BIOBAR: a proposal of biological barriers for a sustainable landfill design

Waste management and final disposal cause severe environmental impacts. Even in modern landfills, installed engineered barriers worsen their hydraulic performance after 8 years of landfill operation, which can lead to leachate leakage and environmental pollution in the medium to long term. In addition, the use of clay as landfill barriers relies on a non-renewable resource and entails high economic and environmental costs when such a resource is not locally available. Therefore, it is necessary to develop barriers made of renewable and/or recycled sources, which not only promote leachate containment but also enhance its in-situ treatment and attenuation. This project will take advantage of the bacteria naturally occurring in leachate that grow and form biofilms by consuming the organic compounds. We will apply the biofilm-forming bacteria in a novel liner made of the rejected fraction of fine aggregates and plastic waste. Adopting such a bio-barrier between the liner and the drainage system could reduce both the leachate flow (because of the natural clogging) and the contaminants concentrations that actually reach the liner (due to chemical and biochemical attenuation). In this regard, the proposed project will 1) develop bio-barriers for landfill design, combining the rejected fraction of fine aggregates, plastic waste and biofilm-forming bacteria, 2) verify the long-term performance of these new designs for representative conditions, and 3) develop guidance for real-world implementation to reduce barrier permeability and increase contaminant attenuation. The effectiveness of the developed bio-barrier could enable the reduction of clay liner thickness, in a renewable and sustainable design perspectiveThis research will be supported by a grant from HORIZON-MSCA-2021-PF-01-10106705

Selective ion-exchange separation of scandium(III) over iron(III) by crystalline alpha-zirconium phosphate platelets under acidic conditions

A continuous worldwide increase in scandium (Sc) criticality leads to a quest for secondary scandium resources. Among them, bauxite residue (BR) – a waste product from alumina refineries – often contains substantial amounts of scandium. However, the complexity in BR composition drives the need for developing a selective, efficient and cost-effective process to achieve the separation and purification of scandium. Insoluble salts of tetravalent metal ions are inorganic, acid-resistant ion exchangers with well-established preparation procedures, but their potential use in rare-earth recovery and purification has not been extensively explored yet. Zirconium and titanium phosphates, both in amorphous and α-layered crystalline forms, were screened for Sc(III)/Fe(III) separation, as Fe(III) is one of the base elements in BR that is the most challenging to separate from Sc(III). The studied α-zirconium phosphate (α-ZrP, Zr(HPO4)2·H2O) exhibited the highest Sc(III)/Fe(III) separation factors (up to approximately 23) from HCl solutions. The metal selectivity of α-ZrP was considered to be affected by the solution pH, and the size and hydration enthalpy of the metal cations. Breakthrough curves for a binary Sc(III)/Fe(III) solution, composed of metal concentrations realistic to a typical BR leachate, revealed the selectivity of α-ZrP for Sc(III). Furthermore, chromatographic separation of Sc(III) from a real HCl leachate of BR was successfully achieved on an α-ZrP column. After a two-step elution with HCl about 60 % of Sc(III) was collected in fractions without measurable Fe(III), Al(III) or other rare-earth impurities. Overall, this study highlights the possibility for direct and simplified separation of Sc(III) from a much higher concentration of Fe(III) in BR, without the need of using reducing agents.Peer reviewe

Lime mortar-compacted bentonite-magnetite interfaces: An experimental study focused on the understanding of the EBS long-term performance for high-level nuclear waste isolation DGR concept

The aim of this study was to obtain evidences regarding the physical and geochemical processes occurring as a result of the combined effects of cementitious materials from the concrete degradation and magnetite from steel corrosion on the bentonite barrier during disposal of high-level radioactive waste.A series of six experiments were done that attempt to reproduce the repository conditions prevailing from 1000 to 3000 years after emplacement of wastes. A lime mortar was used as the source of calcium and alkalinity as this is the presumed reactive product produced during concrete degradation at long-term. Magnetite powder was used to simulate the final corrosion product of cast iron and C-steel under anaerobic conditions. Either a natural FEBEX bentonite or a pretreated "aged" sample, depleted in exchangeable Mg and enriched in K, were used as the swelling clay component. Experiments, with both types of bentonite, were performed simultaneously in cylindrical specimens (50 mm diameter, 25 mm length), confined in a Teflon® sleeve/steel case cells. These specimens were composed of cement mortar in contact with compacted bentonite, which was in turn in contact with compressed magnetite powder. They were hydrated with an artificial Na+-Ca2+×SO42-type Spanish reference clayey formation water for 18 months at 60 °C and constant hydraulic pressure applied through the base of the mortar.After dismantling and sampling the specimens, distribution of soluble ions, exchangeable cations and mineralogy were studied in the bentonite by different instrumental techniques. Iron migration or any impact of the corrosion products in the bentonite was not noticeable in the clay. Both, mortar and magnetite acted as sinks of chloride and sulfate. Small quantities of Ca-Al-sulfates and carboaluminates, which can allocate chlorides, were determined near the mortar-bentonite interface. Portlandite dissolved near the bentonite interface and induced the formation of calcium silicates hydrates (C-S-H) phases cementing the clay interface characterizing a calcium front that was developed from the mortar towards the bentonite. Magnesium silicate hydrates (M-S-H) phases were also concentrated at the interface with mortar in the natural bentonite. It was also determined that natural bentonite has potentially higher buffering capacity attenuating the calcium alkaline front than the pretreated clay. In both cases, a low porosity bentonite-mortar zone was experimentally created at the interface. This type of material should be carefully studied in order to predict the potential for further development of a diffusive alkaline alteration, the radionuclides retention and the consequences in the hydration rate of the unaffected bentonite bufferThe research leading to these results has received funding from the European Atomic Energy Community's Seventh Framework Program (FP7/2007–2011) under grant agreement no. 249681

Selection criteria of diluents of tri-n-butyl phosphate for recovering neodymium(III) from nitrate solutions

The selection of a proper diluent should be based on several criteria such as the distribution ratio, phase disengagement time, cost, safety and environmental impact of the process. The effect of different diluents on the solvent extraction of Nd(III) by the neutral extractant tri-n-butylphosphate (TBP) from nitrate feed solutions was studied. The nature of the diluent had little effect on the extraction kinetics of Nd(III) by TBP above 2.5 min. In general, phase disengagement times were relatively shorter for aromatic diluents compared to aliphatic diluents. Conversely, extraction efficiencies were the highest for aliphatic diluents, slightly lower for mixed aliphatic-aromatic diluents and much lower for aromatic diluents. The poorer extraction efficiencies of aromatic diluents maybe due to the lower concentration of free extractant as a result of the stronger interactions of the diluent with water and/or of the diluent with the extractant. Under the experimental conditions, the differences in extraction between aliphatic and aromatic diluents decreased with increasing the salting-out effect of nitrate ions in the feed. At nitrate concentrations of 4.5 mol L−1 or more, the different diluents had a limited influence on the metal extraction with 1 mol L−1 TBP from feed solutions of 1 g L−1 Nd(III). Thus, under these conditions, the selection of the diluent can be preferably based on its cost, safety and biodegradability rather than on its physico-chemical properties

Mercedes Regadío's Quick Files

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Separation of rare earths by mixtures of an ionic liquid and a neutral extractant

Oral presentation by Mercedes Regadiostatus: publishe

Difusión de contaminantes bajo vertederos urbanos en suelos arcillosos

Tesis doctoral inédita. Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Geología y Geoquímica. Fecha de lectura: 02-03-201

Extraction of rare earths from chloride solutions to a nitrate ionic liquid by the neutral extractant Cyanex 923

Poster presented by Mercedes Regadiostatus: publishe

Solvoleaching of (landfilled) industrial residues and a low-grade laterite ore with diluted HCl in the ionic liquid Aliquat 336

This work focuses on the recovery via solvometallurgical leaching of valuable metals like Zn, Pb, Ni and Cr from four different industrial process residues: (1) a low-grade nickel laterite ore from Poland (LAT), (2) a chromium-rich sludge from the stainless steel industry (CRS), (3) jarosite residue from zinc production (JAR) and (4) a zinc-rich sludge from the metal industry (ZRS). The selective dissolution against the main impurities (Fe) was also assessed. The content of HCl in the ionic liquid Aliquat 336 had a major influence on the leaching efficiencies and the selectivity: the lower the acid content in Aliquat 336, the higher the selective leaching, and the lower the leaching efficiency. Only in the case of Pb from JAR, there was no change in its leaching selectivity against Fe: the leaching of Fe, As and Pb from JAR was coupled together and had the same tendencies, suggesting that the major Pb mineral phase (galena) has also Fe and As entrapped. Although leaching tests were performed with one organic lixiviant, two immiscible leachates were normally produced: the corresponding organic one (a large part of the total volume) and an aqueous leachate (a small part of the total volume). This is important for the separation of the metals, because the different metal complexes formed showed different affinities towards one or another leachate. Thus, Ni and Cr were concentrated in the aqueous leachate, while Pb, Zn and Fe in were concentrated in the organic leachate.status: publishe

Selective solvometallurgical leaching of lead and zinc from jarosite residues from the zinc industry

The relatively new branch in extractive metallurgy called solvometallurgy was investigated for selective leaching of Pb and Zn from iron-rich jarosite residues, which are typically landfilled. After screening of several lixiviants, the ionic liquids [A336][Cl] and [C101][Cl], equilibrated with HCl, leached the most Pb and Zn of the ionic liquids investigated. When the ionic liquids were equilibrated with relatively lower HCl concentrations, the dissolution of Fe decreased drastically and, thereby, the selectivity for Pb and Zn improved. [A336][Cl] equilibrated with 0.5 M HCl leached 62 wt% Pb, 27 wt% Zn and 7 wt% Fe, while [C101][Cl] equilibrated with 0.5 M HCl leached 73 wt% Pb, 31 wt% Zn and 10 wt% Fe.status: publishe