A Research On Electron Transfer Capacity Mechanism Of Pyrite（FeS₂） Via Different Pyrolysis Temperature Biochar Passivation Coating

Pyrite（FeS₂）is one of the most common and abundant sulfide minerals in the earth’s crust.In sulfide mines,acid mine drainage（AMD）produced by the oxidation of pyrite is a very serious environmental problem.Surface passivation is an emerging method proposed in recent years to inhibit oxidation of tailings.It advocates passivating coated sulfide ore particles from a microscopic point of view,that is,forming a thin organic or inorganic protective coating on the surface of pyrite.To prevent it from contacting the atmosphere,water and bacteria that promote oxidation,so as to achieve the purpose of inhibiting the oxidation of sulfide ore.This thesis takes pyrite as the research object and uses different pyrolysis temperature biochar to treat tailings to inhibit tailings oxidation.Through chemical leaching analysis,the ion dissolution situation and oxidation inhibition rate of pyrite before and after biochar passivation change with pyrolysis temperature,various spectroscopy methods are used to characterize the chemical composition and structural changes of biochar,and the analysis is combined with electrochemical methods.The changes in the electron transport capacities（ETC）[electron accepting capacities（EAC）,electron donating capacities（EDC）]of biochar at different pyrolysis temperatures were used to explore the mechanism of the effect of biochar under different pyrolysis temperatures.In order to explore the mechanism of the effect of biochar under different pyrolysis temperature on the electron transfer ability of pyrite.The main research results and conclusions are as follows:（1）After mixing and passivation of rice straw biochar（RSB）and pyrite,new Fe-containing peaks were found at 695 and 561 cm^-1in the composite material,and the carboxylic acid group occurred at about 40 cm^-1.The blue shift of the wave number indicates that biochar chelates Fe ions through C=O groups to form Fe-O passivation bonds,which weaken the redox process of Fe ions.RSB above 500℃effectively inhibits the leaching of heavy metal ions caused by the chemical oxidation process of pyrite.After the bagasse biochar（SBB）is mixed with pyrite for passivation,it has no significant inhibition on the heavy metals produced during the oxidation process of pyrite within the pyrolysis temperature of 300-900℃.（2）In the pyrolysis temperature range of 300℃-600℃,the basic functional groups of RSB are mainly C=O functional groups when the pyrolysis temperature is300-600℃,with the content reaching 56.08%,53.15%,41.80%and 41.39%;When the pyrolysis temperature of SBB is 300-600℃,the basic functional groups are mainly C=O functional groups,and the contents are 48.55%,42.53%,66.66%and67.36%respectively.The functional group content of biochar changes with the increase of pyrolysis temperature,and the redox functional group of biochar is the main source of its ability to gain and lose electrons.In this pyrolysis temperature range,biochar EAC accounts for a relatively high proportion,EDC/EEC first decreases and then gradually increases,while EAC/EEC first increases and then gradually decreases.（3）After the rice straw and bagasse biochar is compounded with pyrite,the electrons on RSB500 and RSB600 are transferred to the conduction band of pyrite;the electrons of RSB300,RSB400 and SBB300-SBB600 are transferred from the conduction band of pyrite to the biochar.The accumulation of electrons on the surface of pyrite means more negative surface charges.The surface charge of PY-RSB has a positive charge when the p H range is below 8.5,which may generate a built-in internal electric field,which will greatly promote biochar Transfer of electrons with pyrite.（4）In the pyrite-biochar system,the contribution of O₂in the oxidation process of PY-RSB500 and PY-RSB600 is about-43%;the contribution of O₂in the oxidation process of PY-SBB is about 10%;PY-The hydrophobic angle of RSB and PY-SBB is not significantly different from that of pyrite;the signal of composite DMPO-·OH is weaker than that of FeS₂itself;the surface of RSB and SBB has more negative charges.Therefore,the influence of O₂,H₂O,·OH and surface charge on the oxidation of pyrite is excluded.