Process modelling and analysis of ikaite production for atmospheric CO₂ removal through ocean alkalinity enhancement

The production of ikaite, a metastable calcium carbonate hydrate, offers a promising pathway for atmospheric CO₂ removal through ocean alkalinity enhancement. This study explores the feasibility of ikaite production through a three-step process, involving calcite (CaCO₃) dissolution under elevated CO₂ pressure, CO₂ degassing from the calcium carbonate rich solution, and subsequent crystallisation. Here, a mathematical model was developed and validated against experimental data, and the effect of key operational parameters was examined. The calcite loading/dosage, particle size and CO₂ pressure for dissolution, seed loading and particle size for crystallisation, and degassing pressure as critical factors have significant impact on process efficiencies. Under optimal conditions, involving CO₂ pressures of 2 bar for dissolution, 0.01 bar for degassing, and 0.001 bar for crystallisation, with seed loading of 5 kg/m³ and seed particle sizes of 3 μm, the process achieved steady state ikaite production of 1.64 kg/m³ from a calcite feed of 0.83 kg/m³. This investigation demonstrates the technical viability of ikaite production through CO₂ pressure swing and informs its future development as a potential contributor to climate change mitigation.