Research Of Removal And Capture Mechanism Of Clay Particles By Calcium Sulfate Dihydrate

The sedimentation of tiny slime particles, especially clay particles (mainly kaolin and montmorillonite), is one of the major problems in the field of industrial separation. In the treatment process of slime containing wastewater, such as low grade brine, slime water generated from coal industrial, coal water produced from mineral separation, the efficiency of desliming (especially the sedimentation of clay) is the key factor that affecting the field of recycling and standardized emission of wastewater and the quality of production. Occasionally, it is found that the co-sedimentation phenomenon can occur between the calcium sulfate dihydrate generated from brine and the suspending clay particles. Therefore, in order to guide the desliming optimization process, the mechanism of co-sedimentation between calcium sulfate dihydrate and clay is studied and attempted to uncover the reasons of calcium sulfate dihydrate particles selectively capturing clay in brine and implement application in desliming optimization.The interaction between Ca2+ and clay particle, the characteristics of crystal growth of calcium sulfate dihydrate and their process of capturing clay particles are investigated to explore the mechanism of co-sedimentation between calcium sulfate dihydrate and clay. The structure representing the particles surface is constructed on the basis of surface properties and charged situation of clay particles. The tendency of co-sedimentation between calcium sulfate dihydrate and clay is studied using molecular dynamics simulation which determines simulation algorithm based on spherical water. The change rule of coulomb force, van der waals force, particle diffusion and the corresponding free energy are investigated using the mentioned algorithm and DVLO calculating method to evaluate the co-sedimentation tendency between different particles.According to the analysis and assumption based on experiments and simulation, the coagulation or co-sedimentation mechanism between calcium sulfate dihydrate and clay can be concluded as follows. In the sedimentation process of clay, besides the condensing double layer electric causing by Ca2+, calcium sulfate and other hydrated salts can decrease the dispersity. The value of charge/mass is one of the indexes evaluating the co-sedimentation process with regard to ions and insoluble particles owing the ability of nucleation crystallization. In general, particles with high value of charge/mass are more easily to proceed adsorption and sedimentation. Compared with potential energy such as van der waals interaction energy, the electrostatic interaction is considered to be a key factor determining the co-sedimentation between insoluble substances and calcium sulfate salts. Among the tendency of the co-sedimentation from the view point of data of particles potential energy, clay occupies a high coagulation tendency. In accordance with binding energy, charge-neutralization and ion-exchange may also result in co-sedimentation between calcium sulfate dihydrate and clay, among which Al-OH groups are more sensitive and active in capturing Ca2+ in comparison with Si-O groups. Moreover, the growth of calcium sulfate and their particles capturing other particles are believed to promote the sedimentation process of clay. The Ca2+ naked at the surface of calcium salts and dissociate in the liquid phase is assumed to coax the attachment of slime particles on calcium salt crystals.The co-sedimentation process of calcium salts and slime belongs to brine is optimized on the basis of the mentioned investigation. Considerable desliming efficiency can be obtained using both natural sedimentation and air-sparged hydrocyclone method. However, the calcium sulfate dihydrate can hardly enchance the separation effect when using air-sparged hydrocyclone method. It is recommended to take the quantity of water, cost, energy consumption and operation conditions into account when choosing treatment method of dealing practical problems.In a word, a molecular dynamics simulation algorithm of solid-liquid facing particle co-sedimentation is constructed which may provide reference to the mechanism investigation of sedimentation & separation process to some degree. Moreover, the synchronous removal of calcium sulfate dihydrate and clay is developed and optimized in application which may promote efficiency of the treatment of slime loaded water.