PNNL-13501 - Pacific Northwest National Laboratory

monolith is mechanically robust and tough and is much
more homogeneous than samples produced using a slower
cross-linking agent.
Figure 3. 50% polystyrene-butadiene/50% epoxy resin
waste form loaded with 20 wt% NaNO 3 synthesized using a
fast acting cross-linking agent
The impact of this improved homogeneity on leach
resistance is shown in Figure 4, which shows the
percentage of salt retained in samples loaded with 20 wt%
NaNO3 as a function of time immersed in water. Salt
retention was calculated from the conductivity of the
immersion solution. The data indicate that using a faster
cross-linking agent (20 minutes versus several hours)
reduces the leaching rate by a factor of about 50. Similar
improvements in salt retention were measured for waste
forms loaded with 30 and 40 wt% NaNO3. It is
speculated that speeding up the cross-linking rate
counteracts a tendency for the emulsion to coarsen with
time in the presence of the high salt concentration.
Summary and Conclusions
Commercially available styrene/butadiene and acrylic
latex emulsions are good precursors for use in the
aqueous fabrication of waste forms. When mixed with
emulsified epoxy resins, they react to form monoliths
with tough physical properties and good water resistance
without generating significant volatile organic compound
or flammability problems. The resulting waste forms can
% Salt Retained
100
90
80
70
60
50
40
30
20
PAC-EP composite
10
0
PSB-EP composite (slow crosslinking)
PSB-EP composite (fast crosslinking)
0 10 20 30
Time (min)
40 50 60
Figure 4. Leaching behavior of aqueous-based waste forms
loaded with 20 wt% NaNO 3 measured as percentage of salt
retained in the sample
physically incorporate large amounts of salt (up to 60%
sodium nitrate) and their leach resistance is markedly
improved by using fast acting cross-linking agents.
These results represent an important step in developing
aqueous-based polyceram flowsheets. While preliminary
in nature, they indicate that optimization of the current
system and extension to systems which incorporate an
inorganic or ceramic component should produce materials
with very attractive characteristics for encapsulating and
storing a wide variety of low-level wastes. Future work
will establish the optimal performance of the current
formulations through adjustment of solution pH, salt
content and composition, surfactant, cross-linking
initiator, curing time and temperature, and micelle
concentration. Also, quantum improvements in
performance will be sought by developing routes to
incorporate an inorganic component to form polyceram
waste forms.
Reference
Smith G and BJJ Zelinski. 1999. Stabilize High Salt
Content Waste Using Sol Gel Process. OST Reference
#2036, Mixed Waste Focus Area, Prepared for U.S.
Department of Energy, Office of Environmental
Management, Office of Science and Technology,
Washington, D.C.
Materials Science and Technology 313