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The transesterification of used soybean oil with methanol was carried out over hydrated lime (HL), Ca(OH)2, and its decomposition products in the 200–500 °C range. The catalysts were characterized by X-ray powder diffraction (XRD), thermogravimetric analysis, and scanning electron microscopy. The XRD powder patterns demonstrated that the pristine sample consisted of a mixture of calcium hydroxide and calcite. It was noticed that the coexistence of CaO, Ca(OH)2, and CaCO3 remained up to 400 °C. At 500 °C, Ca(OH)2 is transformed into CaO so that this and CaCO3 are the only remaining phases. In the transesterification reaction, the influence of calcination temperature, reaction time, catalyst amount, methanol:oil ratio, and reaction temperature was studied. Full conversion of the raw materials into biodiesel (BD) was obtained with the fresh HL. In order to determine any change in the solid, it was recovered after 10, 30, and 60 min of reaction and analyzed by XRD analysis. Only Ca(OH)2, CaCO3, and traces of monohydrocalcite were detected. From the results it was demonstrated that the active phase for biodiesel production was calcium hydroxide. Furthermore, the catalyst was used up to three times without deactivation. A simple, economic, and environmentally friendly way to obtain biodiesel was developed considering (a) used soybean oil, considered waste, was employed as raw material, (b) hydrated lime is cheap and readily available, and (c) full conversion of the raw materials into BD was achieved with the as-received HL.

Coralline red algae assimilate HCO3– to precipitate CaCO3 in their tissues in the form of calcite or aragonite. A characterization of the biomolecular content and the crystalline structure of the biomineral of coralline red algae from the Pacific coast of Mexico was performed by powder X-ray diffraction (XRD), scanning electron (SEM) and tunneling microscopy (STM), and Fourier transform infrared spectroscopy (FTIR). The preliminary conclusion drawn from the results is that this type of calcite-aragonite biomineral has a very low organic content occluded within the crystals. FTIR bands at 2945 and 2889 cm–1 indicate that the most likely organic molecules are carbohydrates; moreover, peptide bond bands (amide I ~1640 and amide II ~1540 cm–1) were not detected, suggesting that proteins are not related to mineral synthesis or their stabilization. This could be explained if the biomineral is synthesized by a biologically controlled extracellular mineralization process. The XRD study showed two main mineral phases, calcite and aragonite, with very similar structural parameters to the inorganic mineral counterparts. The crystallite shapes, seen by STM, were found as plates and needles with different sizes, between 20 and 100 nm.