Gallium (Ga) and germanium (Ge) are technologically important critical elements. Lead blast furnace slags from Tsumeb, Namibia, comprise over two million metric tons of material that contains high levels of Ga (135–156 ppm) and Ge (128–441 ppm) in addition to significant Zn concentrations (up to 11 wt.%) and represent a potential resource for these elements. A combination of mineralogical and chemical methods (PXRD, FEG-SEM-EPMA and LA-ICP-MS) indicated different partitioning of Ga and Ge within the individual slag phases. Gallium is predominantly bound in small euhedral crystals of Zn–Fe–Al spinels (<10 μm in size), exhibiting concentrations in the range of 480–1370 ppm (up to 0.004 atoms per formula unit, apfu). Concentrations of Ga in other phases (e.g. melilite) are systematically below 90 ppm. The principal host of Ge is the silicate glass and, to a lesser extent, silicates (melilite and olivine group phases). Concentrations of Ge in glass attained a concentration of 470 ppm (EPMA), but the LA-ICP-MS analysis of glass matrix containing submicrometre spinel crystallites indicated that average Ge levels vary in the range of 113–394 ppm. In the potential extraction of Ga and Ge, the results indicate that ultrafine milling is needed to liberate the Ga- and Ge-hosting phases prior to metallurgical processing of the slag.

The south-eastern Black Sea area is a key region for understanding the history of iron metallurgy. While Classical texts mention the people living in this area as producers, and perhaps even inventors, of iron, material evidence has been lacking. Recent archaeological survey and scientific analyses now make it possible to investigate iron technologies in the region during the mid to late first millennium BC and the medieval period, providing new insights into the metallurgical tradition that inspired such admiration in the Graeco-Roman world. These results have implications for the smelting of iron in liquid state, although it remains unclear where and when this technology first appeared in Western Eurasia.

Pyrometallurgical slags from three Cu-Co smelters (Nkana, Mufulira, Chambishi) in the Copperbelt Province, Zambia, were studied from mineralogical and chemical points of view. The slags were enriched in metals and metalloids, mainly Cu (up to 35 wt.%), Co (up to 2.4 wt.%) and As (up to 3650 ppm). The following primary phases were observed in slags: Ca-Fe silicates (clinopyroxene, olivine) and leucite, oxides (spinel-series phases), ubiquitous silicate glass and sulphide/metallic droplets of various sizes. The presence of glass and skeletal/dendritic crystal shapes indicated rapid cooling of the slag melt. Copper and cobalt were found in low concentrations in the majority of silicates (olivine, clinopyroxene) and oxides, substituting for Fe in their structures (up to 7.15 wt.% CoO in olivine, 4.11 wt.% CuO in spinel). Similarly, up to 0.91 wt.% CoO and 6.90 wt.% CuO were observed in the interstitial glass. Nevertheless, the main carriers of these metals in the slags studied were Cu sulphides (digenite, chalcocite, bornite, chalcopyrite), Co-Fe sulphides (cobaltpentlandite), Co-bearing intermetallic phases ((Fe,Co)2As) and alloys. Weathering features corresponding to the presence of secondary metal-bearing phases, such as malachite (Cu2(CO3)(OH)2), brochantite (Cu4SO4(OH)6) and sphaerocobaltite (CoCO3), were observed on the slag surfaces. They indicate that the slags studied are reactive on contact with water/atmosphere and that their environmental stability and release of potentially harmful metals and metalloids must be evaluated further.

Samples of granulated slag from Scunthorpe, Humberside, collected over several years, vary somewhat in chemical composition reflecting differences in iron-making practice. All contain some melilite and oldhamite crystals and minor amounts of iron along with the glass. Granulated slag from Usinor, Dunkirk, France, has a little more CaO than the Scunthorpe material with crystals of merwinite and oldhamite. Pelletised slag from Redcar, Teeside, is much more vescicular than the granulated material and contains melilite and oldhamite.

The melilite crystals contain many inclusions of oldhamite and iron. They span a wide range within the akermanite-gehlenite series and are non-stoichiometric in composition. The merwinite may have formed largely by quench crystallization. Oldhamite is probably the first phase to form in all the slags. The silicate mineralogy can be explained in terms of the phase relationships within the CaO-SiO2-Al2O3-MgO quaternary system. The small difference in composition of the French slags is sufficient for them to fall into the primary phase field of merwinite rather than melilite. Assuming that only a minor proportion of crystals is acceptable in slags for use in Portland Blastfurnace Cement, the present low Al (< 11 % Al2O3) British and French slags are approaching an optimum composition.