Finding minerals can be a real needle in a haystack effort, even when prospecting in a well-established area. And once you’ve located a likely area and taken the samples, you still need to test it to determine whether the deposit is commercially viable or not.
For years the area of mineral testing has been dominated by large commercial labs that closely guard their techniques and charge large amounts of money to run the tests. This could all be set to change, however, as two researchers – Dr Ryan Noble of Australia’s CSIRO Cooperative Research Centre for Landscape Environment and Mineral Exploration (CRC LEME) and Dr Cliff Stanley of Department of Earth and Environmental Science, Acadia University, Canada – have discovered that with a tipple of wine (or soft drink for that matter) the same results can ultimately be achieved.
Noble admits that, at least initially, the experiment was ‘a bit tongue in cheek’.
In the extraction industry, there’re about ten or so companies and groups that have these proprietary extraction techniques they sell for A$50 to A$100 a sample. We wanted to show that you could use some pretty basic and commonly available products, such as wine or Coca-Cola, and get equivalent results to extractions that some of these companies keep very secret – and charge a lot of money for,” Noble says.
Wine and Coke contain some organic acids similar to those used in traditional testing techniques – nitric or hydrochloric acids are usually used to extract metals from soils but citric and phosphoric acid can play a similar role.
A testing company, Genalysis, allowed Noble and Stanley to compare one of its techniques by submitting the samples blind and comparing the two results.
“Genalysis’s techniques worked well but no better than with the wine,” says Noble.
“And then there’s the cost difference. We did the extraction – not including our time – for about three to four dollars a sample and got pretty good contrasts in soils containing positively charged minerals such as copper, zinc, nickel, lead and silver.”
Noble and Stanley took the soil samples and put a couple of grams of each sample into a test tube followed by the soft drink or wine. Wine goes into the test tube straight out of the bottle – the soft drink is let stand to degas a little –and the tubes are shaken for about two hours. The test tubes containing the solution are then put into a centrifuge and spun down, the liquid is taken off the top and analysed by routine methods such as inductively coupled plasma with optical emissions spectroscopy (ICP OES), ICP mass spectroscopy (ICPMS) and atomic absorption spectroscopy (AAS).
“The wine and Coke contain a whole lot of organic acids such as citric acid and phosphoric acid,” explains Noble.
“They’re basically weak organic acids of the carboxylic group and they exchange a hydrogen ion with the metal cation. So if there’s a Cu²+ bound to the outside of the soil particle, the solution interacts with that soil, the hydrogen comes off the compound within the solution and switches places with the copper. The copper is then in solution and it’s quite soluble and easily analysed.
“By contrast, a lot of traditional techniques use some sort of weak or not so weak acid such as nitric or hydrochloric acid to extract the metals of the soils. Some of the less-aggressive techniques are things like a weak hydrogen peroxide solution and then there is quite a few proprietary techniques commercial laboratories use, which are a closely guarded secret. This was part of the reason why we wanted to test some of these more common products to see how they compared to the secret commercial techniques.”
While Noble and Stanley are pleased the experiment has confirmed their hunch that wine or soft drink would work every bit as well as the ‘secret’ techniques of the commercial laboratories, Noble doesn’t see the methodology taking off any time soon.
“The idea was just to show there’s potential out there to use other techniques than what the commercial groups are touting. I think it’s just as valid as doing any other extraction that they’ll do on five, 100, or 1,000 samples but I don’t really expect this to be taken up on a big scale.”
Using wine or soft drink does have disadvantages.
“There are potentially batch variations, so you’d have to have a lot of the one wine to compare across a large number of samples,” says Noble.
“If you’re just doing a couple of hundred samples you could buy a few bottles of the same batch but if you were trying to do it on a commercial scale it would be more difficult that way because you’d need a large enough quantity to give you consistency across the whole
This is because wine does contain metals in trace amounts and people doing the test need to be aware of what the background levels are.
“It’s not difficult to account for but you’d have to account for it on a batch basis and you wouldn’t be able to compare perfectly across batches,” says Noble.
“But the way the commercial companies are doing their extractions they’re not telling you anything about what they’re doing so there’s no way you can compare their results to anything anyway.”
But while there may be variations between batches of wines, Noble and Stanley don’t believe there would be much more than subtle differences between varietals.
“The main active ingredients, the organic acids, are consistent across all wines so you could use white if you wanted to. We used red – a Spanish Tempranillo – because we presented our research at a conference in Spain so we picked a local wine to give a local flavour to the presentation.”