Christina Tzvetkova

• PhD
• Bulgarian Academy of Sciences

Moderate consumption of wine 1-2 glasses a day during meals contributes to the supply of various antioxidants and essential elements for the body. Wines from the region of the Thracian lowland of varieties Dimiat, Sauvignon Blanc, Cabernet Fran, Rubin, Syrah, Merlot, and Chardonnay have been studied. Fluorescence spectra at the wavelength for excit...

The aggregate of various chemical substances useful for the functioning of the human body are known as nutrients. Spirulina has been present in human nutrition since ancient times, but in recent years the interest in it has been particularly increased due to the emergence of numerous alternative methods of nutrition. This study aimed to compare the...

Introduction: Aloe (Aloe barbadensis Miller ) is the most used medicinal plant in the world. Many of its beneficial properties are due to the presence of proteins, carbohydrates, amino acids, trace elements, etc. in the gel found in its leaves. It is part of various nutritional supplements, juices, cosmetic products, etc. Aim: The aim of the presen...

The study assesses the role of the various potential and active sources of impact on the quantity and quality of surface and groundwater in the area of the Regional Landfill for Solid Household Waste in Yambol. The focus is on the geological and hydrogeological characteristics of the terrain and the anthropogenic load on the catchment basin of the...

Melon wine and white cherry wines purchased from the commercial market were studied. The aim of the present work is to evaluate the elemental composition, antioxidant activity and optical properties of these fruit wines. The analysis of certain elements in wines is of interest because the concentrations of some of them are regulated, others because...

Activated carbons were prepared based on hydrolyzed lignocellulosic biomass, and were chemically activated with potassium hydroxide and phosphoric acid. The texture parameters of the adsorbents obtained were determined by low-temperature nitrogen adsorption; their thermal stability was studied by DTA/ TG and the surface functional groups-by FTIR sp...

Rhenium (Re) is one of the scarcest and more broadly dispersed elements on Earth. Due to its paucity and high demand by the aerospace and petroleum industries, it is also one of the most valuable metals in the international market. In recent years, reports about the occurrence of Re in soils surrounding copper-molybdenum mines and its uptake by the...

The present study aims at removal of hexavalent chromium from aqueous solution using manganese ferrite (MnFe 2 O 4) nanoparticles. The investigated material was obtained by solution combustion method using starting reagents Mn(NO 3) 2 .4H 2 O and Fe(NO 3) 3 .9H 2 O (as oxidizers) and citric acid (as a re-ducer). Nanoparticles of MnFe 2 O 4 were cha...

In this study, the concentrations of 14 elements in two brands of Bulgarian (three products of each) and a Romanian beer were determined. As a low alcoholic beverage, beer is often consumed in large quantities, therefore the concentration of the elements is compared with the rules for their content in drinking water. The fluorescence spectra for in...

The formation of silicagel from sodium silicate solution obtained by alkaline autoclave treatment of copper slag was investigated. The influence of the parameters of the gelation process (type of acid used, the pH of the medium, and drying conditions) on the structure and properties of the resulting silicagel, were studied. Silicagels obtained unde...

Oxidation of waste slag from copper production was studied in oxygen-nitrogen gaseous mixtures (21, 43, 63 and 100 vol.% of O 2) under non-isothermal conditions using DTA-TG analysis at constant gas flow rate of 30 ml min-1 and varying heating rate. The results revealed that the mechanism of slag oxidation does not change with changing the oxygen c...

A technological scheme for copper slag processing is proposed. It comprises 5 stages, namely: (i) air oxidation of the copper slag at a temperature above 800 °C for 2 h; (ii) hydrothermal treatment of the oxidized slag with sodium hydroxide solution (140 g/l) at 190 °C for 3 h; (iii) separation of the solid from the liquid phase by hot filtration;...

Glass transition temperatures, T-g, are determined for a series of multicomponent borate glasses with composition xPbO. (33.33 - x)Na2O center dot yAl(2)O(3)center dot 1.3ySiO(2). (66.67 - 2.3y)B2O3, (where x and y take values from 0 up to 13.5 mol%, and from 0 up to 5.3 mol%, respectively). For this purpose, differential scanning calorimetry is us...

The studied hybrid material, based on diatomite and active carbon (KAC), is suitable for adsorption of phenol. The nature of the initial components (diatomite K and active carbon AC) exerts strong influence on the hybrid adsorbent texture. The pore size distribution curve indicates that the sample is mesoporous with comparatively non-uniform pore s...

The relationship between the structure and glass transition temperature, Tg, is investigated for a series of multicomponent borate glasses with compositions xPbO.(33,33- x)Na2O. yAl2O3.1,3ySiO2.(66.67-2,3y)B2O3, (x = 0 -13.5 mol%, y = 0 - 5.3 mol%). The Tg values of these glasses containing two types of modifier oxides, Na2O and PbO, are determined...

Re phytomining is applied as an inexpensive and environmentally friendly technique that leads to remediation of exhausted soils of copper mines and ore-dressing regions. Investigative results on Re distribution in the vegetation in the vicinity of three copper mines in Bulgaria showed that rhenium was not uniformly distributed in the areas. It was...

535 We have previously found that a rare trace element rhenium, of which the average abundance in the earth's crust is 7 × 10 –8 % (Vinogradov's clark [1]), is efficiently accumulated in the green matter of plants in amounts exceeding the clarke by hundreds and thouu sands of times, reaching a concentration of 10 –4 – 10 ⎯3 % [2–10]. A correlation...

The basic disadvantages of classical methods for Re recovery from ores and concentrates were shown. An alternative method by phytoextraction of Re from ore dressing soils was proposed. The content of Re in phytoconcentrates of lucerne (46 586 g Re/t dry mass) and clover (35 090 g Re/t dry mass) obtained at laboratory conditions were compared with t...

Kinetics of structural relaxation and crystallization of NaPO3 glassforming melt is studied by means of thermal analyses. It is demonstrated that activation energy depends strongly on fictive temperature Tf. The dependence of the onset temperature To of the glass transition interval on the heating rate q+ is investigated for samples that were previ...

The distribution of Pb, Cd, Bi, and Cu in Black Sea brine system (solution--colloidal particles--biota) produced in Burgas and Pomorie salterns is studied. The established distribution of the title elements among the brine components is as follows: Pb--25% in the salt solution, 30%--in colloidal particles, 45%--in biota (Halobacterium salinarium an...

The solubility diagrams of the systems CsBr- Me2+Br 2-H 2O ( Me2+=Mn, Co, Ni) and NH 4Br-MnBr 2-H 2O have been determined at 25°C. Four previously unreported double salts, 2NH 4Br·MnBr 2·2H 2O (space group P4 2/ mnm, a=7.886(1) Å, b=7.886(1) Å, c=8.529(2) Å, Z=2, V=530.4(2) Å 3, Dx=2.797), 2CsBr·MnBr 2·2H 2O (space group Poverline1, a=5.993(1) Å, b...

The ability of the Co2+and Ni2+ions to form double salts of the carnallite formula type (Me+X·Me2+X2·6H2O) in aqueous-halide solutions is established. Two new double salts, KBr·NiBr2·6H2O (PDF 45-196) and RbBr·CoBr2·6H2O (PDF 45-198), are found in the KBr–NiBr2–H2O and RbBr–CoBr2–H2O systems, respectively. The structure of NH4Br·NiBr2·6H2O (1) (PDF...

Investigation was carried out on leaves of green geranium (Pelargonium) grown on soil spiked with perrhenate and containing a known amount of bioaccumulated rhenium. Two ways of rhenium extraction and preconcentration from green leaves of geranium were studied: i) direct incineration of the raw leaves and alkaline leaching of rhenium from the ash;...

The plant Biosphere was shown to be a natural biocollector and concentrator of dispersed rhenium in environment. The bioaccumulation and preconcentration of rhenium in plants can be used for its recovery from soils and waters from ore dressing and work processing regions. A new approach to the development of a procedure for rhenium phytorecovery is...

An approach using plants growing in ore dressing and mining regions as a source for Re recovery was proposed. Regional investigations on the degree of rhenium accumulation in various plant species from the "Asarel" mine in Bulgaria were carried out. It was established that the plant biosphere in this vicinity was enriched in rhenium in amounts exce...