Is it
a. Micro-organisms used for leaching are neutrophiles.
b. The leaching (metal solubalization) happens at neutral pH.
c. Both a and b
d. Neutrophiles produce lixiviant (which is at lower pH). This lixiviant is further used for leaching.
also kindly mention advantages of "Neutral pH bioleaching" over "acidophilic bioleaching".
Mouna,
I don't think that neutral pH bioleaching is adventageous and I didn't study on neutral pH bioleaching but, here is a summary of circumneutral pH leaching that I used in one of my unpublished reports, citing Schippers (2004). Check out the references below that might answer your multiple questions.
"...When the pH of the environment is increased to circumneutral (pH 5.5 – 7.4) and alkaline conditions, bioleaching is no longer a matter of the subject as ferric iron is out of its stability limits (Schippers, 2004). Moderately acidophilic bacteria like Thiomicrospira frisia and Thiomonas intermedia take place in metal sulfide oxidation (Brinkhoff et al., 1999) by oxidizing the sulfur moiety of the acid soluble metal sulfur to generate protons (Schippers, 2004). As Fe(II) oxidizers are not present at an environment with neutral pH, only the intermediate sulfur compounds can be oxidized of an acid soluble metal sulfide, which are formed by chemical oxidation (Schippers, 2004)...
References
Brinkhoff, T., Muyzer, G., Wirsen, C.O., and Kuever, J., 1999. Thiomicrospira kuenenii sp. nov. and Thiomicrospira frisia sp. nov., two mesophilic obligately chemolithoautotrophic sulfur oxidizing bacteria isolated from an intertidal mud flat: International Journal of Systematic Bacteriology, v. 49, p. 385–392.
Schippers, A., 2004. Biogeochemistry of metal sulfide oxidation in mining environments, sediments and soils. In: Amend, J.P., Edwards, K.J., Lyons, T.W. (Eds.), Sulfur Biogeochemistry — Past and Present. : Special Paper, 379. Geological Society of America, Boulder, Colorado, USA, pp. 49–62."
Hope this would help.
Regards
Neutral pH bioleaching is mostly under development. I don't know of any exploitation using actively. In any case, this would apply to non-sulfidic ores where the pyrite and other sulfides that sustain the typical bioleaching communities are not present (or just in traces).
You can start with the following review, a bit old but still a good reading to get into the topic.
Article Biohydrometallurgy for Nonsulfidic Minerals—A Review
leaching at pH 7.0 will be very slow and it is if happens may be for oxide ores. Some time Pseudomonas do phosphate solubilisation but normally it is not included in the process of bioloaching.
If your question is about resolubilizing metals from sediment into the water column in an ecotoxicological context; the answer is much more complicated. The underlying driver is in that case not pH, but O2 concentration. 2 references that might give some insight:
De Jonge M, Teuchies J, Meire P, Blust R & Bervoets L (2012) The impact of increased oxygen conditions on metal-contaminated sediments part I: Effects on redox status, sediment geochemistry and metal bioavailability. Water Research 46: 2205-2214.
De Jonge M, Teuchies J, Meire P, Blust R & Bervoets L (2012) The impact of increased oxygen conditions on metal-contaminated sediments part II: Effects on metal accumulation and toxicity in aquatic invertebrates. Water Research 46: 3387-3397
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