| To systematically study the interfacial behavior of mechanical ball-milling pyrite powder in liquid medium, this thesis utilized various characterization techniques to investigate the interfacial behavior of pyrite powder dispersed in organic acids and organic alcohols from disperisibility, wettability, surface tension and kinematic viscosity. The effects of sodium salt additives on the interfacial behavior of pyrite powder as well as the related theoretical calculations were demonstrated. Moreover, the density functional theory-plane wave pseudopotential method was employed to study the density of states of structure model and Fermi level before and after mechanical activation of FeS2crystal. The essential relations among density of states, Fermi level and mechanochemical lattice distortion were deduced. The main conclusions were summarized as follows.(1) For preparation of pyrite powder, adding sodium hexametaphosphate as grinding additive could obtain ultrafine powder with uniform size and small diameter. The XRD results indicated that adding sodium hexametaphosphate as grinding additive reduced the crystal size but increased the lattice distortion degree. The Zeta potential for obtained pyrite in ethanol was negative, indicating that the prepared pyrite was negatively charged. Under the same condition, the wettability of pyrite powder in organic acid-ethanol solutions followed the order: oleic acid> hexanoic acid> acetic acid> propionic acid> lactic acid> formic acid. Moreover, oleic acid-ethanol showed the best dispersibility to pyrite powder. The optimum technical condition for pyrite dispersed in oleic acid-ethanol was obtained by the UV-visible spectrometric measurement, namely pH≤2,2%volume percentage of added oleic acid, and ultrasonication time of30min.(2) The wettability of four alcohols to pyrite powder followed the order:methanol> ethanol> butyl alcohol> cyclohexanol. However, the surface tension of four alcohols followed the order:ethanol<methanol<butyl alcohol<cyclohexanol. The dispersibility followed the order: ethanol<methanol<butyl alcohol<cyclohexanol, indicating that the dispersibility of pyrite in alcohols was consistent with the surface tension order of alcohols. On the other hand, the weak dispersion stability of pyrite powder could be remarkably improved by adding polyethylene glycol (PEG) with different molecular weights. Among these, PEG-20000with8%addition amount showed the best dispersion stability of pyrite powder. The wettability experimental results also indicated that PEG-20000had the best wettability to pyrite powder. The optimum condition was pH at5-6and100-W ultrasonication power. The infrared adsorption spectrum analysis showed that the adsorption between the PEG and pyrite ore powder was via the hydrogen bonding and there was no new compound formed between them. The adsorption of PEG onto the surface of pyrite powder provided a high degree of steric stabilization, which effectively prohibited the aggregation of pyrite powder, and thus the dispersion stability of as-formed aqueous suspension was promoted.(3) According to the dispersion stability of pyrite in five sodium salt additives namely sodium hexametaphosphate, sodium oleate, sodium silicate, sodium polyphosphate, and sodium dodecyl sulfate, the dispersion effects of sodium oleate and sodium dodecyl sulfate were obvious better than other three additives. For2g/L pyrite powder suspended in different additives, the optimum suspension conditions were different. When sodium oleate was employed as the additive, the optimum concentration was0.008mol/L, pH was1-3, ultrasonication time was45min. While sodium dodecyl sulfate was employed as the additive, the optimum concentration was0.008mol/L, pH was10-11, ultrasonication time was45min. The wettability of sodium oleate and sodium dodecyl sulfate to pyrite powder was much better than that of distilled water and sodium oleate was superior to sodium dodecyl sulfate. The calculation results for pyrite in sodium dodecyl sulfate aqueous solution at different pH showed that the solvation interaction played the main role. That was to say, the excellent dispersion stability between pyrite particles were mainly dependent upon the solvation interaction. With decreasing pH, the total interaction potential between pyrite particles was increased, and sodium dodecyl sulfate aqueous solution at low pH showed the best dispersion stability of pyrite. While in sodium oleate aqueous solution at different pH, the total interaction potential between pyrite particles was always positive, and the pyrite powder had excellent dispersion stability. In sodium oleate aqueous solution at pH1or10, the dispersion of pyrite particles was mainly dependent upon electrostatic interaction. Nevertheless, the dispersion of pyrite particles was mainly dependent upon solvation interaction for sodium oleate aqueous solution at pH6. In sodium oleate aqueous solution under alkaline conditions the total interaction potential was high, thus the pyrite powder had the best dispersion stability.(4) During the mechanical activation, the lattice distortion degree was increased, the energy gap of FeS2was decreased and Fermi level was increased. With the process of mechanical activation, the lattice distortion degree was increased; the density peak of state was decreased and showed the tendency to shift to low energy; whereas the energy distribution domain was increased. The FeS2under the interaction of lattice distortion showed more phenomenons of valance bond overlapping and orbital hybridization, and its oxidized ability was improved. This further demonstrated that the lattice distortion caused by the mechanical activation could promote the activity of pyrite. With the increase of the lattice distortion degree, the energy of FeS2gap reduced, and the Fermi level increased, the electrochemical reaction activity increased, thus the surface adsorption characteristics change significantly. |
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