Modeling geochemical factors controlling fluoride concentration in groundwater
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ORIGINAL PAPER
Modeling geochemical factors controlling fluoride concentration in groundwater Wei Zhang 1,2 & Li Zhou 1 & Hongfeng Tang 1 & Heping Li 1 & Wenlei Song 3 & Zhu Chen 1,2
Received: 18 January 2015 / Accepted: 13 April 2015 # Saudi Society for Geosciences 2015
Abstract The fluoride in groundwater can affect human health. The concentration of fluoride ions in groundwater is influenced by geogenic processes and is limited by the solubility of fluoride-containing minerals, especially fluorite. In this work, we summarize and assess fluorite solubility and the Pitzer interaction model parameters of related species, by which a quantitative model for calculation of the phases and chemical speciation in the Na–Ca–H–F–Cl–SO 4 –OH– HCO3–CO3–CO2–H2O aqueous system for temperatures 0– 100 °C, and a pressure of 1 bar was established. Based on this model, we evaluate factors that govern the levels of fluoride, e.g. temperature, solution composition, pH, CO2 partial pressure, and concentration of carbonate minerals in the aquifer. The fluorite solubility increases with temperature and varies in different aqueous solutions. The fluoride concentration is highest in NaHCO3 type aqueous solutions. In acidic solution, HF is the dominant species, and free fluoride becomes dominant with increasing pH. Dissolved CO2 in solution slightly increases the concentration of fluoride in non-bicarbonate aqueous solution and non-calcite-bearing aquifer systems. In contrast, it has a significant negative effect in calcite and bicarbonate-bearing aquifer systems, where it greatly decreases the fluoride concentration. In calcite-bearing aquifer
* Li Zhou [email protected] 1
Key Laboratory of High-Temperature and High-Pressure Study of the Earth’s Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China
2
University of Chinese Academy of Sciences, Beijing 100039, China
3
Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China
systems, the fluoride concentration is lower than in non-calcite mineral aquifer systems. Keywords Fluorite . Fluoride . Pitzer interaction model . Geogenic processes . Quantitative model evaluation
Introduction Fluorine is widely dispersed in nature and is an essential element in the human body, playing an important role in bone mineralization and formation of dental enamel. However, it can also have a detrimental effect in the form of fluorosis (Dissanayake 1991). Groundwater is thought to be the main source of human fluoride intake (Jha et al. 2011). Based on the World Health Organization’s recommended permissible fluoride limit of 1.5 mg/L (World Health Organization 2006), it is estimated that more than 200 million people in over 20 countries are affected by excessive fluoride consumption, particularly in northern China, India, Sri Lanka, Mexico, western USA, Argentina, and many countries in Africa (Edmunds and Smedley 2013). Considerable research has been carried out to investigate the factors r
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