Vapour/liquid fractionation of rare earths, Y3+, Na+, K+, NH4+, Cl−, HCO3−, SO42− and borate in fluids from the Piancastagnaio geothermal field, Italy

Vapour/liquid fractionation of rare earth elements and yttrium (REY), Na+, K+, NH4+, HCO3−, SO42−, Cl− and borate in geothermal fluids from the Piancastagnaio geothermal field (Mt. Amiata geothermal area, Tuscany, central Italy) were evaluated based on the chemistry of collected liquids and condensed vapours. Apparent vapour–liquid partitioning factors (appDV/L) of REY vary from 0.3 to 0.01. These factors are much higher than those of Na (<0.001) and K (∼0.001). Volatile components are ion pairings such as NH4HCO3o, NH4Clo, NaHCO3o, CaSO4o and REYO(HCO)3o ⇔ REY(OH)CO3o. In vapour, REY and NH4+ are negatively correlated. High and low appDV/L(REY) indicate variations of NH4+ concentrations in liquids. The results of this study are relevant to the understanding of element migration and deposition under hydrothermal boiling conditions.