A new bacterium, Thiobacillus cuprinus, can extract copper from chalcopyrite as rapidly as T. ferrooxidans. On solution with and without nutrient amendments and bacterial growth media were supplemented with T. ferrooxidans or T. cuprinus in shake flask studies. Both species extracted -42% of the copper using growth media. In one case, T. cuprinus solubilized approximately twice as much copper as T. ferrooxidans utilizing a seeded On solution.
Variables that were evaluated included: Nutrient addition, seeding with T. ferrooxidans or T. cuprinus, and growth media comparison. Leach solutions used included unmodified On solutions as baseline controls. In other cases, nutrients were added to favor the growth of either T. ferrooxidans, (designated TFN), or T. cuprinus, (designated TCN). Adequate nutrients were added to match concentrations found in Medium 64, or Medium 30 respectively.
Copper sulfide ore sample A had a head assay of 0.22% copper of which 22.7% was acid soluble. According to a mineralogical analysis, most of the copper was in the form of chalcopyrite with a minor quantity of digenite present. The ore also contained 2.65% iron and 1.6% sulfur of which 97% was in the sulfide form.
Chalcopyrite leaches much more slowly than most other forms of sulfide copper as shown by Paul et al., 1988, and it is not very acid soluble. Therefore, biooxidation is very important for the extraction of copper from chalcopyrite. The results of these studies further attest to the importance of microorganisms for the leaching of such refractory sulfide compounds. As shown in Table 1, sterilization of the On solution and ore by the addition of 0.01% sodium benzoate resulted in a significant decrease in copper extraction (p = 0.011).
Significantly more copper was extracted using Medium 64- seeded with T. ferrooxidans than by using Medium 30 seeded with T. cuprinus (Table 1). In this case, where the ore microcosm was eliminated.
In order to test modifications that could be implemented in the field, the effects of nutrient additions and bacterial seeding of On solution were also evaluated in this study. Figure 2 shows rates of copper extraction achieved using unmodified On solution,
Seeding On solution amended with TCN with T. cuprinus did not result in substantially more copper extraction than addition of TCN alone as shown in Table 1. These results suggest that managing dump leach solutions in such a manner as to enhance the activity of the native microorganisms will result in increased copper extraction and that seeding of On solution is not necessary.
The addition of TCN to the On solution and seeding with T. cuprinus enhanced copper extraction much more than the addition of TFN and seeding with T. ferrooxidans during shake flask tests utilizing sulfide ore sample 2. Indeed, 64% of the copper was extracted using nutrient-amended On solution seeded with T. cuprinus. Equivalent concentrations of copper (42%) were extracted from the sulfide ore sample using T. ferrooxidans and T. cuprinus in appropriate laboratory growth media.