Research On Adsorption Mechanism Of Water Molecules And Hydrated Cations On The Fine Quartz Particle Surface

Mineral surface hydration is an important reason for the difficult treatment of mineral processing wastewater,especially in the high muddy slime water treatment,which contains a large amount of fine quartz and clay mineral particles.These hydrophilicity particles have strong electronegativity,and easily form a hydration layer to affect the aggregation and dispersion of the particles,thus bringing great difficulty to the high muddy coal slurry water treatment.In the coal slurry water,metal ions form hydration ions with neighboring water molecules and interact with the mineral particles,thus affectting the surface hydration characteristics.However,the microscopic mechanism of the formation of hydrated cations and its adsorption mechanism on the quartz surface are not clear.To deeply understand the hydration characteristics of particle surface and its influencing factors.In this study,the fine quartz particles and the common metal ions(Na+,K+,Mg2+ and Ca2+)in the coal slurry are studied.The experimental analysis and density functional simulation/molecular dynamics simulation were used to study the interface properties and hydration of quartz particles,the formation mechanism of hydrated cations,and the adsorption mechanism of water molecules/hydrated ions on the quartz surface,and the hydration characteristics of the fine quartz particle surface were experimentally studied following the viscosity method was modified.The main conclusions of this study are as follows:Fine quartz particles are negatively charged in aqueous solution.Na+,K+ and Ca2+could not reverse the zeta potential of the quartz surface.However,Mg2+ and its hydrolyzed components are adsorbed onto the quartz surface by electrostatic adsorption,hydroxyl complex adsorption and hydroxide precipitation adsorption,resulting in three charge reversal points CRi(pH=3.01),CR2(pH=9.35)and CR3(pH=10.85)on the zeta potential of the quartz surface,wherein the Mg(OH)2(s)plays a major role.Density functional theory(DFT)studies of ion hydration show that the hydration numbers of Na+,K+,Mg2+ and Ca2+ are varied in the range of 4～6,5～7,4～6 and 6～8,respectively;Molecular Dynamics(MD)studies results are consistented with the DFT study,and the hydration numbers of Na+,K+,Mg2+ and Ca2+ in aqueous solution.are 5.6,6.7,6.0,and 7.8,respectively.At the same concentration,the self-diffusion coefficient of water molecules in the salt solution is in the order of K+>Na+>Ca2+>Mg2+.The ion hydration layer overlaps with the increase of ion concentration,which hinders the movement and diffusion of ions and water molecules.Hydrated ions primarily affect the structure and kinetics of the first hydration shell.Water molecule adsorption on the α-quartz(001)surface through two hydrogen bonds(Hs-Ow and Os-Hw).The optimal adsorption configuration is bridge adsorption(B6)5 and the adsorption energy is-0.752 eV.Metal ions adsorption on the α-quartz(001)surface through electrostatic interaction,and interact with water molecules,thus affecting the hydration characteristics of quartz surface.In the presence of Na+,Mg2+ and Ca2+,the adsorption energy is-1.688 eV,-1.661 eV,-1.961 eV and-1.779 eV,respectively.And ions promote the adsorption of water molecules on the quartz surface in the order of Mg2+>Ca2+>Na+>K+.Na(H2O)5+,K(H2O)6+,Mg(H2O)62+ and Ca(H2O)82+ adsorption on the α-quartz(001)surface by the hydrogen bonding and electrostatic attraction,wherein the electrostatic attraction dominates.And the adsorption energies are-1.779 eV,-1.765 eV,-4.225 eV and-2.219 eV,respectively.The stability of the four hydrated ions adsorption on the α-quartz(001)surface is Mg(H2O)62+>Ca(H2O)82+>Na(H2O)5+>K(H2O)6+.The hydration layer on the fine quartz surface is composed of three layers of water molecules with a thickness of 8-10A,and the density of water molecules in the hydration layer gradually decreases from the quartz particle interface.In the presence of ions,the interaction energy change from-1.071 eV in water to-1.821 eV(Na+),-1.748 eV(K+),and-1.896 eV(Ca2+),respectively.The order of enhancement of the interaction between water molecules and surface by ions is Ca2+>Na+>K+,which is consistent with the hydration ability of metal ions.And the self-diffusion coefficient of water molecules confirms that.Namely,when K+ is present,the self-diffusion coefficient of water molecules is greater than that in Na+and Ca2+ salt solution.Fine quartz particles have strong hydration on the surface in the alkaline environment.Metal ions form hydrated cations owing to the dipole action,which enhances the structure of the water molecules and enhances the surface hydration parameters of the particles.Ions enhance the hydration parameters of fine quartz particles in the order of Mg2+>Ca2+>Na+>K+.The hydration experimental results of effects of ion on the hydration parameters of particle surface are consistent with the theoretical calculation results about the ions enhance the adsorption of water molecules on quartz,which verifies the correctness of theoretical calculations.The paper reveals the properties of the fine quartz particle surface in coal slurry water,and explains the adsorption mechanism of quartz particles with water molecules and hydrated cations.The hydration mechanism of cation and quartz surface have been explained by molecular dynamics simulation from the atomic level.This study can provide theoretical support for the selection or design of agents,as well as cracking or weakening hydrated layer and efficient treatment of mines and mineral processing wastewater.Figure[66] table[36] References[214]...