CaCO3 growth in conditions used for direct air capture

Abstract

A fluidized environment is used in a direct air capture system for the purpose of crystallizing carbonate ions from an alkaline liquid. The crystallization of calcium carbonate, in the conditions necessary for a direct air capture system, requires a pH range that has not been studied in the current literature. Beaker and lab-scale fluidized bed experiments were used to assess the effect of temperature, surface area availability, and pH on primary and secondary nucleation. The highest retention was found in the conditions where mass transport is favored for the beaker experiments, i.e., high loading, small pellet sizes, and low temperatures. Lab-scale reactor experiments confirmed these findings with the highest retention of 58.8 ± 1.8% observed for mid-size pellets. The pellets and fines produced had the calcite morphology. An inversion of morphology from calcite to vaterite was found as pH was lowered to 11.8.