Rare earth elements in thermal water from the Sob-1 well,Murska Sobota,NE Slovenia

Thermal water produced from the Sob-1 well is a water mixture contributed from several stratified aquifers that belong to two hydrogeological subsystems termed Middle- and Upper Subsystem. The subsystems’ thermal waters differ appreciably in the REE and Y signatures; ΣREE + Y averages to about 10 and 0.2 ppb for the Middle- and Upper-subsystem, respectively. As the Sob-1 well experiences pressure cycling, the inflow from the subsystems’ aquifers is not constant but cycles as well causing the cycling of chemical composition of abstracted thermal water mixture, including REEs and Y. PAAS normalized cycling REE and Y distribution for thermal water mixture from the Sob-1 well indicates that the abundance of REEs and Y is mainly controlled by solubility of their carbonate and bicarbonate species, and therefore by availability of free and dissolved carbon dioxide in the aquifer.