Crustal abundance

Elements Crustal Abundance Mean in Oregon Rock Types Western Surface Soils Total Recoverable uses Mean DEO Max ... 

Phosphorus is the tenth most abundant element on Earth with an average crustal abundance of 0.1% and may be found in a wide variety of mineral phases. There are approximately 300 naturally occurring minerals in which PO4 is a required structural component. Phosphate may also be present as a trace component in many minerals either by the substitution of small quantities of POt into the crystal structure or by the adsorption of P04 onto the mineral surface (Nriagu and Moore, 1984 Slansky, 1986). 

The extraction of metals fundamentally relies on their availability in nature. Three terms are important while one refers to availability. One is the crustal abundance and the other two are the terms resources and reserves. The average crustal abundance of the most abundant metals, aluminum, iron and magnesium, are 8.1%, 5.0% and 2.1% respectively. Among the rare metals titanium is the most abundant, constituting 0.53% of the Earth s crust No metal can be economically extracted from a source in which its concentration is the same... 

All ore mineral deposits lie in or on solid rocks of which the Earth s crust is predominantly composed. The geological processes which are responsible for the formation of rocks also form the ore bodies associated with them. For the formation of an ore body, the metal or metals concerned must be enriched to a considerably higher level than their normal crustal abundance. The degree of such enrichment below which the extraction cost makes the processing of the ore uneconomical is termed the concentration factor. Typical values of the concentration factor for some of the common metals are given in Table 1.5. 

Metals Average crustal abundance (%) Average minimum exploitable grade Concentration factor... 

The average crustal abundance of molybdenum is 1 to 2 parts per million. It occurs most readily in conjunction with silica - as the silica content in the igneous rocks goes up, so does the quantity of molybdenum. It is sometimes also found associated with uranium, as well as with coals and petroleum residues. In its host rock, molybdenum tends to occur in thin, tabular, and hexagonal plate forms, or simply as fine specks. 

Uranium is not a very rare element. It is widely disseminated in nature with estimates of its average abundance in the Earth s crust varying from 2 to 4 ppm, close to that of molybdenum, tungsten, arsenic, and beryllium, but richer than such metals as bismuth, cadmium, mercury, and silver its crustal abundance is 2.7 ppm. The economically usable tenor of uranium ore deposits is about 0.2%, and hence the concentration factor needed to form economic ore deposits is about 750. In contrast, the enrichment factors needed to form usable ore deposits of common metals such as lead and chromium are as high as 3125 and 1750, respectively. 

Silver is usually found in extremely low concentrations in natural waters because of its low crustal abundance and low mobility in water (USEPA 1980). One of the highest silver concentrations recorded in freshwater (38 pg/L) occurred in the Colorado River at Loma, Colorado, downstream of an abandoned gold-copper-silver mine, an oil shale extraction plant, a gasoline and coke refinery, and a uranium processing facility (USEPA 1980). The maximum recorded value of silver in tapwater in the United States was 26 pg/L — significantly higher than finished water from the treatment plant (maximum of 5.0 pg/L) — because of the use of tin-silver solders for joining copper pipes in the home, office, or factory (USEPA 1980). 

Multi-Element Analytical Scheme The 76 elements analyzed include 39 elements originally analyzed in the RGNR Projects, and 37 new elements. The analytical scheme is based largely on ICPMS, ICPAES and XRF, supplemented with other techniques (Table 1). The lower levels of detection of all elements are less than their crustal abundances (Table 2). 

Schematic depth ocean profiles for elements. This figure is based on a classification of elements according to their oceanic profiles given by Whitfield and Turner (1987). Uptake of some of the elements, especially the recycled ones, occurs somewhat analogously as that of nutrients. There are some elements such as Cd that are non-essential but may be taken up (perhaps because they mimick essential elements) the same way as nutrients. The concentration ranges given show significant overlap, since the concentrations of the elements also depend on crustal abundance.

Relationship between the trace elemental composition of phytoplankton, continental crust and seawater. Phytoplankton and crustal abundances are normalized to phosphorus (ppm trace metal ppm P). Seawater trace elements abundances are normalized to phosphate (ppb trace metal ppb P as phosphate). Source-. From Quigg, A., et al. (2003). Nature 425, 291-294. 

Figure 1. Enrichment factors with respect to crustal abundances (39) for elements attached to urban aerosols from (9) Washington, D.C. (16), (O) Tucson, AZ f40j, (y,) St. Louis, MO (based on data from Loo et al. (41)),(A) Charleston, WV (42), (Ls) Portland, OR (21), and fB) Boston, MA (3,43). See Table IV, Footnote a...

Iron was chosen as the reference element because its major source is likely to be soil and it is measured with good accuracy and precision by FIXE. Crustal abundances were taken from Mason (21). Enrichment factors greater than 1 indicate an enrichment of that element relative to crustal abundances values less than 1 indicate a depletion. The results of this calculation are shown in Table 4. For this calculation it was assumed that ammonium and nitrate accounted for all aerosol nitrogen. It is seen that Si and Ca are near their crustal abundance, indicating a probable soil dust source. The low EF for Al is probably due to a systematic error in the Al measurement rather than a true depletion. Potassium, although present in small concentrations, is slightly enriched relative to crust. The other fine aerosol species, C, N, S, and Pb are enriched by factors of thousands over their natural crustal abundance, indicating that they are not due to wind-blown dust. 

The results presented a variety of evidence for the identity of Ca sources near our rural sampling site. The distribution of mean crustal element concentrations as a function of wind direction in summer and fall, from the streaker data, suggest a combination of road and soil sources. This agrees with a comparison of crustal abundances in aerosols and source materials. The comparison showed that most of the elements examined had abundances in the aerosol that often fell between those characteristic of roads and soil. This was not the case for Si, but Si may be expected to be less abundant in aerosol samples than in bulk surficial materials because of the preponderance of quartz (Si02) in the larger particles. 

Iodine is concentrated in humans by the thyroid gland to form the iodo-amino acid thyroxine, which is essential to normal health and development. Iodine is a rather rare element (crustal abundance 0.00003 weight %, cf. Table 1.1), so the thyroid gland has become very efficient at scavenging iodide ion. As iodine is deficient in the diet in some locations, a small amount of iodide ion is routinely added to commercial table salt ( iodized salt ). 

When the data for vanadium, nickel, cobalt, copper, and iron in petroleum of the Western Interior Region (15) shown below are divided by the average crustal abundance of these elements, the relation, V>Ni>Co>Cu>Fe is... 

As reported by Olmez and Gordon (University of Maryland), the concentration pattern of rare earth elements on fine airborne particles (less than 2.5 micrometers in diameter) is distorted from the crustal abundance pattern in areas influenced by emissions from oil-fired plants and refineries. The ratio of lanthanum (La) to samarium (Sm) is often greater than 20 (crustal ratio is less than 6). The unusual pattern apparently results from tlie distribution of rare earths in zeolite catalysts used in refining oil. Oil industry emissions have been found to perturb the rare earth pattern even in very remote locations, such as the Mauna Loa Observatory in Hawaii. 

Cs are more depleted in western coals. Silicon is also depleted in coal, probably because of the presence of clay minerals. Most lithophile elements (i.e., those normally associated with the earth s crust) have EF values near one, but it is interesting that the rare earth elements show slightly, but consistently higher enrichments in eastern coal. The apparent depletion of Ta is probably not real, but an artifact resulting from Wedepohl s use of too large a crustal abundance for it (14). 

Table 1-1. Elements with a crustal abundance >0.1% (data from Emsley, 1989).

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