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宁夏银川平原是继河套平原之后,在黄河流域发现的又一个高砷地下水分布区.为了总结其高砷地下水的水化学特征,并探索水化学因素对地下水砷释放和富集的影响机制,本文以银川平原北部(银北平原)作为典型研究区,采取野外水文地质调查、水样采集与测试、砷与水化学组分散点图相关分析及水文地球化学方法进行了综合研究.结果表明,银北平原地下水砷含量在0.2~177μg/L之间;高砷地下水(大于50μg/L)pH值多在7.5~8.5,水化学类型主要为HCO_3-Na·Ca、Cl·HCO_3-Na及Cl·HCO_3-Na·Ca型,E_h多在-200~-100 mV.银北平原砷含量较高的地下水中COD、NH_4、HCO_3含量相应也较高,而NO_3和SO_4含量较低.高砷富有机质的冲-湖积含水层经过长期演化,形成偏碱性的中强还原性地下水环境和特殊的水化学特征,也具备极大的砷释放能力.较高的pH导致砷从铁锰氧化物或氢氧化物等水合物或黏土矿物表面解吸.其次部分铁锰氧化物在高pH、低E_h条件下可被还原为低价态可溶性铁锰,从而使与其结合的砷也得以释放进入地下水中.此外重碳酸根与砷酸根、亚砷酸根的竞争吸附行为促使含水层砷的解吸.
Yinchuan Plain in Ningxia is another high-arsenic groundwater distribution area found in the Yellow River Basin after the Hetao Plain.In order to summarize the hydrochemical characteristics of the high-arsenic groundwater and explore the mechanism of water chemistry affecting the release and enrichment of arsenic in groundwater, Taking the northern part of Yinchuan Plain (Yinbei Plain) as a typical study area, the field hydrogeological survey, water sample collection and testing, the scatter diagram correlation analysis of arsenic and water chemical components and hydrogeochemical methods were conducted to study the results. The arsenic content of groundwater in the northern plain ranged from 0.2 to 177 μg / L. The pH value of high-arsenic groundwater (more than 50 μg / L) was mostly in the range of 7.5-8.5. The main chemical types of water were HCO 3 Na Na, Cl HCO 3 Na and Cl HCO_3-Na · Ca, and E_h mostly ranged from -200 to -100 mV. The contents of COD, NH_4 and HCO_3 in groundwater with higher arsenic content in Yinbei Plain are higher, while the contents of NO_3 and SO_4 are lower. - The lacustrine aquifers have evolved over a long period of time to form an alkaline, moderately strong reducing groundwater environment and have special hydrochemistry characteristics and also have great arsenic release capacity. Higher pH results in the removal of arsenic from the ferromanganese oxide or hydroxide Other hydrates or clay minerals Surface desorption.The second part of the iron-manganese oxide can be reduced to low-priced soluble iron-manganese under high pH and low E_h conditions, so that the arsenic bound to it can also be released into the groundwater.In addition, bicarbonate and arsenate, Competitive adsorption of arsenate promotes desorption of arsenic in aquifers.