Bioleaching

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Hi, everyone. I'm Yang Guo, an exchange student from Shanghai Normal University. I major in biotechnology and this is my last year in university.

Bioleaching is mysterious and attractive. The principles are simple but the actual process is still unclear to me. Following my confusion and curiosity ,I choose this topic, trying to have a better understanding of this process as well as its industrial importance. By the way, ores are really beautiful and useful.

Enjoy it !Yang Guo 31950921

Bioleaching

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A brief introductionBioleaching is a simple and effective technology for metal extraction from low-grade ores and mineral concentrates. Metal recovery from sulfide minerals involves chemolithotrophic bacteria,while heterotrophic bacteria play an important role in the treatment of non-sulfide ores and minerals.(Bosecker 1997)

Here is a typical process of pyrite bioleaching:4FeS2 + 15O2 + 2H2O → 2Fe2(SO4)3 + 2H2SO4

FeS2 + 7Fe2(SO4)3 + 8H2O → 15FeSO4 +8H2SO4 (Watling 2008)

Extraction of metals by bioleaching is affected by a lot of physicochemical parameters,including the biomass availability of CO2, particle size, mineralogy of the ore, and pulp density. (A.K.Mathur 1995)

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BioleachingModeling of uranium bioleaching by Acidithiobacillus ferrooxidans

In this paper,a mathematical model including three reactions and four equations describing the main process of uranium bioleaching by Acidithiobacillus ferrooxidans is developed.Based on this,a series of experiments and computer analyses were carried out to evaluate the model.The results proved the model can be well applied to bioleaching under similar conditions.Three reactions:UO2 +2Fe3+→2UO2

2++2Fe2+

2Fe2++0.5 O2 +2H+→2Fe3++H2O3 Fe3++X++2SO4

2-+6H2O→XFe3(SO4)2(OH)6+6H+ Where: X=Na+,K+,NH4

+or H3O+.Four equations:

) ed)precipitat (3+)(-r_(Fe^-(-rU) 2M_Fe/M_U-)(rcell) (2+)Fe^1/(Y_cell?=]/dt (3+)d[Fe^

)(rcell) (2+)Fe^1/(Y_cell?-(-rU) 2M_Fe/M_U=]/dt (2+)d[Fe^

m))^ ] (2+)[Fe^+n(2+)]))^e^(3+)])/([F(([Fe^(3+)])/(k2[Fe^(2+)]))n((e^(3+)])/([F-k1(([Fe^=dU/dt=rU

[cell] )]) +(2〗̂[Fe〖+(2+)])/(Ksuma([Fe^=u[cell]=dt(d[cell])/=rcelluraninite

Pic 1 http://www.johnbetts-fineminerals.com

Pic 1

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Acidithiobacillus ferrooxidans

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BioleachingResults showed that the proposed model fit the experimental data well.

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BioleachingBioleaching of molybdenite

This paper maily talks about what affects the bioleaching of molybdenite,which produce Molybdenum as an end product.There are two main source of molybdenite, molybdenite-containing mine and high purity molybdenite in solutions .Several experiments were done to determine the influence of particle size, temperature, ferric iron on the bioleaching rate,redox potential and maximum bioextraction.The factors affecting microbial resistance to molybdenum were also covered in this paper.The overall reaction of molybdenite biooxidation is summarized (Eq. 1):MoS2+4.5O2+3H2O→H2MoO4+2H2SO4

molybdenite

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Bioleaching1.Mo extraction from molybdenite became apparent when Eh excedded approximately 750 mV to 800 mV.2. Mo bioleaching rate increased with decreasing particle size and increasing temperature.3. Mo extraction from waste stream molybdenite was 50% after 1 month, but slowed after this time.4.The resistance against Mo of microbial increased with growing concentration of ferric iron.5.No selection of microbial cultures with greatly enhanced Mo resistance can be proved.6. A promising application of molybdenite bioleaching wouldbe bioheap leaching of waste stream molybdenite agglomeratedon support rock(Harvey and Bath, 2007).

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molybdenite

http://www.phy.mtu.edu http://www.saint-hilaire.ca

BioleachingBoth two papers focused on bioleaching made hypothesis and carried out experiments to test and verify what they thought.

The first paper used the mathematical model as a tool to optimize and control the process of uranium bioleaching. Further experiments were conducted and compared to previous literatures to see whether this model was right and whether it worked well or not. The second one mainly focused on the difficulties of molybdenite bioleaching, experiments were performed to find properties of molybdenite bioleaching and what affected this process.

The model developed in the first paper involved bacterial growth rate, the uranium dissolution rate, the accumulation rate of ferrous and ferric iron in solution. While the second one discussed the effect of Eh, particle size, temperature on molybdenite bioleaching in detail. Maximum bioextraction of Mo and microbial resistance to molybdenite were also explored.

Though concentrating on different aspects, both papers intended to explain the essence of bioleaching process, get the maximum bioleaching rate and best suitable condition. The influence of ferrous iron and ferric iron were also covered. Bacteria obtain energy only from the oxidation of Fe2+ .High concentration of ferrous iron could lead to substrate inhibition, while high concentration of ferric iron contributes to molybdenite resistance.

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Bioleaching

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Critical comments Generally speaking, both papers followed the scientific principles: put up reasonable hypotheses or models, then out experiments to verify them. Nevertheless, some minor mistakes can hardly be avoided.

In the first paper, By assuming that bacteria obtain energy only from the oxidation of Fe2+ and all the energy is spent on bacterial growth, their growth rate rcell with no inhibitory effects, the model for microbial growth rate was developed. However, no further experiments were conducted to test other possible energy sources, and inhibitory effects happened inevitablely.

In the second paper, all relative influences were carefully verified and discussed in detail. Microbial cultures with significantly enhanced Mo resistance had not been found. But it seems that the author neglected the possibility of combining the influence of ferric iron with resistant microbial, which may led to a great increase in the ability to against Mo inhibition.

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Bioleaching

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Personal commentsPersonally, I think bioleaching is an important and promising process. It is an environmental-friendly process. The equipments are not that complex. And the cost is relatively low. In many aspects, it’s a good way to get metal from ores.

However, there are still many problems exited. Thus the researches on bioleaching properties and relative influences are significantly important for the increase in bioleaching rate as well as in maximum extraction of metal. Besides, this can also optimize the conditions in factory to make more profit.

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Bioleaching

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References

A. Rashidi, J. Safdari,R. Roosta-Azad,S. Zokaei-Kadijani. "Modeling of uranium bioleaching by Acidithiobacillus ferrooxidans." Annals of Nuclear Energy, May 2012: 13-18.A.K.Mathur, K.K.Dwivedy. "Bioleaching — Our experience." Hydrometallurgy, May 1995: 99–109.Bosecker, Klaus. "Bioleaching: metal solubilization by microorganisms." FEMS Microbiology Reviews, July 1997: 591-604.Gregory J. OlsonR. ClarkThomas. “Bioleaching of molybdenite.” Hydrometallurgy, 2008: 10-15.Harvey, T.J., Bath, M., 2007. The GeoBiotics GEOCOAT® technology—progress and challenges. In: Rawlings, D.E., Johnson, D.B. (Eds.), Biomining.Springer-Verlag, Berlin, pp. 97–112.Watling, H.R. "The bioleaching of nickel-copper sulfides." Hydrometallurgy, March 2008: 70–88.