Study On The Preparation Of Calcium Sulfate Whiskers And High Strength Gypsum By Waste Sulfuric Acid

With the rapid development of industry in recent years,China has become a country with huge sulfuric acid production capacity.But at the same time,China is also a country with a large output of waste sulfuric acid.More than 70 million tons of waste sulfuric acid needs to be discharged every year.The problem of waste sulfuric acid treatment needs to be solved urgently.In this paper,waste sulfuric acid was used as reactants to prepare calcium sulfate whiskers and high-strength gypsum.To study and determine the process conditions of calcium sulfate whiskers with good uniformity,large aspect ratio and high-strength gypsum with high compressive strength.It aims to develop a waste sulfuric acid treatment method that can not only protect the environment,but also realize resource utilization.Firstly,preparation of dihydrate calcium sulfate precursor was performed by using a high-speed dispersion homogenizer,The effects of the way of adding reaction solution,the concentration of calcium hydroxide,reaction time,reaction temperature,reaction p H and aging time on the uniformity and morphology of precursor were studied by one-factor experiments.By using SEM,XRD,TG-DSC comparative characterization analysis,the optimal precursor preparation conditions were obtained:adding together,the concentration of Ca（OH）₂was 1.63 mol/L,the concentration of H₂SO₄was 0.37 mol/L,the reaction temperature of 80°C,the reaction p H of 3,the reaction time for 25 min and aging for 2 h.Under these conditions,the long columnar homogeneous calcium sulfate dihydrate precursor can be prepared.Secondly,based on the better preparation conditions obtained by high-speed dispersion homogenizer,the superior conditions for calcium sulfate by rotor-stator reactor are discussed.The effects of equipment speed and circulation on the synthesis of calcium sulfate dihydrate precursors were mainly investigated.Through SEM and XRD comparative characterization analysis,the optimal equipment speed is 1500 rpm and the cycle volume is42.0 L/h.Comparing different reaction equipment preparation of dihydrate calcium sulfate precursor,found that using the rotor-stator reactor can get small and uniform precursor.Because the high-speed rotating rotor in the rotor-stator reactor can disperse and refine the fluid,so that the fluid is redistributed on the stator.Then through the cross-series connection of multi-layer stator and rotor,increase the degree of fluid turbulence and surface update speed,microscopic mixing degree become better.Finally,the precursor of calcium sulfate dihydrate prepared by the rotor-stator reactor was used as raw material to synthesize calcium sulfate whiskers and high-strength gypsum with economic value through hydrothermal reaction.Optimal conditions for calcium sulfate whiskers obtained by one-factor experiments:the hydrothermal reaction was carried out for 4 hours under 150°C,the solid addition of 5%,the reaction solution p H of3,and the Mg SO₄addition of 0.5%.Anhydrous calcium sulfate whiskers with mean aspect ratio of 60 are obtained by roasting.The hydrothermal reaction was carried out for 2 hours under 150°C,the solid addition of 50%,the reaction solution p H of 5 and the C₆H₅Na₃O₇addition of 0.06%.A anhydrous high-strength gypsum with a compressive strength of 36.01 MPa was obtained by roasting.