Preparation, characterization, and application of nano-silica from agricultural wastes in cement mortar

This work aimed to prepare and characterize nano-silica (SiO₂) from agricultural waste (palm ash) through a leaching treatment process using citric acid (C₆H₈O₇). These waste materials (if present in large quantities) could lead to environmental issues, since palm waste materials are burned in a furnace at 700 °C for 5 h. The produced palm ash (PA) was treated with different concentrations of citric acid solution (1–5%). Subsequently, the PA was crushed for 1 h in a ball-milling machine to minimize particle size and enhance reactivity for the leaching process. The pure extracted silica balls were then milled for 2 h. The results showed that silica could be extracted from PA using citric acid leaching treatment under the optimum extraction conditions with a solution temperature of 70 °C, a 1 h reaction time, and a concentration of 4% citric acid. The purity of the extracted silica was greater than 92%, and the average particle size was 80 nm. Various techniques (X-ray fluorescence, X-ray diffraction, particle size analyzer, atomic force microscopy, the Brunauer–Emmett–Teller method, and scanning electron microscopy) were used to detect the compositions, structures, particles distribution, surface area, and morphology of the prepared palm ash nano-silica (PANS). The PANS can be used as admixtures to enhance the mechanical properties of cement mortar. The results showed a 31% and 29% improvement in compressive and tensile strengths, respectively, under optimum conditions, and a weight of 6% and 10%, respectively, at 28 days of age. To the best of our knowledge, no work has previously prepared nano-silica from PA for use in cement mortars.