Substantial Copper (Cu2+) Uptake by Metakaolin-Based Geopolymer and Its Resistance to Acid Leaching and Ion Exchange.

Geopolymers are inorganic, chemically resistant aluminosilicate-based binding agents, which remove hazardous metal ions from exposed aqueous media. However, the removal efficiency of a given metal ion and the potential ion remobilization have to be assessed for individual geopolymers. Therefore, copper ions (Cu2+) were removed by a granulated, metakaolin-based geopolymer (GP) in water matrices. Subsequent ion exchange and leaching tests were used to determine the mineralogical and chemical properties as well as the resistance of the Cu2+-bearing GPs to corrosive aquatic environments. Experimental results indicate the pH of the reacted solutions to have a significant impact on the Cu2+ uptake systematics: the removal efficiency ranged from 34-91% at pH 4.1-5.7 up to ~100% at pH 11.1-12.4. This is equivalent to Cu2+ uptake capacities of up to 193 mg/g and 560 mg/g in acidic versus alkaline media. The uptake mechanism was governed by Cu2+-substitution for alkalis in exchangeable GP sites and by co-precipitation of gerhardtite (Cu2(NO3)(OH)3) or tenorite (CuO) and spertiniite (Cu(OH)2). All Cu-GPs showed excellent resistance to ion exchange (Cu2+ release: 0-2.4%) and acid leaching (Cu2+ release: 0.2-0.7%), suggesting that tailored GPs have a high potential to immobilize Cu2+ ions from aquatic media.

Synthesis of Zeolites from Fine-Grained Perlite and Their Application as Sorbents.

The hydrothermal alteration of perlite into zeolites was studied using a two-step approach. Firstly, perlite powder was transformed into Na-P1 (GIS) or hydro(xy)sodalite (SOD) zeolites at 100 °C and 24 h using 2 or 5 M NaOH solutions. Secondly, the Si:Al molar ratio of the reacted Si-rich solution was adjusted to 1 by Na-aluminate addition to produce zeolite A (LTA) at 65 or 95 °C and 6 or 24 h at an efficiency of 90 ± 9% for Al and 93 ± 6% for Si conversion. The performance of these zeolites for metal ion removal and water softening applications was assessed by sorption experiments using an artificial waste solution containing 4 mmol/L of metal ions (Me2+: Ca2+, Mg2+, Ba2+ and Zn2+) and local tap water (2.1 mmol/L Ca2+ and 0.6 mmol/L Mg2+) at 25 °C. The removal capacity of the LTA-zeolite ranged from 2.69 to 2.86 mmol/g for Me2+ (=240-275 mg/g), which is similar to commercial zeolite A (2.73 mmol/g) and GIS-zeolite (2.69 mmol/g), and significantly higher compared to the perlite powder (0.56 mmol/g) and SOD-zeolite (0.88 mmol/g). The best-performing LTA-zeolite removed 99.8% Ca2+ and 93.4% Mg2+ from tap water. Our results demonstrate the applicability of the LTA-zeolites from perlite for water treatment and softening applications.

Impact of green clay authigenesis on element sequestration in marine settings.

Retrograde clay mineral reactions (reverse weathering), including glauconite formation, are first-order controls on element sequestration in marine sediments. Here, we report substantial element sequestration by glauconite formation in shallow marine settings from the Triassic to the Holocene, averaging 3 ± 2 mmol·cm-²·kyr-1 for K, Mg and Al, 16 ± 9 mmol·cm-²·kyr-1 for Si and 6 ± 3 mmol·cm-²·kyr-1 for Fe, which is ~2 orders of magnitude higher than estimates for deep-sea settings. Upscaling of glauconite abundances in shallow-water (0-200 m) environments predicts a present-day global uptake of ~≤ 0.1 Tmol·yr-1 of K, Mg and Al, and ~0.1-0.4 Tmol·yr-1 of Fe and Si, which is ~half of the estimated Mesozoic elemental flux. Clay mineral authigenesis had a large impact on the global marine element cycles throughout Earth's history, in particular during 'greenhouse' periods with sea level highstand, and is key for better understanding past and present geochemical cycling in marine sediments.

Green inhibitors reduce unwanted calcium carbonate precipitation: Implications for technical settings.

Mineral scale deposits in water drainage and supply systems are a common and challenging issue, especially by clogging the water flow. The removal of such unwanted deposits is cost intensive arguing for case-specific and sustainable prevention strategies. In the present study, a novel on-site approach to prevent calcium carbonate (CaCO3) scale formation was assessed in two road tunnel drainages: Application of the eco-friendly green inhibitor polyaspartate (PASP) caused (i) a significant inhibition of CaCO3 precipitation, (ii) a more porous or even unconsolidated consistence of the deposits, and (iii) a shift from calcite to the metastable aragonite and vaterite polymorphs. Even relatively low PASP concentrations (1-33 mg/l) can significantly decrease CaCO3 scale deposition, removing up to ∼7 t CaCO3/year at an efficiency up to 84%. Application of PASP for water conditioning should also consider case-specific microbial activity effects, where consumption of PASP, e.g. by Leptothrix ochracea, can limit inhibition effects.

A novel nZVI-bentonite nanocomposite to remove trichloroethene (TCE) from solution.

Nanoscale zero-valent iron (nZVI) based (nano)composites supported by clay mineral substrates are a promising technology for the in-situ remediation of groundwater and (sub)soils contaminated with chlorinated hydrocarbons, such as trichloroethene (TCE). However, the physicochemical processes and interaction mechanisms between nZVI particles, clay minerals and TCE are poorly understood, yet. We immobilized nZVI particles on a commercial bentonite substrate to prepare a novel nZVI-B nanocomposite and tested its performance for TCE removal from solution against pure nZVI in batch reactors. The nZVI-B exhibited a higher reactivity (2.2·10-3 L h-1·m-2) and efficiency (94%) for TCE removal than nZVI (2.2·10-4 L h-1·m-2; 45%). Sorption of TCE onto the clay surfaces and reductive de-chlorination in "micro-reactors" developing within the nZVI-B controlled the kinetics and the magnitude of TCE loss from solution. Contrary to pure nZVI, no signs of nZVI particle agglomeration or inactivation due to oxide shell formation were found in nZVI-B. We attribute this to the uptake of dissolved Fe species that are liberated via progressing nZVI particle corrosion by the bentonite substrate to form Fe-smectite (nontronite domains), which prevented from a deterioration of the properties and reactivity of the nZVI-B. The use of nZVI-B in permeable reactive barriers at contaminated field sites could be feasible, where a system-inherent reduction of the soil-bearing capacity has to be minimized.

Chemical weathering and progressing alteration as possible controlling factors for creeping landslides.

Landslides can behave as dynamic processes, which emerge from the complex interplay of tectonics, erosion, weathering and gravitational influences, triggered by various hydrological, mineralogical, biological and geotechnical factors. Integral studies to assess the mechanisms underlying landslide initiation and progression are mainly focussed on specific cases with high geohazard potential. The landslide near Stadtschlaining (Austria) represents a key study site to elucidate the impacts of pelitic sediment composition, weathering regime, alteration patterns and hydrochemistry on recurrent damage progression in the local infrastructure. Based on field work, soil-mechanical logging (Atterberg limits, undrained strength, friction angles), water chemistry (ICP-OES, IC, hydrochemical modeling), solid-phase characterization (XRD, XRF, SEM) and sorption experiments we establish a conceptual model for initiating and progressing of landslides: Infiltration of low mineralized meteoric water (EC: <200 µS/cm) in permeable limonitic gravels triggers chemical weathering of greenschist-derived detritus and promotes its transformation into kaolinite and smectite. The clayey strata (>50 wt% of clay minerals) create zones of mechanical and chemical weakness in the underground (~4-6 m below ground level), which are characterized by particle disintegration/delamination, slip bedding and deformations, and development of porous layers depicting water flow paths. Subsequent Na+ exchange for bivalent ions in the smectite interlayer delivered by percolating, highly mineralized water (EC: 1600-5100 µS/cm) is caused by de-icing salt and fertilizer applications during winter and late summer, and yield in i) decohesion and physical breakdown of the particle aggregates and ii) swelling of the clay matrix in early spring and autumn. These processes reduce the shear strength of the pelitic sediments, resulting in failure and initiation of landslides (deformation: ~500 mm within a month) and subsequent steady creeping motion (deformation: ~100 mm in 6 months). Customized engineered solutions to prevent landslides in this area are presented, which can be conveyed to analogous landslide-affected areas worldwide.

Removal of Barium from Solution by Natural and Iron(III) Oxide-Modified Allophane, Beidellite and Zeolite Adsorbents.

Efficient capture of barium (Ba) from solution is a serious task in environmental protection and remediation. Herein, the capacity and the mechanism of Ba adsorption by natural and iron(III) oxide (FeO) modified allophane (ALO), beidellite (BEI) and zeolite (ZEO) were investigated by considering the effects of contact time, temperature, pH, Ba2+ concentration, adsorbent dosage, the presence of competitive ions and adsorption-desorption cycles (regenerability). Physicochemical and mineralogical properties of the adsorbents were characterized by XRD, FTIR, SEM with EDX and N2 physisorption techniques. The Ba2+ adsorption fitted to a pseudo-first-order reaction kinetics, where equilibrium conditions were reached within <30 min. BEI, ALO and ZEO with(out) FeO-modification yielded removal efficiencies for Ba2+ of up to 99.9%, 97% and 22% at optimum pH (pH 7.5-8.0). Adsorption isotherms fitted to the Langmuir model, which revealed the highest adsorption capacities for BEI and FeO-BEI (44.8 mg/g and 38.6 mg/g at 313 K). Preferential ion uptake followed in the order: Ba2+ > K+ > Ca2+ >> Mg2+ for all adsorbents; however, BEI and FeO-BEI showed the highest selectivity for Ba2+ among all materials tested. Barium removal from solution was governed by physical adsorption besides ion exchange, intercalation, surface complexation and precipitation, depending mainly on the absorbent type and operational conditions. BEI and FeO-BEI showed a high regenerability (>70-80% desorption efficiency after 5 cycles) and could be considered as efficient sorbent materials for wastewater clean-up.

Geochemistry and mineralogy of the Oligo-Miocene sediments of the Valley of Lakes, Mongolia.

The Valley of Lakes is approximately a 500-km elongate depression in Central Mongolia, where Eocene to Miocene continental sediments are long known for their outstanding fossil richness. The palaeontological record of this region is an exceptional witness for the evolution of mammalian communities during the Cenozoic global cooling and regional aridification. In order to precisely elucidate the climatic evolution of the region, we studied the mostly siliciclastic sediments with several levels of paleosols for their sedimentology, mineralogy, major and trace element composition and δ13C and δ18O composition. The obtained results show that temperate hydrothermal fluids induced a strong illitization of the fluvial and lacustrine sediments. This finding contradicts the current conceptual view that the fine fraction of the sediments is of aeolian origin. Moreover, the diagenetic growth of illite resulted in a strong overprinting of the sediments and, subsequently, largely disturbed the pristine mineralogical and geochemical composition of the sediments that could have carried any palaeo-climatic information. An exception is the δ13C (and δ18O) isotope values of authigenic carbonate found in calcrete horizons that still record the ambient climatic conditions prevailing during paleosol formation. Our novel δ13C and δ18O record suggests an early Oligocene aridification in Central Asia at ∼31 Ma, whereas the Oligocene glacial maximum shows no increase in aridification. A second, regional-scale aridification occurs at ~25 Ma and corresponds to a late Oligocene marked mammalian turnover in the Valley of Lakes sediments.