A fast one-pot synthesize of crystalline anglesite by hydrothermal synthesis for environmental assessment on pure phase.

Anglesite (PbSO4) is a lead sulfate that belongs to the barite group and is naturally ubiquitous in the environment. This work describes a simple way to synthesize crystalline lead sulfate by using a straightforward hydrothermal procedure. Typically, Pb(NO3)2 and Fe2(SO4)3 precursors were mixed and heated at 94 °C for 24 h. The synthesized samples have been characterized by coupling X-Ray diffraction (XRD) to spectroscopic methods (FTIR and micro-Raman), X-ray absorption spectroscopy (XAS), and electronic microscopy (SEM and TEM). In fine, the results about this new well crystalline synthetic anglesite confirm the efficiency and the importance of this cheap protocol and the synthesized phases obtained. Moreover, the environmental stability and bioaccessibility of anglesite have been done to evaluate environmental stability of anglesite under various physico-chemical conditions and sanitary risks. Finally, the paper allows to obtain precise data on a pure phase in order to be able to more easily evaluate and understand the role of anglesite in as-polluted sites and soils.

Investigating the relationship between speciation and oral/lung bioaccessibility of a highly contaminated tailing: contribution in health risk assessment.

Anthropogenic activities such as industrial, mining, or agricultural are the main sources of environmental contamination. One of the most problematic contaminations concerns metals and metalloids from mining activities. This contamination raises the question of the environmental risk induced and the spread of this pollution (geographical and trophic) and the associated health risk. The integrated, multi-analytical approach of this study conducted on the mining district of Cartagena-La Union (Murcia, Spain) as part of the Interreg SUDOE European project "Soil Take Care" aims to (i) precisely define the speciation of contaminants of interest (Zn, Pb, Cd, As), (ii) predict the environmental risk related to storage stability, and (iii) establish the link between the speciation of the bearing phases and the associated health risk. To do this, a representative zone in the Cartagena-La Union mining district close to the populations was chosen. A physic-chemical characterization of the samples was performed (pH, electrical conductivity, CEC, and total metal(loid) concentrations), and the mineralogy was determined using XRD and SEM-EDS. The environmental risk was highlighted from sequential BCR-type extractions and EN-12457 leaching tests. Finally, the health risk was defined using the PSF inhalation bioaccessibility test and UBM bioaccessibility protocol (based on an operational chemical methodology mimicking soil ingestion and its residence in the gastrointestinal tract of the human body). These analyses revealed 2 groups of samples with distinct behavior. The first group of samples presents relatively stable bearing phases, mainly found in the residual fraction (As and Pb), presenting only a low health risk (very low bioaccessible). The second group consists of Cd and/or Zn-bearing phases, mainly labile (resulting from dissolution/precipitation phenomena), while gastric bioaccessibility reaches more than 85%. Note that Pb, Cd, and Zn have the potential to cause non-carcinogenic risks to children and As and Pb present a carcinogenic risk for children and adults even if only the bioaccessible fraction is considered. It has therefore been shown that the meteoric alteration of the tailing induces a change in speciation leads to an increase in environmental and health risks. These results are essential because they highlight the need for an integrated approach in order to clearly highlight the presence of risks but also that this approach will allow a better understanding of the potential rehabilitation path of this site.

Environmental stability and oral bioaccessibility of synthetic Pb-bearing phases to better evaluate soil health risks.

A large amount of contaminated sites is shown around the world which may induce a health risk due to the presence of contaminants such as metal (loïd)s bearing phases. Health risk assessment is based on contaminant bioaccessibility. However, it is needed to understand every contaminant behavior in physiological matrix to be a realistic way to assess and interpret these sanitary risks. Due to the complexity of contaminated soil matrix, the use of synthetic minerals seems to be the better tool to understand their behavior in physiological matrix. Then, this study aims to highlight the environmental stability and the behavior during bioaccessibility ingestion (UBM) of selected synthetic lead-bearing phases. For this purpose, three Pb phases (galena, beudantite, and anglesite) commonly found in contaminated environments (particularly mining sites) were synthesized and characterized (structurally and morphologically). The sequential BCR extractions have shown that most of the lead is in a stable and non-mobilizable form (up to 93%). The lead present in these phases represents very few risks of migrating into the environment during physicochemical condition changes. The results of the bioaccessibility revealed a relatively high stability of the pure bearing phases in the physiological matrix. Lead is stable for 97.0% to 99.2% during the gastric phase and 97.0% to 99.9% during the gastro-intestinal phase. Moreover, the synthetic mixtures of galena/beudantite and anglesite/beudantite have been realized considering the proportions commonly found in the mining contexts. This has shown a similar behavior compared to pure phases except in the case of the anglesite mixture inducing a clear cocktail effect (drastic increase of Pb amount from gastro-intestinal phases). At last, this study is a first and interesting step to assess the behavior of these bearing phases in heterogeneous and complex medium such as soil.

Key parameters influencing metallic element mobility associated with sediments in a daily-managed reservoir.

In a hydroelectric reservoir, sediments are subject to remobilization events, water-level fluctuations and physicochemical changes. Depending on their associated metallic content, surficial oxic to suboxic sediments could constitute a major source of metals. To identify the key parameters that control metallic elements in terms of their mobility and sensitivity to reservoir management, sediments were subject to resuspension and drying/wetting cycle experiments over a wide range of pH values, solid/liquid ratios (S/L) and redox (Eh) conditions. During these tests, special attention was also paid to the influence of pretreatments on samples, i.e., drying, aeration and the leachate composition (ultrapure water vs. natural water); on the preservation of the sediment characteristics; and especially on metallic element release. The results of this study show that the pH, S/L ratio and Eh parameters are key variables in metal solubilization; the pH influences metal mobility primarily through sorption-desorption phenomena as well as the dissolution of metallic-bearing phases, the S/L ratio modifies the sorption-desorption equilibria, and the Eh primarily affects the reducible sensitive phases and associated metallic elements through dissolution-precipitation processes. Under environmental conditions, evolution of these parameters can lead to a >20% solubilization of the most mobile elements, i.e., As and Cd. These results are influenced by the sample pretreatment and experimental conditions. In fact, even if the solubilization patterns show no significant differences between dry and wet sediment depending on the physicochemical conditions, the magnitude of their release is significantly affected. Drying pretreatment induces changes in metal speciation, notably altering the distribution of the most weakly bound elements; there is almost half the amount of metallic elements associated with the exchangeable fraction in dry compared to wet sediments. The solubilization percentages were higher in the ultrapure phase than in reservoir water primarily due to the low pH, which influenced the sorption equilibria.

Phosphate removal from aqueous solution using ZVI/sand bed reactor: Behavior and mechanism.

This research reports on phosphate removal from aqueous solution using ZVI/sand packed columns. The influence of column preconditioning, consisting of ZVI pre-oxidation before feeding the columns with phosphate solution, revealed that a column aged for 1 day was more efficient than un-conditioned column, 5-days and 10-days preconditioned columns. The distribution of phosphate trapped inside the columns was evaluated by measuring phosphate concentration in the solids at different levels (P1, P2 and P3) along the depth of the columns. The distribution of phosphate inside the columns was determined for a time period up to 46 days, corresponding to column saturation. Results showed heterogeneous trapping along the column before saturation and homogeneous distribution upon saturation. The maximum cumulative trapped phosphate after column dismantling was determined before saturation (after 17 days running) at 130, 68 and 31 mgP/gFe at the inlet-P1, P1-P2 and P2-P3 layers, respectively, whereas the homogeneous distribution of phosphate upon saturation was determined at 132 mgP/gFe throughout the column. Solid supports were characterized using SEM, XRD and XPS. Lepidocrocite and maghemite/magnetite were the only iron oxidation products identified at the different layers inside the columns. XPS results confirmed the sorption of phosphate at the surface of ZVI and its oxidation products and highlighted the formation of an iron phosphate complex.

Impact of sediments resuspension on metal solubilization and water quality during recurrent reservoir sluicing management.

In dam contexts, sluicing operations can be performed to reestablish sediments continuity, as proposed by the EU Water Framework Directive, as well as to preserve the reservoirs' water storage capacity. Such management permits the rapid release of high quantities of reservoir sediments through the opening of dam bottom valves. This work aims to study the impact of such operation on the evolution of environmental physicochemical conditions notably changes in dissolved metallic elements concentrations (Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn) through field and laboratory investigations. Results were interpreted in terms of concentrations and fluxes, and compared with data collected on an annual basis regarding both suspended matter and metallic elements. The release of high quantities of sediments (4,500tons dry weight in 24h), with concentrations representing up to 300 times the inter-annual mean suspended sediments discharge, significantly modified water parameters, notably solid/liquid (S/L) ratio, pH and redox conditions. Despite the fact that they are mainly trapped in stable phases, a clear increase of the solubilized metals content was measured, representing up to 60 times the maximum values of current exploitation. This solubilization is related to desorption phenomena from sediments through changes in chemical equilibriums as highlighted by laboratory characterizations and experiments. These chemical modifications are mainly attributed to S/L ratio variations. Indeed, the low S/L ratios (≤1.3g·L(-1)) measured in situ are typically the ones for which metals solubilization is the highest, as shown by laboratory experiments. Additional thermodynamic modeling highlighted that the decrease in pH measured during the operation favors the release of the free forms of metallic elements (Al and Cu), and decreases the OM complexation influence. These changes, either in term of physical conditions or speciation, increasing metals long term bioavailability notably during redeposition phase, may have adverse effects on aquatic biota.

Influence of dams on sediment continuity: A study case of a natural metallic contamination.

Sediments play an important role on the quality of aquatic ecosystems, notably in the reservoir areas where they can either be a sink or a source of contaminants, depending on the management and hydrological conditions. The physicochemical properties of 25 surface sediments samples of a reservoir catchment (Vaussaire, Cantal, France) were studied. Results show a strong influence of dam presence, notably on the grain size and organic matter (OM) contents. The concentrations of trace metals and metalloids (As, Cd, Cr, Cu, Ni, Pb and Zn) were also measured and compared with worldwide reservoir concentrations and international sediment quality guideline levels in order to assess the intensity of the metallic contamination. Cr and Ni are the trace elements presenting the significantly highest values at the catchment scale. Enrichment Factors (EF), calculated using both local and national backgrounds, show that metals have mainly a natural origin, explaining especially the Cr and Ni values, linked with the composition of parental rocks. Unexpectedly, all the observed metal concentrations are lower in the reservoir than upstream and downstream, which might be related to the high fresh OM inputs in the reservoir, diluting the global metallic contamination. Multivariate statistical analyses, carried out in order to identify the relationship between the studied metals and sediment characteristics, tend to support this hypothesis, confirming the unusually low influence of such poorly-degraded OM on trace element accumulation in the reservoir.

Evidence for the incorporation of lead into barite from waste rock pile materials.

Because Pb is one of the most toxic elements and is found as a major contaminant in mining environments, this study aims to identify the distribution of this element in host phases issued from the alteration of mine wastes. The sampling location was a former mine near Oakland, California (USA). This mine was once a source of sulfide minerals from which sulfuric acid was made. The material discussed in this paper was collected in iron hardpans that were formed within the waste rock pile resulting from the excavation work. In most contaminated environments (soils, mine waste), secondary metal-bearing phases arising from alteration processes are usually fine-grained (from 10 microm to less than 1 microm) and highly heterogeneous, requiring the use of micron-scale techniques. We performed micro-Raman spectroscopy, microscanning X-ray diffraction (SXRD), and microextended X-ray near edge spectroscopy (XANES) to determine the relationships between Pb and a Ba/Fe-rich host phase. Micro-Raman spectroscopy suggests that Pb is preferentially incorporated into barite rather than goethite. Results from micro-Raman experiments show the high sensitivity of this analytical tool to the incorporation of Pb into barite by being especially sensitive to the variations of the S-O bond and showing the characteristic bands due to the contribution of Pb. This association is confirmed and is well-illustrated by micro-SXRD mineral species maps showing the correlation between Pb and barite. Microfocused XANES indicates that Pb is present as Pb2+, agreeing with the in situ physicochemical parameters.