Jun 2, 2017 - Valdes Jorge, Pedroso Inti, Quatrini Raquel, Dodson Robert J., Tettelin Herve, Blake Robert, Eisen, Jonathan A., Holmes David S., 2008,.
INTERNATIONAL SYMPOSIUM PRESENT ENVIRONMENT AND SUSTAINABLE DEVELOPMENT 2-4 JUNE 2017, IAȘI, ROMANIA
Microbial noble metals bioleaching: in vitro preliminary results for future environmental friendly dissolution technique Loredana Brinza1, Carmen - Madalina Cismasiu2, Ioan Ardelean2, Madalina Paiu3, Georgiana Bulai3, Iuliana Gabriela Breaban3. University “Alexandru Ioan Cuza” from Iași Faculty of Geography and Geology Department of Geography
1
Alexandru Ioan Cuza University of Iasi, Department of Interdisciplinary Research- Field Science, Lascar Catargy Str., No 54, 700107, Iasi, Romania 2 Institute of Biology Bucharest, Romanian Academy, Department of Microbiology, Splaiul Independentei, No. 296, 060031, Bucharest, Romania 3 Alexandru Ioan Cuza University of Iasi, Integrated Center Of Environmental Science Studies In The North East Region (CERNESIM), Carol I Blvd, No 11, 700506, Iasi, Romania
CERNESIM
ABSTRACT Gold (Au) and silver (Ag) are important elements, metals and minerals of economical, financial and technical - scientific value, but limited resources on the Earth. Au extraction imply the use of toxic cyanide - fact which led to various mining closures due to environmental policies constrains. This research aim to investigate new environmental friendly technique for Au dissolution from secondary sources by using specific iron bioleaching bacteria. Preliminary results show that Au and Ag are indirectly released from its iron containing (mineralogical) hosts (i.e., pyrite and jarosite) but more importantly is also directly dissolved by the Acidithiobacillus ferrooxidans IBB-AR. Also we noticed that the second mechanism is due to the addition of ferrous iron to microcosm experiments – which acted as a catalyst and stimulated the direct dissolution and also microbial metabolism. These very promising results have important implications in developing greener gold extraction techniques in support of sustainable development of mining industry.
METHODS
Valdés et al 2008
Tailings sample characterization: pH, bulk chemistry by microwave digestion Microcosm bioleaching experiments design: (CEM, MARS 6 in Aqua Regia using Platinum metals method and WMG1 as CMR) and Inductively - Samples size: 80µm; Coupled Plasma Mass Spectrometry (Algient 7700x, with LOD:1.80*10-7; 1.32*10-5; and 5.63*10-4 - 3 grams of A/B 1-5 samples + culture medium (Leathen) + A. ferrooxidans IBB-AR inoculum mg/Kg for Au, Ag, and Fe, respectively)) and mineralogical characterization (by X-Ray (10% of of two different populations noted T2 Diffraction, Shimadzu 6000). Microorganisms characterization: Acidithiobacillus ferrooxidans, IBB-AR isolated and T4); (Cismasiu, 2005), size < 1,5 um). - Incubation: 60 days, T=30ºC under stirring Biofluorescence analysis: cells were treated with both Syber green (labelling all cells) and conditions (150 rpm); Ethidium bromide (labelling only dead cells) - Filtration through 0,2µm (Milipore, type GTBP)
Figure 1. Overview of supposed IBB bioleaching/ dissolution mechanisms (Valdes et al 2008)
OBJECTIVES
- Characterise mine tailings as potential secondary source for gold extraction - Test specific IBB for gold an silver bioleaching/dissolution and bio mineralization - Bioleaching kinetics of noble metals and their associated minerals
B 1-5
Jarosite; Pyrite; Quartz; Sanidine, Feldspar; Kyanite; Basanite;
2,43,7
Quartz; Feldspar; Jarosite; Basanite; Orthoclase, Cuprorivaite
2,84,2
Table 2. Elemental* bulk chemistry of tailing samples
Ag Sample ID [mg/kg]
Fe [mg/kg]
Cu [mg/kg]
Zn [mg/kg]
A1
0.32
79546.05
436.69
488.27
A2
0.42
108659.34
657.89
700.17
A3
0.57
77785.49
547.29
515.73
A4
1.87
205562.02
367.63
314.43
A5
0.95
92448.06
415.54
1369.61
B1
0.78
148941.47
447.09
2198.46
B2
0.65
134547.20
687.68
1564.04
B3
0.37
80089.38
443.16
1545.16
B4
0.25
145961.78
7719.93
4799.00
B5
0.41
96494.19
1654.46
4830.45
*Au content was also determined, but we reserve the right to keep these values confidential
(a)
Au in A1-5
0,2
6 A1 A2 A3 A4 A5
5 4 3 1
0,15
0
10
20
30
40
50
B1 B2 B3 B4 B5
0,1 0,05
0
0
60
0
Time (days)
(b)
Ag in A1-5
1,4 1,2 1
A1 A2 A3 A4 A5
0,8 0,6 0,4 0,2 0 0
10
20
30
40
50
60
(c) 35
20
30 40 Time (days)
50
60
Ag in B1-5
1,8 1,6 1,4 1,2 1 0,8 0,6 0,4 0,2 0
B1 B2 B3 B4 B5
0
Fe in A1-5
10
(b)
Time (days)
Most of the cells have became dormant after 60 days, possible due to limited amounts of available iron, nutrients or O2.
Au in B1-5
7
2
Considerable amounts Ag2+ (up to 1.9 ppm) in tailings - as secondary noble metals sources. High iron content (up to 20 wt%) supports the occurrence of iron containing minerals (see Table 1 - XRD) as mineralogical hosts for noble metals.
(a)
0,25
%
pH
%
A1–5
Summary of main mineralogical phases
%
Sample ID
Figure 2. Microcosm bioleaching experiments set up for A (left) and B (right) tailing samples.
%
Table1. Mineralogical characterisation and pH of tailing
Presence of pyrite and its oxidized product jarosite are the main mineralogical hosts of noble metals. The presence of these phases is supported by bulk chemistry data (i.e., 20 wt%Fe; see Table 2)
10
20
30 40 Time (days)
50
60
(c)
30 25
%
RESULTS AND DISCUSSIONS
A1 A2 A3 A4 A5
20 15 10 5 0 0
10
20
30 40 Time (days)
50
60
Figure 3. The kinetic profiles of dissolved (%) Au (a), Ag (b) and Fe (c) bioleached during the experiment for samples from site A (left) and B (right)
Figure 4. Bio-florescence label of unwashed cells: all cells (green fluorescence) and of dead cells (red-fluorescence), after 60 days from the beginning of the experiment
CONCLUSIONS
The kinetic profiles of Au, Ag and Fe bioleached by A. ferrooxidans IBB-AR in solution (as mg/L from gr solid) generally respects the same trend for all samples from both sites. Besides iron, noble metals have been dissolved, too. Au, Ag and Fe concentration in solution increases after 30 days of testing, indicative of important bioleaching activity of A. ferrooxidans IBB-AR in the presence of ferrous iron. After 60 days of incubation period at 300C in continuous agitation conditions (150 rpm) the decreases of soluble metals could be due to limited bioavailable iron content (see B profiles) for A. ferrooxidans IBB-AR, limited metabolic activity of A. ferrooxidans IBB-AR (see Figure 4) or possibly lack of nutrients / O2 from the system. However, this lead to new approaches for further experiments.
Tailings can be considered a secondary source of noble metals, hosted by unprocessed pyrites and primary ores extraction end products; A. ferrooxidans IBB-AR does oxidize iron bioavailable in tailings, bioleaching Au and Ag from secondary sources. Bio-solubilization mechanisms occurs directly as well as indirectly (via gold containing iron based host minerals dissolution by A. ferrooxidans IBB-AR ). By comparison, with Cismasiu 2010 it can be noted that ferrous iron had a very important catalytic effect in noble metal bioleaching by A. ferrooxidans IBB-AR . More experiments are planed varying microbiological as well as process conditions. New lab based (i.e., iron oxidation states) and very high resolution tools, such as synchrotron, will be involved to investigate mechanisms at atomistic scale. Future work: Bio-perspectives: quantify cell density during the experiment; quantify aerobic respiration during the experiment; quantify of the intensity of general metabolism (e.g., gross dehydrogenase activity) during the experiment; the use of SG/HD labelling also for washed (oxalic acid solution) cells. Bio-process engineering: use of different bacterial biomass (number) and mineral/inorganic substrate ratios; vary catalyst, nutrient and O2 addition in batch vs. columns reactor types, etc. References: 1. Cismaşiu Carmen Mădălina, 2005. The biosolubilization metals of the pyrite concentrates with cultures of Thiobacillus ferrooxidans resistant to high concentrates of metallic ions, Proceedings of the Institute of Biology, Romanian Academy, vol. VII, p. 147-158 2. Cismaşiu Carmen Mădălina. 2010. The taxonomic and physiologic diversity of the acidophilic chemolithotrophic bacteria of the genus Thiobacillus used in ores solubilization processes. Travaux de L’Institut de Speologie «Emile Racovitza». Bucharest. 49: 97-112. 3. Valdes Jorge, Pedroso Inti, Quatrini Raquel, Dodson Robert J., Tettelin Herve, Blake Robert, Eisen, Jonathan A., Holmes David S., 2008, Acidithiobacillus ferrooxidans metabolism: from genome sequence to industrial applications, BMC Genomics, DOI: 10.1186/1471-2164-9-597
AKNOWLEDGEMENT Dr. Carmen - Madalina Cismasiu and Dr. Ioan Ardelean contribution is supported by Project nr. RO1567-IBB05/2017. We acknowledge the help of skilled technician: Mrs Marilena Cîrnu and Mrs. Mariana Enciu at the IBB. The study is the result of the collaboration between the Institute of Biology Bucharest, Department of Microbiology and “Alexandru Ioan Cuza” University of Iasi, Department of Interdisciplinary Research- Field Science and CERNESIM. Many thanks are addressed to Dr. Cristina Moisescu who has facilitated this networking.
