Angela Laurora

Heavy metals in sediments from canals for water supplying and drainage: mobilization and control strategies.

One of the most critical aspects of the maintenance of canals for water supplying and drainage is the managing of deposited sediments, which must be periodically removed. Deposited sediments, if containing anthropogenic pollutants with a concentration exceeding specific law limits, must be stored as industrial wastes, thus raising additional economic and logistic problems to deal with. Our research considers polluted sediments from an area close to the south side of Po river, in order to characterize heavy metals associated with different mineral species, thus defining effective treatments for their inertization, and suggesting a possible process for their recycle. Our results demonstrate that the composition of these sediments is suitable for the production of tiles and bricks. Several tests were thus performed to optimize sample treatment and other process parameters, finally giving very encouraging results. Releasing tests on fired products reveal that all the heavy metals are well retained.

Crystal chemistry of trioctahedral micas in alkaline and subalkaline volcanic rocks: A case study from Mt. Sassetto (Tolfa district, Latium, central Italy)

Abstract This work provides a crystal-chemical description of trioctahedral micas from volcanic rocks (lavas, tuffs, ignimbrites, and xenoliths) outcropping at Mt. Sassetto (Tolfa district, Tuscan Province, central Italy). Mica crystals vary in composition from ferroan phlogopite to magnesian annite. Heterovalent octahedral substitutions are mainly related to Al3+, Ti4+, and, only in a few samples, to Fe3+. The two main mechanisms regulating Ti inlet into the mica structure are the Ti-oxy [VITi4+VI(Mg,Fe)2+-1(OH)--2O2-2] and Ti-vacancy [VITi4+VI □VI(Mg,Fe)2+-2] substitutions. In these micas, Ti content is the predominant crystal-chemical parameter and significantly affects octahedral and interlayer topology as well. Micas with the highest Ti contents deviate from the expected fractional crystallization trend in the Ti vs. Mg/(Mg + Fetot) diagram, possibly as a consequence of a variation in intensive parameters (T, P, fH₂, fO₂, fH₂O) during crystallization in the magmatic chamber. In micas with significant Fe3+ contents, the layer charge balance is accomplished by the following mechanisms: VIFe2+-3VIFe23+VI□, VIFe2+-1VIFe3+(OH)--1O2-, and VIFe2+-1VIFe3+IVSi-14+IVAl3+. These micas show mean electron counts greater for the octahedral M2 site than for M1, and unit-cell parameters signifcantly smaller than usual for other micas. Atmospheric weathering is unlikely to produce the observed Fe oxidation. The Fe3+-vacancy and Fe-oxy substitutions could represent secondary, re-equilibration effects related to post-eruptive water-rock hydrothermal processes (acid-sulfate alteration).

Weathering of phlogopite to beidellite in a karstic environment

The extent of natural weathering of phlogopite crystals in a karstic environment and the composition of its weathering products have been examined through a multi-method investigation carried out on a volcanoclastic deposit discovered in the Grotta del Cervo cave, Pietrasecca, central Italy. Phlogopite crystals are a mixture of 1M and 2M1 polytypes and show mixed-layering with a low amount (1-4%) of smectite in the glass groundmass. Phlogopite crystals vary in composition from phlogopite to ferroan phlogopite. Their average structural formula is \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[(\mathrm{K}_{0.92}\mathrm{Na}_{0.03}\mathrm{Ba}_{0.03}\mathrm{Ca}_{0.02})(\mathrm{Mg}_{2.05}\mathrm{Al}_{0.01}\mathrm{Fe}_{0.19}^{2{+}}\mathrm{Fe}_{0.40}^{3{+}}\mathrm{Mn}_{0.01}\mathrm{Ti}_{0.15}{\square}_{0.19})(\mathrm{Si}_{2.63}\mathrm{Al}_{1.37})\mathrm{O}_{10.16}(\mathrm{OH}_{1.57}\mathrm{F}_{0.27}).\] \end{document} Micromorphological, X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), scanning electron microscopy (SEM), and microprobe analyses (EMPA) showed that the mineralogical evolution of phlogopite crystals is consistent with in-situ pseudomorphic weathering of mica to Al-rich dioctahedral (rather than Mg-rich) clay minerals (beidellite-like) via phlogopite-smectite mixed-layer phases. The main mechanism of transformation is a layer-by-layer modification in which water composition, enriched in Si and Al from glass dissolution, is a major control. Mg loss, Ca and Na exchange for K, enrichment in Si and Al are the main processes required for beidellitization of phlogopite. Glass alteration produced sequentially smectite, chabazite, phillipsite and analcime, as leaching progressed and the interstitial fluids became increasingly alkaline. The type of zeolite found in the several samples (in the chabazite, phillipsite, analcime series) indicates that the alteration extent increases from wall to the ceiling and to the floor of the cave.

Ammonium-exchanged zeolitite preparation for agricultural uses: from laboratory tests to large-scale application in ZeoLIFE project prototype

Water nitrate pollution is one of the biggest environmental issues in all those Countries whose economy is largely based on agriculture. Limiting the nitrogen compound input in the soil-water-air system requires the development of innovative and sustainable farming practices, allowing the reduction of fertilizer amounts but assuring good yields. This study describes the optimization of the uptake of swine manure-derived ammonium by zeolitite, as one of the first result of ZeoLIFE project (“Water pollution reduction and water saving using a natural zeolitite cycle”, LIFE+10 ENV/IT/000321). Natural Italian chabasite-bearing zeolitite has been mixed with swine manure at different zeolitite/manure ratios and operative conditions, in a series of laboratory batch tests. The effective NH 4 + -uptake has been measured with different methods, in order to validate the best criteria to reproduce the cation exchange reaction at large scale in a prototype, specifically conceived and built for the industrial production of NH 4 + -charged zeolitite. Experimental results indicate that the best conditions for maximum ammonium uptake are matched using a zeolitite/manure ratio of 25 g/L, a stirring time of 45 minutes and a resting time of 12 hours. These experimental conditions, when operatively applied at the prototype, always led to a good absorption of ammonium, although appreciably less than that obtained in laboratory tests. The obtained material has been spread into an agricultural field, where an increase of the yield has been obtained notwithstanding a significant reduction of the chemical fertilization.

Determination of Hg binding forms in contaminated soils and sediments: state of the art and a case study approaching abandoned mercury mines from Mt. Amiata (Siena, Italy)

This paper, after an introduction about the state of the art in the methods for the evaluation of Hg chemical speciation, focuses on Hg polluted soils and sediments from Siele mining area (Piancastagnaio, Siena, Italy). In particular, the mineralogical composition was evaluated via X-ray powder diffraction, total Hg was determined via inductively coupled plasma optical emis- sion spectroscopy on acid digested samples, and Hg binding forms were investigated both via sequential selective extraction and pyrolytic extraction. Solutions obtained via sequential selective extraction were checked for Hg content using inductively coupled plasma optical emission spectroscopy, whereas to carry out pyrolytic extraction a thermogravimetric analyser coupled with an evolved gas mass spectrometer was used. To our knowledge, this last method was never used for this purpose on natural samples. Experimental results enhance that: i) Hg detection via thermal analyses can qualitatively distinguish among different Hg com- pounds. ii) The temperature of Hg thermal release is affected by both the sample matrix and the Hg bond type. iii) Thermal analyses fail in the attempt of a quantitative determination of the evolved species; this goal is better achieved via the selective chemical leach- ing. iv) Most of the Hg is related to HgS-like bonds, thus pointing to the presence of very stable Hg compounds. v) Only in some samples we found also organo-complexed Hg-like compounds and, in a limited amount, hydrosoluble Hg and/or Hg species soluble in weakly acid environment. vi) No correlation between sampling point and both total Hg and/or Hg speciation was observed.

Trioctahedral Fe-rich micas: Relationships between magnetic behavior and crystal chemistry

Abstract Six Fe-bearing mica samples with different Fe ordering, Fe2+/(Fe2++Fe3+) ratio, octahedral, and tetrahedral composition were studied. Four micas belong to the phlogopite-annite join (space group C2/m), two are Mg-rich annite and two are Fe-rich phlogopite, one is a tetra-ferriphlogopite (space group C2/m) and one is Li-rich siderophyllite (space group C2). Thus these samples had a different environment around the Fe cations and layer symmetry. These micas were characterized by chemical analyses, single-crystal X‑ray diffraction, X‑ray absorption spectroscopy, and magnetic measurements. In samples with Fe mostly in octahedral coordination, dominant magnetic interactions among Fe atoms are ferromagnetic, which reach a maximum at higher Fe2+/(Fe2++Fe3+) ratios. Samples with higher Fe2+/(Fe2++Fe3+) ratio are also characterized by higher values of the Curie-Weiss θ constant. Where Fe2+/(Fe2++Fe3+) ratios decrease, θ values also decrease. The Fe3+-rich phlogopite shows predominant Fe3+ in tetrahedral coordination and shows anti-ferromagnetic interactions with a negative value of the Curie-Weiss θ constant (i.e., θ = -25 K). Fe ordering in octahedral trans- and in one of the two cis-sites accounts for a greater θ value in Li-rich siderophyllite when compared to other samples showing similar octahedral Fe content. Our data suggest that Fe3+ cations and other non-ferromagnetic cations hinder long range magnetic ordering. This observation may produce for the different role of octahedral Fe magnetic interactions that can in principle develop along long Fe-rich octahedral chains, when compared to tetrahedral-octahedral interactions that are confined within the layer by the non-ferromagnetic cations of the interlayer. Spin glass behavior is indicated by the dependency of the temperature to produce maxima in the susceptibility curve. These maxima are related to the frequency of the applied AC magnetic field.

Layer charge and heavy metals structures in hydrated 2 : 1 silicates: state of the art and new advances on cadmium

Abstract This study will discuss how layer charge can affect chemical speciation and topology of heavy metals adsorbed to 2 : 1 layer silicates, by providing: i) an overview of literature data; ii) experimental data on Cd complexes adsorbed by 2 : 1 layer silicates with different layer charge (montmorillonite and vermiculite); iii) a comparison between our results and literature data. This study will also be supported by several different experimental techniques such as chemical and thermal analyses, X-ray powder diffraction and X-ray absorption spectroscopy. Based on our data Cd atoms were found to complex water molecules in both clay minerals and to show four-fold coordination in montmorillonite (Cd–O distances of 2.24 Å) and six-fold coordination in vermiculite (Cd–O distances of 2.16 and 2.28 Å). Furthermore our models clearly suggest that Cd mainly bonds to interlayer water, without neglecting the more limited, but still significant, Cd multinuclear surface complexes at the octahedral broken edges. Both clay minerals show H2O/Cd ratio, as evidenced by thermal analyses, drastically higher than expected from X-ray adsorption spectroscopy data, thus implying that most of the water molecules are only loosely coordinated to interlayer cations.