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

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.