Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China.
Environ Sci Technol. 2011 Apr 1;45(7):2704-10. doi: 10.1021/es1033553. Epub 2011 Mar 8.
Interaction of aqueous Se(IV) with pyrite was investigated using persistently stirred batch reactors under O2-free (<1 ppm) conditions at pH ranging from 4.5 to 6.6. Thermodynamic calculations, an increase in pH during the experiments, and spectroscopic observation indicate that the reduction of aqueous Se(IV) by pyrite is dominated by the following reaction: FeS2+3.5HSeO3−+1.5H+=2SO4(2−)+Fe2++3.5Se(0)+2.5H2O. The released Fe(II) was partitioned between the bulk solution and pyrite surface at pH≈4.5 and 4.8, with the Fe2+ density at pyrite-solution interface about 4 orders of magnitude higher than that in the bulk solution, while iron oxyhydroxide precipitated at pH≈6.6, resulting in the decrease of dissolved iron. In the Se(IV) concentration range of the experiments, aqueous Se(IV) reduction rate follows the pseudofirst order which is in the form of ln mSe(IV)=−k′t+ln mSe(IV)0, where k′ is apparent rate constant combining the rate constant k and pyrite surface area to mass of solution ratio (A/M). And the aqueous Se(IV) reduction rate constant for a standard system (k) with 1 m2 pyrite surface area per 1 kg solution was obtained to be 1.65×10(−4) h(−1), 3.28×10(−4) h(−1), and 4.76×10(−4) h(−1) at pH around 4.5, 4.8, and 5.1, respectively. The positive correlation between reaction rate and pH disagrees with the theories that protons are consumed when HSeO3− is reduced to Se0, and negative charge density on pyrite surface increases as pH increases. Thus, a ferrous iron mediated electron transfer mechanism is proposed to operate during the reduction of aqueous Se(IV) by pyrite. pH and iron concentration affect significantly on Se(IV) reaction rate and reaction product.
在无氧（<1 ppm）条件下，使用持续搅拌的分批反应器研究了水相中 Se(IV)与黄铁矿的相互作用，pH 值范围为 4.5 至 6.6。热力学计算、实验过程中 pH 值的升高以及光谱观察表明，黄铁矿还原水相中的 Se(IV)主要由以下反应主导：FeS2+3.5HSeO3−+1.5H+=2SO4(2−)+Fe2++3.5Se(0)+2.5H2O。在 pH≈4.5 和 4.8 时，释放的 Fe(II)在溶液主体和黄铁矿表面之间分配，黄铁矿-溶液界面处的 Fe2+密度比溶液主体高约 4 个数量级，而在 pH≈6.6 时则形成铁的氢氧化物沉淀，导致溶解铁的减少。在实验的 Se(IV)浓度范围内，水相中 Se(IV)的还原速率遵循准一级反应形式，即 ln mSe(IV)=−k′t+ln mSe(IV)0，其中 k′是表观速率常数，结合了速率常数 k 和黄铁矿表面积与溶液质量比 (A/M)。对于标准体系（k），获得了 1 m2 黄铁矿表面积/1 kg 溶液的水相中 Se(IV)还原速率常数为 1.65×10(−4) h(−1)、3.28×10(−4) h(−1)和 4.76×10(−4) h(−1)，分别在 pH 约为 4.5、4.8 和 5.1 时。反应速率与 pH 值之间的正相关与 HSeO3−还原为 Se0 时消耗质子以及黄铁矿表面负电荷密度随 pH 值增加而增加的理论不符。因此，提出了一个亚铁离子介导的电子转移机制，用于黄铁矿还原水相中 Se(IV)的过程。pH 值和铁浓度对 Se(IV)反应速率和反应产物有显著影响。
