Image-Based Analysis of Weathered Slag for Calculation of Transport Properties and Passive Carbon Capture

Abstract

Weathering of silicate-rich industrial wastes such as slag can reduce emissions from the steelmaking industry. During slag weathering, different minerals spontaneously react with atmospheric CO2 to produce calcite. Here, we evaluate the CO2 uptake during slag weathering using image-based analysis. The analysis was applied to an X-ray computed tomography (XCT) dataset of a slag sample associated with the former Ravenscraig steelworks in Lanarkshire, Scotland. The element distribution of the sample was studied using scanning electron microscopy (SEM), coupled with energy-dispersive spectroscopy (EDS). Two advanced image segmentation methods, namely trainable WEKA segmentation in the Fiji distribution of ImageJ and watershed segmentation in Avizo ® 9.3.0, were used to segment the XCT images into matrix, pore space, calcite, and other precipitates. Both methods yielded similar volume fractions of the segmented classes. However, WEKA segmentation performed better in segmenting smaller pores, while watershed segmentation was superior in overcoming the partial volume effect presented in the XCT data. We estimate that CO2 has been captured in the studied sample with an uptake between 20 and 17 kg CO2/1,000 kg slag for TWS and WS, respectively, through calcite precipitation.

The mechanisms and drivers of lithification in slag‐dominated artificial ground

“…The calcite cement is the key component in the lithification of the slag‐dominated artificial ground in this study. Thin coatings and pore linings of calcite have been observed on slag surfaces by the authors and in the studies of Hobson et al (2017) and Khudhur et al (2022) but these are much smaller volumes than those documented in the slag heap at Glengarnock in this study. The driver for initiating the process of calcite precipitation is water (Equation ), and the slag samples in the studies of Hobson et al (2017) and Khudhur et al (2022) appear only to have had thin films of moisture/rainwater on the surfaces where Ca was leached and calcite precipitated.…”

“…Thin coatings and pore linings of calcite have been observed on slag surfaces by the authors and in the studies of Hobson et al (2017) and Khudhur et al (2022) but these are much smaller volumes than those documented in the slag heap at Glengarnock in this study. The driver for initiating the process of calcite precipitation is water (Equation ), and the slag samples in the studies of Hobson et al (2017) and Khudhur et al (2022) appear only to have had thin films of moisture/rainwater on the surfaces where Ca was leached and calcite precipitated. In the tufa in the Howden Burn, a much larger volume of calcite was precipitated as the volume of water in the stream facilitated greater leaching of Ca from the Consett slag heap, resulting in the large volume of tufa precipitated in the stream bed, downstream from the slag heap (Mayes et al, 2018; Renforth et al, 2009).…”

“…At Glengarnock, the volume of calcite precipitated as cement in the slag heap is large relative to the studies of Hobson et al (2017) and Khudhur et al (2022), although not at the same scale as the Howden Burn tufa. In common with that site though is the presence of a large volume of water, in this case Kilbirnie Loch.…”

Interrogation of Ecotoxic Elements Distribution in Slag and Precipitated Calcite through a Machine Learning‐Based Approach Aided by Mass Spectrometry

“…The BSE and EDS imaging of the studied samples portray typical features of slag shown in previous studies performed on slag samples collected from this site and from different sites. [ 31,32 ] These features include the coexistence of multiple phases with variable compositions as well as the existence of pore space within the samples, thereby providing potential permeability and surface area at which slag dissolution and calcite precipitation reactions can occur. Raman spectroscopy and EDS clustering analysis of samples A and C show that they contain åkermanite‐gehlenite minerals, which are commonly observed in BF slag, and their presence has been documented in this site and several sites worldwide.…”

“…Details about the location of this site and its history were summarized in the previous study. In light of the previous observations of microstructural features of slag and previously acquired backscattered electron images of slag, [31,36,32] three samples (A, B, and C) were shortlisted for the present analysis. These samples were selected so that they reflect the variation in slag sample microstructure (e.g., presence of pores space, presence of materials with different atomic numbers, presence of pore filling materials and precipitates) and so they demonstrate different calcite precipitation patterns (i.e., in pore space and on the external surface of the slag).…”