Effects of Experimental Parameters on the Extraction of Silica and Carbonation of Blast Furnace Slag at Atmospheric Pressure in Low-Concentration Acetic Acid
Kyungsun Song, Sangwon Park, Wonbaek Kim, Chi Jeon, Ji-Whan Ahn
2017
Metals
Blast furnace slag (BFS), a calcium-rich industrial byproduct, has been utilized since 2005 as a mineral carbonation feedstock for CO 2 sequestration, producing calcium carbonate precipitates. In this study, the conditions for the dissolution of Ca and Si in acetic acid, and subsequent carbonation, were elaborated. For this purpose, the retardation of the polymerization of silicon was attempted by varying the concentration of acetic acid, temperature, and leaching time. An inductively coupled
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... asma (ICP) analysis revealed that both the Ca and Si dissolved completely within 30 min in 5% acetic acid at room temperature. This high dissolution value can be attributed to the fact that Ca was bound to O rather than to Si, as determined by X-ray photoelectron spectroscopy (XPS). The use of CO 2 -absorbed monoethanolamine enabled the complete carbonation of BFS at ambient conditions without the need for a pH swing. The presence of dissolved silica was found to affect the polymorphs of the precipitated CaCO 3 . We believe that this process offers a simple method for manipulating the composites of products obtained by mineral carbonation diminishing the leaching residues. considered as an attractive feedstock because its chemical composition is similar to that of silicate minerals, and the steel industry is a large source of anthropogenic CO 2 emissions [5] . Most studies into the mineral carbonation of slag have focused on selective Ca dissolution and the production of relatively pure CaCO 3 . Other elements, including Si, were regarded as being impurities [6] [7] [8] . Silica polymerization is the main drawback affecting mineral carbonation using an acid-leaching process, because the formation of silica gel makes the solid-liquid separation challenging. Therefore, for the selective Ca leaching from BFS with a high Si content, the use of temperatures higher than 50 • C was recommended for the removal of the Si in the gel state during the dissolution process [9] . However, SiO 2 and Al 2 O 3 , along with CaCO 3 , are valuable materials. Binary composition SiO 2 -Al 2 O 3 has traditionally been used in the ceramics industry [10] . In addition to these applications, they have also been used as important additives in the polymer industry in either a discrete or mixed state (e.g., as inorganic fillers) [11] . The combination of CaCO 3 and SiO 2 (CaCO 3 -SiO 2 composite) has been suggested as being an ideal alternative to SiO 2 for the strengthening of silicon rubber [12] . Moreover, recent studies have shown that mineralization of alkaline-earth carbonates in silica-rich media leads to fascinating and intricate nanoparticle-based silica-carbonate composites referred to as "biomorphs" [13, 14] . These processes are driven by pH-oscillation despite the absence of organic matters. The solubility or crystallization of silica depends on the environment of the solution but it is generally known that its gelation is accelerated under conditions of high pH, high ionic strength, or high temperature in the acidic solution below pH 9 [15]. In an acidic solution, amorphous silica with the highest solubility is known to become monomer silicic acid, Si(OH) 4 . At high concentrations of dissolved silica (more than 17 mmol/L as SiO 2 ), it can also be aged to amorphous silica, in the form of a colloid, a silica gel, or a filterable precipitate. However, a notable point is that a supersaturated silica solution can be kept in the liquid state for a relatively long duration by delaying its aggregation [16] . In the present study, we focused on the maximum recovery of not only Ca, but also Si simultaneously from BFS in the acid leaching process by preventing the silica aggregation. The aim of this study was to suggest a route for controlling the silica aggregation in the mineral carbonation of BFS to prepare silica (or calcium carbonate) compounds diminishing the leaching residues. Acetic acid (pKa of 4.76) was tested as a mild acid, with the anticipation that it could aid the carbonation without a separate pH-swing process. The phases of the calcium carbonate produced by this method were compared to determine whether they contained dissolved silica. The purity and phase of the silica were studied after being obtained through post-separation from the leachate. To prevent the inclusion of other external cations (e.g., Na from the NaOH used for the neutralization), representative amines (ammonia and monoethanolamine (MEA)) for CO 2 sorption were employed for the carbonation process.
doi:10.3390/met7060199
fatcat:kvshbddedrgztct3zp64anvpii