Arsenic geochemistry in geothermal systems

Journal Article · Mon Feb 01 04:00:00 EST 1988 · Geochim. Cosmochim. Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(88)90102-0· OSTI ID:6992658

Ballantyne, J M; Moore, J N

Arsenic is an important trace constituent in geothermal fluids, ranging in concentration from less than 0.1 to nearly 50 ppm. An evaluation of published fluid analyses from geothermal systems indicates that the As content of the reservoir fluids varies inversely with P/sub H/sub 2/S/ and directly with temperature. Aqueous As species occur in two oxidation states, As/sup III/ and As/sup V/. As/sup III/ predominates in the reservoir fluids, where H/sub 3/AsO/sub 3/ is inferred to be the dominant aqueous species. Both AS/sup III/ and As/sup V/ occur in hot spring fluids. The concentration of As in high-temperature reservoir fluids is regulated by reactions involving pyrite. Concentrations up to 3.8 weight percent As have been measured in pyrite from two systems. The erratic distribution of As in the samples studied is interpreted as resulting from local fluctuations in redox conditions. Arsenopyrite and other As minerals are undersaturated with respect to the high temperature fluids found in most reservoirs. In contrast, orpiment, realgar, As-rich stibnite and marcasite, and iron oxides control the deposition of As in hot spring environments. These minerals become stable in response to decreasing temperature and pH and increasing P/sub O/sub 2//.

• Research Organization: Univ. of Utah Research Institute, Salt Lake City (USA)
• OSTI ID: 6992658
• Journal Information: Geochim. Cosmochim. Acta; (United States), Journal Name: Geochim. Cosmochim. Acta; (United States) Vol. 52:2; ISSN GCACA
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
152001 -- Geothermal Data & Theory-- Properties of Aqueous Solutions
58 GEOSCIENCES
580400* -- Geochemistry-- (-1989)
ARSENIC
CHALCOGENIDES
CHEMICAL COMPOSITION
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISTRY
ELEMENTS
FLUIDS
GEOCHEMISTRY
GEOTHERMAL FLUIDS
GEOTHERMAL SYSTEMS
IRON COMPOUNDS
IRON SULFIDES
KINETICS
MINERALS
OXIDATION
PH VALUE
PYRITE
REACTION KINETICS
SEMIMETALS
SULFIDE MINERALS
SULFIDES
SULFUR COMPOUNDS
TEMPERATURE EFFECTS
TRACE AMOUNTS
TRANSITION ELEMENT COMPOUNDS