Influence of calcium concentration and dosage regime on calcification mediated dissolved inorganic carbon capture efficiency

Calcification mediated dissolved inorganic carbon (DIC) sequestration, in the form of insoluble CaCO₃, is an environmentally important geochemical process. In this study, the influence of calcium concentration and its dosing regime (single vs. partitioned multiple additions) on DIC capture efficiency (mole of DIC loss per mole of soluble calcium consumed, i.e. {increment}DIC/{increment}Ca²⁺) and calcification kinetics has been investigated. For this purpose, liquid medium containing 80mM DIC, generated through microbial ureolysis, was dosed with either varying amount of initial Ca²⁺ (50-300mM) or 300mM Ca²⁺ equivalent in three equally partitioned doses with the intermittent removal of the precipitate. The analysis of precipitation kinetics revealed a unique precipitation rate constant (0.0836mMd^-1) and a saturation state change rate constant (19.66±1.61d^-1) across all batch experiments. The results suggest that the apparent loss of both soluble Ca²⁺ and DIC increased along with the initial Ca²⁺ concentrations, until reaching a plateau. However, {increment}DIC/{increment}Ca²⁺ continued to decrease, signifying an increased loss of Ca²⁺ without proportional DIC capture. On the other hand, addition of an equivalent amount of Ca²⁺ (300mM) in multiple partitioned dosages not only improved the cumulative DIC removal (from 50.84mM to 62.27mM) but also ensured a better {increment}DIC/{increment}Ca²⁺ ratio. The results could be extended to design an efficient engineered calcification system for carbon sequestration. Calcification is an effective way to sequester dissolved inorganic carbon into stable calcium carbonate. However, the carbonate precipitation rate and the extent vary non-linearly on the amount of initial calcium added. This study exploits this non-linearity, by adopting multiple partitioned dosing of calcium salt over an equivalent single dose. Precipitation kinetics reveals that a simple intermediate alteration of the calcite saturation state can offer improved calcification process performance.