School of Minerals and Energy Resources Engineering, The University of New South Wales, Sydney, NSW 2052, Australia.
Chemical Engineering Department, Faculty of Engineering and Technology, Chulalongkorn University, Bangkok 10330, Thailand; Department of Physics, School of Science and Engineering, Ateneo de Manila University, Quezon City 1108, Philippines.
Chemosphere. 2019 Oct;233:946-953. doi: 10.1016/j.chemosphere.2019.06.020. Epub 2019 Jun 3.
Scorodite is an important mineral not only for arsenic (As) removal from industrial wastewaters but also in the mobility and final fate of As in waste rocks, contaminated soils and sediments, and mine tailings. Because of the mineral's high As-loading capacity and stability, numerous studies have been done to understand its formation. Unfortunately, most of these studies were limited to elevated temperatures (>70 °C), so the processes involved in scorodite formation under ambient conditions remain unclear. This study provides evidence of the catalytic effects of hematite on the formation of scorodite at 25 °C in a pyrite-rich natural geologic material. Scorodite peaks were detected in the XRD patterns of the leaching residues with and without hematite, but those in the former were stronger and more pronounced than the latter. These results suggest that the formation of scorodite was catalysed by hematite, a generalisation that is further supported by strong characteristic IR absorption bands of scorodite at 819 cm (As-O bending vibration), 785 and 725 cm (As-O stretching vibrations), and 2990 cm (OH-vibration) as well as the distinct XPS binding energies of Fe(III)-As (709.7 eV), As(V)-O (44.8, 44.31 and 43.7 eV), O (530.5 eV) and coordinated water (531.3 eV) in scorodite. This phenomenon could be attributed to three possible mechanisms: (1) more rapid precipitation promoted by the "seeding" effect of hematite particles, (2) additional supply of Fe from hematite dissolution under acidic conditions, and (3) enhanced oxidations of Fe to Fe and As(III) to As(V) on the surface of hematite.
硫砷铁矿不仅是从工业废水中去除砷的重要矿物，而且对废石、污染土壤和沉积物以及尾矿中砷的迁移和最终归宿也具有重要意义。由于该矿物具有高砷负载能力和稳定性，因此已经进行了许多研究来了解其形成过程。不幸的是，这些研究大多数仅限于高温（>70°C），因此在环境条件下形成硫砷铁矿的过程仍不清楚。本研究提供了在富含黄铁矿的天然地质材料中，赤铁矿在 25°C 下催化形成硫砷铁矿的证据。在有无赤铁矿的浸出残渣的 XRD 图谱中都检测到了硫砷铁矿峰，但前者的峰比后者更强且更明显。这些结果表明，硫砷铁矿的形成是由赤铁矿催化的，这一结论得到了进一步的支持，即硫砷铁矿在 819cm（As-O 弯曲振动）、785 和 725cm（As-O 伸缩振动）以及 2990cm（OH-振动）处具有强烈的特征红外吸收带，以及 Fe（III）-As（709.7eV）、As（V）-O（44.8、44.31 和 43.7eV）、O（530.5eV）和配位水（531.3eV）在硫砷铁矿中的独特 XPS 结合能。这种现象可能归因于三种可能的机制：（1）赤铁矿颗粒的“成核”效应促进了更快速的沉淀，（2）在酸性条件下赤铁矿溶解提供了额外的铁，以及（3）在赤铁矿表面促进了 Fe 的氧化为 Fe 和 As（III）氧化为 As（V）。
