Characteristics of hydrochemical distribution of mineral water in Huangshui River Catchment and source analysis of threshold value elements
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摘要: 天然矿泉水不仅是宝贵的矿产资源,还能够为地表水环境系统(例如湿地与河岸带)提供补给水源,在保持生态系统多样化方面扮演重要角色。发源于青海省海晏、湟源的湟水河流域内发现了大量富锶矿泉水,少量泉水同时富含锂和偏硅酸。然而,目前对矿泉水中这些界限指标的来源及其相关水化学演化过程尚缺乏研究,同时个别采样点存在限量指标超标的情况,直接影响了矿泉水的开发利用,是目前亟待解决的问题。本文以青海湟水河流域为研究区,通过采集流域内天然泉水样品,采用水文地球化学分析及物质迁移模拟方法揭示矿泉水水化学特征与成因机制,这对理解湟水河流域地下水水化学演化过程具有重要意义。研究区地下水样品中大部分达到了国家饮用天然矿泉水的标准,且锶含量全部大于0.2 mg/L,少数样品富含锂和偏硅酸。水化学分析结果表明,地下水从补给区到排泄区,其水化学类型逐渐从HCO3-Ca·Mg型过渡到SO4-Na型,这是地下水在运移过程中不断溶解石膏层的结果。从Sr与HCO3-、SO42-和Cl-的相关性分析中可以看出,碳酸盐岩对地下水Sr含量的贡献程度有限;相反,由于Ca与Sr化学性质相似,在矿物中易发生原子交换,从而石膏层或蒸发岩类矿物中可能富集含Sr矿物,此类岩层在水岩作用下会释放一定量的Sr。地下水中锂的来源主要与古咸水湖沉积环境有关,过量的偏硅酸则来源于地热水在深循环过程中溶滤的铝硅酸盐矿物。通过物质迁移模拟分析发现,在北部流径上,地下水主要溶解石膏、石盐和伊利石,而天青石和锂辉石的溶解贡献了锶和锂;在南部流径上,石膏和石盐的溶解导致高TDS值,且去白云石化过程显著。研究成果能够为矿泉水资源的合理开发利用和保护提供科学依据。Abstract: Natural mineral water is not only a kind of valuable mineral resource, but also a water supply source for surface water system (e.g., wet land and riparian zone), which is critical for keeping the biological diversity. A large amount of strontium-rich mineral water has been discovered in the Huangshui River catchment, which originates in Haiyan and Huangyuan, Qinghai Province, with a few springs also containing lithium and metasilicic acid. However, the study on the genesis of threshold-value elements and the related hydrochemical evolution processes are rare. In addition, some sampling points have exceeded the threshold value, which directly affects the development and utilization of mineral water and is an urgent problem that needs to be solved. In this study, the Huangshui River Catchment was considered as a target area. Hydrogeochemical and modeling methods were employed to uncover the hydrochemical features and genesis of mineral water by collecting spring samples from the catchment, which can play an important role in understanding the hydrogeochemical processes within the groundwater system in the Huangshui River Catchment. Most of the groundwater samples in this study area reach the standards of the National Drinking Natural Mineral Water, and all the strontium concentration is higher than 0.2 mg/L with a few samples being rich in lithium and metasilicic acid. The Hydrogeological result shows that the groundwater moving from recharge area to discharge area has a transition of hydrochemical type from HCO3-Ca·Mg to SO4-Na, which is the result of gypsum dissolving in groundwater. The relationships between Sr and the major anions such as HCO3-、SO42- and Cl- show that carbonates have a limited contribution on Sr concentration in groundwater. Instead, the gypsum layers may contain a certain number of Sr-bearing minerals because of the atom exchange between Ca and Sr. Those Sr-bearing minerals are responsible for the high concentration of Sr in groundwater. In terms of the genesis of Li and Si in groundwater, the ancient salt lake sedimental environment may explain the former one and the dissolving of aluminumsilicate minerals may explain the latter. The inverse modeling shows that the groundwater mainly dissolves gypsum, rock salt and illite, while the dissolution of azurite and lithium pyroxene contributes strontium and lithium in the northern catchment. The dissolution of gypsum and halite leads to the high TDS of groundwater in the southern catchment, combined with the dedolomitization process. The whole research findings can serve as scientific basis for exploration and preservation of mineral waters.
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