Antonio Lettino

Effects of ultrasonic treatment on zeolite synthesized from coal fly ash.

The synthesis of zeolites from three samples of fly ash was carried out through a low-temperature (25-60°C) hydrothermal process with a NaOH pre-fusion treatment preceded by sonication. The results were compared with those of conventional hydrothermal syntheses. XRD and SEM investigations demonstrate that the application of ultrasonic treatment facilitates the formation of zeolites at a lower-temperature (25°C) than syntheses not preceded by sonication. No significant difference in type, temperature of crystallization, or amount of zeolites synthesized was noted between the three different samples of fly ash, implying that the chemical composition of fly ash had little influence on the zeolite product within the compositional range of these fly ash precursors. Although there appears to be a correlation between the SiO(2)/Al(2)O(3) ratio of the fly ash and the temperature of zeolite formation by conventional synthesis, no correlation was apparent when ultrasonic pre-treatment was used at low-temperatures.

Zeolite Synthesised from Fused Coal Fly Ash at Low Temperature Using Seawater for Crystallization

A sample of coal fly ash from an Italian thermoelectric power plant was used in order to synthesize zeolite by hydrothermal activation after a pre-treatment fusion with NaOH. The experiments involved were performed at different temperatures of crystallization, ranging from 35 up to 60uC, with seawater and distilled water, separately, during hydrothermal process. A comparison between the results obtained from the use of the different kinds of water showed that at low temperature (35–40 uC) the synthesis yield of zeolite X is higher using seawater as crystallizing agent than using distilled water. This implies a possible application for seawater in the solution to the problem of high water volume involved in the zeolite synthesis on a pilot plant

Provenance of inorganic aerosol using single-particle analysis: a case study.

A total of 137 samples of airborne particulates with an aerodynamic equivalent diameter of 10 μm or less (PM10) were collected from April 2007 to July 2008 in four different areas (Potenza, Lavello, Viggiano, Matera) of the Basilicata region in southern Italy. A total of approximately 140,000 particles were analysed using a Field Emission Scanning Electron Microscope (FESEM) equipped with an Energy-Dispersive X-ray Spectrometer (EDS). To formulate a hypothesis on the origin of particles, the dataset was numerically reduced using mineralogical criteria. Eight particle groups were established (Silicate, Silica, Carbonate, Sea Salt, Polymineral, Industrial, Sulphur, and Biogenic Particles) among which Silicate, Sulphur and Industrial Particles were found to be the most abundant. Among the Silicate Particles, the alumosilicates were the most commonly occurring particles (mineral and fly ash particles), and the presence of a small metallurgical factory located in the industrial area of Potenza significantly affects the presence of metal particles (mainly Fe-Zn spinels). The anthropogenic pressure exerted by different types of Sulphur-rich (e.g., Na-Ca-Sulphates, S-only) Particles in the other areas is most likely linked to industrial combustion processes, i.e., waste incinerator oil and oil extraction. Significant differences were found in the particulate concentrations and the compositions of samples collected in different seasons as well as during the night and daytime periods. Crustal Particles were the most abundant in spring-summer, and both Sulphur-rich Particles and Industrial Particles increased in autumn-winter. The proportion of latter category of particles increases in the samples collected during the night periods due to weather conditions (atmospheric stability, thermal inversion, etc.). Sulphur-rich Particles were observed to be more abundant during the daytime due to anthropogenic processes (combustion) and solar radiation. In summary, mineralogical and geochemical approaches are fundamental to delineate the human and natural contributions from automated microscopic analyses.

Degradation of citrate promotes copper co-precipitation within aluminium-(hydr)oxides in calcareous soils

In this study, we provide experimental evidences that in calcareous soils microbial degradation/decomposition of citrate can promote Al-(hydr)oxide precipitation concurrently decreasing copper (Cu) solubility by a coprecipitation process. Citrate is an organic acid anion commonly released by roots to increase nutrient availability or to limit Al toxicity. However, under specific environmental conditions (i.e. high microbial activity of Al-citrate-degrading bacteria, alkaline pH), this organic acid may become ineffective in mobilizing Cu for the plant acquisition process. To demonstrate this, a calcareous soil and an artificial soil system have been treated with citrate solutions; then, changes in Al and Cu solubility and the formation of Cu-containing Al-(hydr)oxides were monitored. Both in experiments with the artificial soil and in those where the soil was inoculated with microbial strains, the formation of Cu-Al coprecipitates not only occurred but was also concurrent with the decrease of Cu and Al solubility. The role of bacteria in metal-citrate complex degradation has been assessed, and the 16S rDNA of bacteria related with these processes has been sequenced for genus identification. Bacteria belonging to Pseudomonas, Sphingomonas, Bradyrhizobium and Sphingopixis have been identified as possible candidates to degrade Al- and Cu-citrate complexes thus triggering the metal precipitation phenomena.

Influence of Synthesis Method on LTA Time-Dependent Stability

Time-stability of LTA zeolite formed by hydrothermal method with or without the action of ultrasonic irradiation was investigated by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The results show that 6 months after the synthesis by hydrothermal process with continuous sonication, LTA evolves into a more stable sodalite, whereas no differences are detected 12 months after LTA synthesis by conventional pre-fused hydrothermal process. These data confirm that using the two approaches, different mechanisms control both zeolite crystallization and time-stability of the newly-formed mineral at solid state. The results are particularly important in the light of the synthetic zeolite application.