| The solid-liquid interface is the main place where reagent molecule reacts with the mineral during flotation,and the nature of sulfide mineral flotation behaviors are determined by the properties of this interface.Using quantum chemistry method base on density functional theory(DFT),in this thesis,the surface structures and electronic properties of sulfide minerals and adsorption behaviors of reagent molecules on the mineral surface under solid-liquid interface system are studied.The influence of water molecule adsorption on surface structures and properties of sulfide minerals are focused.The influence of adsorption configuration and arrangement of water molecules on the mineral surface wettability are studied and the hydrophilic/hydrophobic models for sulfide mineral surface are simulated.The surface oxidation model of sulfide minerals and interaction model of sulfide minerals with flotation reagent molecules under solid-liquid interface system are calculated through studying the effects of water molecules for surface oxidation and on the adsorption behavior of flotation reagents on mineral surface.The main results are as follows:(1)The surface configuration and atomic relaxation of sulfide mineralThe models of FeS2(100),ZnS(110),PbS(100),MoS2(001),Sb2S3(010)and Cu2S(110)surface contains nine,eight,ten,eight,four,four,seven atomic layers,respectively,and each model of the clean surface is 15 A in vacuum.After optimizing calculation,the relaxation partly occurs on these sulfide mineral surfaces,but no reconstruction is observed;meanwhile,dangling bonds and uncoordinated chemical bonds is forming on the mineral surface.(2)Influences of surface atomic relaxation and electronic structure and property for water molecules adsorption on sulfide mineral surfacesThe structure of sulfide minerals surfaces have been changed in presence of H2O molecule.The certain relaxation is observed on sulfide mineral surfaces after adsorbing water molecule.The DOS of FeS2,PbS and Cu2S surfaces activates evidently after adsorbing H2O.Especially,the the Fe 3d states occupy in the Fermi level(EF).But while that of MoS2 and Sb2S3 surfaces change little.Little electron transfers appear between hydrophobic minerals surfaces(such as MoS2 and Sb2S3)and water molecule,and the Mulliken atomic charges change slightly.However,the the Mulliken atomic charges hasa great change on the hydrophilic mineral surface,such as ZnS and FeS2,due to the electron transfers,leading to losing of balance and redistribution of electrons on the minerals surfaces.The covalency of surface atoms is enhanced after the adsorption of water molecules on the hydrophobic mineral surface,and the atomic bonds of sulfide minerals surfaces are not easy to break.Moreover,the ionicity of surface atoms is enhanced on the hydrophilic mineral surface.The adsorption of the flotation reagent at the interface of mineral-water would be different with that of mineral surface due to the changes of surface structures and electronic properties caused by H2O molecule.(3)Influences of hydrophily and hydrophobicity of sulfide surfaces for water molecules adsorption on sulfide mineral surfaces and thermokinetic analysisH2O molecule prefers to stay with pyrite and sphalerite surfaces rather than water,whereas for galena,chalcocite,stibnite,and molybdenite,H2O molecule prefers to stay with water rather than the mineral surfaces.On the other hand,pyrite surface favors N2 more than water,while sphalerite surface cannot adsorb N2.These results show that galena,stibnite,chalcocite,and molybdenite are hydrophobic,while sphalerite is hydrophilic.Although pyrite has certain hydrophilicity,it tends to be aerophilic because the reaction of pyrite with H2O is weaker than pyrite with N2.Thus,pyrite,galena,chalcocite,stibnite and molybdenite all have natural floatability.The H2O adsorptions on sulfides surfaces were simulated using DFT method.The results show that galena and molybdenite are natural hydrophobic,while pyrite and sphalerite are hydrophilic.The measured adsorption heats are in good agreement with the calculation results.The interaction between water molecules and pyrite surface is the strongest,and then sphalerite,galena,and molybdenite in order.The reaction rates of hydrophobic galena and molybdenite surface are close,while those of hydrophilic sphalerite and pyrite surface are significantly different.The reaction rate of sphalerite is much larger than that of pyrite.(4)Influences of multilayer water adsorption on the hydrophobic and hydrophilic sulfide mineral surfacesOn the hydrophobic galena surface water adsorption is mainly via the strong hydrogen bonds between water H atoms and the surface S atoms,while on the hydrophilic pyrite surface,the adsorption of water is mainly via the interaction between the surface Fe atom and O atom.For the hydrophobic galena surface,the two-dimensional hydrogen bonding of monolayer water strengthens the S...H bonding;however,three-dimensional hydrogen bonding is stronger than S...H bonding and consequently weakens the interaction of water and the galena surface.However,for the hydrophilic FeS2 surface,the hydrogen bonding among additional water molecules including two-dimensional and three-dimensional structure promotes the activity of the O 2p orbital and consequently enhances the interaction of the O 2p and Fe 3d eg orbital.(5)Adsorption of oxygen and water on the FeS2(100)and PbS(100)surface and mechanisms of galena and pyrite oxidationIt has been confirmed by the isotope testing that oxygen sulphate derived largely from water molecule but not oxygen molecule.The multimolecular interaction involving water and oxygen molecules on the pyrite and galena surfaces is simulated,and the coadsorption model of water and oxygen molecules had been proposed.The results indicates that the dissociation of oxygen molecule plays a decisive role in the interaction involving sulfide mineral surface,water and oxygen molecules.The dissociation of oxygen could attract H atom from the water molecule and consequently leading the formation of stable adsorption products including metal-hydroxyl and sulphate.(6)Influence of water molecules for collector molecules adsorption on sulfide mineral surfacesThe presence of water molecule has an obvious effect on the electron distribution,covalent bonding,Fukui indices and reactivity of surface atoms and consequently influences the interaction between the collector and mineral surface.Water adsorption reduces the reactivity of Zn atom with respect to the interaction with thiol collectors,but has little influence on PbS(100)surface.In the presence of water molecule,the interaction order of three thiol collectors on ZnS(110)surface and PbS(100)surface agrees well with the flotation practice.The adsorption of ethyl xanthate on the ZnS surface is dependent upon surface states,such as adsorption of waters and copper substitution on the surface.Copper substitution of ZnS surface decreases the band gap of the surface and favors the adsorption of xanthate.The adsorption of water molecules dramatically change the properties of ZnS surface,resulting in the localization of Zn 3d 4s and 4p orbitals,which decreases the reactivity of surface Zn atoms with xanthate.The presence of waters has little influence on the properties of Cu-substituted ZnS surface,and the DOS of surface Cu atom varies little after water adsorption.In the absence of waters,two surface Cu atoms interacting with two EX S atoms,while after the adsorption of water,one of EX S atoms interacted with surface S atom,which would result in the formation of dixanthogen. |
PDF Full Text Request