Influence of alkalis on microstructure of belite - sulfoaluminate clinkers

Sintetizirali smo cementni klinker z naslednjimi deleži faz: 60 mas. % C2S (belit), 20 mas. % C4A3Ś (kalcijev sulfoaluminat), 10 mas. % C4AF (ferit) in 10 mas. % CŚ (kalcijev sulfat). Mešanici za klinker smo dodali dve vrsti alkalij (K2O in Na2O) v treh različnih deležih (0,5, 1 oz. 2 mas. %). Proučevali smo vpliv alkalij na tvorbo glavnih in manj zastopanih faz, nadomeščanje ionov in vpliv na mikrostrukturo ter reaktivnost klinkerja. Ugotovili smo, da se količina C2S in C4AF z dodajanjem alkalij povečuje, zmanjšuje pa se količina C4A3Ś in CŚ. V vzorcih z dodatkom alkalij pride do tvorbe manj zastopanih faz: trikalcijevega aluminata (C3A), arkanita (KŚ) in Ca-langbeinita (KC2Ś3), opazili smo nadomeščanje ionov tako z alkalijskimi kationi kot tudi z nekaterimi drugimi ioni (Ca2+, Al3+, Fe3+, S2-, S6+, Si4+). Nadalje, alkalije vplivajo na velikost in obliko glavnih faz belitno-sulfoaluminatnega klinkerja. Večja količina alkalij na splošno zmanjša zrna C2S in C4AF ter poveča zrna C4A3Ś. Zrna C2S so v referenčnem vzorcu sferična, v vzorcih z dodatkom alkalij pa so subhedralna in anhedralna. Zrna C4A3Ś so v referenčnem vzorcu evhedralna, v vzorcih z manjšo količino alkalij tudi heksagonalna, medtem ko so v vzorcih z večjo količino alkalij subhedralna in sferične oblike. Zrna C4AF so v referenčnem vzorcu in vzorcih z manjšo količino alkalij evhedralna in večinoma paličasto oblikovana. Z večanjem količine alkalij pa postanejo čedalje bolj subhedralna. Na velikost in obliko zrn C4A3Ś in C4AF močno vpliva razmerje Al/Fe, določeno v teh dveh fazah. Alkalije uravnavajo tudi hitrost hidratacije. Najbolj reaktiven je vzorec z dodanima 2 mas. % K2O, najpočasneje pa reagira vzorec z enako količino Na2O. Na hitrost hidratacije poleg količine glavnih faz za klinker vpliva še prisotnost manj zastopanih faz (C3A, KŚ in KC2Ś3), poroznost klinkerja ter razmerje posameznih elementov v glavnih fazah.The cement clinker with the following phase composition: 60 wt.% C2S (belite), 20 wt.% C4A3Ś (calcium sulfoaluminate), 10 wt.% C4AF (feritte) and 10 wt.% CŚ (anhydrite) was synthesized. Two types of alkali (K2O and Na2O) were added to this clinker mixture in three different proportions (0,5, 1 oz. 2 wt.%). The main aim of this work was to determine the influence of the alkalis on the formation of main and minor phases, the ion substitutions and the influence on the microstructure and hydration rate of the clinker. It was found that the amount of C2S and C4AF increases with the addition of alkalis, while the amount of C4A3Ś and CŚ decreases. In addition, minor phases such as C3A (tricalcium aluminate), KŚ (arcanite) and KC2Ś3 (Ca-langbeinite) are formed in the samples with added alkalis. Furthermore, the ions were substituted by alkali cations and by some other ions (Ca2+, Al3+, Fe3+, S2-, S6+, Si4+). Alkalis also influence the size and shape of the main phases of belite-sulfoaluminate clinker. A higher amount of alkali generally reduces the C2S and C4AF grains and increases the C4A3Ś grains. In the reference sample, the C2S grains have a spherical shape, whereas in the alkali-added samples, subhedral and anhedral grains predominate. C4A3Ś grains are euhedral in reference sample and hexagonal in lower alkali samples, while subhedral and spherical grains predominate in the higher alkali samples. C4AF grains are euhedral in both the reference and lower alkali samples. These grains are usually long prismatic. With increasing alkali content they become subhedral. The size and shape of the C4A3Ś and C4AF grains are strongly influenced by the Al/Fe ratio. Alkalis also influence the hydration rate. The sample with the addition of 2 wt% K2O is most reactive, but the sample with the same amount of Na2O is the least reactive. The hydration rate is influenced not only by the number of main phases for clinker, but also by the presence of minor constituents (C3A, KŚ, KC2Ś3), the porosity of the clinker and the ratio of individual elements in the main phases

Heavy minerals in soils and dolomite bedrocks from the Postojna, Zaplana and Stična area

Na treh območjih v Sloveniji - v okolici Postojne, Zaplane in Stične - smo želeli preveriti prisotnost in količino težkih mineralov v matični podlagi, zgornjetriasnem dolomitu ter v tleh. Zanimalo nas je, ali so težki minerali v tleh avtohtoni ali alohtoni. Preveriti smo želeli tudi vpliv rabe tal (travnik, gozd) na njihovo porazdelitev. Praškovna rentgenska difrakcija (XRD) je v vzorcih tal pokazala prisotnost dolomita, kremena, muskovita/illita ter minerale kloritove skupine, v vzorcih matične kamnine pa le dolomit. S pomočjo optične mikroskopije smo poleg dolomita določili še posamezna zrna glinencev, kremena, muskovita, temnih nepresevnih mineralov in litična zrna. Delež netopnih težkih mineralov v matični kamnini je majhen. Po končanem raztapljanju dolomita s HCl smo pridobili le med 0,03 % in 0,70 % netopnega ostanka. Analiza SEM/EDS netopnega ostanka in poliranih zbruskov je pokazala prisotnost sedmih mineralov: cirkona, TiO2 (najverjetneje rutila), mineralov monacitove in apatitove skupine, sfalerita, pirita in fluorita. Velikosti omenjenih mineralov so do 10 μm. Mineralna zrna večinoma ne kažejo znakov daljšega transporta in preperevanja. Delež težke frakcije v tleh je med 0,01 % in 0,16 %. S SEM/EDS analizo smo določili 13 mineralov oz. različkov. V večini vzorcev tal so prisotni cirkon, ilmenit, TiO2 (najverjetneje rutil), minerali monacitove skupine in kromit. Pogosti so tudi železovi oksidi/hidroksidi in minerali ksenotimove. Minerali apatitove skupine, titanit in magneziokromit so zastopani v dveh oziroma treh vzorcih, medtem ko smo titanomagnetit, svinčev oksid/karbonat in pirit našli le v posameznih vzorcih. Velikost omenjenih mineralov je v povprečju 60 μm. Znaki transporta in preperevanja so izrazitejši kot v kamnini. V travniških tleh smo določili dvanajst, v gozdnih tleh devet različnih mineralov. Menimo, da raba tal (travnik, gozd) bistveno ne vpliva na vsebnost težkih mineralov v tleh. Rezultati analiz kažejo, da imajo minerali v tleh tako avtohton kot alohton izvor.Our intention was to check the heavy mineral content in both the Upper Triassic dolomite, and the soil in three areas in Slovenia, around Postojna, Zaplana and Stična. Heavy minerals could be autochthonous or allochthonous. Also, we examined the influence of the land use (meadow, forest) on their distribution. XRD showed the presence of dolomite, quartz, muscovite/illite and the chlorite group mineral in the soil samples and only dolomite in rock samples. By using optical microscopy, we also determined separate grains of feldspar, quartz, muscovite, dark opaque minerals and lithic fragments. The percentage of insoluble heavy minerals residue in the dolomite is small, between 0,03 % and 0,70 %. The SEM/EDS analysis of insoluble residue and thin sections showed the presence of 7 minerals: zircon, TiO2 (most probably rutile), minerals of the monazite and the apatite group, sphalerite, pyrite and fluorite. The sizes of the mentioned minerals are up to 10 μm. Mineral grains mostly do not show signs of longer transport and weathering. The percentage of heavy fraction in soils ranged between 0,01% and 0,16%. With SEM/EDS analysis we determined 13 minerals. Zircon, ilmenite, TiO2 (most probably rutile), monazite group mineral and chromite are present in most of the soil samples. Iron oxides/hydroxides and xenotime group minerals are frequent as well. Apatite group minerals, titanite magnesiochromite, titaniferous magnetitie, lead oxide/carbonate and pyrite appear only in one, two or three samples.The average size of the minerals is 60 μm. Signs of transport and weathering are more pronounced than in rock. We determined twelve different minerals in the meadow soil and nine in the forest soil. Nevertheless, we believe that the land use (meadow, forest) has not got a fundamental influence on the heavy mineral content in the soil. The results show that the minerals in the soil may have autochthonous and allochthonous origin

Distribution of Pb, Zn and Cd in stream and alluvial sediments in the area with past Zn smelting operations

The sources of Zn, Pb and Cd in alluvial and stream sediments have been studied in the area of historical Zn smelting tradition. 30 samples of stream sediments and samples from 4 alluvial sediment profiles were collected. Fractions 0.125–0.063 and < 0.063 mm were analysed by the means of ICP-MS prior 4-acid digestion. The highest levels of Zn, Cd and Pb were detected in the alluvial sediments in the closest vicinity to the abandoned slag and ore roasting residue waste dumps, reaching 96 and 4520 mg/kg, 522 and 26,800 mg/kg and 3.7 and 31 mg/kg for Pb, Zn and Cd in stream and alluvial sediments, respectively. The Voglajna River then transports contamination particles into the Savinja River, which afterwards flows into the Sava River. Consequently, the anomaly can even be detected in the Sava River, more than 30 km downstream. Higher levels of Pb, Zn and Cd have been found in fraction < 0.063 mm compared to 0.125–0.063 mm fraction. Impacts of historically contaminated soil erosion and in particular the wash-out of Zn-smelting waste from the improperly managed waste dump were recognised as the dominant sources of Zn, Cd and Pb in the stream and alluvial sediments

Influence of alkalis on the phase development of belite-sulfoaluminate clinkers

This paper presents a study on the influence of different amounts of alkalis (K2O and Na2O) on clinker phase formation, microstructure, phase composition and reactivity of belite-sulfoaluminate cement clinker. Using X-ray powder diffraction and scanning electron microscopy with energy dispersive spectrometry, it was found that the amount of C2S and C4AF increases with the incorporation of alkalis, while the amount of C4A3Ś and CŚ decreases. In addition to the major phases, the samples with alkalis also consist of minor phases such as C3A (tricalcium aluminate), KŚ (arcanite), and KC2Ś3 (Ca-langbeinite). The major ions in the major phases were substituted by alkali cations and some other ions (Ca2+, Al3+, Fe3+, S2-, S6+, Si4+). The alkalis also affect the microstructure of the clinker, e.g., the shape of the grains. Consequently, isothermal calorimetry was used to detect differences in hydration kinetics. The clinker with 2 wt. % K2O content was the most reactive, while the sample with 0.5 wt. % Na content was the least reactive. The latter was primarily influenced by the content of the main and minor phases of the clinker

Mining and Metallurgical Waste as Potential Secondary Sources of Metals—A Case Study for the West Balkan Region

The aim of this paper is to present a chemical composition and quantities of mining and processing waste landfills material developed during historical mining and smelting. After detailed inspection, it was found that approximately 2.6 gigatons of the waste had been deposited at 1650 sites, covering almost 65 km2. More than half of this material, 55%, is characterized as conventional mining waste, 37% belongs to the processing tailings, and 8% to metallurgical waste. Most of these tailing sites are unclaimed, presenting a source of contamination for nearby communities. According to the literature data collected and additional chemical analyses, in accordance with zero-waste philosophy, about 42 promising locations (c. 270 million tons) could be selected, where various advanced eco-innovative methods of recovery could possibly apply. The areas with the highest prospective recovery are Serbia and Kosovo. In accordance with the metal prices achieved in March 2022, it is estimated that the recovery of tailings could bring up to 18,100 million USD, which is much more compared to the prices of March 2020—10,600 million USD—when the commodity market was governed by the COVID-19 restrictions. In addition to the commercial value of the metals, the environmental aspect should not be forgotten after the application of reuse and recycling concepts

Heavy minerals as indicators of source material in soils on carbonates

The origin of the soils formed on carbonate rocks remains uncertain, as they are probably of polygenetic origin. Of particular interest are the elevated contents of some trace elements detected in these soils, as they can hardly be attributed to insoluble residues of carbonate rock. The aim of this study was to uncover the relationship between heavy minerals in bedrock and soil and to identify other sources that influence the mineral and chemical composition of soil. We investigated representative samples of soils and dolomite bedrock as well as sandstones and marlstones from the nearby flysch basin as an expected source of the aeolian contribution. XRD and SEM/EDS showed that mineral diversity is higher in soils compared to the dolomites. Heavy minerals found in dolomite insoluble residue include sphalerite, Ti-oxide (probably rutile), zircon, fluorite, pyrite, minerals of REE phosphates and apatite group, interpreted as terrigenous detrital material. The mineral composition of soil heavy fraction is only partly following insoluble residues of bedrock and indicates possible aeolian contribution. Comparison with nearby flysch sandstones and marlstones showed similarities in mineralogical diversity by the presence of chromite and Fe-Cr(Mn) oxides (probably carmichaelite). Other minerals present in soils and flysch layers, such as Ti-oxide (probably rutile), zircon, REE phosphates, and pyrite grains, however, show similarities in mode of occurrence and transport indications. Signs of aeolian transport on the grains detected in soils were further confirmed by SEM/EDS