Iron removal from kaolins by bacterial leaching

Microorganisms may play an important role in the dissolution of silicate st ructure in the rock weathering process and in the genesis of clay minerals. Bacteria of Bacillus species are considered to be relatively active in thi s process. The samples from Horna Prievrana kaolin pit are characteristic b y a high number of bacteria, especially of Bacillus species. The dissolutio n activity of two selected Bacillus cereus strains from these samples was i nvestigated on three kaolin samples contaminated with iron oxyhydroxides an d mica. The experimental results showed that these bacteria are able to rem ove 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 showe d the removal of 53% bound Fe from kaolin (KS3 sample), which was taken fro m Vysny Petrovec. The biodegradation of iron oxyhydroxides and a partial de struction of mica structure were confirmed also by X-ray analysis. Bacteria subsequently destroyed some of mica surfaces, observed by SEM before bacte rial leaching, when Fe tons were released from mica structure what resultin g in illite development. The enrichment by fine-grained fraction as a resul t of bacterial leaching was ascertained by granulometric analysis especiall y in KS1 sample. The knowledge obtained could be important for the improvem ent of qualitative properties of kaolins and quartz used in ceramic and gla ss industry. An economical advantage of bioleaching is also suggested becau se the bacterial treatment is economically as well as ecologically more sui table than classical technologies such as magnetic separation and flotation , although not so rapid.