| Niobium resources are an important strategic resource in the world and play an indispensable role in many industries.The Bay an Obo mine is a world-famous polymetallic deposit containing iron,niobium and rare earths.And the reserve of niobium resources is the first in China.Since the composition of niobium minerals in Bayan Obo is complex and their characteristics are "many,poor,fine and miscellaneous",the extraction and utilization of niobium resources are difficult and the utilization rate is low.Therefore,the extraction of niobium from the niobium resources in Bayan Obo has become an important problem to be solved.In this work,the alloy phase of Bayan Obo niobium-rich ore after carbothermic reduction melting is taken as the research object.The alloy phase is composed of ferrosilicon and(Nb,Ti)C.The(Nb,Ti)C in the alloy phase is separated and extracted by electrochemical selective oxidation in ferrous sulfate solution with pH=0.35.The oxidation mechanism of alloy phase was studied,and the separated ferrous sulfate solution was used for electrochemical extraction of iron.It was found that the pH of FeSO4 solution had a significant effect on the electrochemical oxidation process of the prepared alloy.The iron in the metal phase can only be oxidized to iron oxides and cannot be separated from(Nb,Ti)C in the solution with pH=3.25.Iron in the solution with pH<0.7 could exist in the form of Fe2+ by the calculation used Factsage software.Two oxidation peaks at 0.3 V and 1.3V were observed by cyclic voltammetry in the solution with pH=0.35.The oxidation mechanism of the alloy at different potentials was discussed.The alloy was still dominated by ferrosilicon after oxidation at 0.3V,and the alloy phase was transformed into Fe3Si by XRD.It can be seen from the SEM images of the alloy surface that a small amount of(Nb,Ti)C is exposed on the surface of the alloy.Many black particles were appeared in the solution after oxidation at 1.3V.The black particles were detected by XRD as(Nb,Ti)C.And more(Nb,Ti)C was exposed on the surface of the alloy as seen from SEM images,forming pits.The Fe3Si alloy phase was oxidized to Fe2Si by the XRD results.It indicates that the iron in the alloy was selectively oxidized reaction and dissolved into the solution at the potential of 1.3V while(Nb,Ti)C in the alloy was separated.By comparing the ion concentration in the solution after the reaction,it was found that the silicon in the alloy cannot be oxidized by electrochemical oxidation reaction,and only iron was oxidized.During the acid leaching process,both iron and silicon were dissolved into the solution.By comparing the SEM morphology of the alloy surface after the reaction,it was found that electrochemical oxidation reaction occurred at the interface between the alloy and(Nb,Ti)C,while the reaction during acid leaching occurred on the surface of the alloy.(Nb,Ti)C can be separated by acid leaching until the ferrosilicon is completely dissolved.Therefore,the electrochemical reaction is selective.Electrochemical extraction of iron and kinetics of the reaction process were investigated in the solution after electrochemical oxidation.Pure iron particles were prepared under-1.34V vs.MSE in the solution with pH=4 at 298.15K.The sulfur-doped iron oxide with flake morphology was prepared under-1.8V vs.MSE in the solution with pH=1.The reaction kinetics of Fe2+ on Pt electrode was studied.The reduction process was a quasi-reversible process controlled by diffusion,and the heterogeneous charge transfer rate constant ks and diffusion coefficient D of the reduction process were calculated. |
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