Document ID: EPA-HQ-RCRA-2004-0010-0007
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Document Type: Supporting & Related Material
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Posted Date: 2006-07-28T04:00Z

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<META content="Volatilization Studies of a Lanthanide Lead Borosilicate Glass" 
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<META content="R.F. Schumacher, D.S. McIntyre, D.K. Peeler, and J.M. Pareizs" 
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<META content="August 12, 1998" name="date published">
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content="Special glass compositions and melter systems are being developed by the Savannah River Technology Center (SRTC) to immobilize a stored nitric acid solution containing relatively large quantities of lanthanides and the radioactive isotopes: americium-243 and curium-244.  These materials are presently stored in Tank 17.1 at the Separations Canyon in F Area at the Savannah River Site.  Immobilization of this material will permit shipment of the material to the Oak Ridge National Laboratory - Heavy Element and Advanced Neutron Facility where it will be transformed by nuclear reactions into other useful transplutonium isotopes.  The glass compositions for this program were based on a lead borosilicate optical glass composition developed during World War II by Loeffler.[1]  This glass system was initially selected based on its ability to incorporate large quantities of lanthanides and potentially actinides into the glass network structure. These glasses melt sharply at normal glass melting temperatures and have unusually low viscosity making them desirable from a vitrification processing standpoint.  Research has shown that increasing levels of lanthanide oxides acts as a flux or softening agent and reduces the melt viscosity." 
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<H3>WSRC-MS-98-00240</H3>
<H2>
<CENTER><A name=Heading1>Volatilization Studies of a Lanthanide Lead 
Borosilicate Glass</A></CENTER></H2>
<P>
<CENTER>R.F. Schumacher, D.S. McIntyre, D.K. Peeler, and J.M. 
Pareizs<BR>Westinghouse Savannah River Company<BR>Savannah River Technology 
Center<BR>Aiken, SC 29808</CENTER>
<P></P>
<P><FONT size=1>
<CENTER>This document was prepared in conjunction with work accomplished under 
Contract No. DE-AC09-96SR18500 with the U. S. Department of 
Energy.</FONT></CENTER>
<P><FONT size=1>
<CENTER>DISCLAIMER</CENTER>
<P>This report was prepared as an account of work sponsored by an agency of the 
United States Government. Neither the United States Government nor any agency 
thereof, nor any of their employees, makes any warranty, express or implied, or 
assumes any legal liability or responsibility for the accuracy, completeness, or 
usefulness of any information, apparatus, product or process disclosed, or 
represents that its use would not infringe privately owned rights. Reference 
herein to any specific commercial product, process or service by trade name, 
trademark, manufacturer, or otherwise does not necessarily constitute or imply 
its endorsement, recommendation, or favoring by the United States Government or 
any agency thereof. The views and opinions of authors expressed herein do not 
necessarily state or reflect those of the United States Government or any agency 
thereof. 
<P>This report has been reproduced directly from the best available copy. 
<P>Available to DOE and DOE Contractors from the Office of Scientific and 
Technical Information, P. O. Box 62 Oak Ridge, TN 37831; prices available from 
(423) 576-8401. 
<P>Available to the public from the National Technical Information Service, U.S. 
Department of Commerce, 5285 Port Royal Road, Springfield, VA 
22161.</FONT></P><BR>
<H4><A name=Heading2>Abstract</A></H4>
<P>The gravimetric weight loss of lead oxide and boric oxide from lead 
lanthanide borosilicate type glasses was investigated by remelting glass grains 
in small platinum crucibles at varying temperatures and times. A simple linear 
equation was developed to describe the volatilization rate of the glass in the 
crucibles with changes in temperature. The holding time at temperature does not 
have a very strong impact on the calculated volatilization rate when the time is 
within a two day period. The volatilization rate was calculated and compared to 
values obtained from the pilot facility bushing melter off-gas studies at the 
same temperatures. The calculated volatilization rate from crucibles was 
approximately twice that measured in the bushing melter off-gas which indicates 
that either the bushing may have a colder air/glass interface temperature or 
possibly the off-gas investigations did not capture all of the volatile 
material.</P>
<H4><A name=Heading3>Introduction</A></H4>
<P>Special glass compositions and melter systems are being developed by the 
Savannah River Technology Center (SRTC) to immobilize a stored nitric acid 
solution containing relatively large quantities of lanthanides and the 
radioactive isotopes: americium-243 and curium-244. These materials are 
presently stored in Tank 17.1 at the Separations Canyon in F Area at the 
Savannah River Site. Immobilization of this material will permit shipment of the 
material to the Oak Ridge National Laboratory - Heavy Element and Advanced 
Neutron Facility where it will be transformed by nuclear reactions into other 
useful transplutonium isotopes. The glass compositions for this program were 
based on a lead borosilicate optical glass composition developed during World 
War II by Loeffler.[1] This glass system was initially selected based on its 
ability to incorporate large quantities of lanthanides and potentially actinides 
into the glass network structure. These glasses melt sharply at normal glass 
melting temperatures and have unusually low viscosity making them desirable from 
a vitrification processing standpoint. Research has shown that increasing levels 
of lanthanide oxides acts as a flux or softening agent and reduces the melt 
viscosity. 
<P>One melter system under development at SRTC is a closed, platinum rhodium 
alloy box; heated by passing large electrical currents through the platinum 
alloy (resistance heat). This type of system was initially developed for use in 
remelting glass marbles for the manufacture of continuous glass fibers[2] and an 
extensive body of patent and journal literature exists for this area of glass 
manufacture. This commercial technology was modified and is being further 
developed for remote operation with the lead-lanthanide borosilicate glasses 
using a coupled liquid-frit feed stream.[3] This modified remelt bushing system 
may be employed for the remote melting and casting of the Am/Cm glass into small 
cans in the Separations Canyon in F Area. 
<P>The volatilization of lead oxide from the Loeffler glasses was considered 
early in the development of the laboratory process hazards review. One of the 
major concerns was the volatilization of lead compounds from the glass melt to 
the off-gas system and the hazards this might cause for personnel working with 
the system. The findings of J. Matousek [4] were employed to provide an initial 
estimate of the volatility of lead from a typical alkali lead silicate glass. A 
rough order of magnitude, estimate of 20 mg/sq.cm/hr for the volatilization at 
1400°C of the lead oxide was chosen based on an alkali lead glass containing 
about 20 wt% lead oxide. 
<P>It has been shown [5-7] that the volatilization of lead oxide is 
significantly increased by increasing temperature, but the rate of 
volatilization decreased with increasing soak time. Most authors also agree that 
under equal conditions, the volatilization of lead increases with the fraction 
of lead in the glass or with reduced SiO<SUB>2</SUB> content in the glass. The 
volatilization products from lead borosilicate glasses consist mainly of lead 
oxide while other volatile constituents, e.g. alkali and boron compounds, begin 
to volatilize at temperatures above 1200°C but at lower rates than the lead 
oxide. Volatilization appears as a complex process of physical chemistry, in 
which three simultaneous sub-processes may take part in series:</P>
<P>a. the volatile component diffuses through the melt to the surface of the 
glass,<BR>b. the volatile component evaporates from the surface of the melt, 
and<BR>c. the diffusion of the volatile component through the gas phase from the 
melt surface into the adjacent gaseous phase.</P>
<P>Diffusion in the gaseous phase is usually assumed to proceed much faster than 
the other processes, a and b, which then places these processes (a & b) as 
the rate controlling processes. The total loss of the volatile component can be 
expressed as:</P>
<P>
<CENTER><IMG src="WSRC-MS-98-00240_files/9800240eq1.gif">
<P></P></CENTER>
<P>where M(t) is the mass of the volatile component after time t, Co is the 
initial concentration of the volatile component, and D is the diffusion 
coefficient of the volatile component. When there is little convection in the 
glass and temperatures are low, diffusion to the surface should be rate 
controlling. As temperatures increase, surface evaporation will have more 
influence and may dominate at extremely high temperatures. In general, the 
amount of lead vaporized should therefore be proportional to the square root of 
time. The diffusion coefficient and evaporation coefficient should be related to 
the reciprocal of temperature expressed in degrees Kelvin. While these 
theoretical relationships deserve consideration, the experimental conditions 
found in the present study may be too complicated for such simple relationships. 
The work described in this report was generally considered scoping in nature due 
to the complexity of relating small-scale crucible melts to large-scale 
processing systems.</P>
<H4><A name=Heading4>Experimental Conditions</A></H4>
<H5><A name=Heading5>Glass Preparation</A></H5>
<P>Approximately 1650 grams of simulated Tank 17.3 solids* prepared from reagent 
grade chemicals. The Tank 17.3 solids were then mixed with the B2000 glass 
frit** in the proportions of 40, 35, 30, 25, and 20 wt% Tank 17.3 solids. The 
one kilogram powder mixtures were mixed by thorough shaking and tumbling in 2 
liter plastic containers for about ten minutes prior to melting. The calculated 
chemical compositions of the frit, the 17.3 solids, and the resulting glasses 
are presented in Table 1.</P>
<P><B>Table 1. Calculated Chemical Composition of B2000 Glass Frit, Tank 17.3 
Solids and Resulting Glasses. </B></P>
<TABLE cellPadding=5 border=1>
  <TBODY>
  <TR vAlign=top align=left>
    <TD align=left><BR></TD>
    <TD align=left rowSpan=2>
      <P><B>
      <CENTER>B2000
      <P>Frit</B></P></CENTER></TD>
    <TD align=left rowSpan=2>
      <P><B>
      <CENTER>Tank<BR>17.3<BR>Simulant</B>
      <P></P></CENTER></TD>
    <TD align=middle colSpan=4>
      <P><B>Tank 17.3 Loading</B></P></TD>
    <TD align=left><BR></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left><BR></TD>
    <TD align=left>
      <P><B>
      <CENTER>40%</B>
      <P></P></CENTER></TD>
    <TD align=left>
      <P><B>
      <CENTER>35%</B>
      <P></P></CENTER></TD>
    <TD align=left>
      <P><B>
      <CENTER>30%</B>
      <P></P></CENTER></TD>
    <TD align=left>
      <P><B>
      <CENTER>25%</B>
      <P></P></CENTER></TD>
    <UL></UL>
    <TD align=left>
      <P><B>
      <CENTER>20%</B>
      <P></P></CENTER></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P><B>
      <CENTER>Oxide</B>
      <P></P></CENTER></TD>
    <TD align=left>
      <P><B>
      <CENTER>wt%</B>
      <P></P></CENTER></TD>
    <TD align=left>
      <P><B>
      <CENTER>wt%</B>
      <P></P></CENTER></TD>
    <TD align=left>
      <P><B>
      <CENTER>wt%</B>
      <P></P></CENTER></TD>
    <TD align=left>
      <P><B>
      <CENTER>wt%</B>
      <P></P></CENTER></TD>
    <TD align=left>
      <P><B>
      <CENTER>wt%</B>
      <P></P></CENTER></TD>
    <TD align=left>
      <P><B>
      <CENTER>wt%</B>
      <P></P></CENTER></TD>
    <TD align=left>
      <P><B>
      <CENTER>wt%</B>
      <P></P></CENTER></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>La<SUB>2</SUB>O<SUB>3</SUB></P></TD>
    <TD align=right>
      <P>7.12</P></TD>
    <TD align=right>
      <P>11.23</P></TD>
    <TD align=right>
      <P>8.76</P></TD>
    <TD align=right>
      <P>8.56</P></TD>
    <TD align=right>
      <P>8.35</P></TD>
    <TD align=right>
      <P>8.15</P></TD>
    <TD align=right>
      <P>7.94</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>Ce<SUB>2</SUB>O<SUB>3</SUB></P></TD>
    <TD align=left><BR></TD>
    <TD align=right>
      <P>12.90</P></TD>
    <TD align=right>
      <P>5.16</P></TD>
    <TD align=right>
      <P>4.52</P></TD>
    <TD align=right>
      <P>3.87</P></TD>
    <TD align=right>
      <P>3.23</P></TD>
    <TD align=right>
      <P>2.58</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>Pr<SUB>2</SUB>O<SUB>3</SUB></P></TD>
    <TD align=left><BR></TD>
    <TD align=right>
      <P>12.90</P></TD>
    <TD align=right>
      <P>5.16</P></TD>
    <TD align=right>
      <P>4.52</P></TD>
    <TD align=right>
      <P>3.87</P></TD>
    <TD align=right>
      <P>3.23</P></TD>
    <TD align=right>
      <P>2.58</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>Nd<SUB>2</SUB>O<SUB>3</SUB></P></TD>
    <TD align=left><BR></TD>
    <TD align=right>
      <P>27.35</P></TD>
    <TD align=right>
      <P>10.94</P></TD>
    <TD align=right>
      <P>9.57</P></TD>
    <TD align=right>
      <P>8.21</P></TD>
    <TD align=right>
      <P>6.84</P></TD>
    <TD align=right>
      <P>5.47</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>Sm<SUB>2</SUB>O<SUB>3</SUB></P></TD>
    <TD align=left><BR></TD>
    <TD align=right>
      <P>6.34</P></TD>
    <TD align=right>
      <P>2.54</P></TD>
    <TD align=right>
      <P>2.22</P></TD>
    <TD align=right>
      <P>1.90</P></TD>
    <TD align=right>
      <P>1.59</P></TD>
    <TD align=right>
      <P>1.27</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>Eu<SUB>2</SUB>O<SUB>3</SUB></P></TD>
    <TD align=left><BR></TD>
    <TD align=right>
      <P>1.25</P></TD>
    <TD align=right>
      <P>0.50</P></TD>
    <TD align=right>
      <P>0.44</P></TD>
    <TD align=right>
      <P>0.38</P></TD>
    <TD align=right>
      <P>0.31</P></TD>
    <TD align=right>
      <P>0.25</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>Gd<SUB>2</SUB>O<SUB>3</SUB></P></TD>
    <TD align=left><BR></TD>
    <TD align=right>
      <P>3.22</P></TD>
    <TD align=right>
      <P>1.29</P></TD>
    <TD align=right>
      <P>1.13</P></TD>
    <TD align=right>
      <P>0.97</P></TD>
    <TD align=right>
      <P>0.81</P></TD>
    <TD align=right>
      <P>0.64</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>Er<SUB>2</SUB>O<SUB>3</SUB></P></TD>
    <TD align=left><BR></TD>
    <TD align=right>
      <P>12.90</P></TD>
    <TD align=right>
      <P>5.16</P></TD>
    <TD align=right>
      <P>4.52</P></TD>
    <TD align=right>
      <P>3.87</P></TD>
    <TD align=right>
      <P>3.23</P></TD>
    <TD align=right>
      <P>2.58</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left><BR></TD>
    <TD align=left><BR></TD>
    <TD align=left><BR></TD>
    <TD align=left><BR></TD>
    <TD align=left><BR></TD>
    <TD align=left><BR></TD>
    <TD align=left><BR></TD>
    <TD align=left><BR></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>Al<SUB>2</SUB>O<SUB>3</SUB></P></TD>
    <TD align=right>
      <P>6.04</P></TD>
    <TD align=right>
      <P>0.64</P></TD>
    <TD align=right>
      <P>3.88</P></TD>
    <TD align=right>
      <P>4.15</P></TD>
    <TD align=right>
      <P>4.42</P></TD>
    <TD align=right>
      <P>4.69</P></TD>
    <TD align=right>
      <P>4.96</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>B<SUB>2</SUB>O<SUB>3</SUB></P></TD>
    <TD align=right>
      <P>9.20</P></TD>
    <TD align=left><BR></TD>
    <TD align=right>
      <P>5.52</P></TD>
    <TD align=right>
      <P>5.98</P></TD>
    <TD align=right>
      <P>6.44</P></TD>
    <TD align=right>
      <P>6.90</P></TD>
    <TD align=right>
      <P>7.36</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>CaO</P></TD>
    <TD align=left><BR></TD>
    <TD align=right>
      <P>0.03</P></TD>
    <TD align=right>
      <P>0.01</P></TD>
    <TD align=right>
      <P>0.01</P></TD>
    <TD align=right>
      <P>0.01</P></TD>
    <TD align=right>
      <P>0.01</P></TD>
    <TD align=right>
      <P>0.01</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>Cr<SUB>2</SUB>O<SUB>3</SUB></P></TD>
    <TD align=left><BR></TD>
    <TD align=right>
      <P>0.26</P></TD>
    <TD align=right>
      <P>0.10</P></TD>
    <TD align=right>
      <P>0.09</P></TD>
    <TD align=right>
      <P>0.08</P></TD>
    <TD align=right>
      <P>0.07</P></TD>
    <TD align=right>
      <P>0.05</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>Fe<SUB>2</SUB>O<SUB>3</SUB></P></TD>
    <TD align=left><BR></TD>
    <TD align=right>
      <P>2.19</P></TD>
    <TD align=right>
      <P>0.88</P></TD>
    <TD align=right>
      <P>0.77</P></TD>
    <TD align=right>
      <P>0.66</P></TD>
    <TD align=right>
      <P>0.55</P></TD>
    <TD align=right>
      <P>0.44</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>K<SUB>2</SUB>O</P></TD>
    <TD align=left><BR></TD>
    <TD align=right>
      <P>0.08</P></TD>
    <TD align=right>
      <P>0.03</P></TD>
    <TD align=right>
      <P>0.03</P></TD>
    <TD align=right>
      <P>0.02</P></TD>
    <TD align=right>
      <P>0.02</P></TD>
    <TD align=right>
      <P>0.02</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>MnO</P></TD>
    <TD align=left><BR></TD>
    <TD align=right>
      <P>8.34</P></TD>
    <TD align=right>
      <P>3.34</P></TD>
    <TD align=right>
      <P>2.92</P></TD>
    <TD align=right>
      <P>2.50</P></TD>
    <TD align=right>
      <P>2.09</P></TD>
    <TD align=right>
      <P>1.67</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>Na<SUB>2</SUB>O</P></TD>
    <TD align=left><BR></TD>
    <TD align=right>
      <P>0.28</P></TD>
    <TD align=right>
      <P>0.11</P></TD>
    <TD align=right>
      <P>0.10</P></TD>
    <TD align=right>
      <P>0.08</P></TD>
    <TD align=right>
      <P>0.07</P></TD>
    <TD align=right>
      <P>0.06</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>NiO</P></TD>
    <TD align=left><BR></TD>
    <TD align=right>
      <P>0.09</P></TD>
    <TD align=right>
      <P>0.04</P></TD>
    <TD align=right>
      <P>0.03</P></TD>
    <TD align=right>
      <P>0.03</P></TD>
    <TD align=right>
      <P>0.02</P></TD>
    <TD align=right>
      <P>0.02</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>SiO<SUB>2</SUB></P></TD>
    <TD align=right>
      <P>44.23</P></TD>
    <TD align=left><BR></TD>
    <TD align=right>
      <P>26.54</P></TD>
    <TD align=right>
      <P>28.75</P></TD>
    <TD align=right>
      <P>30.96</P></TD>
    <TD align=right>
      <P>33.17</P></TD>
    <TD align=right>
      <P>35.38</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>ZnO</P></TD>
    <TD align=left><BR></TD>
    <TD align=right>
      <P>0.01</P></TD>
    <TD align=right>
      <P>0.00</P></TD>
    <TD align=right>
      <P>0.00</P></TD>
    <TD align=right>
      <P>0.00</P></TD>
    <TD align=right>
      <P>0.00</P></TD>
    <TD align=right>
      <P>0.00</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>PbO</P></TD>
    <TD align=right>
      <P>24.38</P></TD>
    <TD align=right><BR></TD>
    <TD align=right>
      <P>14.63</P></TD>
    <TD align=right>
      <P>15.85</P></TD>
    <TD align=right>
      <P>17.07</P></TD>
    <TD align=right>
      <P>18.29</P></TD>
    <TD align=right>
      <P>19.50</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>BaO</P></TD>
    <TD align=right>
      <P>9.02</P></TD>
    <TD align=right><BR></TD>
    <TD align=right>
      <P>5.41</P></TD>
    <TD align=right>
      <P>5.86</P></TD>
    <TD align=right>
      <P>6.31</P></TD>
    <TD align=right>
      <P>6.77</P></TD>
    <TD align=right>
      <P>7.22</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=middle>
      <P>Total</P></TD>
    <TD align=right>
      <P>99.99</P></TD>
    <TD align=right>
      <P>100.01</P></TD>
    <TD align=right>
      <P>100.00</P></TD>
    <TD align=right>
      <P>100.00</P></TD>
    <TD align=right>
      <P>100.00</P></TD>
    <TD align=right>
      <P>100.00</P></TD>
    <TD align=right>
      <P>99.99</P></TD></TR></TBODY></TABLE>
<P>The materials from Table 1 were melted in a small platinum-rhodium bushing 
melter. The mixtures were ramped up to 1475°C and additional batch added to 
bring up the glass level. Problems were encountered with melting and refining of 
the 20 and 25 wt% Tank 17.3 loaded glasses and only half of the one kilogram 
batch was melted.<B> </B>All of the available batch for the higher loaded 
glasses was melted. After melting for two hours at 1475°C the bushing 
temperature was dropped to about 1400°C and the glass drained. 
<P>* Feed Material currently in Tank 17.3 will be retrieved and washed according 
to a specific pretreatment option. The pretreated feed is to be stored in Tank 
17.3 
<P>** Frit B2000 was supplied by Ferro Corporation - Cleveland, Ohio. 
<P>The glasses were observed to be quite fluid when they were drained into 
water. Samples of the "as fabricated" glass were submitted to an analytic 
laboratory for determination of the chemical composition by Inductively Coupled 
Plasma (ICP) chemical analysis.</P>
<H5><A name=Heading6>Volatility Studies</A></H5>
<P>Two distinct approaches were taken to investigate volatilization of the Tank 
17.3 - B2000 system. The first approach involved simple gravimetric studies of 
all of the glasses (i.e., various 17.3 loadings) held under isothermal 
conditions for 48 hours (in addition to the 2 hours at 1475°C during initial 
fabrication) at temperatures ranging between 1200 to 1450°C. Based on mass loss 
alone, one would not be able to tell the volatile species in this system. 
Therefore, the heat treated samples were submitted for chemical analysis by ICP 
and were compared to the "as-fabricated" compositions. The second approach 
involved heat treating only the 40 and 35 wt% Tank 17.3 loaded glasses at 1300 
and 1400°C for varying lengths of time. The objective and general experimental 
technique for each approach follows.</P>
<H5><A name=Heading7>Approach No.1</A></H5>
<P>The objective of this initial task was to gain insight into the 
volatilization as a function of temperature for the Tank 17.3 - B2000 system for 
a given time period. Temperatures ranging from 1450°C (the nominal operating 
temperature of the bushing melter for the B2000 system) to 1200°C were 
evaluated. The lower limit was chosen based on volatilization data from the 
literature dealing with lead-silicate glasses. The amount of dry glass grains 
placed in the weighed platinum crucible was between 40 and 50 grams. The degree 
of volatilization was measured by weight loss for the Tank 17.3 series of 
glasses. An experimental design, as shown in Table 2, was selected for this 
temperature - waste loading investigation.</P>
<P><B>Table 2. Experimental Design No.1 - Volatility After 48 Hours </B></P>
<TABLE cellPadding=3 border=1>
  <TBODY>
  <TR vAlign=top align=left>
    <TD align=left><BR></TD>
    <TD align=left colSpan=5>
      <P><B>
      <CENTER>Tank 17.3 Solids Loading 
      <P></P></B></CENTER></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P><B>
      <CENTER>Temperature</B>
      <P></P></CENTER></TD>
    <TD align=left>
      <P><B>
      <CENTER>40%</B>
      <P></P></CENTER></TD>
    <TD align=left>
      <P><B>
      <CENTER>35%</B>
      <P></P></CENTER></TD>
    <TD align=left>
      <P><B>
      <CENTER>30%</B>
      <P></P></CENTER></TD>
    <TD align=left>
      <P><B>
      <CENTER>25%</B>
      <P></P></CENTER></TD>
    <TD align=left>
      <P><B>
      <CENTER>20%</B>
      <P></P></CENTER></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P><CENTER1450°C< p>
      <CENTER></CENTER>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>
      <CENTER>1400°C
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>
      <CENTER>1350°C
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>
      <CENTER>1300°C
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>
      <CENTER>1250°C
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD></TR>
  <TR vAlign=top align=left>
    <TD align=left>
      <P>
      <CENTER>1200°C
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD>
    <TD align=left>
      <P>
      <CENTER>X
      <P></P></CENTER></TD></TR></TBODY></TABLE>
<P>The open surface area in the platinum crucibles was calculated to be about 
12.57 square centimeters. Upon removal from the furnace the samples were cooled 
to room temperature in a dessicator and weighed again. Total mass loss was 
calculated as a measure of the degree of volatilization. To obtain 
semi-quantitative analysis on the volatile species, heat treated samples were 
submitted for chemical analysis and compared to the "as fabricated" sample 
compositions. It should be noted that the compositional comparison of the "as 
fabricated" glasses (1475°C for 2 hours) to the "heat treated" glasses will 
underestimate the total degree of volatilization. That is, during initial 
fabrication (melting) of the glasses, some degree of volatilization occurs. The 
volatilization during fabrication is not accounted for by these comparisons.</P>
<H5><A name=Heading8>Approach No. 2</A></H5>
<P>Since the initial baseline flow sheet targets a 35 wt% Tank 17.3 loading - 
B2000 glass, a more detailed evaluation of the effects of time and temperature 
on volatilization was undertaken. 
<P>A second glass (40 wt% Tank 17.3 loading) was also evaluated due to the 
potential for higher waste loadings and because it appears that the lower waste 
loading glasses were rather difficult to melt at 1450°C. The "as fabricated" 
glasses were heat treated for various times and temperatures. The degree of 
volatilization was determined by gravimetric analysis as in the initial study 
(approach No.1). The same crucibles were employed for these measurements. This 
will allow for the compilation of data between the two approaches. Table 3 
summarizes the experimental design for this approach.</P>
<P><B>Table 3. Experimental Design No.2 - Volatility at 1400 and 1300°C with 
Increasing Time.</B></P>
<TABLE cellPadding=1 border=1>
  <TBODY>
  <TR vAlign=top align=left>
    <TD align=left rowSpan=2><BR></TD>
    <TD align=middle colSpan=4>
      <P><B>Tank 17.3 Solids Loading at Temperature </B></P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=middle colSpan=2>
      <P><B>1400°C</B></P></TD>
    <TD align=middle colSpan=2>
      <P><B>1300°C</B></P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=middle>
      <P><B>Time<BR>(hours) </B></P></TD>
    <TD align=middle>
      <P><B>40%</B></P></TD>
    <TD align=middle>
      <P><B>35%</B></P></TD>
    <TD align=middle>
      <P><B>40%</B></P></TD>
    <TD align=middle>
      <P><B>35%</B></P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=middle>
      <P>2</P></TD>
    <TD align=middle>
      <P>Y</P></TD>
    <TD align=middle>
      <P>Y</P></TD>
    <TD align=middle>
      <P>Y</P></TD>
    <TD align=middle>
      <P>Y</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=middle>
      <P>4</P></TD>
    <TD align=middle>
      <P>Y</P></TD>
    <TD align=middle>
      <P>Y</P></TD>
    <TD align=middle>
      <P>Y</P></TD>
    <TD align=middle>
      <P>Y</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=middle>
      <P>8</P></TD>
    <TD align=middle>
      <P>Y</P></TD>
    <TD align=middle>
      <P>Y</P></TD>
    <TD align=middle>
      <P>Y</P></TD>
    <TD align=middle>
      <P>Y</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=middle>
      <P>24</P></TD>
    <TD align=middle>
      <P>Y</P></TD>
    <TD align=middle>
      <P>Y</P></TD>
    <TD align=middle>
      <P>Y</P></TD>
    <TD align=middle>
      <P>Y</P></TD></TR>
  <TR vAlign=top align=left>
    <TD align=middle>
      <P><IMG src="WSRC-MS-98-00240_files/00240tab3.gif"></P></TD>
    <TD align=middle>
      <P>X</P></TD>
    <TD align=middle>
      <P>X</P></TD>
    <TD align=middle>
      <P>X</P></TD>
    <TD align=middle>
      <P>X</P></TD></TR></TBODY></TABLE><IMG 
src="WSRC-MS-98-00240_files/00240tab3ftr.gif"> 
<H4><A name=Heading9>Results and Discussion</A></H4>
<H5><A name=Heading10>Initial Glass Fabrication</A></H5>
<P>The glasses after melting were chemically analyzed by ICP and compared to the 
targeted calculated compositions. The B<SUB>2</SUB>O<SUB>3</SUB> and PbO were 
found to be consistently lower than the calculated values while the other oxides 
were similar. It is expected that some of the lead and boron volatilized during 
the melt preparation of the glasses prior to any gravimetric testing. Closer 
inspection of the lead oxide analyses indicated that the loss during melting was 
usually less than one wt%.</P>
<H5><A name=Heading11>Approach No. 1</A></H5>
<P>Samples of all the glasses were dried and weighed and placed into weighed 
platinum crucibles in a furnace at the selected temperatures (see Table 2). 
After 48 hours at the temperature, the crucibles were removed, cooled and 
weighed again. The weight lost due to volatilization was obtained and plotted in 
Figure 1. This figure is a bar graph showing the average volatilization rate per 
hour from each of the five glasses with Tank 17.3 loadings at the chosen 
temperatures. The data point for the 20 wt% loaded glass at 1250°C appears 
suspect, but all the other data points appear to be acceptable within the limits 
of this test. 
<P>The glass volatilization did not appear to be greatly influenced by the level 
of the Tank 17.3 loading. Accepted theory would lead to the expectation that the 
highly loaded Tank 17.3 glasses would be low in volatility as they contain less 
lead oxide. While the glasses melted at 1400 and 1450°C may show some variation 
due to the content of lead and boron, it is doubtful that these differences 
would be statistically significant. It should also be noted that three of the 
glasses with the lower levels of Tank 17.3 loadings were different in appearance 
after the heat treatment at 1450°C. There was a slight milky opalescence within 
the glasses. The high level of PbO volatilization, greater than 10 wt%, may have 
unstabilized the glass, leading to phase separation or devitrification. The 
glasses treated at 1200 and 1250°C were examined by x-ray diffraction and some 
small level of crystallization was detected. The phase identification was 
extremely difficult but may have been rare earth oxides and lead silicate.</P>
<CENTER><IMG src="WSRC-MS-98-00240_files/ms980024001.gif"></CENTER>
<P><B>Figure 1. Measured Volatilization Rate from Tank 17.3 Glasses After 48 
Hours at Temperature.</P></B>
<P>The glasses heated at 1400°C for 48 hours were analyzed chemically by ICP and 
compared to the "as fabricated" glass composition. A comparison was made by a 
mass balance calculation and this data is presented in Table 4. The numbers 
presented are the product of the composition in weight percent and the weight of 
glass used in the test. This calculation clearly indicates that the lead and 
boron losses were the principle cause for the measured weight loss for the 
1400°C samples. Based on the mass balance calculation, barium (the other toxic 
element of B2000 frit) was not volatile. Further calculations showed that the 
lead loss was approximately 70 to 80% of the total loss and boron was 
responsible for perhaps 10 to 20% of the loss. This finding will later be shown 
to be consistent with off-gas measurements on pilot system.</P>
<P><B>Table 4. Glass Compositions as Fabricated and after 1400°C for 48 
Hours</B><BR><IMG src="WSRC-MS-98-00240_files/00240tab4.gif"></P>
<P>Attempts to plot this data compared to 1/T (Kelvin) did not exactly meet the 
expected linear relationships predicted by simple theory. See Figure 2. There 
was a slight curvature to the combined data. However, when the data was plotted 
with a "best fit" line the following simple linear equation was obtained:<BR>
<P>Average Volatility Rate (mg/sq.cm/hr) = 50.17 - (73,630/Temperature - K) Eq. 
2 
<P>This equation provides an approximation of the average volatility in 
mg/sq.cm/hr after a significant time period (48 hours) at the selected 
temperature in Kelvin. This is the equation for small scale, crucible melts. Use 
of this equation to estimate the volatility from large systems should be used 
with caution due to the complexities associated with volatilization.</P>
<CENTER><IMG src="WSRC-MS-98-00240_files/ms980024002.gif"></CENTER>
<P><B>Figure 2. Volatilization Rate of all Glasses as a Function of 
Temperature.</P></B>
<H5><A name=Heading12>Approach No. 2</A></H5>
<P>The glasses with 35 and 40% Tank 17.3 loading were heat treated for time 
periods between two and twenty-four hours at 1400°C and 1300°C. The resulting 
weight loss data was combined with the appropriate 48 hour data from Approach 
No. 1 and is plotted as volatilization weight loss per square centimeter versus 
time in Figure 3. A continuous almost linear relationship was obtained as shown. 
It appears that the volatilization at 1400°C is approximately double the 
volatilization at 1300°C and this is generally supported utilizing Equation 2. 
This data was also plotted versus the square root of time. The data did not 
support the square root of time linear relationship which would have identified 
diffusion as the rate controlling step. It is possible that the low viscosity 
glasses are experiencing convection at the higher temperatures or other 
experimental factors could be limiting the utilization of the simple theoretical 
relationships e.g. the vapor space above the melt is saturated with PbO 
suppressing volatilization. In addition, the fact that two elements, lead and 
boron, are both volatilizing may be interfering with the simple explanations of 
volatility. Again, Equation 2 should provide a reasonable estimate of the 
volatilization within the temperature range of interest for crucible tests. 
<P>A question was raised as to how this measured data compares to the original 
Process Hazards Review estimate of volatilization. This estimate, of course, was 
intended to be conservative. The 48 hour average volatilization rate was about 
one third of the estimate of 20 mg/sq.cm/hr and since Figure 3 approximates a 
linear relationship this one third ratio would probably hold over the range of 
times investigated.</P>
<CENTER><IMG src="WSRC-MS-98-00240_files/ms980024003.gif"></CENTER>
<P><B>Figure 3. Measured Volatilization per Area as a Function of Time for 35 
and 40% Tank 17.3 Loading Glass.</P></B>
<H5><A name=Heading13>Volatility Compared to Actual Am/Cm Bushing Testing 
</A></H5>
<P>The off-gas system of the Am/Cm bushing melter was tested under a variety of 
processing conditions using the B2000 glass system.[10] Although six test runs 
were completed, only the runs where glass was idled at 1450 °C and 1150 °C are 
comparable to this volatility investigation. Frit and surrogate feed were not 
fed during these two runs. Additionally, only air was introduced into the 
off-gas film cooler. The off-gas stream was sampled between the control air 
inlet and the steam eductor. The sampled stream passed through a cascade 
impactor and then through an EPA Method 29 sampling train. Filter papers 
(retention to 0.18 µm) within the impactor were weighed before and after each 
test run to determine total particulate loading in the off-gas streams. 
<P>The compositions of impinger solutions and material retained on the impactor 
filters were determined by Inductively Coupled Plasma-Atomic Emission 
Spectroscopy (ICP-AES). The ICP-AES was used to measure Pb, Ag, Al, As, B, Ba, 
Ca, Cd, Ce, Cr, Cu, Er, Eu, Fe, Gd, La, Mn, Nd, Ni, Pr, Se, Sm, and Sr 
concentrations. Silicon was not measured because the filter papers within the 
impactor were primarily silicon. Boron results could not be utilized because of 
the probable boron contamination from the borosilicate glassware. Additionally, 
high background levels of aluminum and calcium made results for these elements 
unreliable. 
<P>The bushing melter has a glass/air surface area of approximately 177.8 sq. 
cm. The measured volatilization rates of total emission and PbO were 3.04 
mg/cm<SUP>2</SUP>/hr and 1.91 mg/cm<SUP>2</SUP>/hr respectively while idling at 
1450°C. 
<P>Thus, PbO accounted for 63 percent of the material lost from the glass 
surface. Comparison with the crucible studies showed PbO and 
B<SUB>2</SUB>O<SUB>3</SUB> were responsible for 70 to 80 and 10 to 20 percent, 
of the volatile losses at 1400°C (Approach #1). Considering the major 
differences in equipment and conditions, these results are very similar. 
However, the total rates of volatilization from the crucibles at 1450°C were 
somewhat different. The average total volatility rate at 1450°C (using Equation 
2) was 7.44 mg/sq. cm/hr. The rate of volatilization in crucible melts at 1450°C 
was somewhat more than double the rate in the bushing melter at 1450 °C. 
Assuming that greater convection currents exist in the bushing melter (due to a 
larger thermal gradient and the use of forced convection (bubbler), the rate of 
PbO and B<SUB>2</SUB>O<SUB>3</SUB> volatilization should be greater. One 
possible explanation is the difference between the measured temperature of the 
bushing melter and the unknown true temperature of its glass surface. Another 
explanation may be that the off-gas test did not capture all of the volatile 
material. It is known that some amount of material did plate out on the off-gas 
film cooler and the off-gas line prior to sampling. 
<P>The bushing melter temperature is measured at the outside of the bushing 
wall. The surface temperature of the glass inside the bushing is not normally 
measured but is less than the control temperature. A lower measured 
volatilization rate from the melter may indicate glass surface temperatures 
below 1400 °C. Until the true temperature of the glass surface is determined, an 
absolute comparison between the bushing melter and crucible volatilization 
cannot be made. There was no measurable PbO emission in the bushing melter at 
the 1150 °C, and total emission was only 0.06 mg/cm<SUP>2</SUP> hr. 
Extrapolation of crucible results from Equation 2 also predicts a volatilization 
rate close to zero below 1200°C.</P>
<H4><A name=Heading14>Conclusions</A></H4>
<P>Examination of the data presented in this report provided the following 
general conclusions for the volatility of PbO and B<SUB>2</SUB>O<SUB>3</SUB> 
from Tank 17.3 -B2000 glass melts:</P>
<UL>
  <LI>The level of waste loading (20 to 40 wt%) does not have a strong influence 
  on volatility even though the level of PbO in the glasses decreases from 19.5 
  to 14.6 wt%. 
  <LI>The average volatility rate in crucibles, after 48 hours, was described by 
  the equation: Volatility Rate (mg/sq.cm/hr) = 50.17 - 73,630/(Temperature-°K). 

  <LI>The total volatilization from crucibles after 48 hours at 1400°C appears 
  to be mostly due to PbO loss (70 to 80 wt%) and B<SUB>2</SUB>O<SUB>3</SUB> 
  loss (10 to 20 wt%). 
  <LI>The volatilization rate in crucibles is approximately linear with respect 
  to time between 0 to 48 hours indicating that the volatilization is mass 
  transfer controlled. 
  <LI>Comparing crucible volatility to bushing melter off-gas measurements tends 
  to suggest that the glass/air surface temperature in the bushing is 
  considerably below the bushing control temperature. 
  <LI>Any future volatility studies should strongly consider filling the 
  crucibles with glass to reduce vapor phase considerations. The simple 
  volatilization theories are very likely influenced by the presence in this 
  system of two volatile oxides (PbO and B<SUB>2</SUB>O<SUB>3</SUB>) and the 
  unusually low viscosity of these glass systems. </LI></UL>
<H4><A name=Heading15>Addendum</A></H4>
<P>Due to various problems with glass devitrification with B2000, the 
composition of the frit for the americium/curium solidification program has been 
modified. </P>
<H4><A name=Heading16>References</A></H4>
<OL>
  <LI>M.B. Volf, "Chemical Approach to Glass," Series on Glass Science and 
  Technology - 7, Chapter 27 - Lanthanoids, Elsevier, New York, 1984. 
  <LI>K.L. Lowenstein, "The Manufacturing Technology of Continuous Glass 
  Fibers," Second Ed., p.118-168, Elsevier, New York, 1983. 
  <LI>R.F. Schumacher, W.G. Ramsey, F.M. Johnson, T.M. Jones, D.H. Miller, and 
  B.J. Hardy, "Development of a Remote Bushing System for Americium-Curium 
  Vitrification," Ceramic Transactions, Vol.87, pg 3-12, Amer. Ceram. Soc. 
  Westerville, OH. 
  <LI>J.Matousek, "Volatilization of Lead Glasses within the 1200 to 1400°C 
  Temperature Range," (English) Silikaty, 1 pg 1-12, 1972. 
  <LI>M.B. Volf, "Chemical Approach to Glass," Series on Glass Science and 
  Technology - 7, Chapter 35 Lead, Elsevier, New York, 1984. 
  <LI>O. Andersen, "The Volatilization of Lead Oxide from Lead Silicate Melts," 
  J. Amer. Ceram. Soc., [2], p.784, (1919). 
  <LI>E. Preston and W.E.S. Turner, "A Study of the Volatilization and Vapour 
  Tension at High Temperatures of an Alkali-Lead Oxide-Silica Glass," J. Soc. 
  Glass Technology, p. 219 (1932) 
  <LI>J.R. Zamecnik, Analysis of Cascade Impactor and EPS Method 29 Data from 
  the Americium/Curium Pilot Melter System-(U)," WSRC-RP-97-00937, Rev. 0, 
  November 19, 1997. </LI></OL>
<H4><A name=Heading17>Acknowledgments</A></H4>
<P>The information contained in this article was developed during the course of 
work under Contract No. DE-AC09-89SR18035 with the U.S. Department of 
Energy.</P></BODY></HTML>