Petroleum fluids and their role in lanthanide isomorphism.
The possibility of isomorphous entry of rare earth elements into a variety of natural minerals is described and reported in a number of works, which shows the influence of physical and chemical processes on the lanthanide distribution in the REE composition as a consequence of changes of isomorphic capacity with respect to the REE minerals [1, 2]. The possibility of isomorphous entry of rare earth elements into the hydrocarbons were also found in oil and gas-bearing deposits during the passage of geochemical processes in the contact zones of mineral movable and organic rock complexes, as well as in the high molecular weight compounds of oils--asphaltenes . Adoption of this thesis and establishment of such an effect would not be possible without the new data on the Earth composition , the ionic radii in eightfold coordination  and, of course, determination of REE concentrations in rock fractions through the methods of mass spectrometry with an inductively coupled plasma (ICP MS) and their capabilities in geochemical studies . Based on the unique properties of rare earth elements to change the valence and ionic radius, depending on the redox conditions of the environment, it is quite possible to justify their valence participation in the geochemical processes, thereby, to prove the given thesis about observation of lanthanide isomorphism in environments with petroleum fluids . It should be noted that Gavshin, V.M. and Gurari, F.G. et al.  previously provided for the abnormalities of Tb and Ho in the clays of the Russian Platform and dealt with the imperfection of analysis methods and, as a consequence, the insufficient precision and large roughness of determining the content of elements. In the present work, the study results are based on the sample analysis through the ICP MS method.
For the first time, the possibility of substitution of calcium (Ca), magnesium (Mg) and yttrium (Y), respectively, to neodymium (Nd), terbium (Tb) and holmium (Ho), was presented in the carbonate reef sediments of the Kok-Dumalak oil and gas-bearing field (Uzbekistan) , and later in the REE spectra of high molecular weight compounds (HMWC) of the produced and residual oils of different regions (West Siberia, Bashkortostan, Tatarstan, Kazakhstan, and Uzbekistan) Figure 1.
As it can be seen from the Figure 1, it is impossible to explain the accumulation of neodymium, terbium, and holmium in hydrocarbon media manifested through the differentiated positive anomalies of the lanthanides in the REE composition merely by their trivalent state in geochemical processes. According to the work , cerium (Ce), praseodymium (Pr), and terbium (Tb) as well as europium (Eu), samarium (Sm) and ytterbium (Yb) are capable of changing valence, but only in the oxidizing environment, and preserve stability in the tetravalent state while their screening from water by organic stabilizers . Such stabilizers in the reservoir, as outlined in the work , may be petroleum fluids containing oil and gas hydrocarbons, as there are no other influencing factors on the consideration of physical and chemical processes in the reservoir. Thus, it is evident that the anomaly on terbium within the REE composition may be associated with heterovalent isomorphism in the [Tb.sup.4+] state and similar in ionic radius with [Mg.sup.2+] . If our assumptions are correct, it is obviously required to observe the accumulation of neodymium ([Nd.sup.3+]), in consequence of its replacing calcium (Ca2+), which is also determined by the similarity of their ionic radii (Figure 2). However, this is one of the versions, and not the determining argument. As it is well known , the carboxylic and naphthenic acids are important surface active substances (SASt) and petroleum fluid components, and for solvation of the oil and gas hydrocarbons they form insoluble salts with the divalent calcium ([Ca.sup.2+]) and magnesium ([Mg.sup.2+]) cations. Therefore, in the aqueous solutions, rich in [Ca.sup.2+] and [Mg.sup.2+] (in the fluids there is always present a portion of stratum water enriched with cations of calcium and magnesium), micelles should be destroyed, thus contributing to the migration processes of naphthides . In turn, the organic acids will be precipitating in the form of insoluble calcium ([Ca.sup.2+]) and magnesium ([Mg.sup.2+]) salts . Hence, it is obvious that the isomorphism of terbium (Tb) and neodymium (Nd) is not possible without the carbonate compounds of rocks due to a significant content of calcium and magnesium in stratum waters of oil and gas-bearing deposits, and should always be held together. Furthermore, in the work  there is provided a statement as for the "cations" should fully occupy the space in the lattice and are more inclined to push it apart, than to hang out". Here is an equivalent circuit. [Nd.sup.3+] = 1.109 [Angstrom]--[Ca.sup.2+] = 1.12 [Angstrom] ([DELTA]= 0.011 [Angstrom]) [Tb.sup.4+] = 0.88 [Angstrom]--[Mg.sup.2+] = 0.89 [Angstrom] ([DELTA] = 0.01 [Angstrom]) 
The difference in the ionic radii of the equivalent circuit is 0.01[Angstrom], which indicates the validity of our arguments about the heterovalent substitution of elements . Anomalies of holmium (Ho) in the REE composition of asphaltenes (Fig. 1-2) can be considered by analogy of causes of significant deficiency or accumulation of mineral movable and organic complexes of rocks with yttrium (Y), displayed in the (Fig. 3-4). [Ho.sup.3+] = 1.015 [Angstrom]--[Y3.sup.+] = 1.019 [Angstrom] ([DELTA] = 0.004 [Angstrom]) 
1. From the study analysis it follows that petroleum fluids are the factor of isomorphic capacity and environment changes, particularly for terbium ([Tb.sup.4+]),' for which the solvation of oil and gas hydrocarbons by organic acids leads to the possibility of its interaction with magnesium ([Mg.sup.2+]) and calcium ([Ca.sup.2+]), respectively, with neodymium ([Nd.sup.3+]) in the case of heterovalent isomorphism.
2. Isovalent isomorphism of holmium ([Ho.sup.3+]) and yttrium ([Y.sup.3+]) in oil and gas-bearing deposits, is most likely conditioned upon the thermodynamic conditions and the properties of Y and Ho, how strongly--the positive elements (cations) are to form complex compounds with negative anions of oil and gas hydrocarbons. In addition, the factor of proximity of the ionic radii allows positioning both lanthanides in the spectrum of REE composition, corresponding to the position among the heavy REE, thereby to justify the complexing properties of the lanthanides with the oil components.
3. In the geochemistry of rare earth elements of the sedimentary processes, the differentiation in behavior and abnormal redistributions of lanthanides within the REE composition are probably impossible without the participation of the oil and gas hydrocarbons determining the redox conditions of the environment, and never pass without the isomorphism of lanthanides.
4. In the applied direction, the research results can be used as geochemical criteria of the rocks' oil-bearing capacity in the carbonate sediments. The Tomsk State University
Received 25 May 2014
Received in revised form 12 June 2014
Accepted 25 June 2014
Available online 15 July 2014
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Federal State Autonomous Educational Institution of Higher Education, "The Tomsk National Research State University", 36, Lenina Av., Tomsk, Russia, 634050.
Corresponding Author: Tsoy K.S., Federal State Autonomous Educational Institution of Higher Education, "The Tomsk National Research State University", 36, Lenina Av., Tomsk, Russia, 634050.
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|Publication:||Advances in Environmental Biology|
|Date:||Aug 1, 2014|
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