Roberto Braga

The rare earth elements in municipal solid waste incinerators ash and promising tools for their prospecting

Bottom and fly ashes from Municipal Solid Waste Incinerators (MSWI) are hazardous products that present concern for their safe management. An attractive option to reduce their impact both on the environment and the financial commitment is turning MSWI ashes into secondary raw materials. In this study we present the REE content and distribution of bottom and fly ashes from MSWI after a highly effective digestion method and samples analysis by ICP-MS. The chondrite-normalised REE patterns of MSWI bottom and fly ash are comparable with that of crustal averages, suggesting a main geogenic source. Deviations from typical crustal pattern (e.g., Eu, Tb) disclose a contribution of likely anthropogenic provenance. The correlation with major elements indicates possible sources for REE and facilitates a preliminary resource assessment. Moreover, magnetic susceptibility measurements can be a useful prospecting method in urban ores made of MSWI ashes. The relationship between REE and some influencing parameters (e.g., Pricing Influence Factor) emphasises the importance of MSWI ash as alternative source of REE and the need of further efforts for REE recovery and purification from low concentrations but high flows waste.

H2O content of deep-seated orogenic continental crust: the Ulten Zone, Italian Alps

To estimate the amount of H2O stored at lower crustal levels after burial, we considered the pile of migmatitic paragneisses in the Variscan Ulten Zone as a case study area. We constructed a pseudosection in the system K2O-Na2O-CaO-FeO-MnO-MgO-Al2O3-SiO2-TiO2-H2O for an average paragneiss, a relevant prograde PT path (8.5 kbar, 600°C; 11.5 kbar, 750°C; 14.0 kbar, 1000°C) and H2O contents between 0 and 10 wt.%. Based on an assemblage of garnet + biotite + white mica + kyanite + 20–30 vol.% former melt (now represented mainly by leucosomes composed of plagioclase + quartz), a bulk H2O content of 3.2 ± 1.1 wt.% was estimated for a peak temperature ranging between 770 and 800°C. Before melting, somewhat less than 1.8 wt.% H2O was stored in minerals. Thus, a considerable amount of H2O must have either resided in pore spaces along grain boundaries or, much less likely, infiltrated the paragneisses from below. Evidently, significant quantities of H2O as a free phase may be stored in buried sialic crust, resulting in considerable melting of deep-seated rocks during continent–continent collision.

The potential impact of municipal solid waste incinerators ashes on the anthropogenic osmium budget.

Osmium release from Municipal Solid Waste Incinerators (MSWI), even if acknowledged to occur at least over the last fifteen years, remains overlooked in the majority of recent studies. We present the osmium concentration and (187)Os/(188)Os isotopic measurements of different kinds of bottom and fly ash samples from MSWI plants and reference materials of incinerator fly ash (BCR176 and BCR176R). The analysis of the unknown ash samples shows a relatively wide range of (187)Os/(188)Os ratios (0.24-0.70) and Os concentrations (from 0.026 ng/g to 1.65 ng/g). Osmium concentrations and isotopic signatures differ from those of other known Os sources, either natural or manmade, suggesting a mixture of both contributions in the MSWI feedstock material. Furthermore, the comparison between the BCR176 and the renewed BCR176R indicates a decrease in Os concentration of one order of magnitude over the years (from 1 to 0.1 ng/g) due to improved recycling efficiency of Os-bearing waste. The estimated annual amount of Os from a typical incinerator (using average Os values and MSWI mass balance) is 13.4 g/a. The osmium potentially released from MSWI smokestacks is predicted to be from 16 to 38 ng Os/m(2)/a, considering a medium size country having 50 MSWI facilities; therefore much higher than the naturally transported osmium from continental dust in the atmosphere (about 1 pg Os/m(2)/a). MSWI systems are considered one of the best options for municipal solid waste management in industrialised countries, but their contribution to the Os budget can be significant.

Origin of a mica megacryst in an alkaline dyke from the Veneto Volcanic Province, Italy

We report the first finding of a mica megacryst included in an alkaline basic dyke belonging to the Tertiary Veneto Volcanic Province (northern Italy). The megacryst is surrounded by a corona with a mineral assemblage consisting of fine-grained mica flakes + Ti-magnetite. The megacryst is a biotite with a mg# of 0.75, containing 1.35 wt. % TiO 2 , 1041 ppm Ba and 3.8 wt. % H 2 O. The mica flakes have a mg# of 0.79 and contain 4.33 wt. % TiO 2 ,21 968 ppm Ba and 3.0 wt. % H 2 O. Both mica types show high concentrations of LILE and Nb (461–135 ppm). REE contents are typically below the analytical detection limit. Fractional crystallization modelling shows that the mica megacryst crystallized at depths in the mantle consistent with the spinel-facies stability field. The unusually high Nb N /Sr N and Sr N /Zr N The calculated structural formulae based on 24(O+F+Cl) indicate that full occupancy of the tetrahedral site can only be attained by allowing the entry of a small fraction of Fe 3+ or Ti 4+ . In addition, Ti-oxy (likely coupled with Ba-oxy) substitution occurs to provide charge balance with the excess negative charge at the O4 position. The occurrence of such exchange mechanisms can enhance the thermal stability of the mica flakes that most likely crystallized at shallower depths under high temperature and high f (O 2 ) conditions.

Petrographic, mineral and pressure-temperature constraints on phyllites from the Variscan basement at Punta Bianca, Northern Apennines, Italy

We present a petrological study of phyllites from the Variscan basement at Punta Bianca (Northern Apennines). According to the literature the studied rocks are believed to be the result of Alpine and Variscan metamorphism of pre-Carboniferous pelites, which consist of Fe-chlorite, potassic white mica, quartz, minor paragonite, and accessory hematite, rutile, monazite, zircon, xenotime, and florencite. Microstructural observations indicate a main S2 foliation that had overprinted an earlier S1 foliation. The mineral assemblage can be related to both S2 and S1.Large flakes of relatively Mg-rich potassic white-mica along the two foliations are probably detrital grains that preserved their composition. The calculation of isochemical phase diagrams, their contouring by various mineral chemical parameters and the deformation microstructures of quartz indicate intermediate pressure-low temperature conditions (5-7 kbar and 300-400 °C). The anhedral habit and the very low Pb contents (< 50 ppm) in monazite point to dissolution of this mineral probably during Tertiary times.