Mechanical Activation In The Electrochemical Study Of Pyrite / Aqueous Solution Interface Behavior

During the coal direct liquefaction, the interface character and dispersibility of pyrite catalyst can affect the contiguity of pyrite with coal and the catalytic effect to the liquefaction reaction. As the electrochemical performance of pyrite powder under mechanical activation can reflect its interface character and dispersibility, the electrochemical performance and interface behavior of pyrite powder in organic medium can provide definite theory proof for developing catalysts with excellent performance in the coal direct liquefaction reaction.Pyrite powder was prepared by mechanical activation. By adopting pyrite powder microelectrode as work electrode, the absolute ethyl alcohol as electrolyte, proper amount of cationic surfactants, such as cetylpyridinium chloride, as ion conductor, the electrochemical behavior and its interface behavior of pyrite powder with or without mechanical activation in absolute ethyl alcohol were compared and studied through chronoamperometry and electrochemical impedance. The change of interface behaviour of pyrite micro-electrode/non-aqueous electrolyte in grinding additives was discussed.It is shown that the granularity of pyrite powder under mechanical activation becomes smaller, the specific surface area increases, aberrance of the crystal lattice occurs, the surface energy ascends and the activity becomes larger. The kinetics of the electrochemical process of pyrite is controlled by the electrochemical reactions.The equivalent electrical circuit R_s((R_ctZ_w)Q) was used to fit the impedance spectra for all studied conditions. Mechanical activation has a great effect on the interface performances. The charge transfer resistance and interface capacitance were decreased and the rate of reaction was increased after mechanical activation. Grinding additives can be absorbed on the surface of pyrite powder under mechanical activation by chemical or physical process. As a result, the adsorption of oxygen on the surface of pyrite is weakened. The physical adsorption of Stearic acid on the surface of pyrite under mechanical activation is,but Octadecanol and Span80 are not beneficial for the ball grinding of pyrite in alcohol.When adding additives, the better dispersion of mechanical activation pyrite can be achieved with fewer charge transfer resistance and interface capacitance. The dispersion of mechanical activated pyrite was improved with stearic acid as additive by changing the dielectric constant and by increasing the thickness of double electric layer.