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Ingestion of soil represents one of the critical exposure pathways in the human health risk assessment (HHRA) framework at sites contaminated by inorganic species, especially for residential scenarios. HHRA is typically carried out through starting from the so-called "total concentration", which is estimated from the fraction of inorganic species extracted from the soil using standardized approaches, i.e., microwave acid extraction. Due to the milder conditions, a smaller portion of the inorganics present in the soil is actually dissolved in the gastro-intestinal tract (bioaccessible fraction), and afterward reaches the bloodstream, exerting an effect on human health (bioavailable fraction). Including bioaccessibility in HHRA could then allow for the achievement of a more realistic assessment than using the total concentration. In this paper, the bioaccessible concentration of different inorganics in soil samples collected from a firing range was estimated by applying two in vitro tests, i.e., the Unified Barge Method (UBM) and the Simple Bioaccessibility Extraction Test (SBET). Moreover, different options for incorporating bioaccessibility in HHRA for the estimation of the cleanup goals were also applied and discussed. Despite the notable differences in terms of reagents and procedure between the two methods, the obtained results were quite close, with the SBET method providing slightly higher values. The role of the soil particle size distribution on the calculation of the cleanup goals accounting for bioaccessibility is also discussed. [ABSTRACT FROM AUTHOR]

An assessment of the energetic requirements of slurry-phase accelerated carbonation for CO2 sequestration using steelmaking slag was conducted. The results of dedicated lab-scale carbonation experiments in which the CO2 sequestration yield of basic oxygen furnace slag was investigated at different operating conditions were used for the energy requirement calculations. The operating variables of the process and the associated values adopted were total gas pressure, temperature, and CO2 concentration in the gas phase. The energy duties of the slurry-phase carbonation layout were calculated for the different unit operations, which included slag milling, mixing, slurry pumping, heating, CO2 compression, solid/liquid separation, and CO2 capture (when required). The estimated energy requirements were found to lie in the range 980−6300 MJ t−1 CO2 sequestered, where the lower end of the range was associated with the use of diluted CO2. In all cases, the use of a concentrated CO2 flow proved largely energetically unfavorable over the use of diluted gas streams, since the energy duty of the required CO2 capture stage by far overcame the benefits associated with improved sequestration yields at increased CO2 concentrations in the gas phase. The calculated energy requirements were also processed to derive a second-order model accounting for the main effects and interactions between the operating variables of the carbonation process. The model developed is meant to predict the expected energy demand of the carbonation process under different operating conditions and to define the optimal combination of these in terms of the energetic profile of the process itself. © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

An assessment of accelerated carbonationprocesses applied to industrialresidues for CO2storage was performed with the aim ofgaining insight on the feasibility of this process at larger scale,identifying also the key factors for its implementation. Specifically,the material and energy requirements of two types of direct carbonationroutes, the slurry phase process and the wet route, were evaluated,and the influence of the properties of the residues (i.e., main mineralogyand particles size) and of the reaction routes and operating conditionsapplied (i.e., temperature, CO2pressure, and liquid-to-solidratio) was analyzed. In addition, the possibility of directly treatingdiluted sources of CO2, thus avoiding the capture step,was assessed for the wet route by performing lab-scale tests withgas mixtures containing 40% or 9% CO2. [ABSTRACT FROM AUTHOR]

Abstract: In this work an innovative carbon dioxide removal method that, differently from the currently employed commercial techniques, allows also to capture and store the separated CO2 is investigated. This process, Alkali absorption with Regeneration (AwR), consists in a first step in which CO2 is separated from the biogas by chemical absorption with an alkali aqueous solution followed by a second step in which the spent absorption solution is regenerated for reuse in the first step and the captured CO2 is stored in a solid and thermodynamically stable form. The latter process is carried out contacting the spent absorption solution, rich in carbonate and bicarbonate ions, with a waste material characterized by a high content of calcium hydroxide and leads to the precipitation of calcium carbonate and to the regeneration of the alkali hydroxide content of the solution. The proposed processes were first investigated by preliminary laboratory and simulation analysis. On the basis of the results of these tests, air pollution control (APC) residues from Waste-to-Energy plants were selected as the material to use for the regeneration step and a pilot-scale regeneration plant was designed, built and installed in a landfill site downstream of the already existing absorption column. In this paper the sizing and design of the regeneration plant and the results of the preliminary AwR pilot- plant tests are reported. This study was carried out within the framework of the UPGAS-LOWCO2 (LIFE08/ENV/IT/000429) Life+ project. [Copyright &y& Elsevier]

Abstract: Mineral carbonation is an ex situ CO2 storage option that could allow to fix large amounts of CO2 in a solid and thermodynamically stable form. Its feasibility has been proven at lab-scale both employing natural minerals or alkaline industrial residues. However the energy requirements of this process can be quite significant depending on the type of material and operating conditions adopted and thus represent a crucial factor for its full scale applicability. The focus of this paper is the assessment of the energy requirements of CO2 storage by accelerated carbonation of alkaline materials applying the direct aqueous route. From the analysis of the main studies on energy penalties associated to the carbonation process large differences were observed on the assumptions made, the selected layout and operating conditions, in particular for alkaline residues. In addition most of the evaluations were carried out considering only experimental tests performed with high liquid to solid ratios (slurry phase route) while specific evaluations for tests with liquid to solid ratios lower than 1 (wet route) were not carried out. The overall aim of this study is to estimate the energy duties required to store the CO2 emissions of a small-medium size power plant (20 MW) by carbonation of different types of residues (steel slags and waste incineration residues) applying either the slurry phase or wet routes. In this paper the layouts of the proposed carbonation processes are presented and discussed. [Copyright &y& Elsevier]

Abstract: An innovative biogas upgrading method that, differs from the currently employed commercial techniques, allows also to capture and store the separated CO2 is investigated. This process, named Alkali absorption with Regeneration (AwR), consists in a first step in which CO2 is separated from the biogas by chemical absorption with an alkali aqueous solution followed by a second step in which the spent absorption solution is regenerated for reuse in the first step of the upgrading process and the captured CO2 is stored in a solid and thermodynamically stable form. The latter process is carried out contacting the spent absorption solution, rich in carbonate and bicarbonate ions, with a waste material – air pollution control (APC) residues from Waste-to-Energy plants – characterized by a high content of calcium hydroxide and leads to the precipitation of calcium carbonate and to the regeneration of the alkali hydroxide content of the solution. The process was tested in a specifically designed pilot plant fed with 20 m3 h−1 (gas at standard conditions of 273 K and 1001 kPa) of landfill gas. Results showed that a high CH4 content in the outlet gas can be obtained using a 3.8 mol L−1 NaOH aqueous solution with a solution/landfill gas ratio of about 9 L m−3 (gas at standard conditions of 273 K and 1001 kPa). The regeneration process proved to be feasible, but its efficiency was limited by several factors to maximum values in the range of 50–60 %, showing to decrease with higher NaOH concentrations in the absorption solution. Absorption tests with regenerated load solutions after appropriate NaOH makeup, did not show appreciable differences with respect to raw solutions. [Copyright &y& Elsevier]