Antti Vuorinen

Dissolution and structural alteration of phlogopite mediated by proton attack and bacterial oxidation of ferrous iron

Microbiological weathering of a research-grade mica mineral, phlogopite, was studied using ferrous sulfate media that were inoculated with an acidophilic iron-oxidizing bacterium, Thiobacillus ferrooxidans. Weathering due to dissolution was monitored by analysis of Si, Al, Fe, K, Na, Mg, and Ca in the leach solutions and in chemical controls at pH 1.0, 1.5 and 2.0. Structural alterations of phlogopite were analyzed by X-ray diffraction. At pH 2, the oxidation of Fe(II) by T. ferrooxidans was accompanied by the formation of jarosite within 7 days of incubation at 22°C. The precipitation of jarosite was coupled with partial alteration of phlogopite to vermiculite and an interstratified (mixed-layer) phlogopite/vermiculite. Similar results were obtained with chemical controls containing 120 mM ferric sulfate. The data suggested that K incorporated into jarosite was released from interlayer positions in phlogopite; thus, jarosite constituted a sink for K. The formation of jarosite and expansible layer silicate phases was pH-dependent. At pH<1.5, jarosite was not formed and phlogopite weathering was due to chemical dissolution without detectable structural alteration.

Bacterial pyrite oxidation: release of iron and scanning electron microscopic observations

Abstract The dissolution of iron from pyrite was enhanced by cultures of Thiobacillus ferrooxidans . Data from different analytical methods of iron determination indicated that most of the iron in filtered leachates was in a fine-dispersed (colloidal) or chelated form. Scanning electron micrographs showed extensive pitting of pyrite surfaces after 6 weeks leaching. Hexagonal (rhombohedral) and pseudo-cubic jarosite crystals were found in leach residues of polished pyrite specimens.

Solubilization and speciation of iron during pyrite oxidation by Thiobacillus ferrooxidans

Abstract Various species of soluble iron in pyrite‐grown cultures of Thiobacillus ferrooxidans were determined by colorimetry, atomic absorption spectrometry, and ultraviolet spectroscopy. All the cultures were incubated for six weeks before iron analysis. The effects of the following factors were investigated: particle size, initial pH, shaking (aeration), concentration of pyrite, and concentration of yeast extract. Shaking, but not initial pH nor particle size, influenced the relative proportion of different iron species. Polynomial regressions could be used to describe the functional relationship between the different iron species and concentration of pyrite; fewer relationships were evident with respect to concentration of yeast extract. The variance‐covariance matrices indicated a linear dependence among the different iron species. Canonical correlations indicated perfect correlations between group variables of iron, copper, and zinc, with the exception of an absence of significant correlation with t...

Bacterial weathering of rapakivi granite

Rapakivi granite samples were incubated with Pseudomonas aeruginosa culture solutions in order to elucidate the possible role of bacteria in rapakivi (crumbling stone) disintegration. SEM micrographs showed micromorphological alterations on the incubated rapakivi surface at 21 to 23°C for 20 days. Elevated concentrations of Na, Ca, K, Fe, and Mg were detected in the culture solutions after incubation. Elemental oxide ratios [K2O : (Na2O + CaO)] in culture solutions were similar to those in rapakivi ovoids, suggesting a proportional dissolution pattern of these elements.

Palaeolimnological and limnogeochemical features in the sedimentary record of the polluted Lake Lippajärvi in Southern Finland

Abstract A sediment core from Lake Lippajarvi, sampled by freezing it in situ , was investigated. The sedimentary sequence was dated using the 137 Cs method and the 210 Pb content of the core was also determined. It seems that, during the recent history of the lake, increasing eutrophication is the main factor controlling fluctuations in lake ecosystems. This increase is clearly reflected in the changes in the diatom stratigraphy of the core investigated. Sequential extraction analysis was performed for speciation of elements in the sediment. Ammonium acetate and hydroxylammonium chloride plus acetic acid were used as extractants; acid digestion and extraction by NaClO and NaDDTC/MIBK were also performed. An increase in sedimentation rate is apparent for the upper part of the lithostratigraphy of Lake Lippajarvi. The increased nutrient load and heavy metal input have led to cultural eutrophication and pollution effects in the lake, and black bands of Fe monosulphides have emerged in sediments as a sign of oxygen deficit in the hypolimnion. The eutrophication of Lake Lippajarvi is also accompanied by biogeochemical cycles and limnogeochemical processes apparently responsible for the leaching of chemical elements from sediments and their subsequent redeposition in more loosely bound forms. Fe has been redeposited mainly as Fe oxyhydroxides and monosulphides, and Cu and Zn also seem to be associated with these precipitates. Ca, Mn and Zn are present to relatively large degrees as very loosely bound and sorbed forms. Fe, Mn, Cu and Zn are also associated with sulphides, and Fe and Cu with biogenic matter. There is a clear difference between man-made airborne forms of Pb and natural mineral-bound forms in the sediment column of the lake. In the polluted part of the investigated lithostratigraphy, Pb is mainly present in loosely bound reducible forms. Al and Si also seem to show leaching and redeposition in the sediments of Lake Lippajarvi.

Dissolution of uraninite in acid solutions

The purpose of this work was to assess the oxidative dissolution of uranium from a uraninite-containing rock in acid sulfate solutions under test conditions relevant to uranium leach mines and acid mine waters. Uranium dissolution in acidified mineral salts solution was slow and the predominant carbonate mineral (rhodochrosite) in the rock sample continued to consume acid. Bacterial inoculation (Thiobacillus ferrooxidans) and additional Fe2+ or S0 were tested in efforts to enhance the dissolution. Addition of Fe enhanced the solubilization of uranium, whereas S-addition had little incremental effect on the dissolution with and without bacterial inoculation.

Weathering of Biotite in Acidithiobacillus ferrooxidans Cultures

The purpose of this study was to assess the weathering of biotite under conditions simulating an active bioleaching environment. Finely ground biotite was contacted with Acidithiobacillus ferrooxidans culture solutions for up to 120 days. Biotite was altered under these conditions to interstratified structures comprised of mixed layers of biotite and vermiculite. Interlayer K in biotite was released upon weathering and precipitated with ferric iron and sulfate to form jarosite. Substantial dissolution of biotite was also associated with weathering. The data demonstrate that exposed, biotite-rich rocks in mine tailings and heap and dump leaching systems can undergo acid mediated solubilization and structural changes, which are coupled with the formation of expansive, vermiculite-like minerals and jarosite precipitation.

Solubilization of phosphate, uranium, and iron from apatite- and uranium-containing rock samples in synthetic and microbiologically produced acid leach solutions

SummaryThe solubilization of phosphate was investigated using apatite and P-containing uranium rock samples in acid solutions. The concentration of soluble phosphate usually increased upon 24-h extraction followed by subsequent precipitation. Uranium solubilization was investigated using leach solutions that contained about 3 g/l ferric iron produced by bacterial oxidation of iron pyrite. 1–94% extraction of uranium was attained within 24h, with the poor recovery associated with a rock sample containing an excessive amount of alkaline material. Reducing equivalents (permanganate-consuming substances) in the acid leach solutions could be oxidized by inoculation with iron-oxidizing thiobacilli (Thiobacillus ferrooxidans). Chemical analysis of iron indicated that most of the iron was in the oxidized form. Stable iron colloids were not present in significant amounts in the leach solutions. Acidic ferric sulfate containing about 6 g/l Fe3+ was also used as a leach solution. Repeated use of the leach solution with rock samples did not decrease the efficiency of the leaching but soluble uranium reached a toxic concentration and thus prevented the bacterial re-oxidation of ferrous iron in the leach solution.

Biologically enhanced dissolution of a pyrite‐rich black shale concentrate

Abstract The acid leaching of a pyrite‐rich black shale concentrate (7% S) was tested in this study. The experiments were performed at 5–30% pulp densities and with inoculations of Fe‐ and S‐oxidizing thiobacilli (Thiobacillus ferrooxidans, and Thiobacillus thiooxidans,),. Cultures supplemented with S0 showed strong acid production, with final pH values of 0.9 in T. ferrooxidans, cultures and 0.4–0.5 in the presence of T. thiooxidans,. Fe dissolution was pronounced in the T. ferrooxidans, culture whereas T. thiooxidans, did not dissolve Fe from the black shale. Total dissolved Fe concentrations were 3 to 50 times higher in the cultures inoculated with T. ferrooxidans, when compared to T. thiooxidans, and sterile controls. The dissolution of Mo was enhanced in the inoculated cultures as compared with the chemical controls. With V, Si, and Al this effect was not as pronounced but was still discernible in solutions acidified by bacterial oxidation of S0. The leaching experiments suggested that the black shal...

Redox and precipitation reactions of iron and uranium solubilized from ore materials

Abstract Uranium are samples were leached with acidic ferric sulfate for 25 h. Changes in concentrations of FeOH2+ and Fe2+ were opposite, both reflecting the ferric iron reduction by the ore material. The total soluble iron concentrations first increased because of the solubilization of iron sulfides and then decreased because of the precipitation of Fe(III). Loss of soluble uranium occurred towards the end of the contact time with the leach liquor. Uranium was shown to co-precipitate with Fe(III) in a bacterially produced ferric sulfate solution.