Preparation of Silica-Alumina Nanoparticles via Blast-Furnace Slag Dissolution in Low-Concentration Acetic Acid for Carbonation

Abstract

Blast-furnace slag (BFS) has been used as a feedstock for CO 2 sequestration by indirect mineral carbonation to produce calcium carbonate precipitates and solid residues. The most-abundant elements in these residues, Si and Al, are usually considered to be impurities that need to be removed in acid-dissolution processes involving BFS. The co-production of value-added materials from these residues is an attractive option for strengthening the economic competitiveness of mineral carbonation methods. In view of this, we separated the Si and Al, as their hydrated forms, during the dissolution of BFS in acetic acid prior to carbonation. During the sol-gel processing of Si-Al nanoparticles, a catalyst is usually required during the hydrolysis and subsequent condensation processes. In this study, only condensation occurs because the low-concentrations of acetic acid used facilitate in-situ hydrolysis during the dissolution process. Aging was carried out not only to structurally arrange the Si and Al but also to oxidize the marginal Fe(II) to reddish Fe(III). Silica-alumina nanoparticles (78% Si and 22% Al) were prepared by a simple sol-gel route at ambient pressure. These nanoparticles were amorphous and below 20 nm in size. Fourier-transform infrared (FT-IR) studies reveal that the nanoparticles consist of Si-O-Si and Si-O-Al bonds. 27 Al nuclear magnetic resonance (NMR) spectroscopy reveals a significant resonance corresponding to tetra-coordinated Al inside the particle framework.

Optimization of high alumina slag practice in blast furnace ironmaking: an industrial approach (PART 1: fundamental aspects)

“…By the combined alumina-silica MAS-NMR analysis, the amorphous nature of silica has been observed to be maintained at annealing temperatures whereas alumina has been observed to crystallize at temperatures greater than 1273 K [74]. Through the FT-IR study [75], the presence of Si–O–Si and Si–O–Al bonds in alumino-silicate slags has been detected in different orders of magnitude. The longer Al–O bonds are less mobile and therefore contribute to the slag's increased viscosity [50].…”

“…The longer Al–O bonds are less mobile and therefore contribute to the slag's increased viscosity [50]. The dominant presence of Al tetrahedra units is further supported by NMR analysis [75].…”

Preparation of Mullite-Silica Composites Using Silica-Rich Monophasic Precursor Obtained as a Byproduct of Mineral Carbonation of Blast-Furnace Slag

“…The silica-alumina nanoparticles, i.e., the monophasic precursor for mullite-silica composites, were prepared using the filtered solution obtained after the leaching of BFS under the following experimental conditions: 20 g/L of BFS, 0.87 M acetic acid, 30 • C, and stirring for 1 h. As described in our previous work [15], silica-alumina hydrogels were produced in the filtered solution as a result of increasing temperature to 60 • C at 500 rpm. Marginal amounts of minor impurities (i.e., Ca, Mg, and Fe) were excluded from the gels via aging and washing processes, and silica-alumina powders were formed after drying.…”

“…Previously, we used BFS with high calcium content as a feedstock for mineral carbonation [14,15]. In that study, we successfully obtained pure calcium carbonate in the course of mineral carbonation of BFS.…”