CaCO₃ Precipitation and Polymorph Forms During CO₂ Sequestration from the Atmosphere: Effects of the Basic Buffer Components

CO₂ sequestration and polymorph selection was achieved by CaCO₃ precipitation via the reaction of calcium ions and atmospheric CO₂ in a basic buffer, in a process that mimicked geological sedimentation. Precipitation proceeded in yield exceeding 80% in the presence of basic buffers at room temperature over 10 h. Calcite formed mainly during the early stages of precipitation, within less than 5 h, followed by needle-like aragonite precipitation between 5 and 10 h of aging. The aragonite polymorph selection increased in the presence of carbonic anhydrase and at high solution temperatures. We found that the deposited CaCO₃ polymorphs depended on the rate of calcium ion consumption and precipitation as well as the ionic strength of the basic buffer and the solution pH. We developed a method for depositing high-purity aragonitic CaCO₃ crystals in solutions with temperatures exceeding 60 °C in the presence of basic buffer, using CO₂ from the atmosphere without the need for seed crystals or metal ions.