Abstract
A new heterotrophic strain, named Providencia sp. JAT-1, was isolated and used in bioleaching of low-grade complex copper ore. The strain uses sodium citrate as a carbon source and urea as a nitrogen source to produce ammonia. The optimal growth condition of the strain is 30 °C, initial pH 8, sodium citrate 10 g/L and urea 20 g/L, under which the cell density and ammonia concentration in the medium reached a maximum of 4.83 × 108 cells/mL and 14 g/L, respectively. Ammonia produced by the strain is used as the main lixiviant in bioleaching. Bioleaching results revealed that higher strain growth led to a higher copper recovery, while higher pulp density will cause a greater inhibitory effect on strain growth and ammonia production. The copper extraction reached the highest value of 54.5% at the pulp density of 1%. Malachite, chrysocolla and chalcocite are easy to leach out in this bioleaching system while chalcopyrite is difficult. Results of comparative leaching experiments show that bioleaching using JAT-1 is superior to ammonia leaching at the same condition. The metabolites produced by the strain other than ammonia are also involved in bioleaching.
Highlights
Bioleaching of copper sulfide ores in acid conditions, using autotrophic bacteria such as Acidithiobacillus ferrooxidans [1,2,3,4,5], is a mature process and has been successfully used for the recovery of copper
Groudeva [15] studied the bioleaching of rich-in-carbonates copper ore in an alkaline condition, and the results showed that bioleaching using urease-possessing bacteria can achieve the highest copper extraction of 64.4% within 30 days
The cell density of pure culture and ammonia concentration reached a maximum of 4.83 ˆ 108 cells/mL and 13.96 g/L, respectively
Summary
Bioleaching of copper sulfide ores in acid conditions, using autotrophic bacteria such as Acidithiobacillus ferrooxidans [1,2,3,4,5], is a mature process and has been successfully used for the recovery of copper. Bioleaching in the acid condition becomes ineffective and uneconomical for these copper oxide ores due to the limited energy source in oxide ores for autotrophic bacteria [7], excessive acid consumption [8,9] and undesired impurity dissolution which causes some problems in the further processing of the leaching solution [10]. Many studies reported the leaching of copper ore containing oxides and carbonates in ammonia medium, yet little attention has been paid to the bioleaching in alkaline conditions. Low-grade complex copper ores, dominated with oxides and carbonates, contain few energy sources for bacterial utilization. Such ores may be bioleached in an alkaline condition by heterotrophic bacteria [13]. Avakyan [14] demonstrated the release of silicon from nepheline or plagioclase by using Sarcina ureae, which can grow and produce ammonia
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