Chinese Journal of Applied Chemistry ›› 2020, Vol. 37 ›› Issue (6): 709-718.DOI: 10.11944/j.issn.1000-0518.2020.06.190333

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Electrochemical Oxidation of High Carbon Ferrochrome in Sodium Hydroxide Aqueous Solution

HAN Pingabc,FENG Haitaoab*(),LI Lingabc,DONG Yapingab,TIAN Senabc,ZHANG Boab,LI Boab,LI Wua   

  1. aKey Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Qinghai Institute of Salt Lakes,Chinese Academy of Sciences,Xining 810008,China
    bQinghai Engineering and Technology Research Center of Salt Lake Resources Development,Xining 810008,China
    cUniversity of Chinese Academy of Sciences,Beijing 100049,China
  • Received:2019-12-13 Accepted:2020-03-26 Online:2020-06-01 Published:2020-06-08
  • Contact: FENG Haitao
  • Supported by:
    Supported by the Basic Research Project in Qinghai Province(No.2017-ZJ-786), and the Major Science and Technology Project in Qinghai Province(No.2016-GX-A10)

Abstract:

Although ferrochrome electrolysis technology is a novel method for preparing sodium chromate, the electrochemical oxidation of high carbon ferrochrome in NaOH aqueous solution is still unclear. The electrochemical oxidation of chromium in NaOH aqueous solution was studied by cyclic voltammetry(CV). The electrochemical oxidation of high carbon ferrochrome in NaOH aqueous solution was studied by cyclic voltammetry and linear sweep voltammetry (LSV). Scanning electron microscope (SEM), energy dispersive spectrometry (EDS) and X-ray photoelectron spectroscopy (XPS) were used to characterize the composition of solid phase products after electrolysis of high carbon ferrochrome electrode. The results are as follows:metal chromium has two ways of electrochemical oxidation to form sodium chromate in NaOH aqueous solution: Cr(0)→Cr(VI) and Cr(0)→Cr(Ⅲ)→Cr(VI). The electrochemical oxidation of high carbon ferrochrome in NaOH is different from the metal chromium. It directly generates sodium chromite by Cr(0). Cr(OH)3 occurs electrochemical reaction with Fe(0) to form stable FeCr2O4. Fe(OH)3 is formed by the strong hydrolysis of FeO2-. As the concentration of NaOH aqueous solutions increases, the high carbon ferrochrome is easily passivated in NaOH aqueous solution under low potential range due to the influence of Fe(0). The passive films are Fe3O4 and Fe2O3. The passivation films dissolve at high potential. Then high carbon ferrochrome occurs electrochemical reaction to form Na2CrO4, Fe(OH)3 and FeCr2O4. At the same time, a large amount of oxygen is deposited on the positive electrode surface. As the concentration of NaOH aqueous solutions increases, the amount of Na2CrO4 and Fe(OH)3 increases. The conditions are as follows: alkaline concentration ≥2 mol/L, anodic potential ≥1.6 V(vs.SCE).

Key words: high carbon ferrochrome, metal chromium, NaOH aqueous solution, electrochemical oxidation, anodic polarization