The mineralogy of air granulated converter slag

Abstract

Converter slag, also known as Basic Oxygen Furnace slag, is a by-product of steelmaking that is produced in large quantities worldwide. It currently has few applications, because the presence of free lime often prevents the use as aggregate, while the low reactivity makes it undesirable as a cement replacement. Air granulation is a promising way to increase the reactivity of converter slag and enable recycling as a cement replacement and this is the first in-depth characterization of air granulated steel slag. In this study converter slag was separated into different fractions (0.25-0.5 mm, 0.5-1 mm, 1-2 mm, 2-4 mm) after air granulation to study the influence of size and therefore cooling speed on its mineralogy. The air granulated slag fractions were characterized using X-ray fluorescence, quantitative X-Ray diffraction, large area phase mapping based on scanning electron microscopy, and energy-dispersive X-ray spectroscopy as well as leaching behavior. The results show that the main minerals in air granulated converter slag are the same as in industrially cooled slag, but that additional perovskite was formed, which has not been reported before. All fractions contained large phenocrysts of Ca2SiO4 and Mg-wuestite surrounded by a dense matrix containing the other minerals. The three largest fractions are very similar to each other in chemical composition and microstructure, while the smallest fraction (0.25-0.5 mm) contains a higher content of Mg-wuestite even though the starting composition was the same. Free-lime is only present at the detection limit (0.1 ± 0.1 wt%) in all size fractions. The leaching of chromium and vanadium is greatly increased compared to standard cooled converter slag This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

Air granulated basic Oxygen furnace (BOF) slag application as a binder: Effect on strength, volumetric stability, hydration study, and environmental risk

“…brownmillerite due to quick cooling. A small amount of free lime (1.6 wt %) was observed in CSS while GSS exhibited no lime in the sample [39].…”

“…BOF slag taken from regular production at Tata Steel Europe in IJmuiden was cooled in two different ways: air granulated and conventional cooled at Harsco Metals Holland B.V. [39]. The slag is granulated at Harsco Metals Holland B. V. in a make-shift experimental facility by pouring in front of a strong air fan at a tapping temperature of 1592 ± 40 • C. While one part of the molten slag is cooled conventionally by pouring the liquid slag into pits and cooling it using water.…”

A Bogue approach applied to BOF slag

“…There are multiple reasons that could explain the modelled overestimation: i) the exclusion of C3S in the model, whereas small amounts of C3S could be present in the BOF slag (<3 wt%) [15], ii) all V2O5 is assumed to be incorporated in C2S, while C2(A,F) also incorporates V2O5 [50] and iii) that the C2S is partially weathered during storage. The latter assumption appears realistic because the F-type samples have structurally the lowest amount of C2S and significantly higher amorphous, Cc and CH [35]. C2(A,F) values are the closest to the 1:1 linear correlation for the lowest ωi of 0.25 and overestimated by the Bogue BOF slag calculation when an higher ωi is assumed (Figure 1c).…”

“…The purpose of this study is to forecast the BOF slag phase amounts in relation to the primary phases. Regarding modeling of the phase proportions of BOF slag, it is also important to realize that BOF slag is a highly variable industrial by-product since steel companies [35] are primarily focused on the right composition of the steel and the composition of BOF slag follows to serve this goal. Due to the wide variety of input of blast furnace metal and output steel compositions, there are also a wide variety of slag compositions that are produced in the basic oxygen steelmaking process.…”

“…Basic oxygen furnace slag (BOF slag), also known as Linz-Donawitz slag (LD slag), is an industrial byproduct that has not been extensively employed as SCM or as OPC free binder but the potential [10][11][12]. There are three primary benefits: i) the significant production of BOF slag (more than 100 Mt/year globally) [13];ii) the similar chemical composition of BOF slag and OPCs with high CaO and SiO2 concentration of >35 and >10 wt%, respectively [14]; iii) the similar mineralogical composition of BOF slag to OPCs, since the major phases of BOF slag are C2S and C2(A,F) [15,16]. The application of BOF slag as SCM [12,17,18] or as a standalone binder through thermal [19],…”