Ceramics-Silikáty 47, (1) 20 - 26 (2003) |
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THE RELEASE OF IRON-BEARING MINERALS AND DISSOLUTION OF FELDSPARS BY HETEROTROPHIC BACTERIA OF BACILLUS SPECIES |
Štyriaková Iveta 1, Štyriak Igor 2, Galko Igor 3,
Hradil David 4,
Bezdička Petr 4 |
1 Department of Biotechnology, Institute of Geotechnics of the Slovak Academy of Sciences,
Watsonova 45, 043 53 Košice, Slovak Republic
2 Institute of Animal Physiology of the Slovak Academy of Sciences, Šoltésovej 4 - 6, 040 01 Košice, Slovak Republic
3 EnviTaz s.r.o., Kynceľová 10, 974 11 Banská Bystrica 11, Slovak Republic
4 Institute of Inorganic Chemistry, Academy of Sciences of Czech Republic, Rež, 250 68 Czech Republic
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Keywords: Bioleaching, Feldspars, Bacillus, Oxalic acid, Iron, Weathering |
Dissolution of aluminosilicates and Fe-oxyhydroxide minerals from granitic eluvium using bacteria of Bacillus genus was
monitored with solution chemistry, granulometric and X-ray analyses as well as microscopic techniques to determine the
effects of these bacteria on crystal surface and releasing mechanism of K, Si, Fe, and Al from minerals. Feldspars, quartz and
micas are dominant minerals in granitic eluvium (GE). Oxyhydroxides of Fe are found in the intergranular spaces of minerals,
contaminating and making most feldspar raw materials unsuitable for commercial applications. Bacteria of Bacillus spp.
decrease pH of leaching medium by production of organic acids. These organic acids are directed by glycocalyx of adherent
bacteria to specific sites on mineral surface (e.g. to crystal defects). The impregnated iron minerals are released by bacterial
destruction of intergranular and cleavage spaces of silicate grains. This bacterial activity results in the release of Fe, Si, and
K from feldspar and Fe oxyhydroxides. However, pH of leaching medium is adjusted to neutral value in regular intervals during
bioleaching to maintain bacterial activity. The decrease of fine-grained fraction is the result of bacterial destruction of
GE. Despite the impoverishment of the distribution of fine-grained fraction, there was observed the increase of the surface
area of feldspar grains from the value 3.65 m²/g to value 4.82 m²/g. This fact confirms the activity of bacteria of Bacillus genus
together with hydrolysis in point corrosion of mineral grains. After 120 days of bioleaching, 31 % Fe extraction from granitic
eluvium was observed. It was also possible to accelerate this process by using 0.1 M oxalic acid after 1 month's bacterial pretreatment.
Moreover, the bacterial pretreatment facilitated the access of oxalic acid to Fe-bearing minerals and showed a possibility
to use the oxalic acid in lower concentration. This fact is important especially from the view of producing less-agressive
effluent to the environment and decreasing of costs in subsequent recyclation of oxalic acid. |
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