Iveta Štyriaková

Biodestruction and deferritization of quartz sands by Bacillus species

Abstract Quartz sand containing mineral impurities was subjected to bioleaching with Bacillus spp. strains and subsequent elutriation. Bioleaching of the sample removed visible Fe-bearing minerals that coated quartz grains. During the bioleaching, elements were dissolved from silicate minerals. Poorly crystalline Fe-oxides that sealed siderite nodules were released from intergranular spaces and formed a fine-grained ( 3+ . However, chemical analysis showed a slight increase in Fe 2 O 3 content and a decrease in the FeO content following three months bioleaching in the Bacillus culture. X-ray diffraction analyses showed the loss of Fe-bearing minerals and mica following the bioleaching and the elutriation of the fine-grained fraction. Transmission electron microscopy and energy-dispersive analysis of X-rays showed nucleation of fine-grained Fe,Al-silicates on bacterial surface after three months of bioleaching.

Metal Leaching and Reductive Dissolution of Iron from Contaminated Soil and Sediment Samples by Indigenous Bacteria and Bacillus Isolates

ABSTRACT The purpose of this study was to leach Cu, Zn, As, and Fe from contaminated soil and sediment samples with indigenous heterotrophic bacteria isolated from the study sites. The sediment contained Fe in the form of goethite and low concentrations of other metals. The soil contained hematite and high concentrations of other metals. The environmental conditions affected the bacterial activity in the metals dissolution. As and Fe were the major metals leached from the sediment sample while a minor fraction of Cu was solubilized. Cu and Zn were the major metals leached from the soil sample while only a minor fraction of Fe was dissolved. As a control, a disinfectant was used for partial inactivation of indigenous bacteria. This treatment had a negative effect on the leaching of Fe, Zn and As from soil and sediment samples, but it increased Cu dissolution from the sediment. Bacterial different dissolution of Fe during soil and sediment bioleaching was also investigated with ferrihydrite. The iron concentration was much higher during ferrihydrite dissolution when indigenous bacteria from sediment were used compared to indigenous bacteria isolated from soil. The indigenous bacterial inoculum provided more biological and metabolic diversity which may account for the difference in reductive iron reduction from ferrihydrite. The Bacillus cultures isolated from soil and sediment samples showed similar efficiencies in reductive dissolution of ferrihydrite. The synergetic bacterial inhibition effect created by the environmental conditions can influence bioremediation effect.

Application Possibility of Bentonite and Zeolite in Bioremediation

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.

Influence of Chelators on Iron Solubilization from Quartz and Feldspars by Bioleaching

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.

Biological Purification of Silicate Minerals

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.

Utilization of Fe-Oxide Composites for as Removal from Aqueous Solutions

This work was done to assess the arsenate (AsV ) removal from the model solution by sorbents based on Fe-oxide. Two samples were compared in sorption properties, synthetically prepared Fe-oxide and bentonite/iron oxide (ratio 2:1). The effect of pH and initial metal ion concentration was investigated. The optimum pH for arsenic adsorption by both samples was found to be about 3.0. The adsorption increased very significantly with decreasing pH for both samples. The Fe-oxide sample achieved the maximum adsorption capacity 24,1 mg.g-1 AsV at pH 3, composite sample 14,1 mg.g -1 AsV at pH 3. The adsorption of AsV on Fe-oxide sample increased with the increasing initial metal ion concentration up to 40 mg/l and then equilibrium was established, by contrast of bentonite/Fe-oxide sample shown no significant change at this concentration range.

Intensification of Arsenic and Zinc Mobilization by Combination of Bio-Chemical Leaching with EDTA in the Soil and Sediment Bioremediation

The use of chemical pretreatment with 10mM EDTA to enhance the arsenic microbial mobilization was evaluated in this study. The bioleaching involved the use of the indigenous sedimentary and soil heterotrophic microorganisms, whose leaching media contained 2mM EDTA. The main objectives of using the chemical pretreatment was the removal of metal surface coatings from the iron minerals, such as Cu and Zn, which inhibited the iron microbial dissolution in the soil and sediment environment and thus increasing the mobilization of the retained As. To examine the effect of the chemical pretreatment and the biological leaching on the mobilization of Cu, Zn, and As, batch and column tests were conducted within the laboratory experiments. The removal of As and Zn from the soil and sediment was greatly enhanced by the co-treatment in the batch solution conditions than in the column percolate conditions and had negative effect only for Cu. In the batch tests, the heterotrophic bioleaching of the soil and sediment was found to have a pronounced positive effect on the extraction of As and Zn.

Microbial Dissolution of Iron Surface Coatings in Industrial Minerals

The purpose of this work was to investigate the phenomenon of microbial iron reduction in industrial minerals and materials. These materials are generally not pure, often associated with impurities usually in the form of Fe3+. In all cases, the presence of iron affects the colour and the physical properties of the mineral and therefore lowers their industrial value and limits their application. In this study bentonite, kaolin and quartz sand sample were used for the experiments and compared in effectiveness of iron dissolution. The experimental results showed that after 30 days of bioleaching process, bacteria are able to remove 9.29% of Fe occurring in the kaolin sample (K-I) in amorphous form of oxyhydroxides and approximately 12% of Fe from the bentonite sample (B-JP) also in amorphous form of oxyhydroxides. In the quartz sand sample C3-15D, the concentration of Fe decreased by 15% after 15 days of bioleaching process and in the sample C3-30D after 30 days of bioleaching process by 24.7%.

Ex Situ Biostimulation of Hydrocarbon Degradation by Organic and Inorganic Amendments

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.

In Situ Application of Bioleaching for Improving the Quality of Quartz Sand

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.