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  • From: Alex McGregor <waldenfarm AT sprintmail.com>
  • To: market farming <market-farming AT franklin.oit.unc.edu>
  • Subject: Re: Granite dust
  • Date: Thu, 01 Feb 2001 10:58:06 -0500


Martin,

I'm not an expert on mineralization, but do have a background in Mineralogy.
The
abrasives are called "beads" and the process, "bead blasting." They used to
use sand
(silicon), but found that other abrasives, though more expensive, lasted
longer.

Alumina-zirconia oxide is a manufactured ceramic. These "beads" of abrasive
are usually
used in a closed system with vacuums to remove all the fine dust from what is
blasted
and the abrasives reused- since they are expensive. I don't know about the
monument
business, given the scale of some pieces.

If the abrasives are recycled, the content of the powder will be low in them.
If not,
it will be high. But, the possibility of contamination of soils with
aluminum is not a
possibility, since ceramics a very stable- don't react to acids or bases and
aren't
processed by soil life. However, they will remain in the soil for many years
and can be
weathered out down to the components over many thousands of years. This
would require
mechanical abrasion from erosion and transportation and the ability of water
to remove
ions.

Alex McGregor
Walden Farm

Martin Koenig wrote:

> To all you rock dust and re-mineralization experts:
> A friend is interested in getting free granite dust from a monument
> company for the potassium content. It's available at the rate of about 5
> cu. yds. a month. As it turns out, it is a by-product of sand blasting
> and contains sand blasting abrasive--a worker at the place thought maybe
> it was as much as 50%, the manager tried to tell him it was a lot less
> than that. In trying to find out what the abrasive was, he was told
> that it was some man-made diamond-like substance but on a box of
> abrasive that he saw at the place it said "alumina zirconia". Didn't
> sound like something he'd want to spread on his soil but I said I would
> ask the list. Apparently, lots of folks come by to get this stuff for
> their gardens.
>
> Margaret Hoeffel
> Blue Moon Farm
> Vashon, WA
>
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