Passivation And Self-healing Performance Of Organosilane Passivator For Pyrite

In the process of mining mineral resources,lots of tailings and slag are produced,which are extremely harmful to the ecological environment.Particularly,the oxidation of metal sulfide minerals usually brings a great deal of acid mine drainage(AMD)with low pH and strong toxicity,which has become a major problem in the treatment of environmental pollution.The tailings surface passivation technology mainly inhibits the generation of AMD at the source with the advantages of high efficiency and simple operation.However,traditional passivators are easily disturbed by external factors and lose protective effect.In order to improve the stability and long-term performance of passivation film,3-mercaptopropyl-trimethoxysilane(Prop-SH)and tetraethoxysilane(TEOS)were selected as main passivators(PT)in this paper,and the new composite passivator PT/ATP@HQ was prepared by adding attapulgite clay(ATP)loaded with 8-hydroxyquinoline(8-HQ)into PT coating.Meanwhile,the passivation effects,self-healing performance and mechanisms of passivation agents were investigated.Firstly,the passivation performance of Prop-SH and TEOS mixed in different proportion were evaluated by electrochemical method and chemical leaching method so as to determine the optimal ratio of the main passivation agents Prop-SH and TEOS.The results showed that when the volume ratio of Prop-SH and TEOS was 4:1,the best passivation effect for pyrite was obtained.However,due to the poor density and thickness of the organosilane coating,the passivation efficiencies of total Fe and SO42-were respectively only 57.5%and 50.2%after the passivated pyrite samples were immersed in 0.5 wt%H2O2 solution for 24 hours.In order to improve the physical properties of the organosilane coating,the modified attapulgite clay(ATP)was added into it.When the amount of ATP was 0.8 wt%,the electron transfer resistance of pyrite oxidation(Rct)and passivation film resistance(Rf)increased by 10.7 and 15.4 times,respectively.Furthermore,the passivation efficiencies of total Fe and SO42increased to 85.2%and 75.2%after 24 h oxidation in 0.5 wt%H2O2 solution.In order to further improve the long-term performance of the passivation film,a composite passivation agent PT/ATP@HQ was prepared by adding ATP@HQ to the organosilane coating.According to the scratch test,PT/ATP@HQ coating could inhibit the local oxidation reaction of pyrite and had good self-healing performance.In the 60-day chemical leaching experiment,the passivation efficiencies of total Fe and SO42-of PT/ATP@HQ coated pyrite were 71.8%and 67.9%,respectively,which showed good long-term passivation effect.At last,the passivation and self-healing mechanisms were investigated by FT-IR,XPS,29Si NMR and other characterization methods,which were as follows:the organosilane hydrolyzed to form highly active silanol groups(Si-OH),and then dehydration condensation reaction occurred between Si-OH and nano-fillers to form cross-linked network structure connected by Si-O-Si bonds.Meanwhile,Si-OH groups reacted with the hydroxyl groups of pyrite to form Fe-O-Si bonds,thereby an inert and dense passivation film formed on the surface of the pyrite.Once the passivation film is locally damaged,the pH at local area will decrease because of the oxidation of pyrite,and then 8-HQ loaded in ATP will automatically release to coordinate with pyrite to form 8-hydroxyquinoline-iron complex,thereby repair the damaged passivation film.Therefore,the organosilane passivation agents prepared in this paper had good passivation and self-healing performance for pyrite,and they had a good application prospect in the pollution treatment of tailings and AMD.In addition,the idea,which was to repair the damaged passivation film by stimulating the release of 8-hydroxy quinoline from nano-filler through the changes of local pH and then complexing with iron,also provided a strategy for the development of long-term passivation agents.