Arsenic polluted waters: Application of geochemical modelling as a tool to understand the release and fate of the pollutant in crystalline aquifers.

Arsenic (As) is one of the most investigated elements worldwide due to its negative impact on the natural system. Its geochemical behavior depends on several geogenic processes, which can cause hazardous enrichment into natural waters, even in remote areas, far from anthropogenic sources. In this work the arsenic pollution issue has been addressed by studying water-rock interaction processes and applying reaction path modelling as a tool to understand the rock-to-water release of As and the fate of this natural pollutant in crystalline aquifers. In-depth geochemical characterization of several water samples discharging from crystalline aquifers was performed. The obtained data were used to fix the boundary conditions and validate the modelling outcomes. The performed modelling allowed to reconstruct the water-rock interaction processes which occur (i) in shallow and relatively shallow crystalline aquifers in which no As anomalies were observed and (ii) in As-rich areas, coupling reaction path modelling of granite dissolution with adsorption of dissolved As onto precipitating crystalline and amorphous Fe(III)-oxyhydroxides given the widespread presence of these phases in the studied environment. The results of the geochemical modelling are in agreement with the analytical data and reproduce them satisfactorily. The performed geochemical modelling is of high environmental significance because it is a flexible and powerful tool that correctly defines the water-rock interaction processes occurring in crystalline aquifers, providing valuable data to improve the knowledge on As behavior, not only in the study area, but also in similar geological settings worldwide. Therefore, the present research has broad future perspectives in the environmental field.

Use of reaction path modelling to investigate the evolution of water chemistry in shallow to deep crystalline aquifers with a special focus on fluoride.

Crystalline aquifers are layered systems in which the hydrogeological path of waters extends from highly weathered, shallow and porous rocks to poorly weathered, deep and fissured rocks. This varying hydrogeological setting influences the water chemistry in different ways. The paper aims to reconstruct the water-rock interaction process in these various environments starting from a solid reactant represented by an average granite rock and several waters from the shallow aquifer. Afterwards, the water-rock interaction processes occurring in the deep environment are reconstructed, varying the geochemical conditions (primary reactants, secondary mineral phases allowed to precipitate, fO2 and fCO2), with a special focus on fluoride (F-). The evolution from the F-poor, Ca-HCO3 facies to the F-rich, Na-HCO3 water type of high pH was simulated using reaction path modelling. The obtained results show that the theoretical evolution trends well reproduce both shallow and deep water samples providing detailed information on the behavior of fluoride and other relevant constituents (i.e., Na, K, Ca, Mg, SiO2). The performed model represents a flexible and powerful tool for environmental research, applicable in other areas hosting F-rich groundwater.

A multivariate non-parametric approach for estimating probability of exceeding the local natural background level of arsenic in the aquifers of Calabria region (Southern Italy).

The concept of natural background level (NBL) aims at distinguishing the natural and anthropogenic contributions to concentrations of specific contaminants, as groundwater management and protection tools. This is usually defined as a unique value at a regional scale, even when the hydrogeological and geochemical features of a certain territory are far from homogeneous. The concentration of target contaminants is affected by multiple hydrogeochemical processes. This is the case of arsenic in the Calabria region, where concentrations are definitely variable in groundwater. To overcome the limitation of a traditional approach and to include the intrinsic hydrogeological and geochemical heterogeneity into the definition of the natural contribution to As content in groundwater, an integrated probabilistic approach to the NBL assessment combining aquifer-based preselection criteria and multivariate non-parametric geostatistics was proposed. In detail, different NBL values were selected, based on the aquifer type and/or hydrogeochemical features. Then, these aquifer-based NBL values of arsenic were used in the Probability Kriging method to map the probability of exceedance and to provide contamination risk management tools. This multivariate geostatistical approach that takes advantage of the physico-chemical variables used in the aquifer-based NBL values definition allowed mapping the probability of exceedance of As in a physically-based way. The hydrogeochemical diversity of the study area and all the processes affecting As concentrations in the aquifers have been considered too. As a result, the obtained map was characterized by a short-range and long-range variability due to local hydrogeochemical anomalies and water-rock interaction and/or atmospheric precipitation. By this approach, the NBL exceedance probability maps proved to be less "noisy", because the local hydrogeochemical conditions were filtered, and more capable of pointing out anthropogenic inputs or very anomalous natural contributions, which need to be investigated more in detail and properly managed.

Geochemical modeling of chromium release in natural waters and treatment by RO/NF membrane processes.

In this work, a geochemical approach was used as strong-scientific tool for pre-selection of suitable remediation systems to treat Cr-contaminated groundwaters. The geochemical characterization allowed to select Nanofiltration (NF) and Reverse Osmosis (RO) as suitable remediation processes, whereas through a new geochemical modeling, the evolution of water chemistry during the water-rock interaction was also studied. The new reaction path modelling was performed re-evaluating the role of Fe as main oxidant in the system and the analytic concentrations of relevant solutes, including Cr(VI), were reproduced. The spring with the highest Cr(VI) content was treated to lower its concentration below the threshold values. A laboratory-scale set-up was used to carry out both NF and RO experiments. The experiments were conducted on different commercial membranes varying the operating pressures. The results showed high Cr(VI) rejections (around 95%) for all tested membranes, leading to Cr(VI) concentrations below the threshold limits. The high flux, obtained already at lower operating pressures, combined with high selectivity towards Cr(VI) makes NF a favorable remediation option.

Pressure-driven and thermally-driven membrane operations for the treatment of arsenic-contaminated waters: A comparison.

The presence of arsenic in water beyond the admitted limits is becoming an important concern for many Countries. Methods usually employed for the arsenic removal from water are based on coagulation followed by filtration, ion-exchange, adsorption. Drawbacks like the use of chemicals and the production of sludges (in case of coagulation) have, however, to be mentioned. Membrane operations, based on the features of membrane materials involved in the separation, do not need chemicals and are easy to scale-up, due to their modularity. In this contribution, the potential of membrane operations for the treatment of arsenic-polluted water is presented and discussed. In particular, two classes of membrane operations are illustrated and compared, the pressure-driven, like Nanofiltration (NF) and Reverse Osmosis (RO) and the thermally-driven ones, like Membrane Distillation (MD).

Combined emulsion and phase inversion techniques for the preparation of catalytic PVDF microcapsules.

In this work, polyvinilydene fluoride (PVDF) microcapsules were prepared by using combined emulsion and phase inversion techniques. With this method, microcapsules with different diameters and porosities have been obtained by just controlling the diameter of the membrane used during the preparation. Using a PVDF solution containing the oxidation catalyst ammonium molybdate (20 wt %), catalytic polymeric microcapsules with diameters ranging from 600 to 1,200 microm have been obtained. Characterization of catalytic microcapsules by means of SEM, BSE, and EDX analyses showed a uniform ammonium molybdate dispersion in the polymeric matrix. Catalytic microcapsules have been tested in the oxidation of aromatic primary alcohols to corresponding aldehydes. In the range 600-1,200 microm, the microcapsule diameter influences the formation of oxidation products: in particular, microcapsule diameters >900 microm slightly diminish the formation of aldehyde due to a beginning diffusion limitation. An interesting structure-reactivity behavior, induced by the interaction between the polymeric membrane and the substituted aromatic alcohol, has been observed.

Treatment of dye solutions by vacuum membrane distillation.

In this work, the vacuum membrane distillation (VMD) process has been applied to treat water containing different types of dyes. The influence of operating parameters, as feed temperature, feed flow rate, feed concentration, on the permeate flux and on rejection has been investigated. In all experimental tests, a complete rejection has been achieved and pure water has been recovered at the permeate side. Furthermore, experiments with water as feed have been carried out before and after the tests with dyes, in order to analyze the effect of fouling on the performance of the VMD. The water vapor fluxes immediately after the tests with dyes were higher than the values registered before the tests, probably due to an interaction with the polymeric membrane material which promotes a swelling of the membrane when in contact with the dye solutions. However, initial fluxes are recovered after prolonged cleaning with only water.

Novel composite poly(4-vinylpyridine)/polypropylene membranes with recognition properties for (S)-naproxen.

In the last few years, molecular imprinting technology has entered in different fields of chemistry, biochemistry, biotechnology and medicine. The technique allows us to introduce the molecular memory of the substrate to be recognized in a polymeric material during its preparation. In the present paper, molecularly imprinted enantioselective polymer membranes were prepared by photo-copolymerization of commercial polypropylene membranes with the functional monomer 4-vinylpyridine. The (S)-naproxen was used as a template molecule. Enantioselectivity studies in a dead-end filtration system showed the recognition properties of the imprinted membranes, which exhibited a selective transport of the (S)-enantiomer.

Composite polymeric beads containing N,N,N',N'-tetraoctyldiglycolamide for actinide ion uptake from nitric acid feeds: Batch uptake, kinetic modelling and column studies.

Polyethersulphone (PES) based composite polymeric beads (CPB) containing TODGA (N,N,N',N'-tetraoctyldiglycolamide) as the extractant were prepared by conventional phase inversion technique and were tested for the uptake of actinide ions such as Am(3+), UO2(2+), Pu(4+), Np(4+) and fission product ions such as Eu(3+) and Sr(2+). The CPBs containing 2.5-10wt.% TODGA were characterized by various physical methods and their porosity, size, surface morphology, surface area and the degradation profile by thermogravimetry were analyzed. The batch uptake studies involved kinetics of metal ion sorption, uptake as a function of nitric acid concentration, kinetic modelling and adsorption isotherms and most of the studies involved the Am(3+) ions. The batch saturation sorption capacities for Eu(3+) loading at 3M HNO3 were determined to be 6.6±0.02, 9.1±0.02 and 22.3±0.04mgg(-1) of CRBs with 2.5wt.%, 5wt.% and 10wt.% TODGA, respectively. The sorption isotherm analysis with Langmuir, D-R and Freundlisch isotherms indicated chemisorption monolayer mechanism. Chromatographic studies indicated breakthrough of Eu(3+) (using a solution containing Eu carrier) after about 0.75 bed volume (3.5-4mL). Elution of the loaded Eu was carried out using 0.01M EDTA as the eluent.

Bromide ion exchange with a Keggin polyoxometalate on functionalized polymeric membranes: a theoretical and experimental study.

Noncovalent interactions between the polyoxometalate [PMo12O40](3-) and acryloyloxyundecyltrimethyl ammonium bromide surfactant, used during membrane preparation, were evaluated in the frame of density functional theory. The electronic solvation energy of [PMo12O40](3) and bromide anions was also evaluated, at the same level of theory, in order to predict a probable exchange on the polymeric surface between these anions at the water/polymer interface. Energy balances were theoretically assessed, showing that the bromide cannot be exchanged with this nanosized polyanion in large extent. In order to validate this theoretical conclusion, ad hoc and accurate measurements were carried out by using homemade polymeric membranes and by dipping them in an ca. 0.4 mM solution of Na3[PMo12O40] for 4 days. The Br(-) concentration, released in a polyoxometalate solution, was followed at different times during the test period by gravimetrical analysis. The agreement between the theoretical prediction and experimental data was remarkable, as the quantum calculations correctly accounted for the short-range intermolecular interactions involved in this phenomenon. Bearing in mind that the achieved conclusion is based on an ab initio quantum approach, the findings of this study can be considered rather general and then exploitable for other similar systems.

Polymeric beads containing Cyanex 923 for actinide uptake from nitric acid medium: Studies with uranium and plutonium.

Conventional phase inversion technique has been successfully applied for the preparation of the solid phase extractant (SPE), Cyanex 923 loaded polymer beads. Two types of polymer beads prepared by blending Polyetherether ketone with card (PEEKWC)/DMF with 5% Cyanex 923 (SPE-I, av bead size: 900µm) and 10% Cyanex 923(SPE-II, av. bead size: 1100µm) were evaluated for the uptake of actinide ions. The polymer beads were characterized by various physical methods such as thermal analysis, surface morphology analysis by SEM, EDAX techniques, etc. The polymer beads were used for the experiments involving the uptake of both U(VI) and Pu(IV) at tracer scale and U(VI) at milli molar concentrations from nitric acid feeds. The actinide ion uptake studies involved kinetics of metal ion sorption, adsorption isotherms, and column studies. The metal sorption capacities for U(VI) at 3M HNO3 were found to be 38.8±1.9mg and 54.5±1.7mg per g of SPE-I and SPE-II, respectively. The sorption isotherm analysis with Langmuir, D-R and Freundlisch isotherms indicated chemisorption monolayer mechanism. Column studies were also carried out using 4.5mL bed volume columns containing about 0.4 and 0.45g of SPE-I and SPE-II, respectively. The breakthrough profiles were obtained for U(VI) and the elution profiles were obtained using 1M Na2CO3 as the eluent.

Chitosan hollow fibers as effective biosorbent toward dye: preparation and modeling.

Chitosan hollow fibers were produced via a dry-wet spinning technique with good mechanical properties. The prepared membranes were tested for removal of reactive blue 19 as a model anionic dye. Response surface methodology was employed for the modeling of adsorption capacity of fibers. A second-order empirical relationship between adsorption capacity and independent variables (initial pH, contact time, initial dye concentration and amount of fibers) was obtained. Pareto analysis established that initial pH was the most effective parameter. The adsorption capacity value of reactive blue 19 on chitosan hollow fibers was 454.5 mg g(-1). The adsorption was well described by pseudo-second-order kinetics and Freundlich equation.

Performance of PDMS membranes in pervaporation: effect of silicalite fillers and comparison with SBS membranes.

Laboratory-made silicalite filled PDMS membranes were tested by means of concentration and temperature influence on the membrane performance in removal of ethanol from ethanol/water mixtures. This allowed studying the applicability of solution-diffusion model in the transport mechanism description. Experiments were performed by varying the ethanol concentration in the feed and temperature. Two types of fillers were incorporated into the PDMS network: commercial zeolite silicalite (CBV 3002) and laboratory-made colloidal silicalite-1. Obtained results were then compared with data gathered for unfilled PDMS membranes to examine the effect of fillers incorporation. Moreover, the comparison with novel block co-polymer based porous and dense SBS membranes was done. It was found that the solution-diffusion model was a good representation of ethanol transport through both filled and unfilled PDMS membranes, whereas the water flux did not obey this model due to the swelling effects. Incorporation of the fillers increased membrane stability and improved the selectivity. Performance of the SBS membranes characterized by a dense structure was found to be similar to the performance of filled PDMS membranes.