The Comprehensive Performance Improvement And Mechanism Research Of Flue Gas Desulfurized Gypsum

The low mechanical strength and poor water resistance of flue gas desulfurized（FGD）gypsum limit its application and further development in the field of building materials.Using various functional components to improve the performance of FGD gypsum is an important way,but the modification methods are single.Therefore,relying on the"Research on the Mechanism and Technology of Gypsum Board’s Nail Holding Performance Improvement",in view of the root cause of the poor performance of FGD gypsum products,this paper studies the relationship between the performance of FGD gypsum and the contact points between crystals,and the effects of various waterproof agent containing special functional groups on the water resistance of FGD gypsum were discussed.In addition,the effects of crystal modifier on the crystal morphology of FGD gypsum were also studied,and the relationship between the microscopic crystal morphology and the properties of FGD gypsum products was analyzed.The innovative results are as follows:（1）Aiming at the poor mechanical properties of FGD gypsum,the effects of different types of the crystal contact points on the properties of FGD gypsum were studied by introducing anhydrous calcium sulfate whiskers（ACSW）,calcium carbonate whiskers（CW）and sulfoaluminate cement（SAC）.It was found that both the externally introduced whiskers and the internally generated ettringite crystals can increase the contact points,disperse the stress,fill the pores,and improve the mechanical properties and water resistance of the FGD gypsum.In addition,the gel generated by SAC coated the surface of calcium sulfate dihydrate（Ca SO₄·2H₂O）crystals,reducing the dissolution of crystals and bridging the matrix.The two introduction methods have a synergistic effect.（2）The effect of organic waterproofing agents containing different functional groups on the properties of the FGD gypsum was studied.It is found that the waterproofing agents can be selectively adsorbed in the early stage of slurry hydration,so that the Ca SO₄·2H₂O crystal can be transformed from needle-rod structure to columnar structure;in the later stage of slurry hydration,a film can be formed on the surface of Ca SO₄·2H₂O crystals to change the crystal surface energy,improve hydrophobicity,and improve mechanical properties.Compared with styrene-acrylic emulsion and silicone-acrylic emulsion,because fluorosilicone emulsion contains C-F bonds and Si-O bonds,it has the best modification effect on water resistance.When the dosage is 0.2%,the dry flexural strength is increased by 55%,the nail-pull resistance is increased to 420 N,the softening coefficient is increased from 0.51 to 0.78,and the water absorption rate is decreased from 35.7%to 24.8%.（3）The method of regulating the hydration of hemihydrate gypsum by using crystallizers as admixtures to control the crystal growth was studied,and the differences in the formation of FGD gypsum crystals by maleic acid,aluminum sulfate（Al₂（SO₄）₃）and magnesium sulfate（Mg SO₄）crystallizers were compared.The action mechanism of organic crystallizers is the selective adsorption of crystal surface,and the action mechanism of inorganic salts is the selective adsorption of metal cations and the promotion of hydration by SO₄^2-.Among them,Al₂（SO₄）₃ has the best modification effect on the FGD gypsum.