Angel Irabien

Environmental assessment of polycyclic aromatic hydrocarbons (PAHs) in surface sediments of the Santander Bay, Northern Spain.

Samples of intertidal surface sediments (0-2 cm) were collected in 17 stations of the Santander Bay, Cantabric Sea, Northern Spain. The concentrations of polycyclic aromatic hydrocarbons (PAHs), 16, were analysed by HPLC and MS detection. Surface sediments show a good linear correlation among the parameters of the experimental organic matter evaluation, where total carbon (TC) and loss on ignition (LOI) are approximately 2.5 and 5 times total organic carbon (TOC). A wide range of TOC from 0.08% to 4.1%, and a broad distribution of the sum of sigma16PAHs, from 0.02 to 344.6 microg/g d.w., which can be correlated by an exponential equation to the TOC, has been identified. A qualitative relationship may be established between the industrial input along the rivers and the concentration of sigma6PAHs in the sediments of the estuaries: Boo estuary (8404-4631 microg/g OC), Solia-San Salvador estuaries (305-113 microg/g OC) and Cubas estuary (31-32 microg/g OC). This work shows a dramatic change in the spatial distribution in the concentration of PAHs of intertidal surface sediments. The left edge of the Bay has the main traffic around the city and the major source of PAHs is from combustion processes and estuarine inputs, leading to medium values of PAHs in the sediments; the right edge of the Bay has much lesser anthropogenic activities leading to lower values of PAHs in sediments. The distribution of individual PAHs in sediments varies widely depending on their structure and molecular weight; the 4-6 ring aromatics predominate in polluted sediments due to their higher persistence. The isomer ratio does not allow any clear identification of the PAHs origin. Environmental evaluation according to Dutch guidelines and consensus sediment quality guidelines based on ecotoxicological data leads to the same conclusion, sediments in the Santander Bay show a very different environmental quality depending on the spatial position from heavily polluted/medium effects to non-polluted/below threshold effects. These results indicate that local sources of PAHs, especially estuary discharges, lead to very different qualities of sediments in coastal zones, where traffic and industrial activities take place.

Towards the electrochemical conversion of carbon dioxide into methanol

Various strategies have been proposed to date in order to mitigate the concentration of CO2 in the atmosphere, such as the separation, storage, and utilization of this gas. Among the available technologies, the electrochemical valorisation of CO2 appears to be an innovative technology, in which electrical energy is supplied to establish a potential between two electrodes, allowing CO2 to be transformed into value-added chemicals under mild conditions. It provides a method to recycle CO2 (in a carbon neutral cycle) and, at the same time, a way to chemically store the excess of renewable energy from intermittent sources, thus reducing our dependence on fossil fuels. Among the useful products that can be obtained, methanol is particularly interesting as a platform chemical, and it has gained renewed and growing attention in the research community. Accomplishments to date in the electroreduction of CO2 to methanol have been encouraging, although substantial advances are still needed for it to become a profitable technology able to shift society to renewable energy sources. This review presents a unified discussion of the significant work that has been published in the field of electrocatalytic reduction of CO2 to methanol. It emphasizes the aspects related to process design at different levels: cathode materials, reaction media, design of electrochemical cells, as well as working conditions. It then extends the discussion to the important conclusions from different electrocatalytic routes, and recommendations for future directions to develop a catalytic system that will convert CO2 to methanol at high process efficiencies.

Influence of lead, zinc, iron (III) and chromium (III) oxides on the setting time and strength development of Portland cement

Abstract A fractional factorial design (24−1) of experiments was carried out to study the influence of metal oxides on cement properties: unconfined compressive strength (UCS), setting time (ST), bulk density (BD) and noncombined water (NCW). Four metal oxides, usually contained in inorganic wastes from thermal processes, were studied: ZnO, Cr2O3, PbO, and Fe2O3. The amount of these metal oxides in the formulations was selected according to the composition of inorganic wastes from thermal processes: 0–30% dry wt. for Fe2O3, 0–15% dry wt. for ZnO, and 0–2.5% dry wt. for PbO and Cr2O3. The analysis of the experimental results shows that ZnO retards strongly the ST with respect to that of the cement; it also decreases the UCS of the final product at short ages, but its effect decreases with the sample age. Fe2O3 does not affect the ST and UCS at short sample ages; however, at long sample ages, it decreases the UCS of the product.

Design of ionic liquids: an ecotoxicity (Vibrio fischeri) discrimination approach

Ionic liquids have attracted a lot of attention as potential replacements for conventional volatile organic solvents, although they may pose environmental risks to aquatic ecosystems that have to be assessed. There is strong interest in developing mathematical models to estimate the ecotoxicity of ionic liquids, minimising the experimental investigations and the consequent consumption of time and resources. This paper presents a new approach for estimating the ecotoxicity of ILs, based on the standardised assay with the bacterium Vibrio fischeri, by means of the application of Partial Least Squares-Discriminant Analysis (PLS-DA). The PLS-DA model developed makes it possible to discriminate ionic liquids, formed by combinations of 30 anions and 64 cations, on the basis of their expected toxicity with respect to conventional solvents that they may replace. The successful results obtained in the validation of the model reveal that this approach can be useful as a screening tool to easily aid, from the early stages of the process, the design of aquatic environmentally friendly ionic liquids. This approach may also be useful for the further development of predictive models based on other aquatic organisms, for which more data are expected to be available in the near future.

Extraction of Cr(VI) with aliquat 336 in hollow fiber contactors: mass transfer analysis and modeling

In this work the mass transfer analysis and modeling of the hollow fiber non-dispersive liquid—liquid extraction of Cr(VI) with Aliquat 336 is reported. Experimental results corresponding to different values of the initial concentration of Cr(VI) in the aqueous phase in the range 50 g/m3 ⩽ C0 ⩽ 500 g/m3 showed three different diffusional regimes depending on both the initial concentration of Cr(VI) and the linear velocities of the aqueous phase: (i) kinetic control of the mass transport in the aqueous phase, (ii) kinetic control of the mass transport through the membrane fiber wall and (iii) an intermediate region where the control is shared between the aqueous and the membrane phases. The integration of the mass conservation equation with a nonlinear equilibrium condition at the fiber wall agrees satisfactorily with the results of experiments performed at different initial concentrations of Cr(VI) and different values of the linear velocity of the aqueous phase in the range C0 ⩾ 50 g/m3 and 2.95 × 10−3 m/s ⩽ v ⩽ 1.18 × 10−2 m/s. An optimization of the parameters D, solute diffusivity in the aqueous phase, and Keq, equilibrium constant of the extraction chemical reaction, with all the experimental results, using as criterion the minimum weighted standard deviation, gave as a result the value of the parameter D = 2.3 × 10−9 m2/s and values of Keq dependent upon the initial concentration of Cr(VI) in the feed solution. The mass transfer model and parameters reported in this work are useful for the design and optimization of the nondispersive extraction of Cr(VI) in a hollow fiber module.

Magnetic ionic liquids: synthesis, properties and applications

Magnetic ionic liquids are room temperature ionic liquids, which have paramagnetic properties by themselves without the need of adding magnetic particles. These paramagnetic properties are induced by the anion, the cation or both. Most common paramagnetic ionic liquids are those that contain transition metal or lanthanide complexes in their anion structure. These tuneable fluids present unique physicochemical properties, resulting in responsive materials to an external magnetic field. The reported studies on the synthesis and applications of magnetic ionic liquids have increased in the recent years. Therefore, this review attempts to highlight the achievements and current status concerning the synthesis, properties and main applications of magnetic ionic liquids, providing insights into this research frontier.

Membrane mass transport coefficient for the recovery of Cr(VI) in hollow fiber extraction and back-extraction modules

Abstract This work has been focused to the determination of the membrane mass transport coefficient in the simultaneous non-dispersive extraction and back-extraction of Cr(VI). Following the methodology previously reported by the authors for the kinetic modelling of hollow fiber extraction and back-extraction processes, considering the assumption that the overall mass transport resistance is dominated by the resistance in the organic membrane, when Aliquat 336 is used as carrier, and after the description of the interfacial chemical equilibrium in the extraction process (non-linear model, K eq = 0.35) and in the back-extraction process (linear model, H r = 3.6), it has been possible to describe successfully the experimental results obtaining the optimum value for the membrane mass transport coefficient, K M = 2.2 × 10 −8 m/s, which allows the design and optimization of the recovery of Cr(VI).

Ionic liquids in the electrochemical valorisation of CO2

The development of electrochemical processes for using captured CO2 in the production of valuable compounds appears as an attractive alternative to recycle CO2 and, at the same time, to store electricity from intermittent renewable sources. Among the different innovative attempts that are being investigated to improve these processes, the application of ionic liquids (ILs) has received growing attention in recent years. This paper presents a unified discussion of the significant work that involves the utilisation of ILs for the valorisation of CO2 by means of electrochemical routes. We discuss studies in which CO2 is used as one of the reactants to electrosynthesise value-added products, among which dimethyl carbonate has been the focus of particular attention in the literature. Approaches based on the electrochemical reduction of CO2 to convert it into products without the use of other carbon-based reactants are also reviewed, highlighting the remarkable improvements that the use of ILs has allowed in the CO2 electroreduction to CO. The review emphasises on different aspects related to process design, including the nature of IL anions and cations that have been used, the working conditions, the electrocatalytic materials, the electrode configurations, or the design of electrochemical cells, as well as discussing the most relevant observations, results and figures of merit that the participation of ILs has allowed to achieve in these processes. Several conclusions are finally proposed to highlight crucial challenges and recommendations for future research in this area.

Kinetics of flue gas desulphurization at low temperatures: fly ash/calcium (31) sorbent behaviour

Abstract The reaction rate equation for the flue gas desulphurization at low temperatures using fly ash/calcium sorbents has been determined in a fixed-bed reactor in the range of SO 2 concentration, 2000 ≤ C ≤ 5500 (ppmv), temperature 52 ≤ T ≤ 67°C and relative humidity 0.40 ≤ RH ≤ 0.90, working at conditions prevailing in the exhaust gases of coal-fired plants. The kinetic models discrimination procedure leads to a reaction rate expression based on the SO 2 adsorption on a nonideal surface as the rate-controlling step, in terms of an exponential influence of the calcium conversion in the reaction rate. The influence of the SO 2 concentration in the gas phase has been described by a partial reaction order equal to 1. Concerning the temperature influence, the kinetic constant does not depend on this variable, which can be explained by a sorption equilibrium step previous to the reaction, the observed kinetic constant being an apparent parameter. The relative humidity has been concluded to be the most relevant variable, with a significant influence on the kinetic behaviour of the sorbent, which can be described by the fitting of the parameter which accounts for the nonideal solid surface to the relative humidity. From the obtained conclusions, an appropriate kinetic model based on three parameters has been proposed for the kinetic description of the desulphurization reaction under study, i.e. when a sorbent based on a fly ash-Ca(OH) 2 mixture 3 1 is used in the process.

Overview of the PCDD/Fs degradation potential and formation risk in the application of advanced oxidation processes (AOPs) to wastewater treatment

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are a family of unintentionally produced persistent organic pollutants (POPs) that have received considerable public and scientific attention due to the toxicity of some of their congeners, more specifically those with chlorine substitution in the 2,3,7,8 positions. The environmental management and control of PCDD/Fs is addressed at a global level through the Stockholm Convention that establishes that POPs should be destroyed or irreversibly transformed in order to reduce or eliminate their release to the environment. Several technologies, including advanced oxidation processes (AOPs) such as photolysis, photocatalysis and Fenton oxidation, have been considered as effective methods for destroying PCDD/Fs in polluted waters. Nevertheless, during the remediation of wastewaters it is critical that the treatment technologies applied do not lead to the formation of by-products that are themselves POPs, especially if PCDD/Fs precursors or chlorine are present in the reaction medium. Despite the high effectiveness of AOPs in the oxidation of major contaminants, scarce references deal with the monitoring of PCDD/Fs in the course of the oxidation process, revealing that a detailed assessment of non-combustion technologies with respect to PCDD/Fs formation is still lacking. This study reports a review of the state of the art related to the potential remediation and/or formation of PCDD/Fs as a result of the application of AOPs for the treatment of polluted waters, warning on the correct selection of the operating conditions.