization gypsum appeared three times of weightlessness,the first was the desulfurization gypsum free water lost weight,the second weight loss was the desulfurization gypsum crystal water lost,and the third weight loss is caused by the decomposition of FGD gypsum impurities in calcium carbonate.(2)The gypsum products were prepared by hot pressing forming process with gypsum as raw material in the experiment.The weight loss rate and compressive strength distribution of gypsum products under different pressure,temperature and time were studied.The results showed that the weight loss rate of gypsum products almost increases with the forming pressure,temperature and time.The compressive strength of products increased first and then decreased with the forming pressure,temperature and time.The analysis data of the products by XRD and SEM test showed that CaSO4·2H2O changed into CaSO4·0.5H2 O and CaSO4·2H2O firstly,and then changed into CaSO4 and CaSO4·2H2O,and the corresponding columnar crystals changed into dense fibrous crystals firstly,and then into Porous loose fibrous crystals with the molding temperature increases.Orthogonal experiments showed that the temperature is the main factor influencing the strength of FGD gypsum.When the molding temperature is 120?,the molding pressure is 20 MPa and the molding time is 30 min,the strength of FGD gypsum can reach 43.9MPa.(3)Anhydrous gypsum after calcination of desulfurized gypsum was used as a raw material,and a desulfurization gypsum products was prepared by a press molding process.The distribution characteristics of density and compressive strength of desulfurized gypsum products under different molding pressures,molding time and molding water addition were studied.The results show that the density of the press-molded desulfurized gypsum products increases with the increase of molding pressure,molding time and the amount of water added to the molding;the compressive strength of the products increases first with the increase of the molding pressure,the molding time and the amount of water added to the molding.The trend of lowering after high.With XRD and SEM analysis of the desulfurized gypsum test piece,the anhydrite in the test piece was converted into dihydrate gypsum,and accordingly,the rod-like crystals were converted into dense needle crystals.A new desulfurized gypsum products was developed with desulphurized gypsum raw materials in this paper.The prepared products have the characteristics of strong mechanical properties,energy saving and environmental protection,and simple process,which make up for the current gypsum products with small amount of gypsum,complicated process and high cost and provided a new idea for the large-scale utilization of desulfurized gypsum.