Geometallurgical Characterization of Non-Ferrous Historical Slag in Western Tasmania: Identifying Reprocessing Options

Historical ferrous slag induces modern environmental problems in the Moravian Karst (Czech Republic)

Ferrous slag produced by a historic smelter is washed from a slagheap and transported by a creek through a cave system. Slag filling cave spaces, abrasion of cave walls / calcite speleothems, and contamination of the aquatic environment with heavy metals and other toxic components are concerns. We characterize the slag in its deposition site, map its transport through the cave system, characterize the effect of slag transport, and evaluate the risks to both cave and aqueous environments. The study was based on chemical and phase analysis supported laboratory experiments and geochemical modeling. The slag in the slagheap was dominated by amorphous glass phase (66 to 99 wt%) with mean composition of 49.8 ± 2.8 wt% SiO₂, 29.9 ± 1.6 wt% CaO, 13.4 ± 1.2 wt% Al₂O₃, 2.7 ± 0.3 wt% K₂O, and 1.2 ± 0.1 wt% MgO. Minerals such as melilite, plagioclase, anorthite, and wollastonite / pseudowollastonite with lower amounts of quartz, cristobalite, and calcite were detected. Slag enriches the cave environment with Se, As, W, Y, U, Be, Cs, Sc, Cd, Hf, Ba, Th, Cr, Zr, Zn, and V. However, only Zr, V, Co, and As exceed the specified limits for soils (US EPA and EU limits). The dissolution lifetime of a 1 mm³ volume of slag was estimated to be 27,000 years, whereas the mean residence time of the slag in the cave is much shorter, defined by a flood frequency of ca. 47 years. Consequently, the extent of slag weathering and contamination of cave environment by slag weathering products is small under given conditions. However, slag enriched in U and Th can increase radon production as a result of alpha decay. The slag has an abrasive effect on surrounding rocks and disintegrated slag can contaminate calcite speleothems.

Treasure from trash: Mining critical metals from waste and unconventional sources

To meet future technological demands of our growing global community new sources of industry critical metals need to be identified. To meet these demands, extracting minerals from larger, lower grade deposits across most commodities is required, which in turn generates ever increasing amounts of mine wastes. We propose that agromining could be used to enables access to unconventional resources not viable using existing minerals processing techniques. This innovative technique relies on so-called hyperaccumulator plants to bio-concentrate high levels of metals into living biomass which can then be extracted from the harvested bio-ore. Producing critical metals, such as nickel, cobalt and thallium, efficiently and sustainably using agromining appears to be well within reach, but this technology needs industrial champions to develop demonstration sites that are scaled appropiately in areas where it is feasible.

Editorial for Special Issue “Metallurgical Slags”

Exploitation and further processing of mineral resources are of great importance for modern society [...]

Grinding Kinetics of Slag and Effect of Final Particle Size on the Compressive Strength of Alkali Activated Materials

This study aims to model grinding of a Polish ferronickel slag and evaluate the particle size distributions (PSDs) of the products obtained after different grinding times. Then, selected products were alkali activated in order to investigate the effect of particle size on the compressive strength of the produced alkali activated materials (AAMs). Other parameters affecting alkali activation, i.e., temperature, curing, and ageing time were also examined. Among the different mathematical models used to simulate the particle size distribution, Rosin–Rammler (RR) was found to be the most suitable. When piecewise regression analysis was applied to experimental data it was found that the particle size distribution of the slag products exhibits multifractal character. In addition, grinding of slag exhibits non-first-order behavior and the reduction rate of each size is time dependent. The grinding rate and consequently the grinding efficiency increases when the particle size increases, but drops sharply near zero after prolonged grinding periods. Regarding alkali activation, it is deduced that among the parameters studied, particle size (and the respective specific surface area) of the raw slag product and curing temperature have the most noticeable impact on the compressive strength of the produced AAMs.