Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Environ Sci Technol. 2012 Aug 7;46(15):8140-7. doi: 10.1021/es301268g. Epub 2012 Jul 18.
The phases and stability of ferric iron products formed early during neutralization of acid mine drainage waters remain largely unknown. In this work, we used in situ and time-resolved quick-scanning X-ray absorption spectroscopy and X-ray diffraction to study products formed between 4 min and 1 h after ferric iron sulfate solutions were partially neutralized by addition of NaHCO(3) ([HCO(3)(-)]/[Fe(3+)] < 3). When [HCO(3)(-)]/[Fe(3+)] = 0.5 and 0.6 (initial pH ∼ 2.1 and 2.2, respectively), the only large species formed were sulfate-complexed ferrihydrite-like molecular clusters that were stable throughout the duration of the experiment. When [HCO(3)(-)]/[Fe(3+)] = 1 (initial pH ∼ 2.5), ferrihydrite-like molecular clusters formed initially, but most later converted to schwertmannite. In contrast, when [HCO(3)(-)]/[Fe(3+)] = 2 (initial pH ∼ 2.7), schwertmannite and larger ferrihydrite particles formed immediately upon neutralization. However, the ferrihydrite particles subsequently converted to schwertmannite. The schwertmannite particles formed under both conditions aggregated extensively with increasing time. This work provides new insight into the formation, stability and reactivity of some early products that may form during the neutralization of natural acid mine drainage.
亚铁铁产品在中和酸性矿山排水时早期形成的阶段和稳定性在很大程度上仍然未知。在这项工作中，我们使用原位和时间分辨快速扫描 X 射线吸收光谱和 X 射线衍射来研究亚铁铁硫酸盐溶液部分中和后 4 分钟至 1 小时内形成的产物，添加的 NaHCO(3)使[HCO(3)(-)]/[Fe(3+)] < 3。当[HCO(3)(-)]/[Fe(3+)] = 0.5 和 0.6（初始 pH 分别约为 2.1 和 2.2）时，形成的唯一大物种是硫酸盐络合的类水铁矿分子簇，在整个实验过程中都很稳定。当[HCO(3)(-)]/[Fe(3+)] = 1（初始 pH 约为 2.5）时，最初形成类水铁矿分子簇，但大多数后来转化为水钠锰矿。相比之下，当[HCO(3)(-)]/[Fe(3+)] = 2（初始 pH 约为 2.7）时，中和后立即形成水钠锰矿和较大的水铁矿颗粒。然而，水铁矿颗粒随后转化为水钠锰矿。在这两种条件下形成的水钠锰矿颗粒随着时间的增加而广泛聚集。这项工作提供了对天然酸性矿山排水中和过程中可能形成的一些早期产物的形成、稳定性和反应性的新见解。
