The Study Of Passivation Effects Of PSPT Composite Passivator On Pyrite And Its Passivation Mechanism

Pyrite,as well as other metallic sulphide minerals,can be produced widely in the mining process.These sulfide mine tailings suffer from a series of chemical reactions when exposed to water and oxygen,resulting in the formation of acidic mine wastewater?AMD?.The pollution caused by AMD is often serious and difficult to repair.In order to control and suppress AMD from the sources,A composite passivator with?-mercaptopropyltrimethoxysilane?PropS-SH?as the main passivator and natural sepiolite clay materials sepiolite?SPT?as a"filler"was prepared and used to inhibit pyrite oxidation.In this study,electrochemical test method,chemical extraction method and biological extraction method were used to explore the influence of this new type of passivating agent on the passivating performance of pyrite.Also,the passivation mechanism of the studied composite passivtor on pyrite was studied.The results of open circuit potential?OCP?measurements,cyclic voltammetric?CV?curves,Tafel polarization curves and electrochemical impedance spectra showed that PSPT composite passivator has better antioxidant performance than the pure PropS-SH passivator and the passivation performance of the composite passivator is influenced by the additive amount of sepiolite.The composite passivator with 0.8% of sepiolite exhibited the best passivation effect on pyrite oxidation.The results of these electrochemical measurements have also been comfirmed by chemical and biological leaching experiments.When pyrite was coated with P-0.8%SPT composite passivator,the chemical leaching rates of pyrite based on total iron and SO₄^2-were reduced by 76.9% and 71.2% respectively.P-0.8%SPT composite passivator also showed good passivation effect in the biological leaching experiments.These results demonstrated that PSPT composite passivator can effectively inhibit the oxidation of pyrite and thus favor to AMD source control.In order to study the passivation mechanism of PSPT on pyrite,FT-IR,XPS and ²⁹SiNMR tests were carried out on coated and uncoated pyrite samples.The related characterization results showed that the hydrolysis condensation reaction between PropS-SH molecules can be occurred so as lead to the formation of a silane coupling network structure by the bonds of Si-O-Si;when sepiolite is added to the PropS-SH passivation agent,the silica hydroxyl on the sepiolite surface can directly couple with the silane,so that the sepiolite is chemically bonded into the structure of the PropS-SH silane network to increase the network density.The silane network formed in the above process can be coated on the surface of pyrite by bonds of Fe-O-Si to form a dense passivation layer,which plays an important role in inhibiting pyrite oxidation.At the same time,the effect of different amount of sepiolite on the morphology and surface properties of the passivation film was investigated by using contact angle measurement and TEM.By measuring the surface contact angle and calculating the free energy of the coating interface,it was found that the surface of the pyrite sample changed from hydrophilic state to hydrophobic state after passivation.The free energy of film formation and the hydrophobic property of passivated film were changed when adding different amount of sepiolite.Appropriate addition of sepiolite in PropS-SH passivation agent can enhance the coating's surface hydrophobicity.But contrarily,excessive sepiolite reduced its hydrophobicity.TEM test showed that excessive sepiolite can cause serious aggregation,which may affect the integrity and oxidation resistance of the passivation coating.