| Molten salt electrolysis(MSE)is a highly efficient,environment-friendly and universal metallurgical method.With the discovery and proposal of FFC molten salt electrolysis process by research group of Cambridge University in 2000,a method of preparing metal by in-situ electro-deoxidation of metal oxides has attracted extensive attention.Similar feasibility has been demonstrated in the process of desulfurization of metal sulfide.In the traditional molybdenum metallurgy process,the oxidation roasting process for molybdenum disulfide will inevitably generate sulfur oxides,which can only be used with limited ways and consumption,and will cause great harm when discharged into the air.This process not only possesses a potential threat to the environment,but also puts forward a higher requirement for tailing gas treatment.Therefore,the development of an environment-friendly and short process with high-attached value byproduct metallurgical method has become a research focus of molybdenum metallurgy.Based on the facts mentioned above,the metallurgical process and mechanism of in situ desulfurization of molybdenum from molten salt electrolytic molybdenum disulfide were systematically studied.The principle and related process parameters of electro-desulfurization process of molybdenum disulfide were analyzed by selecting suitable electrolyte,investigating and comparing the electrochemical behavior of molybdenum disulfide and molybdenum ions in molten salt,adjusting the process parameters of electrolytic process and introducing liquid electrode to enhance the desulfurization process.The main contents of this paper are as follows:Firstly,the preparation process of molybdenum disulfide tablet was explored based on the requirements for the precursor of the MSE process.Then the stability of molybdenum disulfide in four kinds of commonly used eutectic chloride molten salt with different ion radius was studied.XRD and SEM were employed to study both chemical stability and physical stability of molybdenum disulfide in each of the selected molten salt system,and Na Cl-KCl was chosen as the supporting electrolyte for the subsequent electrochemical experiments.Secondly,the electrochemical behavior of molybdenum disulfide and molybdenum ion in molten salt was characterized by various transient electrochemical methods.The test results show that the reduction steps of Mo S2 in molten salt are mainly divided into two steps,which correspond to two electron transfer processes respectively.Based on the subsequent results of intermediate products,the reduction path of Mo S2 in molten salt is revealed as Mo S2?L2Mo3S4?Mo(where L is an alkali metal element),and the corresponding potential is-0.37V and-0.61V(vs.Pt).Electrochemical impedance spectroscopy(EIS)was employed to study the impedance of the system under different applied voltages.Constant voltage electrolysis process of molybdenum disulfide was analyzed by recording I-t curves and collecting and analyzing corresponding products.The elemental sulfur components mixed with volatile molten salt were successfully collected in the electrolysis process by a self-designed anode product collecting apparatus,and the loose sulfur elemental components were successfully separated by washing with deionized water,which verified the feasibility of electro-desulfurization of Mo S2.Molybdenum powder with residual sulfur content of 372 ppm was obtained by 20 h electrolysis at the cathode.Thirdly,by employing a liquid zinc electrode as the current colletor,the desulfurization process of Mo S2 is improved and successfully.The electrochemical behavior of ions in Na Cl-KCl-Zn Cl2-Mo Cl5 system was obtained by transient electrochemical test methods,and the phenomenon of co-deposition process of zinc and molybdenum ion was observed.At the same time,the reduction potential of molybdenum ion showed obvious shift towards positive,which was beneficial to the reduction of molybdenum.After electrolysis with constant voltage applied,in situ Mo S2 electro-desulfurization process was successfully achieved on the liquid zinc electrode.The distribution of zinc and molybdenum in the product was characterized by SEM and EPMA.Finally,the zinc in the electrolytic product was successfully removed by distillation at a high temperature,and molybdenum metal was obtained,which verified the feasibility of the process.The point of this paper is to prove the feasibility of in-situ electro-desulfurization process of Mo S2,to reveal the reaction mechanism and process conditions of this process and to improve the process of electrolysis by introducing a liquid zinc electrode.This study provides a reliable theoretical and technological fundamentfor industrial application... |
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