Abstract
Bioleaching is a mature technology, which is widely employed commercially in the leaching of primary sources of metals (ores, concentrates, and mine residues). The current work discussed the effects of aluminum sulfate additions to the growth medium, PLS recirculation and bleeding on the column bioleaching of secondary copper sulfide ores with a significant content of fluoride-containing minerals. Fluoride is toxic to bacteria at the pH of bioleaching but its toxicity may be overcome in the presence of soluble aluminum and ferric iron. Therefore, experiments were carried out in 10 × 100 cm height aerated columns, loaded with 10 kg of crushed and agglomerated copper ore and inoculated with Sulfobacillus thermosulfidooxidans. Initially, fluoride concentrations of up to 2.5 g/L in the pregnant leach solution were observed due to the fast dissolution of fluoride-bearing minerals. Aluminum was added to the leaching solution to reduce the Al/F ratio so that the concentration of HF (the main toxic species) was decreased, but while the total fluoride concentration was higher than that of aluminum, the bacterial population as low. Therefore, the current work emphasizes that it is possible to set up conditions to enable bioleaching even at high fluoride concentrations. Following this approach, copper extractions above 90% were achieved for a H2SO4 consumption ranging from 128.8 to 206.1 Kg/ton.
Highlights
Mining companies constantly search for new process routes to treat low-grade ores and metal–bearing mining residues
As the SEM analyses of bioleaching residues showed the absence of elemental sulfur it was assumed that the element was bio-oxidized during bioleaching in the current work
It is important to highlight that the high concentrations of copper iron aluminum and fluoride were a result of the ore agglomeration with sulphuric acid (10 Kg/ton), which reacted with the minerals and dissolved such elements
Summary
Mining companies constantly search for new process routes to treat low-grade ores and metal–bearing mining residues. The discovery and application of microorganisms, which can produce ferric iron and protons (depending on the mineral) either in solution or the mineral surface provided several advances in terms of leaching. Such a technology is already integrated into general leaching processes, and the term bioleaching is associated with hydrometallurgical practice for sulfides, especially in heap operations. With its conversion to treat secondary sulfides in the presence of microorganisms and along with solvent extraction and electrowinning, it became a major breakthrough in the copper industry and currently accounts for nearly around 15% of the overall metal production worldwide, for low and moderate copper grades (Acevedo and Gentina, 2013)
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