The final Hf column, and my last few days in Lyon

The past week has been a bit of a whirlwind.  We learned that Janne Blichert-Toft (my supervisor here in Lyon) will have to undergo some pretty serious surgery, which will mean she will be out of the lab all of November.  So that means I am coming home early.  Despite this bad news, we managed to finish all my hafnium chemistry last week, as well as finish dissolving another sample (the kelyphitized garnet separate that will replace the "pure" garnet separate we lost early on after difficulty with the bombs).  So, one last look at our scheme:

So now, my Hf fraction is ready to go on the mass spectrometer!  The only other chemistry left to do is the separation of the REE.

To pick up where we left off from Column "1".  After Column "1", we're left with our sample stripped of everything else except for Hf, Zr, and Ti.  In Column "1", a dilute solution of HF and HCl was used so that Hf, Zr, and Ti "stuck" onto the resin (via complexation with the F- in HF.  Amazingly, the F- is so strong that this works even in such a dilute solution!).  While those elements were sticking on to the resin, all the other elements were stripped away.  Finally, to remove the stuck Hf, Zr, and Ti, we eluted with a stronger concentration of HCl (6 M).

So, at this point, all we have left to do is remove Ti, which is what Column "2" is for.  Column "2" is by far the most spectacular looking (IF everything in the previous 2 columns went perfectly!).  The reason is because the very first step of Column "2" is the addition of a small amount of H2O2 to the sample.  H2O2 complexes with the high field strength elements.  All the complexes are colorless, with the exception of the Ti complex - this one is bright orange-red.  We definitely had a highly nervous moment when we added the H2O2 to my samples (everyone in the lab watched) - because if nothing turned red, that means the Hf and Ti got lost somehow earlier.  Thankfully, all the samples did change color, meaning all the previous columns ran fine.  Below, here's the sample + H2O2 loaded onto the column.  You can see the bright red bands that represent Ti:

 
Below, here are two subsequent photos of the column being run.  So cool how you can watch the Ti (well, watch it very slowly... the narrowness of this column means it takes ~1 hour or more for each elution step):

So, that was it.  All hafnium chemistry done.  The final thing I did was then to evaporate the Hf separates.  So there's about 6 ml of solution at the final step, and after it was completely dried down, all that was left was literally a SPECK in the bottom of the beaker.  That speck is all the Hf and Zr contained in the sample (well, not exactly 100%, but we're hoping at least 90%).  That was definitely a cool moment - after three columns, all we have left is a few black specks.

One thing I have learned about column chemistry is that it can be tedious and take a long time.  Particularly when you re-use columns (which is a good thing, because resin is very expensive).  Re-using columns means they must be cleaned exceptionally well, which is often a whole-day affair, if not more.  I'm amazed by the amount of acid we have gone through in running columns and cleaning them.  With three people running Hf chemistry in the lab, we've probably gone through a liter of HF just in cleaning columns, and more for HCl.  And that's just in 3 weeks.  At one point, we ran out of acid and had to wait a few days for it to be distilled.  Then after distillation, it has to be titrated - which in itself can take an entire afternoon.  Then there is the continual washing and cleaning of beakers so that everyone has enough stuff to use.  It's definitely a lot of work to run and maintain an isotope geochemistry lab!

That was a bit of a stressful week, but the nice thing is now I have a couple days to see as much more of Lyon as possible.  Unfortunately the weather took a nasty turn here:  temperatures around 35 F, rainy, and with a biting wind.  Of course, that has to happen the last few days I am here, while all of October was wonderfully pleasant and anomalously warm.  I wonder if this sudden change to freezing weather has something to do with Hurricane Sandy moving along the Eastern US Seaboard.  The North Atlantic was unusually warm this year, with sea surface temperatures over 2 degrees above average.  These anomalously warm waters are probably what's feeding the hurricane and allowing it to intensify.  Western intensification at its most intense?  While the hurricane is sucking up all that warmth, the eastern side of the ocean basin (Europe) isn't getting any more of that warmth, and instead is now freezing (intensification of what would normally happen for cold eastern boundary currents).  Anyway, as I write this, I can hear the wind roaring outside and I even had to turn the heat on.

So the bad weather is keeping me indoors for now, and giving me some time to work on some job applications.  My brain is kind of dead after this crazy week, so I just decided to work on "easier" stuff like applications, and to relax a bit.  I feel like this whole month has been intense.  With the nature of my samples being so rare and precious (in the sense that it took 5 months to glean enough sample), every step in the lab had to be orchestrated perfectly.  And some parts were pretty dicey.  A few samples behaved really oddly, like being strangely viscous and forming a gel at the bottom of the bomb.  We then had to stick those back into the oven for several more days until a homogenous solution was obtained.  One sample even got stuck in the resin while we were running one of the columns, and lagged behind all the other samples (which meant waiting till late in the evening for it to go through, and hoping it would!).  So, I will be amazed if at the end, we actually get a meaningful number out of all this!  Even if we don't, I still walked away with an invaluable experience.

While being cooped up inside last night, I decided to finally do some drawing.  I used to draw a lot, and took several art classes in college, and have always drawn for fun.  I find it a stress reliever - to be able to concentrate on something that just requires hand-eye-brain coordination and nothing intellectual.  But I literally have not had time to draw anything serious in months, probably years.  Thankfully I still carry around these thin colored pens with me, just in the random event I feel like drawing something.  You can get these at any art supply store or even Staples and Officemax - they're Triplus fineliners, made by Staedtler.  Pretty inexpensive, and highly portable.  I drew two birds I've seen here in France, the blue tit and European robin:

And then I decided to do something more complicated, one of my favorite American birds, the American kestrel:

A walk in the Parc de la Tete d'Or

Yesterday, the weather was incredibly warm (mid 70's), and it was actually sunny and clear.  The weather in Lyon is really mercurial.  One day, it will be cold, rainy, and foggy, the next (or even in the latter part of the same day), all of that will blow away and the sun will come out.  Since it was Saturday, and nice out, I decided to go up to the Parc de la Tete d'Or.  I had been there one time before a couple weeks ago, but the weather was pretty bad so I didn't stay long.  This time I got to see more of the park, and some new birds too!  Those include little grebe, black-headed gull, greylag goose (I think that's what those were, but the bird book says I shouldn't be seeing them around here right now... so maybe they're something else, or domesticated), coal tit, blue tit, and my favorite one, the European robin.  I didn't bring my DSLR with me, so I just had binoculars and a small point & shoot camera.  Amazingly, this little robin hopped out right in front of me as I was approaching to examine something on a tree.  It paused long enough for me to actually get a somewhat decent photo (on a camera that has like 4x zoom).  It was cool to watch them, they're shy bird but they will occasionally hop out right into the open and sort of look at you quizzically. 

I was inspired to draw one.  For some reason, I serendipitously had a pen that was almost the exact orange of the robin!

Some more photos from the park:

This is the incredibly ornate front gate to the park. 

I thought this was a cool play on "Lyon".

Greylag goose? Also some lovely autumn colors.  Nice to experience a real fall again.

Reminds me of burr oak acorns, must be some Eurasian Quercus.

Sycamore tree bark.  Or maybe it's London plane tree - how does one tell the difference?

A magpie in a tree ablaze with autumn colors. 

Column chemistry

It's been a productive week in the lab.  On Monday, I observed the Nu Plasma 54 mass spectrometer in action, on Wednesday I ran the second round of Column "0", and today I ran Column "1".  Running Column "0" twice is necessary for samples >300 mg (most of my samples are around 600 mg), due to the limited capacity of the column.  Columns "1" and "2" don't have to be run twice, though, which is nice.  So here's the cartoon again, updated:

After running Column "0" twice, we have collected all the Hf separate (which goes on to Columns "1" and "2" to purify Hf) and the REE separate (which goes on to extraction chromatography to separate individual REE, to be done later, after Hf chemistry).  Of course, the "Hf separate" obviously doesn't just contain Hf (or else we would be done!), but contains Ti (which we need to eradicate via Column "2"), Zr (which we fortuitously don't need to worry about because there isn't a mass interference), and some other elements, such as W (which we do need to worry about, as W 180 interferes on Hf 180, even more important because our spike is Hf 180), and Ta (and probably Nb).  After running Column "1", all we will be left with is Hf, Zr, and Ti.  Column "2" will then take care of Ti, leaving us with just Hf and Zr (and I just told you Zr is OK to have together with Hf).

In contrast to Column "0", Column "1" is an anion-exchange column.  This means that anions (negatively charged ions) will adhere ("stick") onto the resin.  We first take up the sample in 1 ml of 0.5 M HF:0.5 M HCl, do the necessary heating, ultrasonicating, and centrifuging, then load the sample onto the resin.  Next, we elute with this same acid combination (0.5 M HF:0.5 M HCl).  Note this is a pretty dilute acid.  In such a dilute acid, Hf will complex with the F- ion in HF, forming an anion complex that will stick to our resin.  However, all the other elements will fortunately not complex with F-, and will thus be eluted.  So how do we get that Hf (and Zr and Ti) out?  We next elute with a stronger acid, 6 M HCl, which is strong enough to strip away the complexed Hf on the resin.  This is what we collect at the final step, and which will go on to the final column (Column "2") to remove Ti leaving behind just Hf and Zr.

Here's a picture of Column "1".  It's a smaller column that "0", but with a wider resin bed diameter, meaning that care must be taken while loading sample and acids in order to not disturb the resin.

 
Unfortunately no cool colored band representing an element within the resin in this one.

After we've collected our Hf, Zr, and Ti in clean teflon beakers, the next step is to add ~10 drops (1 drop ~ 30 ul) of perchloric acid, and then we evaporate on a hot plate, but NOT to complete dryness.  If everything gets evaporated, an insoluble precipitate will form and you'll have to re-dissolve it all over again using HF.  We don't want HF on the next column (Column "2"), because if we had HF on this column, it will just strip all the Hf away.  So we are faced with the delicate task of keeping Hf in solution, which means not forming a precipitate, before we can run the next column.  This is done by evaporating with perchloric and leaving a small drop behind in the beaker.  If a precipitate does form (or even if it doesn't and you want to pre-empt one from forming), add 2 drops of HF to keep Hf in solution.  Then when ready to run Column "2", evaporate a little to remove as much of that HF as possible.

Next week, I'll run Column "3".  Till then. 

Photos of Lyon

I can't believe I've been in Lyon for 3 weeks!  It's definitely flown by.  Some pictures of things around town:

Statues in Parc de la Tête d'Or at the northern end of the city.

Main square in Bellecour

One of the many bridges that cross the Rhone and Saone rivers and that you can walk across.

Chickens from the famous Bresse regions (which is famous for chickens) at Les Halles de Lyon, an indoor market.

Porcini mushrooms.  October is wild mushroom season!

Chrysanthemums.

This looks suspiciously like chard, right in the middle of the park!

Queen for a night in the most elaborate chair I've ever sat in at La Comptoir de la Bourse.

Yes, I went to Starbucks in France... :-P  I missed American-style brewed coffee and American-style huge mugs :-)

Running my first ion exchange column

So, we finally achieved complete dissolution and homogenization of my samples after 2 weeks in high-temperature, high-pressure bombs.  Now, the actual chemistry to separate the elements can begin.  Recall the scheme I showed earlier:

In this post, I'll describe a bit about running the first column (Column "0", named so because it was added into an older scheme which didn't originally deal with Mg-rich samples like pyroxenites and komatiites - my type of sample).  This column separates Hf along with the other HFSE (high field-strength elements: Zr, Ti, Nb, Ta) from the REE (rare earth elements, including Lu, Sm, and Nd).  Note that if your sample is not Mg-rich (defined here as >15% MgO), you wouldn't have to go through with this step and could simply add conc. HF to your attacked sample residue and heat in a closed beaker.  In this case, REE would be bound up into insoluble fluorides (which are centrifuged out), whereas Hf (and other HFSE) would remain in solution.  

First, a very introductory bit about ion-exchange chromatography.  Chromatography is a separation method that utilizes a stationary phase (the ion-exchange resin) and a mobile phase (an aqueous solution containing the sample).  Different ions are separated from each other based on their varying affinities for the solid phase, in this case an ion-exchange resin.  The strength of this affinity dictates the strength (normality) of the acid needed to elute that particular ion.  There are cation-exchange and anion-exchange resins; a cation exchange resin takes up cations from the sample solution and in turn releases an equal amount of resin cation into solution, vice versa for anion exchange.  A cation (or anion) exchange column must be calibrated (I didn't do that) before samples are run on it.  Calibrating involves collecting and analyzing (on an ICPMS) each successive eluate (what drips out of the column), so that one knows when an element of interest is eluted (washed through the column) during a particular analytical scheme.

Shown below are the steps involved in running Column "0".  For simplicity I omit some analytical details like eluent volume, resin bed volume, etc. The point is to show overall what goes on:

 An interesting thing about this column is that the resin bed contracts with increasing acid normality (we start with 1 M HCl and end with 6 M).  This has to do with the chemistry of the resin and different solvents.  A resin is a hydrocarbon skeleton which has functional groups added to it to give it particular ion exchange properties.  The functional group is composed of a fixed functional group and mobile counter ion, which reacts with the ions in the sample solution.  Water, because it is polar, is attracted to the charged functional groups in the resin.  Thus, when you make a resin from initially dry resin beads and mix with water, it is swelled up to the max because all the functional groups are hydrated.  Thus, as you sequentially elute stronger and stronger acids through the resin, the resin will shrink.  Because of this, if you were to use the resin again, you have to backwash it with water so that it can swell up to its original size.

Here is a photo of Step 3, when the sample is going through and we are collecting (in nice clean teflon beakers) Hf, Zr, and Ti.  The darker band in the middle of the resin is Fe from the sample going through.  The reason it appears "smeared" out throughout the column is because of turbulence within the column (due to the large diameter of this particular column).

  

Here is a photo of Step 4.  Here, we've finished collecting our elements of interest (Hf, Zr, Ti), and so we now elute to get rid of all the other elements except REE.  This includes Fe, which as you can see has made it all the way through the column (no more dark band).  It's now in the trash beaker below.  Fe in solution with HCl has a Gatorade-like yellow color.

 

Next time, I'll show you how Column "1" goes! :-)

What am I doing here? Isotope Geochemistry.

As most of you know, I'm currently in Lyon, working in Dr. Janne Blichert-Toft's isotope geochemistry lab.  I spent the past several months at Rice separating minerals (garnet and clinopyroxene) from 3 pyroxenite xenoliths from the Sierras.  These two minerals, combined with their respective whole-rocks, will be used to get Lu/Hf and Sm/Nd internal isochrons for the 3 pyroxenites.  The slopes of these isochrons will give the ages at which the pyroxenite samples record their final equilibration P-T conditions.  Garnet is an excellent mineral to use for the Lu/Hf method (and likewise clinopyroxene for Sm/Nd) because of this mineral's strong preference for the parent isotope (Lu for garnet).  Another advantage of Lu/Hf is the higher closure temperatures compared to Sm/Nd.   So, we have very good candidate samples to do this with, plus the results could potentially be very interesting geologically.  What age will these pyroxenites give?  Will it be an age coeval with formation of the Sierran batholith, or an age reflecting a tectonic event much later, such as the Laramide orogeny?  Either way, whatever we get will be interesting.  I just hope that we don't get the age of the volcanic eruption that brought up these xenoliths - but the high closure temperatures of Lu-Hf should prevent that.

Below is a sketch of an isochron.  For better explanation, see intro isotope geology textbooks, like Dickin or Faure.  This is just to illustrate some basic principles.  The dashed line represents "time zero", meaning when the whole rock and its constituent minerals (garnet, clinopyroxene) became homogenized and closed to diffusive exchange.  At this time, they will all have the same 176Hf/177Hf ratio, but different 176Lu/177Hf ratios due to the different affinities for Lu of the different minerals (garnet has a high Lu/Hf ratio because garnet prefers Lu over Hf).  Over time, these different initial Lu/Hf ratios will decay, rotating the dashed line to the solid black line, the isochron.  It is the slope of the solid black line that yields the age (for the math behind this, you can go to any intro isotope geology textbook or even Wikipedia).  The black points are what we measure in the lab, after going through complex chemistry procedures that separate the individual elements of interest. 

But, I'm nowhere yet close to getting the isochrons yet.  Before you can even get there, a lot of chemistry must be done, which is what I am doing now. Below is a flow-chart of the whole process (see Blichert-Toft, 2001, Geostandards Newsletter and Blichert-Toft et al., 1997, CMP for full details):

I'm only barely done with the very first step, sample attack and dissolution.  Of course, this is the most important step because it dictates everything that will go on next.  We first weigh the samples and add mixed spikes to them (a Sm-Nd spike and a Lu-Hf spike).  Usually, you would add a separate spike for each element, but a mixed-spike makes things easier because you could make a mistake weighing your separate spikes, thus irrevocably screwing up your parent/daughter ratios.  What is a spike and why do we need to add it?  First, the spike is a solution of an artificially enriched isotope of the element(s) of interest, which you know exactly the concentration of (this requires carefully making and calibrating of the spike).  Why do we need it?  When you make isotopic measurements in which the parent nuclide is of interest, as in my case (or any case when you want to get an age from an isochron), you need to measure the parent/daughter ratio very precisely.  However, when you go and measure your samples on the mass spectrometer, you usually do not know exactly how much of your total sample actually makes it all the way through the complex machinery of the instrument and to the detector.  Several things can occur, such as unequal transmission of the parent and daughter isotopes because they have different ionization potentials.  So, because you added a spike of which you know the exact amount of and composition of, when you go and measure your spiked samples on the mass spectrometer, you know that the ratio of spike sampled to spike detected will give you the detection efficiency.  The ratio of spike to natural isotope gives the isotope's concentration. 

Before any chemical separation of the elements can proceed, the sample and spike must both be completely homogenized.  This can take weeks especially for refractory minerals like garnet or zircon.  To ensure complete homogenization, we use high-pressure, steel-jacketed Teflon bombs.  HF (the only acid readily capable of dissolving silicates) is added to the bombs, and then they are heated at 156 C for a week.  A spring inside the bomb ensures the samples are kept under high pressure.  Then after a week they are taken out, and we add perchloric acid (HClO4) to them. HClO4 is added to help expel any remaining HF (HClO4 has a higher boiling point than HF) from the digestion, thus decreasing the probability of insoluble fluorides from forming.  At this point, the sample should be completely attacked.  If it is, we can add 6N HCl to the bombs, close them up, and put them back in the oven for another several days.  After this last step, the sample and spike should be fully homogenized and the separation chemistry can begin.

Below is a sketch of how the bombs work:

Next time, I'll explain a bit about the column chemistry and element separation.  Toodles. 


 

It has been a while...

Oh blog, I've neglected you for months!  During all the time I wasn't writing down what I was doing/thinking in here, I was actually doing/thinking a lot of stuff (and wanting to write it down, but never got around to it).  To recap what has transpired since June 15, the date of my last post:

• I analyzed the rest of my Sierran peridotite data set for trace elements by solution ICP-MS.
• I picked 3 Sierran pyroxenites for garnet and clinopyroxene (Gosh, that took forever!).  And I'm now in Lyon doing all the complex chemistry involved to measure them for Lu, Hf, Sm, and Nd isotopes.  I promise, my next post will be soon, and it will be ALL about what I am doing in Lyon.
• I went to Papua New Guinea for 10 days:  4 days of hardcore birding, which I can't even begin to describe in a blog post (and I haven't even finished going through the 900 photos I took in PNG yet... but suffice it to say, we saw some mind-blowing birds, and lots of them!); followed by 6 days of pre-IGC field trip where we glimpsed some ophiolites (and really, it was just glimpsing, doing actual geology that involves bare-faced rock was pretty difficult in the intensely vegetated country, not to mention the substantial amount of time just getting around the country and logistics).
• Then I went to Australia for the 34^th IGC (International Geology Conference), where I presented a paper on my cpx-enriched Sierran peridotites.  I think this refertilization story has finally progressed to a point where it’s interesting enough to write up into a short paper.  While in Australia, I also got to visit my uncle and cousins, who were gracious enough to take me and labmate Monica around to see some of the sights in and around Brisbane for a couple days after IGC.  These included:  Birding in Lamington National Park (where the birds were literally coming up to us!), cuddling koalas at Lone Pine Koala Sanctuary, and touring the city and enjoying its nascent and awesome café scene.
• Next, I returned to the US, which I was definitely missing after nearly 3 weeks in the Southern Hemisphere.  Then Ben and I went for a visit to my home on Long Island.  It was Ben’s first time in NY and first time in NYC, which I think he enjoyed, if not being slightly overwhelmed by the hyperactivity.  Nevertheless, it was nice to go to the beach and actually jump into cold, refreshing, Atlantic seawater (compared to the mud in Galveston), eat cheap lobster that we cooked at home (the best way!), hang out with my sister in Manhattan and do all those touristy things (like climb to the observation deck of the Empire State Building, only 10 hours before that shooting by the disgruntled employee happened), and of course eat the best pizza and bagels (because NYC/LI tapwater is delicious tasting, it makes dough taste extra good). 
• After a week back home, I was back at Rice, picking the last of my minerals with the help of a very capable undergrad.  September was a busy month, and now I’m in France! 

 Now Fall is here.  The Harvest Moon and Mid-Autumn Festival was just last weekend, and I definitely missed out on eating some mooncakes this year, but I told my Mom to freeze me some for when I go home for Christmas.  Leaves are not changing here in Lyon yet, but I think they will soon.  Ben has been keeping me abreast of the subtle seasonal changes going on back in Houston.  The first cold front is always welcomed, along with all the migrating birds it brings.  Warblers are still passing through campus I hear, but the sparrows are beginning to arrive too.  I haven't had much time yet to try and go birding here in Lyon, but I did go to the Parc de la Tete d'Or (Park of the Golden Head) which is the largest urban park in France, last Sunday.  Unfortunately, it was a cloudy, rainy and cold day, and I didn't see much.  The park was also pretty crowded with joggers, so I'm not sure if that's the best place to see birds.  I did see a blue tit, which was really cool-looking and they sound like chickadees, a magpie, blackbird, and whatever gallinule is here in Europe.  But I do miss early morning birding on Rice campus.  I'm living in a much more urban city compared to Houston, and it's taking some getting used to!  

Here is a spider with a neat little backstory:

So every day for most of September I've been seeing this spider on top of a hedge next to the tennis courts on Hazard Street, a few blocks north of Rice.  Why is this spider so interesting?  Well, for one thing, I had dreamed of seeing one since I saw a painting of one in this little mini book of Audubon's bird paintings that I've had since I was a kid (I didn't birdwatch or know much about birds throughout my childhood, but I did have this book and would look at it all the time, so it's kind of funny now that I am more seriously into birds):

 

 It's hard to see the tiny spider in the painting, but when I first saw it, I had no idea what it was.  It looked really weird, like an alien, or a spaceman in a suit!  Then I showed Ben and he reassured me that it was indeed a real thing - a type of spiny orb-weaver.  I've found other interesting tiny things in some of the other Audubon paintings - like an assassin bug and a Quaker.  There is so much detail in some of the paintings that maybe the more I look at them, the more I'll find something I never found before.  Anyway, it's cool when you see something in a book that you never saw before in real life, and then one day, you do see it in real life.  I've definitely experienced that with things I've seen only in geology textbooks too.

And finally, here's just one photo of something really neat in Lyon - a huge sculpture of a bouquet of flowers in the middle of the city:

    
Next time - I'll blog a more science-oriented blog about what I'm doing here in Lyon.