February 28, 2012

The Secrets Of Algae, Continued

Northwestern University

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Nuclear energy holds great promise if, among other things, its radioactive waste can be better disposed. Compared to solar panels, wind farms and biofuels, it produces a large amount of energy with low carbon dioxide emissions at a relatively small cost; the technology is mature. In addition, river and ocean habitats need not be disturbed as in the case with hydro power.

But nuclear plants also produce a lot of spent fuel and suffer from the latent risk of a meltdown. Human and design errors like the 1986 Chernobyl explosion and natural catastrophe like last year’s Fukushima Daiichi disaster have led some countries to shutdown old plants and cease building new ones.

The Chernobyl incident made a huge impression on a young Derk Joester, now the Morris E. Fine Junior Professor of Materials and Manufacturing at Northwestern University. Back then he was a teenager living in southern Germany, when the radioactive dust started raining down. Today his research includes finding materials that can help with a clean-up.

The difficulty lies in finding a cost-effective, efficient solution that separates radioactive elements from non-radioactive ones. But Joester is hopeful that last year’s discovery in his lab will lead to a novel solution in the near future.

One of the hardest selectivity problems to solve has been calcium strontium-90 versus calcium. Calcium is common in the environment, but has similar properties to strontium-90. During remediation efforts, scientists have to separate the strontium from calcium, whether the elements are in water, soil or elsewhere. Commercial ion-exchange materials are mostly non-organic and expensive to make. They also create a large amount of waste.

But he and Minna Krejci, a recently graduated PhD student in Joester’s lab and lead scientist on the research findings, along with Lydia Finney and Stefan Vogt of the Argonne National Laboratory, found that the pea-pod-shaped green algae Closterium moniliferum is highly selective and can be concentrated to a much smaller volume before and after the selection process.

“The algae right now aren’t better than the available materials but they have significant advantages,” explains Joester. “Once these get developed further you can take a test tube of them anywhere in the world and let them grow and divide without having to have to airlift in a large volume or weight of material. The use of living organisms that reproduce themselves can be advantage.

C. moniliferum shuttles strontium, barium and calcium through circular vacuoles located at the tips of its pod. The vacuoles can act like a liver and remove waste product from the organism. (Vacuoles have many functions this being one of them.) Specifically, they create strontium, barium sulfate crystals using a co-precipitation process.

“The presence of aqueous [barium] lowers the solubility product of the precipitate relative to pure [strontium sulfate] (which does not precipitate) and enables the sequestration of strontium in the barite crystals,” wrote the authors. By controlling the amount of sulfate in them, the vacuoles control how much strontium is sequestered.

Afterward, the algae can be easily filtered and burned in a controlled process, leaving only the crystals.

Argonne’s Vogt, who is also an adjunct professor at Northwestern, says, “The interest in the project is very fundamental. How the algae go about doing this, there may be other ways to exploit that.” He adds that the research institution partially funded Krejci’s PhD research in order to address a question that is relevant to both the institution and the US Department of Energy, and at the same time develop methods that would improve the techniques the scientists use such as interfaces. The research is mainly funded by the Initiative for Sustainability and Energy at Northwestern (ISEN).

Joester’s lab is now looking at how to make the algae more efficient and scale the process.

Original post available here.

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