Ferrous Iron Oxidation by Acidithiobacillus ferrooxidans Immobilized on Refractory Clay Tiles

Refractory clay tiles are composed of kaolin, which is the commercial name of clay, and this consists mainly of kaolinite mineral. Two such tiles and caowool packed in glass columns were used for the immobilization of Acidithiobacillus ferrooxidans cells in a ferrous iron medium, which was percolated through the supports. Colonization was carried out by several media replacements with no further inoculation until maximum ferric iron productivity was reached. One of the tiles was discarded due to the high iron precipitation during bacterial growth. The columns with the other supports were used for ferrous iron oxidation in batch and continuous flow modes of operation and these appeared to be promising supports for A. ferrooxidans. A ferrous iron oxidation rate of 14.5 mmol.l –1 .h –1 was reached in one of the columns in the continuous culture. After being used for several cultures, pieces of tiles with immobilized cells were stored at 4 oC. Samples at different times were incubated in ferrous medium and these showed high cell activity even after 6 months.