You buy Thiobacillus Ferrooxidans from: http://www.atcc.org

In order to use the culture properly you need it to condition to the ore you are trying to leach. You need to add micronutrients http://www.google.com/patents/US5413624 and establish the right starting pH (start at about 3.0 with sulfuric acid). Cultures usually grow well at about 35 degrees.

The bacteria should be adapted to your ore. Before using it for any kind of kinetic experiment you should leach a stirred beaker that has been inoculated. Assuming that there is an iron sulphide that you will be leaching, you should see the pH go down to the hydrolysis pH of iron (1.8 or so) and stay there. Let it sit for about a week so that the bacteria adapts through a number of generations. The adapted bacteria will leach your ore up to an order of magnitude faster than the unadapted bacteria. To use the adapted culture, decant off 50 ml of solution and use it as your inoculant.

I have done a number of these experiments but don't make a living from it. Just trying to be helpful. If there is anyone with better experience or advice, please don't hesitate to chime in.

I was also once told that there is so much of this stuff in our natural environment that inoculation is more of a convenience to speed things up than a necessity. If you create the right conditions, the various bacteria will appear like mold on bread.

You might consider letting someone do some initial testing and culturing for you. Not trying to plug any one company, but just speaking from what I know - I used to work for Kappes, Cassiday & Associates in Reno, Nevada. They are extremely experienced in all forms of heap / dump / tank leaching including bioleach. I'm sure there are also many others out there. Bactech used to be in the business, although they seem to be more environmental now. Mintek has been in the field for years, and holds a number of patents.

Bioleach work is not particularly expensive, and you can get a good head start (and a lot of valuable info) just by affiliating yourself with someone who is already a professional in the field. Then once you are comfortable with the techniques you can set up your own testing.

On three copper leach projects i have been associated with the bacteria occurred naturally within those ore bodies and we were able to examine each specific occurrence from column leach testing using various ore samples and local water sources in that testing. It is a good idea to have someone familiar with the biology look at the species that form here.

It seems that these bacteria appear naturally where there is sulphur and iron containing soil that has been exposed to the environment for years. Such environment could be mine dumps, ore bodies, etc.

Natural population of bacteria on Bor mine site. Mesophiles, acidithiobacillus < 2.3x104 cells/gram and leptospirillum ferrooxidans, < 2.3x104 cells/gram, iron-sulphur oxidising bacterial organism present in Mining Company Bor resources (copper ores, concentrates, tailings and mine waters), have been identified using molecular tools based on Quantitative Polymerase Chain Reaction (Q-PCR analysis) and quantified them in different bioleaching processes. The relative proportions of the cultures present in the mine samples analysed did not change much, except in tailing where exist fairly high amount of bacteria (4,3x106 cells/gram) and archaea (3.0x105 cells/gram). It was shown that the dominant organism are acidianus sp., with metallosphaera sp. and sulfolobus sp. present in lower numbers.

6 I. Dinkla, B. Geurkink, “Biotechnology for metal bearing materials in Europe” (BioMinE), Priority 3.4, EU Project, Contract Number: NMP2-CT-2005-500329-1, Nov 2005-Oct 2008, Deliverable DII.5, report entitled as "3rd interim report on the use of molecular biology tools for detecting, identifying & monitoring bioleaching microbial systems", (2008) 15.

Thiobacillus ferrooxidans was renamed Acidithiobacillus ferrooxidans in 2000. See http://ijs.sgmjournals.org/content/50/2/511.short and depending on your process, At. ferroox may not be the best choice. As already pointed out, the most efficient bioleaching systems are usually a mixture of organisms. If you do not sterilise your ore, and observe aseptic technique despite putting a pure culture of At. ferroox, you will end up with a mix. Many people say they are bioleaching with pure culture, but you would need to observe basic safeguards to be sure.

What exactly are you trying to do with your test work? As Gregg points out, adaptation is key.

There are some tailings dumps that contain about 0.7% Cu and we would like to heap leach it. It has been deposited over 20 years ago. Do you think these bacteria can be found on the surface of the tailings, as the tailings themselves contain high values of sulphur (16%) and Iron (40%). Mind you that the material is from a flotation plant.

Check out http://www.sciencedirect.com/science/article/pii/S0304386X06000880

Yes, tailings are ideal for bioprospecting. They're weathered so plenty of time for indigenous microorganisms to establish. However, heap leaching tailings is not going to be possible - the particle size will mean it is not possible (problems with solution flow, heap stability etc.). You would need to tank leach, but at 0.7% Cu this will not be economic. Is there anything else in there? Are there any other motivations for reprocessing the tailings (environmental protection etc.)?

Look at the Pinto Valley Magma Copper example (http://infohouse.p2ric.org/ref/15/14369.pdf) and the reprocessing of the tailings at the old Kasese copper mine (various references available).

At KCCL, they were old copper tailings that contained significant amounts of Co.

Sounds interesting in any case. As a microbiologist I would love to promote bioleaching for your tailings, but it will depend on the economics. 0.7% Cu is very low - heap leaching would be great but you'll struggle to make a heap.

Have you tried taking sample and do mineralogy of the ore? In what form are the oxide copper? How much is simply tarnished? Would other route of processing show possible economic significance?

I have done tests and all the copper is in the form of chalcopyrite and bornite. It will probably require the formation of granules before bio heap leaching.

Chalcopyrite will require higher temperatures for effective leaching - certainly above 50°C. However, I think you have enough pyrite to enable this. Are the heaps hot at depth? Either way, At. ferrooxidans will not do a decent job.

That said, your first problem is ensuring decent solution flow if you really do wish to pursue a heap leaching approach.

Are you sure agglomeration will work? I'm not an expert in heap construction, but I think you'll have problems. Perhaps someone else can chip in. The GeoCoat process agglomerates concentrates on carrier material to allow heap leaching of fine grain material, but it was reserved for gold recovery and never reached full-scale commercialisation.

Remember, with only 0.7% Cu, you have a very small margin - any additional processing upfront will erode that. You have hit upon the no-man's land of bioleaching - what does one do with material which is too low grade to tank leach, but too fine grain to heap leach?

BRGM are working on a low-duty bioreactor which should try and bridge the gap between heaps and tanks, but I'm not sure what their economic grade cut-off is, and they are not yet ready to roll out the technology.

Is Cu the only metal of interest? How many tonnes are you looking to re-process in this way? What is the PSD?

I have been working on improving the oxidation kinetics of sulfides for over 20 years. The most important aspect that I have identified for free drained biooxidation/bioleaching is the permeability of the ore layer. As the rate controlling step is the delivery of the air to the sulfide surface, the system must have adequate permeability to add enough air to achieve the required temperature of operation, which for your case is in the ranges of extreme thermophiles. I have been able to construct ore beds that have equal proportions of macropores and micropores which results in the most ideal bed hydrodynamics to then achieve the best practical oxidation rates. If your heaps have already been stacked, then you are pretty much limited by whatever the air addition rate that your system will accept. If you cannot pass enough air through your ore bed to achieve the required sulfide oxidation rate to achieve the required temperature of operation, it does not matter what varieties of bacteria that have been introduced in to the heap. The key is always in the construction if the ore bed. I have worked with Amado Guzman of HydroGeo-Sense to develop procedures to quantify the critical parameters of existing heaps and how to best enhance the existing system. If you are interested, we could certainly provide you with some additional information.

Thank you, the amount of gold and silver in the ore makes heap reconstruction economical. We might just need to build an agglomeration plant.

Zinc and copper is present at 2% and 0.7% respectively. Silver is about 5 g/t. We produce 500 mt of this material per day.

How much gold? I still don't think you can agglomerate tailings, but I could be wrong. You’d need to do a lot of stability testing (won't the aggregates simply fall apart at depth?) and solution flow and aeration. Jody is absolutely correct - any issues with any of these will prevent sufficient sulfide oxidation to achieve the required temperatures.

I had wondered about Jody's sand mining, but this process still requires larger p80.

Do you really produce 500 million tonnes per day?

The gold is 1g/t. We produce 500 metric tonnes. The material is from a milling and flotation circuit, so P80 is about 75 micron.