Undesirable adsorption of asphaltenes on rock minerals was studied. Asphaltenes are an important component of crude oil, being also natural surfactant stabilising water/crude oil emulsions. Owing to their chemical nature, asphaltenes are able to associate, form micelles and create a surface charge at the interface. Asphaltenes may be adsorbed on rock reservoir from the organic solvents in crude oil and as an organic colloid, they can adsorb electrolyte ions from aqueous solution. In order to simulate natural conditions we used asphaltenes from local drills, toluene as solvent and several typical oxides and carbonate rock components or minerals as adsorbents. Our study included natural Brazilian quartz, dolomite, calcite and kaolin, as well as pure oxides: Fe 2 O 3 and TiO 2 . The typical shape of asphaltene adsorption isotherms was obtained for all systems studied with the characteristic 'steps' which indicate changes in the state of asphaltene molecules in the solution and at the mineral surface. Those changes are related to the asphaltene association and further formation of hemimicelles and micelles.

Adsorption of asphaltenes on soils is one of the important problems, though largely underestimated, in environment protection of Lublin region. Asphaltene adsorption properties affect the way the contamination spreads in soil. Analysis of this phenomenon may help in localisation and elimination of oil spills. The asphaltenes studied were obtained from local drills (Ś widnik near Lublin, Poland). In our previous paper, we investigated adsorption of asphaltenes from toluene on rock components (quartz, dolomite, calcite, kaolin as well as pure iron and titanium oxides). In order to simulate the natural oil spill conditions, we used toluene as solvent and typical soils from Lublin region as adsorbents (black earth, peat soil, lessive soil, brown soil, sandy podsolised soil, pararendzina soil). Main physicochemical properties of these soils were reported. Moreover, basic adsorption properties (nitrogen adsorption, adsorption of surfactants from water solutions, acidity, etc.) of several soil fraction were studied. We decided to use only certain mineral fractions with highest adsorption capacity, as other fractions have limited impact on total adsorption. Adsorption on soil fraction gives also some insight into relative importance of various soil components on summary soil properties. The results of adsorption measurements are described in terms of physical adsorption on heterogeneous solids. # 2002 Published by Elsevier Science B.V.

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Ascorbic acid (AA, H 2 A) can be solubilized up to 60% by weight into a microemulsion formed by water, pentanol, and sodium dodecylsulfate (SDS). Addition of AA to the aqueous solution caused systematic reduction of the microemulsion region in the phase diagrams of the system. Ascorbic anion interacts with dodecylsulfate association structures changing W=O microemulsions towards O=W systems. The polar part of AA is exposed to the aqueous solution and subject to oxidation. The results of kinetic determination of AA decomposition are in accordance with a suggested model. They show enhanced oxidation of AA with increasing pentanol concentration in the system. The system aqueous AA solution=SDS, of concentration in excess of critical micellization concentration (cmc), was found to be more resistant to oxidation in air than aqueous AA solution. This was confirmed by electrochemistry studies of the anodic oxidation of AA on glassy carbon electrode. Sodium dodecylsulfate shifted the AA oxidation potential E pa to more positive values and decreased the peak current I pa . Antioxidation activity of AA was diminished in the presence of SDS micelles.

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In aqueous acid (pH <4) solutions, in the dark, and in the absence of reductants, arenediazonium ions, ArN 2 + decompose spontaneously through the rate-limiting formation of the extremely unstable aryl cation that reacts with any nucleophile present in its solvation shell (D N + A N mechanism). However, in weak acidic and alkaline solutions, + to determine, for the first time, the equilibrium constants K R of formation of 4-substituted X-ArN 2 OH (X¼H, Me, MeO, Br, and NO 2 ), which can decompose in several ways including Z-E isomerization or further reaction with OH À to give diazoate ArN 2 O À . The technique applied was differential pulse polarography, which is very selective and sensitive. The determined pK R values are 5-6, and they are somewhat higher than those obtained for the reaction of ArN 2 + with alcohols ROH (pK DE = 3-5) under similar acidic conditions. The K R values are not very sensitive to changes in the nature of the substituent in the aromatic ring and a linear Hammett plot with a slope of ρ = 0.58 was obtained.