Experimental and isotopic insights into mineral-fluid interactions at Earth’s surface in natural and engineered systems

Mineral-fluid interactions underpin element cycles, mobility of hazardous and valuable metals, and removal of CO2 from the atmosphere. The fractionation of isotopes provides insights into the processes controlling mineral-fluid reactions in both natural and human-influenced environments. Similarly, the isotopic compositions of minerals reflect the environmental conditions, such as temperature and fluid composition, at the time of mineral formation. Interpreting environmental conditions of the Earth’s past and designing strategies for remediation of pollutants and greenhouse gases requires an understanding of the mechanisms of mineral-fluid interaction. We use experimental approaches and analysis of stable isotopes (Mg, C, O, Ca, Si) to investigate processes controlling mineral-fluid interactions and the isotopic composition of minerals at Earth’s surface conditions, with a focus on the weathering reactions that remove CO2 from the atmosphere. Our experiments demonstrate that element exchange between carbonate minerals and fluids continues at bulk mineral-fluid equilibrium potentially resulting in alteration of isotopic signatures and immobilization/remobilization of metals. Similarly, isotope fractionation during non-stoichiometric wollastonite [CaSiO3] dissolution suggests mass exchanged is not unidirectional even far from chemical equilibrium. On the other hand, mineral dissolution-precipitation reactions are revealed to be dependent on water activity, controlled by relative humidity, with reactions effectively arrested below a threshold relative humidity. Together, our research explores the processes controlling mineral-fluid interactions at the mineral-surface scale, with implications for the global scale element cycles operating over geologic timescales.