Case Studies: Full-Scale Operations and Delivery Systems - Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes - page 344

FIGURE 13.6 In situ mixing with a tractor-mounted disk harrow.
of a common breed. The many varieties of in situ systems are rarely, if ever, applied
at fixed installations because they are not needed. Normally, a wide variety of wastes
are delivered to a treatment facility
Pit Mixing Methods . Figure 13.7 shows a typical pit mixing installation at a
TSDF. Most of these installations today are well controlled, using reagent storage
and feeding equipment that can accurately proportion the reagent/waste ratio and
also the water addition, if required. The pit is generally a steel- or concrete-lined
basin with secondary containment. Because it is relatively small, 38 m 3 (50 yd 3 ) or
less, and configured to eliminate dead areas that the backhoe bucket can't get into,
it can do a good mixing job with most waste streams. The nature of the backhoe
allows the method to work well with debris and other large particles that could not
be handled with a mechanical mixer-based system. Pit mixing is a large-batch process
that is an efficient method for TSDFs where each waste load, typically 20 tons,
coming to the stabilization plant may require a different formulation. A continuous
mixer-based system is less practical for such sudden changes in waste characteristics
with each waste load delivery. While a batch, mechanical mixer-based setup could
be used in the same way, it is not practical to use a pugmill or other mixer to make
FIGURE 13.7 Ex situ pit mixing at a TSDF.