A generalized procedure for determining thermal resistivity of soils

Estimation of thermal resistivity of soils is very important for various engineering projects. Many researchers have demonstrated that, soil thermal resistivity is a property of the soil that depends on various parameters such as type of soil, particle size distribution, and compaction characteristics and hence its estimation based on existing empirical and mathematical models is difficult. This calls for fabrication of a device that can be used for determining soil thermal resistivity directly. Usually, small size, laboratory thermal resistivity probes have been used for this purpose and their efficiency in measuring soil thermal resistivity has already been established. However, as natural soils consist of various size fractions, ranging from clay to gravel, the laboratory thermal probes cannot be used very efficiently. This necessitates fabrication of a field thermal probe that can be used to measure thermal resistivity of a soil either in its remolded state or under in situ conditions. With this in view, efforts were made to develop a field thermal probe, which works on the principle of transient method and is a magnified version of the laboratory thermal probe developed by the authors. Based on the results obtained efforts have been made to develop generalized relationships for estimating the soil thermal resistivity by knowing the dry density, moisture content and percent size fraction of the various particle sizes, and validation of the proposed generalized equations have been done with the results available in the literature.© Elsevie

Determination of distribution coefficient of geomaterials and immobilizing agents

Les caracteristiques de sorption et de desorption des geomateriaux (sols et roches) et des agents immobilisants gerent la destinee et le transport de contaminant(s) reactif(s) dans les geomateriaux, ainsi que l'efficacite des methodes d'immobilisation et de rehabilitation des geomateriaux contamines. Pour cette raison, il est necessaire d'etablir les caracteristiques de sorption et de desorption de ces materiaux. Generalement, des essais par lots sont effectues et les coefficients de distribution sont obtenus a partir des isothermes de Freudlinch, lineaires et de Langmuir. Cependant, l'efficacite relative de ces isothermes doit etre evaluee afin de bien selectionner le coefficient de distribution pour un systeme contaminant geomateriau - agent immobilisant. Pour ce faire, des essais par lots conventionnels ont ete realises sur differents geomateriaux et agents immobilisants dans le but d'etablir leurs caracteristiques de sorption et de desorption. Par contre, les essais par lots ne representent pas l'interaction re[]elle entre le contaminant, le geomateriau et l'agent immobilisant et sont plutot difficiles et longs. Dans ces circonstances, une methode alternative possible est de correler les caracteristiques de sorption et de desorption de ces materiaux avec la conductivite electrique de leurs solutions. L'utilisation de ce concept pour modeliser des cas reels d'interaction contaminant geomateriau - agent immobilisant a ete bien demontree dans cette etude

Phosphate Adsorption from Aqueous Solutions onto Goethite, Bentonite, and Bentonite-Goethite System

The present paper examines the phosphate adsorption from aqueous solutions onto goethite, bentonite, and bentonite-goethite system. The properties of the materials were studied by X-ray diffraction (XRD), attenuated total reflectance (ATR), and NMR spectra and by the measurement of the specific surface area, the point of zero charge (p.z.c.) and the pore-specific volume. ATR and NMR spectra of bentonite and bentonite-goethite system show peaks which correspond to tetrahedrally and octahedrally coordinated Al. The specific surface area of the system differs according to the appropriate method used, while system's p.z.c. is higher than bentonite and lower than goethite. The pore-specific volume of bentonite-goethite system is higher than that of bentonite or goethite. According to XRD spectrum of bentonite-goethite system, goethite coats the (001) spacing of bentonite while the coating of (010) plane of bentonite is limited. The crystallinity of the system decreases and the negative permanent charge increases. Phosphate adsorption experiments took place at different pH (3.8-9.0) and concentrations (40.3-443.5 mu mol L-1) and constant capacitance model was applied to describe adsorption. A ligand exchange mechanism characterizes the model because the charge is divided among adsorbate and adsorbent. The constant capacitance model describes the adsorption mechanism in all examined pH. This model can be utilized in such systems using the surface protonation-dissociation constant of goethite and showing the exact shape of the adsorption isotherms for different pH values. The produced low-cost bentonite-goethite system presents the highest adsorption of P per kilogram of goethite