Low-Cost and Rapid Production of Calcium Formate from Cockle Shell Waste for Sustainable Waste Recycling

Calcium formate (Ca(HCOO)₂) is an important industrial chemical widely used in construction, feed additives, and various chemical processes. In this work, calcium formate was synthesized from cockle shell waste and concentrated formic acid (50%, 60%, and 70% w/w) by a simple, rapid, low-cost, and environmentally friendly process, denoted as CF50, CF60, and CF70, respectively. The chemical and physical properties of as-synthesized calcium formate using cockle shells as a renewable calcium source were investigated by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), X-ray fluorescence (XRF), Thermal gravimetric analysis (TGA), and scanning electron microscopy (SEM) techniques. The FTIR and XRD results revealed that the samples prepared using 50% and 60% formic acid produced well-crystallized α-calcium formate. In contrast, the reaction using 70% formic acid generated a strongly exothermic reaction, which hindered the complete conversion of calcium carbonate and resulted in the presence of residual CaCO₃ in the final product. Similarly, the SEM images of the CF50 and CF60 samples show the slick surface of orthorhombic crystals of calcium formate; on the other hand, the SEM image of CF70 shows some small particles of aragonite on the surface of the calcium formate crystals. The 60% formic acid provided the optimal synthesis condition, yielding pure calcium formate with the shortest synthesis time. Overall, the proposed approach provides a simple, rapid, and cost-effective route for producing calcium formate from shell waste. Furthermore, the utilization of cockle shell waste as a renewable calcium source contributes to waste valorization, reduces environmental impacts associated with shell disposal, and minimizes dependence on mined limestone resources, supporting sustainable resource utilization within a circular economy.