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-Mn^IIIOOH) 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, 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.

对地下环境中锰、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态中间价和物种形成所掩盖。硫化砷矿物可能会受到自然或人为活动的干扰，并会遇到氧气和活性三价锰等氧化剂，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，目前尚不清楚。在本研究中，我们研究了溶解的 Mn(III) 和亚锰酸盐 (γ-Mn ^III OOH) 对雌蕊 (As ₂ S _{3 ) 溶解行为的影响。}) 和雄黄 (AsS) 在缺氧和好氧条件下。还用不减少硫的溶解亚砷酸盐进行了补充对照实验。氧气、溶解的 Mn(III) 或亚锰酸盐在几周内不会引起溶解的亚砷酸盐的氧化。雌蕊的初始溶解是亚砷酸盐和硫化物释放的非氧化还原过程，上述三种氧化剂通过溶解硫化物的快速氧化促进雌蕊的溶解。然而，只有当溶解的 Mn(III) 和溶解氧都存在时，才观察到砷酸盐和硫酸盐的大量积累。这些结果表明硫物质在非生物砷转化中的关键作用以及锰和氧对硫氧化的协同作用。与雌蕊相比，雄黄的溶解是一种氧化还原反应，涉及 As(II) 氧化为 As(III) 和硫化物的直接释放，溶解氧和锰酸盐均可促进硫化物的释放。在雄黄溶解过程中也清楚地观察到溶解的 Mn(III) 和氧气对砷酸盐和硫酸盐形成的影响。尽管溶解的亚砷酸盐在溶解的 Mn(III) 和氧气存在下缓慢非生物氧化为砷酸盐，但硫化物的共存可以使砷酸盐快速积累，并伴随大量转化为硫酸盐。这些实验中硫砷物种的证据提供了一个合理的解释，作为溶解的 Mn(III) 氧化两种元素的替代途径。这些结果为氧化还原过渡环境中的 Mn-As-S 循环提供了新的见解。