Clays adsorption characteristics

Sorption on oxides and hydrous oxides has been extensively studied both experimentally and theoretically. In order to define an ideal oxide or hydrous oxide exchanger, we will rely on experiments with well-defined sorbents such as chromatographic alumina (1-4). Briefly, the adsorption characteristics of oxides and hydrous oxides are (1) At high pH, they act as cation exchangers but with less sensitivity to the total salt concentration than clay minerals. This behavior is illustrated in Figure 2, where sorption of strontium on alumina is shown. 

The X-ray diffraction patterns for the sand and silt fractions had a nearly identical predominance of quartz and feldspar peaks. The "clay" fraction, however, showed X-ray peaks from quartz and feldspars as well as for chlorite/montmorillonite. Our use of the silt fraction in the following adsorption experiments is supported by the similarity in composition (i.e., mostly quartz and feldspars and no clays) between the silt and sand fractions. The silt fraction, more easily suspended than sand, was an indicator of the adsorption characteristics that might logically be expected of the sand fraction as well. 

Performance improvement in 1102 is achieved by doping the titania with platinum or vanadium oxide and copper. In order to improve the adsorption characteristics of Ti02, attempts have been made to support fine Ti02 on the porous adsorbent materials such as silica, alumina, activated carbon, clay, and zeolites. Ti02-supported adsorbent provides higher specific surface area and introduces more effective adsorption sites than bare Ti02. Decomposition rates of the substrates are found to increase due to one or... 

McBride, M. B. (1982). Cu-+-adsorption characteristics of aluminum hydroxide and oxyhydroxides. Clays Clay Miner. 30, 21-28. 

Petroleum (16). Where applicable, samples are distilled and the 200°C+ fraction retained, spiked with 14C BaA and BaP, and analyzed for PNA content. Samples are first separated on Attapulgus clay to remove the very polar heteroatom portion of the sample. The Attapulgus clay was purchased from the National Bureau of Standards to have adsorptive characteristics as specified in ASTM D 2007. The column, 760 mm X 22 mm, is fitted with a 500-mL reservoir and a Teflon stopcock 170 g of clay is placed in the column and prewet with 50 mL of n-pentane. A 15- to 20-g sample, dissolved in 100 mL of pentane, is placed on the column. The sample is then successively eluted with 600 mL of n-pentane and 500 mL of acetone. The entire separation is carried out in a blanket of nitrogen. Each fraction is carefully evaporated on a steam bath under nitrogen until a constant weight is obtained. 

In the classical diffusion theory the adsorption term of bentonite is commonly treated by the distribution factor K. Instead of this macroscopic phenomenological treatment we propose a microscale HA procedure which exactly represents the edge adsorption characteristics at the edges of clay minerals. 

In the present study, we show an example of the application of this experimental methodology to the investigation of adsorption characteristic of local bentonite clay. Adsorption / desorption experiment were performed at laboratory scale with model-contaminated gaseous stream containing o-xylene that has been selected as rep resentative VOC because it is environmentally relevant regarding industrial concern. The work aimed to help further development of low cost materials involved in environmental engineering control. 

Cool et al. (80,81) performed a templated synthesis of Zr-pillared laponite using ethylenediamine in an amount exceeding the CEC of laponite. Here, the amines not only have a positive influence on the pillar distribution, but also favor the parallel orientation of the clay sheets, resulting in a more homogeneously pillared structure with increased microporosity. Thus, on laponite, the main function of the template is not to block exchange sites, but to influence the stacking of clay layers. The porosity and adsorption characteristics of the different pillared clays are summarized in Table 6. 

Table 6 Porosity and Adsorption Characteristics (N2 and O2 at 273 K on Al- and Zr-PILC and at 194 K on Fe-PILC) of Pillared Clays, Prepared Without and With Templates...

Clays.—The adsorption properties of clays have been extensively studied in the past and the situation up to 1976 is dealt with in van Olphen s book. A major feature of recent work has been the study of the effect on their adsorption characteristics of modification of clays by exchangeable organic cations. The earlier work of Dekany and his collaborators, outlined in a previous Report (Vol. 3, p. 147) and a publication in Hungarian, has been continued. They have been concerned mainly with the adsorption of benzene + alkane and benzene + alcohol mixtures on montmorillonites and kaolinites treated to varying extents with hexadecylpyridinium chloride (HDPCl) to form HDP-complexes of known HDP-content and having a partially organophilic surface. 

For all processes that involve the adsorption step, such as physical processes of separation or catalytic transformations, the usage of solid materials with optimised activity as adsorbents and catalysts is necessary. Various solids, such as porous materials (zeolites—molecular sieves with hierarchical porosities and natural clays), activated carbons, mesoporous silica-based materials, pillared clays and metal oxides, have shown the ability to act as adsorbents or as catalysts for the conversions of previously mentioned atmospheric pollutants. Solid materials are also used for the removal of pollutants that can be found in wastewaters. The possibilities to remove polyaromatic hydrocarbons (PAHs) and heavy metal particles using the adsorptive characteristics of activated carbon and porous materials from wastewaters have been proven [15-17]. The same classes of solids are used for the elimination of organic pollutants form wastewaters by heterogeneous catalytic oxidation processes one of the most important tasks is to eliminate phenolic compounds [13]. 

Clay Adsorbent, 500 to 250 pm (30 to 60 mesh) Attapulgus. Oay quality may be determined using the azobenzene equivalence test shown in Annex Al. The azobenzene activity test measures the adsorptive characteristics of the clay. Azobenzene equivalence value should be 30 to 35. Clay outside of these limits should be discarded. 

An additional important characteristic of clays is their surfaces, which are distinguished as being either external or internal. Internal surfaces occur, for example, in nonexpanding 2 1 clays, such as the fine-grained micas, and are generally not available for adsorption, chemical, or exchange reactions. 

Of the various equilibrium and non-equilibrium sorption isotherms or sorption characteristics models, the most popular are the Langmuir and Freundlich models. The correct modeling of an adsorbate undergoing both transport and adsorption through a clay soil-solid system necessitates the selection of an adsorption isotherm or characteristic model which best suits the given system. The use of an improper or inappropriate adsorption model will greatly affect the... 

Nonionic surfactants, as mentioned previously, have been widely adopted due to their characteristics and properties and, in particular, because they do not require the presence of undesirable phosphate or caustic builders in detergent formulation. However, the relatively lesser degree of biodegradability is an important disadvantage of the nonionic surfactants compared to the ionic ones. Adsorption on activated carbon and various types of clay particles is, therefore, one of the processes that has been effective in removing heterodisperse nonionic... 

Liu, Z., S.A. Clay, D.E. Clay, and S.S. Harper (1995). Ammonia fertilizer influences atrazine adsorption-desorption characteristics. J. Agric. Food Chem., 43 815-819. 

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