BayCEER, Department of Hydrology, University of Bayreuth , D-95440, Bayreuth, Germany.
Environ Sci Technol. 2014 May 6;48(9):5076-84. doi: 10.1021/es405612f. Epub 2014 Apr 23.
Polysulfides are often referred to as key reactants in the sulfur cycle, especially during the interaction of ferric (hydr)oxides and sulfide, forming ferrous-sulphide minerals. Despite their potential relevance, the extent of polysulfide formation and its relevance for product formation pathways remains enigmatic. We applied cryogenic X-ray Photoelectron Spectroscopy and wet chemical analysis to study sulfur oxidation products during the reaction of goethite and lepidocrocite with aqueous sulfide at different initial Fe/S molar ratios under anoxic conditions at neutral pH. The higher reactivity of lepidocrocite leads to faster and higher electron turnover compared to goethite. We were able to demonstrate for the first time the occurrence of surface-associated polysulfides being the main oxidation products in the presence of both minerals, with a predominance of disulfide (S2(2-)(surf)), and elemental sulfur. Concentrations of aqueous polysulfide species were negligible (<1%). With prior sulfide fixation by zinc acetate, the surface-associated polysulfides could be precipitated as zerovalent sulfur (S°), which was extracted by methanol thereafter. Of the generated S°, 20-34% were associated with S2(2-)(surf). Varying the Fe/S ratio revealed that surface polysulfide formation only becomes dominant when the remaining aqueous sulfide concentration is low (<0.03 mmol L(-1)). We hypothesize these novel surface sulfur species, particularly surface disulfide, to act as pyrite precursors. We further propose that these species play an overlooked role in the sulfur cycle.
多硫化物通常被称为硫循环中的关键反应物，特别是在三价（水合）铁氧化物与硫化物相互作用时，形成亚铁硫化物矿物。尽管它们具有潜在的相关性，但多硫化物的形成程度及其对产物形成途径的相关性仍然是个谜。我们应用低温 X 射线光电子能谱和湿化学分析方法，在中性 pH 值、缺氧条件下，研究了针铁矿和纤铁矿与水溶液中的硫化物在不同初始 Fe/S 摩尔比下反应时的硫氧化产物。纤铁矿的高反应性导致电子转化率比针铁矿更快、更高。我们首次证明，在两种矿物存在的情况下，表面结合的多硫化物是主要的氧化产物，其中二硫化物（S2(2-)(surf)）和单质硫占主导地位。水溶液中多硫化物的浓度可忽略不计（<1%）。用醋酸锌预先固定硫化物后，表面结合的多硫化物可以沉淀为零价硫（S°），随后用甲醇提取。生成的 S°中，有 20-34%与 S2(2-)(surf)结合。改变 Fe/S 比表明，只有当剩余的水溶液中硫化物浓度较低（<0.03 mmol L(-1)）时，表面多硫化物的形成才占主导地位。我们假设这些新型的表面硫物种，特别是表面二硫化物，是黄铁矿的前体。我们进一步提出，这些物质在硫循环中扮演了一个被忽视的角色。
