search  current discussion  categories  materials - cobalt 

clay plasticity/co2

updated wed 17 jul 02


Michael Banks on wed 17 jul 02

Carbon dioxide is moderately soluble in water (1ml (vapour) per 1.8mls water
at 0 degrees C). It is more soluble in cold water than warm (hence the max
solubility at 0 degrees). It is only slightly ionised in solution
(producing H+ and HCO3- ions) -carbonic acid. Otherwise known as soda
water. Carbonic acid is ubiquitous in rainwater, more concentrated in cold
rainwater. In day to day life it reaches it's maximum concentration in cold
carbonated drinks (which are under pressure), beer, coke etc.

The effect of soluble CO2 (the anhydrous gas has no effect) on clay, is
limited to the concentration of H+ ions (protons) produced. As the acid is
weak and only slightly ionised, the concentration of protons is low.
Therefore it is only a weak flocculant. The acid is too weak to attack
feldspars etc, to produce clays. To illustrate how weakly reactive this acid
is, note how long it takes it to attack copper roofing. The thin green
coloured patina on old copper sheathing (verdigris, copper carbonate), takes
at least 50 years to develop - constantly exposed to the carbonic acid in

Being only a very weak flocculant, the effect on plasticity of clay is
likely to be negligible, compared to stronger acids..

Michael Banks,
New Zealand

----- Original Message -----
Ivor Lewis wrote:

.....prompt me to ask,
....." What is the roll of Carbon Dioxide in the enhancement of the property
of Plasticity in Clay ? "......
knowing that this gas will be a dominant bye-product of the biological
processes of "Souring" due to Bacterial or other biological activity.
Any bright ideas out there?