Yu Runlan

Effect of EPS on adhesion of Acidithiobacillus ferrooxidans on chalcopyrite and pyrite mineral surfaces

Extracellular polymeric substances (EPS) were extracted from Acidithiobacillus ferrooxidans through sonication method associated with centrifugation, which was evaluated tentatively with 2-keto-3-deoxyoctonic acid (KDO) as the indicator of EPS by spectrophotometry. Then the effect of EPS of A. ferrooxidans on the adhesion on chalcopyrite and pyrite surfaces was studied through a series of comparative experiments. The untreated cells and EPS-free cells of A. ferrooxidans were mixed with EPS suspension, Fe2+ or Fe3+, respectively. The planktonic cells were monitored in 2 h during bioleaching. The results indicate that the presence of EPS on the cell is an important factor for the adhesion to chalcopyrite and pyrite. A decrease of attachment of A. ferrooxidans to minerals was produced by the deficiency of EPS, which can recover mostly when the EPS was re-added into the EPS-free cells. The restoring extent is more obvious in pyrite than in chalcopyrite. The extent of cell adhesion to chalcopyrite increased when EPS and Fe3+ added, and decreased when Fe2+ added, which imply the electrostatic interaction plays a main role in initial adhesion between bacteria and minerals and it is a driving force for bacteria to produce EPS probably as a result of regaining their attachment ability to copper sulphides.

Relationship and effect of redox potential, jarosites and extracellular polymeric substances in bioleaching chalcopyrite by acidithiobacillus ferrooxidans

Abstract The changes of pH, redox potential, concentrations of soluble iron ions and Cu 2+ with the time of bioleaching chalcopyrite concentrates by acidithiobacillus ferrooxidans were investigated under the different conditions of initial total-iron amount as well as mole ratio of Fe(III) to Fe(II) in the solutions containing synthetic extracellular polymeric substances (EPS). When the solution potential is lower than 650 mV (vs SHE), the inhibition of jarosites to bioleaching chalcopyrite is not vital as EPS produced by bacteria can retard the contamination through flocculating jarosites even if concentration of Fe(III) ions is up to 20 g/L but increases with increasing the concentration of Fe(III) ions; jarosites formed by bio-oxidized Fe 3+ ions are more easy to adhere to outside surface of EPS space on chalcopyrite; the EPS layer with jarosites acts as a weak diffusion barrier to further rapidly create a high redox potential of more than 650 mV by bio-oxidizing Fe 2+ ions inside and outside EPS space into Fe 3+ ions, resulting in a rapid deterioration of ion diffusion performance of the EPS layer to inhibit bioleaching chalcopyrite severely and irreversibly.

EPS-contact-leaching mechanism of chalcopyrite concentrates by A. ferrooxidans

Abstract The effect of extracelluar polymeric substances(EPS) on the bioleaching chalcopyrite concentrates in the presence of iron- and sulphur-oxidizing bacteria ( A. ferrooxidans ) was studied. The bacterial number, pH, redox potential, and the concentrations of Fe 2+ and Cu 2+ ions were investigated. The leached residues were analyzed by the X-ray diffraction and FT-IR. The results indicate that the EPS makes the bacteria adhere to the chalcopyrite surface easily and it is helpful for bacteria in disadvantageous environment. At the same time, EPS film layer with Fe 3+ deposits on the surface of chalcopyrite and becomes a barrier of oxygen transfer to chalcopyrite to passivate chalcopyrite, and creates the high redox potential space through concentrating Fe 3+ ions to accelerate bioleaching pyrite in chalcopyrite concentrates. The results suggest that EPS formation promotes bioleaching pyrite and inhibits bioleaching chalcopyrite, especially under high potential condition.

Optimization of separation processing of copper and iron of dump bioleaching solution by Lix 984N in Dexing Copper Mine

Abstract The effects of the concentration of Lix 984N, phase ratio, initial pH value of aqueous phase and extraction time on the extraction of copper and iron under the condition of low Cu2+/Fe3+ ratio in dump bioleaching solution of Dexing Copper Mine were explored. The optimal conditions of extraction are as follows: the concentration of Lix 984N 10%; the phase ratio (O/A) 1:1; the initial pH value of aqueous phase 1.5 and the mixing time 2 min. The stripping experiments show that H2SO4 solution could efficiently recover copper from the organic phase under the optimal conditions.

Interaction mechanism of Cu2+, Fe3+ ions and extracellular polymeric substances during bioleaching chalcopyrite by Acidithiobacillus ferrooxidans ATCC2370

Abstract The extracellular polymeric substances (EPS) of Acidithiobacillus ferrooxidans ATCC 23270, and iron and copper enclosed in EPS were extracted by ultrasonication and centrifugation methods to determine the interaction mechanism of Cu 2+ , Fe 3+ and EPS during bioleaching chalcopyrite. Generally, Cu 2+ ions can stimulate bacteria to produce more EPS than Fe 3+ ions. The mass ratio of Fe 3+ /Cu 2+ enclosed in EPS decreased gradually from about 4:1 to about 2:1 when the concentration of Cu 2+ ions increased from 0.01 to 0.04 mol/L. The amount of iron and copper bound together by EPS in ferrous-free 9K medium containing 1% chalcopyrite was about 2 times of that in 9K medium containing 0.04 mol/L Cu 2+ ions. It was inferred that the EPS with jarosites on the surface of chalcopyrite gradually acted as a weak diffusion barrier for Cu 2+ , Fe 3+ ions transference during bioleaching chalcopyrite.

Really active form of fluorine toxicity affecting Acidithiobacillus ferrooxidans activity in bioleaching uranium

In order to determine the mechanism of bacterial tolerance to fluorine, Acidithiobacillus ferrooxidans ATCC 23270 was domesticated and studied under the conditions of different fluorine concentrations and pH values with or without treatment by Proteinase K. The bacterial activities were observed through measuring the changes of solution potentials by platinum electrode with Ag/AgCl reference electrode and the intracellular fluorine was determined by fluorine ion-selective electrode. The results indicated that the tolerance of Acidithiobacillus ferrooxidans ATCC 23270 to fluorine could be obviously improved by domestication, HF was the effective form of fluorine to affect the bacterial activity, and pH increase or concentration change of ions of strong complex ability with fluorine ions in solution could result in false appearance of high fluorine-resistant strain. Some proteins located in cell wall or cell membrane were intimately relative with the bacterial fluorine tolerance.

Removal of SO42−, uranium and other heavy metal ions from simulated solution by sulfate reducing bacteria

Abstract In the case of in-situ leaching of uranium, the primitive geochemical environment for groundwater is changed since leachant is injected into the water bearing uranium deposit. This increases the concentration of SO 4 2− , uranium and other heavy metal ions and results in the groundwater contamination. The effects of pH values of the simulated solution on the reduction of SO 4 2− and the removal of uranium and other heavy metal ions by sulfate reducing bacteria(SRB) were studied. The results show that, when the pH value of the simulated solution is about 8, the reduction rate of SO 4 2− by SRB and the removal rate of uranium, Mn 2+ , Zn 2+ , Pb 2+ and Fe 2+ will reach their highest values. A bioremediation technique for remediation of groundwater in in-situ leaching uranium mine can be developed.

Removal of copper from nickel anode electrolyte through ion exchange

Abstract An novel method for removal of copper from nickel anodic electrolyte through ion exchange was studied after cupric deoxidization. Orthogonal design experiments show the optimum conditions of deoxidizing cupric into Cu + in the nickel electrolyte are the reductive agent dosage is 4.5 times as the theoretic dosage and reaction time is 0.5 h at 40 °C and pH 2.0. Ion exchange experiments show that the breakthrough capacity( Y ) decreases with the increase of the linear flow rate( X ): Y =1.559–0.194 X + 0.006 7 X 2 . Breakthrough capacity increases with the increase of the ratio of height to radius(RRH). The higher the initial copper concentration, the less the breakthrough capacity(BC). SO 4 2i and nickel concentration have no obvious change during the process of sorption, so it is not necessary to worry about the loss of nickel during the sorption process. Desorption experiments show that copper desorption from the resin is made perfectly with NaCl solution added with 4% (volume fraction) H 2 O 2 (30%) and more than 100 g/L CuCl 2 solution is achieved.

Effect of pH values on extracellular protein and polysaccharide secretions of Acidithiobacillus ferrooxidans during chalcopyrite bioleaching

Abstract The effect of pH values on the extracellular protein and polysaccharide secretions of Acidithiobacillus ferrooxidans was comparatively investigated in different phases of bacterial growth during chalcopyrite bioleaching. The results indicate that the extracellular protein is always more than the extracellular polysaccharide secreted by attached cells on the chalcopyrite, on the contrary, and is always less than the extracellular polysaccharide secreted by free cells in the solution at bacterial adaptive phase, logarithmic phase and stationary phase whenever pH value is at 1.0, 1.5, 2.0 or 2.5; free cells are mainly through the secretion of extracellular polysaccharide rather than the extracellular protein to fight against disadvantageous solution environment, such as high concentration of metal ions and unsuitable pH solution; both amounts of polysaccharide and protein secreted by attached cells are mainly positively related to the solution acidity rather than the total concentration of soluble metal ions. The experimental results imply that bacteria are mainly through secreting more extracellular polysaccharide to fight against disadvantageous environment and the extracellular protein perhaps plays an important role in oxidation–reduction reactions in the bioleaching system.

Enrichment of ferric iron on mineral surface during bioleaching of chalcopyrite

In order to investigate the enrichment of ferric iron bound by extracellular polymeric substance (EPS) on the mineral surface during bioleaching of chalcopyrite, several methods including sonication, heating and vortexing were used and sonication at 48 °C was shown as a good way to extract ferric iron. Scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDX) analysis showed that lots of cracks and pits can be found on the chalcopyrite surface after bioleaching and that iron oxide was filled in these cracks and pits. The variations of contents of ferric iron and EPS on the chalcopyrite surface were investigated. The results indicated that the content of EPS increased rapidly in the first 10 d and then maintained at a stable level, while ferric iron content increased all the time, especially in the later stage of bioleaching.