Rare earth element normalized concentrations

Fig. 13.12 Rare earth element (REE) concentrations in hydrothermal fluids versus Atlantic seawater at 2,500 m (Elderfield and Greaves 1982) normalized to MORE (Sun 1980). Symbols indicate measurements of different vent fluids from the Lucky Strike hydrothermal field at 37°17 N Mid-Atlantic Ridge (after Klinkhammer et al. 1995).

The X-ray determination of REE in geological samples is normally complicated by the relatively low concentrations of the REE, their complex X-ray spectra, the high concentration of matrix elements and the lack of reference standards with certified values for REE. A rapid and sensitive ion exchange and X-ray fluorescence procedure for the determination of trace quantities of rare earths is described. The REE in two U.S.G.S. standards, two inhouse synthetic mixtures and three new Japanese standards have been determined and corrections for inter-rare earth element interferences are made. 

The rare earth elements (REE) form a group of elements that have coherent geochemical behaviour due to their trivalent charge and similar ionic radii. They can, however, be fractionated from one another as a result of geochemical processes operating under specific physico-chemical conditions. In order to outline general trends within and differences between the individual REE, concentrations are usually normalized to a reference system (e.g. to shale). Deviations of individual elements from the generally smooth trend are referred to as anomalies. 

Figure 10.6. Observed secular trends in the chemical composition of sedimentary rocks. Eu/Eu = ratio of observed normalized Eu concentration to that predicted (Eu ) from extrapolation between REE Gd and Sm. REE = rare earth element LREE = light REE HREE = heavy REE. Data from several authors as presented in Veizer (1988).

Figure 2. Rare earth elements concentrations (normalized to chondrites) for the original rocks (serpentinite and hornblende diorite) and their alteration products...

Fig. 9.24. Cl chondrite normalized rare earth element concentrations for geological glasses. The Ll-MS data are compared with the results of other analytical techniques. ( ) LI-MS (O) LA-ICP-MS (A) HPLC (V) SY-XRF ( ) INAA (X) TI-MS. (Reproduced with permission of Springer-Verlag.)...

In geochemistry, rare earth element (REE) patterns constitute a useful tool for interpreting geological processes. LI-MS produces reasonably good REE patterns, as shown in Fig. 9.24, which is a plot of Cl normalized REE concentrations alongside the results obtained with INAA, HPLC, LA-ICP-MS, synchrotron X-ray fluorescence (SY-XRF) spectroscopy and secondary ion mass spectrometry (Tl-MS). INAA and TI-MS surpass... 

As viewed from the top, the plasma has a circular, doughnut shape. The sample is injected as an aerosol through the centre of the doughnut. This characteristic of the source confines the sample to a narrow region and provides an optically thin emission source and a chemically inert atmosphere. Normally, samples are introduced as a solution into the plasma and argon is used as a carrier gas for the sample introduction. The much higher temperatures of the plasma compared to flame make ICP-AES more effective in detecting lower concentrations of refractory elements such as Ta, W and Zr, and rare earth elements. 

Rare earth element concentrations in rocks are usi lly normalized to a common reference standard, which most commonly comprises the values for chondritic meteorites. Chondritic meteorites were chosen because they are thought to be relatively unfractionated samples of the solar system dating from, the original nucleosynthesis. However, the concentrations of the RZE in the solar system are very variable because of the different stabilities of the atomic nuclei. REE with even " atomic numbers are more stable (and therefore more abundant) than REE with odd atomic numbers, producing a zig-zag pattern bn a composition-abundance diagram (Figure 4.19). This pattern of abundances is also found in natural samples. 

Concentrations of rare earth elements In average seawater and average river water normalized to NASC The data are given in Table 4.6, columns 9 and 10. Normalizing values are from Table 4.6 column 5. Note that the concentrations in seawater and river wamr are quoted in mol and must in this case be multiplied by the atomic weight. Concentrations shown are X 10". ... 

A process has been developed by Ayres for the purification of zirconium, in which the various impurities are absorbed upon a cation-exchange resin. The zirconium itself is not absorbed as it is in the colloidal condition. This state is not difficult to achieve with, for example, zirconyl nitrate ZrO(NOs)2, since it is normally hydrolysed to the highly insoluble hydrated oxide in a neutral or near neutral solution. A zirconium ore is therefore broken in concentrated sulphuric acid and the soluble zirconium sulphate converted to the nitrate by suitable means and passed through a column of resin in the usual manner. Amberlite I.R.-100 has been used, in the hydrogen form. Impurities such as iron, beryllium and rare earth elements are absorbed completely, together with about 80 per cent of the titanium. The resin capacity for zirconium, however, is as low as 0-84 mmoles/100 cm of resin, and it is therefore recovered virtually completely in the pure column effluent. The very small amount of zirconium taken up by the resin is probably retained by a surface absorption process rather than true ion-exchange. The zirconium can be precipitated by alkah from the effluent as the hydrated oxide, in massive form, for conversion to other compounds and finally to metal. The resin is regenerated for further use by elution of the cation impurities with, for example, dilute sulphuric acid. 

Figure 10.22 shows the structure. Eight S(Se) atoms at the corners of a cube enclose an octahedron formed by Mo atoms. These units are arranged as indicated. The third element X is normally surrounded by 8 such cubes. The Pb atoms can be substitutionally replaced by rare earth atoms. Figure 10.22 shows Tc as a function of concentration for R = La, Lu and Gd in the series Pbi-xRxMogSg. The interesting point is that the compound GdMo6Sg is a super-... 

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