17 research outputs found
Tratabilidade de solos tropicais contaminados por resÃduos da indústria de revestimentos cerâmicos
A qualidade das águas na região dos garimpos de topázio imperial na sub-bacia do rio da Ponte, Ouro Preto-MG
Adsorp, a chemical equilibria computer program accounting for adsorption processes in aquatic systems
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Modeling the diffusion of Na+ in compacted water-saturated Na-bentonite as a function of pore water ionic strength
Assessments of bentonite barrier performance in waste management scenarios require an accurate description of the diffusion of water and solutes through the barrier. A two-compartment macropore/nanopore model (on which smectite interlayer nanopores are treated as a distinct compartment of the overall pore space) was applied to describe the diffusion of {sup 22}Na{sup +} in compacted, water-saturated Na-bentonites and then compared with the well-known surface diffusion model. The two-compartment model successfully predicted the observed weak ionic strength dependence of the apparent diffusion coefficient (D{sub a}) of Na{sup +}, whereas the surface diffusion model did not, thus confirming previous research indicating the strong influence of interlayer nanopores on the properties of smectite clay barriers. Since bentonite mechanical properties and pore water chemistry have been described successfully with two-compartment models, the results in the present study represent an important contribution toward the construction of a comprehensive two-compartment model of compacted bentonite barriers
Natural attenuation of inorganic pollutants (copper, sulfate) in the aquifer below an industrial site
The contamination of soils and aquifers by inorganic pollutants is so widespread in industrial sites that it does not seem
economically feasible to decontaminate the large areas or soil volumes involved. It is therefore interesting to investigate
whether the local environment is capable to attenuate this contamination. Natural attenuation by degradation seems realistic
for many organic pollutants. Here we show that it can take place also for inorganic pollutants. The phreatic fill aquifer
underlying an industrial plant located on the river banks of the Garonne River is contaminated by acidic water (pH down to
1) and high concentrations of sulfate (up to 50 g/L) and copper (up to 30 g/L). As acid water, rich in Cu and sulfate. migrates
away from the contamination source, pH increases due to buffering of aquifer solids, dissolved Cu concentrations decrease
by 6 orders of magnitude, while sulfate concentrations decrease little
Characterization of the chromium retention potential of non polluted aquifer solids in an industrial site
A hydrogeochemical study of an industrial site where sulfuric acid and copper sulfate (“bouillie
bordelaise") are manufacture showed that the phreatic aquifer is contaminated by copper, sulfate, chromium, arsenic
and has an acid pH. Field observations and laboratory experiments, both necessary if we are to understand the
processes controlling tranfers at the solid-liquid interface, were used to investigate the behaviour of chromium. In the
field, monitoring the mixing of polluted and unpolluted water with a conservative tracer, we shows that chromium
disappears from solution. In the laboratory, the potential for retendon of dissolved chromium by an unpolluted aquifer
solid was studied as a function of pH, with and without a complexing agent. Adding high concentrations of a
complexing agent, EDTA, mobilizes the previously fixed chromium at basic pH (90%). Addition of Cr(III) with
EDTA gathered, sorption is greatest (50%) for neutral and basic pH values. Unpolluted aquifer solids have a high
sorption capacity for Cr(III). However, adding a complexing agent significantly mobilizes the chromium. Sorption of
the complexed chromium is also considerably decreased. There should, therefore, be little risk of immediate
chromium pollution in the absence of dissolved complexing agents, as long as the pH of the system is neutral
Factors controlling the migration and attenuation of priority pollutants in landfill pollution plumes
Interaction of selenite with MX-80 bentonite: Effect of minor phases, pH, selenite loading, solution composition and compaction
We propose a simple model describing the retention of selenite, Se(IV), by the MX-80 bentonite in a synthetic groundwater (SGW) in dispersed and compacted states. The model was calibrated on a pure montmorillonite from data obtained for 4 < pH < 10 and total selenite concentrations between 10−7 and 5 × 10−3 mol/L. Furthermore, the matrix solution covers a wide range of conditions regarding the ionic strength and the nature of the background electrolyte. Three selenite surface species had to be considered. Below pH 5, sorption is governed by a ligand exchange reaction with H2SeO3. Between pH 5 and 7, the experimental data are well described considering the formation of a surface complex implying HSeO3−. Finally, at pH above 7, we propose ternary surface complexes involving Ca2+ and Mg2+. The model, which we consider as operational, appears in agreement with spectroscopic data available in the literature and predicts surprisingly well selenite sorption on MX-80 bentonite even in the compacted state at a dry density of 1100 kg/m3. Based on the model, the solid phase montmorillonite is responsible for selenite retention. Minor solid phases containing iron (pyrite, hematite) had not to be considered in the modelling. Interestingly, calcite (an important phase in MX-80 bentonite) has an indirect effect via the release of calcium into solution and its subsequent contribution to Se(IV) sorption through a ternary surface complex