TY - JOUR

T1 - Hydrothermal experiments at in-situ conditions to identify Li release reactions by water-mineral interactions in deep sedimentary basins of the North German Basin and Upper Rhine Graben

AU - Schmidt, Kevin

AU - Oeser, Martin

AU - Stechern, André

AU - Ostertag-Henning, Christian

N1 - Publisher Copyright: © 2025 The Authors

PY - 2025/12

Y1 - 2025/12

N2 - Lithium (Li) production from brines circulating in deep sedimentary basins as a byproduct of deep geothermal energy use could contribute to cover a significant proportion of the increasing global Li demand. Additionally, co-produced formation waters from the oil and gas industry represent another potential source of Li that could be utilized in a similar manner. Feasibility assessments for these operations require estimates for a possible Li replenishment by the recirculation of the Li-depleted brine after aboveground Li extraction. Currently, information about Li contents in reservoir rocks, the main Li carrier mineral phases of the respective reservoirs and possible Li release reactions are scarce. In this study, drill core material from two geothermal wells, Groβ Buchholz Gt1 (Triassic Bunter sandstone) in the North German Basin (NGB) and Soultz-sous-Forêts EPS1 (granitic basement) in the Upper Rhine Graben (URG), as well as from the gas well Unterlüß T1 (Triassic Bunter sandstone) in the NGB, were investigated for both Li contents and Li release behavior. The bulk rock Li concentrations of the sample collection vary slightly in the range of 47–79 ppm. The main Li-bearing minerals were identified to be (i) chlorite (575 ppm) and illite (68 ppm) for Bunter sandstone samples and (ii) biotite for the Soultz sous forêts granite with maximum concentrations of up to 597 ppm. By grain-size fraction analysis phyllosilicates in the clay fraction were confirmed to exhibit the highest Li concentrations for the sandstones. To explore the Li release behavior, hydrothermal experiments were conducted at conditions of low enthalpy geothermal reservoirs (100–160 °C, 370 bar) for 14–60 days. The above described core samples were investigated by using ground rock powder and for one example the clay fraction. These solids were mixed with either bi-dist. H 2O or synthetic brine in Au capsules or in flexible Au–Ti reaction cells and installed in high pressure reactors. Results of the experiments show that a nearly constant Li concentration was attained after 6–12 days in all experiments with the bi-dist. H 2O. In these experiments, a total of 0.2–0.7 % of the Li contained in the granitic sample and 0.9–3.2 % of the Li contained in the Bunter sandstone samples were leached into the solution. It was found that different reaction mechanisms involving silicate minerals, as well as halogenide and carbonate minerals, contribute to the Li release. The experiment conducted with a clay fraction consisting mainly of illite and chlorite showed an enhanced leach of 6.9 % Li, indicating that Li is preferentially released by illite and chlorite in all experiments. Variations in temperature point only to a minor influence on the amount of Li released in the experiments. Experiments conducted with a synthetic brine instead of bi-dist. H 2O stimulated the release of Li by a factor of up to 2 for the Bunter sandstone samples and by a factor of 5 for the granitic sample. The results of hydrothermal experiments implicate that replenishment of Li in a geothermal extraction operation is occurring and is only slightly dependent on the reservoir temperature in the range of 100–160 °C.

AB - Lithium (Li) production from brines circulating in deep sedimentary basins as a byproduct of deep geothermal energy use could contribute to cover a significant proportion of the increasing global Li demand. Additionally, co-produced formation waters from the oil and gas industry represent another potential source of Li that could be utilized in a similar manner. Feasibility assessments for these operations require estimates for a possible Li replenishment by the recirculation of the Li-depleted brine after aboveground Li extraction. Currently, information about Li contents in reservoir rocks, the main Li carrier mineral phases of the respective reservoirs and possible Li release reactions are scarce. In this study, drill core material from two geothermal wells, Groβ Buchholz Gt1 (Triassic Bunter sandstone) in the North German Basin (NGB) and Soultz-sous-Forêts EPS1 (granitic basement) in the Upper Rhine Graben (URG), as well as from the gas well Unterlüß T1 (Triassic Bunter sandstone) in the NGB, were investigated for both Li contents and Li release behavior. The bulk rock Li concentrations of the sample collection vary slightly in the range of 47–79 ppm. The main Li-bearing minerals were identified to be (i) chlorite (575 ppm) and illite (68 ppm) for Bunter sandstone samples and (ii) biotite for the Soultz sous forêts granite with maximum concentrations of up to 597 ppm. By grain-size fraction analysis phyllosilicates in the clay fraction were confirmed to exhibit the highest Li concentrations for the sandstones. To explore the Li release behavior, hydrothermal experiments were conducted at conditions of low enthalpy geothermal reservoirs (100–160 °C, 370 bar) for 14–60 days. The above described core samples were investigated by using ground rock powder and for one example the clay fraction. These solids were mixed with either bi-dist. H 2O or synthetic brine in Au capsules or in flexible Au–Ti reaction cells and installed in high pressure reactors. Results of the experiments show that a nearly constant Li concentration was attained after 6–12 days in all experiments with the bi-dist. H 2O. In these experiments, a total of 0.2–0.7 % of the Li contained in the granitic sample and 0.9–3.2 % of the Li contained in the Bunter sandstone samples were leached into the solution. It was found that different reaction mechanisms involving silicate minerals, as well as halogenide and carbonate minerals, contribute to the Li release. The experiment conducted with a clay fraction consisting mainly of illite and chlorite showed an enhanced leach of 6.9 % Li, indicating that Li is preferentially released by illite and chlorite in all experiments. Variations in temperature point only to a minor influence on the amount of Li released in the experiments. Experiments conducted with a synthetic brine instead of bi-dist. H 2O stimulated the release of Li by a factor of up to 2 for the Bunter sandstone samples and by a factor of 5 for the granitic sample. The results of hydrothermal experiments implicate that replenishment of Li in a geothermal extraction operation is occurring and is only slightly dependent on the reservoir temperature in the range of 100–160 °C.

KW - Hydrothermal experiments

KW - water-rock interactions

KW - Bunter sandstone

KW - Upper Rhine Graben

KW - North German Basin

KW - Li-extraction

KW - Li-brines

KW - lithium

KW - North German basin

KW - Li release

KW - Upper rhine graben

KW - Lithium

KW - Granite

KW - Batch experiments

KW - Deep sedimentary basins

KW - Water-rock interactions

KW - Li

KW - Sandstone

UR - http://www.scopus.com/inward/record.url?scp=105022152998&partnerID=8YFLogxK

U2 - 10.1016/j.apgeochem.2025.106622

DO - 10.1016/j.apgeochem.2025.106622

M3 - Article

VL - 195

JO - Applied Geochemistry

JF - Applied Geochemistry

SN - 0883-2927

M1 - 106622

ER -