How heavy and light isotopes separate in magma

 In the crash-car derby between heavy and light isotopes vying for the coolest spots as magma turns to solid rock, weightier isotopes have an edge, research led by Case Western Reserve University shows.

This tiny detail may offer clues to how igneous rocks form.

As molten rock cools along a gradient, atoms want to move towards the cool end. This happens because hotter atoms move faster than cooler atoms and, therefore, hotter atoms move to the cool region faster than the cooler atoms move to the hot region.

Although all isotopes of the same element want to move towards the cool end, the big boys have more mass and, therefore, momentum, enabling them to keep moving on when they collide along the way.

"It's as if you have a crowded, sealed room of sumo wrestlers and geologists and a fire breaks out at one side of the room," said Daniel Lacks, chemical engineering professor and lead author of the paper. "All will try to move to the cooler side of the room, but the sumo wrestlers are able to push their way through and take up space on the cool side, leaving the geologists on the hot side of the room."

Lacks worked with former postdoctoral researcher Gaurav Goel and geology professor James A. Van Orman at Case Western Reserve; Charles J. Bopp IV and Craig C. Lundstrum, of University of Illinois, Urbana; and Charles E. Lesher of the University of California at Davis. They described their theory and confirming mathematics, computer modeling, and experiments in the current issue of Physical Review Letters.

Lacks, Van Orman and Lesher also published a short piece in the current issue of Nature, showing how their findings overturn an explanation based on quantum mechanics, published in that journal last year.

"The theoretical understanding of thermal isotope separation in gases was developed almost exactly 100 years ago by David Enskog, but there is as yet not a similar full understanding of this process in liquids," said Frank Richter, who is the Sewell Avery Distinguished Professor at the University of Chicago and a member of the National Academy of Sciences. He was not involved in the research. "This work by Lacks et al. is an important step towards remedying this situation."

This separation among isotopes of the same element is called fractionation.

Scientists have been able to see fractionation of heavy elements in igneous rocks only since the 1990s, Van Orman said. More sensitive mass spectrometers showed that instead of a homogenous distribution, the concentration ratio of heavy isotopes to light isotopes in some igneous rocks was up to 0.1 percent higher than in other rocks.

One way of producing this fractionation is by temperature.

To understand how this happens, the team of researchers created a series of samples made of molten magnesium silicate infused with elements of different mass, from oxygen on up to heavy uranium.

The samples, called silicate melts, were heated at one end in a standard lab furnace, creating temperature gradients in each. The melts were then allowed to cool and solidify.

The scientists then sliced the samples along gradient lines and dissolved the slices in acid. Analysis showed that no matter the element, the heavier isotopes slightly outnumbered the lighter at the cool end of the gradient.

Computer simulations of the atoms, using classical mechanics, agreed with the experimental results.

"The process depends on temperature differences and can be seen whether the temperature change across the sample is rapid or gradual," Lacks said.

Thermal diffusion through gases was one of the first methods used to separate isotopes, during the Manhattan Project. It turns out that isotope fractionation through silicate liquids is even more efficient than through gases.

"Fractionation can occur inside the Earth wherever a sustained temperature gradient exists," Van Orman said. "One place this might happen is at the margin of a magma chamber, where hot magma rests against cold rock. Another is nearly 1,800 miles inside the Earth, at the boundary of the liquid core and the silicate mantle."

The researchers are now adding pressure to the variables as they investigate further. This work was done at atmospheric pressure but where Earth's core and mantle meet, the pressure is nearly 1.4 million atmospheres.

Lacks and Van Orman are unsure whether high pressure will result in greater or lesser fractionation. They can see arguments in favor of either.

Story Source:

The above story is reprinted from materials provided by Case Western Reserve University.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Daniel Lacks, Gaurav Goel, Charles Bopp, James Van Orman, Charles Lesher, Craig Lundstrom. Isotope Fractionation by Thermal Diffusion in Silicate Melts. Physical Review Letters, 2012; 108 (6) DOI: 10.1103/PhysRevLett.108.065901

Novel device removes heavy metals from water

Ridding water of trace metals "is really hard to do," said Joseph Calo, professor emeritus of engineering who maintains an active laboratory at Brown. He noted the cost, inefficiency, and time needed for such efforts. "It's like trying to put the genie back in the bottle."

That may be changing. Calo and other engineers at Brown describe a novel method that collates trace heavy metals in water by increasing their concentration so that a proven metal-removal technique can take over. In a series of experiments, the engineers report the method, called the cyclic electrowinning/precipitation (CEP) system, removes up to 99 percent of copper, cadmium, and nickel, returning the contaminated water to federally accepted standards of cleanliness. The automated CEP system is scalable as well, Calo said, so it has viable commercial potential, especially in the environmental remediation and metal recovery fields. The system's mechanics and results are described in a paper published in the Chemical Engineering Journal.

A proven technique for removing heavy metals from water is through the reduction of heavy metal ions from an electrolyte. While the technique has various names, such as electrowinning, electrolytic removal/recovery or electroextraction, it all works the same way, by using an electrical current to transform positively charged metal ions (cations) into a stable, solid state where they can be easily separated from the water and removed. The main drawback to this technique is that there must be a high-enough concentration of metal cations in the water for it to be effective; if the cation concentration is too low — roughly less than 100 parts per million — the current efficiency becomes too low and the current acts on more than the heavy metal ions.

This video is not supported by your browser at this time.

Brown engineers have devised an automated system that combines chemical precipitation with electrolytic techniques in a cyclic fashion to remove mixtures of trace heavy metals from contaminated water. Credit: Joseph Calo lab, Brown University

Another way to remove metals is through simple chemistry. The technique involves using hydroxides and sulfides to precipitate the metal ions from the water, so they form solids. The solids, however, constitute a toxic sludge, and there is no good way to deal with it. Landfills generally won't take it, and letting it sit in settling ponds is toxic and environmentally unsound. "Nobody wants it, because it's a huge liability," Calo said.

The dilemma, then, is how to remove the metals efficiently without creating an unhealthy byproduct. Calo and his co-authors, postdoctoral researcher Pengpeng Grimshaw and George Hradil, who earned his doctorate at Brown and is now an adjunct professor, combined the two techniques to form a closed-loop system. "We said, 'Let's use the attractive features of both methods by combining them in a cyclic process,'" Calo said.

It took a few years to build and develop the system. In the paper, the authors describe how it works. The CEP system involves two main units, one to concentrate the cations and another to turn them into stable, solid-state metals and remove them. In the first stage, the metal-laden water is fed into a tank in which an acid (sulfuric acid) or base (sodium hydroxide) is added to change the water's pH, effectively separating the water molecules from the metal precipitate, which settles at the bottom. The "clear" water is siphoned off, and more contaminated water is brought in. The pH swing is applied again, first redissolving the precipitate and then reprecipitating all the metal, increasing the metal concentration each time. This process is repeated until the concentration of the metal cations in the solution has reached a point at which electrowinning can be efficiently employed.

When that point is reached, the solution is sent to a second device, called a spouted particulate electrode (SPE). This is where the electrowinning takes place, and the metal cations are chemically changed to stable metal solids so they can be easily removed. The engineers used an SPE developed by Hradil, a senior research engineer at Technic Inc., located in Cranston, R.I. The cleaner water is returned to the precipitation tank, where metal ions can be precipitated once again. Further cleaned, the supernatant water is sent to another reservoir, where additional processes may be employed to further lower the metal ion concentration levels. These processes can be repeated in an automated, cyclic fashion as many times as necessary to achieve the desired performance, such as to federal drinking water standards.

In experiments, the engineers tested the CEP system with cadmium, copper, and nickel, individually and with water containing all three metals. The results showed cadmium, copper, and nickel were lowered to 1.50, 0.23 and 0.37 parts per million (ppm), respectively — near or below maximum contaminant levels established by the Environmental Protection Agency. The sludge is continuously formed and redissolved within the system so that none is left as an environmental contaminant.

"This approach produces very large volume reductions from the original contaminated water by electrochemical reduction of the ions to zero-valent metal on the surfaces of the cathodic particles," the authors write. "For an initial 10 ppm ion concentration of the metals considered, the volume reduction is on the order of 106."

Calo said the approach can be used for other heavy metals, such as lead, mercury, and tin. The researchers are currently testing the system with samples contaminated with heavy metals and other substances, such as sediment, to confirm its operation.

Provided by Brown University (news : web)

Novel device removes heavy metals from water

 Engineers at Brown University have developed a system that cleanly and efficiently removes trace heavy metals from water. In experiments, the researchers showed the system reduced cadmium, copper, and nickel concentrations, returning contaminated water to near or below federally acceptable standards. The technique is scalable and has viable commercial applications, especially in the environmental remediation and metal recovery fields.

Results appear in the Chemical Engineering Journal.

An unfortunate consequence of many industrial and manufacturing practices, from textile factories to metalworking operations, is the release of heavy metals in waterways. Those metals can remain for decades, even centuries, in low but still dangerous concentrations.

Ridding water of trace metals "is really hard to do," said Joseph Calo, professor emeritus of engineering who maintains an active laboratory at Brown. He noted the cost, inefficiency, and time needed for such efforts. "It's like trying to put the genie back in the bottle."

That may be changing. Calo and other engineers at Brown describe a novel method that collates trace heavy metals in water by increasing their concentration so that a proven metal-removal technique can take over. In a series of experiments, the engineers report the method, called the cyclic electrowinning/precipitation (CEP) system, removes up to 99 percent of copper, cadmium, and nickel, returning the contaminated water to federally accepted standards of cleanliness. The automated CEP system is scalable as well, Calo said, so it has viable commercial potential, especially in the environmental remediation and metal recovery fields. The system's mechanics and results are described in a paper published in the Chemical Engineering Journal.

A proven technique for removing heavy metals from water is through the reduction of heavy metal ions from an electrolyte. While the technique has various names, such as electrowinning, electrolytic removal/recovery or electroextraction, it all works the same way, by using an electrical current to transform positively charged metal ions (cations) into a stable, solid state where they can be easily separated from the water and removed. The main drawback to this technique is that there must be a high-enough concentration of metal cations in the water for it to be effective; if the cation concentration is too low -- roughly less than 100 parts per million -- the current efficiency becomes too low and the current acts on more than the heavy metal ions.

Another way to remove metals is through simple chemistry. The technique involves using hydroxides and sulfides to precipitate the metal ions from the water, so they form solids. The solids, however, constitute a toxic sludge, and there is no good way to deal with it. Landfills generally won't take it, and letting it sit in settling ponds is toxic and environmentally unsound. "Nobody wants it, because it's a huge liability," Calo said.

The dilemma, then, is how to remove the metals efficiently without creating an unhealthy byproduct. Calo and his co-authors, postdoctoral researcher Pengpeng Grimshaw and George Hradil, who earned his doctorate at Brown and is now an adjunct professor, combined the two techniques to form a closed-loop system. "We said, 'Let's use the attractive features of both methods by combining them in a cyclic process,'" Calo said.

It took a few years to build and develop the system. In the paper, the authors describe how it works. The CEP system involves two main units, one to concentrate the cations and another to turn them into stable, solid-state metals and remove them. In the first stage, the metal-laden water is fed into a tank in which an acid (sulfuric acid) or base (sodium hydroxide) is added to change the water's pH, effectively separating the water molecules from the metal precipitate, which settles at the bottom. The "clear" water is siphoned off, and more contaminated water is brought in. The pH swing is applied again, first redissolving the precipitate and then reprecipitating all the metal, increasing the metal concentration each time. This process is repeated until the concentration of the metal cations in the solution has reached a point at which electrowinning can be efficiently employed.

When that point is reached, the solution is sent to a second device, called a spouted particulate electrode (SPE). This is where the electrowinning takes place, and the metal cations are chemically changed to stable metal solids so they can be easily removed. The engineers used an SPE developed by Hradil, a senior research engineer at Technic Inc., located in Cranston, R.I. The cleaner water is returned to the precipitation tank, where metal ions can be precipitated once again. Further cleaned, the supernatant water is sent to another reservoir, where additional processes may be employed to further lower the metal ion concentration levels. These processes can be repeated in an automated, cyclic fashion as many times as necessary to achieve the desired performance, such as to federal drinking water standards.

In experiments, the engineers tested the CEP system with cadmium, copper, and nickel, individually and with water containing all three metals. The results showed cadmium, copper, and nickel were lowered to 1.50, 0.23 and 0.37 parts per million (ppm), respectively -- near or below maximum contaminant levels established by the Environmental Protection Agency. The sludge is continuously formed and redissolved within the system so that none is left as an environmental contaminant.

"This approach produces very large volume reductions from the original contaminated water by electrochemical reduction of the ions to zero-valent metal on the surfaces of the cathodic particles," the authors write. "For an initial 10 ppm ion concentration of the metals considered, the volume reduction is on the order of 106."

Calo said the approach can be used for other heavy metals, such as lead, mercury, and tin. The researchers are currently testing the system with samples contaminated with heavy metals and other substances, such as sediment, to confirm its operation.

The research was funded by the National Institute of Environmental Health Sciences, a branch of the National Institutes of Health, through the Brown University Superfund Research Program.

Editors: Brown University has a fiber link television studio available for domestic and international live and taped interviews, and maintains an ISDN line for radio interviews. For more information, call (401) 863-2476.

Story Source:

The above story is reprinted from materials provided by Brown University.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Pengpeng Grimshaw, Joseph M. Calo, George Hradil. Cyclic electrowinning/precipitation (CEP) system for the removal of heavy metal mixtures from aqueous solutions. Chemical Engineering Journal, 2011; 175: 103 DOI: 10.1016/j.cej.2011.09.062

New sensor promises rapid detection of dangerous heavy metal levels in humans

 Work by University of Cincinnati researchers to create a sensor that provides fast feedback related to the presence and levels of heavy metals -- specifically manganese -- in humans is published in the August issue of the journal, Biomedical Microdevices.

Described in the article is the development of a low-cost, disposable lab-on-a-chip sensor that detects highly electronegative heavy metals more quickly than current technology generally available in health-care settings. It's envisioned that the new UC sensor technology will be used in point-of-care devices that provide needed feedback on heavy-metal levels within about ten minutes.

It's expected that the sensor will have potential for large-scale use in clinical, occupational and research settings, e.g., for nutrition testing in children.

The new sensor is environmentally friendly in that its working electrode is made of bismuth vs. the more typical mercury, and it's child friendly in that it requires only a droplet or two of blood for testing vs. the typical five-milliliter sample now required.

Explained one of the researchers, UC's Ian Papautsky, "The conventional methods for measuring manganese levels in blood currently requires about five milliliters of whole blood sent to a lab, with results back in 48 hours. For a clinician monitoring health effects by measuring these levels in a patient's blood -- where a small level of manganese is normal and necessary for metabolic functions -- you want an answer much more quickly about exposure levels, especially in a rural, high-risk area where access to a certified metals lab is limited. Our sensor will only require about two droplets of blood serum and will provide results in about ten minutes. It's portable and usable anywhere."

Papautsky, UC associate professor of electrical and computer engineering, is co-author of the Biomedical Devices-published research, "Lab-on-a-Chip Sensor for Detection of Highly Electronegative Heavy Metals by Anodic Stripping Voltammetry." Other co-authors are Erin Haynes, assistant professor of environmental engineering; William Heineman, distinguished research professor of chemistry; and just-graduated electrical and computer engineering doctoral student Preetha Jothimuthu, just-graduated chemistry doctoral student Robert Wilson, and biomedical engineering undergraduate research co-op student Josi Herren.

First Field Test of Sensor Expected in in Marietta, Ohio

One specific motivation for developing the sensor was an ongoing project by UC's Erin Haynes, who is studying air pollution and the health effects of manganese and lead in Marietta, Ohio. Manganese is emitted in that area because it is home to the only manganese refinery in the United States and Canada. Preliminary results from UC's Mid-Ohio Valley Air Pollution Study (M.A.P.S.) found elevated levels of manganese in Marietta residents when compared to those who live in other cities.

How the UC Sensor Works

The new UC sensor uses a technology called anodic stripping voltammetry that incorporates three electrodes: a working electrode, a reference electrode and an auxiliary electrode.

A critical challenge for such sensors is the detection of electronegative metals like manganese. Detection is difficult because hydrolysis, the splitting of a molecule into two parts by the addition of a water molecule, at the auxiliary electrode severely limits a sensor's ability to detect an electronegative metal.

To resolve this challenge, the UC team developed a thin-film bismuth working electrode vs. the conventional mercury or carbon electrode. The favorable performance of the bismuth working electrode combined with its environmentally friendly nature means the new sensor will be especially attractive in settings where a disposable lab-on-a-chip is wanted.

In addition, the UC team also optimized the sensor layout and working-electrode surface to further reduce the effects of hydrolysis and to boost the reliability and sensitivity in detecting heavy metals. The new sensor layout better allowed for its functioning, which consists of taking of a blood serum sample, stripping out the heavy metal and then measuring that heavy metal.

The end result is the first lab-on-a-chip able to consistently pinpoint levels of highly electronegative manganese in humans. The new sensor also exhibits high reliability over multiple days of use, with hours of continuous operation. With further developments, the chip may even be converted into a self-check mechanism, such as with glucose screening for diabetics.

Funding for this research has been provided by the National Institute of Environmental Health Sciences, the National Institute of Occupational Safety and Health Pilot Research Project Training Program and the University of Cincinnati.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by University of Cincinnati.

Journal Reference:

Preetha Jothimuthu, Robert A. Wilson, Josi Herren, Erin N. Haynes, William R. Heineman, Ian Papautsky. Lab-on-a-chip sensor for detection of highly electronegative heavy metals by anodic stripping voltammetry. Biomedical Microdevices, 2011; 13 (4): 695 DOI: 10.1007/s10544-011-9539-1

Heavy metal: Titanium implant safety under scrutiny

A new strategy to quantify the levels of titanium in the blood of patients fitted with titanium orthopaedic implants is presented in Analytical and Bioanalytical Chemistry, a Springer journal. Yoana Nuevo-Ordónez and colleagues of the Sanz-Medel research group from the University of Oviedo in Spain have developed a highly sensitive method to determine the levels of titanium in human blood, establishing a baseline for natural levels of titanium in untreated individuals as well as measuring levels in patients with surgical implants.

Titanium implants are routinely used for bone fractures as well as dental work. It has recently been shown that titanium-based implants both corrode and degrade, generating metallic debris. There is some concern over the increased concentrations of circulating metal-degradation products derived from these implants, and their potential harmful biological effects over a period of time, including hepatic injury and renal lesions. In order to assess the implications of these 'leaks', it is essential to accurately measure the basal, normal levels of titanium in the bloodstream, as well as quantify how much higher levels are in patients with implants.

Nuevo-Ordónez and team collected blood from 40 healthy individuals and 37 patients with titanium implants - 15 had tibia implants, eight had femur implants, and 14 had humerus implants (eight internal and six external fixation implants). They used their new method, based on isotope dilution analysis and mass spectrometry, or IDA-ICP-MS, to analyze the blood samples.

They found that control individuals had very low levels of titanium in the blood whereas titanium concentrations were significantly higher for all the patients with implants. The sensitivity of the method was such that the researchers were also able to show significant differences in titanium levels for different types of bone fixation devices. The more invasive implants shed more metallic debris into the blood than the external, superficial designs. The work also identified how the titanium from the implants is transported in the bloodstream and potentially distributed and accumulated.

The authors conclude: "The simplicity of the methodology based on isotope dilution analysis and the accuracy and precision of the obtained results should encourage the use of the proposed strategy on a routine basis."

More information: Nuevo-Ordónez Y, Montes-Bayón M, Blanco-Gonzalez E, Paz J, Dianez Raimundez J, Tejerina Lobo J, Pena M, Sanz-Medel A (2011). Titanium release in serum of patients with different bone fixation implants and its interaction with serum biomolecules at physiological levels. Analytical and Bioanalytical Chemistry; DOI 10.1007/s00216-011-5232-8

Provided by Springer

Heavy metals open path to high temperature nanomagnets

 How would you like to store all the films ever made on a device the size of an I-phone? Magnets made of just a few metallic atoms could make it possible to build radically smaller storage devices and have also recently been proposed as components for spintronics devices. There's just one obstacle. Nano-sized magnets have only been seen to work at temperatures a little above absolute zero.

Now a chemistry student at the University of Copenhagen has demonstrated that molecular magnets using the metals ruthenium and osmium retain their magnetic properties at higher temperatures. Most likely due to the larger spin-orbit coupling and more diffuse electron cloud present in these heavier elements. Some of his findings have recently been published in Chemistry -- A European Journal.

Iron not heavy enough

Kasper Steen Pedersen is studying for a Masters degree at the University of Copenhagen. Like many others in his chosen field of molecular magnetism he had been working with magnets based on 3d metal ions from iron. This seems an obvious choice when working with ordinary magnets which usually consist of about a trillion atoms. Single-molecule magnets are isolated molecules behaving like real magnets but they do not exhibit a three-dimensional order characteristic of a magnet.

Frozen magnets useless

Though interesting from a perspective of fundamental research, the need for very low temperatures make the miniscule magnets useless for any practical applications. So Pedersen wanted to see if another tack was possible. "When you take a look at the periodic table of the elements the solution seems obvious. Ruthenium and osmium are in the same group in the periodic table as iron, so it ought to be possible to create magnets out of these substances as well by using our knowledge about molecular magnets based on iron," says Pedersen.

Surprising properties for non-iron metals

As it turned out the chemical synthesis needed to build molecular magnets out of the substances was relatively simple. But the measured properties were surprising. "The chemical properties are the same for these metals as for iron. But the physical properties of the new magnets turned out to be very different from those made of iron. Basically, the magnetism arises from the electron spin but also from the motion of the electron around the nucleus. The latter contribution, which is very large for ruthenium, osmium and other heavy elements, has been largely ignored by the scientific community but we have now shown, experimentally, that is a very pronounced effect. And this is utterly new and exciting," explains Kasper Steen Pedersen.

Not quite a breakthrough

Using the unconventional metals for his magnets enabled Pedersen to raise the critical temperature only by a few Kelvin. However, the intriguing result that electron motion plays a large role for the magnetic properties paves the way for new synthetic approaches to molecular nanomagnets with unprecedented high critical temperatures.

"You'll not get me to call this a breakthrough. But it is a remarkable result for the field," concludes Kasper Steen Pedersen.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by University of Copenhagen.

Journal Reference:

Kasper S. Pedersen, Magnus Schau-Magnussen, Jesper Bendix, Hogni Weihe, Andrei V. Palii, Sophia I. Klokishner, Serghei Ostrovsky, Oleg S. Reu, Hannu Mutka, Philip L. W. Tregenna-Piggott. Enhancing the Blocking Temperature in Single-Molecule Magnets by Incorporating 3d-5d Exchange Interactions. Chemistry - A European Journal, 2010; 16 (45): 13458 DOI: 10.1002/chem.201001259

.