The Study On The Passivation Properties And Mechanism Of Pyrite Chemical Oxidation By The Montmorillonite/organossilane Composite Passivator

Pyrite is easily oxidized by weathering and leaching during the mining process.The oxidation of pyrite results in the formation of acid mine drainage(AMD),which is one of the most serious environmental problems in the mining industry.In order to control AMD at source,a novel montmorillonite/organossilane composite passivator is synthesized in this paper.This passivator is prepared by incorporateing nano montmorillonite into ?-mercaptopropyl trimethoxy silane(PropS-SH,PS)coating so as to enhance its passivating effect at low concentrations.Additionlly,cationic and polymer dispersants were further added in the passivating agents to make the better dispersion of montmorillonite The passivation performance of the as-preapred composite coatings was studied by electrochemical and chemical leaching experiments.The passivation mechanism was investigated by FT-IR,XPS and 29Si solid-state nuclear magnetic tests.In the electrochemical experiments,coating,PropS-SH/Montmorillonite(PSM)coated pyrite showed higher open-circuit potential(OCP)value,higher electron transfer resistance,higher surface film impedance,higher corrosion potential and lower corrosion current than that coated by pure PS coating.These results indicated that the addition of montmorillonite nanoparticles can enhance the passivation efficiency of PS coating,particularly when the concentration of montmorillonite nanoparticles was 1wt%.Moreover,the chemical leaching experiments revealed that the passivationefficiencies of total iron and SO42-were the highest when the amount of montmorillonite addition was 1 wt%,which reach to 85.20%and 77.98%,respectively.On the basis of the above experiments,hexadecyl trimethylammonium bromide(CTAB),polyethylene glycol(PEG),polyvinyl alcohol(PVA)and their mixture were also introduced into 1.0 PSM passivating agent(containg 1 wt%montmorillonite nanoparticles)to improve the dispersion of montmorillonite nanoparticles.The results of sedimentation experiments and zeta potential experiments showed that the dispersion of the composite passivate suspensionwas increased in varying degrees after added with dispersants.Especially when added with CTAB-PVA PSM passivating agent exhibits the longest settling time,the highest zeta potential and the best dispersion stability.Electrochemical and chemical leaching experiments were performed to evaluate the effects of different dispersants on the passivation ability of 1.0 PSM coating on pyrite oxidation.Compared with 1.0 PSM coating without any dispersants,the composite coating added with dispersant presented higher OCP value,higher electron transfer resistance,higher surface film impedance,higher corrosion potential and lower corrosion current density,suggesting that the addition of dispersants can increase the passivation ability of PSM coating.Among all of these dispersants,CTAB-PVA exhibits the most advantageous to the passivation efficiency of PSM.Chemical leaching experiment further confirmed this conclusion,in which the C-PVA-PSM coating decreased pyrite oxidation by 92.15 and 93.23%,respectively.The SEM results showed that the surface morphology of PS coated pyrite could be changed with the addition of montmorillonite nanoparticles.It can be clearly observed that the agglomerates of montmorillonite were loaded on the surface pyrite,and the number of nanoparticles and the degree of agglomeration increased as the additon of montmorillonite nanoparticles increased.This indicated that nano montmorillonite was filled in the PS coating film.Contact angle experiment results showed that the pyrite coated by 1.0 PSM coating was more hydrophobic than the uncoated pyrite,as indicated by the increase of static water contact angle from 52.27°for uncoated pyrite to 96.62° for 1.0 PSM coated prytie.After the addition of the dispersant C-PVA within 1.0 PSM,the contact angle was further increased to 118.81°making the pyrite surface more hydrophobic,which was beneficial to suppress the pyrite oxidation in the wet environment.At last,FT-IR,XPS and 29Si solid-state nuclear magnetic tests were used to explore the interaction between pyrite and PSM composite passivator.According to these results,the coating mechanism of PSM on pyrite is proposed as follows:PS(Simple formula R-Si(OCH3)3)was hydrolyzed to form silanol(R-Si(OH)3)in water and ethanol solvent.Then the hydrolysis productions condense with each other and generate a Si-O-Si network.At the same time,the hydroxyl groups on the surface of the montmorillonite nanoparticles were also cross-linked with silanols through Si-O-Si bonds,thereby being encapsulated in the PS coating to form PSM coatings.Finally,the PSM coatings are coated on pyrite surface via Fe-O-Si bonds.