Carbonate Analysis

Objective

  • To determine the percentage of the <63m m fraction of the sediment that is composed of calcium and magnesium carbonate

Equipment and Reagents

0.5litre Pyrex beakers

Pestle and mortar

Temperature-controlled oven, preset to 105oC + 5

Balance capable of weighing to 0.0001g

A desiccator containing anhydrous silica gel.

Extractor fan

Pyrex beakers 30ml capacity

Washbottle with distilled water

Log sheets

Concentrated hydrochloric acid 30% w/w. Reagent quality.

Methodology

  1. Grind sample in a mortar and pestle to remove all aggregations.

  2. Place approximately 5g of the powder into a pre-weighed (4dp) 30ml Pyrex beaker.

  3. Dry the beaker in oven for half day at 105oC..

  4. Weigh the sample to 0.0001g.

  5. Wash sample into 0.5l beaker with washbottle; ensure all powder is wetted.

  6. Add hydrochloric acid, 5ml per sample NOTE use acid with  extractor fan/hood.

  7. Wait until effervescence ceases. Add another 5ml aliquot. Repeat until no effervescence occurs on adding acid.

  8. Add tap water to 0.5litre. Allow to stand until all sediment is settled.

  9. Carefully remove supernatant water without losing sediment (CAUTION, weak acid).

  10. Drain sediment into pre-weighed 30ml Pyrex beaker, using washbottle to rinse-in all sediment

  11. Allow to settle in 30ml beaker; carefully decant supernatant liquid (CAUTION, weak acid)

  12. Dry at 105OC to constant weight, place in desiccator to cool, then weigh to 0.0001g.

  13. Enter data into EXCEL programme for calculation of percentages.

NOTE: This analysis can be efficiently performed with batches of about 12 samples.