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If the samples have already been dried the treatments will still work but using fresh, wet samples is easier. Below are outlined various treatments and methods we do on board the JOIDES Resolution.

Health, Safety and Environment

Clay separation requires the use of hazardous chemical reagents. Please read carefully the following before starting.

Reagents necessary for Clay Separation

• Ethylene glycol or ethanediol: used for clay glycolation
• 2 M HCl 16.4% v/v: used for carbonate dissolution
• Glacial acetic acid, 10% v/v solution: used for carbonate dissolution
• Distilled (dionized reagent) water (DI)
• 1% w/v Borax solution

Chemical Hazards

Ethylene Glycol (Ethanediol)

Ethylene glycol is toxic and should not be ingested. It is also harmful if inhaled or absorbed through the skin and eyes. Proper personal protective equipment (PPE) should be used when handling this compound. Ethylene glycol is kept in a safety cabinet in the Thin Section Lab (Figure 1).

Figure 1. Safety cabinet in the Thin Section Lab

Hydrochloric Acid, Concentrated, or 2 M for Carbonate Dissolution

Concentrated hydrochloric acid HCl (~12M) is highly dangerous. It can cause severe tissue damage on contact, is highly toxic, and the fumes present similar risks of poisoning and chemical burns. When mixed with water, hydrochloric acid liberates large quantities of heat, so appropriate care should be used when diluting this compound. Note that the 2M hydrochloric acid used in the carbonate dissolution procedure is still dangerous and should be treated with the appropriate care.

Acetic Acid, Glacial, or 10% for Carbonate Dissolution

Glacial acetic acid (~100%) is highly dangerous. It can cause severe tissue damage on contact. When mixed with water, glacial acetic acid liberates a lot of heat, so appropriate care should be used when diluting this compound. When diluted to ~10% concentration, it is very similar to white vinegar, so while it is still acidic and could cause tissue damage, it is not as hazardous. Acetic acid (10%) is kept with Borax below the sink in the ICP preparation part of the Thin Section Lab (Figure 2).

Image Modified

Figure 2. Acetic acid (10%) stored in the Thin Section Lab

Borax

This chemical largely consists of potassium sulfate and is not expected to be a health hazard. It is used as a laundry booster (Figure 3). It is stored in the Thin Section Lab with the Acetic acid (Figure 2).

Figure 3. Borax

Disposal of acid solution

Technique for clay separation requires the use of acetic acid. To dispose acid solution properly and environment-friendly, use the black sink in the Chemistry Lab or in the Thin Section Lab (Figure XX). These sinks are directly connected to a specific container in the ship dedicated to acid treatment. DO NOT USE OTHER SINKS !!! Use flowing water to dilute.

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Figure 4. Black sink to dispose acid solution

Clay Separation Procedure

XRD analyses on clay separation requires several preparation steps:

1. Removing carbonates (to better identify the clay minerals)
2. Suspending material particles (to separate the < 2 μm clay size fraction from the rest of the particles)
3. Heating samples (to identify the presence of kaolinite and chlorite)

Removing Carbonates before Clay Separation

It may be necessary to dissolve the carbonates in the sediment to better identify the clay minerals. The goal is to remove as much carbonate as possible to isolate the material contained within the carbonate for analysis. There are two standard methods for removing carbonate aboard the JOIDES Resolution: (i) hydrochloric acid (HCl) and (ii) acetic acid. Ask the Science party which method they prefer. If there is no preference, use acetic acid.

Acetic Acid Treatment

This is the recommended treatment for carbonate removal. The process is slightly more involved than the HCl procedure, but far less damage is done to the mineral structure. The following steps are from Kitty Milliken (UT-Austin) and are shown in Figures 5 to 8.

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Figure 8. Disposal of acid solution and DI washing cycle.

Hydrochloric Acid Treatment

HCl is the simplest method for removing carbonate from sediment but does have severe drawbacks. Strong acids damage the mineral structure, especially within trioctahedral minerals. Before proceeding, be aware that this treatment may affect clay crystallinity.

1. Place undried sample on a glass slide or quartz disk.
2. Using a Pasteur pipette, slowly drop 2M HCl on the sample until bubbling/fizzing stops.
3. Desiccate and transfer sample to sample holder for analysis.

Separating Clay

There are various methods for separating clay from coarser material involving a series of centrifuging or gravity settling. Those listed below are methods used on-board. If you removed carbonates first, start here after your water washes are finished and the water has been decanted. If you did not remove carbonates, take approximately 5 mL of sample material and put into a centrifuge tube.

Suspending Material

Get the sonic dismembrator case and probe power source (either in the Thin Section Lab or Chemistry Lab). Using the dismembrator is a very effective way to fully and randomly suspend the material. Suspended material can then separate out according to size, with the largest grain size on the bottom and the very small clay size fraction on top.

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Figure 10. Dismembrator set up and Probe with power source. Dismembrator power source control Panel. (A) On/Off switch (B) Start button (C) Set button (D) Mode button (E) Start button

Standard IODP Clay Separation Method: Not for Semi-quantitative Analysis

1. In a centrifuge tube, mix a small amount of bulk sample (~5 mL; fresh, not dried) with 1% Borax solution. Use the shaker (in the cold room of the Chemistry Lab) or the dismembrator, if necessary to suspend particles.
2. Centrifuge the Borax solution/sample mix at 750 rpm for 4 minutes to remove the >2 µm size fraction
3. Decant the supernatant liquid (containing suspended clay) into a new centrifuge tube 
4. Centrifuge the <2 µm fraction for 15 mins at 1500 rpm to remove the Borax solution
5. Decant the Borax solution and add 25 mL of nanopure (DI) water to wash the clay
6. Repeat Steps 4 and 5 as necessary to remove the Borax (USGS recommends repeating up to 4-5 times)

Alternative method from Exp. 379

1. Add 25 mL of 1% Borax solution to the clay plug 
2. Dismembrate the sample (machine is auto set on time), to remove the >2 µm clay fraction
3. Centrifuge for 4 mins at 750 rpm, decant the supernatant liquid into a separate centrifuge tube (you should end up with a ~full centrifuge tube of suspended clay)
4. Repeat steps 1–3 on the remaining >2 µm fraction
5. Centrifuge the <2 µm fraction for 15 mins at 1500 rpm to remove the Borax solution 
6. Decant and add 25 mL of nanopure water
7. Centrifuge for 60 mins at 3000 rpm, the liquid is decanted before loading onto a zero background silica disk.

Preparing the Mount

Clay mounts are different either you are using the D4 Bruker or the Aeris for the analyses.

Clay Mount to use with the D4 Bruker

Clay mounts are put onto a zero-background silicon disk that fits into a 2 mm steel sample holder (Figure 11). Only put the disks into sample holders that have a hole drilled in the bottom (Figure 11). The hole allows the disks to be taken out, otherwise they are stuck inside the holder.

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Figure 11. Steel sample holder with quartz insert disk and zero-background silicon disk. Clay Mount for the D4 Bruker.

Clay Mount to use with the PANalytical Aeris

Insert a zero-background silicon disk in a sample holder in a 'back loading' way (Figure 12, Step #1). Add on top of it an Aluminum spacer disk (Figure 12, Step #2) and clip the whole thing (Figure 12, Step #3). Flip the sample holder (Figure 12, Step #4).

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Figure 12. Clay Mount with Aeris Sample Holders.

Putting Material on Mounts

1. Remove the <2 µm size fraction by collecting the uppermost 1 cm of solution with an eye dropper (Figure 13). It helps to add a little isopropanol. If necessary, resuspend flocculated clay particles using the dismembrator and add more Borax solution.
2. If material is still very suspended, try centrifuging the samples for 4 minutes at 750 rpm. In this instance, the >2 µm size fraction will be the only fraction suspended in the liquid and all the larger grains will be packed in the bottom. Take the suspended material with an eyedropper and put it on the quartz disk.
3. Make an oriented clay mount by placing 2–3 drops (enough to cover the disk) of clay suspension directly onto the silicon disk (Figure 11, Step #3 and Figure 12, Step #5). If the material is not spreading evenly, add a drop or two of 70% isopropanol and spread the material around with a small glass rod (Figure 11, Step #4 and Figure 12, Step #6). Once spread, let the sample dry in the desiccator (Figure 14A).

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Figure 14. A. Dessicator and oven for glycolation. B. Dried sample preparation after dessication.

Additional Clay Treatments before Scanning

Treating with Ethylene Glycol

The following techniques are modified from the U.S. Geological Survey Open-File Report 01-041, A Laboratory Manual for X-Ray Powder Diffraction (hard copy available in the X-Ray Lab Library). Ethylene glycol can be used to expand swelling clays (e.g., smectites, montmorillonite, nontronite, and beidellite), some mixed-layer clays, and vermiculite as an aid to mineral identification. There are two ethylene glycol treatment methods:

1. Vapor Treatment (recommended)
2. Quick Treatment (aggressive)

 Vapor Treatment

The advantage of the vapor treatment is less disturbance of the sample and less amorphous scattering of X-rays by excess liquid than in the Quick method (below).

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Before placing samples in the XRDs, wipe all sides of the sample holder with a Kim Wipe to remove any ethylene glycol. Ethylene glycol is sticky and can damage the grabber arm and sample spinner.

Quick Treatment

1. Using a glass rod or eye dropper, apply a drop of ethylene glycol directly to the surface of the sample mount.
2. Samples are ready to be analyzed as soon as the glycol is uniformly absorbed on the sample mount. Excess ethylene glycol may be gently mopped up with a Kim Wipe.

Heating Samples

Several clays have intensity peaks at very similar angles making it difficult to distinguish one clay from another. Heating clays is a way to work around this. We can run a sample through one of our XRDs, heat the sample in the muffle furnace, run again, and then compare the scans. For example, kaolinite and chlorite have overlapping peaks, making it hard to differentiate one from another. Heat morphs kaolinite, and it develops an amorphous signal, essentially removing its presence in the scan and leaving only the chlorite signal. The amount of kaolinite and chlorite can be determined by comparing these scans.

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Figure 16. A. Muffle furnace in the Chemistry Lab. B. Clay Mount in the muffle furnace. Note that only the Si disk of Aeris sample holder is put in the furnace. C. After heating.

Clay Separation Method for removal of Chlorite (not recommended onboard the JR)

For the double peaks of Kaolinite and Chlorite, heating the sample only suggest that one of the minerals is present, it will not give final and complete results for a sample that contains both Kaolinite and Chlorite. In order to determine which mineral is present, an additional treatment is necessary.

1. Take the <2 µm clay fraction, this should be rinsed and free of any treatments.
2. In centrifuge tube, add ~20 mL of 1N HCl.
3. Vortex the sample to completely dislodge all material before pouring sample into a 100 mL beaker, add stir bar once sample is in place.
4. Set hotplate to 300°C (boiling point of HCl is ~101ºC, but in order to maintain a continuous boil the hotplate needs to be much hotter)
5. Set the stir RPM below 100, this is only to keep the material suspended within the HCl
6. Start time once the samples have come to a complete boil, leave for 2 hours — add more HCl as necessary (DO NOT let the sample go dry and burn)
7. Once the sample has boiled for 2 hours, turn off the hot plate and allow sample to return to room temperature before pouring beaker contents back into a clean centrifuge tube. Rinse beaker with DI water to collect all material
8. Centrifuge down for 15 mins at 1500 rpm, decant acid and rinse with 25 mL nanopure (DI) water. Repeat the washing cycle 3 times.
9. After samples has been washed 3 times and is free of HCl, centrifuge for 60 mins at 3000 rpm

Troubleshooting

If the dismembrator does not start the program after pressing the button "Start", i.e., if the screen still displays 'P  0' (Power=0) and not 'rdy' (Ready), press the "Reset" button, then press "Test" and finally "Start". The dismembrator should clear the error and starts the program normally. Power on the display screen should be 'P  11' when a sample is vibrating. The cause of this error is unknown and happens when the dismembrator is turn on.

References

Jackson, M.L., 1956. Soil Chemical- Analysis Advanced Course by Hsueh-Wen Yeh, Hawaii Institute of Geophysics, 1980.
Moore, D.M., and Reynolds, R.C., Jr., 1989. X-ray Diffraction and the Identification and Analysis of Clay Minerals: New York (Oxford University Press).

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