Leaching of iron from kaolins by a spent fermentation liquor: Influence of temperature,pH, agitation and citric acid concentration

Summary The efficiency of a biological bleaching process on a highly contaminated iron oxides kaolin was analyzed. The bio-bleaching method consists of two steps: first, the fermentation of a chemically-defined medium byAspergillus niger leads 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°C for 5 h and the whiteness index was increased to 67%. Extracellular enzymes were not responsible for leaching, which is basically due to organic acids produced during the fermentation.