Precipitated aragonite can be synthesized at relatively low temperatures by combining the application of low-frequency sonication with the use of magnesium chloride additive, as demonstrated by our prior study. In the present study, new process conditions were found that promote aragonite formation while accelerating and increasing the reaction yield. It was found that Mg-to-Ca molar ratio of 3:1, together with higher slurry concentration (74 g/L Ca(OH) 2) and higher power-tovolume ratio (800 W/L gross, achieved by reducing slurry volume), promoted the aragonite formation while working at a higher CO 2 flow rate (2.0 NL/min), and consequently higher PCC production rate (1g/(L•min) CaCO 3). The yield was thus improved while conserving the desired product properties: high polymorph purity (95.7 wt%), small and narrow particle size distribution (D[3,2] = 0.74 μm), and unique shape (hubbard squash-like).