Rare earth element concentrations

McKenzie D, O Nions RK (1991) Partial melt distribntions from inversion of rare earth element concentrations. J Petrol 32 1021-1091... 

For comparison, steady-state cathodoluminescence spectra (Fig. 4.7) are presented from two scheelite samples with different rare-earth elements concentrations (Table 4.5). It is clearly seen that only broadband emissions are detected, while the narrow Unes of several rare-earth elements, mostly Sm + are extremely weak. 

In addition, there exist a multitude of different applications in water analysis by ICP-MS for environmental control. For example, Lawrence et cdP determined rare earth element concentrations in natural waters (these are river, lake, sea or groundwater) by quadrupole ICP-MS using external calibration and employed river water reference material SLRS-4 to validate the analytical data. The speciation of yttrium and lanthanides in water samples by SEC-ICP-MS was studied by Haraguchi et a/.18 whereby the detection of La, Ce and Pr corresponded to the occurrence of large organic molecules. 

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

Schnetzler C. C. and Philpotts J. A. (1971) Alkah, alkaline earth, and rare earth element concentrations in some Apollo 12 soils, rocks, and separated phases. Proc. 2nd Lunar Sci. Conf, 1101-1122. 

McKenzie D. and O Nions R. K. (1991) Partial melt distributions from inverstion of rare earth element concentrations. / Petrol. 32, 1021-1091. 

Keasler K. M. and Loveland W. D. (1982) Rare earth elemental concentrations in some Pacific Northwest rivers. Earth Planet. Sci. Lett. 61, 68-72. 

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.)...

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. 

The production of rare earth oxides from the Mountain Pass mine started in 1964 and remained the main source of light rare earths in the west until approximately the middle of the 1990s (Castor 2008). In approximately 1985, China began to export rare earth element concentrates, and by 1990, China was producing more than the USA (Geschneider 2011). 

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. 

An interesting variant of Group I is the determination of thorium in monazite concentrates.73 Here the variations that may occur in the chemical composition of the matrix leave its x-ray absorbance virtually unaltered. This simplicity is possible because the principal individual rare-earth elements present in the samples lie in the range of atomic numbers from 57 to 60, a range so small as to preclude marked variations in the over-all mass absorption coefficient. 

Total Elements There is a dearth of elemental concentration data for a wide range of nutritionally, toxicologically, clinically, and environmentally pertinent elements. Some of the elements for which total concentration information is still required, usually at the low end of concentration range but occasionally at the high end, are Al, Ba, B, Be, Br, Cs, F, I, Li, Mo, N, Pt, S, Sb, Si, Sn, Th, Ti, TI, U, V, W, rare earth elements, and radionuclides. Thus, it would seem advisable to certify each new RM for as many elements as possible so that certified values would be available for a larger number of elements in addition to the small number of core elements typical of many current RMs. 

Several methods have been used to separate the lanthanides chemically solvent extraction, ion exchange chromatography, HPLC using Q-hydroxyisobutyric acid and, in limited cases, selective reduction of a particular metal cation.40-43 The use of di(2-ethylhexyl)orthophosphoric acid (HDEHP) for the separation of various rare-earth elements via solvent extraction has also been reported.44 16 This separation method is based on the strong tendency of Ln3+ ions to form complexes with various anions (i.e., Cl- or N03 ) and their wide range of affinities for com-plexation to dialkyl orthophosphoric acid. When the HDEHP is attached to a solid phase resin, the lanthanides can be selected with various concentrations of acid in order of size, with the smallest ion being the most highly retained. 

Elderfield and Greaves [629] have described a method for the mass spectromet-ric isotope dilution analysis of rare earth elements in seawater. In this method, the rare earth elements are concentrated from seawater by coprecipitation with ferric hydroxide and separated from other elements and into groups for analysis by anion exchange [630-635] using mixed solvents. Results for synthetic mixtures and standards show that the method is accurate and precise to 1% and blanks are low (e.g., 1() 12 moles La and 10 14 moles Eu). The method has been applied to the determination of nine rare earth elements in a variety of oceanographic samples. Results for North Atlantic Ocean water below the mixed layer are (in 10 12 mol/kg) 13.0 La, 16.8 Ce, 12.8 Nd, 2.67 Sm, 0.644 Eu, 3.41 Gd, 4.78 Dy, 407 Er, and 3.55 Yb, with enrichment of rare earth elements in deep ocean water by a factor of 2 for the light rare earth elements, and a factor of 1.3 for the heavy rare earth elements. 

Ion exchange chromatography using Chelex 100 resin has been used for the concentration of rare earth elements from large volumes of seawater, with recoveries of 85-112% [636]. 

Wen et al. [950] used 8-hydroxyquinoline immobilised on a polyarylonitrile hollow fibre membrane to achieve a 300-fold concentration factor for rare earth elements in seawater. 

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. 

Tordo concentrates more rare earth elements especially in samples 16 and 18 which is probably due to the presence of some heavy minerals that are potential carriers of rare earth elements (Kasper-Zubillaga et at. 2008b). The possible... 

Trace elements and rare-earth elements (REEs) of the same calcite samples used for the stable isotope analysis have significantly lower concentration of REE as well as most trace elements relative to typical carbonatites. The total REE contents of the Ulsan carbonates range from 3 to 17 ppm, which are much lower than any igneous rocks and even lower than those of some sedimentary rocks. REE and trace-element abundances may have changed sufficiently due to alteration, thus, affecting petrogenetic... 

The dependence of the solubility of LaCl3-7H20 on acid concentration at 25°C is indicated in Table XIX (205). The dependence at 50°C is the same. The dependence of solubilities of trichlorides of scandium (263), yttrium (264,265), and several rare-earth elements (265) on hydrochloric acid concentration has been established at 0°C. 

Assuming that half a percent liquid is trapped with the residue, equating the concentration in the rock to that in the solid residue will result in a severe bias for incompatible elements with Df<0.01 and in pure nonsense for elements with Dt<0.001. A typical example is represented by rare-earth elements in peridotites. Even separated clinopyroxenes can be suspected to have incorporated most of the REE from whichever trace amounts of liquid happened to be trapped in the cooling rock. If the rest of the minerals do not take any REE, it is left to the reader as an exercise to show that the concentration in clinopyroxene after uptake of incompatible elements is related to that in the clinopyroxene from a liquid-free residual peridotite through... 

---