In bio-hydrometallurgical operations, several studies found that besides having inhibitory effects chloride may also enhance the bacterial leaching of metal sulfides. This study compares the effect of chloride on bacterial growth, iron oxidation activity and bioleaching performance of Leptospirillum ferriphilum and Sulfobacillus thermosulfidooxidans. The exposure to elevated NaCl concentrations affected cell growth and iron oxidation rate in both strains. Sb. thermosulfidooxidans showed better tolerance to NaCl than L. ferriphilum, with the concentration that inhibited biological iron oxidation and bacterial growth completely being 325 mM and 525 mM NaCl for L ferriphilum and Sb. thermosulfidooxidans, respectively. At 100 mM NaCl, cell growth and iron oxidation of L. ferriphilum were severely slowed down while for Sb. thermosulfidooxidans, in contrast, they appeared almost unaffected. Additionally, while only 22% of L. ferriphilum cells survived after 18 h exposure to 100 mM NaCl, viability of Sb. thermosulfidooxidans was not strongly affected by 300 mM NaCl. Bioleaching of chalcopyrite and sphalerite were studied. For chalcopyrite, bioleaching by Sb. thermosulfidooxidans in the presence of 200 mM was similar to its performance in the absence of NaCl. However, bioleaching by L. ferriphilum was reduced by 50% in the presence of 200 mM NaCl. For sphalerite, bioleaching by both bacteria, L. ferriphilum and Sb. thermosulfidooxidans, was inhibited significantly in the presence of 200 mM NaCl. This study indicates that Sb. thermosulfidooxidans will be more suitable than L. ferriphilum to operate bioleaching with high chloride concentrations. Additionally, since bioleaching performance of chalcopyrite differed from bioleaching of sphalerite under similar conditions, further investigations on bioleaching with different sulfidic minerals in the presence of chloride ions are necessary.

Arsenic is one of the main contaminants in soil, especially in (former) mining areas, but arsenic can also be a source of exploitable metals, if present as arsenides. In the following paper we report the microbial leaching of an arsenide (e.g. safflorite (CoAs2)) for the first time. Bioleached cobalt yielded up to 92% in presence of citric acid, while the non-inoculated and chemical controls yielded in merely 4% and 10%, respectively. Even though high yields were achieved, the arsenide turned out to be a difficult leaching substrate, leading to a diverse activity. While the addition of citric acid improved the cobalt liberation and resulted in a more stable activity, the absence led to yields ranging from 35% to 82%, depending on the ability to cope with the arsenide. From the comparison of the leaching with 1% and 2% (w/v) ore, it can be concluded that the decreased activity resulted in an unfinished leaching. Furthermore, the typestrains of Acidithiobacillus ferrooxidans and Leptospirillum ferriphilum were not able to grow in presence of the arsenide.

The application of acidophilic iron oxidizing bacteria is an established technique in tank and heap leaching of mainly sulfidic minerals. Even though bioleaching is broadly studied, there are still several issues to solve. Especially, the formation of iron precipitates, leading to co-precipitation of valuable metals, as well as the inhibition due to coating, considerably decrease the leaching efficiency. Consequently, the addition of chelating agents should result in an increased dissolution rate.However, organic acids, which have chelating characteristics, are generally regarded as highly toxic for leaching bacteria. Nonetheless, we found that both the addition of sodium citrate and citric acid leads to an increased iron oxidation rate of 42% and 84%, respectively, compared to standard culture medium without citrate. Chemical leaching tests with ZnS and ferric iron showed similar concentrations of dissolved zinc with and without citrate. However, the actual leaching efficiency is yet to be evaluated.

Tank bioleaching of ore promises to give high yields due to the ability to control the leaching process. For that, various parameters like pH, EH and pO(2) must be measured regularly. However, the measurement of oxygen is especially difficult to realise since oxygen probes are relatively expensive and possess only a low durability. Through the use of an optode system, we propose an easy and less expensive alternative for oxygen measurements. Furthermore, we demonstrate the optode achieves similar and possibly more accurate readings than the conventional electrode. Since we were able to fix the optode sensor at the lower end of a glass tube, this system is suitable for various reactor designs and hence allows for non-invasive, in-situ oxygen measurements. The proof of concept was demonstrated by cultivating Escherichia coli, Rhodococcus erythropolis, Acidithiobacillus ferrooxidans, and Sulfobacillus therrnosulfidooxidans inside 2 L bioreactors. Both optode and oxygen electrode showed similar concentration values, which demonstrates the optode is a reliable tool for oxygen measurements during bioreactor cultivation, especially of iron-oxidisers. Subsequent leaching tests, performed with fine grained residue from copper smelting and copper-rich black shale, demonstrated that the optode is resistant to mechanical wear. Therefore, the optode was found to be a suitable alternative to the amperometric oxygen probe. (C) 2016 Elsevier B.V. All rights reserved.

Quantification of biomass and estimation of cell numbers are essential tasks in the calculation of specific bioleaching rates and thus are important for process characterisation and optimisation. As a fast and convenient alternative to the laborious and expensive technique of qPCR, we present here a fluorometric approach which allows the sensitive and reliable quantification of the iron-oxidising Acidithiobacillus ferrooxidans.Following two different methods of sample preparation, total fluorescence of PicoGreen-stained cells could be measured with good reproducibility by means of a microplate reader. Calibration of these data with results from a parallel cell enumeration by epi-fluorescence microscopy allowed the reliable estimation of cell densities as low as 1.0 x 10(5) cells/mL.In order to determine the potential respiration activity of the investigated cells we provide an oxygen-specific optode-based approach. Due to its fast response, the lack of oxygen consumption, and the insensitivity towards mineral deposits the optode was shown to be an attractive alternative to the frequently used Clark electrode.Moreover, respiration rate and total oxygen consumption could easily be followed of iron-oxidising (and bioleaching) cultures of At ferrooxidans over days and weeks using the manometric OxiTopC system. The observation of transitional plateaus during the pressure decrease of a gas phase from a ZnS-leaching culture of At. ferrooxidans indicated the occurrence of different oxygen-consuming processes. (C) 2015 Elsevier Ltd. All rights reserved.

•Overview of Kupferschiefer geology/mineralogy with special emphasis on copper and valuable associate metals.•Bioleaching for metal recovery from Kupferschiefer blackshale (primary and secondary resources).•Discussion of scientific bottlenecks related to the(bio)treatment of blackshale type of ores.•Perspectives in Ecometals project to develop an innovative eco-efficient biohydrometallurgy process.

Tank bioleaching promises high yields due to controllability of the leaching process. For that various parameters like pH, EH and pO2 have to be measured regularly. However, especially the measurement of oxygen is difficult to realise, since oxygen probes are very expensive and posses only a low durability. With optode measurements we propose an easy and less expensive, but still very accurate alternative. Since we were able to fix the optode sensor spot at the lower end of a glass tube, this system is applicable with various reactor designs and hence allows non-invasive in-situ oxygen measurements between each second and every hour.In order to show the principal applicability of this system inside a bioreactor, Escherichia coli was cultivated at a defined oxygen level. Both optode and oxygen probe showed similar concentration values. In the following, a cultivation of Acidithiobacillus ferrooxidans was performed in a 2 L bioreactor with different oxygen levels set by controlling the air flow. Again, both systems showed similar concentrations. This demonstrates the optode to be a reliable tool for oxygen measurements during the cultivation of iron-oxidisers in bioreactors. Furthermore, we performed leaching tests with fine grained residue from copper smelting in order to show the durability of the optode in terms of mechanical wearing and hence a suitable alternative to oxygen probes.