| Pyrite(Fe S2) is the most common metal sulfide mineral in tailings, waste rocks and valuable mineral raw minerals. Pyrite is easy to be oxidized under natural weathering conditions. The oxidation of pyrite results in the formation of acid mine drainage(AMD), which could enter into the human body through food chain and do harm to the health of people. For control the pollution of AMD at source, electrochemical techniques and conventional chemical leaching approach were applied to screen a suitable organosilane passivant for pyrite. The passivation effect and mechnism of pyrite dealt with organosilane were also studied. The main original conclusions of the work are shown as follows:The three selected organosilane passivants including γ-aminopropyltrimethoxysilane(APS), vinyltrimethoxysilane(VTMS) and γ-mercaptopropyltrimethoxysilane(Prop S-SH) could inhibite the anodic reaction of pyrite electrode, which were proved as anode passivation agents. The results of cyclic voltammetry(CV), tafel polarization and electrochemical impedance spectroscopy(EIS) have showed that the surface electrochemical behavior decreased significantly, corrosion current density reduced sharply, and surface film impedance increased obviously compared with bare pyrite. In the chemical leaching experiments, APS, VTMS and Prop S-SH coatings decreased total Fe leaching by 49.4%, 71.4% and 89.2%, respectively, while SO42- were reduced by 45.1%, 69.1% and 89.6%, separately. These results of electrochemical and chemical leaching experiments have indicated that the studied three organosilane coatings(APS, VTMS and Prop S-SH) have the obvious effect on inhibiting electrochemical behavior and suppressing chemical oxidation of pyrite. Moreover, In comparison with APS, VTMS and Prop S-SH coating, the most remarkable effect was Prop S-SH and the inhibition efficiency followed the sequence of Prop S-SH > VTMS > APS.In order to determine the best passivation effect of pyrite coated with Prop S-SH, the influence of different factors in coating process on pyrite passivation effect has been studied, and the result has showed the best passivation conditions of pyrite coated by Prop S-SH were as follows: organosilane concentration of 10%, organosilane solution p H of 4.0, hydrolysis time of 4 h and hydrolysis temperature of 40℃. Under the best coating conditions, four-months of pyrite leaching experiment has been carried out to evaluate the long-term stability of Prop S-SH coating. It turned out that the surface passivation coating of pyrite showed a good antioxidation capacity to obstruct the contaction between pyrite and water, bacteria or other oxidant of environment, which could slow down the pyrite surface oxidation reaction to reduce the formation of AMD over a period of time, and it has practical application value.At the end of the paper, powder contact angle and natural water absorption have been tested for study the wettability of pyrite coated with Prop S-SH. Results showed that the contact angle of coated pyrite increased by 89.64°relative to bare pyrite, and hydrophobic performance improved significantly. Additionally, natural water absorption of pyrite with Prop S-SH film was less than 0.01%. Moreover, the results of FT-IR and XPS analysis proved that the mechanism of studied organosilane coatings on pyrite oxidation suppression involves the formation of Si-O-Fe bonds at the coating/pyrite interface and Si-O-Si cross-linking network surrounding pyrite, thus resulting in an effective barrier from aggressive species. |
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