Coupling of Li-Fe: Li Isotope Fractionation during Sorption onto Fe-Oxides

Area of Science:

• Geochemistry
• Environmental Science
• Mineralogy

Background:

• Chemical weathering regulates global climate over geological timescales.
• Lithium (Li) isotope composition is a proxy for weathering and secondary mineral formation.
• Li interaction with iron (Fe)-oxides is inferred but lacks experimental data.

Purpose of the Study:

• Investigate Li geochemical behavior during sorption onto individual Fe-oxides.
• Determine Li uptake by goethite, hematite, wüstite, and magnetite.
• Constrain Li-Fe-oxide interactions experimentally.

Main Methods:

• Sorption experiments of Li onto Fe-oxides (goethite, hematite, wüstite, magnetite).
• Analysis of Li uptake across a pH range (4-12).
• Measurement of Li isotope fractionation (Δ⁷Li) between oxide and fluid.

Main Results:

• Poorly crystalline goethite nanoparticles exhibit significant Li sorption (20% at pH 4-10, 90% at pH 12).
• Well-crystallized Fe-oxides show negligible Li sorption.
• Goethite preferentially sorbs light ⁶Li isotopes, with fractionation Δ⁷Li_oxide-fluid of -16.7 to -20.1‰.
• Li uptake by goethite is linked to dissolution-reprecipitation reactions.

Conclusions:

• Li sorption onto poorly crystalline goethite is a key process in Fe-oxide-rich, highly weathered environments like laterites.
• Mineral surface chemistry significantly influences Li-mineral interactions.
• Provides insights into Li cycling and potential for large-scale Li extraction.