| The flotation process of galena is an electrochemical process. During this process, the existence of lattice defect has serious impact on its surface property, molecular absorption of flotation reagent and electrochemical behavior. Galena reveals different flotability due to impurities existed in natural galena, e.g. Ag, Zn etc. In this dissertation, the influence of lattice defect on surface property, molecular absorption of flotation reagent and electrochemical behavior of galena was studied by using the First-principle method based on density functional theory (DFT). The adsorption model of flotation reagents on galena with lattice defect was established. Six doped galena samples with Ag, Cu, Zn, Bi, Sb and Mn, respectively, were synthesized via. chemical precipitation. The flotation and depression of doping galena have been investigated. The adsorption thermodynamics and kinetics of butyl xanthate (BX) and dimethyl dithiocarbamate (DD) on doped galena were investigated microcalorimetrically. The dynamic model of adsorption of flotation reagent on doped galena has been established. The effects of impurity on electrochemical oxidation, collecting and depression of galena were studied by cyclic voltammetry. The electrochemical model for the effect of lattice defect on flotation of galena has been established. The main results are as follows:(1) The impact of lattice defect on surface property of galena (100)The semiconductor type of galena has been changed in the absence of S, which enhanced its surface electro-conductibility. However, the absence of Pb did not change its semiconductor type. In addition, the covalent bond for all the impurity atoms with surrounding S atoms is stronger than that for Pb on the surface of perfect galena. Compared with the surface of perfect galena, the surface of galena containing Ag, Zn and Cu impurities do not change its semiconductor type, and the state density distribution did not change obviously. However, both orbits of4d for Ag and3d for Cu from impurities of Ag and Cu pass through Fermi level and result in obsolete band gap, which enhanced the electro-conductibility and reaction activity of galena surface. The semiconductor type of galena changed with the addition of Bi, Sb and Mn impurities, and dramatic change for the state density distribution could be observed. New state density peak was found on the surface state of Fermi level, and then their reaction activity was heightened.(2) Impact of lattice defect on adsorption of O2molecule on galena (100) surfaceThe configuration of absorption of oxygen molecules on the galena surface is that the two O atoms are toward to two S atoms via. chemical absorption. Dioxygen molecule did not dissociate after absorption in the absence of S, while02molecules were dissociated after adsorption on surface of perfect galena, Pb absent and galena with six impurities. Except Mn. the absence and defect of galena with other five impurities enhanced the absorption of dioxygen molecule on galena surface.(3) Influence of lattice defects on the adsorption of collector molecules on galena (100) surfaceThe absorption configurations of xanthate, dithiocarbamat and dithiophosphate molecules on the surface of perfect galena are that two sulfur atoms bonded toward two lead atoms at the diagonal of hollow. Except dithiocarbamat which is not adsorbed on Pb vacancy, three other collectors can all be adsorbed on the surface of perfect galena and galena defected by six kinds of impurities via. chemical absorption. Compared with the surface of perfect galena, the S vacancy and defects with six kinds of impurities can promote the adsorption of xanthate on galena surface. Except Cu, the absence and defects with other kinds of impurities can promote the adsorption of dithiophosphate molecules on galena surface. In addition, Pb vacancy and defects with six kinds of impurity can enhance adsorption of dithiocarbamat molecules on galena surface.(4) Influence of lattice defects on the adsorption of depressant molecules on galena (100) surfaceThe oxygen atom in OH group bonded with Pb atom on galena surface via. chemical adsorption. While CaOH groups were chemically absorbed on galena surface, Ca atoms were absorbed on the hollow and bonded with the surrounding S atoms. Both absences of Pb or S were helpful for adsorption of OH on galena surface. Pb absent was very helpful for the adsorption of CaOH while S absent has the reversed effect on the adsorption of CaOH on galena surface. The depression of galena by NaOH is weakened by Ag and Mn impurities, while the interaction is enhanced by Bi, Sb, Cu and Zn impurities. The adsorption of CaOH will not be affected by Zn impurity, but it will be enhanced by Ag, Bi, Sb, Cu and Mn impurities. Ag and Cu impurities can greatly enhance the adsorption of CaOH.HS was chemically adsorbed on galena surface, and the S atom in HS covalently bonded with Pb atom on the surface. Pb vacancy will weaken the depression of galena by Na2S, while S absent will enhance it. Impurity defects will enhance the depression of galena by Na2S. Sb, Bi and Mn impurities can greatly enhance the adsorption of Na2S.Chromate was adsorbed on the galena surface by chemisorption either. The oxidized surface is more conducive to the adsorption of chromate. The effect of Pb and S absent on adsorption of chromate on the galena surface is little. Silver, zinc and copper, these three impurities are not conducive to the adsorption of chromate on galena surface, while manganese, antimony and bismuth can promote the adsorption.(5) Impact of impurity on flotation behavior and thermal kinetic parameters of xanthate adsorbed by synthetic galena. Six kinds of galena with different impurities were synthesized respectively. The defects of impurities on flotability of galena were studied. The thermodynamic and kinetic parameters of BX adsorbed on galena with different impurities were measured. The results show that silver and bismuth impurities can promote the galena recovery rate significantly, while zinc, antimony, manganese and copper impurities reduce the flotation recovery of galena. Zinc impurity can reduce it dramatically.Micro thermokinetic results show that the relationship between adsorption microcalorimetry of xanthate and its flotation recovery is direct proportional on galena surface which contains impurities. The adsorption heat and reaction rate coefficients are high when xanthate was adsorbed on the galena surface which contains Ag or Bi impurity. So their flotation recoveries are high. While for galena which contains Cu or Sb, its heat adsorption and rate coefficients are relatively small, correspondent to lower flotation recoveries. The relationship between unsaturated adsorption heat of xanthate (ΔH) and adsorption energy of impurity atom on galena surface (ΔG) was demonstrated.(6) The influence of impurity on electrochemical behavior of galena flotation.Synthetic galena has good electrochemical activity. The reaction product of pure galena or impurity galena with xanthate was determined by infrared spectroscopy and cyclic voltammetry. The influence of impurity on electrochemical behavior of galena flotation is consistent with the flotation experiment and simulation results.From the cyclic voltammetry curves, the depression effect of calcium hydroxide on doping galena is stronger than that of sodium hydroxide. Silver and bismuth impurities promote the electrochemical reaction of xanthate significantly, while zinc, manganese, antimony and copper impurities inhibite the electrochemical reaction of xanthate. In lime medium Ag-doping promotes the oxidation and decomposition of xanthate on the galena surface; thereby the flotability of galena is reduced. While Zn-doping and Sb-doping impede the electrochemical reaction of xanthate with galena, thereby reduced the amount of xanthate adsorbed.The depression effect of sodium sulfide on galena is electrochemical suppression and competitive adsorption, where the electrochemical factors play a major role. The electrochemical adsorption with doping galena and xanthate has been suppressed. The electrochemical reaction, which produces metal salts by the action of xanthate on the galena containing antimony, copper and silver, is greatly impacted. The galena containing manganese and zinc is less affected. |
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