Synthesis and characterization of nano-crystallite triple superphosphate from waste Pila globosa shells for sustainable industrial production

Abstract

The purpose of this research work was to explore the sustainable industrial application of waste Pila globosa (P. globosa) shells, commonly known as apple snail shells, via synthesizing nano triple superphosphate [TSP, Ca(H₂PO₄)₂·H₂O]. An exothermic reaction between P. globosa shells and phosphoric acid, which were the precursors of calcium and phosphate respectively, facilitated the production of TSP. The synthesized TSP was characterized by using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Raman spectroscopies, field emission scanning electron microscopy (FESEM), UV-Vis-NIR spectroscopy, and wavelength-dispersive X-ray fluorescence (WDXRF) spectroscopy. TGA showed promising results by providing the remaining mass (including 2.42% free water) value as 77.63%, which is very close to the theoretical remaining mass percentage (78.57%). Thus, this observation acts as good evidence for the formation of TSP in nearly pure phase. Furthermore, crystallite size was assessed with the aid of different model equations, and a reasonable value of crystallite size was achieved from the Sahadat–Scherrer model (99 nm) and three peaks model (88 nm). The WDXRF analysis of the synthesized TSP showed good evidence that it contained 76.9% of P₂O₅, much higher than the minimum requirement for commercial applications. A fixed amount of water was added to this reaction process to eliminate the drying procedure, which will minimize the production cost but increase the yield. This research revealed that P. globosa shells are a potential precursor of calcium as a new raw material source of P-fertilizer and 60% (w/w) phosphoric acid to minimize the production cost by eliminating the extra drying process with 76.9% P₂O₅ content. Hence, P. globosa shells will certainly be an alternative source to meet the demands of raw materials to synthesize phosphate-based fertilizers.