Effect of Solidification and Cooling Methods on the Efficacy of Slag as a Feedstock for CO₂ Mineralization

Abstract

Iron and steel making (ISM) slag is often utilized to partially offset CO 2 emissions associated with metal production. Currently, the primary recycling method for slag is as β-Ca 2 SiO 4 utilized in the cement industry, termed ground granulated blast furnace slag (ggbs). However, the cement market is not large enough to exploit the entirety of ISM slag as ggbs, relegating a large quantity of slag to reuse pathways with minor impacts on CO 2 reduction. Recent years have seen an increase in research into mineralizing CO 2 using the Ca and Mg content of ISM slags as a feedstock. Unfortunately, it has not been widely recognized that the solidification and cooling processes of slag dramatically effects its efficacy as a CO 2 mineralizing feedstock via modification of mineralogy, crystallinity, grain size, and micromorphology. This paper clarifies the key properties determining mineralization effectiveness and elucidates how to control these properties during the solidification and cooling process. The effect of solidification and cooling method on net CO 2 reduction is shown to be strongly dependent on solidification and cooling method along with the CO 2 intensity of energy generation.

Numerical Modeling of Argon‐Oxygen Decarburization Slag Cooling

“…This is due to the effect of degree of crystallinity on the solidified slag properties, such as reactivity, leaching, and conductivities. [ 21 ] Furthermore, problematic phases, such as dicalcium silicate, may form during the slower cooling of AOD slags and cause disintegration of larger particles into dust due to volumetric changes related to mineralogical changes as temperature decreases. [ 34 ] If the crystallization during the cooling cannot be avoided, i.e., the cooling rate of the slag is not fast enough, the formation of the most harmful minerals, such as dicalcium silicate mentioned earlier, could be avoided by mixing different kinds of slags before the cooling and thus directing the slag composition into an area in which less harmful minerals are formed.…”

“…[ 35 ] Generally speaking, the amorphous structure is more easily obtained for slags with higher SiO 2 contents because the required cooling rates for the basic slags are extremely high. [ 21 ]…”

“…[16] Furthermore, the properties of the slag are affected by the cooling method. [18][19][20][21] The simplest method for AOD slag cooling is cooling in an ambient atmosphere in a slag yard, [15] but other methods, such as water cooling [22] or airgranulation, [15] have been proposed for achieving a faster cooling rate. The literature on modeling the cooling of AOD slags remains scarce.…”

Effect of Cooling Method on the Mineralogy and Stability of Steel Slag

“…[11][12][13][14] Many researchers have paid attention to the effect of different cooling methods on slag properties and crystallization behavior. [15][16][17][18][19][20][21][22] For blast furnace slag, the crystallization behavior are determined using time-temperature-transformation (TTT) and continuous cooling transformation (CCT) diagrams by the hot thermocouple technique. The relationship between the cooling method and the properties of blast furnace slag has been established successfully.…”

Prediction of Nucleation Lag Time from Elemental Composition and Temperature for Iron and Steelmaking Slags Using Deep Neural Networks

“…6) Regardless of the usage pathway, control of slag solidification is critical to achieve high performance as it governs the degree of crystallinity (equivalently, the amorphous extent) and the mineralogy. 7) For instance, many countries require ggbs to be > 67% amorphous, 8) slag-based CO 2 mineralization improves as crystal grain size increases, 9) and heat recovery methods must consider the interplay between heat content, conductivity, and reactivity that arise from crystalline extent and mineralogy. [10][11][12][13] The critical phenomenon in controlling crystallinity is the kinetics of the phase change from the liquid to solid.…”