Oxidative Dissolution of Orpiment and Realgar Induced by Dissolved and Solid Mn(III) Species
Oxidative Dissolution of Orpiment and Realgar Induced by Dissolved and Solid Mn(III) Species
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DOI：
10.1016/j.gca.2022.06.028
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发表时间：
2022-06
影响因子：
5
通讯作者：
Xingxing Wang;Jiajia Wang;Xiaona Lu;M. Zhou;Qihuang Wang;Z. Pan;Naresh Kumar;M. Zhu;Zimeng Wang
中科院分区：
文献类型：
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作者：
Xingxing Wang;Jiajia Wang;Xiaona Lu;M. Zhou;Qihuang Wang;Z. Pan;Naresh Kumar;M. Zhu;Zimeng Wang
地下环境中锰、砷、硫和氧之间复杂的氧化还原耦合的透彻理解仍然被它们的亚稳中间价态和形态所掩盖。硫化砷矿物可能受到自然或人为活动的干扰，并遇到氧化剂，如氧气和活性三价锰物种，以及这些非生物相互作用如何影响矿物溶解和砷和硫物种的转化，仍然是未知的。研究了缺氧和好氧条件下溶解态Mn（III）和锰氧化物（γ-MnIIIOOH）对雌黄（As 2S 3）和雄黄（AsS）溶解行为的影响。补充控制实验也进行了溶解的亚砷酸盐没有还原硫。氧，溶解锰（III）或亚锰酸盐没有引起溶解的亚砷酸盐在几个星期内的氧化。雌黄的初始溶解是一个非氧化还原过程，释放出砷和硫化物，三种氧化剂通过快速氧化溶解的硫化物促进雌黄的溶解。然而，只有当溶解锰（III）和溶解氧都存在，大量积累的砷酸盐和硫酸盐观察。这些结果表明硫物种在砷的非生物转化过程中起着关键作用，锰和氧对硫的氧化有协同作用。与雌黄不同，雄黄的溶解是一个氧化还原反应，包括As（II）氧化为As（III）和硫化物的直接释放，溶解氧和锰氧化物都能促进雄黄的溶解。在雄黄的溶解过程中，也清楚地观察到溶解的Mn（III）和氧对砷酸盐和硫酸盐形成的影响。尽管在溶解的Mn（III）和氧的存在下溶解的亚砷酸盐缓慢非生物氧化为砷酸盐，硫化物的共存可以使砷酸盐快速积累，伴随着大量转化为硫酸盐。在这些实验中的硫代砷物种的证据提供了一个合理的解释，作为一个替代途径的两种元素的氧化溶解锰（III）。这些结果为Mn-As-S在氧化还原过渡环境中的循环提供了新的见解。
A thorough understanding of the complex redox coupling among manganese, arsenic, sulfur and oxygen in subsurface environments is still obscured by their metastable intermediate valances and speciation. Arsenic sulfide minerals may be disturbed by natural or anthropogenic activities, and encounter oxidants such as oxygen and reactive trivalent Mn species, and how these abiotic interactions impact the mineral dissolution and transformation of arsenic and sulfur species, remains unknown. In this study, we investigated the effects of dissolved Mn(III) and manganite (γ-MnIIIOOH) on the dissolution behaviors of orpiment (As2S3) and realgar (AsS) under anoxic and oxic conditions. Complementary control experiments were also performed with dissolved arsenite without reduced sulfur. Oxygen, dissolved Mn(III) or manganite did not induce the oxidation of dissolved arsenite within several weeks. Orpiment’s initial dissolution is a non-redox process releasing of arsenite and sulfide, and the three above oxidants promoted the dissolution of orpiment by rapid oxidation of dissolved sulfide. However, only when both dissolved Mn(III) and dissolved oxygen were present, substantial accumulation of arsenate and sulfate were observed. These results suggested the critical role of sulfur species in abiotic arsenic transformation and a synergetic effect of Mn and oxygen on sulfur oxidation. In contrast to orpiment, the dissolution of realgar was a redox reaction that involved the oxidation of As(II) to As(III) and the direct releasing of sulfide, which could be promoted by both dissolved oxygen and manganite. The effect of dissolved Mn(III) and oxygen on the formation of arsenate and sulfate was also clearly observed during the dissolution of realgar. Despite of the slow abiotic oxidation of dissolved arsenite to arsenate in the presence dissolved Mn(III) and oxygen, the coexistence of sulfide could enable rapid accumulation of arsenate, accompanied by substantial transformation to sulfate. The evidence of thioarsenic species in these experiments provided a plausible explanation as an alternative pathway for the oxidation of the two elements by dissolved Mn(III). These results provide new insights for the Mn-As-S cycling in redox transition environments.