11, Number 10
A Gossman Consulting, Inc.
last 25 years
there have been reoccurring attempts to use spent aluminum potliner
(SPL) in cement kilns. There are two major difficulties to overcome
relative to the use of SPL, other than the off and on again approach to
the issue that the aluminum industry has had on the issue. The first of
these is regulatory and perception related – SPL has cyanide.
cyanide is certainly toxic it will also clearly be destroyed in a
cement kiln, and unless mixed with acid or blown as powder into the air
is unlikely to present a significant safety concern to employees in a
plant. Nevertheless, the combination of the perception of problems with
this issue and the fact that it is the cyanide that renders this waste
hazardous in the eyes of the USEPA and other regulators around the
world makes this a difficult problem to overcome. Only a handful of
cement plants already permitted to burn hazardous waste are in a
position to deal effectively with this issue in order to use SPL as a
fuel, mineralizer and alternative raw material.
New Developments in Treatment
Spent Aluminum Potliner
David Gossman, Gossman Consulting, Inc.
The other issue is not as well known but is of far more concern. SPL is
highly water reactive generating ammonia, methane, hydrogen and heat on
contact with as little water as can be found in humid air! There have
been fires and explosions in enclosed shipping containers. The finer
the material is ground, as is done prior to injecting it into a cement
kiln, the greater the potential for hazardous gas release. Any cement
plant using SPL, even one used to dealing with other hazardous wastes,
needs to take extra precautions when handling this material.
All of that said, imagine my pleasant surprise during a recent visit to
a cement plant in Australia to find that a company had developed a
process to both destroy the cyanide in SPL and the reactivity,
rendering the SPL non-hazardous. The plant I was visiting, as well as
two others in southern Australia, are now using SPL as easily as most
plants use coal or coke – no special permitting, no special
Trucks are pneumatically unloaded into a storage tank and from there
fed to the kiln like any other solid powdered fuel. The plant gets not
only the fuel value but also the mineralizing benefits of the fluoride
present in SPL and the material value from the aluminum.
The process for rendering hazardous waste SPL non-hazardous has been
developed and patented by a company called Regain Services Pty Ltd
(Regain). Regain has worked for years to refine and develop the process
into a truly elegant solution – speaking as a chemist, of
I cannot go into details because of the confidential nature of what I
seen but the process is certainly ready for prime time. While not
mobile it is easily set up in a relatively small amount of space right
at the aluminum plant generating the SPL. The process results in a
blended product with a relatively consistent quality that gets tested
prior to shipment to the cement plants. The process is currently
operating at two aluminum plants (soon to be a third) and provides
nonhazardous SPL to three cement plants.
The development of the Regain process opens up all kinds of
possibilities for both further processing and other end uses. For
cement plants that might be limited in their potential use of SPL
because of the sodium content it would certainly be possible to leach a
portion or most of the sodium fluoride from the SPL prior to use in the
kiln. The aqueous based sodium fluoride solution could then be used at
a different wet process plant where the mineralizing properties are not
the only benefit. Sodium fluoride acts as a viscosity reducing agent in
wet plant slurry tanks reducing the percent of water required in the
slurry and thus reducing overall energy consumption. Without the issue
of cyanide and reactivity other industries may also find treated SPL to
be a valuable additive for its fluxing action and fuel savings. The
brick industry is one that comes to mind.
The folks at Regain have proven that innovation is alive and well in
the hazardous waste treatment and recycling industry. It will be
interesting to see how the USEPA embraces this new option for treating
and reusing SPL.
contact David Gossman at 847-683-4188 or
by e-mail at email@example.com
for additional information.