The long-term stability of calcium arsenates: Implications for phase transformation and arsenic mobilization
The long-term stability of calcium arsenates: Implications for phase transformation and arsenic mobilization
复制标题
砷酸钙的长期稳定性：对相变和砷迁移的影响
DOI：
10.1016/j.jes.2019.04.017
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发表时间：
2019
影响因子：
6.9
通讯作者：
Jia Yongfeng
中科院分区：
文献类型：
--
作者：
Zhang Danni;Wang Shaofeng;Wang Ying;Gomez Mario A.;Jia Yongfeng
众所周知，砷酸钙在湿法冶金实践中可能不是一个很好的脱砷和固定砷的选择。然而，由于各种原因，它们仍然在世界上的一些工厂生产。此外，砷酸钙在某些特定环境下也会自然沉淀。然而，低结晶砷酸钙（PCCA）的转化过程和这些样品在大气CO2下的稳定性尚未得到很好的理解。本文研究了在大气CO2存在下，不同Ca/As摩尔比的中和剂（CaO与NaOH）在pH 7-12条件下生成的PCCA的转化过程。在室温下老化一段时间后，对于用NaOH中和并在pH 10和12下沉淀的样品，发生砷释放回到液相中。相反，对于在pH 8下沉淀的样品，观察到砷的水溶液浓度降低。XRD、拉曼和SEM结果表明，各种类型的结晶碳酸钙和/或砷酸钙的形成控制了砷的行为。此外，石灰的应用可以增强生成的PCCA的稳定性。然而，无论使用何种中和剂，生成的PCCA的稳定性仍然令人担忧。
It is well known that calcium arsenates may not be a good choice for arsenic removal and immobilization in hydrometallurgical practices. However, they are still produced at some plants in the world due to various reasons. Furthermore, calcium arsenates can also naturally precipitate under some specific environments. However, the transformation process of poorly crystalline calcium arsenates (PCCA) and the stability of these samples under atmospheric CO2are not yet well understood. This work investigated the transformation process of PCCA produced by using different neutralization reagents (CaO vs. NaOH) with various Ca/As molar ratios at pH 7–12 in the presence of atmospheric CO2. After aging at room temperature for a period of time, for samples neutralized with NaOH and precipitated at pH 10 and 12, release of arsenic back into the liquid phase occurred. In contrast, for the samples precipitated at pH 8, the aqueous concentration of arsenic was observed to decrease. XRD, Raman, and SEM results suggested that the formation of various types of crystalline calcium carbonates and/or calcium arsenates controls the arsenic behavior. Moreover, the application of lime may enhance the stability of the generated PCCA. However, no matter what neutralization reagent is used, the stability of the generated PCCA is still of concern.