Study On The Preparation Of Short Columnar Anhydrite And The Whiteness α-calcium Sulfate Hemihydrate Of Flue Gas Desulfurization Gypsum

With the improvement of national environmental requirements,the coverage of flue gas desulfurization（FGD）devices increases largely.The amount of FGD gypsum which is the by-product of flue gas desulfurization produced in the wet-desulfurizing process rises perpendicularly,which will not only occupy too much land resources but also cause the secondary pollution.The application range of FGD gypsum is greatly limited due to color problems caused by the quality of limestone and collection efficiency of devices.As for the low performance of products obtained by FGD gypsum,large-grained short columnar anhydrite（Ⅵ）γ-CaSO₄ can be obtained by hydrothermal autoclave method with a low salt content in this paper.Taken the large granularity,high efficiency circulation and low length-diameter ratio as the objective function,this paper uses physical purification firstly to remove enriched impurities of FGD gypsum.And the influences of washing times,slurry concentration,salt content,the amount of succinic acid,reaction temperature and p H on product performance were investigated.And short columnar anhydrite（Ⅵ）γ-CaSO₄with the length of 100μm and length-diameter ratio of 1 can be obtained.What’s more,the influence of mother liquid circulation on product performance was investigated and this paper shows that the technology is feasible and has high efficiency circulation.As for the low whitness of products obtained by FGD gypsum,the effects of dosage of N.N-methylenebisacrylamide（MBA）,aging time,temperature and p H on the property of products were investigated using CaSO₄·0.5H₂O whiskers obtained in pure water solution as raw material,and crystal morphology and whiteness were taken as the objective function.The research shows that:whitening and large prismatic dihydrate gypsum with average length of 200μm and whiteness of 82.61%can be obtained under the optimal conditions.And short columnarα-hemihydrate gypsum with the length of 100μm and the whiteness of 85.72%can be prepared by dihydrate gypsum obtained under optimum conditions mentioned above.As for the large particle size of products obtained by FGD gypsum,this paper uses MBA-H₂O solution as the reaction medium to adopt two-step conversion method.Under the addition of MBA,the morphology of the product formed by the dissolution and recrystallization process of raw materials is controlled,the dosage and reaction of MBA are investigated.The effect of temperature and p H on the morphology of the intermediate product,and the angular prismatic hemihydrate gypsum was obtained.short columnarα-hemihydrate gypsum with the length of 3-5μm and length-diameter ratio of 1 can be obtained under the optimal conditions.