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Changes in pH, redox potential and concentrations of soluble Fe ions and of Cu2+ ions were studied during the bioleaching of a flotation concentrate from the Dexing mine in China using solutions containing synthetic extracellular polymeric substances (EPS) and different initial total Fe concentrations and Fe(III)/Fe(II) ratios. At solution potentials below 650 mV vs. SHE, inhibition of bioleaching by jarosites at Fe(III) concentrations up to 20 g/l was not significant since the EPS retarded contamination by flocculating the jarosites. Inhibition increased at higher Fe(III) concentrations due to the formation of jarosites by the bio-oxidation of Fe3+ ions which adhered more easily to the outside surface of the EPS. The EPS layer containing jarosites acted as a weak diffusion barrier to rapidly create a high redox potential of more than 650 mV by the bio-oxidation of Fe2+ ions to Fe3+ inside and outside the EPS space. The ion diffusion performance of the EPS layer rapidly deteriorated, leading to severe and irreversible inhibition of the bioleaching process., Changes in pH, redox potential and concentrations of soluble Fe ions and of Cu2+ ions were studied during the bioleaching of a flotation concentrate from the Dexing mine in China using solutions containing synthetic extracellular polymeric substances (EPS) and different initial total Fe concentrations and Fe(III)/Fe(II) ratios. At solution potentials below 650 mV vs. SHE, inhibition of bioleaching by jarosites at Fe(III) concentrations up to 20 g/l was not significant since the EPS retarded contamination by flocculating the jarosites. Inhibition increased at higher Fe(III) concentrations due to the formation of jarosites by the bio-oxidation of Fe3+ ions which adhered more easily to the outside surface of the EPS. The EPS layer containing jarosites acted as a weak diffusion barrier to rapidly create a high redox potential of more than 650 mV by the bio-oxidation of Fe2+ ions to Fe3+ inside and outside the EPS space. The ion diffusion performance of the EPS layer rapidly deteriorated, leading to severe and irreversible inhibition of the bioleaching process.

Extracellular polymeric substances (EPS) were extracted from Acidithiobacillus ferrooxidans by ultrasonic treatment and centrifugation. Spectrophotometry was used to confirm that the cells were EPS-free using 2-keto-3-deoxyoctonic acid as an EPS indicator. Untreated and EPS-free A. ferrooxidans cells were mixed with EPS suspensions and the cells were monitored during 2 h of bioleaching. The effects of additions of Fe2+ or Fe3+ ions were also studied. The results showed that the presence of EPS on the cell is an important factor in their adhesion to chalcopyrite and pyrite. A decrease in attachment of A. ferrooxidans to the minerals was observed as a result of a deficiency of EPS. A recovery in the degree of attachment could be achieved by the addition of EPS to the EPS-free cells, and the recovery was higher for pyrite than for chalcopyrite. The extent of cell adhesion to chalcopyrite increased with the addition of EPS and Fe3+ and decreased when Fe2+ was added, indicating that electrostatic interaction plays a major role in the initial adhesion between the bacteria and the minerals and is a driving force for bacteria to produce EPS., Extracellular polymeric substances (EPS) were extracted from Acidithiobacillus ferrooxidans by ultrasonic treatment and centrifugation. Spectrophotometry was used to confirm that the cells were EPS-free using 2-keto-3-deoxyoctonic acid as an EPS indicator. Untreated and EPS-free A. ferrooxidans cells were mixed with EPS suspensions and the cells were monitored during 2 h of bioleaching. The effects of additions of Fe2+ or Fe3+ ions were also studied. The results showed that the presence of EPS on the cell is an important factor in their adhesion to chalcopyrite and pyrite. A decrease in attachment of A. ferrooxidans to the minerals was observed as a result of a deficiency of EPS. A recovery in the degree of attachment could be achieved by the addition of EPS to the EPS-free cells, and the recovery was higher for pyrite than for chalcopyrite. The extent of cell adhesion to chalcopyrite increased with the addition of EPS and Fe3+ and decreased when Fe2+ was added, indicating that electrostatic interaction plays a major role in the initial adhesion between the bacteria and the minerals and is a driving force for bacteria to produce EPS.