RAND-based geochemical equilibrium algorithms with applications to underground geological storage of CO<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si5.svg"><mml:msub><mml:mrow /><mml:mn>2</mml:mn></mml:msub></mml:math>

Abstract Chemical and phase equilibrum (CPE) calculations are indispensable to the geochemical simulation of natural systems, such as freshwater, groundwater, mineral formations. In environments, many chemical reactions occur, both at interface between rocks fluids (e.g., dissolution reactions) in bulk phases aqueous speciation). Moreover, typical ionic species found nature require thermodynamic models for electrolytes, increasing calculation complexity. this work, we present RAND-based algorithms, which originate from Gibbs energy minimization, CPE problems closed systems open systems. The system specify fixed potentials non-charged species, a constant partial CO 2 pressure problem, or charged pH problem. We showcase robustness efficiency these algorithms using Mg-Si-Ca-CO -H O because its relevance underground geological storage. show quadratic convergence coupled tangent plane distance analysis can determine most stable assemblage. generate results agreement with PHREEQC, whereas they much faster than PHREEQC. described be potentially used reliable fast storage formations, other processes environments involving equilibrium.