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!

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.

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.

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.

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.

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.

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.