Electrolytic Refining Of High Carbon Ferrochromium To Produce Pure Ferrochromium

Chromium is one of the important alloying elements in steel because of its high hardness,strength and corrosion resistance.With the increasing demand for the purity of steel,the purity of ferrochromium as an alloying additive also needs to be improved.In order to improve pure ferrochromium that can replace metal chromium,the development of new process for ferroalloy refining is particularly important.In this paper,molten salt electrorefining is conducted by using low-cost high carbon ferrochromium as anode to achieve the goal of obtaining p ure ferrochromium at the cathode.Firstly,the behavior of Cr²⁺in NaC l-KCl-CrC l₂ molten system was tested;then,the electrolytic refining of high carbon ferrochromium（HCCrFe）to produce pure ferrochromium in NaC l-KCl molten salts was investigated,the main conclusions are as follows.（1）The electrochemical behavior of Cr²⁺was investigated by cyclic voltammetry,square wave voltammetry and chronopotentiometry in molten NaCl-KCl-CrC l₂system at 710℃,and constant voltage electrolysis was carried out to prepare chromium metal.The results show that in NaC l-KCl-CrCl₂ system at 710℃,the electrochemical reduction of Cr²⁺on the Pt electrode is controlled by the diffusion.The diffusion coefficients obtained by cyclic voltammetry and chronopotentiometry are 1.31×10^-5cm²/s and 1.15×10^-5cm²/s,respectively,which are close.The reduction process Cr²⁺+2e^-=Cr is a quasi-reversible process with two electrons exchanged in a single step.During the potetiostatic electrolysis,the deposit is metallic Cr,demonstrating that it is feasible to produce metallic chromium by constant voltage electrolysis in this system.（2）Based on the above electrochemical tests,high carbon ferrochromium was used as the working electrode,tungsten wire was applied as the counter electrode,and potentiostatic（0.3V vs.Ag/AgC l）electrolysis was studied in NaC l-KCl system at710℃.Pure ferrochromium was successfully produced with a low content of C（0.26wt%）at the cathode.The existing state of C contained in the cathode deposit is mainly elemental form,rather than a carbide with Cr or Fe,and the content of S and P are 0.0017wt%and 0.008wt%,respectively.The left anode was mainly composed of carbon,containing carbon sheets with porous structure,which is worthy of study in the later work.（3）The effect of different current densities on the composition and morphology ofthecathodeproductwasinvestigatedduringconstantcurrent（100mA/150mA/175mA/200mA）electrolysis.The electrolytic cathode product under different electrolysis conditions was characterized by XRD and SEM.It is found that with the rise of the current density,the particle size of the deposits become coarser and the product tends not to be oxidized.