Silicon isotope fractionation during abiotic silica precipitation at low temperatures: Inferences from flow-through experiments

Calculated magnitudes of silicon isotope fractionations between precipitated and dissolved silica (Δ30Si = δ30Siprecipitate (calculated) − δ30Siinput solution) were −2.1‰ at 10 °C, −1.2‰ at 20 °C, −1.0‰ at 30 °C, −0.5‰ at 40 °C, 0.1‰ at 50 °C, and 0.2‰ at 60 °C (s.d. ⩽ 0.6‰, based on replicate experiments). Hence, fractionation was nearly insignificant at temperatures ⩾50 °C. Apart from this relationship with temperature, our results indicate that the effective Si isotope fractionation during precipitation from a solution is subject to changes in the saturation state, reactive surface area and flow regime. We therefore infer that, to a significant extent, solid-fluid fractionation in natural (near-) surface environments is system dependent.