Experimental Study On Preparation Of Building Gypsum With Carbide Slag-Waste Acid Neutralization Gypsum

Industrial by-product gypsum accumulation is large, it is necessary to study and reuse it due to the large occupation of land and environmental pollution. Carbide slag-waste acid neutralization gypsum is industrial waste residue produced by carbide slag and waste acid. To study its comprehensive utilization has important significance. According to study researches of related utilization of carbide slag-waste acid neutralization gypsum, after fully studying the properties and characteristics of carbide slag-waste acid neutralization gypsum, we made the calcination conditions and modification tests of carbide slag-waste acid neutralization gypsum and explored the effects of various neutralization process factors on the development of gypsum crystal.Carbide slag-waste acid neutralization gypsum is pale yellow, the content attached water is about 32%, pH is 7.82. It contains oxygen, sulfur, calcium, natrium, ferrum and other elements. Size distribution of particles is between 1μm to 10μm. Its main phase is dihydrate calcium sulphate. Crystals are nubby, granular and poor. The main dehydration process is between 130℃ to 280℃.The content of dihydrate gypsum is about 85%.The results of orthogonal test shows that the biggest influence is the calcination temperature, the second is calcination time and the aging time during the preparation of building gypsum. The best calcination condition is 170℃, the calcination time is 2h, the aging time is 3d. The standard consistency water consumption is 1.4, the initial setting time is 4.0min,the final setting time is 13.0min, the flexural strength is 0.91 MPa and the compressive strength is 2.24 MPa under the best calcination condition.The water reducing effect of naphthalene water reducer FDN is better than melamine water reducer SM, organic acid retarding effect of citric acid is better than protein retarder SG-10 at standard consistency water consumption. Too high admixture is bad to strength and has on effect. Both water reducer FDN and water reducer SM have retarding effect. Water reducer SM has little effect on the strength of building gypsum.The flexural strength of building gypsum is 1.59 MPa, the compressive strength is2.24 MPa at 0.85 water-solid ratio. When the dosage of water reducer FDN is 0.4%, the flexural strength of building gypsum is 1.62 MPa and the compressive strength is 5.15 MPa.The compressive strength increased by 15.47% than no admixture. When the dosage of citric acid is 0.2%, the initial setting time is 5min,final setting time is 9.5min, the strength is the best, the flexural strength is 1.61 MPa, and the compressive strength is 4.73 MPa, which can reach the national standards. Under best condition that citric acid dosage is 0.2%, water reducer FDN dosage is 0.4%, the flexural strength of building gypsum is 1.62 MPa, the compressive strength is 5.30 MPa, the setting time is 5.5min, final setting time is 10.5min and all indicators are higher than national standards.Temperature and stirring speed have effect on crystal growth, the concentration of lime-milk have no effect on the growth of crystal growth. How to promote the growth of gypsum crystal by adjusting the neutralization process factors need to be further studied.