The development of an environmentally friendly, energy conserving and economical bioprocessing of oxidic ores is essential in the sustainability of the metal industry. The incentive for green technologies, such as bioleaching processes, have been

cultivated because of government regulations and research policies that aim to address the ecological impacts of mineral processing .

Yes it is a good question. Though acidic leaching has shown good results for oxidic ores of copper, still strict environmental laws hold good for the associated problems in the process and to the environment. On the other hand, safer biotechnological approaches have shown promising results for sulphidic ores. Now these microorganisms derive their energy from the sulphic ores such as chalcopyrite which is unavailable from oxidic ores. Also adding to the problem, if we add other supplements such as sulphur or iron for the growth of microoorganisms to be used for oxidic bioleaching, it will end up uneconomic.

Having an organism which actively transports your metal into the cell and accumulates it without adversely affecting cell growth - do look into the bugs that make paricles actively without cell death (i.e magnetotatic bacteria). Then there is the recovery of the collection of you bacteria afterwards...a bugbear of the bioremediation community for a very long time. When you think about oxidised ores and a bacteria, think about why the organism would have anything to do with the metal in the first place. Usually its being used for enzymes, but sometimes its simply external respiration (i.e. look into Geobacter and Shewanella). There is also a new example of external electron transport coming out soon of this that myself and collegues have happened upon ; ). But external electron transport is NOT recovery....but oxidation state may alter solubility of your metal which may also help recovery.

The leaching of low grade ore is attracted considerably in recent years. One of the most important sources of low grade ores in zinc mineral processing is zinc mining tailings. Smithsonite (ZnCO3), hydrozincite (2ZnCO3·3Zn(OH)2), zincite (ZnO), willemite (ZnSiO4), gahnite (ZnAl2O4), descloizite (PbZnVO4OH), hardystonite (Ca2ZnSi2O7) and hemimorphite (Zn2SiO3·H2O), are mostly zinc oxide ores, an abundance of which include smithsonite and hemimorphite.There are many studies showing that zinc oxide sources were treated by organic acids produced by microorganism.

. Anaerobic iron-reducing bacteria(IRB) reduce Fe3+ to Fe2+ as part of their respiration. These organisms are continually being discovered, and many of these have promise for reductive bioleaching of iron. Applications of IRB include decolorization of kaolin and silica, iron removal from bauxite, recovery of iron from low-grade or difficult-to-process ores, and promoting breakdown of iron-rich rocks to liberate other metals. Reductive iron leaching in these applications has been shown to be most effective for dissolving the more hydrated and amorphous iron oxides, with low dissolution rates for highly crystalline oxides such as hematite. It has also been shown that, the given sufficient adaptation and leaching time, these microorganisms can produce iron-bearing solutions containing as much as 1800 mg of Fe2+ per liter.

http://10.1080/08827508.2012.703627

Indeed, I hav spent quite a bit of time studying the molecular mechanisms behind this Fe reduction.

Dear Dr McMilan, its good to see that you have worked on the Fe Reduction and its molecular mechanisms. We are currently working in this area of DIRB for Nickel extraction from lateritic ores. If you have published some papers in this area, you can send me at [email protected].

Its good to see some interesting conversation. In the proposal given by Dr.McMillan, magnetotatic bacteria is recommended. It would be very kind of him, if some information on this kind of bacteria be available.

Dear all, thank you for raising discussion upon an interesting area in bio-mineral processing of oxidic minerals. The oxidic minerals are dead in terms of the nutritional point of view for chemotherapeutic microbes. However the acidophillic chemolithotrophes have been used successfully in large scale operation of metal extraction from sulphidic minerals. The use of acidophiles in large scale is less susceptible to microbial contamination which is an major challenge for large scale operation of the process. So microbial reduction process via the acidophiles can be used for co-bioleaching of sulphidic minerals mixed with oxidic minerals to extract metal values from both the types of minerals. Furthermore anoxic microbial reduction process is gaining momentum for the processing of oxidic minerals.

Alkaline bioleaching is an important way for treating low grade metal oxide ore which has some advantages such as low corrosion and low pollution.

Dear Sandeep and Lala, If you woud like some information that might help then send me a message with an email address and I will point you in the direction I was discussing.

The nickel present in nickel laterites is not usually present as discrete minerals, but as cations substituted within manganese oxides, goethite, and/or clays. Because of this, it is difficult to upgrade the ore by beneficiation. As a result, nickel laterites are traditionally processed using pyrometallurgical and hydrometallurgical methods. In recent years, microbiological leaching has been found to be a promising novel technology for recovering valuable minerals from traditionally difficult-to-process ores. Microbial leaching of low-grade ores offers many advantages over other conventional methods due to its relative simplicity, requiring mild operating conditions, low capital costs, low energy input, relatively unskilled labour requirements, and being environmentally friendly. Because of the importance of bio leaching, recent advances in microbial assisted leaching of nickel laterites are being developed using fungal (chemoorganotrophic) and chemolithotrophic microorganisms.

Thank you Dr. Duncan McMillan.We are at present working on Iron Reducing Bacteria.Application of IRB for improving the nickel extraction from laterite ore is being tried.([email protected])

The potential of microbial mobilization of metals as cyanide complex from solid materials and represent a novel type of microbial metal mobilization(termed “biocyanidation”).Regarding biological cyanide formation, cyanide is formed by a variety of bacteria as secondary metabolite, e.g. Chromobacterium

violaceum, Pseudomonas fluorescens, or P. aeruginosa, many of

them belonging to the soil microflora. In the presence of cyanide, many metals and metalloids (such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, Mo, Tc Ru, Rh, Pd, Ag,

Cd, W, Re, Os, Ir, Pt, Au, Hg, Tl, Po, and U) form well-defined

cyanides complexes which show often very good water solubility

and exhibit high chemical stability. Regarding metal recovery from solutions, cyanide-complexed metals might be easily separated by chromatographic methods and sorbed onto activated carbon.

Bioleaching is a profitable alternative to the conventional chemical process of uranium recovery. The leaching of U from low-grade ores and solid wastes is realized by chemoautotrophic bacteria such as Acidithibacillus ferrooxidans. Uranium reducing bacteria, particularly Shewanella putrefaciens and Shewanella oneidensis, can be used for UO2 particles synthesis. The bioreduction of U(VI) in the presence of hematite particles can be a way to new catalyst fabrication. (Physicochem. Probl. Miner. Process. 49(1), 2013, 71−79 )

http://www.minproc.pwr.wroc.pl/journal/pdf/ppmp49-1.71-79.pdf