O. A. Tyutyunnik

Sorption on Humic Acids as a Basis for the Mechanism of Primary Accumulation of Gold and Platinum Group Elements in Black Shales

In order to asses the contribution of sorption by complexation to the concentration of noble metals at early stages of the formation of their deposits in black shales, the sorption of Au(III), Pt(IV), Rd(II), Rh(III), Ru(IV), and Os(IV) ions was studied on ash-free preparations of humic acids (HA) separated from peat of the Tver region and marine sediment samples taken on the Peruvian shelf. Data on the nature and protolytic characteristics of oxygen-containing HA functional groups were obtained. It has been shown that carboxyl groups and phenol oxygroups, which ensure the HA complexation with ions of noble metals, are present in the HA structure. The dissociation constant values for HA carboxyl groups (pKa) and the distribution function of these groups in their pKa values have been established. It has been revealed that the pKa value for both of the HA groups varies within two orders of magnitude: the average value is equal to 6.1 for HA from peat and 7.0 for HA from marine sediments. A fairly high and similar for both of the HA groups sorption capacity with respect to Au(III), Rd(II), Rh(III), Ru(IV), and Os(IV) ions was established in model experiments. It is equal to 320–350 mg g–1 for Au, 100–110 mg g–1 for Pd, 11–12 mg g–1 for Rh, 16–19 mg g–1 for Ru, and 23 mg g–1 for Os. The study of platinum(IV) sorption revealed that humic acids from peat and marine sediments do not virtually sorb Pt(IV), and this observation is important for understanding genetic features of the formation of noble metal deposits in black shales. Based on sorption isotherms for Au(III), Pd(II), Rh(III), and Ru(IV), the conditional affinity constant values for HA sorption centers with respect to ions of these metals were calculated by the method of quantitative physicochemical analysis. These values prove that complex compounds forming at the HA surface possess a high strength: the logβ values for the Au(III)–HA, Pd(II)–HA, Rh(III)–HA, and Ru(IV)–HA compounds are equal to 6.0, 5.0, 3.2, and 3.5, respectively.

Migration of platinum, palladium, and gold in the water systems of platinum deposits

In order to explore the behavior of platinum group elements in the ecosystems of mineral deposits, the migration characteristics of platinum and palladium were determined in the pH range typical of surface waters. Model sorption experiments on the precipitation of platinum and palladium on iron oxyhydroxide in the presence of major natural inorganic and organic ligands showed that platinum interacts most actively with an iron oxyhydroxide (ferrihydrite) precipitate within the whole pH range, both in the absence and presence of natural organic substances, whereas palladium is preferentially bound to dissolved, suspended, and sedimentary humic substances. The thermodynamic calculation of coexisting platinum and palladium species is qualitatively consistent with experimental data on the character of accumulation and migration of these elements. The obtained data suggest that the migration of platinum and palladium into highly colored waters in the zones of platinum group element deposits results in their extensive deposition on natural geochemical barriers.

Role of organic matter in the accumulation of platinum in oceanic ferromanganese deposits

In order to elucidate possible processes leading to platinum accumulation in ferromanganese deposits, we analyzed published data on the interaction of dissolved platinum species in different valence states with iron and manganese oxyhydroxides under oceanic conditions and experimentally studied the kinetics of sorption of inorganic and organic complexes of platinum (II) and platinum (IV) on synthetic iron and manganese oxyhydroxides and natural materials (marine colloids, and ferromanganese crust samples). The role of dissolved and suspended particulate aquatic organic matter in the sorption accumulation of platinum was evaluated. Possible reasons for the preferential (compared with other noble metals) accumulation of platinum in oceanic ferromanganese deposits were discussed.

Microwave synthesis, properties and analytical possibilities of magnetite-based nanoscale sorption materials

An approach is proposed to the preparation of magnetic sorption materials based on the synthesis and surface modification of nanomagnetite by organic compounds under microwave heating. The optimum conditions for the preparation of nanomagnetite are found, its structure and particle sizes are studied. Data on the stabilization and modification of the prepared particles by surfactants are obtained. The magnetic materials modified by oleic and mercaptopropionic acids and also by cetyltrimethylammonium bromide are synthesized and thoroughly characterized. Conditions of the formation of a modifying layer are studied and its stability is estimated. Sedimentation properties of the modified adsorbents are studied. The sorption capacity and kinetic properties of the modified nanomagnetite for a number of inorganic and organic natural water pollutants (cadmium, lead, copper, phenol, and toluene) are determined. The possibility of the efficient extraction of heavy metals in the presence of macrocomponents of natural waters is shown and data on the possibility of their desorption are obtained.

Microwave preparation of natural samples to the determination of mercury and other toxic elements by atomic absorption spectrometry

Methods have been developed for the preparation of samples containing organic matrices (natural high-color waters, soils, bottom sediments, aquatic organism tissue) to the determination of mercury and other toxic elements (As, Cd, Pb, Se) by different procedures of microwave digestion under elevated pressure (closed systems, vessels with partial removal of the gas phase). It is found that, under optimal oxidative and temperature-time conditions, the partial removal of the gas phase does not lead to losses of volatile elements if sample portions under 2 g are used. The duration of preparation of a series of samples does not exceed 40 min. The detection limits for mercury in the cold vapor atomic absorption spectrometry and for Cd, Pb, As, and Se by electrothermal atomic absorption spectrometry are 5 and 0.13, 6, 13, and 13 μg/kg, respectively. The accuracy of determination is confirmed by the results of analysis of certified reference materials of water and plant materials and also by the standard addition method. The selected conditions of preparation of sludge samples have ensured the determination of mercury by the cold vapor atomic absorption spectrometry in drinking, natural, and sewage waters with a detection limit of 0.07 μg/L.

Possible reasons for elevated fluorine concentrations in groundwaters of carbonate rocks

The concentration of dissolved F did not change in long-term (four months) experiments on the interaction of crushed limestone and marl with water (at R/W = 1) at room temperature. The comparison of the activity products and equilibrium constants of the mineral dissolution reactions indicates that the experimental solutions were undersaturated with respect to fluorite and oversaturated with respect to F-apatite. The long-term existence of such unequilibrated solutions is explained by the steady state of the system at which the primary F-bearing mineral (fluorite, mica, or palygorskite) is transformed into a secondary one (F-apatite). The dissolved F concentration is controlled under these conditions by the ratios of the dissolution reaction rates for the primary mineral and the precipitation rate of the secondary one.In the experiments with the association fluorite + calcite + dolomite (duration up to seven months), the solution was saturated with respect to these minerals. Their dissolution constants were utilized to derive dependences of the activity of the dissolved F ion on the activities of the Ca, Mg, and carbonate ions in the solutions. The experimental data are consistent with these dependences. If the solution is saturated with respect to gypsum, the activity of the dissolved F ion should also depend on one more parameter: the activity of the sulfate ion.When groundwaters filtrate for a long time or are stagnant, the association F-apatite + calcite + dolomite (+ gypsum) is stable; dependences of the activity of the F ion on the activities of aqueous species in the solution were derived for this association. These dependences are much stronger than those for the association fluorite + calcite + dolomite (+ gypsum).

Geochemical zoning in ferromanganese crusts of Ita-MaiTai guyot

Samples of ferromanganese crusts dredged from Ita-MaiTai guyot (Magellan seamounts, Pacific Ocean) were studied. They are made up of a complete stratigraphic section of different-age layers, including unique oldest relict layers in some samples. The study of trace, rare-earth, and noble element (including Pt and Pd) distribution showed that old layers differ from young ones in terms of Co, TR, S, As, and P. In addition, composition of the crusts significantly varies depending on the spatial position of sample in the guyot. In some zones, crusts enriched in trace elements were generated both in the Pleistocene and Paleogene. Significant variations established in trace element composition of different-age layers indicate that trace element composition of the crusts notably evolved with time, which could be caused by productivity of biocenosis or change in the formation depth of crusts on the guyot due to vertical tectonic movements.

Geochemistry of Cenomanian/Turonian boundary sediments in the mountainous part of Crimea and the northwestern Caucasus

Detailed data obtained on the chemistry of sedimentary rocks from the mountainous part of Crimea and the northwestern Caucasus that were dated at the Cenomanian/Turonian boundary and were formed during Oceanic Anoxic Event 2 (OAE 2) make it possible to calculate the dissolved oxygen concentration in the bottom waters of the sedimentation basin. The enrichment coefficients of trace elements in the black shales are revised and an explanation is suggested for the genesis of the rocks with regard for unusual climatic changes.

Migration behavior of platinum group elements in natural and technogeneous systems

Data were summarized on the speciation of the main platinum group elements (PGE) platinum, palladium, and rhodium in aqueous media, forms of their input into the environment, and mechanisms of accumulation by natural sorptive phases. In some cases, the results obtained for PGE were compared with those for gold. Data on PGE speciation in a number of natural environments were analyzed. It was found that the main factor controlling the migration ability of PGE (Pd > Pt»Rh) is the formation of stable compounds with dissolved organic matter, hydroxyl, and thiosulfate ions and nanometer-sized particles. The transport of dissolved PGE species by marine, riverine, and technogeneous suspended materials was evaluated as an alternative way of an increase in PGE mobility. Significant differences were revealed in the migration behavior of platinum, palladium, and rhodium indicating the dominance of palladium dissipation in a dissolved state. The possibility of the prediction of PGE accumulation and dissipation in technogeneous systems was demonstrated.

Distribution of siderophile and chalcophile elements in serpentinites of the oceanic lithosphere as an insight into the magmatic and crustal evolution of mantle peridotites

The paper reports result of comparative analysis of the distribution of siderophile (Au, Pt, Pd, Co, Ni, and Cr) and chalcophile (Ag, Cd, Sb, Pb, Zn, Cu, As, and S) elements in ultramafic rock samples of various types of abyssal peridotites. One of the objectives of this research was to obtain reference estimates for the concentrations of siderophile and chalcophile elements in the two end members defining the geochemical evolutionary trends of the material of the suboceanic mantle: a sample of insignificantly depleted mantle material (spinel lherzolite) and extensively carbonated serpentinite after harzburgite, which was formed at the “endpoint” of the ascent of mantle material to the seafloor surface. The distribution of siderophile and chalcophile elements is proved to record information on the whole compositional evolution of abyssal peridotites corresponding to the trajectory of their exhumation from mantle depth levels to seafloor outcrops. These data indicate that the bulk-rock compositional parameters of abyssal peridotites can be utilized to estimate the contribution of magmatic and hydrothermal process to the distribution of siderophile and chalcophile elements.