Development And Application Of Chemical Reaction Thermodynamics Model For Electrolyte Solution Of The Strong Hydration And Association Interactions

Strong hydration, association and competition between hydration and association in themultiple metal chlorides aqueous solution of CuH₂2–MH₂n–H2O （M=Li, Na, K, Mg, Ca） leadto complexity of solution structure and properties inlcuding component asctivities, solubility.Developed thermodynamic models up to now for electrolyte solution, such as the Pitzermodel, cannot describe or predict their thermodynamic properties, and cannot explain therelation of the solution structure and properties either.To overcome this difficult, based on the Stokes–Robinson stepwise hydration model, weintroduced ion–association interaction into the stepwise hydration model, develop a newthermodynamic model is called reaction model （RM）. The reaction model consists of thelong–range electrostatic interaction and short interaction of hydration and association. It is notonly simple in mathematical, high symmetrical, but also built on solid theoretical foundationand strictly abides Gibbs–Duhem regulation. There is a minimum value of free Gibbs energyof the electrolyte solution to reach a thermodynamic equilibrium. By this principle, reactionmodel obtains the various species concentration under chemical or phase equilibriumcondition by energy optimization, then further calculate series thermodynamic properties withthem. Because of the large number of variables, complicated, large scale computation and lowreliability of results, many difficults were encountered in direct parameter fitting. To solvethis problem, a framework design of the nested two–step optimization was adopt in this work.An algorithm named Partitioning Quantum–behaver Particle Swarm Optimization （PQPSO） isapplied in parameters evauation. The simulation tests show that the success rate and thereliability of the optimization results have improved significantly than primary method.As examples of application, we use the reaction model to calculate the thermodynamicproperties of six binary aqueous systems and15ternary aqueous systems of metal chloridesLiH₂, NaH₂, KH₂, MgH₂2,CaH₂2and CuH₂2. Calculations results show that the reaction modelcan accurately describe the thermodynamic properties of not only the binary system, but alsothe ternary system if adding small number of the ternary parameters. The reaction model canpredict the thermodynamic properties of the ternary system only with the correspondingbinary parameters, such as the predicted awvalue of LiH₂–CaH₂2–H2O and LiH₂–MgH₂2–H2Osystem, the corresponding calculated average deviations are0.0027and0.0029, the maximumdeviation are0.0065and0.0081, respectively. The predicted isotherm of LiH₂–CaH₂2–H2Oand LiH₂–MgH₂2–H2O system are highly consist with the experimental data. In particular, ourpredicted Cu-containing species concentration distribution curve of trace CuH₂2in LiH₂–H2Osystem is highly consistent with Brugger’s analytical results of UV spectra; at the same time, the predicted same result in the NaH₂–H2O system is very similar to thermodynamic modelcalculation results by Haung.By a large amount of computing, it is found that the reaction model can act as a bridge,which connects the microscopic structure and the thermodynamics properties. It helps usunderstand the mechanism how the microscopic structure characteristic of electrolytesolutions affect their thermodynamics properties.In some electrolyte aqueous solutions, hydration, association and the competition betweenhydration and association play important role to the thermodynamics properties. Theseinteraction not only seriously impact the binary water activities, determine the electrolytesolubility with the different structural characteristics in aqueous solution; but also cause astrong effect on water activities, solubility isotherms in the ternary system, as well as on thespecies concentration distribution curve. For example, the Cu–containing speciesconcentration distribution curve of the trace CuH₂2in MH₂n–H2O（M=Li, Na, K, Ca） systemsis affected by the coordination competition between anions and water molecules which is alsoa form of competition of hydration and association. Different H₂–donation ability of metalchloride MH₂nleads to that the competition coordination of the anions and H2O molecules toCu–H₂complex is also differences, so the concentration distribution curves of Cu–containingspecies of trace CuH₂2in MH₂n–H2O （M=Li Na, K, Ca） systems present variation regularly.When a salt–salt association species will generate in the ternary system due to the strongsalt–salt association, thermodynamic properties of the ternary system can not be directlypredicted simply with the binary parameters. One must evalue the parameters of salt–saltassociation species with fitting solubility isotherm data to better describe ternary solubilityisotherms.With the competition between hydration and association, it can also well explain why theformation of salt–salt association complex makes the solubility of solid phase larger than thepredicted results near the eutectic points. Either the competition coordination of the anion andthe H2O molecule, or the formation of salt–salt association species, the competition ofhydration and association will make iso awlines in the ternary system bending in differentdegrees.The reaction model developed in this work can well explain above described seriesphenomena caused by the impaction of hydration, association and the competition ofhydration and association, exhibits a powerful analytical ability.