1. Extraction of “clay fraction”.
Objective: Obtain <2µm size fraction rich in clay minerals.
Basis: Application of Stoke’s Law.
Restrictions: Based on settling of 2µm spherical quartz particle under specific laboratory conditions.
DO NOT MODIFY!

2. Preliminary
Determine whether sample will slake (disaggregate) in water.
Gently crush by impact to produce 1-2 mm particles.
Use pH control or selective dissolution (CBD, etc.) to remove cementing compounds.

3. Settling Add about 40 g of sample to 400 ml beaker.
Fill to top mark with water or 0.01wt% Na-phosphate solution.
Let stand overnight.
Stir vigorously.
Allow to settle for 3 hrs and 30 min.

4. Problem
Flocculation is evident by the formation of a particle-dense fluid layer after a short time.
Alleviate by diluting clay concentration, adjusting pH to about 9.0, or washing to remove interstitial salts.

5. Extraction
Remove material in top 5 cm of the suspension by slowly extracting with a syringe or siphon.
Begin extraction at the top and follow declining liquid to avoid inclusion of coarser particles from below.

6. Concentration Repeat extraction 2-3X and combine.
Pour into 50 ml tubes and weigh so that pairs are within 0.1 g of each other.
Centrifuge in IEC HT at 60% setting for 15 min.
Discard clear supernatant and scrape paste from tube.

7. Step-by-Step
1. Obtain a representative sample with 1-2 mm particle size.
2. Add 40 g to a marked, 400 ml beaker.
3. Add distilled water and soak overnight. Rinse to remove soluble salts.
4. Fill to upper mark and stir vigorously.
5. Allow to settle for 3 hrs. and 30 min. Check for evidence of flocculation.
6. Siphon or use syringe to remove suspended material between the 5 cm-apart marks.
7. Repeat steps 3-6 several times and combine suspensions.
8. Centrifuge to concentrate clay-sized material.