Reactivity of rice husk-derived lithium silicates followed by in situ Raman spectroscopy

Abstract

Lithium silicates were synthesized using rice husk ash as a precursor of silica to be used in CO2 capture. Two different treatment steps, with water (SiO2-W) or HCl 3 M (SiO2-A), were carried out prior to the rice husk burning. Silica with a high surface area of 303 m2g-1, a yield of 16.9% and a purity of 96.8% was obtained for the acid treatment. Subsequently, silica was impregnated with LiNO3 employing different Li/Si molar ratios and two different methods, successive incipient wetness impregnation and wet impregnation. SEM images showed agglomerates of nanometric spheres (70?100 nm) for the silica, and polyhedral particles for the silicate samples. The presence of three silicate phases, Li2Si2O5, Li2SiO3, and Li4SiO4, with different proportions was found by XRD and Raman spectroscopy measurements. In addition, the effect of particle size, temperature and sorption time over the CO2 capture capacity was analyzed. The best performance was found in the Li/Si = 4.1-HW sample with a particle diameter of 0.3 mm and 2 h of isothermal capture at 863 K. In situ Raman experiments were carried out to follow the phase transformations during the capture/regeneration steps. All samples remained in a stable value of capture capacity after several sorption/desorption cycles.