Renee Renn : Week #6 : Leaching

This week I am learning how to process the sediment samples that we have collected from our cruise.  On the ship, once we were through extracting the pore water from the centrifuge tubes the samples were then placed in a freezer.  While out to sea, one of the cores that we collected was cut up into twelve intervals instead of nine like the rest.  Once we got back to campus, this was the core that I began to process.  The first step is to take the samples to the core lab on the south side of campus.

Since 1960, the College of Earth, Ocean and Atmospheric Sciences (CEOAS) at Oregon State University (OSU) has maintained an active program in Marine Geology, and CEOAS continues to be one of the leading oceanographic institutions involved in exploration, research and the collection of marine samples. To preserve these materials for future research, Drs. Ted C. Moore and LaVerne Kulm in 1971 established the OSU Core Lab, now known as the OSU Marine Geology Repository.  At present, the OSU Marine Geology Repository archives 6,094 sediment cores totaling 15,952 m of core, 10,025 rock samples from 545 dredges, 2,200 deep-sea manganese nodules, 1,627 sediment trap samples, 693 plankton tow samples, and other materials, including lake sediments and lake drill cores. Sample requests are increasingly high with more than 27,000 samples distributed over the last three years and more than 175,000 since 1972.
(from:  http://core-repository.coas.oregonstate.edu/about-us/#history)

I enjoy going to the core lab because it is like walking into a marine sediment museum.  You are sure to find something fascinating to look at!  But alas, we take our samples there because they have freeze dryers that are available for use.  Since the samples are in centrifuge tubes, it takes about two days for them to be completely freeze dried.  After they are done, we then take them to the lab and break up the sediments and pour them into appropriately labelled bags.  The next step is to break up the sediment and then use the scale to weigh out approximately 2-3g of sample.  We keep the samples separated by interval, and we place the samples into falcon tubes that have previously been cleaned with nitric and Milli-q water.  Falcon tubes are tubes that can be used in a centrifuge, but they are nicer then the ones used on the cruise because they have measurement marks.  Milli-q water is water that goes through a purification processes involving successive steps of filtration and deionization to achieve a purity expediently characterized in terms of resistivity.

  

The next step for the samples is to complete a process called leaching.   In this process, we are removing soluble or other constituents from by the action of a percolating liquid.  There are two reagents that we use on the sediments to complete the leaching.  The first one is buffered acetic acid, and the second is hydroxylamine.

   The first thing I do in the morning to prepare for leaching is to make these reagents from a recipe that they have been using to leach all of the sediment samples from this proposal.

Next, I begin the process by using Milli-q (MQ) to wash the sediments and putting them in the centrifuge and repeating this step three times.  Then, we add the first reagent, buffered acetic acid.  Then we use the vortex to shake the samples for the next two hours.  The vortex is simply a machine that moves back and forth shaking the samples you have placed on it.

After they are done shaking, I then put them into the centrifuge, and after they are done spinning I very carefully pipet 12mL out of the tube and put it into a teflon vial.  This is the sample that will carry through to the next step, and I will learn how to continue processing them next week.

Next, I do the entire process over again, except on the second time I use hydroxylamine.  In this leaching process we are attempting to remove the ferromanganese coating that develops around each sediment particle.  This is also called the labile phase.  We are looking at this phase to find out how does the biology react, and also is there a way to balance the Rare Earth Elements, and the Neodymium (Nd) in the ocean.  The microbes make these coatings, and we extract the coatings by reducing with the hydroxylamine.

Overall, I have really enjoyed working on this part of the process.  It is relatively time consuming, and one must be very detailed oriented on the follow through.  Next week, I will be heading back into the clean room for the next step.