Papers by Author: M. Viera

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Authors: J. Plaza, Eric Guibal, J.M. Taulemesse, M. Viera, Edgardo R. Donati
Abstract: Macrocystis pyrifera was used for the recovery of Zn2+ and Cd2+ from slightly acidic solutions (i.e., pH 4). Sorption isotherms were obtained from mono- and bi-component solutions. For the study of metal desorption, EDTA, HNO3 and Ca(NO3)2 were used as eluents. Metal release (Ca2+, Mg2+, K+ and Na+) was monitored in order to evaluate ion exchange mechanisms. After metal sorption/desorption steps the sorbent was characterized using SEM-EDAX analysis. SEM-EDAX analysis also allowed identifying the presence of elements such as Si, Al, Co, Ag, S, P, and Fe in the cell wall. Zinc desorption was almost complete when using 0.1 M nitric acid solution and the sorbent was not significantly damaged by the acidic treatment. Cadmium was completely removed from loaded sorbent when using EDTA, but at the expense of a partial degradation of the biomass as evidenced by the decrease in the intensity of the C and O peaks (SEM-EDAX).
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Authors: J. Huergo, C. Bernardelli, M. Viera, Wolfgang Sand, Edgardo R. Donati
Abstract: Bioleaching is the biological conversion of an insoluble metal compound into a water soluble form. In this process metal sulfides are oxidized to metal ions and sulfate by acidophilic microorganisms capable of oxidizing Fe2+ and/or sulfur-compounds. The metal solubilization from sulfide minerals is a chemical process which requires Fe3+ reduction. It is an environmentally friendly technique and an economical method for recovering metals that requires low investment and operation costs. In this work we studied the bioleaching of two kinds of acid-soluble copper sulfides, one easily leached by mesophilic bacteria (covellite), and the other one refractory to their activity (chalcopyrite), in acidic media with or without Fe2+ ions. We studied attached and planktonic populations of autotrophic bacteria, such as Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans in pure or mixed cultures. The influence of a heterotrophic microorganism, Acidiphilium cryptum, was also studied. Attachment was evaluated with fluorescence staining and FISH using four specific probes. L. ferrooxidans showed highest initial attachment in all cases. The presence of Ap. cryptum increased the cell attachment compared with the autotrophic pure cultures. It was possible to correlate experimental data with a mechanism of bacterial-metal sulfide oxidation, the polysulfide pathway for acid- soluble metal sulfides.
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Authors: P. Kikot, M. Viera, C. Mignone, Edgardo R. Donati
Abstract: Metallurgical processes and mining are the main source of heavy metal contamination of water sources, rivers and lakes. There are a large number of physicochemical processes that can be applied for the immobilization of heavy metals from a liquid matrix. However, many of them are not particularly desirable because their low selectivity and inefficiency when high volumes of low metal concentration liquids must be treated. In such conditions, alternative biological processes have shown to be more useful than traditional physicochemical processes. One of those processes, bioprecipitation of metal sulphides is relevant due to the possibility of forming stable solids (very low solubility) with small volumes compared with other solids. This process is mediated by a broad group of organisms called sulphate reducers that are able to catalyze, under anaerobic conditions, the reduction of sulphate with organic compounds as electron donors. In this paper, we study the effect of the presence of various heavy metals and the pH on the ability to reduce sulphate by sulphate-reducing bacteria. We compare the reduction of sulphate by a microbial community obtained from the effluent of a tannery with a strain isolated from that community. Our results showed that sulphate reduction was significantly affected by pH changes whereas the presence of heavy metals did not show a significant effect. In addition, metal precipitation by the isolated strain was similar than that produced by the community.
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Authors: Nadia Yagnentkovsky, M. Viera, Edgardo R. Donati
Abstract: Sludge generated in automotive and related industries often contains heavy metals. Bioleaching is an attractive alternative for the treatment of metal containing solids. Bacteria of the genus Acidithiobacillus are the most important microorganisms applied to metal solubilisation. These microorganisms are able to produce sulphuric acid from the aerobic oxidation of elemental sulphur. The biogenerated sulphuric acid can be applied to the solubilisation of metals from a solid matrix. In this paper we present the results of our experiments aimed at the removal of nickel and zinc from sludge generated in the water treatment plant of an automotive industry. Acidithiobacillus thiooxidans cells were immobilised on sulphur pearls in a column reactor. The effects of sulphur pulp density and the dilution rate on the production of sulphuric acid were studied. In a second stage, sulphuric acid was used to solubilise the nickel and zinc from the sludge. The effects of different sludge pulp densities and initial acid pH were studied. High recoveries of zinc and nickel were obtained when the pH value of the sulphuric acid solution was lower than 2.0 for 1 and 2 % of pulp density.
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