Partitioning of lithium between smectite and solution: An experimental approach

The results show that the structural (octahedral) Li content of hectorites increases with Li concentration in solution, with temperature and with synthesis duration. A steady-state is reached after 4 weeks at 150 °C and after 2 months at 70 and 90 °C. Calculated partition coefficients, expressed either as DLi = [Li(clay)]/[Li(aq)] (ppm/ppm) or as DLi/Mg′ = (Li/Mg)clay/(Li/Mg)solution (ppm/ppm), increase with the synthesis temperature which is consistent with a true Li-Mg substitution within the clay lattice. DLi also increases when the Li concentration in solution decreases, and reaches 22 at 150 °C (using a 1.5 mg/L Li solution). A general expression for DLi can be established: logDLi = −1319/T(K) + 5.5 ([Li(aq)])−0.0806. The main conclusion is that neoformed smectites which crystallize during water-rock interactions can be efficient Li sinks in the external geochemical cycle. Quantitative applications to several natural systems are assessed.