Abstract
Geothermal waters usually have elevated tungsten concentrations, making geothermal systems important sources of tungsten in the environment. To study the transport of tungsten in hot springs to hot spring sediment, which is one of the key processes for the release of geothermally derived tungsten to the surface environment, geochemical investigations of the hot springs and their corresponding sediments in Rehai (a representative hydrothermal area in southwestern China) and systematic laboratory experiments of tungstate and polytungstate adsorption onto typical iron-bearing minerals in hot spring sediments (i.e., pyrite and goethite) were conducted. The results demonstrate that considerable tungsten concentrations (i.e., not much less than 10 µg/L), formation of polytungstates under acidic conditions, and enrichment of iron oxide minerals represented by goethite are the prerequisites for extreme enrichment of tungsten in hot spring sediments (e.g., 991 µg/g in the ZZQ spring outflow channel). The absence of any of these conditions would weaken the immobilization of aqueous tungsten and result in higher mobility of tungsten in the hot springs and its further transport downstream, possibly polluting the other natural waters in and around Rehai that serve as local drinking water sources. This study provides an insight for identifying the key geochemical processes controlling the transport and fate of undesirable elements (in this case, tungsten) in geothermal systems.
Highlights
In recent years, environmental toxicology studies of tungsten (W) have overturned the misconception that tungsten is non-toxic [1–4]
Further inspection indicated that the transfer of geothermal tungsten from hot springs to sediments was controlled primarily by the sorption of tungsten to iron-bearing minerals, iron-rich sediments was controlled primarily by the sorption of tungsten to iron-bearing typically goethite and pyrite, as there were no tungsten-bearing minerals found in the minerals, typically andsprings pyrite,were as there were no tungsten-bearing found sediments, and thegoethite
Transport of aqueous tungsten to hot spring sediment is one of the key processes for the release of geothermal-system-derived tungsten to the surface environment that is an important part of the global geochemical cycle of tungsten
Summary
Environmental toxicology studies of tungsten (W) have overturned the misconception that tungsten is non-toxic [1–4]. Sources of tungsten can generally be divided into two categories: natural processes and anthropogenic activities The former category includes the release of tungsten from magmatic fluids [16,17], weathering of tungsten-rich minerals [18], desorption of tungsten from iron or manganese oxides/hydroxides [19,20], etc. The latter category includes studded tires and deicing salts used in snowy conditions [21], ammunition [14], agricultural fertilizer application, domestic sewage discharge [22,23], etc. In contrast to other natural waters (e.g., meteoric, seawater, and river), geothermal waters usually have higher tungsten concentrations due to the input of magmatic fluid and the lithology of reservoir host rocks [24], making geothermal systems one of the important sources of tungsten in the environment.
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