Intensifying The Desulfurization Of High-sulfur Bauxite By External Field And The Mechanism Of Oxidation Of Pyrite By Hydroxyl Radicals

The high-sulfur bauxite with high ratio of aluminum to silicon has application potential,it can relieve the shortage of high-grade bauxite resources after desulfurization.In this paper,based on quantum chemical density functional theory,the mechanism of oxidation path of pyrite by hydroxyl radical produced in the process of electrolytic desulfurization was studied.Based on the improvement of the desulfurization efficiency of electrolysis and the electrochemical characterization,the mechanism of the electrolytically generation of hydroxyl radicals enhanced by ultrasonic water was studied.Finally,for the industrialization,according to three indicators of electrode activity,corrosion and resistance,nickel was selected as the best anode under alkaline conditions among 6 kinds of conventional electrode materials.A method of external field coupled with nickel electrolysis was proposed to provide possibilities for the industrial application.The main results are as follows:(1)The changes of pyrite and alkaline solution before and after electrolysis were studied.The electrolyzed pyrite surface was activated with the appearance of pores and wrinkles.XPS results showed that the surface valence S was oxidized to +4 or +6,and Fe(OH)3 was produced.In the solution after electrolysis,thiosulfate ions(up to 82 ppm)and small amounts of sulfate ions(≤3 ppm)were detected in the solution.Simultaneously,the pH of the electrolyte is reduced of 0.8 in one hour.ESR results showed that the hydroxyl radical concentration was 41.010 μmol/L after electrolysis in alkaline solution for 1 h.Electrochemical characterization results showed that the iron metamorphic potential of the pyrite electrode in alkaline solution was-0.79V,and the sulfur valence potential was-0.32V.Ultrasonic electrolysis can increase the diffusion coefficient of the oxidation reaction precursor,thereby strengthening the mass transfer in the electrolyte.(2)The result of density functional theory(DFT)calculation shows that when oxygen radicals are continuously adsorbed on the 100 surface of pyrite alone,it is difficult to dissociate the minerals;when hydroxyl radicals are continuously adsorbed on the 100 surface of pyrite,oxygen radicals combine with S and Fe continuously,which lead to disconnection of S-S bond.Finally,iron hydroxide,SO2,SO32-,SO42-,S2O32-,etc.are generated,and the chemical reaction equation is given.The oxygen element in the final hydroxyl radical participates in the formation of sulfur-containing ions,and hydrogen generates hydrogen ions.Therefore,the pyrite oxidation of hydroxyl radicals is an alkali-consuming process.(3)The effect of ultrasound on the formation of hydroxyl radicals by electrolysis of water was studied.The results show that the ultrasonic can not only enhance the mass transfer in the liquid phase,but also enhance the electron gain and loss.Ultrasound suppresses the release of oxygen,strengthens the dispersion of hydroxyl radicals,promotes the desorption process on the electrodes,and increases the activation space,resulting in an increase in the amount of hydroxyl radicals.By analyzing the Tafel and EIS curves,it is known that ultrasound makes a positive shift in the equilibrium potential of the OER and increase the equilibrium current,which indicates that the ultrasound suppresses the thermodynamic conditions of the OER and improves the dynamic conditions of the OER.Ultrasound increases the Rct of OER and decreases Rs.Regardless of Pt or Ni electrode,the desulphurization of bauxite can be improved by ultrasonic.Electrolysis desulphurization with ultrasonic coupled nickel electrode can achieve the effect of platinum electrode without ultrasonic.(4)By examining the corrosion behavior,desulfurization effect,and electrochemical behavior of the six electrode materials,the ideal anode material was optimized.Sodium thiosulfate solution was used as a simulated electrolyte,Tafel and CV curves show that corrosion potentials of six electrode materials are Ni>C>SS>Fe>Cu>Pb-Ag.The desulphurization rate and cell voltage of the bauxite electrolysis are Cu>Ni>Fe>SS>C>Pb-Ag and Ni>Fe>SS>Cu>C>Pb-Ag respectively.Finally,Ni was selected as the ideal anode material for the desulphurization of bauxite,which provided the possibility for industrial application of electrolytic desulfurization.