Elaboration of a variant of chemical analysis (on example of the Lovozero massif rocks)

Kolesov G.M., Ermolaeva V.N., Mikhailova A.V., Kogarko L.N., Savvin S.B.

GEOKHI RAS, Moscow, Russia

cvera@mail.ru

 

In the aspect of further development of the geo-technological methods of mining, in particular, underground leaching method, we have carried out a work on the search of solvents for leaching of the most valuable components (uranium, thorium, rare-earth elements, hafnium, tantalum, zirconium) from the rocks of Lovozero massif (Kola Peninsula), their concentration using polymeric strong-swollen hydrogels and determination their contents by means of neutron-activation analysis (INAA).

The application of the underground leaching method of the most valuable components requires carrying out of analytical control on all stages of this process. We have carried out a number of experiences on leaching of rare elements from some alkaline rocks of Lovozero massif (lujavrite and foyaite).

Initial sample with mass of 100 mg has been pounded into small particles and placed in a vessel with 20 ml of a reagent, stirred and left for 30 days under normal conditions in closed bottles. The extract obtained was filtered, a part destined for the analysis was selected and placed in a vessel with 0.2 g of polymeric hydrogel on a polyacrylamide support. After total absorption of solution in the course of swelling during 1 to 3 min, hydrogel has been dried up. Thereafter a part of the dry hydrogel with mass 7÷15 mg was packed in a bag of Al foil, put in cage (together with standard samples) and irradiated in nuclear reactor. Irradiated samples have been analyzed by semiconductor Ge-detector using 4096-channels impulse analyzer. Registered signals (photo-peaks of radionuclide gamma-lines) have been decoded with use of special computer programs developed in GEOKHI RAS [1]. Reactants from different groups of chemical compounds for leaching have been tested in order to select ones giving maximum degree of extraction of interest elements from the rocks. The following reagents have been used: HCl, NaOH, Na₂CO₃, (NH₄)₂C₂O₄ (ammonium oxalate) [2] and C₁₀H₁₄O₈N₂Na₂∙2H₂O (disodium salt of EDTA).

The data obtained show that solutions of HCl, (NH₄)₂C₂O₄ and disodium salt of EDTA are most effective for leaching of radioactive and rare-earth elements from alkaline rocks.

Polymer nanocompositional hydrogels (so-called “superabsorbents” [3,4]) are shown to be sorbents of the most practical interest because absorbed water and dissolved components are distributed uniformly in them. We used anionic polyacrylamide, copolymer: —[—CH₂—CH(CONH₃)—]—[—CH₂—CH(COO^-)]— and Na⁺ (as counter ion). On the basis of the studies carried out in the present work it was shown that hydrogels can be used for the determination of elements by the NAA method directly (i. e. without preliminary desorption). It is high-sensitive (up to 10^-14 g), nondestructive, multielement, informative method, which can be applied directly to the analysis of samples with complex chemical compositions including salt, organic and colloid components where chemical elements are present in different forms (ions, complexes, nanoparticles), including small-volume samples. Using of compact solid samples for this method are preferable, as packing in quartz capsules liquid samples is limited by working space of reactor.

This study was made with according to plane of research work of GEOKHI RAS.

 

References:

1. Kolesov G.M. Determination of microelements. Neutron-activation analyze in geochemistry and kosmochemistry // Journal of analytical chemistry. 1994. Vol. 49. № 1. P. 56 (in Russian).

2. Polyakov A.I. Geochemistry of thorium in alkaline rocks of the Kola Peninsula. M.: Science, 1970. 165 p (in Russian).

3. Dubrovskii S.A., Kazansky K.S. Application of super-swelling hydrogels as water absorbers: basic thermodynamics //  Polymer Science, Series A. 1993. V. 35. No. 10. P. 1712–1720 (in Russian).

4. Savvin S.B., Kolesov G.M., Mikhailova A.V. Water systems: concentration and determination of metals with use of polymer hydrogels and neutron-activation analyze // Water: chemistry and ecology. 2009. № 9. P. 37-40 (in Russian).