Lenka Borecka

The Czech Academy of Sciences | AVCR · Department of Geochemistry

Exotic carbonate – siliceous coralloid speleothems of the Koněprusy Caves, which consist of dominant aggregates of feather‐like, radial fibrous, dogtooth and gothic‐arch calcite crystals, contain a diversity of petrified fossil microbes entombed in siliceous parts of the speleothems. Although a complete diagenetic continuum of SiO2 polymorphs, rang...

Raman mapping microspectroscopy was used as an advantageous high spatial resolution method for detailed assessment of the structure of radiation-induced halos in bituminous coal (Upper Paleozoic) with numerous inclusions of uraninite and coffinite. The uranium content in inclusions in the samples studied ranged from 40 to 50 wt%. Raman structural p...

This work presents a characterization of the textural properties and the CO2 adsorption capacity of carbonized products prepared by pyrolysis of sewage sludge. A comparison is made between variants with and without water steam activation. A solid residue is prepared as a low-cost adsorbent for removing and capturing CO2 and pollutants. The CO2 adso...

The tufas of the presently shallow Chlupáčova sluj Cave document an unusual history of deeper to shallower hydrologic processes in cave evolution. The wider geological context of the cave, along with fluid inclusion and stable isotope (C and O) analyses of calcite from tectonic veins cutting through its wallrock, are evidence of the origin of the c...

Moganite, a metastable polymorph of SiO2 has been identified in carbonate-siliceous speleothems of the Koněpruské jeskyně Cave, the Bohemian Karst. Moganite was detected by means of Micro-Raman spectroscopy in partially silicified corraloid speleothems (so called Koněprusy rosettes) the carbonate matrix of which consists of exotic calcite crystals...

Opening of the Blanka Tunnel Complex (BTC) in Prague, Czech Republic, the longest city tunnel in Europe, significantly increased traffic on a connected main road, the V Holešovičkách street (VHS). To study environmental changes in VHS connected with BTC opening, sampling of road dust and airborne particulate matter in the VHS vicinity started 3 yea...

Gothic arch calcite, a specific crystallographic variety of calcite known from some hot springs and tufa streams, has been newly recognized in the Koněprusy Caves. The gothic-arch calcite occurs on the exteriors of exotic coralloid speleothems where it coexists with scalenohedral (dogtooth) spar crystals. The crystals exhibit microscopic ultrastruc...

The infrared (ATR-FTIR) and Raman spectroscopy was used for the structural characterization of honeybee wings. Protein, chitin, and lipid characteristic spectral features were detected using both methods. The protein secondary structure was predominantly composed of the β-sheet molecular conformation with β-turns or coil contributions. The vibratio...

The presence of uranium, with a bulk mass fraction of about 1.5 wt% and radiolytic alterations are a feature of Cenomanian amber from Křižany, at the northeastern edge of the North Bohemian Cretaceous uranium ore district. Pores and microcracks in the amber were filled with a mineral admixture, mainly in the form of Zr-Y-REE enriched uraninite. As...

Considerable amount of waste in the form of polyethylene terephthalate (PET) bottles could be utilized in the form of dispersed microreinforcement in concrete. PET fibres, however, have poor wettability and adhesion to cement paste, which can be modified by alkaline hydrolysis with sodium hydroxide at elevated temperature. The alkaline treatment wa...

A combined sorbent was prepared by impregnation of lignite mined in the South Moravian Coalfield, Czech Republic, with chitosan. Sorption performance of the combined sorbent and the untreated lignite was tested for Co(II), Cu(II), and Cd(II) in equilibrium sorption experiments with respect to pH and metal concentration. The amount of metal retained...

Inexpensive regenerable natural sorbents of toxic metals and radionuclides with high capacity, good mechanical properties and stability have been developed. They are used in waste water treatment, groundwater remediation and in construction of active geochemical barriers. The review deals with sorption properties of humic substances and chitosan as...

Poly(ethylene terephthalate) (PET) fibres have been used as a dispersed micro-reinforcement in a cementitious matrix. The micro-reinforcement in the fibre reinforced concrete absorbs tensile strain and prevents formation of microcracks originating from concrete shrinkage. The present work has been aimed at studying the effects of aging PET fibres b...

Potential low-cost sorbents of metals based on combined action of coal and chitosan have been investigated. Sorption of Cs, Co and Eu on oxidized coals in mixture with chitosan was studied as function of pH ( approximately 3-6) in batch experiments using radiotracer method. An improved sorption efficiency of the coal sorbents at neutral pH was obta...

Oxycarbides were produced by pyrolysis of polysiloxanes with different contents of methyl/phenyl groups at 1000 °C under nitrogen atmosphere. The structure of the three silicon oxycarbides was studied by elemental analysis, spectroscopy, and X-ray diffraction. The free carbon phase was concentrated by treatment with hydrofluoric acid. The sp2 graph...

The project was aimed to investigate the present-day and ancient geothermal conditions in major sedimentary basins of the Czech Republic and establish a link between its geothermal history and tectonic development. The studies involving illite crystallinity, optical reflectance of organic matter, apatite fission-track analysis, gas chromatography-m...

Projekt GA ČR č. A 3012703 byl zaměřen na prozkoumání současných a fosilních teplotních poměrů ve významných sedimentárních pánvích České republiky a na zjištění souvislostí mezi jejich geotermálním a tektonickým vývojem. Na základě výsledků stanovení stupně krystalinity illitu, optické odraznosti organické hmoty, analýzy stop štěpení uranu v apati...