| The oxidation of pyrite(Fe S2)in the tailings is an important origin of acid mine drainage(AMD).As one of the important methods to inhibit the oxidation of pyrite at the source,surface passivation method has attracted the attention of many researchers.The previous research on surface passivation mainly focused on the chemical and biological oxidation of pyrite controlled by passivation agent.However,pyrite is used as a semiconductor.After passivation,the pyrite is exposed to sunlight for a long time.Whether the passivation agent can continue to maintain the passivation effect,and its mechanism of inhibiting photocorrosion of pyrite is not clear.This paper takes the passivation coating pyrite of triethylenetetramine dithiocarbamate(DTC-TETA)as the research object.The photochemical leaching analysis of the passivation of pyriteion dissolution and oxidation inhibition rate changes with time.Different characterization methods were used to explore the mechanism of DTC-TETA's inhibition of carrier migration on pyrite surface.The main research contents are:(1)The DTC-TETA molecules are supported on the surface of pyrite by Fe-S bonding.Using field emission scanning electron microscope-energy dispersive X-ray spectroscopy(SEM-EDS)to study the surface morphology and element distribution of pyrite,C and N were loaded on the surface of pyrite.X-ray diffraction spectroscopy(XRD)and transmission electron microscope(TEM)was used to analyze the crystal form of pyrite before and after passivation.The Fourier Infrared Spectroscopy(FT-IR)and shows that the characteristic peaks of the C-S and C=S bonds on the surface of Fe S2/DTC-TETA at 1155–1130 cm-1 are merged,and the characteristic peaks of the C-N bond wavenumber are blue-shifted by 29 cm-1,combined with X-ray photoelectron spectroscopy(XPS)methods were used to study DTC-TETA formed passivation layers on the surface of pyrite through the coordination group of NC(S)2-Fe and repassivation adsorption of Fe.Thermogravimetric analysis(TGA/DTG)and specific surface area analysis(BET)combined with density functional theory(DFT)modeling calculation analysis of the passive coating has a stable envelope configuration,and the stable binding energy is4.95 e V.(2)The novelly formed NC(S)2-Fe group has a double-shielding effect,which shields the surface phase migration of photo-generated electrons and photo-generated holes internally,and partially shields O2 and H2O from the outside.DTC-TETA enhances the photochemical stability of pyrite.The sacrificial DTC-TETA passivation layer molecule's C-S,C-N and C-C bonds replace Fe S2 and are oxidized by photogenerated holes and ROS(Superoxide radicals(·O2-)and hydroxyl radicals(·OH))(FT-IR,XPS).The 10 h exposure to Fe S2/DTC-TETA results in a positive shift of 398.8 e V of the C-N bond by 0.2 e V,and the N-H bond energy does not change significantly,indicating that the C-N bond is broken under the exposure.Under illumination and dark conditions,the content loss rate of elements C and N containing groups(TOC/TN)are small,and does not affect the main molecular structure of the Fe S2/DTC-TETA.(3)Molecular photoluminescence fluorescence spectrophotometry(PL)was used to quantitatively analyze the process of pyrite photogenerated carriers'migration and activation of inorganic oxygen under continuous illumination conditions,indicating that ROS was effectively inhibited within 10 hours.The inhibition rate of the passivation coating on·OH from the surface of Fe S2 is 87.4%.Ultraviolet-visible-near infrared diffuse reflectance spectroscopy(UV-vis-NIR DRS),fluorescence spectroscopy(FL/TR-PL),synchrotron radiation spectroscopy(SR-PES)and valence band photoelectron spectroscopy(VB-XPS)obtained that the band gap of the Fe S2/DTC-TETA composite is narrowed.The recombination rate of photogenerated carriers is increased.The fluorescence lifetime is shortened by 6.3 ns.The conduction band potential is negatively shifted from-0.30 e V to-1.56 e V,and the valence band potential is negatively shifted from 0.41 e V to-0.81 e V,so that the surface oxidation reaction barrier energy of Fe S2/DTC-TETA is increased.At the same time,the electrochemical test methods(CV,I-T)were used to analyze the photoelectric conversion and transformation rules of the pyriteleaching system.The relative migration rate of photogenerated electrons increases by 2×10-3±0.001?A/(cm2·s).The passivation coating inhibits pyrite's self-corrosion process caused by direct and indirect oxidation of photogenerated carriers in the environment,thereby reducing the AMD leaching rate under light conditions.The dithiocarbamate deactivator is feasible to control the migration path of photogenerated carriers on the surface of pyrite and Fe-containing semiconductor natural minerals. |
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