Cerium removal from solution via oxidative precipitation with hydrogen peroxide was investigated in a batch reactor to identify optimum conditions for maximum Ce removal. Tests were performed under ambient temperature at pH 2, 3, 4 and 5, using the exact stoichiometric requirement and 30 % and 50 % excess, respectively. It was found that, unlike the usual direct Ce(OH)4 formation presented in the literature for most oxidants, the reaction with hydrogen peroxide proceeded via a metastable ceric hydroxide, with conversion rates increased by increasing temperature. Standard free energies of reaction were calculated for both routes. To better understand the process, the oxidation of Ce(III) to Ce(IV) and the precipitation of Ce(OH)4 were studied separately via a decoupled approach at low pH and reaction mechanisms for each process were proposed. The Ce(III) oxidation reaction was identified as the rate-limiting step, whereas Ce(IV) precipitation was fast and quantitative. In the pH range of 3–5, Ce removal extents varied between 80 and 95 %, depending on the hydrogen peroxide excess. Following the Ce removal step via oxidative precipitation, it was found that a 2 h ageing stage at 80 °C and pH 2.5 was required to complete the transition of cerium hydroxy-peroxide to the more stable ceric hydroxide and decompose any residual H2O2.

中文翻译：

---

通过过氧化氢氧化沉淀从溶液中分离铈：反应机理


在间歇式反应器中研究通过过氧化氢氧化沉淀从溶液中去除铈，以确定最大程度去除 Ce 的最佳条件。在 pH 2、3、4 和 5 的环境温度下进行测试，分别使用精确的化学计量要求和 30% 和 50% 的过量量。研究发现，与文献中大多数氧化剂通常的直接 Ce（OH）4 形成不同，与过氧化氢的反应通过亚稳态氢氧化铈进行，转化率随着温度的升高而增加。计算两条路线的标准反应自由能。为了更好地了解该过程，在低 pH 值下通过解耦方法分别研究了 Ce（III） 氧化为 Ce（IV） 和 Ce（OH）4 的沉淀，并提出了每个过程的反应机理。Ce（III） 氧化反应被确定为限速步骤，而 Ce（IV） 沉淀是快速且定量的。在 3–5 的 pH 值范围内，Ce 去除率在 80% 到 95% 之间变化，具体取决于过氧化氢过量。在通过氧化沉淀去除 Ce 步骤之后，发现需要在 80 °C 和 pH 2.5 下进行 2 小时的老化阶段，以完成铈羟基过氧化物向更稳定的氢氧化铈的转变并分解任何残留的 H 2 O 2。