氢氧化钠水溶液体系中金属铬的电化学氧化过程

铬铁电氧化溶出技术是一种全新的制备铬酸钠的方法,具有反应条件温和、过程可控、工艺环保等优点,然而金属铬在NaOH水溶液中的电化学氧化过程尚不明确. 本文采用循环伏安法（CV）和阳极极化法（LSV）对金属铬在NaOH水溶液中的电化学氧化过程进行研究. 使用EDS、SEM、XRD和XPS对电解前后的金属铬表征,判断中间物的产生,使用紫外可见分光光度计验证电解液中生成了铬酸钠. 结果表明,金属铬和中间产物Cr(OH)₃可能依次发生电化学氧化直接生成Na₂CrO₄,阳极极化为金属铬的活化. 随着NaOH溶液浓度的增加,Cr(OH)₃和Na₂CrO₄的生成量在增加,金属铬电化学氧化制备铬酸钠的适宜条件为碱浓度≥ 2 mol·L^-1,阳极电势≥ 1.6 V（vs. SCE）.

Electrochemical Oxidation of Metal Chromium in odium Hydroxide Aqueous Solution

Ferrochrome electrolysis technology is a novel method for preparing sodium chromate (Na₂CrO₄). Although the method performs well at soft reaction conditions, controllable process, environmentally friendly production process, etc., the electrochemical oxidation process of metal chromium in NaOH aqueous electrolyte is still unclear. At present, there are few research articles about specific electrochemical oxidation of metal chromium in NaOH aqueous electrolyte. It is, therefore, meaningful to carry out the research in electrochemical oxidation mechanism of chromium. The electrochemical oxidation of metal chromium in 0.01 mol·L^-1 ~ 10 mol·L^-1 NaOH aqueous electrolytes at 20 °C was studied by cyclic voltammetry (CV, Scan rate: 100 mV·s^-1) and linear sweep voltammetry (LSV, Scan rate: 1 mV·s^-1) through controlling the potential range. The working electrode (WE) was a chromium rod, the counter electrode (CE) was a platinum sheet, and the reference electrode (RE) was a saturated calomel electrode (SCE). EDS, SEM, XRD and XPS were used to characterize the metal chromium before and after the electrolysis to determine intermediate during electrochemical oxidation. Ultraviolet-visible (UV) spectrophotometer was used to analyze the electrolyte solution after the electrolysis to confirm the formation of Na₂CrO₄. The results indicated that Cr(0) and Cr(OH)₃ might undergo electrochemical oxidations in sequence to directly form Na₂CrO₄. When the anode potential was negative, chromium generated Cr(OH)₃ film through electrochemical oxidation, while hydroxide ions (OH^-) underwent electrochemical oxidation to form oxygen. On the othere hand, when the anode potential was positive, two electrochemical reactions: (1) Cr(0) → Cr(VI); (2) Cr(OH)₃ → Cr(VI) took place. Thus, the anodic polarization included activation of Cr(0). The dissolution reaction of chromium was stimulated by OH^- at a higher concentration of NaOH aqueous solution. Futhremore, the amounts of Cr(OH)₃ and Na₂CrO₄ formed were increased with the increased concentration of NaOH aqueous solutions. At the same time, a large amount of oxygen was deposited on the anode electrode surface with the alkaline concentration ≥ 2 mol·L^-1 and anodic potential ≥ 1.6 V (vs. SCE).