Components, rocks, soil oxides

Specific adsorption on well defined materials has been the subject of many reviews [8-13]. Specific adsorption plays a key role in transport of nutrients and contaminants in the natural environment, and many studies with natural, complex, and ill defined materials have been carried out. Specific adsorption of ions by soils and other materials was reviewed by Barrow [14,15]. The components of complex mineral assemblies can differ in specific surface area and in affinity to certain solutes by many orders of magnitude. For example, in soils and rocks, (hydr)oxides of Fe(IH) and Mn(IV) are the main scavengers of metal cations and certain anions, even when their concentration expressed as mass fraction is very low. Traces of Ti02 present as impurities are responsible for the enhanced uptake of U by some natural kaolinites. In general, complex materials whose chemical composition seems very similar can substantially differ in their sorption properties due to different nature and concentration of impurities , which are dispersed in a relatively inert matrix, and which play a crucial role in the sorption process. In this respect the significance of parameters characterizing overall sorption properties of complex materials is limited. On the other hand the assessment of the contributions of particular components of a complex material to the overall sorption properties would be very tedious. 

Silicon and aluminum oxides and hydroxides are the most abundant compounds on our earth. They exist in rock, soil, the dust we breathe, and as components or trace components in just about all we touch or consume. Over decades, they have made their appearance in a number of segments of medicine such as fibrotic diseases, tumor induction, Alzheimer s disease, and aluminum related bone diseases. Of these Alzheimer s disease is perhaps one of the most serious diseases in our society. Here a still mysterious role of "aluminum" is observed and acknowledged by many researchers. 

Smectite is the first secondary mineral to form upon rock weathering in the semi-arid to sub-humid tropics. Smectite clay retains most of the ions, notably Ca2+ and Mg2+, released from weathering primary silicates. Iron, present as Fe2+ in primary minerals, is preserved in the smectite crystal lattice as Fe3+. The smectites become unstable as weathering proceeds and basic cations and silica are removed by leaching. Fe3+-compounds however remain in the soil, lending it a reddish color aluminum is retained in kaolinite and A1-oxides. Leached soil components accumulate at poorly drained, lower terrain positions where they precipitate and form new smectitic clays that remain stable as long as the pH is above neutral. Additional circumstances for the dominance of clays are ... 

If sediment was collected from a particular waterway, the distribution of the element of interest between different components of the sediment was found to vary with the degree of exposure to air and the temperature of any drying stages (Rapin et al., 1986 Kersten and Foerstner, 1986). The minor elements present in sediments (and soils) are not uniformly distributed. Part can be present as mineral fragments derived from the original parent rock, while other parts can be associated with distinct component phases such as carbonate compounds, hydrous oxides of Fe, Al, Mn and organic matter. Some fractions are loosely sorbed on particle surfaces or are held on ion exchange sites. 

As a result of the interfacial processes on rocks and soils, the structure and chemical bonds of the sorbed compounds can be changed. For this reason, different chemical reactions can be initiated in which the components of rocks or soils act as catalysts. The most important mineral catalysts are zeolites and clay minerals. Naturally, the different oxides also have catalytic effects, and nowadays some of them are being artificially produced for catalytic purposes such as framework silicates (zeolites), the most effective and selective catalysts in organic syntheses. The catalytic applications of zeolites are too wide to summarize in this book, so we deal with the catalytic effects of clay minerals. 

Silicon dioxide is the main component of the crust of the earth. Combined with the oxides of magnesium, aluminum, calcium, and iron, it forms the silicate minerals in our rocks and soil. 

Oxides, especially those of Al, Si, Fe, and Mg, are essential components of the earth s minerals their surface sites may have either Bronsted or Lewis acid-base properties. The weathering of rocks and the formation of soils are processes at the solid/liquid interface between minerals and natural waters or solutes from the medium in which solid phases are either formed, altered, or dissolved. Dissolution of solid minerals is controlled by slow surface reactions rather than... 

Some components, for example, Fe(II), are oxidized by air to Fe(lll). Water will dissolve the chemical substances in rocks. The presence of carbon dioxide usually helps dissolution process, because it makes water acidic. The fragmented and/or dissolved material may be redeposited on land, which forms soil. The fragmented and dissolved material may be carried to the ocean and eventually deposited and compacted at the bottom, which forms sedimentary rocks. 

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