Agromining: farming metals for biosourced materials

Objectius de Desenvolupament Sostenible::12 - Producció i Consum Responsable

Selection of oxidant doses for in situ chemical oxidation of soils contaminated by polycyclic aromatic hydrocarbons (PAHs): A review

International audienceIn situ chemical oxidation (ISCO) is a promising alternative to thermal desorption for the remediation of soils contaminated with organic compounds such as polycyclic aromatic hydrocarbons (PAHs). For field application, one major issue is the selection of the optimal doses of the oxidizing solution, i.e. the oxidant and appropriate catalysts and/or additives. Despite an extensive scientific literature on ISCO, this choice is very difficult because many parameters differ from one study to another. The present review identifies the critical factors that must be taken into account to enable comparison of these various contributions. For example, spiked soils and aged, polluted soils cannot be compared; PAHs freshly spiked into a soil are fully available for degradation unlike a complex mixture of pollutants trapped in a soil for many years. Another notable example is the high diversity of oxidation conditions employed during batch experiments, although these affect the representativeness of the system. Finally, in this review a methodology is also proposed based on a combination of the stoichiometric oxidant demand of the organic pollutants and the design of experiments (DOE) in order to allow a better comparison of the various studies so far reported

Characterization of sulphate sorption on Callovo-Oxfordian argillites by batch, column and through-diffusion experiments

International audienceCallovo-Oxfordian argillites are under investigation as a potential host rock for a high-level radioactive waste repository. The purpose of this study was to investigate sulphate sorption on two borehole samples (EST205 K119c and K100c), using three different and complementary laboratory techniques. Batch experiments revealed a fast, weak and reversible sorption of sulphate ions on Callovo-Oxfordian argillites. Quantification was difficult with this method due to uncertainties on low Kd values obtained. Column and through-diffusion experiments confirmed this retention and allowed a better quantification. A clear dependence of sulphate sorption on both mineralogical composition and sulphate content was shown. For the K119c argillite, the sulphate isotherm was fitted with a Langmuir isotherm. Kd values are ranging from 0.15 to 0.37 mL g−1, depending on total sulphate content

Characterization of iodide retention on Callovo-Oxfordian argillites and its influence on iodide migration

International audienceIodine-129 is commonly considered to belong to the largest contributors to the calculated impact on health associated with the longterm nuclear underground waste disposal. Its behaviour in Callovo-Oxfordian argillites, an argillaceous host rock studied by ANDRA, therefore must be fully characterized. Investigated cores have been extracted from a place outside the Meuse/Haute Marne underground laboratory. Thus, batch and through-diffusion experiments were performed to investigate iodide sorption and transport, on two different test samples. Batch experiments give evidence of a kinetically limited slight retention of iodide at low total iodine concentration. This sorption, dependent on the oxic/anoxic conditions, has been modelled with an initial quick reaction and a long-term steady loss of iodide from the solution. Through-diffusion experiments have confirmed this retention but to a lower extent than observed in batch experiments and differences were found between both samples. These differences have been explained by anionic exclusion, which potentially blocks sorption site access

Phenanthrene and pyrene oxidation in contaminated soils using Fenton's reagent

International audienceFenton's reagent has shown its applicability to oxidizing these biorefractory organic contaminants. The purpose of this contribution was to investigate the influence of operating parameters on the process efficiency for soil highly contaminated by PAHs. Five variables were selected: pH, reaction time, UV irradiation, hydrogen peroxide concentration and Fe (II) amendment. Their effects on the oxidation of (i) phenanthrene and on (ii) phenanthrene and pyrene present in freshly contaminated soil samples were studied through batch reactor experiments following factorial designs. For phenanthrene oxidation run with a soil contaminated at 700 mg kg−1, one set of variables enabled us to reach a residual concentration lower than 40 mg kg−1 (Dutch legislation threshold). The most important factor was the reaction time, followed at a certain distance by UV irradiation, Fe (II), H2O2 concentration and pH, this last variable being the least significant. The possibility of operating without pH adjustment is of importance in the treatment at the field scale. This shows the feasibility of photo-Fenton-like oxidation for the treatment of soil highly contaminated with PAH and the relative importance of the process variables

Sorption of selenium oxyanions on TiO2 (rutile) studied by batch or column experiments and spectroscopic methods

International audienceSelenium is a known toxic element released in the environment by anthropogenic activities. The present study is devoted to the aqueous sorption behaviour of selenium oxyanions (selenate and selenite) on a reference oxide surface, namely rutile TiO2. Batch sorption kinetics and isotherms have been studied using different physico-chemical conditions of the solution (changes of pH and ionic strength). The sorption was favoured for both anions in acidic conditions, in agreement with a surface complexation mechanism and CD-MUSIC predictions. Spectroscopic investigations of the sorbed rutile powder were also consistent with such a mechanism. EXAFS spectra confirmed that for selenite anions, an inner-sphere mechanism was the most probable process observed. Dynamic sorption experiments using a column filled with rutile powder also substantiated that a part of the surface complexes follows the inner-sphere mechanism, but also evidenced that an outer-sphere mechanism cannot be excluded, especially for selenate anions

Agromining for nickel : A complete chain that optimizes ecosystem services rendered by ultramafic landscapes

Serpentine (i.e. ultramafic) outcrops in Europe cover more than 10,000 km2 and have a low-fertility and low-productivity, making them unattractive for traditional agriculture. In general, these areas are slowly abandoned by local farmers, affected by strong rural exodus and landscapes undergo a process of closure. However, ultramafic landscapes have the potential to provide multiple ecosystem services that can contribute to Europe’s goals towards insuring food security, production of renewable raw materials and renewable energy. Phytomining (agromining) aims at cultivating metal hyperaccumulator plants that are able to accumulate Ni and other strategic elements from metal-rich soils and transport them to the shoots (>1%), which can then be harvested as a bio-ore. Such metal-rich biomass can be used to recover highly valuable metals, e.g. nickel (Ni) and also to produce energy (heat, electricity). Nickel agromining can thus offer an eco-efficient alternative to classical pyro- or hydrometallurgical processes without disturbing the soil cover and the geology from soils and rocks that would be considered as low grade ores or sterile material for conventional mining methods. Phytomining agroecosystems can lead to better soil resource efficiency and can offer a fully integrated, new agromining agriculture that could cover thousands of km2 in Europe, benefit local communities with a sustainable rural development and provide a wide array of ecosystem services which will need to be optimised under a life cycle assessment methodology: 1. Production of bio-sourced metal products 2. Production of energy biomass 3. Restoration of soil fertility for conventional agriculture (Ni stress) 4. Limiting Ni intake by local populations and farmers 5. Use and conservation of local biodiversity (plant and soil fauna and microflora) as cultivated ecosystems 6. Store carbon in cultivated soils 7. Enhance pollination activity at landscape level. Nickel agromining could therefore change the economical balance in historically-disadvantaged ultramafic regions of Europe