Pietro Melis

Sorption processes and XRD analysis of a natural zeolite exchanged with Pb2+, Cd2+ and Zn2+ cations

In this study the Pb(2+), Cd(2+) and Zn(2+) adsorption capacity of a natural zeolite was evaluated in batch tests at a constant pH of 5.5 by polluting this mineral with solutions containing increasing concentrations of the three cations to obtain adsorption isotherms. In addition X-ray powder diffraction (XRD) was used to investigate the changes of zeolite structure caused by the exchange with cations of different ionic radius. The zeolite adsorption capacity for the three cations was Zn>Pb>Cd. Moreover a sequential extraction procedure [H(2)O, 0.05 M Ca(NO(3))(2) and 0.02 M EDTA] was applied to zeolite samples used in the adsorption experiments to determine the chemical form of the cations bound to the sorbent. Using this approach it was shown that low concentrations of Pb(2+), Cd(2+) and Zn(2+) were present as water-soluble and exchangeable fractions (<25% of the Me adsorbed), while EDTA extracted most of the adsorbed cations from the zeolite (>27% of the Me adsorbed). The XRD pattern of zeolite, analysed according to the Rietveld method, showed that the main mineralogical phase involved in the adsorption process was clinoptilolite. Besides structure information showed that the incorporation of Pb(2+), Cd(2+) and Zn(2+), into the zeolite frameworks changed slightly but appreciably the lattice parameters. XRD analysis also showed the occurrence of some isomorphic substitution phenomena where the Al(3+) ions of the clinoptilolite framework were replaced by exchanged Pb(2+) cations in the course of the ion exchange reaction. This mechanism was instead less evident in the patterns of the samples doped with Cd(2+) and Zn(2+) cations.

XRD, FTIR, AND THERMAL ANALYSIS OF BAUXITE ORE-PROCESSING WASTE (RED MUD) EXCHANGED WITH HEAVY METALS

The present work shows the results of X-ray diffraction (XRD), Fourier transform infrared (FTIR), and thermal analysis of untreated (RMnt) and acid-treated red mud (RMa), a bauxite ore-processing waste, exchanged with Pb2+, Cd2+, and Zn2+ cations. These studies were performed in order to investigate the changes in the sorbent structure caused by the exchange with metals of different ionic radii.The XRD pattern of RMnt, analyzed according to the Rietveld method, showed a mixture of eight different phases. However, just three phases made up 78 wt.% of the RMnt: cancrinite (33 wt.%), hematite (29 wt.%), and sodalite (16 wt.%). X-ray diffraction patterns of RMnt exchanged with Pb2+ and Cd2+ cations revealed two additional phases, namely hydrocerussite [Pb3(CO3)2(OH)2 (10 wt.%))] and octavite [CdCO3 (8 wt.%)].These two phases probably originated from the carbonate precipitation processes which were due to the decarbonation of cancrinite. Hydrocerussite and octavite were not found in the case of acid-treated red mud samples.In the FTIR spectra, the introduction of cations caused a distinct shift to higher wavenumbers in the peak at ∼1100 cm−1, which is attributed to the asymmetric stretch of Si-O-Al. This effect may be associated with the Pb2+, Cd2+, and Zn2+ adsorbed by the red muds which caused a deformation of the initial structure.Thermal analysis data of the red mud samples were obtained by thermogravimetric/differential thermogravimetric analysis, and these methods were employed to evaluate the desorption behavior of water and to clarify the thermal stability of the chemical phases of the different red mud samples. The loss of metal-bound water in the red mud samples was found to depend on the size of non-framework cations and water loss consistently followed the order: Zn2+>Cd2+>Pb2+.

Study of sorption processes and FT-IR analysis of arsenate sorbed onto red muds (a bauxite ore processing waste)

In this study we evaluated the arsenate adsorption capacity of red muds (RM), wastes tailing from the alumina production, at different pH values (4, 7, and 10). RM samples were artificially enriched in batch tests with solutions containing increasing concentrations of As(V). The pH of the solution significantly affected the adsorption, which increased with the decrease of pH. Moreover a sequential extraction procedure [H(2)O; (NH(4))(2)SO(4); NH(4)H(2)PO(4); NH(4)(+)-oxalate; NH(4)(+)-oxalate+ascorbic acid] was applied to RM samples exchanged with arsenate. Using this approach it was shown that low concentrations of arsenate sorbed in RM were present as water soluble and exchangeable fractions, while NH(4)(+)-oxalate and NH(4)(+)-oxalate+ascorbic acid extracted most of the adsorbed arsenate from RM at different pH values. Besides, FT-IR spectroscopy was used to better understand the nature of RM surface configuration after As(V) sorption. In the FT-IR spectra the presence of As(V) species was highlighted by a well resolved band at 865 cm(-1). The intensity and broadness of this band increased at the decreasing of pH. This band could be related to nu(As-O) vibration of an inner-sphere Al-O-As complex and/or due to As-O bonds of the adsorbed As(V) species on Fe oxides of RM samples.

Growth and Yield Characteristics and Heavy Metal Content on Tomatoes Grown in Different Growing Media

Abstract This work studied the effects that different growing media (compost and beached Posidonia oceanica) have on the growth, yield, and heavy metals concentrations of tomatoes (Lycopersicon esculentum Mill.) hydroponically grown in a greenhouse. A commercial substrate exclusively composed of pumice was used as a control sample. The choice of beached Posidonia oceanica as a growing media and as a matrix in order to obtain compost is due to the extraordinary accumulation of deposits of the seaweed Posidonia oceanica on the beaches of Sardinia and in general on the beaches of countries of the Mediterranean. Leafy deposits of Posidonia oceanica are treated as refuse and disposed off in waste dumps. In fact, the Italian law prevents the agricultural use of beached P. oceanica plants considering them as heavy metal accumulators and then, a cause of heavy metals contamination in the environment. Nevertheless, it is important to pay great attention to physical and chemical characteristics of the growing media used in order to avoid soil pollution and the danger of introducing harmful substances in the food chain. Growth and yield parameters were calculated during the different stages of plant growth. The total concentrations of some heavy metals [lead (Pb), cadmium (Cd), zinc (Zn), chromium (Cr), copper (Cu)] were determined in growing media, tomato fruits, and in leaves. No statistically significant differences were found between the growth and yields of plants grown in different growing media. The heavy metal concentrations of compost were higher than those of beached Posidonia oceanica or the control sample. However, most metals strongly interacted with the organic matter of compost, limiting the vegetal absorption. Metals concentration in fruits and leaves was essentially the same in all the plants. According to these observations the use of compost and beached Posidonia oceanica as growing media did not cause a metals accumulation in fruits and plants of tomatoes grown in hydroponics.

INFLUENCE OF CLIMATE ON THE IRON OXIDE MINERALOGY OF TERRA ROSSA

Terra rossa samples were taken from the B horizons of soil profiles and from cracks within limestone in Italy. The average annual temperature (AAT) of the sites ranged from 8.4 to 20.3°C and the average annual precipitation (AAP) from 511 to 3113 mm, with either a 5–6 month water deficit or a large water surplus. Goethite and hematite were identified in all the samples. Under a moist (> 1700 mm AAP) and cool (13°C AAT) climate, a xeric, hematitic pedoenvironment was preserved by the well-litified carbonate rock. Hematite occurred in trace amounts, even with an AAT of 8.4°C and an AAP of 3300 mm, confirming the specific role of the hard limestone on the pedoclimate of terra rossa. The lowest mean crystallite dimension of goethite and hematite was found in the samples from the wettest sites, and in these samples hematite was nearly free of Al substitution. Rubification in terra rossa appeared to be due to the specific pedoenvironment. The hematite cannot be considered a relict phase formed under another climate. Mite and kaolinite were the main clay minerals in samples from xeric sites whereas more weathered clays, such as Al-interlayered vermiculite, occurred in cool, moist sites. We postulate that the processes of rubification and vermiculitization could have taken place at the same time.

Methods for remediation of metal‐contaminated soils: Preliminary results

Abstract Contamination of soils by heavy metals is one of the environmental problems that the scientific community faces today. Such soils are difficult to treat because the heavy metals cannot be destroyed. Moreover, they are usually bonded with other contaminants, in particular organic ones. The presence of these organic pollutants can make the removal of metals from soils substantially more complicated. One way of coping with the problem which has been studied in recent years is the use of fixing agents which make the heavy metals unavailable to the plants, or prevent their leaching towards the groundwater. Inorganic fixing agents in particular have been tested and found to be suitable, but some organic ones can also be used, at least as temporary fixing materials. This paper gives preliminary results on remediation techniques using compost and Trichoderma viride Pers.: Fr. as heavy metal fixing agents.