Other Binders - Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes - page 144

TABLE 6.5.4
7-Day PCT Results

Normalized Sodium Leach Rate
(g/m 2 /day) Material

EA glass 0.96

PUREX glass 0.73

SRL-131 glass 0.67

HC#1 NaAlO 2 /NaOH/
Crude metakaolin

0.40

HC#2 NaOH, NaNO 3 (25 wt% of the Na), Crude
metakaolin

0.39
(2.6 wt% of the NO 3 - leached)

HC#3 38 wt% alumina-type INEEL
calcine/NaOH/DEA/Crude metakaolin

0.40

HC#4 46 wt% INEEL zirconia calcine/NaOH/Crude
metakaolin

0.43

HC#6 NaOH/Englehard Metamax™ metakaolin,
9-hr cure @ 200°C

0.13
(ANSI/ANS-16.1-2003 LI Na = 11.6)

bulk constituents (for a borosilicate glass that means sodium, boron, lithium, and
silicon) than does a benchmark “Environmental Assessment” (EA) glass. Because
the PCT involves 1-week exposure of a relatively large specific surface area (SSA)
to a small volume (V) of 90°C water (i.e., 1 g of 75- to 150-μm sample particles
per 10 cc water — SSA/V 30 cm -1 ), it generates an estimate of the material's
solubility under conditions that promote back reaction or saturation. Table 6.5.4
compares several HCs with “representative” radwaste-type glasses 12 with respect to
the dissolution of sodium (their most readily solubilized common component) under
PCT conditions. The HCs outperformed these glasses even more for constituents
such as 90 Sr and TRU.
To make the PCT more relevant, more conservative, and more accurate for these
sorts of applications, the following modifications were used for the HC samples
tested:

1. No minimum particle size (< 150 μ).

2. No prewashing of the sample powder.

3. For the surface area, use the geometric surface area for 150-micron

spheres. (This underestimates an HC sample's “true” [BET] surface area
by about three orders of magnitude.)

The reasons for these changes are as follows: a) calcines and calcine-containing
concretes are usually inhomogeneous at the relevant size scale (75 to 150 μm), which
means that the deliberate screening out of a specific size subsample is apt to generate
a nonrepresentative result; b) a brief “prewash” meant to remove surface dust from
75- to 150-μm glass particles is apt to seriously bias results generated from a