Bacterial leaching of nickel literites using chemolithotrophic microorganisms
Date
2009-07-17T12:48:51Z
Authors
Simate, Geoffrey Simate
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Abstract
Biohydrometallurgy, an interdisciplinary field involving geomicrobiology, microbial
ecology, microbial biochemistry, and hydrometallurgy, is a promising novel
technology for recovering valuable minerals from traditionally difficult-to-process
ores. In this study, the possibility to treat nickel laterites biohydrometallurgically
using chemolithotrophic microorganisms was investigated. Nickel laterite contains
metal values but is not capable of participating in the primary chemolithotrophic
bacterial oxidation because it contains neither ferrous iron nor substantial amount of
reduced sulphur. Its metal value can, however, be recovered by allowing the primary
oxidation of pyrite, or similar iron/sulphur minerals to provide sulphuric acid
solutions, which solubilise the metal content.
In order to have an insight on the use of chemolithotrophic bacteria in this process, it
was important to first understand the role and effects of sulphuric acid. Its effect was
compared to citric acid and ferric sulphate. Results showed that sulphuric acid
performed better, in terms of nickel recovery, than citric acid or ferric sulphate of the
same initial concentration. However, citric acid performed better at the same initial
pH. A synergic effect was observed in a mixture of sulphuric and citric acids.
In the bacterial leaching test works, sulphur substrate exhibited better effects in terms
of acidification and nickel recovery than pyrite substrate. Using a statistically-based
optimization strategy called response surface methodology, the theoretical optimum
conditions for maximum nickel recovery (79.8%) within the range of conditions
studied was found to be initial pH of 2.0, 63μm particle size and 2.6% pulp density.
This work has shown that by the addition of a sulphur containing material, nickel
laterites can be leached by chemolithotrophic microorganisms via the sulphuric acid
produced.