Microstructural analysis of slag properties associated with calcite precipitation due to passive CO2 mineralization.

CO2 mineralization in slag has gained significant attention since it occurs with minimal human intervention and energy input. While the amount of theoretical CO2 that can be captured within slag has been quantified based on slag composition in several studies, the microstructural and mineralogical effects of slag on its ability to capture CO2 have not been fully addressed. In this work, the CO2 uptake within legacy slag samples is analyzed through microstructural characterization. Slag samples were collected from the former Ravenscraig steelmaking site in Lanarkshire, Scotland. The collected samples were studied using X-ray Computed Tomography (XCT) to understand the distribution and geometry of pore space, as well as with scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) to visualize the distribution of elements within the studied samples. Electron backscatter diffraction (EBSD) was used to study the minerals distribution. The samples were also characterized through X-ray diffraction (XRD) and X-ray fluorescence (XRF), and the amount of captured CO2 was quantified using thermogravimetric analysis (TGA). Our results demonstrate that CO2 uptake occurs to the extent of ∼9-30 g CO2/ kg slag. The studied samples are porous in nature, with pore space occupying up to ∼30% of their volumes, and they are dominated by åkermanite-gehlenite minerals which interact with the atmospheric CO2 slowly at ambient conditions. EDS and EBSD results illustrate that the precipitated carbonate in slag is calcite, and that the precipitation of calcite is accompanied by the formation of a Si-O-rich layer. The provided analysis concludes that the porous microstructure as well as the minerals distribution in slag should be considered in forecasting and designing large-scale solutions for passive CO2 mineralization in slag.

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

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 utilization of alkaline wastes in passive carbon capture and sequestration: Promises, challenges and environmental aspects.

Alkaline wastes have been the focus of many studies as they act as CO2 sinks and have the potential to offset emissions from mining and steelmaking industries. Passive carbonation of alkaline wastes mimics natural silicate weathering and provides a promising alternative pathway for CO2 capture and storage as carbonates, requiring marginal human intervention when compared to ex-situ carbonation. This review summarizes the extant research that has investigated the passive carbonation of alkaline wastes, namely ironmaking and steelmaking slag, mine tailings and demolition wastes, over the past two decades. Here we report different factors that affect passive carbonation to address challenges that this process faces and to identify possible solutions. We identify avenues for future research such as investigating how passive carbonation affects the surrounding environment through interaction with the biosphere and the hydrosphere. Future research should also consider economic analyses to provide investors with an in-depth understanding of passive carbonation techniques. Based on the reviewed materials, we conclude that passive carbonation can be an important contributor to climate change mitigation strategies, and its potential can be intensified by applying simple waste management practices.

Novel internal analysis of metal irrigation/aspiration tips could explain mechanisms of posterior capsule rupture.

INTRODUCTION: Posterior capsule rupture (PCR) rates are used to measure cataract surgeons' quality. We wished to evaluate the internal non-visible surfaces of metal irrigation/aspiration (I/A) tips to identify potential mechanisms for PCR via novel metallographic imaging. METHODS: Ten metal I/A instruments underwent metallographic preparation by fine sectioning to expose inner surfaces near the aspiration opening. Analysis of inner bore, lumen, and opening aperture of metal aspiration tips was performed by optical microscopy, scanning electron microscopy (SEM), and 3D volume X-ray computational tomography (XCT). Distances from external aperture to first sharp metal surface were obtained and compared with a silicone-tipped instrument. RESULTS: We identified metal burrs near the aspiration apertures and manufacturing defects within all tips. XCT confirmed optical and SEM findings of significant defects and metal irregularities within aspiration tips. Samples also showed variation in lumen size/thickness, rough surfaces and material inhomogeneity, most pronounced at the internal tip. Median distance from outer aperture opening to first metal burr was 30 microns (range 10-120) and to internal tip irregularity (manufacturing flaw) was 250 microns (range 100-350). By comparison, distance to metal from the silicone outer aperture opening was 850 microns. CONCLUSIONS: We have demonstrated the hidden sharp metallic irregularities within commonly used metal I/A tips. If an aspirated capsule encounters these sharp metal flaws, PCR could result. Minimising this risk would require lengthening potential distance between capsule and bare metal (as with polymer/silicone tips). Our study provides unique imaging evidence endorsing this principle and illustrates a hidden mechanism contributing to PCR.

A separated vortex ring underlies the flight of the dandelion.

Wind-dispersed plants have evolved ingenious ways to lift their seeds1,2. The common dandelion uses a bundle of drag-enhancing bristles (the pappus) that helps to keep their seeds aloft. This passive flight mechanism is highly effective, enabling seed dispersal over formidable distances3,4; however, the physics underpinning pappus-mediated flight remains unresolved. Here we visualized the flow around dandelion seeds, uncovering an extraordinary type of vortex. This vortex is a ring of recirculating fluid, which is detached owing to the flow passing through the pappus. We hypothesized that the circular disk-like geometry and the porosity of the pappus are the key design features that enable the formation of the separated vortex ring. The porosity gradient was surveyed using microfabricated disks, and a disk with a similar porosity was found to be able to recapitulate the flow behaviour of the pappus. The porosity of the dandelion pappus appears to be tuned precisely to stabilize the vortex, while maximizing aerodynamic loading and minimizing material requirements. The discovery of the separated vortex ring provides evidence of the existence of a new class of fluid behaviour around fluid-immersed bodies that may underlie locomotion, weight reduction and particle retention in biological and manmade structures.