Research On Synthesis Of Barium Sulfate By Ion-exchange Approach And Its Reaction Mechanism

As an important chemical raw material,barium sulfate is used in many industries.With the development of the application field of barium sulfate,the new requirements for the quality of barium sulfate have been proposed,especially research on the new varieties of ultra-fine barium sulfate with high purity and controllable morphology has attracted wide attention.At present,precipitated barium sulfate is synthesized by direct precipitation in China,but the crystal growth rate cannot be controlled duo to the faster reaction rate and is difficult to control the morphology of barium sulfate crystals.As a novel synthesis method,the principle of the ion-exchange method is to use the difference in the solubility product between the reactants and the product to achieve ion-exchange and precipitation transformation in the solid-liquid system.The essence of that is the displacement reaction,which makes it easier to control the reaction rate.Based on that,the ion-exchange method for generation barium sulfate with various shapes by using barium carbonate and potassium sulfate as raw materials was proposed.In addition,the changes of crystal structure and morphology of barium sulfate with reation conditions were investigated,the synthesis mechanism of barium sulfate crystal was analyzed by using materials studio software,which provide theoretical support for the following study of synthetic barium sulfate crystal controllability.In this paper,the effects of reaction conditions on the yield of barium sulfate was investigated by using barium carbonate and potassium sulfate as raw materials.The results show that the best yield of barium sulfate is about 98.25%and the shape is hexagonal prism with good crystallinity under the optimal process conditions.Moreover,the reaction process belongs to the liquid-solid phase non-catalytic exothermic reaction,and the nucleation stage belongs to external diffusion,the kinetic parameters have been calculated:kinetic equation?y=509.7X-5.82682?and activation energy?-4.238k J/mol?of this reations;The grain growth stage belongs to internal diffusion,and the kinetic parameters have been calculated:kinetic equation?y=597.3X-6.44104?and activation energy?-4.966k J/mol?of this reations.Secondly,mechanisms of NH₄⁺,Na⁺and K⁺ions in the crystallization process of barium sulfate were investigated.It turns out that compared with Na⁺and NH₄⁺,K⁺can promote the formation of barium sulfate under the same conditions.NH₄⁺,Na⁺and K⁺ions can replace Ba²⁺of the lattice,and form impurity-defect.The cell volume was changed due to the difference in ion radius.The morphology of barium sulfate changes with the type and concentration of sulfate,The morphology of barium sulfate is irregular shape in ammonium ions solution;The morphology of barium sulfate changes form cuboid to sheet shape with increase of Sodium ions concentration;The morphology of barium sulfate changes form cuboid to hexagonal prism with increase of Potassium ions concentration.The effect of CTAB and DTAB on reaction system crystal structure and morphology were disscussed.The results show that cationic surface active agent cannot promote or inhibit the reaction.However,the morphology of barium sulfate changed with surfactant type,surfactant concentration and reaction temperature.The morphology of barium sulfate changes form hexagonal prism to cuboid with increase of CTAB concentration,the morphology of barium sulfate changes form sheet shape to cuboid with increase of temperature in CTAB.The morphology of barium sulfate changes forms irregular shape to cuboid with increase of DTAB concentration,the morphology of barium sulfate changes form sheet shape to hexagonal prism with increase of temperature in DTAB.At last,the equilibrium growth morphology of barium sulfate have been simulated by using BDFH model and AE model of Materials Studio software.Interaction between surfactant and barium sulfate have been simulated through Forcite module of Materials Studio software.The results show that the morphology of the barium sulfate was hexagonal bipyramid by simulation of two models.The crystal faces?110???1^—10???^—1^—10???^—110???0^—20?and?020?constitute the six cylinders of barium sulfate,the family of crystal planes{111},{101}and{021}constitute the cones of barium sulfate.Compared with CTAB,Interaction between DTAB and barium sulfate was strong,DTAB is easy to stick to the crystal.With the increase of temperature,interaction between surfactant and barium sulfate was weak,surfactant is not easy to stick to the crystal,this can result in changing the morphology of barium sulfate.