María Eugenia Parolo

Potential use of calcareous mudstones in low hydraulic conductivity earthen barriers for environmental applications

Earthen layers play a significant role in isolating contaminants in the subsurface, controlling the migration of contaminant plumes, and as landfill liners and covers. The physical, chemical and mineralogical properties of three calcareous mudstones from the Jagüel and Roca formations in North Patagonia, Argentina, are evaluated to determine their potential for the construction of liners. These mudstones were deposited in a marine environment in the Upper Cretaceous–Paleocene. The tested specimens mainly comprise silt and clay-sized particles, and their mineralogy is dominated by a smectite/illite mixed layer (70–90% Sm) and calcite in smaller proportion. Powdered mudstone samples have little viscosity and swelling potential when suspended in water. The hydraulic conductivity of compacted mudstones and sand–mudstone mixtures is very low (around 1–3×10−10 m/s) and in good agreement with the expected hydraulic behaviour of compacted earthen layers. This behaviour can be attributed to the large amount of fine particles, high specific surface and the close packing of particles as confirmed by scanning electron microscope analysis. The tested materials also show a high cation exchange capacity (50–70 cmol/kg), indicating a high contaminant retardation capability. The calcareous mudstones show satisfactory mineralogical and chemical properties as well as an adequate hydraulic behaviour, demonstrating the potential use of these materials for the construction of compacted liners for the containment of leachate or as covers in landfills. These findings confirm the potential usage of marine calcareous mudstones as a low-cost geomaterial in environmental engineering projects.

From biowaste to magnet-responsive materials for water remediation from polycyclic aromatic hydrocarbons

Composted urban biowaste-derived substances (BBS-GC) are used as carbon sources for the preparation of carbon-coated magnet-sensitive nanoparticles obtained via co-precipitation method and the subsequent thermal treatment at 550 °C under nitrogen atmosphere. A multitechnique approach has been applied to investigate the morphology, magnetic properties, phase composition, thermal stability of the obtained magnet-sensitive materials. In particular, pyrolysis-induced modifications affecting the BBS-GC/carbon shell were highlighted. The adsorption capacity of such bio-derivative magnetic materials for the removal of hydrophobic contaminants such as polycyclic aromatic hydrocarbons was evaluated in order to verify their potential application in wastewater remediation process. The promising results suggest their use as a new generation of magnet-responsive easily-recoverable adsorbents for water purification treatments.

An integrated approach for assessing the migration behavior of chlorpyrifos and carbaryl in the unsaturated soil zone

ABSTRACT Chlorpyrifos (O, O-diethyl O-3,5,6-trichloropyridin-2-yl phosphorothioate) and carbaryl (1-naphthyl methylcarbamate) are often applied concurrently as insecticides in food production. The aim of this study was to research their migration behavior in a real environment. We researched the leaching of both pesticides by setting up field lysimeters on a farm with the typical soil used in fruit production today. In order to analyze the variables involved in this process, we performed complementary adsorption studies, we performed complementary adsorption studies using batches and undisturbed soil laboratory columns for both compounds. The results for pesticide transport through the lysimeters showed that less than 1% of chlorpyrifos was recovered in the leachates, while almost 17% was recovered for carbaryl. Having completed the experiment in undisturbed laboratory columns, soil analysis showed that chlorpyrifos mainly remained in the first 5 cm, while carbaryl moved down to the lower sections. These results can be explained in view of the sorption coefficient values (KD) obtained in horizons A and B for chlorpyrifos (393 and 184 L kg−1) and carbaryl (3.1 and 4.2 L kg−1), respectively. By integrating the results obtained in the different approaches, we were able to characterize the percolation modes of these pesticides in the soil matrix, thus contributing to the sustainable use of resources.

ARCILLAS ESMECTÍTICAS DE LA REGIÓN NORPATAGÓNICA ARGENTINA COMO BARRERAS HIDRÁULICAS DE RELLENOS SANITARIOS Y AGENTES DE RETENCIÓN DE METALES PESADOS

Groundwater contamination through leachates migration in landfills is one of the main concerns in this kind of disposal sites. To control this migration, compacted clay liners of low hydraulic conductivity and high retention capacity are widely used to isolate urban waste leachate. The aim of this work was to evaluate the hydraulic conductivity and heavy metal adsorption capacity of two smectitic clays to determine their hydraulic and geochemical properties to be used as clay barriers in landfills. Hydraulic conductivity tests of sand-clay mixtures permeated with distilled water and a real leachate were performed. Adsorption of Cu(II), Zn(II), Ni(II) and Cd(II) from monometal solutions on clay fractions was evaluated through batch adsorption tests. Hydraulic conductivity of the specimens permeated with a real leachate was of 1 to 3 orders of magnitude higher than the ones permeated with water. This could be attributed to the highly salinity of the leachate which contributed to a more flocculated state of the clays and the dissolution of soluble mineral phases. The heavy metal adsorption data were fitted with Langmuir model. The adsorption capacities of the analyzed metals were in the following order: Zn(II) > Cu(II) > Ni(II) > Cd(II) for CATAE bentonite and Zn(II) > Ni(II) > Cu(II) > Cd(II) for NTOL mudstone. The adsorption capacity of Cu(II) and Zn(II) was higher than the cation exchange capacity (CEC) of the analyzed clays, whereas for Cd(II) and Ni(II), the retained quantity is lower than the CEC. On the other hand, the hydraulic conductivity of the sand-clay mixtures was lower than 1 x 10 -9 m/s. These results indicate the suitability of the tested clays to be used as hydraulic and geochemical barriers in landfills according to the international legislation requirements for clay liners.