Metal-loaded clays

TABLE III. ATOMIC RATIO IN TWO METALS-LOADED CLAYS AND REFERENCE COMPOUNDS... 

Lazaridis, N.K., Hourzemanoglou, A. and Matis, K.A. (2002) Flotation of metal-loaded clay anion exchangers. Part II the case of arsenates. Chemosphere, 47(3), 319-24. 

Transport in solution or aqueous suspension is the major mechanism for metal movement from the land to the oceans and ultimately to burial in ocean sediments. In solution, the hydrated metal ion and inorganic and organic complexes can all account for major portions of the total metal load. Relatively pure metal ores exist in many places, and metals from these ores may enter an aquatic system as a result of weathering. For most metals a more common sequence is for a small amount of the ore to dissolve, for the metal ions to adsorb onto other particulate matter suspended in flowing water, and for the metal to be carried as part of the particulate load of a stream in this fashion. The very insoluble oxides of Fe, Si, and A1 (including clays), and particulate organic matter, are the most important solid adsorbents on which metals are "carried."... 

Aqueous ammonium heptamolybdate (Alfa, (NH4)6Mo70244H20, 99.999%) solutions were prepared so that a metal loading of 6 wt % Mo would fill 80% of the available pore volume of the mesoporous synthetic clays. Following Mo impregnation and recalcination at 400°C for 5 hr, the pore volumes were measured again using an established LN2 physisorption... 

The behaviour of landfill liners with respect to metal sorption has also been investigated by the novel technique of combined sequential extraction-sorption isotherm analysis (CSSA) (Salim et al, 1996). The study demonstrated that Pb and Ni would be effectively immobilised by the clayey calcareous sediment studied, but Cr would not. Roehl and Czurda (1998) applied a similar approach in their investigation of clay landfill liners and showed that speciation was dependent on heavy metal load, with weaker binding at higher concentrations of Cd and Pb. 

However, the activity of these metal-loaded pillared clays is more than 10 times lower that for carbon-supported catalysts (15) for both unsaturated nitriles. This loss of activity could be explained in two ways the first supposes a lower accessibility of the metallic surface in the case of the pillared clays catalyst as compared with carbon based catalysts. We may suppose some strong diffusional effect. This would indicate that, assuming a good repartition of the metal into the layers of the pillared clay, the most active accessible metallic sites would just be those near the outer edge of the clay. 

The Pd-mordenite catalysts used for NO decomposition were characterized in [lODl]. After reduction at 573 K, a large fraction of Pd particles and Pd ions were found. A sample prepared using a natural clay was found to exhibit mairdy ionic Pd. The amoimt of Pd, relative to Pd, depends on the oxidation temperature and the metal loading. Natural H-form and Pd-containing mordenite and clinoptiloUte were studied [06K1]. The initial natural adsorbents have a small specific surface area which increases significantly after modification. 

Special surface modifications are available to further improve reinforcement. The objective of the surface treatment is to increase filler loading and/or improve physical properties without loss of rheological characteristics. A variety of surface-modified kaolins have been introduced including clays treated with silane, titanate, polyester, and metal hydroxide. Silane-treated kaolin is used in applications requiring maximum aging characteristics in the service environment. 

The proposed approach is a universal method that can be applied for successful fabrication of metal-clay nanocomposites with high thermal stability, high dispersity of metal nanoparticles inside the clay matrix and catalytic activity. This work provides original insights into the production of layered naiocomjwsites loaded with inorganic nanoparticles. The ultrasonic treatment accelerates the incorporation process. The Au nanoparticle /clay nanocomposites can be useful for creation of different devices such as nanocondenser systems, sensors, optoelectronic elements. 

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