Oksana Velgosová

Study of Ni And Cd Bioleaching from Spent Ni-Cd Batteries

Abstract In the present work the Ni and Cd extraction from the electrode material of spent Ni-Cd batteries by bioleaching using the bacteria Acidithiobacillus ferrooxidans was examined. The possibility of the use of the bacteria for both the Ni and Cd recovery was analyzed. The anode of Ni-Cd batteries contains Ni0, Ni(OH)2, Cd0 and Cd(OH)2. The cathode is covered by nickel hydroxides and nickel oxy-hydroxides. The pH values and content of Ni and Cd in the solution were monitored throughout the experiment (the initial pH was 1.5, the experiment took 28 days). The bioleaching efficiency of Ni and Cd from anode powder reached 5.5% and 98%, respectively. During the cathode powder bioleaching Ni and Cd efficiency reached 45% and 100%, respectively. Throughout the bioleaching process mainly the dissolution of hydroxides occurred meanwhile Ni0 leaching was not observed. The AAS analysis was used to analyze the amount of Ni and Cd in the solutions. The amount of Ni and Cd present in the solid samples before and after bioleaching was examined using X-ray analysis.

Assessment Of Biologically Synthesized Ag Nanoparticles Toxicity Against E. coli, Staphylococcus aureus, Parachlorella kessleri And Sinapis alba

Abstract In general, Ag+ ions and AgNPs are considered to be the most toxic for bacterial cells and less toxic for higher organisms. In the present work inhibitory effects of biologically prepared silver nanoparticles on the growth of bacteria E. coli CCM 3954 and Staphylococcus aureus CCM 3953, green microscopic alga Parachlorella kessleri LARG/1 and seed germination and root growth of plant Sinapis alba seeds were investigated. Surprisingly, silver nanoparticles showed much stronger inhibitory effects on plant seed germination and root growth than on the bacterial growth. At concentration of 75 mg/l AgNPs both seed germination and root growth of Sinapis alba was inhibited whereas inhibition of the growth of E. coli and S. aureus was observed at >195 mg/l. Growth inhibition of alga Parachlorella kessleri was recorded at 300 mg/l AgNPs concentration. The inhibitory effect of silver ions was much higher compared to silver nanoparticles. Even 20 mg/l concentration of Ag+ ions inhibited the root growth and concentration > 45 mg/l inhibited germination of Sinapis alba seeds. Inhibition zones in both studied bacteria were found at concentration > 140 mg/l.

Influence Of Used Bacterial Culture On Zinc And Aluminium Bioleaching From Printed Circuit Boards

Abstract Bioleaching processes were used to solubilize metals (Cu, Ni, Zn and Al) from printed circuit boards (PCBs). In this study, a PCBs-adapted pure culture of Acidithiobacillus ferrooxidans, pure culture of Acidithiobacillus thiooxidans and PCBs-adapted mixed culture of A. ferrooxidans and A. thiooxidans were used for recovery of the metals. The study showed that the mixed bacterial culture has the greatest potential to dissolve metals. The maximum metal bioleaching efficiencies were found to be 100, 92, 89 and 20% of Cu, Ni, Zn and Al, respectively. The mixed culture revealed higher bacterial stability. The main factor responsible for high metal recovery was the ability of the mixed culture to maintain the low pH during the whole process. The pure culture of A. thiooxidans had no significant effect on metal bioleaching from PCBs.

The Effect of Culture Age and Initial Silver Concentration on Biosynthesis of Ag Nanoparticles

Abstract Many organisms or their extracts have the ability to reduce Ag+ ions to Ag0 and stabilize them what results in nanoparticle formation in solution. The aim of the article was to study the influence of two selected parameters - initial silver concentration and culture age, on Ag nanoparticles production by green algae Parachlorella kessleri. The presence of Ag nanoparticles in the solution was confirmed by the UV-vis spectroscopy and TEM analyses. Typical curve with the peak at app. 420 nm was found for nanoparticles produced by algae. While culture age did not have any significant effect, the initial silver concentration had significant influence on nanoparticle production which influenced the rate of nanoparticle production, their amount, their size and stability, as well

Effect of storage conditions on long-term stability of Ag nanoparticles formed via green synthesis

Spherical Ag nanoparticles (AgNPs) with a diameter of 20 nm or smaller were biologically synthesized using algae Parachlorella kessleri. The effect of storage conditions on the long-term stability of AgNPs was investigated. UV/Vis spectrophotometry, transmission electron microscopy, and dynamic light scattering measurements revealed that the long-term stability of AgNPs was influenced by light and temperature conditions. The most significant loss of stability was observed for the AgNPs stored in daylight at room temperature. The AgNPs stored under these conditions began to lose their stability after approximately 30 d; after 100 d, a substantial amount of agglomerated particles settled to the bottom of the Erlenmeyer flask. The AgNPs stored in the dark at room temperature exhibited better long-term stability. Weak particle agglomeration began at approximately the 100th day. The AgNPs stored in the dark at about 5°C exhibited the best long-term stability; the AgNPs stored under such conditions remained spherical, with a narrow size distribution, and stable (no agglomeration) even after 6 months. Zeta-potential measurements confirmed better dispersity and stability of AgNPs stored under these conditions.

Limitations and possibilities of green synthesis and long-term stability of colloidal Ag nanoparticles

In this paper the influence of algae life cycle and the solutions pH on the green synthesis of colloidal Ag nanoparticles (AgNPs) as well as effect of different storage conditions on AgNPs long-term stability was investigated. Silver nanoparticles were biologically synthesized using extracts of Parachlorella kessleri algae cultivated 1, 2, 3 and 4 weeks. The formation of AgNPs was monitored using a UV–vis spectrophotometer and verified by TEM observation. The results confirmed formation of polyhedron and/or near polyhedron AgNPs, ranging between 5 and 60u2005nm in diameter. The age of algae influenced the synthesis rate and an amount of AgNPs in solution. The best results were obtained using tree weeks old algae. UV–vis analysis and TEM observation also revealed that the size and the stability of AgNPs depend on the pH of solution. AgNPs formed in solutions of higher pH (8 and 10) are polyhedron, fine, with narrow size interval and stabile. Nanoparticles formed in solutions of low pH (2, 4 and 6) started to lose their stability on 10th day of experiment, and the particle size interval was wide. The long-term stability of AgNPs can be influenced by light and temperature conditions. The most significant stability loss was observed at day light and room temperature (21°C). After 200-days significant amount of agglomerated particles settled on the bottom of the Erlenmeyer flask. AgNPs stored at dark and room temperature showed better long-term stability, weak particles agglomeration was observed. AgNPs stored at dark and at temperature 5°C showed the best long-term stability. Such AgNPs remained spherical, fine (5-20u2005nm), with narrow size interval and stable (no agglomeration) even after more than six months.In this paper the influence of algae life cycle and the solutions pH on the green synthesis of colloidal Ag nanoparticles (AgNPs) as well as effect of different storage conditions on AgNPs long-term stability was investigated. Silver nanoparticles were biologically synthesized using extracts of Parachlorella kessleri algae cultivated 1, 2, 3 and 4 weeks. The formation of AgNPs was monitored using a UV–vis spectrophotometer and verified by TEM observation. The results confirmed formation of polyhedron and/or near polyhedron AgNPs, ranging between 5 and 60u2005nm in diameter. The age of algae influenced the synthesis rate and an amount of AgNPs in solution. The best results were obtained using tree weeks old algae. UV–vis analysis and TEM observation also revealed that the size and the stability of AgNPs depend on the pH of solution. AgNPs formed in solutions of higher pH (8 and 10) are polyhedron, fine, with narrow size interval and stabile. Nanoparticles formed in solutions of low pH (2, 4 and 6) started to l...

Influence of technological factors on dispersion strengthened materials deformation mechanism studied by ‘in-situ tensile test in SEM’

Direct observation of deformation process until formation of fracture on extreme small samples of composite in SEM is interesting from practical and interpretation aspects. In the present work the effects of composite composition, volume fractions of secondary phases as well as the matrix grain sizes (micro and nano size) on deformation and failure processes of Al and Cu-based composites were evaluated. Experimental materials were prepared by the different powder metallurgy methods. Interpretation of results was based on the quantification of the physical parameters of material phases depending on the preparation methods and on the analysis of deformation processes using the ‘in-situ tensile test in SEM’. The mechanism of deformation and fracture for each composite system was estimated and models of fracture were proposed.