PYRITE OXIDATION AND REDUCTION - MOLECULAR-ORBITAL THEORY CONSIDERATIONS
PYRITE OXIDATION AND REDUCTION - MOLECULAR-ORBITAL THEORY CONSIDERATIONS
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DOI：
10.1016/0016-7037(87)90127-x
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发表时间：
1987-12-01
影响因子：
5
通讯作者：
LUTHER, GW
中科院分区：
文献类型：
--
作者：
LUTHER, GW
利用分子轨道理论方法可以证明黄铁矿氧化和还原的非均相反应机理。该机制表明，氧化剂或还原剂附着在FeS 2表面需要它们有一个空轨道（溶液相）或位置（固相），以将氧化剂或还原剂结合到FeS 2中的S 2− 2中的硫。因此，该方法需要在黄铁矿中的铁与氧化剂（如Fe 3+）或还原剂（如Cr 2+）之间形成过硫化物（二硫化物）桥。氧化过程中的第一个电子转移发生在FeS 2中S 2− 2的π π轨道（最高占据分子轨道，HOMO）到氧化剂的π轨道（最低未占据分子轨道，LUMO）。还原过程中的电子转移是从还原剂的σ π轨道（HOMO）转移到FeS 2中S2 − 2的σ π轨道（LUMO）。两种金属之间通过共同配体（过硫化物）形成的桥和电子转移与内球型机制一致。然而，在FeS 2中，配体S2 − 2充当电子源或电子汇，而不是Fe 2+。电子转移后过硫桥中硫-硫键的强度是理解FeS 2氧化和还原的关键。在氧化过程中，FeS 2表面会形成额外的桥，直到生成初始氧化产物S 2 O 2− 3。建议的机制允许Fe 3+，但不是O2容易黄铁矿氧化。这与实验观察一致。该机制不需要在溶液中形成自由基。它确实预测了黄铁矿表面离子自由基的形成。提出的机制给出了相同的初始中间体（FeS 2 O）最近提出的Moses等人。（1987），但使用分子轨道理论方法解释了氧化剂和随后的FeS 2氧化的可能的表面附着。提出的表面机制与几位研究者的实验观察结果一致（Goldhaber，1983; McKibben和巴恩斯，1986; Wiersma和Rimstidt，1984）。根据黄铁矿的氧化作用和以前关于海洋孔隙水中硫代硫酸盐存在的报道，讨论了硫代硫酸盐形成和与Fe 3+反应的重要性
It is possible to demonstrate a heterogeneous reaction mechanism for both pyrite oxidation and reduction using a molecular orbital theory approach. The mechanism demonstrates that attachment to the FeS 2 surface by an oxidant or reductant requires that they have a vacant orbital (solution phase) or site (solid phase) to bind the oxidant or reductant to a sulfur from S 2− 2 in FeS 2. The approach thus requires the formation of a persulfido (disulfide) bridge between the iron in pyrite and the oxidant (eg Fe 3+) or the reductant (eg Cr 2+). The first electron transfer in oxidation occurs from the π∗; orbital (highest occupied molecular orbital, HOMO) of the S 2− 2 in FeS 2 to the π orbital (lowest unoccupied molecular orbital, LUMO) of the oxidant. Electron transfer in reduction occurs from the σ∗ orbital (HOMO) of the reductant to the σ∗ orbital (LUMO) of the S 2− 2 in FeS 2. The bridge formation between two metals by a common ligand (persulfido), and the electron transfer, is consistent with an inner sphere type mechanism. In FeS 2, however, the ligand S 2− 2 acts as the electron source or sink rather the Fe 2+. The strength of the sulfur-sulfur bond in the persulfido bridge after electron transfer is key to the understanding of FeS 2 oxidation and reduction. Additional bridges can be formed on the FeS 2 surface during oxidation until the initial oxidation product S 2 O 2− 3 is produced. The proposed mechanism allows for facile pyrite oxidation by Fe 3+ but not O 2. This is consistent with experimental observations. The mechanism does not require the formation of a free radical in solution. It does predict the formation of an ion radical on the pyrite surface. The proposed mechanism gives the same initial intermediate (FeS 2 O) as recently proposed by Moses et al.(1987), but explains possible surface attachment by an oxidant and subsequent FeS 2 oxidation using a molecular orbital theory approach. The proposed surface mechanism is consistent with experimental observations of several investigators (Goldhaber, 1983; McKibben and Barnes, 1986; Wiersma and Rimstidt, 1984). The importance of thiosulfate formation and reactivity with Fe 3+ is discussed in light of pyrite oxidation and of previous reports on the presence of thiosulfate in marine porewaters