Electrochemical Study On Surface Passivation Of Typical Metal Sulfide Minerals

Metal sulfide minerals is mostly associated with mineral minerals,the tailings in the accumulation process after the mining,due to weathering will make it dissolve a lot of heavy metals and acidic substances,While the release of acidic solution has accelerated the oxidation and dissolution of metal sulfide minerals and other rock-forming minerals.Under the action of runoff or seepage,these pollutants can migrate and transform in the horizontal or vertical direction.In order to solve the problem of tailings pollution from the source,we must understand the oxidation of metal sulfide minerals.In this paper,four typical metal sulfide minerals?pyrite,chalcopyrite,pyrrhotite and sphalerite?were studied.Electrochemical methods such as open circuit potential?OCP?,cyclic voltammetric?CV?method,Tafel polarization curve?TPC?and electrochemical impedance spectroscopy?EIS?were used.The four kinds of minerals were treated with stearic acid?SA?and oleic acid?OA?under different conditions,and their oxidation process,passivation mechanism and passivation efficiency were studied.At the same time,in order to compare with the results of electrochemical measurements,ion dissolution experiments were carried out in the optimal passivation effect,and the factors influencing the passivation effect were discussed.The experiment result shows:The order of OCP values of four typical metal sulfide minerals is:pyrite>pyrrhotite>chalcopyrite>sphalerite.The difference between OCP and pyrrhotite OCP is not obvious,but the pyrrhotite itself had the properties of conductors,which were more susceptible to oxidation than pyrite with semiconductor property.The CV curve of the tailings show that the oxidation process of the four kinds of metal sulfide minerals in acid solution was divided into two steps.The first step was that the sulfur film and Fe²⁺or Cu⁺on the mineral surface were oxidized.The second step was that the sulfur film of mineral surface was destroyed,the mineral lattice was destroyed by own oxidation,resulting in the dissolution of metal or metal ions and S^2-were oxidized.X-ray photoelectron spectroscopy?XPS?results show that the addition of SA and OA allows the surface of metal sulfide to be covered with a film.Work electrodes made of metal sulfide minerals treated with different concentrations of SA and OA,electrochemical methods were used to measure these electrodes,the results showed that the layer can significantly reduce the value of OCP,the tailing of the oxidation reaction and reduction reaction are inhibited,but did not change their oxidation-reduction mechanism.Analysis of Tafel polarization curves and EIS:the greatest passivation efficiency was found at 3%SA or 5%OA for pyrite,which 5%SA or 8%OA,5%SA or 5%OA and 5%SA or 3%OA showed the same characterisyics for chalcopyrite,pyrrhotite and sphalerite,respectively.The passivation efficiency of OA was higher than that of SA on the whole.Compared of SA and OA inhibition of four kinds of mineral oxidation reaction differences,EIS of pyrrhotite changed the most obvious,the most sensitive response was pyrrhotite,the difference of sphalerite was the least.After pyrite was treated with different concentrations of SA and OA in ethanol,the oxidation process of pyrite was not changed.Except for the optimum passivation concentration,the passivation efficiency at other concentrations was improved obviously.Fe³⁺can greatly reduce the passivation efficiency of passivator.5g/L Fe³⁺will reduce the passivation efficiency of 8%OA to chalcopyrite from 77%to 17%.The experiment of ion dissolution in pyrite showed that the addition of ethanol improved the overall passivation efficiency,but reduced the passivation effect.The experiment of ion dissolution in chalcopyrite showed that the addition of SA and OA significantly inhibited the rate of ion dissolution and reduced the concentration of ion dissolution,and the inhibitory effect of OA was better than that of SA,Fe³⁺of 5g/L greatly reduces the passivation effect of passivator.