JJHerb@aol.com on sun 8 dec 96
Ken Wetfall offered some observations about cement that are not necessarily
accurate. Portland Cement is manufactured using limestone and shale. The
two materials, calcium carbonate and clay, are powdered, mixed together, and
then fired in a rotary kiln to near stoneware temperatures. The resulting
material, called clinker, is finely ground to produce the familiar gray
powder. This powder reacts with water to form a complex hydrous calcium
silicate with some calcium (oxide?) left over. Pozzolan cements are made by
adding reactive silicate materials, like volcanic ash or industrial flyash,
that combine with the excess calcium to make additional cementaceous
material. Now, this stuff can be attached by acids but it tends to be self
isolating because the soluble materials are removed from the surface leaving
less reactive materials exposed to the acid. If there is no mechanical
action (washing) to remove the outer layers, the rate of removal decreases.
In a buried landfill situation that is supposedly dry and where there is
little movement, the dreaded cement blob should suffer little damage.
The acid that is usually present in natural waters is CARBONIC acid, a weak
acid formed by the solution of carbon dioxide gas in water. That this acid
is capable of dissolving limestone is testified to by the existence of any
number of extensive caverns, Mammoth Cave in Kentucky is an example. The
current model for the formation of caverns requires the removal of much of
the material over several hundred thousand years. The limestone is totally
saturated with CARBONIC acid which slowly removes/dissolves calcium carbonate
from the limestone along an existing crack. The increased density of the
reacted water, now containing calcium ions, causes a slow sinking that allows
new, still acid, water access to the face and removal continues. After a few
tens of thousands of years, a continuous passage large enough to allow flow
may form. Down gradient ground water flow may enhance the process. If the
area is lifted or if the water table drops, the flow of surface water through
the cave changes things.
CARBOLIC acid is phenol. This is an organic compound found in coal and wood
tars and is manufactured in industry. Chemically it is a benzene ring with
one of the hydrogens replaced with an OH group. It is fairly vicious stuff
but there usually is not too much of it in the areas I had envisioned for the
cement lump disposal, entombment, encryption.
Finally, I would like t address the idea of a stable chemical compound. The
stability of any combination of elements depends on the environment to which
they are exposed. There is no absolutely stable compound. Aluminum oxide is
very stable at earth surface conditions but when subjected to strong electric
currents at a temperature of a couple thousand degrees in the presence of
Cryolite, it doesn t do so well. This briefly describes the Hall process,
the reason we have aluminum cans. Another extreme example is acetylene, a
gas made of two carbon and two hydrogen atoms. When dissolved in acetone or
at pressures less than 15 psi, this gas is "stable". If the pressure (of the
undissolved gas) is raised above 15psi the gas spontaneously decomposes
explosively. This was the source of great fun when calcium carbide was more
easily available and commodities came in metal cans with force fit lids. The
search for stability when disposing of unwanted materials is an ongoing
process. You really don t have a guarantee unless you can teleport the stuff
to the core of the Sun or, better, a more distant star.
I guess that wasn t finally. I still think the cement idea, on balance, is a
good idea. The material is cheap and easily available. It is easy to mix
and handle. The process is wet so the problems of dust while you are
preparing the entombment are reduced. If you want that extra protection, mix
your batch of cement in a five gallon plastic bucket and put the lid on
tight. You could then go the extra-extra mile by solvent sealing the seam
between the lid and bucket. Then off to the landfill.
After all this discussion, I feel a small longing for the traditional
solution to this problem which was to put the toxic materials on the surface
of a pot and sell it to a stranger. ;~)
With respect for the environment and sympathy for problems of making
uninformed choices in a complex world, I remain:
Joseph Herbert
JJHerb@aol.com
Kenneth D Wetfall on mon 9 dec 96
I would like to thank Joseph for clearing up my mistakes. I is
unfortunate the spell check doesn't check for content or intent. I did
intended to use CARBONIC acid and not CARBOLIC acid.
To my defense landfill are much less that perfectly run operation.
There have and will always be, the disposal of other strong corrosive
that should go else where, being cheaply disposed it landfills. Not all
landfills are dry, lined, monitored and there run off treated correctly.
Yes I know that there are no prefect stable compound, anything that
is done it this less that prefect world can surely be undone. The only
problem is can it be undone before it KILL US ALL. I 100% agree that
using the glaze up it the best solution. I also think that friting the
glaze, using the waste heat from a firing is still a better solution than
add additional bulk and fill up a landfill. The last thing landfills
need is another plastic bucket. Reduce, Reuse, or Recycle not hid in
someone else's back yard.
Kenneth
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