Effect Mechanism Of Anions In Copper Salt On Dissolution Behavior Of Desulfurized Gypsum And Whisker Crystallization

Flue gas desulfurization gypsum（FGD gypsum）,an industrial by-product gypsum produced by flue gas wet desulfurization,has huge emissions.If not treated in time,it will not only occupy a lot of land but also pollute the environment seriously.The preparation of calcium sulfate whiskers has been paid more attention using FGD gypsum as raw materials and using additives to improve the crystallization of whiskers.Presently,the research on inorganic salt additives mainly was focuses on the effects of cations on whisker crystallization and its mechanism of interaction.However,it is less studied of the effects of anions on the crystallization of whiskers,and its interaction mechanism is unclear.Therefore,to study the effect of anions on the crystallization of whiskers and to explore their mechanism of interaction are helpful of improving the theoretical system of the crystallization of inorganic salts on FGD gypsum whiskers.It can also achieve high value utilization of FGD gypsum,which is beneficial to the environment protection.In this thesis,FGD gypsum whiskers were prepared by hydrothermal method using FGD gypsum as raw material,and sulfuric acid,copper chloride,copper sulfate,copper nitrate as additive.By the determination of the solubility and conductivity of FGD gypsum in different solution systems,and the systematic characterization and analysis of the chemical composition,microstructure and surface characteristics of whisker samples prepared under different conditions,the influence of anions on the dissolution behavior of FGD gypsum,the rule of solution composition change,whisker microstructure and surface properties in the presence of copper ions were discussed,and the mechanism of anion whiskers was revealed in the process of the hydrothermal preparation of FGD gypsum.The main results are as follows.The effect of anions in copper salts on solubility of FGD gypsum is great.Cl^-promotes the dissolution of FGD gypsum,and the ionic polarization plays a leading role,increasing the Ca²⁺concentration in the solution by 9%.NO₃^-promotes the dissolution of FGD gypsum to a greater extent,and the salt effect plays a leading role,increasing the Ca²⁺concentration in the solution by 11.40%.And the SO₄^2-hinderes the dissolution of FGD gypsum,the same ion effect playes a leading role,reducing the Ca²⁺concentration in the solution by 21.03%.Copper salts have an important effect on the whisker crystallization.The anion can affect the aggregation rate of Ca²⁺and SO₄^2-by the solubility of FGD gypsum,thereby affecting the crystallization of whiskers.When the concentration of sulfuric acid is5.0×10^-4 mol·L^-1,the concentration of copper chloride,copper sulfate and copper nitrate are 3.75×10^-3 mol·L^-1,2.50×10^-3 mol·L^-1,3.75×10^-3 mol·L^-1 respectively,the granular and short columnar morphologies in hydrothermal products are less,while the fibrous morphology is main,and its characteristic diffraction peaks are relatively stronger.When copper chloride is used as an additive,FGD whiskers are well grown,with a larger length,a more uniform diameter,and better quality.The adsorption degree and the interaction form of Cu²⁺on the whisker surface are different under the synergistic effect of different anions.The degree of adsorption is the weakest at the present of Cl^-,followed by SO₄^2-,and that is the largest when NO₃^-exists.Moreover,at the presence of NO₃^-,Cu²⁺may even partially enter the whisker lattice,which deteriorates the quality of FGD gypsum whiskers to a certain extent.