Renato Baciocchi

Accelerated carbonation of different size fractions of bottom ash from RDF incineration

This paper investigates the effects of accelerated carbonation on the characteristics of bottom ash from refuse derived fuel (RDF) incineration, in terms of CO(2) uptake, heavy metal leaching and mineralogy of different particle size fractions. Accelerated aqueous carbonation batch experiments were performed to assess the influence of operating parameters (temperature, CO(2) pressure and L/S ratio) on reaction kinetics. Pressure was found to be the most relevant parameter affecting the carbonation yield. This was also found to be largely dependent on the specific BA fraction treated, with CO(2) uptakes ranging from approximately 4% for the coarse fractions to approximately 14% for the finest one. Carbonation affected both the mineralogical characteristics of bottom ash, with the appearance of neo-formation minerals, and the leaching behaviour of the material, which was found to be mainly related to the change upon carbonation in the natural pH of the ash.

The effects of accelerated carbonation on CO2 uptake and metal release from incineration APC residues

This work presents the results of a study on accelerated carbonation of incinerator air pollution control residues, with a particular focus on the modifications in the leaching behaviour of the ash. Aqueous carbonation experiments were carried out using 100% CO(2) at different temperatures, pressures and liquid-to-solid ratios, in order to assess their influence on process kinetics, CO(2) uptake and the leaching behaviour of major and trace elements. The ash showed a particularly high reactivity towards CO(2), owing to the abundance of calcium hydroxides phases, with a maximum CO(2) uptake of approximately 250g/kg. The main effects of carbonation on trace metal leaching involved a significant decrease in mobility for Pb, Zn and Cu at high pH values, a slight change or mobilization for Cr and Sb, and no major effects on the release of As and soluble salts. Geochemical modelling of leachates indicated solubility control by different minerals after carbonation. In particular, in the stability pH range of carbonates, solubility control by a number of metal carbonates was clearly suggested by modelling results. These findings indicate that accelerated carbonation of incinerator ashes has the potential to convert trace contaminants into sparingly soluble carbonate forms, with an overall positive effect on their leaching behaviour.

Hydrogen peroxide lifetime as an indicator of the efficiency of 3-chlorophenol Fenton's and Fenton-like oxidation in soils.

In this work the possibility of using the hydrogen peroxide lifetime as indicator of the oxidation efficiency of Fentons and Fenton-like processes for soil treatment was explored. A reactivity scale, in terms of the oxidizing power in the different tested operating conditions (pH, iron sulfate concentration and stabilizer concentration) was built for each soil as a function of the hydrogen peroxide lifetime. Its validity was then confirmed through 3-chlorophenol Fentons and Fenton-like slurry-phase oxidation experiments. The proposed reactivity scale proved to be effective for comparing the different operating conditions for the same soil, but failed when used to compare the oxidation performances for different soils, since the different adsorptive behavior of the tested soils may have influenced the contaminant removal rate.

Fast determination of phenols in contaminated soils.

An extraction method for the determination of phenols in contaminated soils, based on the application of solid-phase microextraction (SPME) coupled with GC-flame ionization detection analysis, was developed and tested. This method was developed using a natural soil spiked with phenol to a concentration level typical of an acute contamination event that can occur in an industrial site. The effects of the extraction parameters (pH, extraction time and salt concentration) on the extraction efficiency were studied and the method was then applied to determine the pollutant concentration at the beginning and during the biological treatment of a soil, contaminated with phenol and 3-chlorophenol, respectively. The SPME results were validated by comparison with those obtained with an US Environmental Protection Agency certified extraction method. The SPME method was also successfully applied to the determination of the adsorption behavior of 3-chlorophenol on a natural clay soil and was shown to be suitable for different matrices and phenolic compounds. Application of SPME technique results in a sharp reduction of the extraction times with negligible solvent consumption.

Separation of binaphthol enantiomers through achiral chromatography.

Chromatography is a key technique for the analytical, preparative, and production scale separation of enantiomers, particularly in the pharmaceutical and fine chemicals industries. Although it is common belief that this separation can be accomplished only using a chiral stationary phase, it has been recently shown that under certain circumstances a non-racemic mixture of specific chiral compounds can be separated in two fractions which differ in enantiomeric excess (e.e.) also on an achiral stationary phase. In this work we show that in the case of the enantiomers of binaphthol in chloroform achiral chromatography on LiChrospher 100 NH2 furnishes two fractions constituted of the pure enantiomer present in excess and of the racemic mixture, respectively. This is demonstrated by on-line monitoring the concentration of both enantiomers at the outlet of a chromatographic column fed with a non-racemic pulse of the two enantiomers by using a UV detector and a polarimeter in series. Furthermore, we provide experimental evidence of the presence of homo- and hetero-dimers in solution through NMR experiments and develop a consistent physico-chemical model of the solution itself and of the competitive achiral adsorption equilibria. When combined with a standard rate model of the chromatographic column this not only confirms the possibility of achieving 100% e.e. through achiral chromatography, but also allows for a qualitative and quantitative description of all the experimentally observed phenomena. Among these, the effect of the enantiomeric excess and of the overall concentration of the injected pulse on the chromatographic behaviour are worth mentioning.

Effects of thin-film accelerated carbonation on steel slag leaching

This paper discusses the effects of accelerated carbonation on the leaching behaviour of two types of stainless steel slags (electric arc furnace and argon oxygen decarburisation slag). The release of major elements and toxic metals both at the natural pH and at varying pH conditions was addressed. Geochemical modelling of the eluates was used to theoretically describe leaching and derive information about mineralogical changes induced by carbonation. Among the investigated elements, Ca and Si were most appreciably affected by carbonation. A very clear effect of carbonation on leaching was observed for silicate phases; geochemical modelling indicated that the Ca/Si ratio of Ca-controlling minerals shifted from ∼ 1 for the untreated slag to 0.5-0.67 for the carbonated samples, thus showing that the carbonation process left some residual Ca-depleted silicate phases while the extracted Ca precipitated in the form of carbonate minerals. For toxic metals the changes in leaching induced by carbonation appeared to be mainly related to the resulting pH changes, which were as high as ∼ 2 orders of magnitude upon carbonation. Depending on the specific shape of the respective solubility curves, the extent of leaching of toxic metals from the slag was differently affected by carbonation.

Influence of the operating conditions on highly oxidative radicals generation in Fenton's systems.

In this work, an indirect method for estimating the total amount and concentration of oxidative radicals in aqueous and slurry-phase Fentons systems was developed. This method, based on the use of benzoic acid as probe compound, was applied for evaluating the effect of the operating conditions on the radicals amount produced, their production efficiency (i.e. moles of radicals generated per mole H2O2 and their concentration. A Rotatable Central Composite design (RCC) was used to select the operating conditions in order to get a statistically meaningful data set. Hydrogen peroxide and ferrous ion concentrations ranged between 0.2-1mM and 0.2-0.5mM, respectively; humic acid concentration between 0 and 15mg/L, whereas the soil/water weight ratio in slurry-phase systems between 1:10 and 9:10. The probe compound concentration was 9 or 0.1mM in experiments aimed to evaluate the total amount or concentration of oxidative radicals, respectively. The obtained results indicated that the amount of radicals generated in both aqueous and soil slurry Fentons system increased with higher H2O2 concentration and, more specifically, that their production efficiency increased with increasing Fe(II):H2O2 molar ratio. Addition of dissolved organic compounds as humic acid did not notably affect the oxidative radicals amount and concentration. On the contrary, a one order of magnitude reduction in both radicals amount generated and concentration was observed when soil was added to the reaction environment.

Modeling of vapor intrusion from hydrocarbon-contaminated sources accounting for aerobic and anaerobic biodegradation

A one-dimensional steady state vapor intrusion model including both anaerobic and oxygen-limited aerobic biodegradation was developed. The aerobic and anaerobic layer thickness are calculated by stoichiometrically coupling the reactive transport of vapors with oxygen transport and consumption. The model accounts for the different oxygen demand in the subsurface required to sustain the aerobic biodegradation of the compound(s) of concern and for the baseline soil oxygen respiration. In the case of anaerobic reaction under methanogenic conditions, the model accounts for the generation of methane which leads to a further oxygen demand, due to methane oxidation, in the aerobic zone. The model was solved analytically and applied, using representative parameter ranges and values, to identify under which site conditions the attenuation of hydrocarbons migrating into indoor environments is likely to be significant. Simulations were performed assuming a soil contaminated by toluene only, by a BTEX mixture, by Fresh Gasoline and by Weathered Gasoline. The obtained results have shown that for several site conditions oxygen concentration below the building is sufficient to sustain aerobic biodegradation. For these scenarios the aerobic biodegradation is the primary mechanism of attenuation, i.e. anaerobic contribution is negligible and a model accounting just for aerobic biodegradation can be used. On the contrary, in all cases where oxygen is not sufficient to sustain aerobic biodegradation alone (e.g. highly contaminated sources), anaerobic biodegradation can significantly contribute to the overall attenuation depending on the site specific conditions.

Pilot-scale ISCO treatment of a MtBE contaminated site using a Fenton-like process

This paper reports about a pilot-scale feasibility study of In-Situ Chemical Oxidation (ISCO) application based on the use of stabilized hydrogen peroxide catalyzed by naturally occurring iron minerals (Fenton-like process) to a site formerly used for fuel storage and contaminated by MtBE. The stratigraphy of the site consists of a 2-3 meter backfill layer followed by a 3-4 meter low permeability layer, that confines the main aquifer, affected by a widespread MtBE groundwater contamination with concentrations up to 4000 μg/L, also with the presence of petroleum hydrocarbons. The design of the pilot-scale treatment was based on the integration of the results obtained from experimental and numerical modeling accounting for the technological and regulatory constraints existing in the site to be remediated. In particular, lab-scale batch tests allowed the selection of the most suitable operating conditions. Then, this information was implemented in a numerical software that allowed to define the injection and monitoring layout and to predict the propagation of hydrogen peroxide in groundwater. The pilot-scale field results confirmed the effective propagation of hydrogen peroxide in nearly all the target area (around 75 m(2) using 3 injection wells). As far as the MtBE removal is concerned, the ISCO application allowed us to meet the clean-up goals in an area of 60 m(2). Besides, the concentration of TBA, i.e. a potential by-product of MtBE oxidation, was actually reduced after the ISCO treatment. The results of the pilot-scale test suggest that ISCO may be a suitable option for the remediation of the groundwater plume contaminated by MtBE, providing the background data for the design and cost-estimate of the full-scale treatment.

Vapor Intrusion Screening Model for the Evaluation of Risk-Based Vertical Exclusion Distances at Petroleum Contaminated Sites

The key role of biodegradation in attenuating the migration of petroleum hydrocarbon vapors into the indoor environments has been deeply investigated in the last decades. Very recently, empirical screening levels for the separation distance from the source, above which the potential for vapor intrusion can be considered negligible, were defined. In this paper, an analytical solution that allows one to predict risk-based vertical screening distances for hydrocarbons compounds is presented. The proposed solution relies on a 1-D vapor intrusion model that incorporates a piecewise first-order aerobic biodegradation limited by oxygen availability and accounts also for the effect of the building footprint. The model predictions are shown to be consistent with the results obtained using a 3-D numerical model and with the empirical screening criteria defined by U.S.EPA and CRC care. However, the different simulations carried out show that in some specific cases (e.g., large building footprint, high methane concentration, and low attenuation in the capillary fringe), the respect of these empirical screening criteria could be insufficient to guarantee soil-gas concentrations below acceptable risk-based levels.