Characteristics of Rare Earth Elements in

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Procedia Earth and Planetary Science 7 (2013) 940 – 943

Water Rock Interaction [WRI 14]

Characteristics of rare earth elements in groundwaters along the flow path in the North China Plain Yanhong Zhan, Huaming Guo*, Lina Xing School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing 100083, P.R. China

Abstract Groundwater samples collected along the flow path in the North China Plain (NCP) were analyzed for the rare earth elements (REEs), as well as other elements (Fe, Mn, Ba). Results showed that the concentration of total REEs gradually decreased from alluvia fans (Zone I), through alluvial plain (Zone II), to the coastal area (Zone III), which is likely controlled by contaminants due to human activities. Distribution patterns of REEs are different between Zone I and Zone II, while the distribution pattern of REEs in Zone III is similar to that of Zone II. The distribution patterns of REEs in the different zones may be affected by redox conditions, pH, hydraulic characteristics in the groundwater, and mineral composition of the aquifer sediments. © 2013 2012The TheAuthors. Authors. Published by Elsevier B.V.access under CC BY-NC-ND license. © Published by Elsevier B.V. Open Selectionand/or and/or peer-review under responsibility of Organizing and Scientific Committee of –WRI Selection peer-review under responsibility of the Organizing and Scientific Committee of WRI 14 201314 - 2013 Key words: The North China Plain; rare earth elements; NASC-normalized pattern; controls.

1. Introduction REEs have unique geochemical properties, which are stable and similar between different REEs, with a low solubility. As a result of weak differences between REEs, enrichment or loss can take place in the process of weathering, denudation, transport, re-deposition and diagenesis [1]. More and more researchers are using REEs in their study of groundwater, especially in study of water-rock interaction [2]. The existing studies mainly focused on shallow groundwater in a single hydrogeologic condition. However, studies of REEs in deep groundwater or in more complexes hydrogeologic conditions have not got enough attention. The North China Plain (NCP) is located in the east of China, with an area of 13.9×104 km2. According to hydrogeological settings, groundwater chemistry, and topography, the NCP can be divided into three zones, including piedmont alluvial fan-recharge zone (Zone I), central alluvial plainintermediate zone (Zone II), and coast plain-discharge (zone III) (Fig.1) [3]. Owing to continuous exchanges between shallow and deep groundwater, and exchanges between deep groundwater in different aquifers, a complex and interconnected groundwater system formed in the NCP. The Quaternary aquifers are divided into shallow and deep groundwater systems according to characteristics of groundwater system and hydrogeological settings. Underlying aquitards of shallow

* Corresponding author. Tel.: +86-10-82321366; fax: +86-10-82321081. E-mail address: [email protected].

1878-5220 © 2013 The Authors. Published by Elsevier B.V. Open access under CC BY-NC-ND license. Selection and/or peer-review under responsibility of the Organizing and Scientific Committee of WRI 14 – 2013 doi:10.1016/j.proeps.2013.03.173

Yanhong Zhan et al. / Procedia Earth and Planetary Science 7 (2013) 940 – 943

groundwater system are generally 40~60 m below land surface (BLS) (120~150 m BLS in Zone I for the intense human activities), when that of deep groundwater are generally 140~180 m BLS in Zone I and 140~380 m BLS in Zone II [4].

Fig.1. Locations of samples and profiles of study area

2. Methodology/Methods Eighty-five groundwater samples were collected along the flow path (Profile B-B′, as is shown in Fig.1), extending from Shijiazhuang through Hengshui to Tanggu, with a length of about 380 km, including twenty-eight samples from shallow aquifers, and fifty-seven from deep. Zone I of profile B-B′ mainly consists of Hutuo River alluvial deposits with coarse particles, alluvial sediments of Zone II is characterized by fine sand, silt, silty clay and lacustrine sediments, and alluvial sediments of Zone III is composed of lacustrine deposits and marine sediments. In general, groundwater flows from west and southwest to northeast [5]. Parameters including total dissolved solids, temperature, dissolved oxygen, pH, Eh and Electric Conductivity (Ec), and alkalinity were measured with a multi-parameter instrument (HANNA, HI 9828) in field. Water samples for major and trace elements were filtered through 0.45-μm filters and acidified (cations and trace elements) with 6 M HNO3 on situ. Concentrations of major cations were analyzed by ICP-AES (ICAP 6300, Thermo), trace elements and REEs by ICP-MS (7500C, Agilent), unacidified anions by ion chromatography (ICS-1000; Dionex). 3. Results 3.1. REE concentrations Total REEs concentration of shallow groundwater, which ranged from 0.083 to 0.448 μg/L and had an average of 0.122 μg/L, was higher than that of deep groundwater, which ranged from 0.067 to 0.327μg/L and had an average of 0.109 μg/L. Concentration of Ce is the highest both in shallow and deep groundwater, with an average of 0.057 μg/L and 0.055 μg/L respectively, while concentration of Eu is low, with an average of 0.004 μg/L and 0.002 μg/L respectively. Generally, total concentration of REEs decreases from Zone I to Zone III. 3.2. NASC-normalized REE patterns The data were normalized to the estimated average composition of the North American Shale Composite (NASC), showing that both shallow and deep groundwater were enriched in heavy rare earth elements (HREEs) and depleted in light rare earth elements (LREEs). Ratios of [Gd/Yb]NASC, [Er/Nd]NASC

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and [La/Yb]NASC in deep groundwater ranged from 0.596 to 3.577 (average 1.528), from 0.693 to 4.853 (average 2.398) and from 0.338 to 2.034 (average 0.950), respectively. All groundwater samples had positive Ce anomalies (Ce/Ce*=CeNASC / ([La]NASC*[Pr]NASC )0.5), with ratios of Ce/Ce* ranging from 1.082 to 2.736 for shallow groundwater and from 1.260 to 2.614 for deep groundwater. Except for few samples in Zone I and Zone II, most of samples in shallow groundwater had positive Eu anomalies (Eu/Eu*=EuNASC /([Sm]NASC*[Gd]NASC )0.5), with ratios of Eu/Eu* ranging from 0.681 to 48.121. All samples in deep groundwater had positive Eu anomalies, with ratios of Eu/Eu* between 1.021 and 30.246. There are differences between normalized curves with respect to the estimated average composition of North American Shale Composite (NASC) for samples in Zone I, Zone II and Zone III. As shown in Fig.2, trends of normalized curve for Zone I and Zone II are obviously different, while those for Zone II and Zone III are more or less the same.

Fig.2. NASC-normalized REE patterns for the shallow groundwaters along profile B-B′ in Zone I (a), Zone II (b) and Zone III (c).

4 Discussions 4.1 Controls on REE concentrations Total concentration of REEs may be affected by redox condition, pH, complexation, and adsorption or complexation of Fe/Mn hydroxides. In reducing condition, Fe/Mn hydroxides would be reduced and dissolved, releasing the adsorbed REEs. On the contrary, in oxic condition, Fe/Mn hydroxides are stable, and tend to adsorb the REEs. But, the correlations between total concentration of REEs and Fe, and Mn are not significant, which may be the result of Fe (II) adsorption or complexation in reducing condition [6]. The correlation between total concentration of REEs and pH is also poor, which means pH is not the main factor controlling REEs. Some studies showed that concentrations of REEs in groundwater were similar to those of the rocks along the groundwater path [7]. As observed, concentrations of REEs in shallow groundwater were higher than those in deep groundwater, possibly resulting from the difference in REEs between deep aquifer sediments and shallow aquifer sediments. The REEs data of the aquifer sediments will attest the hypothesis exposed later. There is more phosphate in Zone III than Zone II and Zone I due to human activities, which may lead to precipitation of REEs with phosphate [8] and decrease of the REEs concentrations from Zone I to Zone III. 4.2 Controls on REEs patterns According to Eh values, samples were mostly under oxic condition and Fe/Mn hydroxides tend to adsorb LREEs first, leading to the HREEs enrichment in groundwater. Moreover, some studies reported that HREEs can form stronger complex than LREEs [9], which has boosted HREEs’ migration, leading to the enrichment of HREEs in groundwater.


In oxic condition, Ce3+ would be oxidized to Ce4+ and adsorbed by Fe/Mn hydroxides, leading to the loss of Ce. In reducing condition, Ce4+ would be restored to Ce3+, resulting in Ce enrichment in the groundwater. However, the studied samples have positive Ce anomalies in oxic condition. This can be related to the sediment composition along the groundwater path, which means the groundwater may inherit Ce enrichment from rocks along the flow path [10]. There are two forms of Eu in groundwater: Eu3+ in oxic condition and Eu2+ in reducing condition. Eu3+ is easily dissolved, leading to positive Eu anomalies, while Eu2+ tends to have isomorphism replacement with Ca2+, resulting in Eu anomalies positive [11]. The NASC-normalized patterns of REEs were different between Zone I and Zone II, while those of Zone II were similar to Zone III. Apart from redox condition, pH, and aquifer sediments, distribution of REEs may also be affected by hydraulic conditions. Closely hydraulic connection existed between Zone II and Zone III, evidenced by the similar REES patterns. 5. Conclusion Hydrologic connections between different zones play an important role in affecting the NASCnormalized patterns of REEs. Zones that have a good hydrologic connection would have a similar pattern, while zones with a poor hydrological connection would distinguish from each other by different NASCnormalized patterns. Redox conditions not only affect the enrichment of HREEs, but are also responsible for positive Ce and Eu anomalies. Aquifer sediments may also affect REEs concentrations and patterns. Acknowledgements The study was financially supported by the National Basic Research Program of China (the 973 program, No. 2010CB428804) and the National Natural Science Foundation of China (Nos. 41172224 and 40872160). References [1] Gui Herong, Sun Linhua. Rare earth element geochemical characteristics of the deep underground water from Renlou Coal Mine, Northern Anhui Province. Journal of China Coal Sociey 2011; 36: 210-216. [2] Jansen RPT, Verweij W. Geochemistry of some rare earth elements in groundwater, Vierlingsbeek, the Netherlands. Water Research 2003; 37: 320-350. [3] Liu FY, Cui JH et al. A View on Geomorphologic Zonalization of North China Plain. Geography and Geo-Information Science 2009; 4: 100-103. [4] Guo YH, Liu FS et al. The Formation Law of Deep-lying Groundwater Resources in Areas of Jingjin in the Hebei Plain. Geological Review 1996; 9: 411-415. [5] Zhang ZJ, Fei YH. Atlas of groundwater sustainable utilization in North China Plain. Beijing: Sinomap Press; 2009; 37-123. [6] Guo HM, Zhang B et al. Geochemical controls on arsenic and rare earth elements approximately along a groundwater flow path in the shallow aquifer of the Hetao Basin, Inner Mongolia. Chemical Geology 2010; 117–125. [7] Fee JA, Gaudette HE, Lyons WB et al. Rare earth elements distribution in lake Tyrrell groundwaters, Victoria, Australia. Chemical Geology 1992; 96: 67-93. [8] Nelson BJ, Wood SA, Osiensky JL. Partitioning of REE between solution and particulate matter in natural waters: a filtration study. Journal of Solid State Chemistry 2003; 171: 51-6. [9] Ward CD. Rare earth element mobility and fractionation during weathering of the Dartmoor granite, southwest England. In: Olafsson J, editor. Proceedings 5th International Symposium on Water-Rock Interaction. Reykjavik, Iceland; 1986. [10] Smedley PL. The geochemistry of rare earth elements in groundwater from the Carnmenellis area, southwest England. Geochimica et Cosmochimica Acta 1991; 55: 2767-2779. [11] Ren Yaowu. The evolutionary characteristics of the rare earth elements and application in the geology. He Nan Geology 1998; 16: 303-308.

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