高碳铬铁在氢氧化钠水溶液中电化学氧化过程

铬铁电化学氧化法是一种新的制备铬酸钠的方法,然而高碳铬铁在NaOH水溶液中的电化学氧化过程尚不明确。 采用循环伏安法(CV)、稳态极化法(LSV)等电化学测试方法对金属铬、高碳铬铁在NaOH水溶液中的电化学氧化过程进行研究,通过扫描电子显微镜(SEM)、能量散射谱(EDS)和X射线光电子能谱(XPS)对高碳铬铁电解后固相产物表征,判断固相产物的组成。 结果表明,高碳铬铁不同于金属铬的电氧化过程,它在NaOH溶液中通过Cr(0)→Cr(Ⅵ)的电氧化方式生成铬酸钠,中间产物Cr(OH)₃和Fe(0)发生电化学反应生成稳定的FeCr₂O₄。 随着NaOH浓度的增加,电势较低时,受高碳铬铁中Fe(0)的影响,高碳铬铁容易在NaOH水溶液中发生钝化;当电势足够正时,钝化膜溶解,生成铬酸钠、氢氧化铁和亚铬酸亚铁,同时,阳极表面有氧气析出。 高碳铬铁电化学氧化制备铬酸钠的适宜条件:碱浓度≥2 mol/L,阳极电势≥1.6 V(vs.SCE)。

Electrochemical Oxidation of High Carbon Ferrochrome in Sodium Hydroxide Aqueous Solution

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).