Ceramics-Silikáty 44, (4) 135 - 141 (2000)

Microorganisms may play an important role in the dissolution of silicate structure in the rock weathering process and in the genesis of clay minerals. Bacteria of Bacillus species are considered to be relatively active in this process. The samples from Horná Prievrana kaolin pit are characteristic by a high number of bacteria, especially of Bacillus species. The dissolution activity of two selected Bacillus cereus strains from these samples was investigated on three kaolin samples contaminated with iron oxyhydroxides and mica. The experimental results showed that these bacteria are able to remove 43 % of free Fe occurring in kaolin in amorphous form of oxyhydroxides (KS1 sample) and approximately 15 % of Fe bound in mica (KS2 sample) after 1 month of bioleaching. The amorphous form of Fe is extractable by bacterial leaching easier than Fe bound in mica. The prolonged bioleaching time showed the removal of 53 % bound Fe from kaolin (KS3 sample), which was taken from Vyšný Petrovec. The biodegradation of iron oxyhydroxides and a partial destruction of mica structure were confirmed also by X-ray analysis. Bacteria subsequently destroyed some of mica surfaces, observed by SEM before bacterial leaching, when Fe ions were released from mica structure what resulting in illite development. The enrichment by fine-grained fraction as a result of bacterial leaching was ascertained by granulometric analysis especially in KS1 sample. The knowledge obtained could be important for the improvement of qualitative properties of kaolins and quartz used in ceramic and glass industry. An economical advantage of bioleaching is also suggested because the bacterial treatment is economically as well as ecologically more suitable than classical technologies such as magnetic separation and flotation, although not so rapid.