We measured unidirectional silicate reaction rates at near-neutral-pH and close-to-equilibrium conditions by introducing a rare Si isotope 29Si into the experimental solutions. Reaction rates were tracked by 29Si/28Si ratios of reacted solutions. Because the precipitation of Si-containing secondary phases or the reverse reaction consume silica but leaves the 29Si /28Si ratios essentially unchanged in experimental solutions, dissolution rates were still measurable when secondary phase precipitation took place in experiments. Results from experiments for albite, K-feldspar, quartz, and kaolinite (Liu et al., 2016; Zhu et al., 2016; Gong et al., 2019) demonstrated that the isotopic contrast and analytical precision allow detection of the dissolution of a minute amount of silicate. The near-equilibrium unidirectional dissolution rates in this study are a new type of rates—unidirectional rates (from the isotope tracer method), which differ from all near-equilibrium silicate dissolution rates in the literature that are based upon Si or Al concentrations and are net rates (dissolution minus precipitation rates). Although the method itself is not new, MC-ICP-MS technology now makes the measurement of a large number of non-traditional isotopes accessible, presenting a new opportunity to utilize the isotope tracer method to advance the field of geochemical kinetics.

Measuring unidirectional silicate reaction rates using silicon isotope tracer

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.