Crustal enrichment factors

From Milford and Davidson (1985). b Calculated crustal enrichment factors. 

Table 7.3 Crustal enrichment factors for elements from various locations using aluminium as the reference element (crustal composition data from Taylor and McLennon, 1985)...

Measurement of Cd in the atmosphere and in rain and snow at various locations on the globe indicate that the primary source of Cd to the atmosphere is anthropogenic and show a pronounced latitudinal gradient in deposition [27,28,33-35]. The deposition of Cd in precipitation and bulk aerosol samples is observed to occur at significant crustal enrichment factors (EFc) where... 

Fig. 5. The log (enrichment factor) for 44 elements in Antarctic atmospheric dust compared with mean crustal concentrations.

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. 

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...

To estimate the contribution of wind-blown dust of crustal origin to the fine aerosol concentration, elemental enrichment factors were calculated using the method of Macias et al. (20). The enrichment factor, EF., for an element i was calculated as follows ... 

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. 

Particulate emissions data for 21 studies of coal-fired power plants were compiled for use in receptor models. Enrichment factors were calculated (relative to Al) with respect to the earth s crust (EFcrust) and to the input coal (EFcoai). Enrichment factors for input coals relative to crustal material were also calculated. Enrichment factors for some elements that are most useful as tracers of coal emissions (e.g., As, Se) vary by more than ten-fold. The variability can be reduced by considering only the types of plants used in a given area, e.g., plants with electrostatic precipitators (ESPs) burning bituminous coal. For many elements (e.g., S, Se, As, V), EFcrust values are higher for plants with scrubbers than for plants with ESPs. For most lithophiles, EFcrust values are similar for the coarse (>2.5 ym) and fine (<2.5 ym) particle fractions. 

For the particle filters we have determined enrichment factors (EF) using Wedepohl s (11) crustal values and the equation ... 

Table 1. World oceanic average of elements in manganese nodoles and enrichment factor for each element in nodules compared to crustal aboundance (from Cronan )...

We turn next to consider the nonvolatile alkali and alkaline earth elements and the insoluble components of mineral origin. Their major natural sources are the Earth s crust and the ocean, respectively. We expect the chemical composition of the aerosol to reflect the relative contributions of elements from both reservoirs, provided other contributions from anthropogenic or volcanic sources are negligible. In Section 7.4.4 it has been noted, however, that his premise does not hold for all constituents of the aerosol. Some trace components are considerably enriched compared with their crustal abundances. It is appropriate, therefore, to inquire whether the observations confirm our expectations at least for the major elements listed in Table 7-13, or whether deviations occur also in these cases. As Rahn (1975a,b) has shown, the problem may be approached in two ways, either by calculating enrichment factors defined by... 

Table 7-lb. Average Absolute and Relative Abundances of Major Elements in Crustal Rock, Soil, and Shale-, Relative Abundances of Elements in Fly Ash from Coal and Fuel-Oil Combustion and Relative Abundances of Major Elements in the Remote Continental Aerosol, with Enrichment Factors (Aerosol) EF= (X)/(AI)aeroso,/(X)/(AI)crusta, rock ... 

Atmospheric deposition is also a major source of metal input into many aquatic ecosystems (Salomons 1986). Helmers and Schrems (1995) reported for the tropical North Atlantic Ocean that wet trace element deposition dominates over dry input. From the increased enrichment factors relative to the Earth s crust, the determined trace metal concentrations were assumed to originate from anthropogenic sources. For atmospheric wet depositional fluxes of selected trace elements at two mid-Atlantic sites, Kim et al. (2000) reported that at least half of the Cr and Mn and more than 90% of the Cd, Zn, Pb, and Ni are from non-crustal (presumably anthropogenic) sources. 

In remote areas, CMB methods are not applicable due to the mixed influence of numberless sources. FA generally tends to uncover obviously influencing sources such as maritime, crustal, and mixed anthropogenic ones (Heidam 1981). More promising for such regions is the use of enrichment factors (Zoller et al. 1974) and of tracer systems (Rahn 1985). The enrich-... 

Here [Mp] and [Mr] are the metal concentrations in particulate matter and in crustal rock, respectively, and [Alp] and [Ah] are the concentrations of aluminum (or any suitable reference element) in particulate matter and crustal rock, respectively. Table 3 lists EEs for SPM or fine sediment in contrasting estuaries. Enrichment factors are close to unity for the baseline sediment and in the pristine Lena Estuary, while the greatest EE values are encountered for cadmium in the Rhine (impacted by the production of phosphate fertilizers) and the Scheldt, and for copper in Restronguet Creek (impacted by historical mining activity). The general sequence of EEs... 

Fig. 18.31 The concentrations of chemical elements in the crystalline micrometeorites (MMs) at Cap Prudhomme, Antarctica, in the size range 100-400 pm deviate significantly from the chemical composition of the rocks in the crust of the Earth. The enrichment and depletion of the MMs is expressed as the logarithm to the base 10 of the ratios of the concentrations of the MMs divided by the concentrations in crustal rocks as reported by Taylor and McLennan (1985). The elements that are enriched in the MMs and their respective enrichment factors include primarily Ir (4700), Au (333), Ni (43), Se (36), Cr (34), Fe (28), Co (8.8), As (4.8), and Sb (2.2). The MMs were analyzed by C. Koeberl by instrumental neutron activation analysis (INAA)...

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. 

The major part of elements are enriched in manganese nodules due to adsorption processes on hydroxides. The limited number of analyse does not allow the conclusion in which phase these elements are concentrated. Table 1 shows factors of enrichment of a number of elements in nodules, compared with the crustal abundance of these elements. 

The contents of some trace elements in the continental crust, shales, soils, bituminous coals and plankton are given in Table 1.1 to provide some perspective when considering other aspects of these elements. In each of these situations, organic matter is associated with the elements to a greater or a lesser degree. This is not usually very marked with crustal rocks except shales, but may be a major factor for some elements in surface soils and coals. The data in Table 1.1 show that, for some elements, e.g. beryllium, cadmium, cobalt and molybdenum, the contents of the various reservoirs are similar, while for others, there may be enrichments relative to the crust, e.g. boron and sulfur in many shales, soils and coals, mercury, nickel and selenium in many shales, and germanium in some coals. 

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