Abstract

The purpose of this investigation was to determine the effectiveness of the leaching streams from waste copper ore dumps as a nutrient solution for subsequent biological oxidation and solubilization of sulfide minerals. The copper in the leaching streams is precipitated by displacement with iron. As a result of this procedure the solution is high in ferrous iron concentration and has a pH of near 3.7. The bacteria in the leaching streams are capable of oxidizing ferrous iron to the ferric state and sulfide minerals to sulfates. The effects of temperatures, pH, urea, and aeration rate on the oxidation of the ferrous iron in the stream were studied. The effect of oxidized and reduced forms of the solutions, pyrite, urea, and pH on the solubilization of chalcopyrite were investigated. It was found that an increase in the rate of bubbling air through the ferrous solutions greatly increased the rate of oxidation of the solution. The optimum pH was found to be near 3.2. The optimum temperature was near 35°C. Added urea had little effect on the rate of oxidation of the ferrous solution. The presence of pyrite slowed the rate of solubilization of chalcopyrite. This was interpreted as being due to the lower pH caused by the oxidation of pyrite. Copper was found in the effluent leachates from the mineral samples when the pH was near 3.0. Little copper was found when the pH was below 2.5. Raising the pH with CaCO3 increased the rate of solubilization of chalcopyrite. Added urea had little effect on the rate. It was concluded that the reduced form of the leaching stream is an effective leaching fluid for the biological solubilization of chalcopyrite because of its relatively high pH and nutrient content. Pyrite is preferentially oxidized in the presence of chalcopyrite in tailing solution.

Degree

College and Department

Physical and Mathematical Sciences; Chemistry and Biochemistry

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