Study On The Process Of Preparing Calcium Sulfate Whiskers By Sodium Sulfate

Industrial waste salt is extremely harmful to the environment,and the development of reasonable treatment and recycling processes has certain economic value and environmental benefits.Based on the resource recycling of industrial waste salt containing sodium sulfate,this paper discusses the precursor of synthesizing calcium sulfate dihydrate using sodium sulfate and calcium chloride as raw materials,and further uses hydrothermal method to prepare calcium sulfate hemihydrate whiskers,so as to explore a new way to solve the dilemma of treatment of waste salt containing sodium sulfate and prepare calcium sulfate hemihydrate whiskers,which provides a theoretical basis for industrial application.(1)Using sodium sulfate and calcium chloride as raw materials,the precursor of calcium sulfate dihydrate was synthesized by high-speed dispersion homogenizer,and the relationship between the process conditions and the particle size and morphology of calcium sulfate dihydrate was explored.Analysed by experimental and characterization tests,the preparation conditions of adding at the same time,reaction temperature of 90℃,raw material ratio of 1 : 1,raw material concentration of 1mol/L,reaction time of30 min and aging time of 3h can promote the formation of calcium sulfate dihydrate precursors,so calcium sulfate dihydrate with uniform particle size and uniform morphology can be prepared.(2)On the basis of the previously obtained better process conditions,the influence of the speed and cycle ratio of the rotor-stator reactor on the preparation of calcium sulfate dihydrate was explored.Analysed by experimental and characterization tests,calcium sulfate dihydrate with small particle size,regular morphology and high crystallinity can be prepared under the conditions of speed of 1100 rpm and cycle ratio of 60,which prepared for the subsequent preparation of calcium sulfate hemihydrate whiskers by hydrothermal method.(3)By comparing the differences in the preparation of calcium sulfate dihydrate by different reaction equipment,it is concluded that the particle size of calcium sulfate dihydrate gradually decreases and the dispersion increases with the improvement of stirring strength.And calcium sulfate dihydrate precursors with regular morphology,uniformity,smaller particle size and better crystallinity can be prepared by using the rotor-stator reactor.This is because rotor-stator reactor are able to enhance the liquid-liquid reaction process in a short time,which has the significant advantage of improving mass transfer efficiency and promoting microscopic mixing.(4)The prepared calcium sulfate dihydrate precursors was used as raw material to prepare calcium sulfate hemihydrate whiskers by hydrothermal method.Through the design of univariate experiments and orthogonal experiments,the effects of reaction temperature,reaction time,solid content and initial p H,as well as the types of additives on whisker morphology during hydrothermal reaction were explored.The hydrothermal reaction temperature of 150°C,reaction time of 4h,solid content of 5% and initial p H=3 were determined as the optimal process conditions,the average aspect ratio of the prepared calcium sulfate hemihydrate whiskers can reach 50～60,and anhydrous calcium sulfate whiskers with good stability were prepared using a roasting process.