Metals retention after weathering of a sulphide ore body: unexploited gossan versus mine tailings.

Numerous studies have highlighted the fact that the bioavailability of potentially toxic trace elements (PTTE), such as As, Cd, Cr, Cu, Ni, and Pb, is strongly related to the redox state and chemical form. Since dissolved forms of trace elements are the most bioavailable, the issue of greatest concern is to define the conditions under which these elements may be remobilized in solution up to levels higher than those recommended by National agencies as e.g. the Environmental Protection Agency (EPA). In order to understand and then ideally to prevent trace element mobilization, the characterisation of the contaminant sources, i.e. the solid fraction, is crucial

Molecular characterisation of fertilizing materials of residual origin for a better understanding of interactions with pollutants

International audienceThe increasing demands on food and drinking water due to the rising world population induces increasing production of organic waste such as manure and sewage sludge. The main sustainable valorization pathway for these biodegradable waste is land farming despite it potentially contain metal traces elements and organic micro contaminants. The consequence can be a pollution of soils, aquatic resources, crops and finally human food chain. Depending on the characteristics of these organic fertilising material of residual origin as well as the treatment it was submitted to, pollutants can be more or less degraded or bio-available. Indeed, processes such as composting can participate to degrade organic pollutants or modify heavy metals bio availability. In this context a better knowledge of the characteristics of organic fertilising material of residual origin is essential to envisage the interactions between organic fertilizing materials of residual origin and pollutants which are eventually present. The impact of several pre-treatments processes such as drying, hygienisation, stabilisation, digestion or composting was studied. For this purpose, 13 samples including sludge, manure, compost and digestat were characterized at the molecular level using elemental analysis, differential scanning calorimetry and double-shot thermochemolysis. In parallel the same samples were analysed for chemical functions and biochemical content according to the methods described in Lachassagne et al (2015), and for their fertilizing properties. Moreover these properties were put in regards to their ability to desorb copper during landspreading. Composted, and reed bed sludge presented high material (organic and mineral material) content and high protonic exchange capacity in particulate phase of sludge. In limed, filter pressed, digested thickened sludge a large protein, polysaccharide and “humic like” substances content was measured in the soluble phase while the distribution of the corresponding fluorescence intensity in the floc (observation of confocal laser scanning microscopy) was low. Large DOC content observed in soluble phase of limed sludge, centri-dried and anaerobic granular sludge corresponded to high protein contents under the 3D-fluorescence observation. High content of carboxyl and phosphoric functional groups was measured in particulate phase of composted and dewatering sludge while they were present in high percentages in soluble phase of limed, digested, thickened sludge.The low C to N ratios (table 1) demonstrated stable organic matter. This ratio is higher for composted sludge than for digested or dried sludge. In parallel the H to C atomic ratio is lower for composted and digested sludge which is characteristic of humified materials.The characterization of the 13 samples by thermochemolysis at 350°C (first shot) showed the presence of fatty acids, hydroxyacids, diacids and steroids. Iso and anteiso C15 and C17 compounds of bacterial origin, demonstrated thanks to the branched to linear ratio a higher bacterial contribution for the digested sludge whereas the composted sludge is more stable. This is confirmed by the hydroxyacids / fatty acid ratio (H/A) or diacids/monoacids (D/A). The second shot at 600oC produced cellulose, lignin and proteins moieties and a series akenes/alkanes. The toluene/styrene ratio higher than 1 outlined the natural origin of organic compounds. Double-shot thermochemolysis is a technique particularly well adapted to the molecular characterization of organic waste from different origin. The pyrolysis results showed differences at the molecular level which can influence the interactions with pollutants and soil organic matter. Low copper desorption efficiency (<5%) were measured in the samples. Copper was more mobile in limed and filter-pressed sludge compared to other CAS (conventional activated sludge) due to the reduction of copper distribution in exchangeable or reducible fraction

Molecular characterisation of fertilizing materials of residual origin for a better understanding of interactions with pollutants

International audienceThe increasing demands on food and drinking water due to the rising world population induces increasing production of organic waste such as manure and sewage sludge. The main sustainable valorization pathway for these biodegradable waste is land farming despite it potentially contain metal traces elements and organic micro contaminants. The consequence can be a pollution of soils, aquatic resources, crops and finally human food chain. Depending on the characteristics of these organic fertilising material of residual origin as well as the treatment it was submitted to, pollutants can be more or less degraded or bio-available. Indeed, processes such as composting can participate to degrade organic pollutants or modify heavy metals bio availability. In this context a better knowledge of the characteristics of organic fertilising material of residual origin is essential to envisage the interactions between organic fertilizing materials of residual origin and pollutants which are eventually present. The impact of several pre-treatments processes such as drying, hygienisation, stabilisation, digestion or composting was studied. For this purpose, 13 samples including sludge, manure, compost and digestat were characterized at the molecular level using elemental analysis, differential scanning calorimetry and double-shot thermochemolysis. In parallel the same samples were analysed for chemical functions and biochemical content according to the methods described in Lachassagne et al (2015), and for their fertilizing properties. Moreover these properties were put in regards to their ability to desorb copper during landspreading. Composted, and reed bed sludge presented high material (organic and mineral material) content and high protonic exchange capacity in particulate phase of sludge. In limed, filter pressed, digested thickened sludge a large protein, polysaccharide and “humic like” substances content was measured in the soluble phase while the distribution of the corresponding fluorescence intensity in the floc (observation of confocal laser scanning microscopy) was low. Large DOC content observed in soluble phase of limed sludge, centri-dried and anaerobic granular sludge corresponded to high protein contents under the 3D-fluorescence observation. High content of carboxyl and phosphoric functional groups was measured in particulate phase of composted and dewatering sludge while they were present in high percentages in soluble phase of limed, digested, thickened sludge.The low C to N ratios (table 1) demonstrated stable organic matter. This ratio is higher for composted sludge than for digested or dried sludge. In parallel the H to C atomic ratio is lower for composted and digested sludge which is characteristic of humified materials.The characterization of the 13 samples by thermochemolysis at 350°C (first shot) showed the presence of fatty acids, hydroxyacids, diacids and steroids. Iso and anteiso C15 and C17 compounds of bacterial origin, demonstrated thanks to the branched to linear ratio a higher bacterial contribution for the digested sludge whereas the composted sludge is more stable. This is confirmed by the hydroxyacids / fatty acid ratio (H/A) or diacids/monoacids (D/A). The second shot at 600oC produced cellulose, lignin and proteins moieties and a series akenes/alkanes. The toluene/styrene ratio higher than 1 outlined the natural origin of organic compounds. Double-shot thermochemolysis is a technique particularly well adapted to the molecular characterization of organic waste from different origin. The pyrolysis results showed differences at the molecular level which can influence the interactions with pollutants and soil organic matter. Low copper desorption efficiency (<5%) were measured in the samples. Copper was more mobile in limed and filter-pressed sludge compared to other CAS (conventional activated sludge) due to the reduction of copper distribution in exchangeable or reducible fraction

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

International audienceBecause 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

Diffusive gradients in thin films, Rhizon soil moisture samplers, and indicator plants to predict the bioavailabilities of potentially toxic elements in contaminated technosols

International audienceThe phytoavailabilities and potential remobilization of potentially toxic elements (PTEs) such as Zn, Pb, Cd, As, and Sb were assessed in contaminated technosols from former mining and smelting sites. The PTE concentrations in soil pore water (SPW) and diffusive gradients in thin films (DGT)-measured concentration (C DGT) methods were used to assess the bioavailabilities of PTE and their remobilization in this study. Together with classical Chelex-100 DGT probes to measure Zn, Cd, and Pb, novel ferrihydrite-backed DGT were used for As and Sb measurements alongside with Rhizon soil moisture sampler method for SPW sampling. To assess the phytoavailabilities of PTE, a germination test with dwarf beans as a plant indicator was used for this purpose. Dwarf bean primary leaves showed high Zn concentrations in contrast to Pb and Cd which showed low phytoavailabilities. Despite As and Sb are present in high concentrations in the mine tailings, their phytoavailabilities indicate very low bioavailabilities. The amounts of Zn, Pb, Cd, As, and Sb extracted with DGT devices correlated well with the total dissolved PTE concentrations in the SPW. The highest R values were observed for Zn, followed by Cd and Pb, indicating the ability of the soil to sustain SPW concentrations, which decreased in that order. Good correlations were also observed between each of dissolved PTE concentrations in SPW, DGT-measured PTE concentrations (C DGT), and the accumulation of PTE in dwarf bean primary leaves. It could be concluded that the use of Rhizon soil moisture samplers and DGT methods may be considered to be a good methods to predict the PTE bioavailabilities in contaminated technosols

Mobilization of lead-zinc rich particles from mine tailing in Northern Tunisia by aeolian and run-off processes

International audienceDispersion of metal rich particles from mine tailings is an important hazard for the environment. Specially, in Mediterranean context, this is potentially more risky because of the violence of climatic events. Northern Tunisia includes about 50 mining districts with an ore mineralogy consisting mainly of galena, iron sulphides and subordinate sphalerite embedded in a calcitic and baritic gangue. A century of mining exploitation left waste rich in potentially toxic elements (PTE) with values up to 46900 mg/kg for Pb and 49501 mg/kg for Zn, stored in uncontrolled and untreated deposits. The PTE contents observed in the surrounding soils generally devoted to agricultural activities are as high as 12488 mg/kg for Pb, 3485 mg/kg for Zn and 15 mg/kg for Cd. The contents in sediments downstream are also high, in the range of 47800 mg/kg for Pb, 5767 mg/kg for Zn and 36 mg/kg for Cd. PTE-bearing phases are mainly sulphides, carbonates and iron oxyhydroxydes. Because of the lack of vegetation and the presence of fine particles in the mining wastes, PTE were dispersed to nearby areas, resulting in the contamination of agricultural soils and river sediments. Under the Mediterranean climate which includes a long dry summer with windy episodes and heavy rainfall in the winter, mine tailings are exposed to two types of erosion: hydraulic erosion with transport during heavy rainfall events and aeolian erosion inducing fine particle dispersion. Dispersion of the PTE from mine tailings in northern Tunisia presents a risk of environmental contamination and of toxicity by inhalation for the habitants near the former mining districts. Furthermore these PTE can be transferred from agricultural soils surrounding the tailings to the cultivated plants (mainly cereals)

Douglas fir (Pseudotsuga menziesii) plantlets responses to As, Pb, and Sb-contaminated soils from former mines

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Effect of organic amendments on the mobility of trace elements in phytoremediated techno-soils: role of the humic substances

International audienceThe efficiency of aided phytostabilization using organic amendments such as ramial chipped wood (RCW) and composted sewage sludge (CSS) was studied on contaminated techno-soils, on nine experimental plots. The objective was to characterize the role of fulvic (FA) and humic acids (HA) on the mobilization of trace elements, specifically As, Cu, Mo, Pb and Zn. Results showed that the addition of CSS increased the total organic carbon and nitrogen content more than with RCW and as a result, the C/N ratio in the CSS soil was higher than in the RCW and non-amended (NE) soil, reflecting the high decomposition of soil organic matter in the CSS soil compared with the other soils. The RCW and CSS amendments increased the hydrogen index (HI) values and the oxygen index (OI) values compared with the NE soil, especially for the soil treated with CSS which contained more aliphatic than aromatic compounds. The addition of CSS to the techno-soil significantly increased the percentage of C org associated with the HA fractions compared with the RCW and NE soils. The soil amended with CSS showed the highest E 4/E 6 ratio and the lowest E 2/E 3 ratio of FA. Zn and As were more abundant in the FA fraction than in the HA fraction, whereas Pb, Cu and Mo were more associated to HA than to FA in the treated and untreated soils, which may explain the difference in their mobility and availability

Potentials of Miscanthus x giganteus grown on highly contaminated Technosols

Mining activities produce a huge amount of contaminated wastes inducing potential risks for groundwater and/or food chain. As classical remediation solutions are very expensive, the necessity to find alternative rehabilitation is needed. The aim of this study was to assess the growth of Miscanthus x giganteus (high lignocellulosic biomass used as biofuel) on highly contaminated mining media. In the way to control the parameters, experiments were conducted during 3 months in phytotron from composite mining soils without inputs developed from a former gold mine rich in arsenic (As), lead (Pb) and antimony (Sb). Results gave evidence of a clear aerial biomass reduction, whereas no real impact on physiological activity and development, as well as a very low translocation factor of contaminants to aerial parts are effective. The major conclusions are (i) the capacity of Miscanthus x giganteus to grow on highly contaminated soils, and (ii) its short-term use as soils phytostabilizer by cropping the plant without any inputs. (C) 2013 Elsevier B.V. All rights reserved

Interfacial reactions between humic-like substances and lateritic clay: Application to the preparation of “geomimetic” materials

International audienceThe aim of this study was to understand the mechanisms responsible for the strengthening of “geomimetic” materials, especially the chemical bonding between clay and humic substances. The mineral matter is lateritic clay which mainly consists in kaolinite, goethite, hematite and quartz. The other starting products are fulvic acid (FA) and lime. The preparation of these geomimetic materials is inspired from the natural stabilization of soils by humic substances occurring over thousands of years. The present process involves acidic and alkaline reactions followed by a curing period of 18 days at 60 °C under a water saturated atmosphere. The acceleration of the strengthening process usually observed in soils makes this an original process for treatment of soils. The consolidation of the “geomimetic” materials could result from two major phenomena: (i) chemical bonding at the interface between the clay particles and iron compounds and the functional groups of the fulvic acid, (ii) a partial dissolution of the clay grains followed by the precipitation of the cementitious phases, namely calcium silicate hydrates, calcium aluminate hydrates and mixed calcium silicum and aluminum hydrates. Indeed, the decrease of the BET specific area of the lateritic clay after 24 h of reaction with FA added to the structural reorganization observed between 900 and 1000 °C in the “geomimetic” material, and to the results of adsorption measurements, confirm the formation of organo-ferric complexes [1]. The presence of iron oxides in clay, in the form of goethite, appears to be another parameter in favor of a ligand exchange process and the creation of binding bridges between FA and the mineral matter. Indeed all faces of goethite are likely to be involved in complexation reactions whereas in lateritic clay only lateral faces could be involved [2]. The results of the adsorption experiments realized at a local scale will improve our understandings about the process of adsorption of FA on lateritic clays and its involvement in the strengthening process of materials