Aluminosilicates levels

Sorption processes are influenced not just by the natures of the absorbate ion(s) and the mineral surface, but also by the solution pH and the concentrations of the various components in the solution. Even apparently simple absorption reactions may involve a series of chemical equilibria, especially in natural systems. Thus in only a comparatively small number of cases has an understanding been achieved of either the precise chemical form(s) of the adsorbed species or of the exact nature of the adsorption sites. The difficulties of such characterization arise from (i) the number of sites for adsorption on the mineral surface that are present because of the isomorphous substitutions and structural defects that commonly occur in aluminosilicate minerals, and (ii) the difference in the chemistry of solutions in contact with a solid surface as compound to bulk solution. Much of our present understanding is derived from experiments using spectroscopic techniques which are able to produce information at the molecular level. Although individual methods may often be applicable to only special situations, significant advances in our knowledge have been made... 

In a typical aluminosilicate zeolite synthesis, sodium aluminate is dissolved in water along with some fraction of the additional sodium hydroxide that is needed in the reactant mixture. Separately, sodium siHcate is mixed with the remainder of the sodium hydroxide. The two solutions are combined using the required mix order and agitation level, resulting in the initial zeolite gel. In some cases this initial gel is aged at an intermediate temperature for a time to allow evolution of... 

The concept zeolites conventionally served as the synonym for aluminosilicates with microporous host lattice structures. Upon removal of the guest water, zeolites demonstrate adsorptive property at the molecular level as a result they are also referred to as molecular sieves. Crystalline zeosils, AlPO s, SAPO s, MAPO s (M=metal), expanded clay minerals and Werner compounds are also able to adsorb molecules vitally on reproval of any of the guest species they occlude and play an Important role in fields such as separation and catalysis (ref. 1). Inclusion compounds are another kind of crystalline materials with open framework structures. The guest molecules in an inclusion compound are believed to be indispensable to sustaining the framework structure their removal from the host lattice usually results in collapse of the host into a more compact crystal structure or even into an amorphous structure. 

Comparisons with Ambient Fine Particles. Above we noted a potential problem of using EFj.j-ust values to determine possible coal contributions to ambient levels of various elements, namely that large, aluminosilicate particles might preferentially settle out of the atmosphere between the source and receptor. Here we have tried to avoid that problem by calculating values only for fine particles from several cities and from coal-fired power plants as shown In Table V. Again, fine particles are those with dlam <2.5 ym. The EFs for coal In Table V are taken from Col. 4 of Table IV. 

Zeolites, which are aluminosilicates that can be regarded as being derived from AI2O3 and SiC>2, function as acidic catalysts in much the same way (Section 7.3). In addition, they catalyze isomerization, cracking, alkylation, and other organic reactions. A structurally related class of micro-porous materials based on aluminum phosphate (AIPO4) has also been developed (Section 7.7) like zeolites, they have cavities and channels at the molecular level and can function as shape-selective catalysts. 

It is believed that, when steaming the gel at high temperatures, the V0+i attacks and breaks the Si-O-Al bonds promoting mullite formation and the collapse of the gel macroporous structure (3). The XRD pattern in Fig. 2B shows that mullite formation in the gel can be observed with only 1.5% V and when this occurs, there is a 81% decrease in surface area, Table 1. Mullite level increased with V-loadings, see Fig. 2. Data in the literature (20) indicates that when the steaming temperature is decreased to 730 C from 760 C (as in the present work) gel stability to V improved and only a 23% reduction in surface area was observed in a similar gel loaded with 1.5% V. Aluminosilicate gels are clearly less resistant than aluminas to V attack at hydrothermal conditions, Table 1. 

The LRS of similarly prepared V-loaded aluminosilicate gels (AAA-aluminas) are shown in Fig. 4 band positions are listed in Table 3. These spectra are essentially featureless for V concentrations below the 1%V level, Fig.4. For loadings in the 1.0 to 3.0% V range, relatively intense bands near 517 cm"1 and 700 cm"1, together with a broad shoulder centered near 815 cm and a very weak band near 1020 cm"1 can be seen in the Raman spectra of these samples, Figs. 4B-4D. Recently, Wokaun, et. al. (25) have shown Raman spectral characteristics for SiO, supporting low V loadings which are similar to those in Fig. 4 but did not indicate whether H20 influenced their results. 

Alkaline aluminosilicate solutions aith a Si/Al ratio close to one, exist only at much loner concentrations than do silicate solutions for a given pH. This results directly from the general expression giving the activity of an oligomer. Indeed, as pH increases, the Sit OH) 4 concentration becomes very Ion nhereas the A1(0H)4 concentration remains practically constant and at a much higher level. 

Aluminum is the third most abundant element in the lithosphere, but its levels in natural waters, plants, and animals are relatively low [1], It occurs in a vast variety of oxide minerals and together with silicon forms the polymorphous aluminosilicates (Al205Si) in rocks and soils upon which all organisms depend [2]. In soils and sediments these clays have many functions they hold trace elements, permit growth of roots, sustain pH balance, and their cavities keep water available [3],... 

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