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|2 6 2 9 @ §
82
fH
Treatments:
+1
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Untreated = virgin soil,
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,
RESULTS AND DISCUSSION
CH,COOH-NH,OH System. The effects of CH3COOH-NH,OH system on the extractability
of 2"Tam from treated and untreated Aiken c. 1. are shown in Fig. 1. With the
untreated soil (control), the ?4lam extractabllity increased only slightly, tf
at all, from pH = 2.5 to pH = 3.8 and then increased noticeably to pH = 4.8.
Between pH 4.8 and pH 7.7, it decreased rapidly to 0.3% of dose and then
remained very low (0.04-0.3% of dose) to pH 10.
Above pH 10, it increased
appreciably.
With standard deviation,
o
.
treatment IV.
oS
residual OM removed after
o
free
The soil matertals were artificially contaminated by 2%JAm (NO3)3 and extracted
by the equilibrium batch method as described before (Nishita, 1976).
Equilibration in the present experiments was done over a 48-hour period with continuous
mixing on a mechanical mixer.
Two extraction systems were used, e.g., CH3COOH-NH,OH
aod HNO3-NaOH systems. To obtain the appropriate pH levels, CH3COOH-NH.OH
extraction solutions were prepared by titrating 1 M CH3COOH with varying
amounts of NH,OH. Since 20 ml of these solutions were diluted to 25 ml in
each tube with distilled H,0, the actual concentration of the CH3C007 tons in
the tubes was constant at 0.8 M throughout the pH range studied. With the
HNO ;-NaOH system, the appropriate pH level was attained by adding varying
amounts of HNO3 or NaOH. The pH values reported are those of the supernatant
liquid From the soil suspensions (soil extracts) after the equilibration
period, The preparation of the soil extracts for radioassay and counting was
done in the same manner as before with 2?8pu and 242cm (Wood et al., 1976).
kk
a
oOo
iron oxides removed after treatment LII, V = free silica, alumina, amorphous alumino-silicate, and
ec
o
II = HCL-soluble OM and
N
Go
removed,
w
Leal
= H,0-soluble OM and salt
n
ou
gent
Chemical characteristics of treated and untreated Aiken clay loam.
uw
co
.
s
goon
HH
Table 1.
2
ct
salts removed, III = OM, Mn oxides, and residual carbonates removed after treatment II, IV
a
Extractable
nn
©
was the digestion of samples in NaqCgH¢07-NaHCO3-Na,$ 0, mixture to remove
free lron oxides. Treatment V was the boiling of samples in 2% Na2CQ3 to
remove partially the free alumina and silica and amorphous alumino-silicates.
Some residual organic matter that was protected against decomposition by
HO) is also removed. With this treatment, the samples were washed five times
with acidified 1 N NaCl to remove the carbonates before the CaCly treatment.
Treatment I, which removed the H;0-soluble organic matter and salts, signifteantly reduced (at the 95% significance level) the extractability of 2*!Am
relative to that of the untreated soil at pH 11.6, At other pH levels, there
wag no significant difference. Treatment II, which removed the HCl-soluble
materials, significantly reduced the 2" 1am extractability relative to the
control at pH 6.5, but otherwise it also did not cause any signiftcant difference. Since the significant differences were small, it was concluded that the
two treatments, in general, had only slight effect on the extractability of
241 Am.
The general pattern of the 2"lan extractability curves were similar to those
obtained with 239pu and 2"7cm, and its intrinsic nature has been discussed
previously (N{shita, 1976).
In essence, the initial increase of 24am extractability to pH = 4.8 was ascribed to increasing complexation of 24 ag by the
acetate fons. As increasing amounts of NH,OH were added to increase the pH,
83