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Uranium from sea water, reinventing the wheel

Dear Reader,

I want to comment on a thing which I saw in a copy of “chemistry world” (The RSC journal) from about one year ago.

It is the reinvention of the wheel, now I suspect that few of you would be willing to fund or otherwise support a research program on a squat cylindrical device designed to be placed at the corners of a sledge thus allowing the sledge to be used when snow is absent. The modified sledge would then be useful for the convenient carriage of goods and persons when pulled by an animal or self propelled by an engine attached to the sledge.

The paper which I want to discuss is a review of a journal paper in question is entitled “Setting traps for uranium”, and deals with some uranium coordination chemistry. Given my past record in organic and inorganic chemistry it will not be a shock for some of my readers to know that I am glad when people do uranium coordination chemistry. However when people reinvent the wheel I am not quite so happy or impressed.

The review of the paper states that this coordination chemistry is a major step forward and is a major step forwards towards a process for the extraction of uranium from seawater. This is not just the view of the reviewer, the original paper authors also stated in their paper that their chemistry is a solution to the problem of how to extract uranium from sea water. I do not like to pour cold water (or cold brine) on things but I can not help but recall that a process for the extraction of uranium from seawater already exists.

Years ago John Pecket worked for the UK atomic energy authority (UKAEA) on a process for extracting uranium from seawater. This process used a titanium solid to absorb uranium from sea water. John told me that the process worked, the only problem was that the extraction of uranium from seawater was not as cheap as it was to buy it from a mining company. From the price difference which John told me about, it appeared to me that if the price of uranium went up then the seawater method could become very attractive.

I have looked at the structure of the uranium carboxylate which is reported by S.Beer, O.B.Berryman, D.Ajami and J.Rebek Junior in Chemical Science, 2010, 1, 43. They used three 2,6-diphenyl benzoate ligands which are arranged in a triangle around the equatorial plane of the uranium. The arrangement of the carboxylic acid groups around the uranium reminds me of the compound formed by the reaction of benzene-1,3,5-tricarboxylic acid and uranium(VI). Here again we have an equatorial hoop of oxygens from the organic ligand and a pair of axial oxide ligands.

2,6-diphenyl benzoic acid and benzene-1,3,5-tricarboxylic acid

Back in the days of beehive hair cuts and other “interesting fashions” R.V. Davies, J. Kennedy, R.W. McIlroy, R. Spence and K.M. Hill published a paper in a not so obscure journal (Nature) on page 1110 of volume 203 (12th Sept) in 1964. Here the paper describes an early attempt with solvent extraction (dibutyl hydrogen phosphate in either butex or kerosene) in passing before explaining how uranium is best harvested from sea water using solid absorbents. After the people of the UKAEA tried organic resins they moved onto inorganic absorbents. The best of the organic resins was an arsenic acid. As this contains arsenic and would be in contact with seawater I can not help but doubt the environmental acceptability of this method. Some of the other solids tested in the paper do also appear to be environmental menaces such as lead(II) sulphide and lead pyrophosphate, but back in the 1960s these were dropped (thankfully) for commercial reasons in favour of titanium hydroxide.

As I understand it the titanium hydroxide is a very insoluble solid, I suspect that in real life it is a partly hydrated titanium dioxide. After the titanium solid was loaded with uranium the uranium was then washed off of the solid using a sodium carbonate solution. This is because carbonate forms a very strong and anionic complex with uranium(VI). When I read the paper in full I saw that John W.A. Pecket was thanked and acknowledged towards the end of the text.

Now I am coming towards the end of my post, I would like to give out some free advice to anyone who is considering inventing a chemical process. This advice is to keep the chemistry required as cheap as possible, if the process can be made to work using a cheap detergent used in dog shampoo then use the dog shampoo chemical rather than insisting on using an expensive custom made detergent. On the other hand if the process gives poor results using “dog shampoo” but good results with your custom made detergent, then you need to make a choice. Does the improvement due to the expensive detergent give an improved outcome which warrants the use of the expensive reagent ?

The general rule is that lab scale chemistry gets done with expensive reagents in cheap (well cheapish) glassware while industrial scale chemistry uses cheap reagents in expensive reactors.


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