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砷在天然环境中的迁移富集与氧化还原状态密切相关.盆地环境地下水中砷的活化迁移机制主要为沉积物中铁/锰氢氧化物由氧化还原条件变化导致发生还原性溶解进而释放吸附在其表面的砷.钼及钼同位素为氧化还原环境的重要指示参数,且铁/锰氢氧化物对钼同位素分馏有着重要的控制作用.将地下水的钼同位素应用于砷的活化迁移规律研究.大同盆地地下水中钼同位素比值(δ98 Mo)范围为-0.12‰~+2.17‰,相比于淡水中钼同位素组成偏重.桑干河河水的δ98 Mo为+0.72‰,与文献报道的河水平均钼同位素比值+0.7‰相当.大同盆地地下水中δ98 Mo与硫化物之间存在正相关关系,表明MoFe-S复合物可能形成于特定条件下,并优先利用水溶液中轻的钼使地下水中δ98 Mo比值升高.砷浓度与钼浓度之间的微弱负相关以及砷浓度与钼同位素之间的正相关说明,Mo-Fe-S的形成过程可能与同环境中As-Fe-S的复合物的形成存在竞争关系,进而使得地下水中砷富集.地下水中相对偏高的δ98 Mo可能来源于铁的氢氧化物对溶液中轻的钼的吸附速率高于先前吸附在铁的氢氧化物的钼的释放,且铁的氢氧化物对水溶液中钼的再吸附这一循环过程会导致地下水中钼浓度降低及钼同位素比值的升高.钼同位素指示的循环性的铁的氢氧化物的还原溶解及再氧化过程对砷的富集也有重要影响.
The migration and enrichment of arsenic in natural environment is closely related to the redox state.The mechanism of arsenic activation and migration in groundwater in the basin is mainly that the iron / manganese hydroxide in the sediment undergoes reductive dissolution and then is released and adsorbed in the iron / manganese hydroxide due to the redox conditions Surface arsenic, molybdenum and molybdenum isotopes are important indicators of the redox environment, and iron / manganese hydroxide plays an important role in the control of molybdenum isotope fractionation.The application of molybdenum isotopes of groundwater to the study of the activation and migration of arsenic in the Datong Basin The molybdenum isotope ratio (δ98 Mo) in groundwater ranged from -0.12 ‰ to + 2.17 ‰, which was more than molybdenum isotope composition in freshwater. Δ98 Mo of the Sanggan River was +0.72 ‰, which was consistent with the reported molybdenum isotope ratio + 0.7 ‰ .The positive correlation between δ98 Mo and sulfide in the groundwater in the Datong Basin indicates that the MoFe-S complex may form under certain conditions, and the use of light molybdenum in aqueous solution to make the δ98 Mo ratio in groundwater higher .The weak negative correlation between arsenic concentration and molybdenum concentration and the positive correlation between arsenic concentration and molybdenum isotope indicate that the formation of Mo-Fe-S may be related to the same ring As-Fe-S complex formation in the competition, and thus make groundwater arsenic enrichment.Cumulative groundwater in the relatively high δ98Mo may be derived from iron hydroxide on the solution of light molybdenum adsorption rate higher than The release of molybdenum, previously adsorbed on iron hydroxides, and the recycle of iron hydroxide to molybdenum in aqueous solution, leads to a decrease in molybdenum concentration in groundwater and an increase in molybdenum isotope ratios. The reductive dissolution and reoxidation of the iron iron hydroxide also have a significant effect on arsenic enrichment.