Historical Slags Research Articles

Potential for the Recovery of Selected Metals and Critical Raw Materials from Slags from Polymineral Zn–Pb Ore Metallurgy—Part I

Slags from the Silesia–Cracow Upland (Poland), including ten historical slags (deposited in waste dumps) and four contemporary slags (from current production), were examined to compare their chemical and mineralogical properties as well as to assess their potential for the recovery of selected metals and critical raw materials. The historical slags associated with the smelting of polymetallic ores originating from Mississippi Valley-type (MVT) deposits consisted primarily of gypsum. The contemporary slags, obtained from industrial waste rich in zinc and lead, were predominantly spinels (magnesium-aluminate and ferric) that exhibited higher iron content (up to 46.6 wt% of Fe2O3) compared to the historical slags (up to 26.1 wt% of Fe2O3). The zinc content was similar for both the slag types (3.5 wt% Zn). The average titanium and arsenic contents in the old and contemporary slags were at the same level as well, with 0.21 wt% (Ti) and 0.13 wt% (As), respectively. The contemporary slags contained higher levels of critical raw materials, such as cobalt, nickel, copper, and manganese, compared to the historical slags. Rare earth elements (REEs) were also more abundant in the contemporary slags, with an average content of 212 ppm, while the historical slags averaged 124 ppm. These findings underscore the potential for recovering valuable metals and critical raw materials from such slags, presenting opportunities for resource optimisation and environmental management.

SLAG—software for reconstruction of historical smelting processes based on slag properties

AbstractThe publication presents the functions of the SLAG software created to recreate historical metallurgical processes. SLAG allows for determining the smelting temperature, the viscosity of the metallurgical melt, and the oxygen and sulfur fugacities during smelting. With software, both liquidus temperature and melt viscosity can be calculated using different models, covering the range of chemical compositions of historical slags as wide as possible. Based on thermodynamic calculations, SLAG allows the performance of O2 and S2 fugacity calculations in the temperature range of 1000–2000 K (727–1727°C). The range of applicability of other properties (viscosity and liquidus temperature) depends only on the limitations of individual models. Using SLAG, it is also possible to create predominance area diagrams (PADs) and diagrams that consider the viscosity's dependence on temperature for slag of a given chemical composition. Based on glass transition temperature (Tg) and melt fragility, it is also possible to reconstruct the conditions that prevailed during the various stages of historical glass manufacturing processes.

Reconstruction of smelting conditions during 16th‐ to 18th‐century copper ore processing in the Kielce region (Old Polish Industrial District) based on slags from Miedziana Góra, Poland

AbstractThis study presents the first reconstruction of the smelting conditions in 16th‐ to 18th‐century smelters from Miedziana Góra (Holy Cross Mountains, Poland). Based on geochemical (inductively coupled plasma mass spectrometry/emission spectrometry, X‐ray fluorescence) and mineralogical analysis (X‐ray diffractometry, scanning electron microscopy, electron probe micro‐analysis) of historical slags, their chemical/phase composition and the basic smelting parameters (temperature, melt viscosity, and oxygen fugacity) were determined. Due to the differences in chemical and phase composition, slags from different smelting stages have been distinguished: hypocrystalline slags (MG6) from speiss/matte production and glassy (MG1–MG5) from matte conversion. In glassy slags, pyroxenes, quartz/cristobalite grains, and aggregates composed of metallic Cu and PbO are dispersed in the glass. Hypocrystalline slags are composed of wollastonites, anorthites, and metallic Cu. The temperature range at which the slags were formed was from ~1100°C (solidus temperature) to 1150–1200°C (liquidus temperature). The silicate melt's viscosity was from log η = 1.19 to 4.42 Pa s (at 1100–1200°C). The higher viscosity of MG1–MG5 slags indicates that, unlike MG6 slags, they were not formed during gravity separation. Information about the phase composition made it possible to determine the oxygen fugacity in the range of log fO2 = −4 to −12 atm. High oxygen fugacity indicates the oxidizing nature of the smelting process.

Experimental weathering of historical slags exposed to rhizosphere-like organic acids and various pH conditions

The long-lasting mining and smelting activity that took place in southern Tuscany since the 1st millennium BCE has left several remains of metallurgical interest, along with metallurgical slags. Over the centuries, these materials were treated as wastes and dumped close to the industrial sites, with no specific disposal or confinement from the surrounding environment. We performed leaching experiments on slag samples from two selected sites, applying conditions to test the effects of various pH conditions, as well as their behavior following the addition of organic acids to simulate a rhizospheric environment. The samples, a crystalline Pb slag and a glass-rich Cu slag, showed a different leachability depending upon their physical and mineral-chemical characteristics, such as the size of the fragments used in the experiments, the mineralogical composition, and the bulk content of metals in the samples. The crystalline Pb slag showed a higher susceptibility to leaching (e.g., 31 % Cu and 65 % Zn) under acidic inorganic conditions, compared to the glass-rich Cu slag, which was prone to organic mediated dissolution (14 % Cu and 6 % Zn). The highest metal mobilization occurred during the pH-dependent leaching experiments at pH 1, reaching 92 % (of leached Pb) and 65 % (Zn) for lead slag and copper slag, respectively.

Gray water footprint evaluation of arsenic in Central China: from the perspective of health risk theory

Central China is one of the areas with the most serious arsenic (As) pollution in the world. However, the local controlling standards of arsenic are not unique, and its toxicities to humans have gender differences, which brings challenges to gray water footprint (GWF) evaluation. The GWF model is improved on the basis of health risk theory to address the abovementioned problems. According to the gender differences in health parameters, the assessment is further divided into male and female GWFs (i.e., GWF (As-M) and GWF (As-F), respectively). The results show that (1) the average annual GWF (As-M) and GWF (As-F) values in Central China from 2011 to 2015 are 97.27 and 105.11 billion m3, respectively. Hunan Province accounts for about 77% of the total GWF (As-M) and GWF (As-F) in Central China (2). The carcinogenic hazard of arsenic load in Hunan Province is the most serious among the three provinces in central China. The water pollution levels of arsenic for male and female in Hunan Province are 0.917 and 0.843 in 2011, both of which belong to the "high" grade. The carcinogenic hazards of arsenic loads in Hubei Province and Jiangxi Province are the second and third highest in Central China (3). For the females, the average daily dose to arsenic is about 1.03 times larger than the male's, and the female carcinogenic risk of arsenic is higher than that of males. Therefore, women are the main protection group of arsenic pollution in Central China (4). The decrease in the GWF (As-M) and GWF (As-F) risk factors in Central China is primarily caused by the closure of Shimen realgar mine in Hunan Province. The leaching of historical slag is a key source to be controlled to further improve water safety of Central China.

Origin of Historical Ba-Rich Slags Related to Pb-Ag Production from Jihlava Ore District (Czech Republic)

The aim of this study was to characterize historical slags which originated during silver production from the Jihlava ore district, Czech Republic. The area was among the head producers of silver within the Lands of the Czech Crown in 13th–14th centuries. The mined ores had complex composition, being formed mostly by pyrite, sphalerite, galena, chalcopyrite, and accessory silver-rich minerals such as silver-bearing tetrahedrite (freibergite) or pyrargyrite, with gangue represented by quartz and Mn-rich carbonates or baryte. Large volumes of slags with contrasting composition were generated during the Pb-Ag production. Altogether, two main types of slags were identified in the district. The first type is characterized by high BaO contents (up to 34.5 wt.%) and dominancy of glass, minor quartz, and accessory amounts of Ba-rich feldspar (up to 93 mol.% of Cls), metal-rich inclusions, Ba-Pb sulphates and only rare pyroxene, wollastonite and melilite. The composition of the second group belongs to fayalitic slags containing glass, Fe-rich olivine, accessory pyroxene, feldspar, quartz, and inclusions of various metallic phases. Fluxes were derived from gangue (quartz, carbonates, baryte) or local host rocks for both types of slag. The calculated viscosity indexes reflect (with minor exceptions) medium-to-high effectivity of metal separation. Smelting temperatures were estimated from a series of ternary plots; however, more reliable estimates for both types of slags were obtained only from experimental determination of melting temperature and calculations using bulk/glass compositions (~1100–1200 °C).

Quantitative metal and metaloid distribution in primary and secondary phases in historical lead-silver smelting slags from Rammelsberg ore deposit (Germany) and implications for their recovery

Historical slags from primary Pb/Ag and Cu smelting can have high contents of valuable metal(loid)s. So far, there are hardly any studies that provide quantitative information on metal(loid) partitioning (deportment) between all slag phases based on automated mineralogy which is important for designing metal recovery from such slags. In this study, slags from the Kanstein Pb/Ag smelter, belonging to the Rammelsberg ore deposit, were studied by SEM-based automated mineralogy (here MLA), EPMA, and LA-ICP-MS on polished sections and by XRF and LA-ICP-MS on sieve fractions of bulk samples. The slags are rich in Fe (21–32 wt%), Zn (7.9–19 wt%), Pb (1.8–3.3 wt%), Cu (0.7–1.4 wt%) with slightly elevated concentrations of Co (309–586 ppm), Sb (155–459 ppm), Sn (84–204 ppm), Ag (19–115 ppm), In (18–64 ppm), Ga (15–25 ppm), Bi (2–20 ppm). A Ba-S-rich slag and a SiO2-rich slag can be distinguished; the first probably formed under more reducing conditions, at higher temperatures (>1200 °C) and without roasting. The weathering phases are the main carriers of all metal(loid)s (up to 45–94 % of total metal(loid) content in individual samples). Larger amounts of up to 13–83 % can be contained in glass (Ga, Sn, Zn, Fe, Ag, In, Co, Ge, Sb, Cu, Pb, Ni), pure metals and intermetallic compounds (Bi, Ag, Sb), sulphides (esp. sphalerite; Zn, Cu, Ag, In, Co), silicates (esp. fayalite; Ni, Co, Zn, Fe, Ga, Ag, In, Sn, Ge), or oxides (esp. wüstite; Fe, Co, Ge, Zn, In, Ga), if their modal proportions in the slags are high enough. Due to the complex and variable metal deportment, processing of the entire slag using leaching or pyrometallurgy is most promising for recovery.

Environmental impact of the historical slag pile at Davenport, Iowa, United States: Trace metal contamination in soils and terrestrial vegetation

Environmental impact of the historical slag pile at Davenport, Iowa, United States: Trace metal contamination in soils and terrestrial vegetation

Heavy metal pollution characteristics and health evaluation of farmland soil in a gold mine slag area of Luoyang in China

The characteristics of eight heavy metals (lead, zinc, copper, nickel, chromium, cadmium, mercury and arsenic) in the surface soil of the historical slag area of the Au ore dressing plant in the South-West of Luoyang City were investigated and evaluated in terms of a pollution index, potential ecological hazards and health risks. The results showed that the average amounts of the heavy metals Pb, Zn and As in the soils of plots S3, S5, S7, S12 and S18 exceeded the soil pollution risk screening values. The Mero comprehensive pollution index in plots S7, S12 and S18 was greater than 3, indicating severe pollution. The severe pollution plot integrated the potential ecological risk index (RI) of each sampling point, which was in the order of RIS12 > RIS18 > RIS7 > RIS5 > RIS3. Among the heavy metals, Cd poses the greatest threat to ecological and human health. The effects of heavy metals in soil on the single non-carcinogenic health risk index (HQ) and the non-carcinogenic total risk index through three exposure pathways were in the order of HQHg < HQCu < HQNi < HQZn < HQCd < HQCr < HQPb < HQAs < 1, which meant that the adult and child total carcinogenic risk (TCR) and individual carcinogenic health risk indices were above the maximum acceptable human health level recommended by the USEPA (10-6). TCRAs and TCRCd accounted for 75.65% and 23.94% of the adult TCR, respectively. TCRAs and TCRCd accounted for 75.93% and 23.97% of the child TCR, respectively. Overall, the TCR of children was greater than that of adults. In summary, the soil in the historical slag area of the Au ore dressing plant constitutes a serious threat to the surrounding ecological environment and to residents. Keywords: historical slag area, heavy metals, pollution assessment, health assessment, farmland soil, ecological hazard DOI: 10.25165/j.ijabe.20211405.6536 Citation: Wang H, Zhang H, Xu R K. Heavy metal pollution characteristics and health evaluation of farmland soil in a gold mine slag area of Luoyang in China. Int J Agric & Biol Eng, 2021; 14(5): 213–221.

Classification of slag material by spectral induced polarization laboratory and field measurements

Historical slag dumps are of increasing interest due to economic, environmental or archaeological reasons. Geophysical investigations can help accessing the potential reuse of slag material to recover metallic raw material or for the estimation of the hazard potential of the buried slag material due to dissolution occurrence.In our study, we have investigated various slag material in the laboratory with the spectral induced polarization (SIP) method, obtained from different historical slag dumps, located in the Harz Mountains, Germany. We also present SIP results from field measurements at a historical slag dump where most of the slag samples reveal high amounts of iron, zinc, silica, and barium.Our results reveal a discrimination between three different slag grades (low, medium, high) by using the imaginary conductivity σ″ at a medium frequency (1–10 Hz) in both laboratory and field. Furthermore, additional information is obtained by a classification based on the spectral polarization behaviour and considering the field frequency range (0.1 Hz – 100 Hz). Five different types of spectra (ascending, descending, constant, maximum and minimum type) can be discriminated and recognized in the laboratory and in distinct areas of the slag dump. Even though a direct comparison between the laboratory and field results still needs to be proven, the buried slag material can be differentiated from the surrounding material by the polarization magnitude.

Heavy metal pollution characteristics and health evaluation of farmland soil in a gold mine slag area of Luoyang in China

The characteristics of eight heavy metals (lead, zinc, copper, nickel, chromium, cadmium, mercury and arsenic) in the surface soil of the historical slag area of the Au ore dressing plant in the South-West of Luoyang City were investigated and evaluated in terms of a pollution index, potential ecological hazards and health risks. The results showed that the average amounts of the heavy metals Pb, Zn and As in the soils of plots S3, S5, S7, S12 and S18 exceeded the soil pollution risk screening values. The Mero comprehensive pollution index in plots S7, S12 and S18 was greater than 3, indicating severe pollution. The severe pollution plot integrated the potential ecological risk index (RI) of each sampling point, which was in the order of RIS12 > RIS18 > RIS7 > RIS5 > RIS3. Among the heavy metals, Cd poses the greatest threat to ecological and human health. The effects of heavy metals in soil on the single non-carcinogenic health risk index (HQ) and the non-carcinogenic total risk index through three exposure pathways were in the order of HQHg < HQCu < HQNi < HQZn < HQCd < HQCr < HQPb < HQAs < 1, which meant that the adult and child total carcinogenic risk (TCR) and individual carcinogenic health risk indices were above the maximum acceptable human health level recommended by the USEPA (10-6). TCRAs and TCRCd accounted for 75.65% and 23.94% of the adult TCR, respectively. TCRAs and TCRCd accounted for 75.93% and 23.97% of the child TCR, respectively. Overall, the TCR of children was greater than that of adults. In summary, the soil in the historical slag area of the Au ore dressing plant constitutes a serious threat to the surrounding ecological environment and to residents. Keywords: historical slag area, heavy metals, pollution assessment, health assessment, farmland soil, ecological hazard DOI: 10.25165/j.ijabe.20211405.6536 Citation: Wang H, Zhang H, Xu R K. Heavy metal pollution characteristics and health evaluation of farmland soil in a gold mine slag area of Luoyang in China. Int J Agric & Biol Eng, 2021; 14(5): 213–221.

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

Pyrometallurgical processing of ore from the Zeehan mineral field was performed intermittently between 1896 and 1948, primarily recovering Pb, Ag and Cu. While Zn recovery was attempted at the time, it was unsuccessful using the available technology. Consequently, Zn reported to the slag during the smelting process. Today, the former smelter site consists of two large slag piles (North and South). Using a range of techniques (including X-ray diffractometry, scanning electron microscopy, laser ablation inductively coupled plasma mass spectrometry, and static testing) the geometallurgical and geo-environmental properties of these slag materials (n = 280) were determined. The South and North piles contain on average 15% and 11% Zn, respectively. A range of complex mineral phases were identified, and are dominated by glass, silicates (i.e., monticellite–kirschsteinite and hardystonite), oxides (gahnite and hercynite) and minor sulfides (sphalerite and wurtzite). Microtextural examinations defined nine mineral phases (Glass A, Silicates A to D, Oxides A and B, Sulfides A and B). Zn was concentrated in Sulfide A (26%), Glass A (24%) and the Silicates (43%), while Pb was concentrated in Oxide B (76%), with Sulfide B host to the highest Ag (45%) and Cu (65%). Considering this, recovery of Zn using conventional hydrometallurgical processes (i.e., sulfuric acid leaching) is suitable, however the application of unconventional biohydrometallurgical techniques could be explored, as well re-smelting. These slag materials are classified geo-environmentally as potentially acid forming, with leachate concentrations of Zn, Pb consistently above ANZECC (2000) aquatic ecosystem 80% protection guideline values, and, for the majority of samples, exceedances of Cu, Ni and Cd were also measured. Considering these findings, reprocessing of these historic slags for Zn extraction may provide an economically feasible management option for rehabilitating this historical site.

Combination of different geophysical techniques for the location of historical waste in the Izery Mountains (SW Poland)

An initial magnetic survey conducted on the soil surface in the Orle forest glade, located in the Izery Mountains (south-western Poland), indicated the existence of a strong magnetic anomaly. Most cores collected in the glade outside the area of magnetic anomaly show a vertical distribution of magnetic susceptibility typical for soils formed on a diamagnetic or paramagnetic background, in unpolluted areas and influenced only by natural processes. The different patterns of magnetic susceptibility values exhibited by cores collected in the area of the magnetic anomaly reveal the source of the magnetic signal as an anthropogenic layer of waste buried in the subsoil, which was dumped in this area during the historical activity of a glass factory that was active in Orle in the 18th and 19th centuries. Topsoil measurements of magnetic susceptibility revealed that this anthropogenic material has completely different magnetic properties than the natural geological background, therefore making possible the use of magnetic and geoelectrical techniques to determine the location of buried historical waste. Application of different magnetic and geoelectrical methods (soil magnetometry, magnetic gradiometry, EM profiling, electrical resistivity tomography), in combination with a previous magnetic survey, enabled assessment of the location, depth and thickness of the anthropogenic layer. The anthropogenic layer consisted of historical slags and ashes from glass production mixed with modern bottom ashes and construction waste dumped here during the second part of the 20th century. The anthropogenic material occurs in the form of a nonhomogeneous layer characterized by high magnetic susceptibility (>100 × 10−5 SI units) and low resistivity (<200 Ωm) as well as high and variable apparent conductivity (>25 mS/m). These properties are firmly different from the properties of the natural soil and parent rocks and enable fairly precise location of the anthropogenic layer using magnetic and geoelectrical measurements.

Mineralogical, geochemical, and leaching study of historical Cu-slags issued from processing of the Zechstein formation (Old Copper Basin, southwestern Poland)

Historical Cu-Slags located at former industrial sites in Poland are exposed to weathering that may trigger release of metallic contaminants to the surrounding soils. However, the extent to which different metals are leached depends on the mineral composition of the slags and the conditions of their deposition. Historical slags are often crystalline and composed of phases with a variable response to weathering. Also, weathering of crystalline slags (CS) is different from that of amorphous slags (AS). To understand how the slag phase composition triggers weathering and the ultimate release of metallic elements, we studied the leaching of historical crystalline and amorphous slag. A combined geochemical and mineralogical approach determined the weathering sequence(s) of slag components subjected to different conditions of specific slag disposal. In detail, experiments under: i) various pH conditions in the range of 2–13 in a batch mode simulated slag deposition within a deep soil profile, whereas ii) exposure to solutions of artificial root exudates (ARE) in a dynamic experimental system simulated slag deposition within topsoil. The results demonstrated that crystalline phases in the order Leucite > Plagioclase > Pyroxene are preferentially dissolved in inorganic conditions of a pH ≤ 7, in contrast to glass, which is preferentially dissolved in alkaline conditions (pH > 7). Also, inorganic conditions better promote the dissolution of metal-bearing phases (sulphides and metals) when compared to silicates. In contrast, artificial root exudates do not show preferential dissolution of any phase and cause the strongest leaching in all of the analyzed conditions. We show that reconstructing the susceptibility of complex crystalline slags to weathering requires a specific approach including analyses and interpretation of all major components such as Ca, Mg and K, not merely a focus on Si and metals.

Metal mobilization from metallurgical wastes by soil organic acids

Three types of Cu-slags differing in chemical and mineralogical composition (historical, shaft furnace, and granulated slags) and a matte from a lead recovery process were studied with respect to their susceptibility to release Cu, Zn and Pb upon exposure to organic acids commonly encountered in soil environments. Leaching experiments (24–960 h) were conducted with: i) humic acid (20 mg/L) at pH t0 = 4.4, ii) fulvic acid (20 mg/L) at pH t0 = 4.4, iii) an artificial root exudates (ARE) (17.4 g/L) solution at pH t0 = 4.4, iv) ARE solution at pH t0 = 2.9 and v) ultrapure water (pH t0 = 5.6). The results demonstrated that the ARE contribute the most to the mobilization of metals from all the wastes analyzed, regardless of the initial pH of the solution. For example, up to 14%, 30%, 24% and 5% of Cu is released within 960 h from historical, shaft furnace, granulated slags and lead matte, respectively, when exposed to the artificial root exudates solution (pH 2.9). Humic and fulvic acids were found to have a higher impact on granulated and shaft furnace slags as compared to the ultrapure water control and increased the release of metals by a factor up to 37.5 (Pb) and 20.5 (Cu) for granulated and shaft furnace slags, respectively. Humic and fulvic acids amplified the mobilization of metals by a maximal factor of 13.6 (Pb) and 12.1 (Pb) for historical slag and lead matte, respectively. The studied organic compounds contributed to different release rates of metallic contaminants from individual metallurgical wastes under the conditions tested.

NÁLEZ HLINÍKEM BOHATÝCH SPINELIDŮ A KORUNDU VE STRUSKÁCH PO TAVBĚ STŘÍBRNÝCH RUD ZE STŘÍBRNÝCH HOR NA HAVLÍČKOBRODSKU

This work deals with the unique association formed by spinelides and corundum in historical slag after smelting of silver ore from the site Stříbrné Hory in the Havlíčkův Brod Ore District. To study these phases, polarizing microscope and electron microprobe (WDX and EDX) were used. The slag consists primarily of glass and residual quartz, which also contained sillimanite needles. During smelting the quartz and sillimanite have been partially melted and aluminium-rich spinelides crystallized in the surrounding glass. Euhedral crystals of spinelides range 5 to 25 μm in size and are composed predominantly of hercynite (55–58 mol. %), to a lesser extent gahnite (21–24 mol. %), spinel (18–24 mol. %) and galaxite (4–5 mol. %). Corundum probably originated during the smelting from secondary mullite at temperatures around 1 300 °C. Corundum together with glass form a paramorphosis aft er sillimanite aggregate.

Environmental impact and potential utilization of historical Cu-Fe-Co slags.

Historical slags from the past Fe and Cu-Co production were investigated in order to evaluate either their potential for utilization or their long-term environmental risk for unsupervised old smelting areas. Here, we studied ferrous slags produced during the recovery of Fe from siderite-Cu ores in Slovakia and two different types of non-ferrous slags produced during the recovery of Cu and Co from Kupferschiefer ores in Germany. The glassy character, rare occurrence of primary silicate phases, and the lack of secondary phases in Cu slags indicate their stability for a prolonged period of time. Electron microprobe analytical work showed that the metals and metalloids (Cu, Co, Fe, Zn, Pb, As) are largely encased in droplets of matte and metal alloys and remain protected by the glassy matrix with its low weathering rate. Fe and Co slags are composed of high-temperature silicates such as wollastonite, cristobalite, as well as olivine, feldspar, quartz, leucite, pyroxene, and pyroxenoids. The presence of secondary phases attests to a certain degree metal release owing to weathering. Assuming minimal contents of metals in slags after a treatment with dilute H2SO4, slags could be used as pozzolanas for addition to cement.

Environmental impact of the historical Cu smelting in the Rudawy Janowickie Mountains (south-western Poland)

Mining and smelting of Cu ores in the Rudawy Janowickie Mountains (southwestern Poland) from the 14th to the 16th century produced pyrometallurgical slags which currently form unconfined slag heaps in forests or are distributed within soils and streambeds. At present, the slag affected area has approximately 10km2. Chemical and mineralogical analyses of the slags, slag-contaminated and slag-free soils and stream sediments are coupled with leaching experiments and speciation modeling to determine the environmental impact of historical smelting activities.Three subtypes of pyrometallurgical slags occur in the studied area: porous slag and two massive slags (equilibrated slag and undercooled slag) having different phase compositions. All of the studied slags still contain considerable amounts of metal(loid)s (up to 1.4wt.% Cu, 1wt.% Zn, 750ppm Pb and 300ppm As). A simple 24-hour laboratory slag-leaching experiment, using three different solutions (distilled water, stream water, citric acid solution), indicate the release of metal(loid)s under simulated natural conditions. Leachates from a stream water solution and distilled water contain lower concentrations of metal(loid)s (<0.1% of total contaminant concentration in the solid) compared to leachates from a citric acid solution. Furthermore, leaching tests indicate that the release of the metal(loid)s is higher for porous slags than for those having a massive texture.Chemical analyses of soils, stream sediments and surface water indicate that some elements reach concentrations exceeding environmentally permissible standards (especially in soils: Cu up to 4000ppm, Zn up to 1500ppm, As up to 300ppm, Pb up to 200ppm). The impact of various sources of pollution including modern ones and those related to historical slag disposal was traced using Pb isotopes and indicate that the contamination by slag fragments and slag-derived metals is currently concentrated in soil B horizons and in river sediments. On the other hand, Pb isotopes and metal concentrations in soil O horizons are additionally affected by airborne contamination not related to the slag disposal.The most important factors controlling slag weathering and metal(loid) release include the following: (i) the textural characteristics and porosity of the slag material, (ii) the slag phase composition derived from the cooling rates of the slag melt and (iii) the environmental conditions (e.g., pH, organic matter content, etc.).

MINERALOGY AND COMPOSITION OF HISTORICAL Cu SLAGS FROM THE RUDAWY JANOWICKIE MOUNTAINS, SOUTHWESTERN POLAND

Two types of slags produced during historical smelting of Cu ores occur in the Rudawy Janowickie Mountains, southwestern Poland. The prevailing massive slag has a chemical composition dominated by FeO (up to 51 wt.%), SiO 2 (up to 43 wt.%) and Al 2 O 3 (up to 12 wt.%). It consists of silicate glass, olivine and hercynite. The second type, a porous slag, is poorer in FeO (up to 28 wt.%) and richer in SiO 2 (up to 70 wt.%). It comprises two types of silicate glass, olivine, ferrosilite and SiO 2 -group minerals (cristobalite and quartz). The morphology of the olivine crystals, phase assemblages, phase composition and distribution of trace elements in slag phases vary from sample to sample, which is consistent with different cooling rates. Phase diagrams used in this study indicate that most of the slag samples have solidified under conditions of strong disequilibrium caused by rapid cooling. A careful investigation of cooling conditions is essential to predict a susceptibility of slags to weathering and to reconstruct historical smelting conditions. For example, samples with longer cooling times are more resistant to weathering; they should be used to reconstruct the temperature of slag formation. Our mineralogical and chemical study of the Rudawy Janowickie slags and a comparison with other historical slags in Europe indicate that: (i) the temperature of slag formation was ca . 1200°C and overlaps with temperature ranges estimated for other historical slags, (ii) the furnace charge was either self-fluxing or silica was added as a flux, which is not so common for historical Cu slags, but was observed for smelting of Pb and Ag ores in the Czech Republic, (iii) preliminary roasting of furnace charge was efficient, as in other historical Cu-smelters, and (iv) the furnace atmosphere was reducing, also as in other historical smelting processes.

Atmospheric helium isotope ratio: Possible temporal and spatial variations

The atmospheric 3He/ 4He ratio has been considered to be constant on a global scale, because the residence time of helium is significantly longer than the mixing time in the atmosphere. However, this ratio may be decreasing with time owing to the anthropogenic release of crustal helium from oil and natural gas wells, although this observation has been disputed. Here, we present the 3He/ 4He ratios of old air trapped in historical slags in Japan and of modern surface air samples collected at various sites around the world, measured with a newly developed analytical system. In air helium extracted from metallurgical slag found at refineries in operation between AD 1603 and 1907 in Japan, we determined a mean 3He/ 4He ratio of (5106 ± 108) × 10 –5 R HESJ (where R HESJ is the 3He/ 4He ratio of the Helium Standard of Japan), which is consistent with the previously reported value of (5077 ± 59) × 10 –5 R HESJ for historical slags in France and United Arab Emirates and about 4% higher than that of average modern air, (4901 ± 4) × 10 –5 R HESJ. This result implies that the air 3He/ 4He ratio has decreased with time as expected by anthropogenic causes. Our modern surface air samples revealed that the 3He/ 4He ratio increases from north to south at a rate of (0.16 ± 0.08) × 10 –5 R HESJ/degree of latitude, suggesting that the low 3He/ 4He ratio originates in high-latitude regions of the northern hemisphere, which is consistent with the fact that most fossil fuel is extracted and consumed in the northern hemisphere.