Papers by Keyword: Iron Oxidation

Abstract: This research aimed to study the recycling process and the feasibility of recovering iron as hematite or red oxide powder (Fe₂O₃) from spent pickling acid (hydrochloric acid). The spent hydrochloric acid waste from the pickling bath in the sheet rolling steel industry contains approximately 233 g of iron dissolved in one liter of the spent acid. To recover iron, 2 M NaOH was added to the spent acid until reaching pH 7. The iron was precipitated as iron oxide and/or hydroxide. Next, the oxidation of ferrous oxide was carried out by adding H₂O₂ 35%v/v to control the shade color. The precipitates were subsequently separated from the acid solution by a filter press. The precipitates were dried at 110°C for 24 h and calcined at 700°C for 2 h to synthesize and modify the crystallinity of ferric oxide. Ferric oxide was subject to water washing, where contaminating sodium chloride could be dissolved and filtered out. After drying at 110°C for 24 h, high-purity hematite was achieved. Hematite recovered from the spent pickling acid via this process provided more than 97% purity at 94.4% recovery.

Abstract: Acidophilic leaching microorganisms have been reported to be in general intolerant to high salinity, namely high concentrations of chloride. At present this restriction hampers the use of sea water for bioleaching technology. Enrichment cultures obtained in this study from a former ore deposit near the Spanish coast oxidize ferrous iron in the presence of up to 50 gL-1 NaCl at pH 2.5 and 37°C. The presence of at least 5 gL-1 NaCl was shown to be an obligate requirement for iron oxidation. The major microbial groups comprise Alicyclobacillus and Arthrobacter. The findings may be of biotechnological relevance.

Abstract: Inhibition of iron oxidation by Leptospirillum ferriphilum in the presence of thiocyanate (SCN^-) was studied in small-scale batch experiments. The L. ferriphilum culture was challenged with SCN^- over a range of 0 mg/l to 10 mg/l. The data showed that L. ferriphilum was able to utilise ferrous iron at low-level concentrations of SCN^- (0.25 mg/l to 1.75 mg/l), however exhibited a reduction in oxidation rate relative to the control (0 mg/l). Moreover, introduction of SCN^- at low-level concentrations resulted in a lag in iron oxidation activity, specifically at concentrations of 1 mg/l, 1.25 mg/l and 1.75 mg/l. No iron oxidation was observed at SCN^- concentrations above 1.75 mg/l, indicating complete inhibition. As L. ferriphilum is the dominant iron oxidising bacteria within biooxidation tanks, evidence of sustained iron oxidation activity at low-level SCN^- concentrations affirms the potential of recycling bioremediated cyanidation wastewater within biooxidation circuits in bioprocesses for gold recovery from sulfidic minerals as residual SCN^- concentrations in remediated effluent are reportedly lower than 0.25 mg/l. The inhibition kinetics of this system need to be explored further in order to develop a deeper understanding of the system such that it may be applied to inform process operation.

Abstract: In bioleaching, the chemiolithotrophic community plays an important role as oxidizers of sulfur compounds and ferrous iron. Ferrous iron oxiding microorganisms are key players in the process, as ferric iron is absolutely required to solubilize metal sulfide ores. Members of the Sulfobacillus genus (able to oxidize ferrous iron) were predominant (22 - 95%) in a chalcopyrite bioleaching columns test. In order to obtain new insight about the mechanism of iron oxidation in Sulfobacillus we investigated the presence and expression of genes potentially related to iron oxidation by Sulfobacillus, especially the group of the so-called blue-copper proteins rusticyanin (rus) and sulfocyanin (soxE) in the course of the experiment. The physicochemical parameters and the population dynamics were monitored periodically in the columns and the metatranscriptome was analyzed by using pyro-sequencing. The average temperature inside the column ranged from 22 to 57 °C and the Fe(II) oxidation rate at 45 °C varied between 8 and 42 mg L^-1h^-1 along 300 days of operation. The metatranscriptomic analysis reveals an over-expression of 9-13 folds of the putative rus and soxE genes in four strains of Sulfobacillus spp. when the Sulfobacillus proportion in the column was >80% and the Fe(II) oxidation rate measured at 45 °C reached 10 mg L^-1h^-1. Some cytochromes from the electron transport chain were also over-expressed, on a range of 7 - 10 folds under those operational conditions. These results support the hypothetical participation of blue-copper proteins in the iron oxidation pathway of Sulfobacilli. Culture assays and more specific expression analysis are necessary in order to confirm this hypothesis. In addition, we attempt to establish the relationship between rusticyanin and sulfocyanin genes and perform a protein sequence analysis that allows us to infer the actual function of these proteins in Sulfobacillus species.

Abstract: Colonies of iron-oxidising acidophilic bacteria were isolated on solid media containing up to 500 mM NaCl from non-saline samples from the Rio Tinto (Spain). One of these isolates was identified as an "Acidithiobacillus ferriphilus" strain. Laboratory cultures of the type strain of Acidithiobacillus ferridurans grown on hydrogen for one year were also found to adapt to the presence of 500 mM salt. This culture also grew on sulfur, but not on ferrous iron, in media containing 500 mM NaCl. It regained its ability to oxidise iron only after protracted incubation in salt-free media. Molecular analysis found an insertion of about 1.5 kb in the regulatory region of the rus operon of the strain that was unable to oxidize iron. This insertion was lost in the strain that had subsequently regained this ability. Our results suggest that chloride tolerance and dissimilatory oxidation of iron by these bacteria do appear to be mutually exclusive.

Abstract: The ferrous iron oxidation by mixed culture of moderately thermophilic microorganisms (Sulfobacillus thermosulfidooxidans Sh 10-1 and Acidiplasma MBA-1) was investigated in continuous experiments in three packed-bed reactors connected in series at temperature 55°C, and a pH of 1.0. Two solutions were used in the experiments. The first one contained (g L^-1) 59 Fe²⁺, the second one contained (g L^-1) 59 Fe²⁺, 16 Fe³⁺, 2 Cu²⁺, 2 Zn²⁺. The hydraulic retention time was 120 hours. Iron oxidation rates in the experiment with the first solution were 0.5, 0.35, and 0.2 g L^-1 h^-1 in first, second and third reactor, respectively. The oxidation rates in the experiment with the second solution were 0.3, 0.2, and 0.185 g L^-1 h^-1 in first, second and third reactor, respectively. Iron oxidation efficiencies in the experiments with the first and second solutions were 77% and 47%. Stable continuous iron oxidation at high temperature was successfully demonstrated, but further investigations are required for improving the rate and efficiencies of oxidation.

Abstract: In the zinc hydrometallurgy process, iron is usually present in leach solutions and its elimination is a major operational problem. The first step of iron removal is iron oxidation by MnO₂, but this process have some disadvantages such as the cost is relatively high and decreased the current efficiency in the electro-winning stage. In this paper, a new iron oxidation process in zinc leaching solution by ozone oxidation was conducted and evaluated. The results showed that Fe²⁺ concentration decreased from 7.45 g/L to 0.51 g/L in 80min at pH 3. Oxidation of Fe²⁺ by O₃ is controlled by chemical reaction. O₃ dissolve rate, pH and initial iron concentration are key parameters for this process. Our finding indicated the potential application of O₃ oxidation in iron removal process of zinc hydrometallurgy.

Abstract: Ferrovum is a recently found new genus of acidophilic iron-oxidizing bacteria. Ferrovum spp. dominate the microbial community of a pilot plant for biological mine-water treatment and together with some Gallionella relatives appear to be key players of the process. Isolation of Ferrovum strains should greatly be facilitated by a new APPW medium. Sequencing of the genome of Ferrovum sp. JA12 so far did not point to any alternative electron donors and also did not reveal genes for nitrogen fixation.

Abstract: Here we describe the potential uptake and assimilation pathways for the essential nutrients C, N, P, and S in the acidophilic iron oxidiser Ferrovum strain JA12, a member of a novel genus among the Betaproteobacteria. Comparative genomics proved to be a powerful approach to give first insights into the biochemical potential of this novel genus and to understand the reasons for the dominating abundance of Ferrovum spp. in a pilot plant to remediate acid mine drainage.

Abstract: Valuable metals as well as ferrous iron and sulfur compounds are released from ore by ferric iron and sulfuric acid chemical attack. Biomining microorganisms allow the recycling of these products by oxidizing ferrous iron and/or sulfur compounds. The energy released from the oxidation of these substrates is used for the growth of the acidophilic chemolithoautotrophic bacterium Acidithiobacillus ferrooxidans. The respiratory pathways involved in these respiratory processes have been deciphered and the expression of the genes encoding these redox proteins is dependent on the electron donor present in the medium. Furthermore, in the presence of both ferrous iron and sulfur, the genes involved in iron oxidation are expressed before those involved in sulfur oxidation. We propose that the global redox responding two component system RegBA is responsible for this regulation since (i) the redox potential increases during iron oxidation but remains stable during sulfur oxidation and (ii) the transcriptional regulator RegA binds the regulatory region of a number of genes/operons involved in iron and sulfur oxidation. To understand the mechanism of the At. ferrooxidans RegBA system, the regA gene and the DNA corresponding to the DNA binding domain of RegA were cloned in an expression plasmid in Escherichia coli. The recombinant proteins, RegA and RegA-HTH respectively, were purified. The binding of RegA-HTH, phosphorylated and unphosphorylated RegA on the regulatory region of some target operons have been compared by gel shift mobility assay.