In this study, PCC (precipitate calcium carbonate) was synthesized from green mussel shell waste via calcination and subsequent carbonation methods. Organic substances were removed from green mussel shell powder using a 5-hour calcination at 900 °C. Furthermore, the carbonation method was used in the Ca (NO 3 ) 2 solution at constant stirring speed with pH control by NH 4 OH, followed by the injection of carbon dioxide at 50, 70, and 90 °C temperature variations to precipitate calcium as CaCO 3 (PCC). According to Rietveld’s quantitative XRD analysis, PCC products at 50 °C, 70 °C, and 90 °C exhibited primarily calcite and aragonite phases, with a significant needle-like morphology of aragonite growth during synthesis. Aragonite growth appears to have increased with increasing temperature. The results show that a simple, low-cost approach to green recycling works.