Understanding Heterogeneity of a Slag-Derived Weathered Material: The Role of Automated SEM-EDS Analyses

Abstract

Slag heaps over years may evolve into complexly weathered zones, which are a challenging material for analyses as they contain phases from numerous sources and at different stages of weathering. However, the weathered zones are important parts of slag heaps, because they contain both primary and secondary phases enriched in metal(oid)s that may become soluble under specific conditions. The weathering reactions related to metal release or precipitation may be recorded in a heavy mineral fraction as the fraction contains predominately minerals with elevated toxic elements concentrations. Therefore, an automated SEM analysis on a polished section of included heavy mineral particles was applied in this paper for a rapid recognition of phases in a complex setting and their classification into detrital, primary and secondary phases. The approach was applied to a slag heap inŚwiętochłowice (Upper Silesia, Poland) and it consisted of analyzing magnetic and non-magnetic heavy mineral fractions from three distinct horizons noted A, B and C. Materials had been previously interpreted as being sourced from the heap itself (lowermost horizon C) and from artificially added materials used later for superficial site remediation (upper horizons A and B). Instead, automated SEM analysis demonstrated that horizon C is derived from the slag heap weathering, horizon B is derived predominately from the artificially added materials, whereas horizon A is a mixture of the B and C horizons. Additionally, when slag particles in horizons A and C are compared, the lowermost horizon C contains more slag-derived secondary phases, whereas horizon A contains more primary slag phases. Therefore, horizon A remains the most prone to releasing toxic elements because, considering its position as the uppermost horizon, it can be submitted to climatic solicitation (fast water circulation).

Studies of technogenic soils in Poland: past, present, and future perspectives

“…gypsum, jarosite, anglesite) in the heap of slag from Zn-ore processing (Świętochłowice, Upper Silesia). Pietranik et al (2018) applied an Automated SEM-EDS to extend the recognition of mineral phases during the slag weathering. Warchulski et al (2019) applied a combination of methods (SEM-EDS, XRD, EM) to track the migration paths of metallic elements in slag heap in Ruda Śląska-Wirek (Upper Silesia).…”

Editorial for Special Issue “Applications of SEM Automated Mineralogy: From Ore Deposits over Processing to Secondary Resource Characterization”

“…Different classification algorithms and four principal SEM-AM measurement routines for point counting modal analysis, particle analysis, sparse phase search and EDS spectral mapping are offered by the relevant software providers [1,[10][11][12]. These measurement routines provide the potential for the SEM-AM applications to scientific topics outside of the raw materials processing chain [13][14][15][16][17][18].…”

Towards Identification of Zircon Populations in Permo-Carboniferous Rhyolites of Central Europe: Insight from Automated SEM-Mineral Liberation Analyses

“…So far, automated Scanning Electron Microscope Mineral Liberation Analysis (SEM-MLA) has been applied in the industry for solving problems of ore mineral processing and extraction [7]. However, there are other assets of automated SEM methodology, including the detailed modal analysis of different rocks [8,9] or quantification of environmental weathering [10,11]. The great asset of automated SEM analyses is that they do not only calculate modal proportions, but also provide detailed quantitative information on grain size distribution, mineral associations, and phase characteristics such as angularity or length/breadth ratio.…”