LEACHING OF IRON FROM KAOLINS BY A SPENT FERMENTATION LIQUOR - INFLUENCE OF TEMPERATURE, PH, AGITATION AND CITRIC-ACID CONCENTRATION

The efficiency of a biological bleaching process on a highly contamina ted iron oxides kaolin was analyzed. The bio-bleaching method consists of two steps: first, the fermentation of a chemically-defined medium by Asperguillus niger lends to a spent liquor which, in a second step, is employed as leaching agent for kaolin. In the leaching process 43% of iron oxides was removed when the kaolin was treated at 60 degrees C for 5 h and the whiteness index was increased to 67%. Extracellular enzymes were not responsible for leaching, which is basically due to o rganic acids produced during the fermentation.