HYDRAULIC AND LEACHING BEHAVIOUR OF BELITE CEMENTS PRODUCED WITH ELECTRIC ARC FURNACE STEEL SLAG AS RAW MATERIAL

Three belite-rich cements consisting of a clinker made with 0 (BC), 5 (BC5) and 10 wt. % (BC10) electric arc furnace steel slag (EAFS) as raw material, were studied for their hydraulic and leaching behaviour. Hydration behaviour was studied by FTIR, TG/DTG and SEM analyses. The cements with EAFS resulted in a higher C2S/C3S and C4AF/C3A ratio compared to the reference body. As a result, the rate of hydration was low at early days whereas the structure was porous with scattered AFm and C–S–H crystals. At 28 days, a comparable dense microstructure consisting largely of C–S–H is observed in all mortars. Leaching was studied for V and Cr by means of tank test according to standard NEN 7345. The results showed V release below 2 μg/l. Chromium release calculated per 24 h was 1.4 μg/l in BC5 and 2.4 μg/l in BC10, which is much lower than the parametric value of 50 μg/l specified by the European Directive for drinking water (98/83/EC)

Shrinkage and mitigation strategies to improve the dimensional stability of CaO-FeOx-Al2O3-SiO2 inorganic polymers

Volumetric stability is an important aspect of the performance of building materials, and the shrinkage of CaO-FeOx-Al2O3-SiO2-rich inorganic polymers (IPs) has not been thoroughly investigated yet. Hence, this paper describes the outcome of a study conducted to investigate ways to minimize their shrinkage using different curing regimes. Two different slags were used as case studies to assess the robustness of the developed mitigation strategies. IP pastes and mortars were cured at (i) room condition, (ii) in slightly elevated temperature (60 \ub0C for 2 d) and (iii) in a water-saturated environment. The reaction kinetics and formed products were examined on IP pastes, while mortars were made to characterize the 28 d pore structure, autogenous shrinkage, drying shrinkage, and strength development. The results showed that the precursors\u2019 reactivity and curing conditions severely affect shrinkage mechanisms and magnitude. Volumetric changes in the plastic stage can be related to the precursors\u2019 reactivity but drying shrinkage was the driving mechanism affecting the volumetric stability of all IP mortars. Understanding the effect of a precursor\u2019s composition and curing conditions on shrinkage is fundamental to develop proper mitigation strategies and to overcome one of IPs\u2019 main technical drawbacks

Magnetic Glass Ceramics by Sintering of Borosilicate Glass and Inorganic Waste

Ceramics and glass ceramics based on industrial waste have been widely recognized as competitive products for building applications; however, there is a great potential for such materials with novel functionalities. In this paper, we discuss the development of magnetic sintered glass ceramics based on two iron-rich slags, coming from non-ferrous metallurgy and recycled borosilicate glass. The substantial viscous flow of the glass led to dense products for rapid treatments at relatively low temperatures (900–1000 °C), whereas glass/slag interactions resulted in the formation of magnetite crystals, providing ferrimagnetism. Such behavior could be exploited for applying the obtained glass ceramics as induction heating plates, according to preliminary tests (showing the rapid heating of selected samples, even above 200 °C). The chemical durability and safety of the obtained glass ceramics were assessed by both leaching tests and cytotoxicity tests

Advances in alkali-activation of clay minerals

To future-proof alkali-activation technology, there is a need to look beyond well-established precursors such as fly ash and blast furnace slag, due to resource competition, geographical distribution and technical limitations. Clay minerals are abundant and diverse aluminosilicate resources available around the world. However, due to the mineralogical complexity amongst the most common 1:1 (kaolinite, halloysite) and 2:1 (montmorillonite, illite) clay minerals, and practical issues such as workability, their use has been more limited. Recent advances have improved understanding both of pre-activation treatments (thermal, mechanical, chemical), and of the factors influencing clay reactivity, phase assemblages and properties of final products. This opens new opportunities for the exploitation of these resources to produce sustainable cements. A one-size-fits-all approach for processing and activating clay minerals is not viable. Instead, activation routes need to be tailored according to the clay mineralogy to achieve the binder properties required for key applications

Dissolution Behaviour of Alkali-activated Fe-rich Non-ferrous Metallurgy Slag in Acetic Acid

The application of Fe-rich non-ferrous metallurgy slag (NFS, within a FeOx-SiO2-Al2O3-CaO system) in alkali-activated materials requires detailed information on the durability performance. The present study investigates the durability of alkali activated NFS (AA-NFS) exposed to acetic acid to simulate the attack of a concrete by organic acids present in animal manure or sewage systems. The dissolution behavior of NFS and alkali-activated NFS (AA-NFS) was assessed by immersing NFS and AA-NFS in a 3 wt. % acetic acid solution at a liquid to solid weight ratio of 1000. The dissolved ions in the acetic solution from NFS and AA-NFS were measured at different time intervals over 7 days. Through the comparison of NFS with AA-NFS, the dissolution behavior of unreacted slag and binder in AA-NFS could be evaluated separately, considering a calculated amount of 47.7 wt.% of unreacted slag was present in the AA-NFS. The results demonstrated that the binder dissolves slightly faster than slag in the first 4 hours. Over half of the dissolution rate of the Ca, Fe and Al in AA-NFS was due to binder. While for Si, 41% total dissolution rate in AA-NFS was from binder and the other 59% was from unreacted slag. After 7 days however, the dissolved fraction of slag was higher than binder. About 90% Ca, 79% Fe and 71% Al in slag was ended up in the acetic acid solution, which is higher than that in binder (74%, 62% and 56%, respectively). A significantly higher difference was found for the total dissolved fraction of Si in slag (86%) compared to that in binder (43%). The highly connected silicate network in the binder remains largely intact as silica gel, while due to the low connectivity of the silicate species in the slag the silicate dissolves after the other elements have left the structure. Overall these results suggest that Ca has the lowest dissolution resistance in binder, followed by Fe, Al and Si

New insights into the mineralogy and geochemistry of sb ores from Greece

Antimony is a common metalloid occurring in the form of Sb-sulfides and sulfosalts, in various base and noble metal deposits. It is also present in corresponding metallurgical products (concentrates) and, although antimony has been considered a penalty element in the past, recently it has gained interest due to its classification as a critical raw material (CRM) by the European Union (EU). In the frame of the present paper, representative ore samples from the main Sb-bearing deposits of Greece (Kilkis prefecture, Chalkidiki prefecture (Kassandra Mines), and Chios Isl.) have been investigated. According to optical microscopy and electron probe microanalysis (EPMA) data, the Greek ores contain stibnite (Sb2 S3), boulangerite (Pb5 Sb4 S11), bournonite (PbCuSbS3), bertherite (FeSbS4), and valentinite (Sb2 O3). Bulk analyses by inductively coupled plasma mass spectrometry (ICP-MS) confirmed, for the first time published, the presence of a significant Hg content in the Kilkis Sb-ore. Furthermore, Kassandra Mines ores are found to contain remarkable amounts of Bi, As, Sn, Tl, and Se (excluding Ag, which is a bonus element). The above findings could contribute to potential future exploration and exploitation of Sb ores in Greece

The role of nano-perovskite in the negligible thorium release in seawater from Greek bauxite residue (red mud)

We present new data about the chemical and structural characteristics of bauxite residue (BR) from Greek Al industry, using a combination of microscopic, analytical, and spectroscopic techniques. SEM-EDS indicated a homogeneous dominant “Al-Fe-Ca-Ti-Si-Na-Cr matrix”, appearing at the microscale. The bulk chemical analyses showed considerable levels of Th (111 μg g−1), along with minor U (15 μg g−1), which are responsible for radioactivity (355 and 133 Bq kg−1 for 232Th and 238U, respectively) with a total dose rate of 295 nGy h−1. Leaching experiments, in conjunction with SF-ICP-MS, using Mediterranean seawater from Greece, indicated significant release of V, depending on S/L ratio, and negligible release of Th at least after 12 months leaching. STEM-EDS/EELS & HR-STEM-HAADF study of the leached BR at the nanoscale revealed that the significant immobility of Th4+ is due to its incorporation into an insoluble perovskite-type phase with major composition of Ca0.8Na0.2TiO3 and crystallites observed in nanoscale. The Th LIII-edge EXAFS spectra demonstrated that Th4+ ions, which are hosted in this novel nano-perovskite of BR, occupy Ca2+ sites, rather than Ti4+ sites. That is most likely the reason of no Th release in Mediterranean seawater