Elution experiments

Overhead shaker

Overhead shaker

Image: Sarah Hupfer

Elution tests can be used to determine the maximum release potential of metals from soils and sediments, e.g. according to DIN 38 414 - S4. Extraction solutions can be analysed for elemental content using  ICP-MS and ICP-OES.

Equipment

For extraction according to Zeien and Brümmer, overhead shakers of the type Rotoshake RS12 (Gerhardt, Königswinter, Germany) and ELU (Edmund Bühler, Hechingen, Germany), a centrifuge of the type Multifuge 3L (Heraeus, Langenselbold, Germany) for tubes with a maximum volume of 50 ml, and a vacuum filtration apparatus (home-made, Lippmann Labortechnik, Dresden, Germany) are available.

Sample preparation

For elution tests, samples must be air dried and sieved to < 2 mm (minimum sample mass 5.0 g). The use of replicates is recommended.

Execution

Determination of elutriability with water according to DIN 38 414 - S4pdf, 20 kb · de(as of April 2017)

Working materials

  • Air-dried substrate samples (fine soil <2mm)
  • Balance (accuracy min. 0.01 g)
  • HDPE bottles 1 litre
  • Ultrapure water (ThermoScientific ‘GenPure UV-TOC’)
  • Centrifuge (Multifuge 3L, Heraeus) including 50ml centrifuge tubes (Greiner, PP material)
  • Overhead shaker (Rotoshake RS12, Gerhardt)
  • Concentrated HNO3 (65%) (subboiled or suprapure)
  • Disposable syringes (e.g. 20 ml)
  • Membrane filter (syringe filter) 0.45 µm (Sartorius, Minisart, cellulose acetate, no. 16555Q)
  • pH/el. Conductivity meters (pH gel electrode instead of electrode with KCl filling to avoid KCl contamination) including calibration solutions (WTW)
  • 15 ml tubes (Greiner, PP material)

 

Procedure

(As an alternative to the specified quantity of 90 g water and 900 g substrate, it is also possible to work with a correspondingly lower sample weight with the same solids-to-liquid ratio in order to minimise the time required for several runs due to the load capacity limit of the shaker when processing several samples at the same time)

  1. Weigh out 90 g of the air-dried substrate samples twice to the nearest 0.01 g and fill them into a 1-litre HDPE bottle.
  2. Fill the HDPE bottle with 900 ml ultrapure water. For a comparison sample (blank sample), a bottle is filled with 900 ml ultrapure water only (without substrate).
  3. The pH value and electrical conductivity are measured in all bottles.
  4. The bottles are shaken in an overhead shaker at 10 to 20 rpm for 24 hours. The sample should remain in motion, further comminution and abrasion should be avoided.
  5. The next day, the bottles are removed from the shaker and the suspension is allowed to sediment for 15 minutes.
  6. All bottles are physicochemically characterised again: Measurement of pH, electrical conductivity.
  7. Now carefully transfer 50 ml of the supernatant from each bottle into a 50 ml centrifuge tube.
  8. The tubes are centrifuged in the centrifuge for 10 min. at 4000 rpm.
  9. The supernatant is transferred to a beaker and divided into two 15 ml tubes as follow:
  • Cation analysis: Draw sample into syringe and filter through 0.45 µm filter unit (discard the first drops!) and add 3 drops of conc. HNO3
  • Anion analysis: Draw up the sample in a syringe and filter through a 0.45 µm filter unit (discard the first drops!) (WITHOUT adding acid!)

Contact

Ulrike Buhler