The Passivation Effect Of Pyrite With Polysiloxane Doped With SiO₂ Nanoparticles And The Study Of Its Passivation Mechanism

Acid mine drainage?AMD?resulting from the oxidation of metal sulfide minerals,such as pyrite,become one of the most serious environmental problems in the mining industry.For the purposes of controlling AMD at the source,a novel nanocomposite coating,based on SiO₂ nanoparticles as nanofiller embedded in ?-mercaptopropyltrimethoxysilane?PropS-SH?coating is introduced in this paper.The performance of the PropS-SH/SiO₂?PSS?nanocomposite coatings was evaluated by electrochemical measurments and chemical/biological leaching testing.In addition,the coating mechanism of the PSS coatings on pyrite surface is presented in this paper.At first,scanning electron microscopy?SEM?and contact angle measurement were used to study the effects of SiO₂ nanoparticles on the morphological and wettability properties of PSS coatings.It is evident that the surface of the PropS-SH coated sample is uniform and smooth,while a rough surface can be observed for the PSS coated samples.Furthermore,the surface roughness increases significantly on the PSS coatings doped with higher content of SiO₂ nanoparticles.The changes in the surface morphology indicate that many SiO₂ nanoparticles are embedded in the PSS coatings.The roughness also changed the wettability of PSS coating.Compared with uncoated pyrite,as the concentration of SiO₂ nanoparticles in PSS coatings is increased to 2 wt%,the contact angle of coated pyrite rises from 57.79° to 99.94°.The increased hydrophobicity of coatings should be beneficial for their protection ability to pyrite in wet environments.Then,the potential of the PSS coatings with different content of SiO₂ nanoparticles to inhibit pyrite oxidation was evaluated by electrochemical measurments and chemical leaching test.The results of electrochemical measurments indicated that PSS coated pyrite electrodes shows higher OCP value,higher corrosion potential and lower corrosion current density than uncoated pyrite.Moreover,the highest film impedance can be observed when the concentration of SiO₂ nanoparticles in PSS coatings is 2 wt%,indicating that adding appropriate concentration of SiO₂ nanoparticles in PropS-SH coating could enhance the passivation efficiency of the coating.The results of chemical leaching test shows that PSS coatings decreased total Fe and SO42-leaching by 81.1% and 80.4%,respectively.After that,biological leaching test was carried out to evaluate the ability of PSS coatings to suppress biological oxidation of pyrite,and the results indicated that PSS coatings can inhibit the oxidation of pyrite in the presence of Acidithiobacillus ferrooxidans effectively.At the end of this paper,the coating mechanism of the PSS coatings on pyrite was analyzed by FT-IR,XPS and 29 Si NMR.In the coating process,the hydrolysis of PropS-SH monomer is occurred in the presence of water and alcohol.Then the hydrolysis productions condense with each other to form a dense network structure linked with Si-O-Si bonds.Simultaneously,silanol groups in the network can react with hydroxyl groups on the surface of SiO₂ nanoparticles,leading to the embedment of SiO₂ in PropS-SH coating and the formation of PSS coatings.Subsequently,PSS coatings are coated on pyrite surface via Fe-O-Si bonds.