Hydrothermal Growth Process And Kinetics Of Flue Gas Desulfurization Gypsum Whiskers

As a fibrous inorganic single crystal material,calcium sulfate whiskers are widely used in plastics,rubber,coatings,paints,papermaking,asphalt,friction materials,etc.due to its advantages of high strength,high modulus,high temperature resistance,easy surface treatment,strong affinity and organic compatibility.For recent years,with the strengthening of environmental protection and the continuous development of industrial solid waste resources,more attention was paid to the use of industrial by-product gypsum such as flue gas desulfurization?FGD?gypsum to prepare high-quality calcium sulfate whisker.The research on hydrothermal growth process and kinetics of FGD gypsum whisker is crucial to the preparation of high quality calcium sulfate whisker,which not only helps to understand and realize the control of the transformation from FGD gypsum to calcium sulfate whisker,but also realizes the resource recycling of FGD gypsum and reducing environmental pollution.In the current work,calcium sulfate whisker was prepared through hydrothermal method by using FGD gypsum as raw materials.To find out the crystallization mechanism during the hydrothermal crystal growth of FGD gypsum whisker,the influence of the transformation kinetics from FGD gypsum to calcium sulfate whisker and the effect of temperature,Cu Cl₂ and H₂SO₄ concentration on the transformation kinetics from FGD gypsum to HH whiskers were verified.In addition,this study combined BP?Back Propagation?neural network and genetic algorithm in artificial intelligence,using 24 sets of experimental data as the training set and 5 sets of experimental data as the test set,the quantitative relationship between the process parameters and the quality parameters of the hydrothermal preparation of FGD gypsum whisker was established by training the experimental data.The process parameters were optimized and determined using genetic algorithm and experimental verification,which aims to provide theoretical basis for the crystal morphology control of FGD gypsum whisker and provide technical support for industrial production.The main experimental and theoretical research results are as follows:?1?The hydrothermal preparation of calcium sulfate whisker by using FGD gypsum as a raw material under hydrothermal environment is a solution-mediated transformation process from DH?Dihydrate?to?-HH?Hemihydrate?,this process is governed by the dissolution crystallization mechanism,and the transformation rate was controlled by the whisker nucleation-growth step.The added of H₂SO₄ would effect the hydrothermal crystallization of calcium sulfate whisker by changing the influence the crystallization of calcium sulfate whisker through selective adsorption on different crystal faces of?-HH crystal.During the growth of FGD gypsum whisker,the average diameter of the whisker would gradually increase with the extension of the reaction time,and the average aspect ratio of the whiskers would first increase then decrease with the extension of reaction time,the increase of temperature,H₂SO₄and Cu Cl₂ concentration.?2?An autocatalytic kinetics model was established for the transformation kinetics from FGD gypsum to HH whiskers based on the change in mole fraction o f HH whiskers with varying time.And the autocatalytic kinetics simulation result well fitted the experimental data with k=1.377,b=-4.741,R²=0.990,which confirmed the reliability of the autocatalytic model for transformation kinetics from FGD gypsum to whisker.Changing the hydrothermal environment for whisker preparation could control the transformation from FGD gypsum to calcium sulfate whisker.The hydrothermal conditions have a vital effect on the transformation from FGD gypsum to calcium sulfate whisker,elevating temperature,increasing the H₂SO₄ concentration,reducing the Cu Cl₂ concentration would shorten the nucleation and growth time of?-HH crystals and create a larger driving force for DH to?-HH conversion,hence,accelerate the transformation from FGD gypsum to whisker.?3?The calculation results of BP neural network program show that the overall error between the predicted data and the experimental data is less than 8%,which better reflects the quantitative relationship between the whisker hydrothermal environmental parameters and the whisker quality parameters.The calculation results of GA program show that the average diameter of the whisker is 0.89?m and the average aspect ratio of the whisker 173.5 under the conditions of hydrothermal preparation at a reaction temperature of 122.6?,a reaction time of 57.4 min,a concentration of H₂SO₄ of 0.99 mmol/L,and a dosage of Cu Cl₂ of 1.4 wt.%.It has been experimentally verified that the average diameter error of whiskers is less than9%,and the average aspect ratio error of whiskers is less than 4%.