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Article

Influence of Mineral Deposition on the Retention of Potentially Hazardous Elements in Geothermal Spring Sediments

by
Yafeng Wang
and
Hefa Cheng
*
MOE Key Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China
*
Author to whom correspondence should be addressed.
Sustainability 2023, 15(10), 8040; https://doi.org/10.3390/su15108040
Submission received: 15 March 2023 / Revised: 3 May 2023 / Accepted: 13 May 2023 / Published: 15 May 2023
(This article belongs to the Special Issue The Generation, Migration and Transformation, Impact Assessment, Prevention and Control Measures of Heavy Metals to Environmental Pollution)
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Abstract

:
Geothermal springs are known to contain a variety of potentially hazardous elements (PHEs), which may threaten human health. Their release on Earth’s surface is largely dependent on the retention by the sediments at the spring outflux. In this study, the hot spring waters and the sediments at the corresponding sites were collected from the Nagqu geothermal field on the Tibetan Plateau. The water geochemistry and sediment mineralogy were analyzed using inductively coupled plasma mass spectrometry (ICP-MS), X-ray fluorescence (XRF), and X-ray diffraction (XRD). The association of PHEs with minerals was analyzed. The results indicate that while the concentrations of PHEs were highly elevated, Be, As, and Tl in some hot springs exceeded the criteria for class III groundwater in China by up to 2, 2, and 19 times, respectively. Cs occurred at relatively high levels, up to 776 μg/L. As, Co, Se, Tl, and U in the hot spring waters were probably captured by iron sulfide minerals in the sediments, while Be and Cs were strongly retained by the carbonate minerals. The releases of V and Cr were apparently regulated by the clay minerals. Overall, the mobility of PHEs from the geothermal springs is controlled by the deposition of minerals at the spring vents.

1. Introduction

Geothermal springs, which are mainly distributed in areas with active geological and structural activities [1,2], are widely developed for power generation and directly used for bathing by the local residents [3]. However, concerns regarding environmental and health risks have gradually emerged along with the rapid development of geothermal energy [4,5]. Because of the contact with the geological formation overlying the reservoir and the input of volatile matter from the magma, the hot spring water might be polluted by a variety of hazardous and toxic materials [6,7,8,9,10,11,12]. The release of hazardous and toxic components, such as heavy metals and hydrogen sulfide, from the geothermal springs could result in the contamination of the surrounding environment [5,13]. The pollution of surface water, groundwater, soil, and crops by geothermal activities has been widely reported [14,15,16,17]. In particular, the potentially hazardous elements (PHEs), including heavy metals from the geothermal springs, deserve attention because excessive exposure to them through water and food consumption could pose unacceptable human health risks [18,19,20,21,22,23,24].
The partitioning of the dissolved PHEs in aquatic environments is geochemically and mineralogically controlled. The declined temperature and pressure of geothermal water on the Earth’s surface result in the precipitation of the dissolved PHEs in various forms [25]. The PHEs from the geothermal sources are mainly discharged into the surface water, while some fractions of them are retained by the hot spring sediments. In the geothermal systems, some elements, such as Ca and Si, are dissolved under the high-temperature and high-pressure environment [26]. These elements, when occurring at elevated concentrations, can precipitate to form sinter after the hot spring water flows to the Earth’s surface [26,27,28]. For example, hydrothermal carbonate deposits, travertines, often form at the geothermal vents due to the degassing of CO2 [29,30,31]. Siliceous sinters, such as opaline silica deposits, are also frequently found at geothermal vents [32,33]. The transfer of elements from the hot spring water to the sediment is a key process influencing their release to surface water [34]. Some elements, such as As, Sb, and Hg, can be trapped by the geothermal spring sinters or enriched in the geothermal spring sediments [35,36]. W was found to be enriched in hot spring sediments with high Fe contents [37]. As concentrations in hot spring sediments from the north-central Andean region of Ecuador reached 717.6 mg/kg [38]. Overall, the release of PHEs from geothermal systems to the surrounding environment depends strongly on the retention by the sediments at the spring vents.
In China, geothermal springs are mainly distributed in the Yunnan-Sichuan-Tibet geothermal province [39]. Previous studies have indicated that PHEs from geothermal springs have caused environmental pollution in Tibet [40,41,42]. In particular, As occurred widely and posed the most significant risk among the PHEs originating from hot springs [40]. The mineralogy and geochemistry of the geothermal deposits have been studied. However, the retention of PHEs by the hydrothermal deposits at the hot spring vents has received little attention. In our study, the association of the minerals and the PHEs in hot spring sediments was analyzed, which provides insights into the mineralogical factors controlling the immobilization of PHEs in the surface environment.

2. Materials and Methods

Twelve pairs of hot spring water samples and the corresponding surface sediments (Figure 1A) were collected at hot spring vents in the Nagqu geothermal field on the Tibetan Plateau, China. Three hot spring sinters (Figure 1B) were sampled for comparison with sediments at abandoned hot spring pipes. The water pH was measured using a portable pH meter, and the temperature was measured using a mercury thermometer. The water samples were filtered in situ using a 0.22 μm syringe filter, acidified to pH < 2, and preserved at 4 °C. The sediment and sinter samples were also stored at 4 °C.
All samples were transported to a laboratory in Beijing within a week. The sediments and sinters were air dried and then ground to pass a 200 mesh sieve for subsequent chemical and mineralogical analysis. Accurately weighed sediment and sinter samples (0.2 g) were digested with a mixture of 9 mL HNO3 and 3 mL HF in a microwave digestion system (MARS 6, CEM, Matthews, NC, USA), following Method 3052 of the United States Environmental Protection Agency (USEPA). The temperature program for sample digestion was as follows: temperature rise to 120 °C within 10 min, hold for 5 min; temperature rise to 150 °C within 5 min, hold for 5 min; temperature rise to 180 °C within 5 min, hold for 10 min. After cooling to room temperature, the digestion liquids were evaporated on a hot plate to near dryness and then redissolved with 3 mL HNO3. The solutions obtained from the above digestion procedures were further diluted with 2% HNO3 for instrumental analysis. The concentrations of the PHEs in the hot spring waters and the digestion solutions of the sediments and sinters were determined on an inductively coupled plasma-mass spectrometer (ICP-MS, NexION 350D, PerkinElmer, Waltham, MA, USA). Sc, Ge, Rh, and Bi were selected as the internal standards. Multi-element solutions containing the target elements were used to establish the calibration curves based on five concentrations (0, 0.1, 1.0, 10, and 100 μg/L), which covered the concentrations of the target elements, with the correlation coefficients ranging from 0.9995 to 1.000. The ICP-MS analysis was performed in the kinetic energy discrimination (KED) mode, and the detection limits for the target elements were as low as 0.01 μg/L.
After being pressed into pellets, the contents of the major oxides in the powderized sediment and sinter samples were measured on an X-ray fluorescence spectrometer (XRF, Zetium PANalytical, Almelo, The Netherlands). The target elements, in concentrations ranging from ppm to 100%, could be detected by XRF. The mineral phases in the solid samples were identified on a powder X-ray diffractometer (XRD, X-Pert3 Powder, PANalytical, Almelo, The Netherlands) with Cu-Kα radiation. The XRD patterns for the sediments and sinters were recorded over a 2θ range of 5–70°, with a step size of 0.013°.

3. Results and Discussion

3.1. Distributions of PHEs in the Hot Spring Waters and Sediments

The pH of the hot spring water was close to neutral, with an average value of 7.3 (ranging from 6.7 to 8.2) (Table 1). The water temperature range was 35.6–78.0 °C, covering low-temperature springs, moderate-temperature springs, and high-temperature springs (>70 °C) [43,44]. Fifteen potentially hazardous elements (Be, V, Cr, Mn, Co, Ni, Cu, Zn, As, Se, Cd, Cs, Tl, Pb, and U) were determined for the hot spring water samples, with their concentrations shown in Figure 2. Except for Cd, whose concentrations were below the instrumental detection limit in all hot spring water samples, the other 14 elements occurred at various levels (U was only detected in five water samples). The concentrations of Cr, Cu, Zn, and Cs in the hot spring waters fluctuated in small ranges, while those of the rest varied largely. The standard for groundwater quality of China (GB/T 14848—2017) sets limits for the total concentrations of Be, V, Cr, Mn, Co, Ni, Cu, Zn, As, Se, Cd, Cs, Tl, and Pb. The concentrations of Be, As, and Tl in some hot spring waters exceeded the corresponding limits for class Ⅲ groundwater by up to 2, 2, and 19 times, respectively. That is, these three elements could pose a significant health hazard if the hot spring waters were consumed directly by local residents. Natural surface water and groundwater generally have low Cs concentrations (typically < 5.0 μg/L) [45,46], and Cs is not currently regulated for groundwater quality in China. However, Cs occurred at rather high concentrations in the hot springs of the Nagqu geothermal field. The average concentration of Cs in the water samples was 549 μg/L, with the highest value of 776 μg/L.
The high concentrations of Be, As, Cs, and Tl in the hot spring waters impacted their contents in the sediments. As shown in Figure 3, only the contents of Be, As, Cs, and Tl in the hot spring sediments exceeded the respective average levels in the Tibetan surface soils [47]. The As contents in the hot spring sediments varied from 1.6 to 717.6 μg/g [35,36,38]. The contents of other PHEs were lower than the corresponding background values in the region’s surface soil. Most of the PHEs occurred at higher levels in the hot spring sediments than in the sinters, except that the concentrations of Be were lower in the sediments. The geoaccumulation index (Igeo) of the PHEs were calculated as follows [48]:
I g e o = l o g 2 C n 1.5 × B n
where Cn is the concentration of the element n in the sediment sample (in μg/g) and Bn is the background value of the element in Tibetan surface soil (in μg/g). The pollution level of soil is classified into seven categories based on the calculated Igeo value: (1) Igeo ≤ 0 (practically uncontaminated); (2) 0 < Igeo ≤ 1 (uncontaminated to moderately contaminated); (3) 1 < Igeo ≤ 2 (moderately contaminated); (4) 2 < Igeo ≤ 3 (moderately to heavily contaminated); (5) 3 < Igeo ≤ 4 (heavily contaminated); (6) 4 < Igeo ≤ 5 (heavily to extremely contaminated); and (7) Igeo > 5 (extremely contaminated). The calculated Igeo values (Figure 4) suggest that the hot spring sediments were uncontaminated to moderately contaminated by the PHEs, except that some sediments were heavily and extremely contaminated by Tl. The sediment sample that had the highest content of Tl was also heavily contaminated by As. Overall, Igeo values indicate that the hot spring sediments in the Nagqu geotherm field were moderately contaminated by Tl.

3.2. Mineralogical Compositions of the Hot Spring Sediments and Sinters

The major oxides identified in the hot spring sediments and sinters from the Nagqu geothermal field are summarized in Table 2. The sediments were mainly composed of the oxides of Ca and Si, with their total contents ranging from 61% to 85% (mean = 77%). The oxides of Al and Fe also occurred at relatively high levels in the hot spring sediments. The major mineralogical compositions of the hot spring sinters were simpler than those of the sediments. Over 90% of the sinters were made of oxides of Si, followed by small amounts of oxides of Sr (3.4–5.1%). Table 3 summarizes the Pearson correlation coefficients between the major oxides in the hot spring sediments, where the correlations are considered positive for r > 0.4973 (p < 0.05). Based on their correlations, the major oxides in the sediments can be classified into three groups: (1) Ca-Sr-Na-Mg, (2) Si-Al-K-Ti-P, and (3) Fe-S-Ba. The probable mineralogical compositions of the sediments could be inferred from the association of the elements. For example, the solid phases with strong positive Si-Al correlation commonly represent the occurrence of clay minerals, while the positive correlation between Mg and Ca indicates the presence of dolomite [31].
The mineralogical compositions of hot spring sediments are generally heterogeneous and significantly correlated with the pH of the spring water [49]. Most of the hot spring water samples in the Nagqu geothermal field were slightly alkaline, and their average pH value was 7.3 (Table 1). Such conditions are favorable for the formation of sinters and the crystallization of hydrothermal minerals [26]. The major mineral phases in the hot spring sediments (Figure 5) and sinters (Figure 6) were identified with XRD. As shown in Table 4, quartz was detected in all the sediment samples. Calcite, albite, and muscovite existed in most of the sediments. Aragonite was identified in most of the sediments, while orthoclase was detected in one sample. The mineralogical compositions of the hot spring sediments were generally simple, while even fewer mineral phases were found in the sinter samples. The hot spring sinters can be defined as travertines, because only carbonate minerals calcite and aragonite were identified [50,51,52]. Calcite and aragonite are the most common minerals deposited from hot spring waters, which could be contributed by both abiotic and biotic processes [28,31,50,51,53].
Calcite crystalized out of the hot spring water with the significant reduction in water temperature [54], and its precipitation happened after that of clay minerals, which are abundant in hot spring sediments and form through a gelatinous substance precursor [55,56]. Aragonite precipitated out of spring water because of the rapid CO2 degassing [28]. Ba in the sediments probably precipitated out of the hot spring water in the form of barite (BaSO4), which has low solubility at the low temperatures in the surface environment [54].

3.3. Immobilization of the PHEs by Mineral Precipitates

The minerals in the hot spring sediments played important roles in the retention of the PHEs. For example, the enrichment of Sb in the hot spring sediments depended largely on the abundance of Fe [39]. Table 5 lists the Pearson correlation coefficients between the PHEs and the major oxides in the hot spring sediments from the Nagqu geothermal field. As shown in Figure 7A, Be was positively correlated with CaO and MgO, which suggests that Be in the hot spring sediments was mainly associated with the Ca-bearing minerals. Thus, the precipitation of calcite and aragonite probably captured the dissolved Be in the hot spring waters. In addition, Be also showed a positive correlation with Sr (Figure 7A). Although the most common Sr-bearing minerals, such as celestite (SrSO₄) and strontianite (SrCO₃), were not detected by XRD, Sr had a strong positive correlation with Ca in the hot spring sediments (Table 3), implying that Sr was probably incorporated into calcite and aragonite [57]. Thus, Be was primarily associated with calcite and aragonite, possibly occurring as bertrandite [58]. The higher contents of Be in the hot spring sinters compared to the sediments also support the conclusion that the carbonate minerals have a stronger ability to capture Be than other minerals.
As in the hot spring sediments showed positive correlations with Fe2O3 and SO3 (Figure 7B). The occurrence of As in natural environments is often controlled geochemically by Fe-bearing mineral phases [59,60,61,62,63,64]. In geothermal systems, As can be retained by the hot spring sinters [65], where As might be present as arsenate sorbed on hydrous ferric oxides and/or as nodular arsenide micro-mineralization [66]. Nonetheless, the positive correlations between As, Fe2O3, and SO3 (Table 3 and Figure 7B) suggest that it was probably associated with the abundant pyrite in the hot spring sediments [54,67]. Cs in the hot spring sediments had positive correlations with CaO, MgO, SrO, and Na2O (Figure 7C), indicating that it was probably associated with carbonates and albite. The contents of Tl in the hot spring sediments were positively correlated with those of Fe2O3, SO3, and BaO, which suggests that it might be associated with pyrite.
Besides As and Tl, Co, Se, and U in the hot spring sediments also showed positive correlations with Fe2O3 and SO3 (Table 5), indicating that these PHEs were also probably controlled by iron sulfides, such as pyrite. Clay minerals often play an important role in the retention of trace elements in natural environments. V often adsorbs onto clay minerals and pyrite through surface complexation and electrostatic interaction (e.g., via Na+ bridge) [68,69]. Cr is also enriched on clay minerals through the formation of stable surface complexes, surface precipitation, and ion exchange [70,71]. In this study, V and Cr both showed positive correlations with SiO2 and Al2O3 in the hot spring sediments (Table 5), which is indicative of their strong retention by the clay minerals. Their positive correlations with K2O further indicate that they were probably associated with muscovite and/or orthoclase. Based on its positive correlation with SO3, Cu in the hot spring sediments was likely present in the form of sulfides, such as chalcopyrite.

4. Conclusions

The influence of mineral deposition on the retention of PHEs in geothermal spring vents was investigated through analyzing the mineralogical and elemental compositions of the hot spring sediments, and waters as well, in the Nagqu geothermal field on the Tibetan Plateau. The results show that the hot spring water samples did not have highly elevated concentrations of PHEs in general. However, the concentrations of Be, As, and Tl exceeded the criteria for class III groundwater of China by up to 2, 2, and 19 times, respectively, in some hot spring water samples. Cs occurred in the hot spring waters at concentrations much higher than those commonly found in aqueous systems (up to 776 μg/L). The contents of PHEs in the hot spring sediments were higher than the background levels of the Tibetan surface soils. The Igeo values indicate that the sediments were moderately contaminated by Cs and Tl. XRD analysis showed that the major mineralogical components of the hot spring sediments included calcite, quartz, aragonite, albite, muscovite, and orthoclase, while the hot spring sinters were mainly made of calcite and aragonite. The results of correlation analysis indicate that carbonate minerals (namely calcite and aragonite) had high affinity to Be and Cs, sulfide minerals (such as pyrite) were probably responsible for the retention of As and Tl, Fe-bearing minerals and/or Fe sulfides effectively captured Co, Se, and U, while clay minerals mainly retained Al, V, and Cr in the geothermal spring sediments. The retention of PHEs by the minerals deposited at the geothermal spring vents could significantly influence their mobility and thus discharge to surface water bodies.

Author Contributions

Conceptualization: Y.W. and H.C.; Methodology: Y.W.; Formal Analysis: Y.W.; Investigation: Y.W.; Writing—Original Draft: Y.W. and H.C.; Writing—Revised Draft: Y.W. and H.C.; Funding Acquisition: H.C. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported in parts by the Second Tibetan Plateau Scientific Expedition and Research Program (2019QZKK0605), the Natural Science Foundation of China (Grant Nos. 41725015 and U2006212), and the China Postdoctoral Science Foundation (2021M700199).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data will be available on request.

Acknowledgments

The authors thank M. Zhai, G. Lv, Y. Yin, X. Wang, H. Zhi, and Y. Hu for their help in field sampling.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Images of the sampling sites of hot spring waters, sediments, and sinters in the Nagqu geothermal field. (A) a hot spring vent; and (B) an abandoned hot spring pipe.
Figure 1. Images of the sampling sites of hot spring waters, sediments, and sinters in the Nagqu geothermal field. (A) a hot spring vent; and (B) an abandoned hot spring pipe.
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Figure 2. Concentrations of the PHEs in the hot spring waters from the Nagqu geothermal field on the Tibetan Plateau, China (solid diamonds represent the data; the minimum value, the first quartile, the median, the third quartile, and the maximum value are shown on each of the box and whisker plot; red lines represent the criteria for class III groundwater in China: Be = 2 μg/L, As = 10 μg/L, and Tl = 0.1 μg/L).
Figure 2. Concentrations of the PHEs in the hot spring waters from the Nagqu geothermal field on the Tibetan Plateau, China (solid diamonds represent the data; the minimum value, the first quartile, the median, the third quartile, and the maximum value are shown on each of the box and whisker plot; red lines represent the criteria for class III groundwater in China: Be = 2 μg/L, As = 10 μg/L, and Tl = 0.1 μg/L).
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Figure 3. Contents of the PHEs in the hot spring sediments and sinters from the Nagqu geothermal field on the Tibetan Plateau, China, along with their average levels in the Tibetan surface soils.
Figure 3. Contents of the PHEs in the hot spring sediments and sinters from the Nagqu geothermal field on the Tibetan Plateau, China, along with their average levels in the Tibetan surface soils.
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Figure 4. Igeo values of the PHEs in the hot spring sediments from the Nagqu geothermal field on the Tibetan Plateau, China (solid diamonds represent the data; the minimum value, the first quartile, the median, the third quartile, and the maximum value are shown on each of the box and whisker plot).
Figure 4. Igeo values of the PHEs in the hot spring sediments from the Nagqu geothermal field on the Tibetan Plateau, China (solid diamonds represent the data; the minimum value, the first quartile, the median, the third quartile, and the maximum value are shown on each of the box and whisker plot).
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Figure 5. XRD patterns of the hot spring sediment samples.
Figure 5. XRD patterns of the hot spring sediment samples.
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Figure 6. XRD patterns of the hot spring sinter samples.
Figure 6. XRD patterns of the hot spring sinter samples.
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Figure 7. Positive correlations (r > 0.4973, p < 0.05) between the contents of selected PHEs and those of major oxides in the hot spring sediments (hollow squares represent the values and only the PHEs with elevated concentrations in the hot spring waters were investigated to identify the mineral phases controlling their mobility: (A) Be versus CaO, MgO, and SrO; (B) As versus Fe2O3, SO3, and BaO; (C) Cs versus CaO, Na2O, SrO, and MgO; and (D) Tl versus Fe2O3, SO3, and BaO.
Figure 7. Positive correlations (r > 0.4973, p < 0.05) between the contents of selected PHEs and those of major oxides in the hot spring sediments (hollow squares represent the values and only the PHEs with elevated concentrations in the hot spring waters were investigated to identify the mineral phases controlling their mobility: (A) Be versus CaO, MgO, and SrO; (B) As versus Fe2O3, SO3, and BaO; (C) Cs versus CaO, Na2O, SrO, and MgO; and (D) Tl versus Fe2O3, SO3, and BaO.
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Table
Table 1. Summary of the pH and temperature values of the hot spring water samples.
Table 1. Summary of the pH and temperature values of the hot spring water samples.
Sample No.pHTemperature (°C)
18.078.0
27.846.0
36.740.0
46.744.0
57.640.0
67.139.4
77.437.0
87.240.6
97.035.6
107.458.2
118.263.8
127.053.0
Table
Table 2. Contents of major oxides in the hot spring sediments and sinters identified with XRF (wt%).
Table 2. Contents of major oxides in the hot spring sediments and sinters identified with XRF (wt%).
Sample No.CaOSiO2Al2O3Fe2O3K2ONa2OMgOSrOTiO2BaOSO3P2O5
Sediment161.024.02.24.10.620.882.562.580.281.250.500.05
210.366.36.36.23.300.790.590.200.850.604.510.14
38.765.37.08.03.420.770.750.161.060.514.230.09
40.478.010.35.43.540.180.510.010.770.120.680.11
52.575.18.15.73.770.840.640.070.910.162.030.16
61.876.67.95.13.360.680.480.071.190.252.490.14
72.274.96.77.12.480.420.390.060.851.173.710.07
81.360.06.114.02.390.490.000.060.822.8811.750.11
90.283.78.81.43.470.180.340.010.820.160.950.04
1010.265.69.16.83.201.111.000.171.051.050.530.14
1152.526.94.38.21.420.870.682.050.662.060.380.09
1233.840.28.98.42.620.951.080.931.041.360.520.19
Sinter191.40.90.50.90.040.371.693.44bdl0.680.100.03
292.20.70.10.90.040.620.324.10bdl0.810.080.04
392.80.50.10.3bdl0.180.345.05bdl0.640.050.03
Note: bdl, below detection limit.
Table
Table 3. Pearson correlation coefficients between the major oxides in the hot spring sediments.
Table 3. Pearson correlation coefficients between the major oxides in the hot spring sediments.
CaOSiO2Al2O3Fe2O3K2ONa2OMgOSrOTiO2BaOSO3P2O5
CaO1.00
SiO2−0.961.00
Al2O3−0.710.72 **1.00
Fe2O3−0.01−0.26−0.141.00
K2O−0.860.87 **0.85 **−0.181.00
Na2O0.52 *−0.57−0.310.20−0.271.00
MgO0.77 **−0.67−0.53−0.31−0.620.51 *1.00
SrO0.99 **−0.93−0.77−0.06−0.900.430.77 **1.00
TiO2−0.640.57 *0.70 **0.160.76 **0.10−0.58−0.731.00
BaO0.40−0.60−0.500.79 **−0.650.22−0.010.39−0.291.00
SO3−0.400.18−0.150.73 **0.06−0.21−0.49−0.370.120.52 *1.00
P2O5−0.150.050.450.320.400.49−0.15−0.270.60 *−0.0501.00
Note: Underlined and bold values represent positive correlations (*, p < 0.05; **, p < 0.01).
Table
Table 4. Major minerals in the hot spring sediments and sinters identified by XRD.
Table 4. Major minerals in the hot spring sediments and sinters identified by XRD.
Sample No.Mineral
Sediment1Calcite, CaCO3Aragonite, CaCO3Quartz, SiO2Albite, NaAlSi3O8/
2Calcite, CaCO3/Quartz, SiO2Albite, NaAlSi3O8/
3Calcite, CaCO3/Quartz, SiO2Albite, NaAlSi3O8Muscovite, KAl2Si3AlO10(OH)2
4//Quartz, SiO2/Muscovite, KAl2Si3AlO10(OH,F)2
5//Quartz, SiO2Albite, NaAlSi3O8Muscovite, (K0.82Na0.18)(Fe0.03Al1.97)(AlSi3)O10(OH)2
6//Quartz, SiO2Albite, NaAlSi3O8Muscovite, KAl2Si3AlO10(OH,F)2
7Calcite, CaCO3/Quartz, SiO2Albite, NaAlSi3O8Muscovite, KAl2Si3AlO10(OH,F)2
8//Quartz, SiO2Albite, NaAlSi3O8Orthoclase, Ba-rich, (K,Ba)(Si,Al)4O8
9//Quartz, SiO2/Muscovite, KAl2Si3AlO10(OH)2
10Calcite, CaCO3/Quartz, SiO2Albite, NaAlSi3O8Muscovite, KAl2Si3AlO10(OH)2
11Calcite, CaCO3Aragonite, CaCO3Quartz, SiO2/Muscovite, KAl2Si3AlO10(OH,F)2
12Calcite, CaCO3Aragonite, CaCO3Quartz, SiO2Albite, NaAlSi3O8Muscovite, (K,Na)Al2(Si,Al)4O10(OH)2
Sinter1Calcite, CaCO3Aragonite, CaCO3///
2Calcite, CaCO3Aragonite, CaCO3///
3Calcite, CaCO3Aragonite, CaCO3///
Table
Table 5. Pearson correlation coefficients between the major oxides and the PHEs in the hot spring sediments.
Table 5. Pearson correlation coefficients between the major oxides and the PHEs in the hot spring sediments.
OxideCaOSiO2Al2O3Fe2O3K2ONa2OMgOSrOTiO2BaOSO3P2O5
Be0.85−0.77−0.78−0.19−0.830.360.910.89−0.770.21−0.29−0.34
V−0.570.650.77−0.390.59−0.75−0.48−0.550.24−0.49−0.20−0.08
Cr−0.690.600.540.200.55−0.59−0.76−0.700.45−0.050.500.25
Mn−0.160.190.41−0.070.21−0.42−0.05−0.14−0.12−0.27−0.200.06
Co−0.470.300.270.520.25−0.51−0.57−0.440.060.320.700.04
Ni−0.500.390.430.330.34−0.63−0.51−0.460.020.100.470.01
Cu−0.540.440.350.250.25−0.80−0.62−0.48−0.010.180.54−0.22
Zn0.27−0.320.120.18−0.110.120.280.23−0.200.04−0.210.36
As−0.350.12−0.080.75−0.06−0.35−0.49−0.300.010.650.92−0.10
Se0.19−0.36−0.400.66−0.380.05−0.360.22−0.180.830.530.01
Cd0.07−0.190.420.380.140.15−0.24−0.050.350.28−0.030.57
Cs0.79−0.78−0.470.08−0.470.760.550.72−0.150.20−0.380.28
Tl−0.310.10−0.130.70−0.07−0.31−0.45−0.2600.630.93−0.11
Pb0.36−0.430.180.26−0.110.440.190.220.260.22−0.240.61
U−0.330.090.310.780.180.03−0.54−0.380.490.570.630.46
Note: Underlined and bold values represent positive correlations (p < 0.05).
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Wang, Y.; Cheng, H. Influence of Mineral Deposition on the Retention of Potentially Hazardous Elements in Geothermal Spring Sediments. Sustainability 2023, 15, 8040. https://doi.org/10.3390/su15108040

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Wang Y, Cheng H. Influence of Mineral Deposition on the Retention of Potentially Hazardous Elements in Geothermal Spring Sediments. Sustainability. 2023; 15(10):8040. https://doi.org/10.3390/su15108040

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Wang, Yafeng, and Hefa Cheng. 2023. "Influence of Mineral Deposition on the Retention of Potentially Hazardous Elements in Geothermal Spring Sediments" Sustainability 15, no. 10: 8040. https://doi.org/10.3390/su15108040

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