Kurt Czurda

Reactive barriers with fly ash zeolites for in situ groundwater remediation

Abstract In situ chemically reactive barriers or in situ treatment zones are permeable zones emplaced within the aquifer, which reacts with contaminants as contaminated groundwater flows through the zone. This treatment technology can be applied in funnel and gate systems where the plume is forced by slurry trench walls, diaphragm walls, etc., to focus and to pass through a permeable gate with added sorptive particles. In the study on hand, fly ash zeolites (FAZ) are the main reactive constituent of cement/bentonite slurries for grouted screens or FAZ geotextile casings or geosynthetic FAZ liners. The FAZ component is aimed at improving the retention or at least the retardation properties of the sorptive zone or sorptive geotextile element especially for nonpolar organic molecules, and of course, heavy metals. The engineered zeolites as tectosilicates show different dimensions of their channels and cages forming the crystal lattice. They act as molecular sieves. Fly ash zeolites are transformation products from hydrothermal treatment processes of hard coal fly ash (HCF) by sodium hydroxide (NaOH) solutions. The main constituents of fly ash are aluminosilicate glass, mullite and quartz. The zeolite synthesis is controlled by temperature, reaction time, solution molarity, SiO 2 /Al 2 O 3 ratios and eventual pressure as variable parameters. Fly ashes from different combustion processes and coal of different geological origin treated by different hydrothermal procedures finally end up in different zeolite phases. The process of hydraulic flow through the reactive zone or wall can be enforced by applying electrokinetics to move the contaminants in the soil pore water into treatment zones where the contaminants can be captured or decomposed. The major feature of the technology proposed in this study is the electrodes energized by a direct current which causes water and soluble contaminants to move into or through the treatment zone, and the treatment zones containing reagents that decompose or adsorb the soluble organic contaminants or adsorb contaminants for immobilization or subsequent removal or disposal.

Diffusion and solid speciation of Cd and Pb in clay liners

Abstract For the assessment of the long-term sorption behavior of landfill clay liners towards contaminants the information given by distribution coefficients or retardation factors is not sufficient. Information regarding the solid speciation, which describes the actual bonding sites of sorbed contaminants, is required. The objective of the study presented in this paper was to analyze the retardation and solid speciation of Cd and Pb migrating into an illitic/smectitic loess loam by diffusion. Apparent diffusion coefficients as obtained from diffusion experiments on compacted loess loam with heavy metal solutions containing 0.001 M Cd or Pb chloride were in the range of 4.9–6.7·10 −8 cm 2 /s for Cd and 3.6–7.4·10 −9 cm 2 /s for Pb. The solid speciation was analyzed using a sequential extraction procedure giving operationally defined fractions (i.e. exchangeable, carbonatic, oxidic, organic, and residual fraction) of the sorbed heavy metals. The amounts of Cd and Pb migrated into the loess loam by diffusion clearly showed weaker bonding than the geogenic fraction. The speciation itself was significantly dependent on the heavy metal load showing weak bonding at high concentrations and strong bonding at low concentrations. Chemical extraction procedures can be used to analyse the sorption capacity of individual phases of the liner material towards heavy metals. Langmuir adsorption isotherms could be constructed for the individual operationally defined fractions, and the adsorption maxima and affinity parameters of these fractions could be determined. The results show that the specific sorption sites only have a limited capacity for heavy metals compared to nonspecific adsorption sites as represented particularly by the exchangeable fraction. Set in relation to the total sorption capacity of the investigated loess loam towards Cd and Pb, nonexchangeable bound species amount to only 7% (Cd) and 28% (Pb) for the carbonatic fraction, 1% (Cd) and 4% (Pb) for the oxidic fraction, and 0.5% (Cd) and 1% (Pb) for each the organic and residual fraction. The results emphasise that chemical extraction procedures can give important indications about the way heavy metals are actually fixed to the components of a landfill clay liner material.

Freezing effect on shear strength of clayey soils

Abstract The design and construction of earth structures influenced seasonally by subzero temperatures requires the determination of mechanical properties of the construction materials under appropriate thermal conditions. Water saturated materials exhibit a zone of partially frozen soil at the frozen-unfrozen soil interface. To define the critical failure surface and governing shear strength in this zone, the effects of partial freezing on the mechanical behaviour as a freezing front advances, must be well understood. This paper presents a testing procedure for five clayey soils. It describes a series of laboratory direct shear tests to evaluate the effects of different freezing conditions at the shearing plane, on the shear strength of the thawing clayey soils. The major goal of this research was to understand these effects. From the results collected it was concluded that variations in the shear strength of frozen soils with time and temperature results primarily from variations in the ice cohesion and that the frictional resistance may be regarded as essentially constant. In practical terms, variations in the shear strength of frozen ground may be investigated in terms of their cohesion.

Cation transport and retardation processes in view of the toxic waste deposition problem in clay rocks and clay liner encapsulation

Abstract The sorption capacity of clay rocks for different metals (Cd, Co, Cr, Cs, Cu, Pb, Sr and Zn) was analyzed in a series of batch and column experiments. The migration behaviour of a metal chloride solution through undisturbed rock samples from different Tertiary and Quaternary clays, silts and marls was investigated by means of diffusion tests (different concentration gradients) as well as percolation experiments (different hydraulic gradients). Cation transport and retardation processes are influenced on the one hand by solution parameters (species and concentration of metal, pH, Eh, salt concentration, etc.) and on the other hand by specific rock parameters (grain size, mineralogical composition, cation exchange capacity and primary cation fixation, bedding and microfabric, specific surface, organic matter and initial pH of pore water). Adsorption isotherms suggest two different sorption mechanisms. Retardation factors calculated from batch tests are in general distinctly higher than those measured in diffusion and percolation experiments.

Migration of radionuclides (Sr-90, Cs-137) in clays from the Austrian Molasse

Abstract The migration behaviour of Sr-90 and Cs-137 in freshwater- and marine clays from the Austrian Molasse was studied by percolating chloride solutions through small columns which contained undisturbed clay samples. The sorption capacity measured in the percolation tests was compared to that of batch tests which were done with the same clays respectively with different standard clay types. The sorption capacity generally increased with an increasing pH and with finer sieve fractions. For both clay types the sorption distribution coefficient K d was higher for Cs than for Sr. The percolation in the column tests was carried out parallel and perpendicular to the bedding plane (ss). The sorption capacity was lower in the percolation test parallel ss because the permeability was higher and so the contact time was shorter. K d is always distinctly higher for the marine clay in comparison to the freshwater clay. This may be explained by the lower permeability, the higher content of swelling clay phases, the different microtexture and the different primary interlayer cations of the marine clay.

The triple multimineral barrier for hazardous waste encapsulation

Abstract According to the present state of science and technology, the ultimate disposal of critical substances such as chemotoxic wastes, metal slurries, radioactive substances, etc., as well as houshold waste, necessitates enclosure within a multi-barrier system. The geology of the disposal site plays an important role. The site itself defines the geological barrier which has to fulfill at least two requirements: namely low permeability and retention, respectively retardation qualities. These can be achieved to a certain degree either by clay minerals, zeolites or an artificial product such as active coal. In order to increase the imperviousness and retardation potentials of e.g. clayey geological barriers, technical barriers have to be added. One of them and the most important is the mineralogic barrier. It consists of clay dominated layers and according to the multimineral barrier concept the different layers have to meet different functions.

Einsatzmöglichkeiten, Aussagen und Grenzen bodenphysikalischer, physikalisch-chemischer und mineralogischer Kenngrößen und Meßmethoden zur Erkundung und Beschreibung der Geologischen Barriere

Mit bodenphysikalischen Mesverfahren lassen sich Kenngrosen gewinnen, welche Aussagen uber die bodenphysikalischen Eigenschaften des Deponieuntergrundes geben. Die Bodenphysik betrachtet dabei keine einzelnen Mineralteilchen sondern die Wirkung aller Minerale, Phasen und Aggregate in ihrer Gesamtheit (Hartge & Horn 1991). Wichtige bodenphysikalische Kenngrosen sind dabei: die Dichte des Bodens, der Wassergehalt, die Wasseraufnahmefahigkeit, die Korngrosenverteilung, die Konsistenzgrenzen sowie die spezifische Oberflache. Hieraus lassen sich indirekt Aussagen uber Durchlassigkeit, Ruckhaltevermogen und Standfestigkeit der Geologischen Barriere ableiten oder aber direkt in entsprechenden Versuchsapparaturen wie Durchlassigkeits- und Diffusionszellen bzw. Kompressions- und Schergeraten bestimmen.

Barriereeigenschaften von Tonen

Der Entsorgungsstandard fur die Bundesrepublik Deutschland wird durch die Verwaltungsvorschriften zum Abfallgesetz festgelegt. Dabei wird der Teil 1 der Zweiten Allgemeinen Verwaltungsvorschrift zum Abfallgesetz vom 10. April 1990, einschlieslich der Allgemeinen Verwaltungsvorschrift zur Anderung dieser Vorschrift vom 17. Dezember 1990, kurz TA Abfall genannt oder auch als TA Sonderabfall bezeichnet. Teil 2 der Dritten Allgemeinen Verwaltungsvorschrift zum Abfallgesetz vom 14. Mai 1993 wird als TA Siedlungsabfall bezeichnet.