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地热能作为一种清洁环保的可持续再生能源,与其他能源相比优势明显且极具竞争力[1-2]. 我国具有非常丰富的地热资源,通过中国大陆地区热流分布图可知我国呈东南部、西南部热流值较高而东北部、西北部热流值较低特点[3],地热资源主要集中于西藏、云南、广东等地. 地热能具有绿色低碳的特点,积极开发利用地热能对我国能源结构优化、能源安全保障具有重要意义[4].
温泉作为地热资源中的浅层地热能资源,广泛出露于热流值较高区域. 对温泉进行水文地球化学研究,可以揭示深部流体在循环过程中热流传输机理和水-岩相互作用的各种信息[5]. 温泉水中普遍存在高氟现象,若不科学利用或随意排放则会导致区域环境氟污染. 随着温泉资源的开发与利用,区域氟污染日益严重,因其会对土壤、地下水、生物等产生不良影响而备受关注.
氟是一种常见元素,饮用水中的氟对人体健康既有正面影响,也有负面影响. 低浓度的氟通过硬化牙釉质和减少龋齿能对人体牙齿产生有益影响[6-7];而高浓度的氟可能会导致一种名为氟斑牙的地方病,甚至会导致人体氟中毒[8]. 我国生活饮用水卫生标准规定水中氟化物不得超过1 mg·L−1,而大部分温泉水中氟含量远远超于此界限,对环境潜在威胁较大. Shupe等[9]早在1984年发现地热水中含有高浓度的氟,会造成野生动物氟中毒现象;Sracek等[10]研究了纳米比亚高氟温泉,发现温泉中氟化物主要来源于萤石矿物的溶解;朱明占等[11]研究了桂南地热水氟的分布及富集规律,发现地热水中氟含量与水体温度呈正相关;欧浩等[12]对广东省信宜-廉江地区高氟温泉进行了水化学分析,总结出控制高氟温泉水化学特征的地球化学过程主要有水-岩相互作用、矿物溶解作用、吸附解吸作用和阳离子交换作用等. 目前针对粤东地区温泉中氟的富集规律研究较少,多数使用水文地球化学方法进行研究,较少涉及定量分析. 本文将结合水文地球化学方法及数值模拟方法定量分析龙川县北部温泉中氟的富集作用,对今后类似区域定量化研究污染物富集提供参考.
广东省龙川县北部温泉中氟的富集作用
Fluorine enrichment of hot springs in northern Longchuan County, Guangdong Province
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摘要: 地热能是一种极具竞争优势的可持续再生能源,已有研究表明,受地热能影响的温泉水中普遍存在高氟现象,其富集机制尚未完全明晰. 本研究在广东省龙川县北部采集温泉水样10个,并对其进行实验室测试和水化学分析,运用水文地球化学方法和数值模拟探究温泉水中氟的富集作用. 结果表明,温泉水中氟含量均已超标,最高达18.27 mg·L−1. 研究区温泉水化学类型有HCO3SO4-Na和HCO3-Na两类,氟含量与pH、温度、Ca2+含量有一定关系. 矿物溶解与沉淀作用、阳离子交换作用、解吸与络合作用是影响温泉氟富集的主要水文地球化学因素,PHREEQC反向模拟量化了研究区水热循环过程和水-岩相互作用,进一步发展了氟的富集过程的研究.Abstract: Geothermal energy is a sustainable renewable energy with great competitive advantages. Studies have shown that hot spring water in geothermal field is characterized by high fluorine content. However, the mechanisms that control fluorine enrichment are still unclear. In this study, 10 hot spring water samples were collected in the northern part of Longchuan County, Guangdong Province, and laboratory tests and hydrochemical analysis were conducted. Hydrogeochemical methods and numerical simulation were used to investigate the fluorine enrichment in hot springs. The results show that the fluorine contents in all hot spring water samples exceed the standard value, with the highest one of 18.27 mg·L−1. The chemical types of hot spring water in the study area are HCO3SO4-Na and HCO3-Na, and the fluorine content is associated with pH, temperature, and Ca2+ values. Mineral dissolution and precipitation, cation exchange, desorption and complexation are the main hydrogeochemical factors affecting fluorine enrichment in hot springs. The hydrothermal cycle process and water-rock interaction in the study area have been quantified by PHREEQC reverse simulation, which further improves our understanding of the enrichment process of fluorine.
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Key words:
- hot spring /
- fluoride /
- water-rock interaction /
- reverse simulation.
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表 1 水样的物理化学特征参数
Table 1. Physicochemical properties of the water samples
编号
No.取样地名
NamepH T/℃ TDS/
(mg·L−1)K+/
(mg·L−1)Na+/
(mg·L−1)Ca2+/
(mg·L−1)Mg2+/
(mg·L−1)HCO3−/
(mg·L−1)Cl−/
(mg·L−1)SO42−/
(mg·L−1)F−/
(mg·L−1)H01 含水村 7.55 56.30 577.78 4.21 75.98 12.83 1.31 180.32 22.17 166.53 7.39 H02 含水村 7.52 60.30 554.44 4.26 80.56 12.80 1.27 119.56 21.84 164.63 7.21 H03 上盘村 8.87 60.50 267.22 2.75 35.90 2.26 0.83 93.24 18.03 23.22 18.27 H04 上盘村 8.53 73.20 295.56 2.96 37.33 2.47 1.35 101.34 18.53 24.85 17.88 H05 上盘村 8.56 70.20 280.00 2.79 38.56 2.26 1.41 99.67 18.66 23.43 18.09 H06 宫下村 8.97 53.80 240.56 2.29 33.40 2.91 0.74 113.97 16.67 21.06 17.46 H07 湖径村 8.58 50.10 225.56 1.99 32.05 2.83 0.79 86.95 11.35 22.82 15.89 H08 湖径村 8.79 34.60 222.78 2.19 33.11 2.89 0.91 92.12 12.67 23.20 16.01 H09 热水村 8.11 83.10 290.56 3.11 40.65 4.27 0.72 135.72 15.06 78.91 14.36 H10 汤湖村 8.22 64.00 237.78 2.47 30.58 6.53 1.08 109.34 5.36 38.84 9.94 表 2 PHREEQC反向模拟结果 (mmol·L−1)
Table 2. Results of reverse simulation by PHREEQC (mmol·L−1)
方解石
Calcite白云石
Dolomite萤石
Fluorite石膏
Gypsum岩盐
HaliteKX NaX CaX2 H05→H10 1.00×10−4 −1.82×10−5 −1.42×10−4 1.06×10−4 −2.48×10−4 1.32×10−5 −2.17×10−4 1.02×10−4 H09→H07 −2.49×10−4 −1.03×10−5 4.85×10−5 −2.18×10−4 8.49×10−5 −6.42×10−5 −6.26×10−4 3.45×10−4 -
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