Solid State Phenomena Vol. 262

Abstract: The aim of this study was to investigate the microbial colonization and arsenic leaching kinetics of South Korean mine tailings containing arsenopyrite at fixed temperatures (20°C, 30°C and 45°C) and at ramped up temperatures (25 to 45°C, with a 2°C daily increase). The experiments were conducted in a packed bed of inert granite pebbles coated with the tailings material and leached with a mesophilic culture dominated by Acidithiobacillus caldus (56%), a lesser percentage of Leptospirillum ferriphilum (29%) and Archaea (15%), using 1 g/L ferrous-enriched 0K medium. The ramped-up temperature experiment was conducted in triplicate and columns were sacrificed after different leach periods to study the evolution of microbial species dominating the colonization. The leaching performance was evaluated using the arsenic released into solution, the iron oxidation rates, the pH and the redox potential. The microbial speciation of the culture attached to the solids during the leach experiment was determined upon completion of each experiment. A steady arsenic solubilisation of between 94 and 97% was observed among the various column experiment after 88 days post inoculation. Microbial speciation performed following the leaching of the mineral indicated a shift of microbial communities in the columns when compared to the initial inoculum.

Abstract: There is a growing interest in the use of Mn (II)-oxidizing bacteria to treat Mn-containing metal refinery wastewaters instead of using conventional chemical approaches since the former could reduce the cost of alkaline agents and oxidants to remove Mn (II) as Mn oxides at alkaline pH. The Mn level was found naturally dropped in the industrial metal refinery wastewater treatment system, where the formation of Mn-enriched sludge was apparent. This observation motived us to investigate the possible involvement of microbially mediated reactions. From the sludge sample, Pseudomonas sp. strain SK3 was successfully isolated and tested for its Mn (II)-oxidation characteristics. Strain SK3 completely removed 100 ppm Mn (II) within 42 hours as birnessite ((Na,Ca,K)_0.6(Mn^IV, Mn^III)₂O₄·1.5H₂O) under optimized conditions. Copper ions were found to be an important factor in promoting Mn (II) oxidation. Changes in the Mn (IV)/Mn (III) ratio during bacterial Mn (II)-oxidation indicated the involvement of 2-step one-electron transfer reactions in the formation of biogenic birnessite with Mn (III) as intermediate. Characteristics of strain SK3 were compared with those of a well-known Mn (II)-oxidizing bacterium, Pseudomonas putida strain MnB1. Strain SK3 displayed more robust Mn (II) oxidation capabilities under several severe conditions, showing its ideal characteristics for use in the industrial water treatment process.

Abstract: Selenate removal from mine waters is required to mitigate human and environmental health impacts. In this study, the performance of an inverse fluidised bed reactor (IFBR) for the biological removal of selenate from synthetic mine water (pH 6.0-7.0) was evaluated. A laboratory-scale IFBR was set up with floating biomass carriers. Selenate reducers were enriched from environmental samples and anaerobic sludge. The synthetic medium contained ~10 mM (~1.4 g L^-1) selenate, nutrients and 10 mM ethanol as electron donor. During stable performance the bioreactor achieved 94 % removal of selenate representing a removal rate of 251 mg L^-1 d^-1 at a hydraulic retention time of 5 d. Selenite concentration remained < 1 mg L^-1 during stable performance, and the formation of a red precipitate indicated that selenate was reduced to elemental selenium. The biological selenate reduction generated alkalinity, increasing the wastewater pH from 6.0 to 8.6. The redox potential gradually approached a value ranging from -300 mV to -400 mV against standard hydrogen electrode. Overall, the results showed that the IFBR can be used for removing selenate and acidity from mine waters. Moreover, it has potential to facilitate recovery of elemental selenium. Therefore, the bioprocess provides an opportunity to reduce the costs and liabilities associated with selenium containing mine drainage and the associated environmental impacts.

Abstract: Biogas is a renewable energy source that can be used to produce heat and energy, replacing fossil fuels. The main factor limiting the use of biogas is contaminants in its composition which H₂S is the most important due to corrosion and environmental problems. A promising technology to remove this contaminant from biogas is the biotrickling filters and the selection of inexpensive and durable supports is an important step for the operation. This work has studied different support materials, for microorganisms immobilization, as Polyvinyl Chloride (PVC), Polyethylene Terephtalate (PET), Polytetrafluoroethylene (Teflon^®) comparing to open pore polyurethane foam (OPP) each one packed in biotrickling filters to evaluate the consumption of thiosulfate by chemolitotrofic microorganisms. The kinetics of substrate consumption in different cycles for each support were distinct suggesting different microbial colonization. The materials tested have presented results very similar polyurethane foam, which has already known by its efficiency on biogas desulfurization, unless Teflon that has showed a divergent result with the increase of the substrate concentration in the system.

Abstract: Adsorption of Cr(VI) and desorption of the Cr that was adsorbed using persimmon gel was examined. Most of the Cr(VI) was adsorbed at a pH value of 2, and a part of that was reduced to Cr(III) in the solution using persimmon gel, which has many polyhydroxyphenyl groups. A small amount of Cr was desorbed using some acidic or alkaline reagents at 30 °C. However, all of the Cr adsorbed using persimmon gel was desorbed at reflux temperature as Cr(III) using 1M HCl. Cycles of Cr(VI) adsorption and desorption as Cr(III) cycles were repeated 9 times. The adsorption of Cr was quantitatively repeated until 8 times and desorption of Cr was almost quantitatively repeated until 9 times.

Abstract: Bioleaching was applied to mobilize metals from printed wire boards (PWBs). PWBs have a rich metal content and are produced in high volume. Operating conditions of bioleaching of PWBs using an adapted mixed culture of Acidithiobacillus ferrooxidans (A. ferrooxidans) and A. thiooxidans to recover Cu, Zn and Ni were optimized in this study. The adaptation phase began at 1 g/L PWBs powder with 10% inoculation and the final pulp density was 20 g/L after about 40 days. Optimization was performed using central composite design method to optimize four effective factors, including initial pH (1.5 to 2), pulp density (15 to 25 g/L), initial sulfur (3 to 7 g/L) and initial FeSO₄ (15 to 25g/L), to achieve maximum recoveries of Cu, Zn and Ni. Also, the present study evaluated the effect of the independent variables initial pH, pulp density, initial Fe³⁺ concentration and initial sulfur content on extraction of metals from PWBs. Results showed that with an initial pH of 1.5, 25g/L pulp density, 25 g/L of FeSO₄·7H₂O and 7 g/L of S₀, copper, zinc and nickel recoveries reached 92%, 96% and 94%, respectively, after 25 days.

Abstract: Pyrometallurgical copper final slag was subjected to leaching by means microbial cultures of three different groups based on their optimum temperature for growth and activity: mesophilic and moderate thermophilic bacteria, and extreme thermophilic archaea. The leaching experiments were performed by the shake-flask technique and in agitated bioreactors under batch and continuous-flow conditions. The effect of the most essential factors (particle size, pulp density, pH, aeration) on this process was studied. The highest rates of extraction of the non-ferrous metals (Cu, Zn, Co) and iron were achieved by means of some archaea but at relatively low pulp densities (5 – 10%). Some moderate thermophilic bacteria were the most efficient at the higher pulp densities (15 – 20 %). The, leaching by some mesophiles at pH 3.0 – 3.5 was also very attractive since it was connected with high extractions of these metals (about 85 – 92% at 20% pulp density), much lower acid consumption and low solubiliation of fayalite which resulted in the production of pregnant solutions suitable for the recovery of the dissolved non-ferrous metals.