Theoretical Study On Complexing Dissolution,metastable Structures And The Nucleation Crystallization Mechanisms In Brine Solutions

The brine solution is the most common liquid on the earth,the seawater and the salt lake are natural and multicomponent brine solutions.In industry,many important primitive processes also take place in brine solutions.Based on the diversification of the salt solution composition,the electrostatic interaction between the ions and the complexity of the water structure,the microstructure of the brine solution system needs to be further researched.In this paper,quantum chemical calculations,molecular dynamics simulations,and spectral calculations were used to gain insight into complexing dissolution,metastable structures,and ion association characteristics before the nucleation in the brine solutions and dissolution nature of salt by water:?1?Cu?II?complexation by chloride is involved in the transport of copper in near-surface geologic environments,nevertheless,the existence of high-order Cu?II?chloro-complexes is still under controversy.The structure characteristics and stabilities of[CuCl_x]^2-x_aq?x=3,4,5?complexes have been investigated using density functional theory calculations and molecular dynamics simulations.[CuCl₃]^-and[CuCl₄]^2-species can both be tracked,while the[CuCls]^3-_aq complex can not be recorded in chloride-rich brines.Meanwhile,the complex[CuCl₄]^2-_aq is found more stable than[CuCl₃]^-_aq.The surrounding water molecules around[CuCl_x]^2-x_aq?x=3,4?enhance their stabilities in Cl^- brines,especially for[CuCl₄]^2-_aq.The hydration shell of[CuCl₄]^2-_aq is more intact in comparison to that of[CuCl₃]^2-_aq species.Compared with[CuCl₄]^2-_aq,the stability of[CuCl₃]^2-_aq may be more susceptible to the concentration of Cl^- and the temperature.?2?In chlorine-enriched and multicomponent brine solutions,as a supplementary charge,does the lithium ion affect the microstructures and electronic spectral characteristics of Cu?II?-Cl association?Density functional theory calculations of[CuCl₃^-Li⁺-nH₂O]and[CuCl₂-LiCl-nH₂O]?n=6,8,10?hydrated clusters show that the presence of Li⁺ has a negligible effect on the structure of Cu?II?-Cl complexation.Meanwhile,their time-dependent density functional theory calculations indicate that the presence of Li⁺ does not affect the characteristics of electronic absorption spectra of[CuCl₃]^-and[CuCl₂]⁰ species.And contact[CuCl₃]^- species are less stable than its solvent separated conformers,in which one Cl^- stays in the second coordination sphere of the centered Cu²⁺.Meanwhile,these solvent separated conformers have the absorption around 385 nm.Therefore,the characteristic peak around 385 nm,which was attributed to the[CuCl₃]^-complex in UV-Vis spectra experiments,could also be resulted from some solvent separated structures of the[CuCl₃]^- complex,or[CuCl₂]⁰ species which is surrounded by Cl^- in the solution with abundant Cl^-.?3?The microstructure of the growth units building the crystals is a fundamental issue in the crystallization processes from the brine solution.Before the formation of amorphous precursors,the characteristics of pre-nucleation clusters in aqueous CaSO₄ solutions are still unknown.Density functional theory calculations,many-body perturbation theory calculations and molecular dynamics simulations were used to systematically study the formation and characteristic of pre-nucleation clusters in aqueous CaSO₄ solutions.The dominant species in aqueous CaSO₄ solutions are monodentate ion-associated structures.Compared with charged ion clusters,ion pair or neutral clusters are apt to be present in CaSO₄ aqueous solutions.Neutral?CaSO₄?,clusters may be the growth units of the nucleation and even crystallization processes.?4?The hydration behavior around ion associated species in brine solutions plays an important role in related phase/polymorphism selections.While there are no related reports about the hydration characteristics of the nucleation clusters in the process of ion aggregation in the CaSO₄ aqueous solution.Density functional theory calculations show that the more bridged hydrogen bonds around the Ca^- OS(O in the SO₄^2-)bond,the more stable the associated species from Ca²⁺ and SO₄^2-.Upon ion clustering in aqueous CaSO₄ solutions during molecular dynamics simulations,the residence of some water molecules around Ca²⁺ in ion-associated species is weakened while the risidence of some bridging waters is enhanced due to dual interaction by Ca²⁺ and SO₄^2-.And these bridging waters may continue to exist during ion association and aggregation progress,and even still remain in crystals.Therefore,the phase/polymorphism selections can be implemented in CaSO₄ aqueous solutions by controlling the hydration around pre-nucleation clusters.?5?The solubilities and salting-out effects of magnesium sulfate and calcium sulfate provide significant guidance for chemical technologies,but why the solubilities of magnesium sulfate and calcium sulfate are different?From the micro perspective,a systematic study is conducted by density functional theory calculations,perturbation theory calculations,and molecular dynamics simulations.In MgSO_{4 aq}ueous solutions,Mg²⁺ ions and SO₄^2-ions tend to exist in the form of solvent shared model,or even free ions.In CaSO₄ aqueous solutions,Ca²⁺ and SO₄^2-tend to be directly associated,and the association trend between calcium and sulfate is found to be relatively strong.This may be the reason why magnesium sulfate can be easily soluble in water but calcium sulfate is only slightly soluble in water.Meanwhile,the association trend of Ca²⁺ and SO₄^2-in CaSO₄ aqueous solution coincides with the solubility trend of calcium sulfate dihydrate with the change of temperature.It also confirms the relationship between the association trend of Ca²⁺ and SO₄^2-in CaSO₄ aqueous solution and the solubility of calcium sulfate in aqueous solution.In summary,results of high-order transition metal chloride complexes,can provide some valuable points to improve the thermodynamic models for salt water systems.A series of research results of pre-nucleation clusters and their hydration characteristics in brine solutions can be helpful to understand the thermodynamic properties,supersaturation phenomena and nucleation crystallization mechanism in aqueous solution,and also be conducive to study the phase transformation or the selection of crystal morphologies in solution.Based on the microscopic point of view,a systematic study of the association and hydration in brine solutions were carried out,providing scientific basis for the development and utilization of seawater resources and salt lake resources.The application prospects are considerable.