PNNL-13501 - Pacific Northwest National Laboratory

concentration of 0.5% AMX was the most effective. In
Figure 1, results are shown for an injection experiment
conducted in a 1.0-meter long column of Hanford
sediment. This experiment was conducted by first
pretreating the column with approximately two pore
volumes of a solution containing only 0.5% AMX at a pH
of 8.0. The injection slurry contained 0.5% AMX and
1.0% Fe 0 at pH 8.0. Three pore volumes of this slurry
were injected at 7.2 cm/min. The results indicate a fairly
even distribution of iron throughout the column, ranging
from 0.5% Fe 0 at 10 cm to about Fe 0 0.3% at the effluent
end of the column.
% Fe 0
1.0
0.8
0.6
0.4
0.2
0.0
0 20 40 60 80 100
Distance (cm)
Figure 1. Distribution of Fe 0 in a 100-cm column of Hanford
sediment resulting from injection of 3 pore volumes of slurry
containing 1.0 % Fe 0 , and 0.5 % AMX, using a flow rate of
7.2 cm/min, and a 2-pore volume pretreatment with 0.5 %
AMX
The results for an experiment in which the pretreatment
step was skipped are shown in Figure 2. In this case, the
Fe 0 distribution is much less even, with lower
concentrations observed in the first part of the column.
Another experiment in which the injection rate was
reduced to 1.6 cm/min is shown in Figure 3. In this case
we can see that the iron concentrations were significantly
higher than for the higher flow rate experiment illustrated
in Figure 1. In addition, the Fe 0 concentrations were
observed to drop off rapidly as a function of distance from
the inlet.
To determine if the injection of Fe 0 into the columns
caused any permanent reduction in permeability, a
column injection experiment was conducted in an
identical fashion to that of the experiment illustrated in
Figure 1. However, in this case the inlet pressure was
monitored prior to, during, and after the injection phase of
the experiment. Prior to and after the pretreatment and
Fe 0 slurry injection phase of the experiment, water was
pumped through at a much slower flow rate. As can be
256 FY 2000 Laboratory Directed Research and Development Annual Report
% Fe 0
1.0
0.8
0.6
0.4
0.2
0.0
0 20 40 60 80 100
Distance (cm)
Figure 2. Distribution of Fe 0 in a 100-cm column of Hanford
sediment resulting from injection of 3 pore volumes of slurry
containing 1.0 % Fe 0 , and 0.5 % AMX, using a flow rate of
7.4 cm/min, and no pretreatment with 0.5 % AMX
% Fe 0
4
2
0
0 20 40 60 80 100
Distance (cm)
Figure 3. Distribution of Fe 0 in a 100-cm column of Hanford
sediment resulting from injection of 3 pore volumes of slurry
containing 1.0 % Fe 0 , and 0.5 % AMX, using a flow rate of
1.6 cm/min, and a 2-pore volume pretreatment with 0.5 %
AMX
seen from Figure 4, injection of water at 0.76 cm/min
resulted in a very low back pressure at the column inlet
(0.7 psig). As the 0.5% AMX pretreatment solution was
injected into the column at a flow rate of 7.0 cm/min, the
back pressure began to increase. During the slurry
injection, the back pressure continues to increase. After
the injection phase of the experiment, water at a flow rate
of 0.85 cm/min was pumped through the column. When
this was done, the back pressure decreased significantly
from about 70 psig to 11 psig. This is a significant
decrease in back pressure; however, it is significantly
higher than the initial back pressure measured prior to the
injection phase. After 3.4 pore volumes of water were
pumped through the column, the back pressure returned to