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The transport diffusivity of the paramagnetic molecule 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) was measured by monitoring its influence on the NMR transverse relaxation time (T2) on surrounding water protons - also known as paramagnetic relaxation enhancement (PRE). Due to the nature of the PRE effect, few paramagnetic molecules are able to simultaneously reduce the T2 of many NMR active nuclei, which represents a significant gain in sensitivity. In an aqueous solution, the minimal detectable TEMPO concentration was around 70 ppm. The value of the diffusivity was estimated by fitting the relaxation data, collected as a function of time, with the appropriate solutions of the second Fick’s law in respect to the corresponding sample geometry and dimensions. Considering the experimentally determined TEMPO relaxivity in water (“TEMPO-water relaxivity”; RTEMPO = (1.05 ± 0.12) × 10–3 ppm–1 s–1), the obtained diffusion coefficients (D) of TEMPO in homogeneous solution and in a water saturated sand column (Dbulk = (6.7 ± 0.4) × 10–10 m2 s–1 and Dsand = (1.4 ± 0.5) × 10–10 m2 s–1, respectively) are in good agreement with the expected values (literature values: Dbulk = 6.6 × 10–10 m2 s–1, 1.3 × 10–10 m2 s–1 < Dsand < 2.3 × 10–10 m2 s–1). This new approach enables one to determine the diffusivity of paramagnetic molecules in homogeneous (aqueous solution) and porous media with basic NMR equipment, at low concentrations and in a noninvasive manner.

Using a novel NMR option, magic angle spinning pulsed field gradient (MAS PFG) NMR, the mobility of aliphatic domains in humic substances in the presence of toluene (about 4.5 wt. %) has been monitored. Results show a strong correlation between the diffusivities of the mobile aliphatic chains and those of the adsorbed toluene molecules in the matrix as a function of temperature. Particularly, a strong influence of structural relaxation of the humic matrix on the diffusivity of toluene is observed. Our findings confirm that the aliphatic domains in humic substances play an important role in the mobility of sorbed contaminants within this matrix. These findings further confirm the potential of MAS PFG NMR method in monitoring diffusion processes in particulate humic substances.

Thermodesorption studies with soil samples from a former filling station for light crude oil contaminated with mineral oil hydrocarbons (mainly benzene, toluene, ethylbenzene, xylenes, naphthalene, alkylnaphthalenes, and C10 to C14 alkanes) have revealed an ambivalent influence of water on desorption rates. Particularly, the influences of soil moisture content, humidity of the purge gas, temperature, and content of soil organic matter (SOM) were studied. At low temperature, purge gas humidity strongly affected the mobility of hydrocarbons in the soil organic matter (SOM) leading to an enhanced release of contaminants at higher moisture contents. Heating resulted in a decrease of thermodesorption when connected with desiccation of soil, in spite of the strong temperature impact on the vapor pressure of contaminants. At high water content of the SOM, the transfer of the pollutant molecules into the gas phase was found to be markedly hindered by the formation of water films or pore-filling by bulk water, both acting as diffusion barriers.

Pulsed field gradient NMR is applied for monitoring the diffusion properties of guest molecules in hierarchical pore systems after pressure variation in the external atmosphere. Following previous studies with purely mesoporous solids, also in the material containing both micro- and mesopores (activated carbon MA2), the diffusivity of the guest molecules (cyclohexane) is found to be most decisively determined by the sample "history": at a given external pressure, diffusivities are always found to be larger if they are measured after pressure decrease (i.e., on the "desorption" branch) rather than after pressure increase (adsorption branch). Simple model consideration reproduces the order of magnitude of the measured diffusivities as well as the tendencies in their relation to each other and their concentration dependence.

Thermal desorption of a wide spectrum of organic contaminants, initiated by radio frequency (RF) heating, was studied at laboratory and pilot-plant scales for an artificially contaminated soil and for an originally contaminated soil from an industrial site. Up to 100 °C, moderate desorption rates were observed for light aromatics such as toluene, chlorobenzene, and ethylbenzene. Desorption of the less volatile contaminants was greatly enhanced above 100 °C, when fast evaporation of soil-water produced steam for hydrocarbon stripping (steam-distillation, desorption rates increased by more than 1 order of magnitude). For hydrocarbons with low water solubility (e.g., aliphatic hydrocarbons), the temperature increase above 100 °C after desiccation of soil again led to a significant increase of the removal rates, thus showing the impact of hydrocarbon partial pressure. RF heating was shown to be an appropriate option for thermally enhanced soil vapor extraction, leading to efficient cleaning of contaminated soils.

A new NMR option for monitoring the mobility of organic contaminants in SOM in the solid state has been successfully applied for the first time. This recently available noninvasive technique, magic angle spinning pulsed-field gradient (MAS PFG) NMR, combines both NMR spectroscopy and diffusometry to selectively monitor the diffusion of compounds sorbed in porous media or polymer matrices. Using this technique, the diffusion of toluene in humic acid particles has been studied. Measurements were performed under varying temperatures from 25 to 80 °C. The obtained diffusion coefficients were found to be in good agreement with those obtained from computer simulations reported elsewhere. Our results show a strong influence of the interaction of toluene with humic acid on its diffusion in the matrix even at elevated temperatures of up to 80 °C. The Arrhenius plot of the diffusivities shows a decrease in the activation energy of diffusion above 50 °C by a factor of 3. This change of activation energy is attributed to a structural change in the humic acid matrix that influences the mobility of toluene.

Dielectric heating of soil using radio waves (RW) can be applied to support various remediation techniques, namely biodegradation and soil vapor extraction, under in situ, on site or ex situ conditions. To improve the spatial resolution of energy dissipation, the design of rod electrodes was modified with an air gap around the electrode allowing thermal treatment focused to the desired soil volume. A combination of low- and high-frequency electrical energy was successfully applied to homogeneously heat the capillary fringe, the boundary region of saturated and unsaturated zones. The energetic efficiency of the method was evaluated showing that an efficient transformation of RW energy to heat in the target volume can be achieved. By comparing biodegradation and soil respiration under conventional and electric (low-frequency resistive and dielectric RW) heating, the compatibility of the electric heating methods with bioremediation processes could be proven. Therefore, RW-supported microbial degradation of pollutants is a real option for accelerated soil remediation.

After developing the radio-wave technique for various conditions in laboratory-scale and technical plant-scale experiments, field tests in combination with biodegradation and soil vapor extraction were carried out at three sites: (i) a bioremediation facility for ex situ cleaning of soil, (ii) in situ remediation of contamination at a former storage facility for organic solvents, and (iii) a polluted soil under a former petrol station. Various electrode arrangements such as parallel plates, rod arrays, and coaxial antenna were applied in order to meet the site-specific requirements optimally. Soil temperatures between 35 and 100 °C were established. The successful tests gave much insight into the engineering, physical, biological, and chemical aspects of radio-wave application. General conclusions on the appropriateness and competitiveness of the radio-wave method as well as on preferred application fields are drawn.

The surface energy of thermal and furnace carbon blacks was determined by inverse gas chromatography (IGC) at infinite dilution. In general, the specific surface energy decreases with decreasing carbon black specific surface area. However, there is also an influence of the concentration of impurities during the carbon black production. The surface energy decreases with decreasing concentration of impurities. The carbon black surface and bulk chemistry was studied by electron spectroscopy for chemical analysis (ESCA), secondary ion mass spectroscopy (SIMS) and Raman spectroscopy. Scanning tunnelling microscopy (STM) was used for characterization of the surface morphology. Thermal grades of carbon black produced from high purity natural gas feedstock do not contain fewer surface functional groups than the other grades. No correlation between the concentration and nature of the oxygen and sulphur surface groups and the carbon black surface energy was found. Instead, a correlation between the surface energy and the polyaromatic character of the carbon black surface exists. Both increased in the order: thermal blacks from high purity natural gas feedstock < thermal black from oil feedstock < furnace blacks. The increase of the surface energy might be related to the formation of active sites which are formed upon removal of non-carbon elements during the carbon black formation. There was no principal difference in the surface morphology of thermal blacks from high purity gas feedstock and other blacks.