Re: [ATM] grit disposal

[Mark Holm <mdholm@telerama.com>]

Except for the inhalation hazard of glass dust, and perhaps of the
finest abrasive powders, none of the grinding or polishing waste stream
is particularly hazardous.  Bob May is perfectly correct to point out
that some economy can be practiced by recycling grit, but it is really
an economic vs. time decision, not an environmental one.  Putting the
grinding mud into the normal solid waste stream is OK since it is non
hazardous.  To keep things safe for yourself and the trash haulers, keep
it damp, so it won't make dust.  Once in a landfill, it will be buried
so that it can't raise dust. Burying it in the yard, or spreading it
over grass has at least a theoretical advantage.  If you live in a
reasonably damp climate, glass dust in soil will eventually degrade to
harmless soluble silicates.  Once that occurs, even the inhalation
hazard is gone.  I wouldn't spread grinding mud on a dry landscape
though.  It would be more likely to dry out and blow around, raising the
silicosis hazard again, and would take much longer to degrade to soluble
silicates.

At least in theory, if you consign it to a land fill, you might be a bit
more responsible to mix it with some dissolved sodium carbonate (washing
soda) before disposal.  The alkalinity of the carbonate would hasten the
decay of the glass to soluble silicates.  Lye (sodium hydroxide or
potassium hydroxide solution) would be even better from the point of
view of speeding up the degradation, but exposes you and the trash
haulers to risk of chemical skin or eye burns.  Also, some jurisdictions
may frown on lye in the trash.  It may be listed as hazardous.

I wouldn't mix it with sodium carbonate before disposing of it on or in
my lawn.  The high pH of the carbonate would be hard on grass and other
plants.

I don't think there is much that can be done to hasten the degradation
of silicon carbide and aluminum oxide.  They are pretty stable.

If you happen to be mixing up some concrete, you could add the mud to
the mix.  It should be fairly compatible in low levels.  Back off the
sand slightly to compensate.  The glass will degrade inside the concrete
since concrete is alkaline.  The abrasives will just be like other sand
in the mix, though the cement probably won't adhere well to the silicon
carbide.

-- 
Mark Holm
mdholm@telerama.com


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