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PAVLE I. PREMOVIC*, NIKOLA D. NIKOLIC, MIRJANA S. PAVLOVIC*, BRATISLAV Z. TODOROVIC, DRAGAN M. DJORDJEVIC, RUZICA S. NIKOLIC, LILIANA LOPEZ** and SALVADOR LOMONACO**
and Cosmochemistry, Department of Chemistry, Faculty of Science,
of Nis, P. O. Box 91, YU-18000 Nis, Yugoslavia,
*Vinca Institute of Nuclear Sciences, P. O. Box 522, YU-11001 Belgrade,Yugoslavia and
**Instituto de Ciencias de la Tierra Facultad de Ciencias, Universidad Central de Venezuela, Aptdo. 3895, Caracas 1010-A, Venezuela
(Received 17 April
Trace metals in the four discrete layers of the Cretaceous-Tertiary boundary (Fiskeler) at Stevns Klint (Denmark) are relatively well studied, yet much remains to be learned about them. Therefore, an integrated study of the trace (meteoritic Ir, partly meteoritic Cr/Ni/Co/Au and terrestrial Zn/Cu/La/Ce/Nd/Sm/Eu/Tb/Yb/Ta/Th) metals in the basal black marl of Fiskeler and in its (carbonate, HCl-soluble, smectite, HCl-insoluble, silicate and kerogen) fractions was undertaken. The mineralogy of the marl is comparatively simple, authigenic calcite (mainly derived from planktonic marine algae: coccoliths), detrital Mg-smectite and quartz being the principal components, with lesser amounts of kerogen, Fe3+-oxides, pyrite, ilite and feldspar. Selective leaching procedures were used to establish geochemical associations and specific mineralogical locations of the trace metals. The results identified the main locations of the major trace metals (Cr/Ni/Co/Zn/Cu/Ir/Au). They occur mainly in the smectite and, to a lesser extent, in the biogenic calcite (Ni/Co/Zn) and kerogen (Ir/Au). The trace metal data are in accordance with the hypothesis that substantial proportions of Cr/Ni/Co/Zn/Cu/Ir/Au were probably contained in the detrital smectite arriving at the site of the deposition. In a general discussion of the results, a geochemical model describing the incorporation of trace metals in the smectite is presented, based on the weathering/trasport of the clay by (impact-induced) acid surface waters and the adsorption of trace metal ions by the smectite particles/colloids in the acidic solution of nearby oxic soil. The distribution/enrichment patterns of Cr/Ni/Co/Zn of the basal black marl and higher Fiskeler layers indicate, on the other hand, that notable proportions of these metals were incorporated into the smectite structure during the formation of the clay. The trace metal data are also considered in light of previously published paleoecological and geochemical information for Fiskeler. It is proposed, for example, that the local (impact-induced) superacid rainfall and wildfires played an important role in providing appropriate humics (i.e. appropriate organics of decaying land green plants) having porphyrin stuctures for the formation of kerogen (enriched with Cu2+-porphyrins). In addition, it has been suggested that the biogenic calcite with high Ni is probably a product of the metabolic uptake of boundary seawater (enriched with this metal) by the coccoliths. The metal enrichment of the seawater was created by a sudden and high influx of (apparently mainly meteoritic) Ni: airborne and laterally redeposited (by the acid surface/river waters) from a nearby soil. Lastly, the lateral distribution of kerogen (enriched withCu2+-porpyhyrins) supports an earlier interpretation presented by Hultenberg that the alleged (Nye Kløv/Dania) boundaries in northwestern Denmark represent erosion and subsequent redeposition of Fiskeler in eastern Denmark.
Keywords: geochemistry, Cretaceous-Tertiary boundary, trace metals, smectite, kerogen.
Influence of the composition of the stationary and mobile phase on the retention factors and solvent strength parameters in RP chromatographic systems in which the Everett equation is valid
T. J. JANJIC, G. VUCKOVIC and M. B. CELAP
Faculty of Chemistry, University of Belgrade, P. O. Box 158, YU-11001 Belgrade, Yugoslavia
(Received 28 May
It is shown how in RPchromatography the Everett equation for ideal phase equilibriums can be used to estimate SP values (SP = log xs/x1, xs and x1 denoting the modifier mole fractions in the stationary and mobile phases, respectively) which are in a linear dependence with the log k values. The described procedure includes the determination of the approximate phase equilibrium constant K. By analysis of the Everett equation it was found that in the field of x1/K there are regions of linear dependence of the SP parameter or log k values and the mole fraction of modifiers or its logarithm. Consequently, only in these regions it is possible for two different chromatographic systems to have the same solvent strength scale: x1 or log x1.
RP column chromatography, capacity factor, SP parameter.
Alumina/silica aerogel with zinc chloride as an alkylation catalyst
ALEKSANDAR M. ORLOVIC, DJORDJE T.
ZORICA MARINKOVIC* and DEJAN U. SKALA
and Metallurgy, University of Belgrade, Karnegijeva 4, P. O. Box 3503,
YU-11120 Belgrade and
*Center for Multidisciplinary Studies, University of Belgrade, Kneza Viseslava 1a, YU-11000 Belgrade, Yugoslavia
(Received 5 April
The alumina/silica with zinc chloride aerogel alkylation catalyst was obtained using a one step sol-gel synthesis, and subsequent drying with supercritical carbon dioxide. The aerogel catalyst activity was found to be higher compared to the corresponding xerogel catalyst, as a result of the higher aerogel surface area, total pore volume and favourable pore size distribution. Mixed Al–O–Si bonds were present in both gel catalyst types. Activation by thermal treatment in air was needed prior to catalytic alkylation, due to the presence of residual organic groups on the aerogel surface. The optimal activation temperature was found to be in the range 185–225°C, while higher temperatures resulted in the removal of zinc chloride from the surface of the aerogel catalyst with a consequential decrease in the catalytic activity. On varying the zinc chloride content, the catalytic activity of the aerogel catalyst exhibited a maximum. High zinc chloride contents decreased the catalytic activity of the aerogel catalyst as the result of the pores of the catalyst being plugged with this compound, and the separation of the alumina/silica support into Al-rich and Si-rich phases. The surface area, total pore volume, pore size distribution and zinc chloride content had a similar influence on the activity of the aerogel catalyst as was the case of xerogel catalyst and supported zinc chloride catalysts.
Keywords: aerogel catalyst, Friedel-Crafts alkylation catalyst, sol-gel derived catalyst.
Lead distribution in water and its association with sediment constituents of the “Barje” lake (Leskovac, Yugoslavia)
Z. TODOROVIC, P. POLIC*, D. DJORDJEVIC** and S. ANTONIJEVIC***
Faculty of Technology,
of Nis, Bulevar Oslobodjenja 124, Leskovac (E-mail:
Faculty of Chemistry, University of Belgrade, P. O. Box 158, Belgrade, (E-mail: email@example.com),
Institute of Chemistry, Technology and Metallurgy, P. O. Box 815, YU-11001 Belgrade and
Hemofarm Concern, Beogradski put bb, YU-26300 Vrsac, Yugoslavia
2000, revised 19 July 2001)
The lead concentrations in the water of the “Barje” lake are presented for the years 1995 to 1998. Sequential extraction was applied to estimate the chemical association of lead in the sediments of the “Barje” lake. Several lead fractions showed highly significant correlations with the corresponding substrate (step II: Mn-oxyhydroxides; step III: Fe-oxyhydroxides) suggesting that lead carbonates were incorporated with amorphous iron and manganese hydroxides. An explanation for this relation can be in the same anthropogenic source of these elements.
Keywords: lead, sediments, sequential extraction, correlation analyses.
ETAAS determination of thallium and silver from water matrix after colloidal precipitate flotation using lead(II) hexamethylenedithiocarbamate
KATARINA CUNDEVA, GORICA PAVLOVSKA and TRAJCE STAFILOV*
Institute of Chemistry, Faculty of Natural Sciences and Mathematics, St. Cyril and Methodius University, P. O. Box 162, 91000 Skopje, Macedonia
(Received 6 March,
18 June 2001)
Afast method for the preconcentration of thallium and silver in nanogram quantities in fresh drinking waters (source, well, tap) and waters for irrigation using colloidal precipitate flotation is described. Lead(II) hexamethylenedithiocarbamate, Pb(HMDTC)2 played the role of flotation collector. The experimental conditions for the successful separation of thallium and silver (mass of Pb, amount ofHMDTC-, pHof the system, induction time, type of surfactant etc.) were optimized. After flotation separation from the mother liquor, the solid sublate containing traces of thallium and silver was dissolved and the analytes were determined by electrothermal atomic absorption spectrometry (ETAAS). The results of the ETAAS analysis are compared with those obtained by inductively coupled plasma-atomic emission spectrometry. The detection limit for thallium by this method is 0.027 mg/l, and for silver 0.005 mg/l.
Keywords: thallium, silver, determination, water, colloidal precipitate flotation, ETAAS, lead(II) hexamethylenedithiocarbamate.
N O TE
The STM analysis of a silver mirror surface
NEBOJSA D. NIKOLIC, ZLATKO RAKOCEVIC* and KONSTANTIN I. POPOV**
Njegoseva 12, Belgrade,
*Vinca Institute of Nuclear Sciences, Belgrade and
**Faculty of Technology and Metallurgy, Karnegijeva 4, Belgrade, Yugoslavia
(Received 23 May
In this work, the structure of a silver mirror surface was examined by the STM technique. It was shown that the structural characteristics which enable a high degree of mirror reflection from this surface, which is very close to the ideal reflectivity of silver, are: flat and mutually parallel parts of the surface which are smooth on the atomic level, and distances between adjacent flat parts which state several atomic diameters.
Keywords: silver mirror, STM technique.
Copyright & copy;
Updated October 8, 2001.
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