Floatability of rare earth phosphors from waste fluorescent lamps

Zeta-potential measurements were made to determine the electric state of phosphor materials on the basis of which a feasibility study could be performed for the use of flotation in the recovery of fine (d₅₀ < 13 μm) rare earth phosphors from waste fluorescent lamps. Tests were carried out with pure specimens of white (calcium halo-phosphate), red, green and blue (rare earth) phosphors, with a 17 : 1 : 1 : 1 ratio of their mixture, and with actual waste phosphor materials. The effects of a cationic (dodecyl ammonium acetate, DAA) and two anionic (sodium dodecyl sulfate (SDS) and sodium oleate (NaOl)) collectors on the floatability of materials, as well as that of Na₂SiO₃ dispersant on the separation characteristics, were investigated at different pH ranges. The process, applied to actual discarded waste phosphors gave, in a two-stage separation scheme, sink products assaying 17.7–23.8% and 21.5–25.9% rare earth phosphors for DAA and SDS flotation, respectively. The recovery and Newton's efficiency were about 70–90% and 0.26–0.37, 66–82% and 0.18–0.20, respectively for DAA and SDS flotation.     

Measuring reactive pools of Cd,Pb and Zn in coal fly ash from the UK using isotopic dilution assays

Large volumes of coal fly ash are continually being produced and stockpiled around the world and can be a source of environmentally sensitive trace elements. Whilst leaching tests are used for regulatory purposes, these provide little information about the true geochemical behaviour and ‘reactivity’ of trace elements in coal ash because they are poorly selective. Isotope dilution (ID) assays are frequently used in soil geochemistry as a means of measuring the reactive pools of trace metals that are in equilibrium with soil pore waters. This paper examines the applicability of multi-element ID assays in measuring the labile or reactive pool of Cd, Pb and Zn in a range of fresh and weathered fly ash, where pH is generally much more alkaline than in soils. The method generally worked well using 0.0005 M EDTA as a background electrolyte as it provided robust analytical ICP-MS measurements as well as fulfilling the important principle of ID that non-labile metal should not be solubilised. Reactive pools were equivalent to 0.5–3% of the total Pb pool and 4–13% of the total Cd pool. For Zn, where samples had pH < 11.5, the reactive Zn pool varied between 0.3% and 2%; when fresh ash samples with pH > 11.5 were tested, the method failed as the spiked isotope appeared to be sorbed or precipitated. Ash weathering was found to exert little impact on the lability of Cd, Pb and Zn. Isotope dilution results were compared with 0.43 M HNO₃ and 0.05 M EDTA extractions, these commonly being used as analogues of the ID assay, and concluded that these can be used as fast, cost-effective and simple proxies for the ID assays. Results suggest that ID methods can be used to enhance knowledge of trace element behaviour in fresh and weathered fly ash.     

Stability and leaching of cobalt smelter fly ash

The leaching behaviour of fly ash from a Co smelter situated in the Zambian Copperbelt was studied as a function of pH (5–12) using the pH-static leaching test (CEN/TS 14997). Various experimental time intervals (48 h and 168 h) were evaluated. The leaching results were combined with the ORCHESTRA modelling framework and a detailed mineralogical investigation was performed on the original FA and leached solid residues. The largest amounts of Co, Cu, Pb and Zn were leached at pH 5, generally with the lowest concentrations between pH 9 and 11 and slightly increased concentrations at pH 12. For most elements, the released concentrations were very similar after 48 h and 168 h, indicating near-equilibrium conditions in the system. Calcite, clinopyroxenes, quartz and amorphous phases predominated in the fly ash. Various metallic sulfides, alloys and the presence of Cu, Co and Zn in silicates and glass were detected using SEM/EDS and/or TEM/EDS. The leaching of metals was mainly attributed to the dissolution of metallic particles. Partial dissolution of silicate and glass fractions was assumed to significantly influence the release of Ca, Mg, Fe, K, Al and Si as well as Cu, Co and Zn. The formation of illite was suggested by the ORCHESTRA modelling to be one of the main solubility-controlling phases for major elements, whereas Co and Zn were controlled by CoO and zincite, respectively. Sorption of metals on hydrous ferric oxides was assumed to be an important attenuation mechanism, especially for the release of Pb and Cu. However, there is a high risk of Co, Cu, Pb and Zn mobility in the acidic soils around the smelter facility. Therefore, potential local options for “stabilisation” of the fly ash were evaluated on the basis of the modelling results using the PHREEQC code.     

Gold losses by cementation and thermal reduction in the gold recovery circuits

In this study, gold losses in a carbon-in-pulp (CIP) cyanidation gold recovery process and potential sources of these losses were investigated. Gold was found in samples from different streams through the CIP-cyanidation process, pointing to incidental losses. Mineralogical studies showed that gold losses occurred in two main forms, either as attached to larger entities or in the form of dendritic precipitates. SEM and EDS studies revealed that iron bearing minerals acted as the major media in cases when gold associations were observed as losses. The highly alkaline pH (≈ 13), elevated process temperature (≈ 145 °C), and high cyanide concentration (≥ 250 ppm) in the elution column along with a fine iron bearing material implied that gold attachment occurred through an electrochemical cementation mechanism. It was anticipated that the presence of iron in the process, which facilitated gold cementation, relied on the oxidative breakdown of the iron bearing minerals in the ore and/or due to the formation of porous iron oxides due to the roasting of iron sulfides in the regeneration kiln. In the elution column some part of the auro–cyanide complexes would remain non-eluted and be discharged into the carbon generation kiln and the carbon generation kiln was another section promoting gold losses. The high temperature condition in the carbon regeneration kiln (> 500 °C) caused thermal reduction of the non-eluted auro–cyanide complexes to metallic gold, leading to the formation of dendritic gold precipitates and their eventual loss.     

Linking wildfire effects on soil and water chemistry of the Marão River watershed,Portugal, and biomass changes detected from Landsat imagery

Wildfires transform the landscape, leading to changes in surface cover and, potentially, in water quality. The purpose of this study was to assess changes in the chemical composition of soils and surface water as a result of a wildfire that burned in 2006 in the Marão Mountains, NE Portugal, by comparing pre- and post-fire hydrochemical data and burned/unburned soil data, and to examine the recovery of vegetation over time using Landsat TM imagery. Studies that have access to pre-fire data are rare and even fewer studies document changes in biomass as a result of fire and during the postfire recovery period. Samples of ash, soil and water, from within and outside the burned area, were collected 5 months, and one year after the fire, for chemical analyses. Landsat TM Images were downloaded and transformed into a vegetation index, in order to analyze landcover dynamics and to calculate biomass. The wildfire effects on the Marão River water quality, resulted in an increase in the total mineralization of water. Five months after the wildfire the electrical conductivity (E.C.) at the mainstem was about 56% higher than pre-fire values (E.C. increased from 25 to 39 μS/cm) and still higher one year after (36 μS/cm). Cations of Ca, Na, Mg and Mn showed the greatest increase. This increase was probably triggered by the movement of ash to the watercourses. This disturbance had already attenuated one year after wildfire to values closer to pre-fire data except for manganese. Manganese had anomalous concentrations in the water within the burned area. The concentration of Mn in ash samples reached values up to 5 times more than values found in underlying soils. One year after the wildfire, almost all the burned area had recovered with herbaceous vegetation and patches of shrub vegetation. The wildfire burned 1194.7 dry tons of biomass which means, on average, 4.9 dry ton/ha. Based on the mass of burned biomass, we calculated approximately 350 g/ha of Mn were released as a result of the fire. We suggest that this type of calculation can be conducted before a fire to help resource managers understand worst-case scenarios for changes in water quality that have the potential to affect aquatic biotic and the suitability of water for drinking water purposes and agriculture.     

Fate of organic matter during aquifer storage and recovery (ASR) of reclaimed water in a carbonate aquifer

Understanding the fate of injected organic matter and the consequences of subsequent redox processes is essential to assess the viability of using reclaimed water in aquifer storage and recovery (ASR). A full-scale field trial was undertaken at Bolivar, South Australia where two ASR cycles injected approximately 3.6 × 10⁵ m³ of reclaimed water into a carbonate aquifer over a 3-a period. Organic C within reclaimed water was predominantly in the dissolved fraction, ranging from 1 to 2 mmol L⁻¹ (10–20 mg L⁻¹), markedly higher than potable supply and stormwater previously reported as source waters for ASR. Between 20% and 24% of the injected dissolved organic C (DOC) was mineralised through reaction with injected O₂ and NO₃. Furthermore, this was achieved mainly within the first 4 m of aquifer passage. Despite the presence of residual DOC, SO₄ reduction was not induced within the bulk of the injected plume. It was only near the ASR well during an extended storage phase where deeply reduced (methanogenic) conditions developed, indicating variable redox zones within the injectant plume. The quality of water recovered from the ASR well indicated that the organic C content of reclaimed water does not restrict its application as a recharge source for ASR.     

Mercury deposition and methylmercury formation in Narraguinnep Reservoir,southwestern Colorado,USA

Narraguinnep Reservoir in southwestern Colorado is one of several water bodies in Colorado with a mercury (Hg) advisory as Hg in fish tissue exceed the 0.3 μg/g guideline to protect human health recommended by the State of Colorado. Concentrations of Hg and methyl-Hg were measured in reservoir bottom sediment and pore water extracted from this sediment. Rates of Hg methylation and methyl-Hg demethylation were also measured in reservoir bottom sediment. The objective of this study was to evaluate potential sources of Hg in the region and evaluate the potential of reservoir sediment to generate methyl-Hg, a human neurotoxin and the dominant form of Hg in fish. Concentrations of Hg (ranged from 1.1 to 5.8 ng/L, n = 15) and methyl-Hg (ranged from 0.05 to 0.14 ng/L, n = 15) in pore water generally were highest at the sediment/water interface, and overall, Hg correlated with methyl-Hg in pore water (R² = 0.60, p = 0007, n = 15). Net Hg methylation flux in the top 3 cm of reservoir bottom sediment varied from 0.08 to 0.56 ng/m²/day (mean = 0.28 ng/m²/day, n = 5), which corresponded to an overall methyl-Hg production for the entire reservoir of 0.53 g/year. No significant point sources of Hg contamination are known to this reservoir or its supply waters, although several coal-fired power plants in the region emit Hg-bearing particulates. Narraguinnep Reservoir is located about 80 km downwind from two of the largest power plants, which together emit about 950 kg-Hg/year. Magnetic minerals separated from reservoir sediment contained spherical magnetite-bearing particles characteristic of coal-fired electric power plant fly ash. The presence of fly-ash magnetite in post-1970 sediment from Narraguinnep Reservoir indicates that the likely source of Hg to the catchment basin for this reservoir has been from airborne emissions from power plants, most of which began operation in the late-1960s and early 1970s in this region.     

Study of preexisting shear surfaces of reactivated landslides from a strength recovery perspective

Residual shear strength is generally considered in the design of preventive measures for slopes consisting of preexisting shear surfaces of large-scale landslides. Recent research suggests that the preexisting shear surface of a reactivated landslide can regain strength with the passage of time, which might also be considered in designing the slope stability measures. In this study, three reactivated landslide soils were tested in a ring shear apparatus for the discontinued shear periods of 1, 3, 7, 15, and 30 days with the following main objectives: (i) to understand the strength recovery behavior of landslide soils in a residual state of shear after as long as 30 days of discontinued shear, (ii) to understand the comparative pattern of strength recovery in highly plastic and less plastic soils, and (iii) to understand the mechanism involved in strength recovery at a residual state of shear. The results indicate that recovered strength measured in the laboratory is hardly noticeable after a rest period of 3 days, but recovered strength is lost after a small shear displacement. This paper primarily focuses on the effect of strength recovery from residual strength on preexisting shear surface soils and the mechanisms behind it.     

30 million years of Permian volcanism recorded in the Choiyoi igneous province (W Argentina) and their source for younger ash fall deposits in the Paraná Basin: SHRIMP U–Pb zircon geochronology evidence

We present four SHRIMP U–Pb zircon ages for the Choiyoi igneous province from the San Rafael Block, central–western Argentina. Dated samples come from the Yacimiento Los Reyunos Formation (281.4 ± 2.5 Ma) of the Cochicó Group (Lower Choiyoi section: andesitic breccias, dacitic to rhyolitic ignimbrites and continental conglomerates), Agua de los Burros Formation (264.8 ± 2.3 Ma and 264.5 ± 3.0 Ma) and Cerro Carrizalito Formation (251.9 ± 2.7 Ma Upper Choiyoi section: rhyolitic ignimbrites and pyroclastic flows) spanning the entire Permian succession of the Choiyoi igneous province. A single zircon from the El Imperial Formation, that is overlain unconformably by the Choiyoi succession, yielded an early Permian age (297.2 ± 5.3 Ma), while the main detrital zircon population indicated an Ordovician age (453.7 ± 8.1 Ma). The new data establishes a more precise Permian age (Artinskian–Lopingian) for the section studied spanning 30 Ma of volcanic activity. Volcanological observations for the Choiyoi succession support the occurrence of explosive eruptions of plinian to ultraplinian magnitudes, capable of injecting enormous volumes of tephra in the troposphere–stratosphere. The new SHRIMP ages indicate contemporaneity between the Choyoi succession and the upper part of the Paraná Basin late Paleozoic section, from the Irati up to the Rio do Rasto formations, encompassing about 24 Ma. Geochemical data show a general congruence in compositional and tectonic settings between the volcanics and Paraná Basin Permian ash fall derived layers of bentonites. Thickness and granulometry of ash fall layers broadly fit into the depletion curve versus distance from the remote source vent of ultraplinian eruptions. Thus, we consider that the Choiyoi igneous province was the source of ash fall deposits in the upper Permian section of the Paraná Basin. Data presented here allow a more consistent correlation between tectono-volcanic Permian events along the paleo-Pacific margin of southwestern Gondwana and the geological evolution of neighboring Paleozoic foreland basins in South America and Africa.     

Breaking the glass ceiling for high resolution Nd isotope records in early Cenozoic paleoceanography

We report an optimized method for extracting neodymium (Nd) from fossil fish teeth with a single-stage column (125 µl stem volume; LN Resin, Eichrom Industries, Darien Illinois) for isotopic analysis by multi-collector inductively coupled mass spectrometry (MC-ICMPS). Three reference materials (basalt: BCR-2, BHVO-2; phosphate: fossil bone composite) and splits of fossil fish teeth samples previously processed with existing two-stage column methods were processed using the single-stage column method. ¹⁴³Nd/¹⁴⁴Nd values of reference materials agree within error with published values, and the values for fish teeth correspond with sample splits processed with two-stage columns. Precision to ± ～ 0.23 ε_Nd was achieved for 30 ng Nd samples of reference materials, and Nd isotope measurements of fossil fish tooth sample replicates as small as 7 ng Nd were reproducible within long term instrumental uncertainty. We demonstrate the utility of the new method with the first high resolution Nd isotope record spanning the ～ 40.0 Ma middle Eocene Climatic Optimum, which shows an excursion of 0.65 ε_Nd during the peak warming at the study site (Ocean Drilling Program Leg 119, Site 738; 30 kyr sample spacing from 40.3 to 39.6 Ma). LN Resin is already used in standard methods for separating Nd, and Nd isotopes are routinely measured by MC-ICPMS with high efficiency inlet systems. Our innovation is a single, small volume LN Resin column for Nd separation. The streamlined approach results in a 10× increase in sample throughput.     

Touristic disaster: Spectacle and recovery in Post-Katrina New Orleans

This paper develops the concept touristic disaster as a heuristic device to examine the conflictual and contradictory aspects of showcasing disaster-devastated neighborhoods as tourist attractions. Touristic disaster refers to the application of tourism modes of staging, visualization, and discourse to reenchant the money making deterrents (stigma) of “destruction” and “ruin” and re-signify disaster to indicate “recovery” and “rebirth.” This paper uses empirical examples from New Orleans to examine the transition from “disaster tourism” to “recovery tourism” in tourism framings of post-Katrina rebuilding. The concept of touristic disaster views disaster-devastated neighborhoods as sites and arenas of contestation in which opposing groups and interests battle to control representations of urban space. The paper illustrates the motivations, processes, and paradoxical impacts of the commodification and global representation of “disaster” and “recovery” and provides insights into the ways in which people can use spectacle to contest marginalization.     

Precise dating of the Middle Permian: Zircon U–Pb geochronology from volcanic ash beds in the basal Gufeng Formation,Yangtze region,South China

Direct radiometric dating of the Lower/Middle Permian epochs has not been well accomplished. Shales and bedded cherts of the geologically well-documented Middle Permian Gufeng Formation are exposed in the Chaohu area, Anhui province, South China. Through detailed field examination and mapping of the Gufeng stratigraphic section, we found at least four volcanic ash beds within the basal shale strata. This new discovery indicates the existence of prominent volcanic activity during Gufeng sedimentation and provides the opportunity to precisely date the age of the Middle Permian. Zircon grains separated from two near-basal horizon yield LA‐ICP‐MS U–Pb ages of 272.0 ± 5.5 Ma (MSWD = 2.6) and 271.5 ± 3.3 Ma (MSWD = 1.7). As the first precise isotopic age (272 Ma) of the Middle Permian Gufeng Formation in South China, our data offer precise geochronological constraints for the division and correlation of Middle Permian not only in South China but also worldwide.     

Factors affecting the dissolution kinetics of volcanic ash soils: dependencies on pH,CO2, and oxalate

Laboratory experiments were conducted with volcanic ash soils from Mammoth Mountain, California to examine the dependence of soil dissolution rates on pH and CO₂ (in batch experiments) and on oxalate (in flow-through experiments). In all experiments, an initial period of rapid dissolution was observed followed by steady-state dissolution. A decrease in the specific surface area of the soil samples, ranging from 50% to 80%, was observed; this decrease occurred during the period of rapid, initial dissolution. Steady-state dissolution rates, normalized to specific surface areas determined at the conclusion of the batch experiments, ranged from 0.03 μmol Si m⁻² h⁻¹ at pH 2.78 in the batch experiments to 0.009 μmol Si m⁻² h⁻¹ at pH 4 in the flow-through experiments. Over the pH range of 2.78–4.0, the dissolution rates exhibited a fractional order dependence on pH of 0.47 for rates determined from H⁺ consumption data and 0.27 for rates determined from Si release data. Experiments at ambient and 1 atm CO₂ demonstrated that dissolution rates were independent of CO₂ within experimental error at both pH 2.78 and 4.0. Dissolution at pH 4.0 was enhanced by addition of 1 mM oxalate. These observations provide insight into how the rates of soil weathering may be changing in areas on the flanks of Mammoth Mountain where concentrations of soil CO₂ have been elevated over the last decade. This release of magmatic CO₂ has depressed the soil pH and killed all vegetation (thus possibly changing the organic acid composition). These indirect effects of CO₂ may be enhancing the weathering of these volcanic ash soils but a strong direct effect of CO₂ can be excluded.     

A significant middle Pleistocene tephra deposit preserved in the caves of Mulu,Borneo

A distinctive white sediment in the caves of Mulu, Sarawak, Borneo is a well-preserved tephra, representing a fluvially transported surface air-fall deposit, re-deposited inside the caves. We show that the tephra is not the Younger Toba Tephra, formerly considered as most likely. The shards are rod-shaped with elongate tubular vesicles; the largest grains ~ 170 μm in length; of rhyolitic composition; and ⁸⁷Sr/⁸⁶Sr ratio of 0.70426 ± 0.00001. U–Th dating of associated calcites suggest that the tephra was deposited before 125 ± 4 ka, and probably before 156 ± 2 ka. Grain size and distance from closest potential source suggests an eruption of VEI 7. Prevailing winds, grain size, thickness of deposit, location of potential sources, and Sr isotopic ratio limit the source to the Philippines. Comparisons with the literature give the best match geochemically with layer 1822 from Ku et al. (2009a), dated by ocean core stratigraphy to 189 ka. This tephra represents a rare terrestrial repository indicating a very substantial Plinian/Ultra-Plinian eruption that covered the Mulu region of Borneo with ash, a region that rarely receives tephra from even the largest known eruptions in the vicinity. It likely will be a valuable chronostratigraphic marker for sedimentary, palaeontological and archaeological studies.     

Magnetostratigraphy of deep drilling core SG-1 in the western Qaidam Basin (NE Tibetan Plateau) and its tectonic implications

The Qaidam Basin is the largest intermontane basin of the northeastern Tibetan Plateau and contains a continuous Cenozoic sequence of lacustrine sediments. A ~ 1000-m-deep drilling (SG-1) with an average core recovery of ~ 95% was carried out in the depocenter of the Chahansilatu playa (sub-depression) in the western Qaidam Basin, aimed to obtain a high-resolution record of the paleoenvironmental evolution and the erosion history. Stepwise alternating field and thermal demagnetization, together with rock magnetic results, revealed a stable remanent magnetization for most samples, carried by magnetite. The polarity sequence consisted of 16 normal and 15 reverse zones which can be correlated with chrons 1n to 2An of the global geomagnetic polarity time scale. Magnetostratigraphic results date the entire core SG-1 at ~ 2.77 Ma to ~ 0.1 Ma and yielded sediment accumulation rate (SAR) ranging from 26.1 cm/ka to 51.5 cm/ka. Maximum SARs occurred within the intervals of ~ 2.6–2.2 Ma and after ~ 0.8 Ma, indicating two episodes of erosion, which we relate to pulse tectonic uplift of the NE Tibetan Plateau with subsequent global cooling.     

Silicon isotopes in allophane as a proxy for mineral formation in volcanic soils

Weathering of basaltic ash in volcanic areas produces andosols, rich in allophane and ferrihydrite. Since the rate of mineral formation is very useful in climate and geochemical modelling, this study investigates Si isotope compositions of allophane as a proxy for mineral formation. Allophane formed in contrasting conditions in five Icelandic soil profiles displays silicon isotope signatures lighter than the basalt in less weathered soils (?0.64 ± 0.15‰), and heavier in more weathered organic-rich soils (+0.23 ± 0.10‰). The fate of the dissolved Si in those volcanic soils strongly depends on Al availability. In organic-rich soils, most of Al is humus-complexed, and the results support that Si precipitates as opaline silica by super-saturation, leaving an isotopically heavier dissolved Si pool to form allophane with uncomplexed Al. This study highlights that Si isotopes can be useful to record successive soil processes involved in mineral formation, which is potentially useful in environmental paleo-reconstruction.     

Surface chemical mechanisms of inadvertent recovery of chromite in UG2 ore flotation: Residual layer identification using statistical ToF-SIMS analysis

In the UG2 ore (Bushveld Complex, South Africa) flotation, normally more than 3% of the gangue minerals, principally chromite with talc and pyroxene, report to the concentrate diluting the PGM recovery and contributing to subsequent processing costs. Previous studies have identified residual talc-like layers on orthopyroxene surfaces in Merensky ore flotation contributing to inadvertent flotation of relatively large particles (20–150 µm) of this mineral. Chromite (75–150 µm) from flotation of UG2 ore has been similarly examined. Statistical comparison of ToF-SIMS analysis of particles from concentrate and tails reveals no significant difference in Cu, Pb, Ni and collector (IBX and DTP) signals between these streams but surface exposure of Mg and Si is favoured in the concentrate. The flotation rate of coarse chromite correlates with the exposures of magnesium and silicon in patches on the chromite surface; higher exposures give earlier flotation. Conversely, there is a negative correlation with signals corresponding to the chromite surface, i.e. Cr, Fe, Al. Flotation of chromite without collector has confirmed this statistical discrimination. Hydrophobic talc-like residual layers, similar to those found on orthopyroxene surfaces, probably from partial alteration, explain this flotation mechanism.     

Roles of xenomelts,xenoliths, xenocrysts,xenovolatiles, residues,and skarns in the genesis,transport, and localization of magmatic Fe-Ni-Cu-PGE sulfides and chromite

Most sulfide-rich magmatic Ni-Cu-(PGE) deposits form in dynamic magmatic systems by partial melting S-bearing wall rocks with variable degrees of assimilation of miscible silicate and volatile components, and generation of barren to weakly-mineralized immiscible Fe sulfide xenomelts into which Ni-Cu-Co-PGE partition from the magma. Some exceptionally-thick magmatic Cr deposits may form by partial melting oxide-bearing wall rocks with variable degrees of assimilation of the miscible silicate and volatile components, and generation of barren Fe ± Ti oxide xenocrysts into which Cr-Mg-V ± Ti partition from the magma. The products of these processes are variably preserved as skarns, residues, xenoliths, xenocrysts, xenomelts, and xenovolatiles, which play important to critical roles in ore genesis, transport, localization, and/or modification. Incorporation of barren xenoliths/autoliths may induce small amounts of sulfide/chromite to segregate, but incorporation of sulfide xenomelts or oxide xenocrysts with dynamic upgrading of metal tenors (PGE > Cu > Ni > Co and Cr > V > Ti, respectively) is required to make significant ore deposits. Silicate xenomelts are only rarely preserved, but will be variably depleted in chalcophile and ferrous metals. Less dense felsic xenoliths may aid upward sulfide transport by increasing the effective viscosity and decreasing the bulk density of the magma. Denser mafic or metamorphosed xenoliths may also increase the effective viscosity of the magma, but may aid downward sulfide transport by increasing the bulk density of the magma. Sulfide wets olivine, so olivine xenocrysts may act as filter beds to collect advected finely dispersed sulfide droplets, but other silicates and xenoliths may not be wetted by sulfides. Xenovolatiles may retard settling of – or in some cases float – dense sulfide droplets. Reactions of sulfide melts with felsic country rocks may generate Fe-rich skarns that may allow sulfide melts to fractionate to more extreme Cu-Ni-rich compositions. Xenoliths, xenocrysts, xenomelts, and xenovolatiles are more likely to be preserved in cooler basaltic magmas than in hotter komatiitic magmas, and are more likely to be preserved in less dynamic (less turbulent) systems/domain/phases than in more dynamic (more turbulent) systems/domains/phases. Massive to semi-massive Ni-Cu-PGE and Cr mineralization and xenoliths are often localized within footwall embayments, dilations/jogs in dikes, throats of magma conduits, and the horizontal segments of dike-chonolith and dike-sill complexes, which represent fluid dynamic traps for both ascending and descending sulfides/oxides. If skarns, residues, xenoliths, xenocrysts, xenomelts, and/or xenovolatiles are present, they provide important constraints on ore genesis and they are valuable exploration indicators, but they must be included in elemental and isotopic mass balance calculations.     

Cement–fly ash stabilisation/solidification of contaminated soil: Performance properties and initiation of operating envelopes

This study was aimed at evaluating the mechanical and pH-dependent leaching performance of a mixed contaminated soil treated with a mixture of Portland cement (CEMI) and pulverised fuel ash (PFA). It also sought to develop operating envelopes, which define the range(s) of operating variables that result in acceptable performance. A real site soil with low contaminant concentrations, spiked with 3000 mg/kg each of Cd, Cu, Pb, Ni and Zn, and 10,000 mg/kg of diesel, was treated with one part CEMI and four parts PFA (CEMI:PFA = 1:4) using different binder and water contents. The performance was assessed over time using unconfined compressive strength (UCS), hydraulic conductivity, acid neutralisation capacity (ANC) and pH-dependent leachability of contaminants. With binder dosages ranging from 5% to 20% and water contents ranging from 14% to 21% dry weight, the 28-day UCS was up to 500 kPa and hydraulic conductivity was around 10⁻⁸ m/s. With leachant pH extremes of 7.2 and 0.85, leachability of the contaminants was in the range: 0.02–3500 mg/kg for Cd, 0.35–1550 mg/kg for Cu, 0.03–92 mg/kg for Pb, 0.01–3300 mg/kg for Ni, 0.02–4010 mg/kg for Zn, and 7–4884 mg/kg for total petroleum hydrocarbons (TPHs), over time. Design charts were produced from the results of the study, which show the water and/or binder proportions that could be used to achieve relevant performance criteria. The charts would be useful for the scale-up and design of stabilisation/solidification (S/S) treatment of similar soil types impacted with the same types of contaminants.     

Mineralogical study of secondary mineral phases from weathered MSWI bottom ash: implications for the modelling and trapping of heavy metals

A mineralogical study of 3 samples of municipal solid waste incineration bottom ash collected from different storage sites and with storage times varying from 3 weeks to 2 years, has enabled identification of the main secondary mineral species formed during weathering. The frequencies of the secondary phases were determined and a diagram is proposed for the relative distribution of the newly formed mineral phases: calcite ≫ Fe oxides quartz ⩾ sulphates and/or ettringite (depending on the amount of reactive Al present in the bottom ash). This approach, involving careful sampling, sample preparation and the combined use of various analytical techniques, also showed the high frequency of Al hydroxides and amorphous phases and helped to identify more than 30 sulphates s.l. (sulphates, chromates, vanadates, etc.). Most of the secondary minerals (carbonates and sulphates s.l.) have broad metal trapping capacities for heavy element uptake (Pb, Zn, Cd, As, V, Cr, etc.) due to their crystal-chemistry characteristics. Ca-oxalates were also identified. Mineralogical data from the study provide new input for thermochemical models. The relative stability of metal uptake and the extent of associated neogenesis occurring during bottom-ash decomposition is discussed. Sulphate minerals (and certain heavy metal oxides (zincite)), which are extremely sensitive to environmental conditions, can trap metals only temporarily, as opposed to Fe oxyhydroxides (As, etc.) and carbonates (Pb, Zn, Cd), which are more stable under atmospheric conditions and constitute more sustainable trapping media with higher liquid/solid (L/S) ratios. Finally, a composite predictive diagram is proposed for the mineralogical evolution of bottom ash that accounts for variations in L/S ratios.