Effect of ageing on the availability of heavy metals in soils amended with compost and biochar: evaluation of changes in soil and amendment properties

Remediation strategies using soil amendments should consider the time dependence of metal availability to identify amendments that can sustainably reduce available pollutant concentrations over time. Drying-wetting cycles were applied on amendments, soils and soil + amendment mixtures, to mimic ageing at field level and investigate its effect on extractable Cd, Cu, Ni, Pb and Zn concentrations from three contaminated soils. The amendments investigated were municipal waste organic compost and biochars. The amendments, soils and mixtures were characterised by their physicochemical properties at different ageing times. The amendments were also characterised in terms of sorption capacity for Cd and Cu. The sorption capacity and the physicochemical properties of the amendments remained constant over the period examined. When mixed with the soils, amendments, especially the compost, immediately reduced the extractable metals in the soils with low pH and acid neutralisation capacity, due to the increase in pH and buffering capacity of the mixtures. The amendments had a relatively minor impact on the metal availability concentrations for the soil with substantially high acid neutralisation capacity. The most important changes in extractable metal concentrations were observed at the beginning of the experiments, ageing having a minor effect on metal concentrations when compared with the initial effect of amendments

Demonstrating sorption analogy of lanthanides in environmental matrices for effective decision-making: The case of carbon-rich materials, clay minerals, and soils

Examining the effect of lanthanide-contaminated wastes, which have the potential to impact to other environmental compartments, requires conducting interaction studies with soils, as feasible first receptors of lanthanide leachates, and, if necessary, with sorbent materials, such as clay minerals and carbon-rich materials, which can serve as natural barriers and immobilisation agents used in remediation strategies. In this context, it is relevant to have available and reliable data on solid–liquid distribution coefficients (Kd) to understand the lanthanide sorption in these environmental matrices. Moreover, confirming lanthanide sorption analogies permits filling data gaps and data extrapolation among different contaminated scenarios, and thus facilitate to have available input data for decision-making related to the impact of a contaminated site. In this study, we demonstrate for the first time an analogous sorption of La, Sm, and Lu in carbon-rich materials (i.e., biochar and activated charcoal), clay minerals and soils, through laboratory batch experiments. The obtained sorption Kd values revealed similar sorption patterns among the three lanthanides for each matrix tested, even at different initial lanthanide concentrations. In all matrices, the maximum Kd values exceeded 104 L kg−1, with a significant decrease when testing high lanthanide concentrations. The analogy was first confirmed by examining the Kd correlations for the La-Sm, Lu-Sm, and La-Lu pairs within each matrix, for which strong linear correlations were obtained in all cases. Data compilations were built with own and literature data, and derived cumulative distribution functions revealed statistically equal lanthanide distributions and Kd best estimates. In addition to this, Kd variability decreased when grouping the data according to significant material properties. For the first time, Kd (Ln) best-estimates for different scenarios and materials were proposed as input data for risk assessment models

Examining sorption of perfluoroalkyl substances (PFAS) in biochars and other carbon-rich materials

The use of carbon-rich sorbents to remove and/or immobilize perfluoroalkyl substances (PFAS) in contaminated environmental scenarios is attracting increasing interest. The identification of key sorbent properties responsible for PFAS sorption and the development of models that can predict the distribution coefficients (Kd) for PFAS sorption in these materials are crucial in the screening of candidate materials for environmental remediation. In this study, sorption kinetics, sorption isotherms, and the effects of pH, calcium concentration and dissolved organic carbon (DOC) content on PFAS sorption were evaluated in four representative carbon-rich materials: two biochars with contrasting properties, a compost, and charcoal fines rejected by the metallurgical industry. Subsequently, the sorption of seven PFAS with numbers of fluorinated carbons ranging from 4 to 11 was evaluated in a total of ten carbon-rich materials, including activated carbons, so as to build up a Kd prediction model. The sorption of PFAS increased with greater fluorinated chain length, suggesting that hydrophobic interactions play a major role in sorption and electrostatic interactions a minor one. These results were confirmed by a principal component analysis, which revealed that the CORG/O molar ratio and the specific surface area of the material were the two main sorbent properties affecting PFAS sorption. Furthermore, the DOC content in solution had a negative effect on PFAS sorption. Using this information, a simple Kd prediction model applicable to a wide range of materials and PFAS was developed, using only a few easily-derived physicochemical properties of sorbent (CORG/O molar ratio and SSA) and PFAS (number of CF2), and was externally validated with data gathered from the literature

Changes in heavy metal extractability from contaminated soils remediated with organic waste or biochar

The effect of the addition of organic waste or biochar on the extractability of heavy metals (Cd, Cu, Ni, Pb and Zn) was assessed in five heavy metal-contaminated soils. The amendments studied were: municipal organic waste compost (MOW), green waste (GW), biochar derived from tree bark (BF) and biochar derived from vine shoots (BS). The amendments were added to the soil at 10% dose. A pHstat leaching test was applied to the soils and soil + amendment mixtures to assess the effects of the amendments on the extractable metal concentration at the initial pH and in the 2-12 pH range. MOW increased the DOC content in the mixtures for most soils, whereas the rest of amendments only increased the DOC content for the soil with the lowest DOC value. Moreover, in the mixtures obtained from soils with a low buffering capacity, the amendments increased pH (up to 3 units) and the acid neutralization capacity, thus decreasing the extractability of heavy metals at the initial pH of the mixtures. In a few cases, the amendments further decreased the concentrations of extractable metal due to an increase in the sorption capacity of the mixture, even though the soil had high initial pH and ANC values. MOW and GW generally led to larger decreases in metal extractability in the resulting mixtures than biochar, due to their higher sorption and acid neutralization capacities

Dependence of samarium-soil interaction on samarium concentration: Implications for environmental risk assessment

The sorption and desorption behaviour of samarium (Sm), an emerging contaminant, was examined in soil samples at varying Sm concentrations. The obtained sorption and desorption parameters revealed that soil possessed a high Sm retention capacity (sorption was higher than 99% and desorption lower than 2%) at low Sm concentrations, whereas at high Sm concentrations, the sorption-desorption behaviour varied among the soil samples tested. The fractionation of the Sm sorbed in soils, obtained by sequential extractions, allowed to suggest the soil properties (pH and organic matter solubility) and phases (organic matter, carbonates and clay minerals) governing the Sm-soil interaction. The sorption models constructed in the present work along with the sorption behaviour of Sm explained in terms of soil main characteristics will allow properly assessing the Sm-soil interaction depending on the contamination scenario under study. Moreover, the sorption and desorption K-d values of radiosamarium in soils were strongly correlated with those of stable Sm at low concentrations (r = 0.98); indicating that the mobility of Sm radioisotopes and, thus, the risk of radioactive Sm contamination can be predicted using data from low concentrations of stable Sm. (C) 2017 Elsevier Ltd. All rights reserved

Effects of the presence of Fe(0) on the sorption of lanthanum and lutetium mixtures in smectites

The sorption of La and Lu mixtures was examined in two bentonites after incubation for three months at 20 and 80 °C with Fe(0), as a laboratory approach to evaluate the effects of waste canister corrosion in a deep repository on the performance of clay engineered barriers. The sorption/desorption parameters were determined from batch tests in two ionic media: deionized water and, to consider the additional effect of cement leachates, 0.02 mol L− 1 Ca. Results from XRD analyses showed the formation of crystalline FeO(OH), goethite, in a few samples and the degradation of the bentonites due to Fe(0) oxidation during incubation. Moreover, the EDX spectra showed that the lanthanides were sorbed primarily at smectite sites, although sorption onto goethite was also observed, whereas Fe(0) particles did not contribute to lanthanide sorption. The formation of goethite could explain the high Kd values measured in a few scenarios (e.g., those with single solutions or mixtures with the lowest initial concentration of the competitive lanthanide in which high affinity sites governed sorption), with up to 3-fold increases over the values obtained without Fe incubation. However, at higher lanthanide concentration, Kd values decreased or remained constant compared to the samples without Fe incubation, which could be explained by bentonite degradation. In the Ca medium, as much as 5 times lower Kd values were obtained, because of the competitive effect of the Ca ions, especially for Lu in the MX80 bentonite. This indicated that the small number of high affinity sites had been diminished. The sorption data were satisfactorily fitted to a two-solute Langmuir model. In addition, Kd values correlated well with desorption data, which showed that the larger the decrease in Kd, the larger the increase in sorption reversibility. It is suggested that corrosion products from the metal canister might compromise the long-term radionuclide retention of the clay-engineered barriers

Education and training in radioecology during the EU-COMET project-successes and suggestions for the future

The 2014 Strategic Research Agenda (SRA) for Radioecology identified the key challenge in education and training (E&T) as being 'to maintain and develop a skilled workforce in Europe and world-wide, through university candidates and professionals trained within radioecology' since 'scientific research in radioecology and application of that knowledge ... requires scientists and workers with adequate competence and appropriate skills.' Radioecology is a multidisciplinary science and E&T is needed by both students and professionals within research, industry and radiation protection. In order to address these needs, the EU COMET project has developed an E&T web platform and arranged a number of field courses, training courses, PhD and MSc courses, refresher courses and workshops, drawing on the COMET consortium to assemble relevant experts. In addition, COMET has been engaged in discussions with stakeholders for more long-term solutions to maintain the sustainability of radioecology E&T after the end of the project. Despite much progress in some areas, many of the challenges outlined in the 2014 SRA remain, mainly due to the lack of sustainable dedicated funding. Future plans within the ALLIANCE radioecology platform and the CONCERT-European Joint Programme for the Integration of Radiation Protection Research must urgently address this lack of sustainability if radioecological competence is to be maintained in Europe

Sorption of perfluoroalkyl substances in sewage sludge

The sorption behaviour of three perfluoroalkyl substances (PFASs) (perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA) and perfluorobutanesulfonic acid (PFBS)) was studied in sewage sludge samples. Sorption isotherms were obtained by varying initial concentrations of PFOS, PFOA and PFBS. The maximum values of the sorption solid-liquid distribution coefficients (Kd,max) varied by almost two orders of magnitude among the target PFASs: 140-281 mL g−1 for PFOS, 30-54 mL g−1 for PFOA and 9-18 mL g−1 for PFBS. Freundlich and linear fittings were appropriate for describing the sorption behaviour of PFASs in the sludge samples, and the derived KF and Kd,linear parameters correlated well. The hydrophobicity of the PFASs was the key parameter that influenced their sorption in sewage sludge. Sorption parameters and log(KOW) were correlated, and for PFOS (the most hydrophobic compound), pH and Ca + Mg status of the sludge controlled the variation in the sorption parameter values. Sorption reversibility was also tested from desorption isotherms, which were also linear. Desorption parameters were systematically higher than the corresponding sorption parameters (up to sixfold higher), thus indicating a significant degree of irreversible sorption, which decreased in the sequence PFOS > PFOA > PFB

Feasibility of using low-cost, byproduct materials as sorbents to remove heavy metals from aqueous solutions

This work investigates the sorption of heavy metals by low-cost, byproducts such as charcoal fines (CF), waste green sand, and rice husk ash, in order to examine the feasibility of their use as alternative filter materials for metal-contaminated waters. The sorption of Cd, Cu, Pb, and Zn was investigated in batch experiments and sorption isotherms were constructed. The three byproducts showed high metal removal efficiencies (>95%, regardless of the metal concentration tested). The highest metal sorption distribution coefficients were obtained for CF, with maximum values within the 105-106 L kg-1 range for all the target metals. The sorption isotherms were satisfactorily fitted using the Freundlich equation and a linear model, the latter only being valid for initial metal concentrations lower than 0.4 mmol L-1. Sorption reversibility was very low, with desorption yields lower than 2% and desorption distribution coefficients often higher than 106 L kg-1. The values of the sorption and desorption parameters indicated that the use of these materials, especially CF, could constitute a low-cost alternative for the remediation of contaminated waters

Examination of competitive lanthanide sorption onto smectites and its significance in the management of radioactive waste

The competitive effect of La and Lu (analogues of radionuclides appearing in radioactive waste) in the sorption in four smectites was examined. Sorption and desorption distribution coefficients (Kd; Kd,des), and desorption rates (Rdes) were determined from batch tests in two media: deionized water and, to consider the influence of cement leachates, 0.02 mol L−1 Ca. The competitive effect was lower when high-affinity sites were available, as in the water medium at the lowest range of initial lanthanide concentration, with high Kd for La and for Lu (5-63 × 104 L kg−1). Lower Kd was measured at higher initial concentrations and in the Ca medium, where Lu showed a stronger competitive effect. This was confirmed by fitting the sorption data to a two-solute Langmuir isotherm. The desorption data indicated that sorption was virtually irreversible for the scenarios with high sorption, with an excellent correlation between Kd and Kd,des (R2 around 0.9 for the two lanthanides). Assuming that radioactive waste is a mixture of radionuclides, and that Ca ions will be provided by the cement leachates, this would reduce the retention capacity of clay engineered barriers