Live optical imaging of dissolution of olivine under conditions relevant to enhanced weathering in a microreactor.

Enhanced weathering, in which mafic and ultramafic rocks react with CO₂ to form stable carbonates, is a promising negative emission technology for long-term carbon sequestration. A key challenge that prevents large-scale implementation of the technology is the slow rate of the process. In-situ study of mineral weathering has led to new insights on how to enhance the process, but the equipment required to carry out these experiments has set a high barrier to entry [1]. To address this challenge, we developed a microreactor made from silicon and glass using standard cleanroom processes (Figure 1a) [2]. Our reactor can withstand temperatures and pressures relevant to enhanced weathering [3] and, to our knowledge, we are the first to demonstrate live optical imaging of individual mineral particles during enhanced weathering.

In our experiments, we studied the size and morphology of olivine particles during dissolution in sulfuric acid. Olivine was loaded in the microreactor (Figure 1b) and a flow of 0.1M sulfuric acid was introduced at the inlet using a syringe pump. A second pressure-regulated syringe pump at the outlet maintained a back pressure of 115 bar while the temperature was controlled at 185°C using a heating element.

Preliminary results show two distinct morphological changes: particle shrinkage (Figure 1c) and fracture (Figure 1d). The fracture likely results from stresses generated between the parent mineral and precipitated phases during mineral replacement reactions [4]. Fracturing is hypothesized to enhance the carbonation process by continuously exposing fresh reactive surfaces, leading to a potential millionfold enhancement of reaction rate under certain conditions [5]. While previous studies, such as those by Zhu et. al., have visualized similar fracturing in olivine using in-situ synchrotron X-ray microtomography [1], the reliance on synchrotron facilities has limited the accessibility of such analysis. The microreactor, with its optical transparency, may be a powerful alternative for studying fracturing in real-time without requiring a synchrotron, potentially offering a more easily accessible and cheaper method for investigating fracturing.

Future research will involve exploration of conditions that optimize weathering such as temperature, pressure, pH, and chemical composition. We expect that the microreactor will provide further insight into parameters that control weathering and phenomena like fracture and may lead to strategies to enhance carbonation rates, contributing to the development of more efficient negative emission technologies.

 

[1] Zhu, W., et al. Experimental evidence of reaction-induced fracturing during olivine carbonation, Geophys. Res. Lett. 2016 .
[2] Kleinsmit, M.H. et al. Microreactor, system and method for investigating a solid-fluid chemical reaction in a microreactor. World Intellectual Property Organization, WO 2025/005863 A2, 2025.
[3] Kleinsmit, L., et al. Microreactors for in-situ study of olivine dissolution rates under conditions relevant to enhanced weathering, Goldschmidt conference, 2024.
[4] Putnis, A. Mineral Replacement Reactions, Rev. Mineral. Geochem. 2009.
[5] Rudge, J. F., et al. A simple model of reaction-induced cracking applied to serpentinization and carbonation of peridotite, Earth Planet. Sci. Lett. 2010.