Papers by Author: Iveta Štyriaková

Abstract: Quartz sands contain various iron and clay minerals which coat silicate grains or are impregnated in silicate matrix. Treatment by basin water bioleaching in combination with electromagnetic separation can substantially improve the quality of quartz sands. The purpose of this in-situ study was to evaluate the feasibility of using a biological basin treatment process to improve the quality of quartz sands. The environmental conditions involved the changes of climate temperature, using fresh surface water without disinfection, inhibition of algae and fungi, and promoting bacteria. Analyses of the solution phase were used to monitor the dissolution of iron during the bioleaching of the quartz sands and to optimize the in-situ conditions for the bacterial activity. The rate of iron dissolution varied with environmental conditions, with the addition of nitriloacetic acid (NTA)/l and organic feedstock in the form of molasses. Bacterial removal of clay and iron minerals can be used to expose the white surfaces of quartz grains. The quartz sands from the Šaštín deposit (Slovakia) were used in glass industry after decreasing the Fe content.

Abstract: To examine the effects of organic and inorganic amendments on the degradation of petroleum hydrocarbons, we conducted a pilot-scale experiment during the winter and summer periods. Soil samples were analyzed periodically to determine the soil gas amount of volatile organic compound, carbon dioxide flux, consumption of O2 and indigenous bacterial numbers during bioremediation. The initial level of the most contaminated site (10 070 mg hydrocarbon kg-1 soil) was reduced successively to 4 800 mg kg-1 after 4 months and to 1 400 mg kg -1 after 6 months in ex-situ amended soils. The hydrocarbon-degrading microbial populations increased during the treatment as also did soil respiration. Both aerobic and methanogenic conditions appeared to be important at these sites. Methane concentration (500-23 000 ppm) and CO2 production (800-17 000 ppm) varied with the extent of contamination. The bioventing system used in this study aerated a wide area of soil. It was concluded that N and P availability within the organic and inorganic nutrients limited the biodegradation of hydrocarbon contamination. By combination of organic and inorganic amendments a 86% removal efficiency was achieved. Nutrient diffusion varied within the 3 m high decontamination biopile but was sufficient to promote bacterial proliferation in all layers.

Abstract: This paper investigates Zn2+ and Cu2+ adsorption capability of bentonite and zeolite taken from the non-raw metallic deposits of Slovakia. Viable biomass of an Bacillus pumilus and Bacillus megaterium enhanced the efficiency of Zn2+ and Cu2+ adsorption from model solution. Initial concentration of Cu and Zn in model solutions initially containing 32.3 mg.Cu.L-1and 42.9 mg Zn.L-1 after six hours sorption and desorption at 25°C, it was observed that 1g bentonite whit bacteria inokulum was found to remove 0.195 mg Zn2+ and 0.17 mg Cu2+ from the solution and 1g zeolite was found to remove 0.088 Zn2+ and 0.051 Cu2+. The ability for Zn and Cu sorption was bentonite > zeolite. The adsorption of metal ions on bentonite and zeolite depends on pH. Between pH 4 and 6, the main mechanism is by ion exchange. In order to prevent contamination of subsoil and groundwater by leachates containing heavy metals, bentonite and zeolite are widely used as cost-effective treatments barriers. For this reason it is important to study the adsorption of metals by these materials.

Abstract: Bioleaching is technology applicable to iron extraction from low-grade non-metallic raw materials. Bioleaching of quartz sands and feldspars involves the action of heterotrophic bacteria. Impurities include fine – grained limonite, goethite, hematite or mica were removed by the reductive dissolution of Fe3+ in linked with the silicate mineral destruction. Heterotrophic bacteria produced organic acids that are able to solubilize Fe oxide and silicates but require organic carbon as a source of energy. Molasses is a relatively inexpensive carbon source used for various industrial fermentations and contains also other nutrients that accounted for the enhancement of iron dissolution in this study. The admixture of pigments in molasses coloured the samples, but the discoloration could be removed by the addition of NaClO following the bioleaching step. The feasibility of the bioleaching treatment has to be tested specifically to each type of silicate raw materials. The Fe content in the quartz sands and feldspar samples by the biological leaching decreased as much as 60% and by subsequent using of electromagnetic separation of feldspars, the decrease of Fe content in 74% was achieved. However, the application of magnetic separation of quartz sands after bioleaching resulted in total iron removal of 93 % and in such combined way prepared product contained 0.024 % of Fe2O3. Achieved results on iron removal point to the fact that combination of leaching and magnetic separation enables to obtain product usable in glass and ceramic industry.

Abstract: Ultra-fine iron particles are difficult to treat by conventional mineral processing methods. Thus bioleaching is an attractive alternative for effective removal of iron minerals. The removal of oxidic Fe-phases from industrial silicates via bioleaching needs to be optimized with regard to the rate of iron reduction and dissolution. A new role for chelators as the low addition of AQDS or NTA during bacterial quality improvement of non-metallics, resulted in stimulating of Fe dissolution under non-controlled anaerobic conditions. AQDS stimulated bacterial iron reduction and Fe2+ concentration in solution was higher than Fe3+. However, NTA non-stimulated iron reduction, but increased bacterial iron dissolution in form of Fe3+. Changes in iron removal from samples were used to assess the chelator effectiveness of the heterotrophic bioleaching process. Chelators might be added to iron-contaminated non-metallics during bioleaching processes for stimulation of rate of iron removal.