Study On The Ionic Hydration Of Ca²⁺, Mg²⁺, Cl^-

The ionic hydration of single ion (Ca²⁺, Mg²⁺, Cl^-) was investigated by moleculardynamics simulations. The effect of temperature and concentration of ions to the ionichydration of ions in CaCl₂ solution and MgCl₂ solution was studied. The experiment of X-raydiffraction to investigate the hydrated structure of solution was also carried out. These workscan provide some theoretical basis for the development and utilization of seawater chemicalresources.Molecular dynamics simulation of ionic hydration of single ion (Ca²⁺, Mg²⁺, Cl^- ) inaqueous solution with a density of 1.0g/cm3 was performed at 298K. The microscopicdistribution of water molecules around the ions was obtained. The result shows that the watermolecules approach the cation with oxygen atoms while they approach the anion with hydrogenatoms. The pair correlation functions, coordinate number curves, hydration number andhydrated radious of three ions were calculated. It shows that the hydration number and hydratedradious of Ca²⁺ is both larger than that of Mg²⁺, which means that the hydratability of Ca²⁺ isstronger than that of Mg²⁺. The self-diffusion coefficients of ions got in this work are in betteragreement with the experimental value.Molecular dynamics simulation of CaCl₂ solution and MgCl₂ solution was performed at298K, 323K and 373K. The result shows that the concentration can influence the short rangehydrated configuration of Ca²⁺ and Cl^-. With the increase of temperature, the coordinate numberof Ca²⁺ is increased, but the coordinate number of Cl^- is decreased in CaCl₂ solution. There isno influence of the temperature to the coordinate number of Mg²⁺. The self-diffusioncoefficients of Ca²⁺,Mg²⁺,Cl^- increase with the raise of the temperature. This may caused by the more active movement at high temperature.A series of constant-temperature (298K) molecular dynamics simulation of CaCl2 solutionwith different concentration, ranging from 0.901mol/L to 5.406 mol/L, was carried out toinvestigate the structure and dynamical properties of ionic hydration. It is found that thecoordinate numbers of Ca²⁺, Cl^- are both decreased with the increasing ion concentration. Anincrease of ion concentration led to an enhancement of the microscopic reverse oscillations ofthe ions, so the self-diffusion coefficients of Ca²⁺ and Cl^- both decrease.The electrolyte solution structure was explored by PXRD. Mylar film with the thickness of0.00625mm was chosen as window material. Also the X-ray diffraction pattern of the solutionwas got.