Release of microspherolites and metals extraction from energetical fly ashes by Bacillus isolates

• Main Authors: tyriaková Iveta, Kunierová Mária
• Format: Article
• Language: English
• Published: Technical University of Kosice 2000-09-01
• Series: Acta Montanistica Slovaca
• Subjects: Bacillus; bioleaching; fly ash
• Online Access: http://actamont.tuke.sk/pdf/2000/n3/19styriakovakusnierova.pdf

The amorphous secondary silicate mineral components formed in the process of coal combustion dominate in the composition of energy fly-ash. Depending on the composition of coal concentrate, this secondary raw material source also contains the industrially interesting components, e.g. titanium (eventually iron and aluminium) and can be considered as a non-metallic material suitable for the construction industry.The main secondary mineral components of the energy fly-ash formed during the coal combustion were studied using SEM (scanning electronic microscope). They can be divided into four groups:1. Amorphous spherical alumocilicate particles in allotriomorphic aluminosilicate grains they represent a main mineral component of fly-ash, which is formed from the accompanying rocks of coal containing silicate minerals,2. Quartz which formed a substantial component of accompanying rocks of coal or accompanying accessory mineral of coal together with kaolinite and mica, was transformed into tridymite at the temperature exceeding 870°C and into cristobalite at the temperature exceeding 1470°C. The spherical particles are products of reaction between cristobalite and aluminosilicate, which is a frequent phenomenon occurring during the formation of volcanic rocks. These particles form together a main amorphous phase of fly-ash.3. Mullite represents a secondary component of fly-ash, which is formed from accompanying clay minerals of coal (kaolinite, mica) together with cristobalite under the effect of temperature exceeding 1150°C,4. Non-combusted residue consists of organic substance, represents a non-combusted ratio of coal as a secondary component of fly-ash.Heterotrophic bacteria of Bacillus genus are capable to remove 66 % of titanium and 33 % of iron from non-deposited fly-ash from Opatovice after 35 days of leaching of samples. The content of solid phase in fly-ash influences the extraction of elements, mainly iron and titatnium, because they have a different resistance to the bacterial destruction. Metals (iron, titanium) are comprised in an oxide form both in a non-combusted residue and allotrimorphic grains with amorphous aluminosilicate spherical particles.SEM enabled us to observe that the fresh fly-ash contains disseminated aluminosilicate spherical particles, with the size 1-70 µm that are released, probably together with metals, especially iron and titanium. The yielding of individual elements show a lower extraction of iron (3,3%) and titanium (15,2%) in the case of sample of 5 year - deposited fly-ash and a slightly higher yielding of iron (6,2%) and titanium (29,1%) in the case of sample of 20 year deposited fly-ash. A long-term deposition of energy fly-ash causes chemical and mineralogical changes as a result of weathering processes demonstrated by a lower extraction of metals from fly-ash.Although acids produced by Bacillus spp. were not measured in these experiments, in our previous experiments were detected several organic acids such as acetic, butyric, pyruvic, lactic, and formic acids after bioleaching of aluminosilicate samples.