Mineralogy and Leachability of Natural Rocks–A Comparison to Electric Arc Furnace Slags

Vollprecht Vollprecht,Raith Raith,Berger Berger,Neuhold Neuhold,Sedlazeck Sedlazeck,Altenburger‐Junker Altenburger‐Junker,Aldrian Aldrian,Van Zomeren Van Zomeren,Dijkstra Dijkstra

doi:10.3390/min9080501

Vollprecht Vollprecht, Raith Raith + Show 7 more

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https://doi.org/10.3390/min9080501

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Abstract

In waste management, recycled and industrial aggregates (e.g., electric arc furnace (EAF) slags) for construction applications have to fulfil the limit values with respect to the total and/or leachable contents of potentially environmentally problematic chemical elements (PEPE, e.g., Cr, Ni, Cu, Mo, V). Natural aggregates, i.e., quarried hard rocks, are neither tested nor regulated for these parameters in most EU member states, e.g., Austria, prior to using them as a construction material. The purpose of this study was to relate the mineralogy to the leachability of natural aggregates with a special emphasis on PEPE and to interpret these findings in comparison with EAF slags. Five samples of Austrian rocks were investigated by polarization microscopy, electron probe microanalyses (EPMA), X-ray diffraction (XRD), and leaching tests as well as by hydrogeochemical modelling using LeachXSTM. Two samples showed elevated total contents of Cr, Ni, and Mo which were present as Cr-spinel, (Fe,Mg)(Al,Cr)2O4, Ni-olivine, (Fe,Mg,Ni)2SiO4, and molybdenite, MoS2. Whereas the former two phases also controlled the leaching of Cr and Ni, the observed leaching of Mo was higher than expected in the case of solubility control by molybdenite. In summary, the leachability of PEPE in natural and industrial aggregates was controlled by similar mineralogical mechanisms.

Highlights

Every year about 100 million tons of constructional aggregates are used in Austria [1] and 3.2 billion tons in the EU [2]
Industrial aggregates, e.g., steel slags, and recycled aggregates obtained from construction and demolition waste are used for construction purposes
In order to evaluate the total contents of potentially environmentally problematic elements (PEPE) in the investigated natural rocks, the Recycling Construction Materials Ordinance (RCMO), which regulates the total contents of recycled and industrial aggregates, serves as a comparison

Summary

Introduction

Every year about 100 million tons of constructional aggregates are used in Austria [1] and 3.2 billion tons in the EU [2]. Industrial aggregates, e.g., steel slags, and recycled aggregates obtained from construction and demolition waste are used for construction purposes. In contrast to natural rocks, for industrial and recycled aggregates, geological, physical-technical, and chemical [3] properties and the environmental impact has to be assessed prior to application. According to the Recycling Construction Materials Ordinance (RCMO) the total contents of Cd, Cr, Mo, Tl, and W (industrial aggregates) and As, Pb, Cd, Co, Cr, Cu, Ni, Hg, and Zn (recycled aggregates) are regulated in Austria [4] because these are considered as environmentally problematic. Data on the average total element contents of rocks in Austria are summarised in the Geochemical Atlas of the Republic of Austria [5]. Data for fluorine are missing for Austria, but its mineralogy and geochemistry is generally known [6] and related to the alkalinity of Minerals 2019, 9, 501; doi:10.3390/min9080501 www.mdpi.com/journal/minerals

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