Download Bioleaching of nickel from olivine using chemoheterotrophic fungi

Bioleaching of nickel from olivine using chemoheterotrophic fungi and
bacteria
Yi Wai Chiang 1, Rafael M. Santos 2, Aldo Van Audenaerde 2, Annick Monballiu 1, Tom Van Gerven 2, Johan
Martens 1, Boudewijn Meesschaert 1
1
KU Leuven, Dept. Microbial and Molecular Systems, Leuven, Belgium
2
KU Leuven, Dept. Chemical Engineering, Leuven, Belgium
The increasing demand and diminishing availability of raw materials requires us to look
beyond conventional sources. The importance of low-grade ores and waste residues as a source for
raw materials is expected to increase in the near future. In particular, the escalating depletion of highgrade sulphidic ores make it necessary to obtain metals from the more abundant but lower grade
silicate-rich ores and mineral processing residues. To overcome the high costs linked to the processing
of such materials using traditional extraction routes (e.g. high pressure acid leaching),
biohydrometallugy rises as a potential sustainable extraction route, since microorganisms can be
considered as renewable chemical producers. In this work, bioleaching of non-sulphidic materials by
applying chemoheterotrophic bacteria and fungi is studied. These microorganisms operate on different
leaching mechanisms than sulphur oxidizing bacteria commonly used for sulphidic ores; these include
the production of organic acids, complexing agents, and surface sorption sites created by free
functional groups.
It was found that the tested fungus, Aspergillus niger, leached substantially more nickel from
olivine than the tested bacterium, Bacillus mucilaginosus. A. niger also outperformed fungal species
Humicola grisae and Penicillium chrysogenum in the leaching of olivine. Contrary to traditional acid
leaching, the microorganisms leached nickel preferentially over magnesium and iron. On average, a
selectivity factor of 2.2 was achieved for nickel compared to iron. This can potentially facilitate postprocessing of the leach liquor and reduce the cost. The impact of ultrasonic conditioning on
bioleaching was also tested, and substantial increase in nickel extraction with A. niger was observed.
This was credited to an increase in the fungal growth rate, the promotion of particle degradation, and
the detachment of the stagnant biofilm around the particles. Furthermore, ultrasonic conditioning
enhanced the selectivity of A. niger for nickel, resulting in a selectivity ratio for Ni/Fe equal to 3.5.
The assistance of ultrasonic conditioning can be further optimized by varying the energy intensity, the
frequency of the ultrasonic waves and the duration and the frequency of the treatment.
The chemical resistance of the selected microorganisms to several heavy metal and metalloid
(As(III,V), Cd, Cr(III,V), Ni, Pb, Zn) was evaluated. It was found that, with the exception of As(v), Cd, A.
niger has high tolerance to these components. Therefore, this biohydrometallurgy route can
potentially be applied to other non-sulphidic materials, such as industrial slags, ashes and sludges.