Study On Preparation Of Pure Ferroalloy And Carbide Derived Carbon By The Electrolysis Of High Carbon Ferroalloy In Molten Salts

With the rapid development of chemical and metallurgical industry,and field of energy materials,application of molten salts electrochemical method in these areas has drawn much more attention.Reactive metals including magnesium,lithium and sodium,a variety of insoluble metals,rare earth and its alloys were prepared by molten salts preparation process.Recently,molten salts electrolysis has been applied to the preparation of porous carbon because of its environmentally friendly features,which also attracts a lot of attention.High carbon ferroalloy is produced by carbon thermal reduction of oxide,which mainly includes high carbon ferromanganese and high carbon ferrochromium.From the phase diagram,high carbon ferromanganese and ferrochromium containing a carbon content of 6-8 wt%are mainly composed of metal carbide.If we could extract all metals from high carbon ferroalloy for the use of steel production,the remained anode residue is a kind of porous carbon having a large number of pores which is also named carbide derived carbon?CDC?.In this paper,we introduce several preparation process for the production of pure metals and its alloys from their carbides by molten salts electrolysis.Simultaneously,a new type of porous carbon,carbide derived carbon,is prepared in anode.Based on the above descriptions,some related investigations were carried out and the main conclusions are as follows:?1?The cathodic behavior of Cr???ion and the feasibility of electrolysis for the preparation of pure Cr at an inert W electrode in NaCl-KCl molten salts at a temperature of 710?was investigated by cyclic voltammetry,square wave voltammetry,chronopotential,and chronoamperometry.The results indicates that the reduction process of Cr???to Cr at W electrode was one step:Cr²⁺+2e^-=Cr.Reduction of Cr???is a quasi-reversible process controlled by diffusion mass transfer.The diffusion coefficients of Cr???calculated by the data of cyclic voltammetry and chronopotentiometry,is 1.27×10^-5cm²·s^-1and 2.24×10^-5cm²·s^-1,respectively.The nucleation process of Cr???was instantaneous three-dimensional nucleation on the W electrode.Potentiostatic electrolysis performed on an inert W electrode proved the feasibility of electrodepositing metallic chromium in molten NaCl-KCl-CrCl₂ system.?2?Based on the study of electrochemical behavior of Cr²⁺and the feasibility of electrolysis for the preparation of pure Cr on the W electrode in molten NaCl-KCl system,high carbon ferrochromium acted as the working electrode,tungsten acted as the counter electrode and Ag/AgCl as reference electrode,for subsequent electrolysis.The exchange electrons number of dissolved Cr ions in this molten salts system during electrolysis was investigated by square wave voltammetry.Microscopic analysis and phase characterization of cathodic products were carried out by scanning electron microscopy?SEM?,energy dispersive spectroscopy?EDS?,X-ray diffraction?XRD?and carbon and sulfur analysis.Results show that the reduction of chromium ions is a one-step reversible process with two electrons exchanged,which is controlled by diffusion mass transfer,and chromium was dissolved prior to iron in molten salts.The produced low carbon ferrochromium is mostly composed of spherical particles with the size ranging from 0.5 to 2?m.The carbon content of the cathode product was measured as 0.24 wt%.?3?The remelted high carbon ferromanganese and the W electrode were chosen as the consumable anode and cathode respectively,and NaCl-KCl molten salts were used as the electrolyte to produce porous carbon monolith and low carbon ferromanganese at the same time by molten salts electrolysis.During potentiostatic electrolysis,the anode fed manganese ions and iron ions into molten salts,with porous carbon left in the anode and ferromanganese deposited on the cathode.The anode residue was characterized by X-ray diffraction,scanning electron microscopy,Raman spectrum and transmission electron microscopy.Results indicated that this type of porous carbon material with a high degree of graphitization has a multimodal pore system consisting of micropores,mesopores and macropores,which is hierarchical carbide derived carbon?CDC?.The results from low temperature nitrogen adsorption test are also in agreement with the above tests and the BET value was calculated to be 171 m²/g.The electrodeposits on the cathode were confirmed to be pure ferromanganese.Its microstructure was characterized by SEM,and it was found to be spherical particles with the particle size from 0.5?m to 2?m.And the carbon content of the cathode products is 0.59wt%.The anode and cathode current efficiencies are estimated to be at least 92%and 80%,respectively.All results implied that it is feasible to prepare carbide derived carbon monolith with a hierarchical pore structure and low carbon ferromanganese simultaneously by molten salts electrolysis.