Catalytic Effect of Graphite Promoting Zn Dissolution from Sphalerite using a Leptospirillum ferrooxidans Dominated Mixed Culture

In this study, the effect of graphite on sphalerite dissolution was investigated using a Leptospirillum ferrooxidans (L. ferrooxidans) dominated meso-acidophilic bacterial consortium. Results of the studies indicated that Zn dissolution enhanced from 18.75% (in control tests) to 78.46% (using L. ferrooxidans) without graphite in the system (the conventional approach). Addition of graphite further improved sphalerite bio-oxidation up to 10%, i.e., from 78.46 to 87.83% indicating bio-catalytic effect and possible galvanic interaction between sphalerite and graphite. Through the conventional route, the system's pH eventually lowered from 1.8 to 1.4 and ORP increased from 300 to 700 mV. In presence of graphite, the pH lowered to nearly 1.0 and ORP reached 600 mV. This indicated efficient bacterial activity and stabilized leaching conditions in both cases. Analytical characterization studies through XRD and SEM-EDAX indicated the presence of sulfur and K-type jarosite (KFe33+(OH)(6)(SO4)(2)), ascribed to the passivation layers formed during sphalerite bioleaching.

Automated summary

The addition of graphite further enhanced the bio-oxidation efficiency of sphalerite, indicating a bio-catalytic effect and possible galvanic interaction between sphalerite and graphite. The presence of graphite also stabilized the leaching conditions of the system, promoting bacterial activity.