WSRC-MS-95-0423

Bench-Scale Vitrification Studies with Savannah River Site Mercury Contaminated Soil

by C. A. Cicero Westinghouse Savannah River Company Savannah River Site Aiken, South Carolina 29808 D. F. Bickford

RECEIVED JAN 3 1 1996 Q S T I

A document prepared for WASTE MANAGEMENT 1996 at Tucson from 02/26/96 - 02/29/96.

DOE Contract No. DE-AC09-89SR18035 .~ ~

This paper was prepared in connection with work done under the above contract number with the U. S. Department of Energy. By acceptance of this paper, the publisher and/or recipient acknowledges the U. S. Government's right to retain a nonexclusive, royalty-free license in and to any copyright covering this paper, along with the right to reproduce and to authorize others to reproduce all or part of the copyrighted paper.

DISTWUTION OF THIS DOCUMENT fS UNLIMITEO DWWUTION OF THIS DOCUMENT IS UNLIMITED

DISCLAIMER

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 Govemment or any agency thereof.

This report has been reproduced directly from the best available copy.

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 (615) 576-8401.

Available to the public from the National Technical Information Service, U.S. Department of Commercet5285 Port Royal Road, Springfield, VA 22161.

WSRC-MS-95-00423 Revision 0

Keywords: low level mixed wastes, vitrification, glass, waste treatment

BENCH-SCALE VITRIFICATION STUDIES WITH SAVANNAH RIVER SITE MERCURY CONTAMINATED SOIL

Connie A. Cicero and Dennis F. Bickford Westinghouse Savannah River Company Savannah River Technology Center P.O. Box 616 Aiken, SC 29808

A Paper Proposed for Publication in the Proceedings of Waste Management 96, February 26-29,1996, in Tucson, Arizona.

This paper was prepared in connection with work done under the U.S. Department of Energy - Office of Technology Development Technical Task Plan No. SR1-3-20-04. By acceptance of this paper, the publisher and/or recipient acknowledges the U.S. Government's right to retain a non-exclusive, royalty-free license in and to any copyright covering this paper, along with the right to reproduce and to authorize others to reproduce all or part of the copyrighted paper.

.I

g - RCURY CONTAMINATED SOIL

C.A. Cicero and D . F . B ick fo rd Westinghouse Savannah R i v e r Company

Savannah River Technology Center Aiken , South Caro l ina 29802

ABSTRACT

The Savannah River Technology Center (SRTC) has been cha r t e red by t h e Department of Energy (DOE) - O f f i c e of Technology Development (OTD) t o i n v e s t i g a t e v i t r i f i c a t i o n technology fo r t h e t rea tment of Low Level Mixed Wastes (LLMW). I n f iscal yea r 1995, mercury conta in ing LLMW streams were targeted. I n order t o s u c c e s s f u l l y apply v i t r i f i c a t i o n technology t o mercury conta in ing LLMW, t h e types and q u a n t i t i e s of g l a s s forming a d d i t i v e s necessary f o r producing homogeneous glasses from t h e wastes have t o be determined and t h e t rea tment fo r t h e mercury po r t ion mus t a l s o be determined. Se lec t ed additives should ensure t h a t a durable and leach res i s tan t waste form is produced, while t h e mercury t r e a t m e n t should ensure t h a t hazardous amounts of mercury are not r e l eased i n t o t h e environment.

The mercury conta in ing LLMW selected f o r v i t r i f i c a t i o n s t u d i e s a t t h e SRTC w a s mercury contaminated s o i l f r o m t h e TNX p i l o t - p l a n t f a c i l i t y a t t h e Savannah River S i t e (SRS). Samples of t h i s s o i l w e r e obtained so bench-scale v i t r i f i c a t i o n s t u d i e s could be performed a t t h e SRTC t o determine t h e optimum w a s t e loading ob ta inab le i n the glass product without s a c r i f i c i n g d u r a b i l i t y and l each r e s i s t a n c e . V i t r i f y i n g t h i s waste stream also requi red o f fgas t rea tment f o r t h e cap tu re of t h e vaporized mercury. Resul t s i n d i c a t e d t h a t a durable , l each r e s i s t a n t glass waste form capable of pass ing t h e Product Consistency T e s t (PCT) and t h e Toxic i ty C h a r a c t e r i s t i c Leaching Procedure (TCLP) could be produced. The optimum g l a s s feed composition contained 60 weight percent s o i l and produced a soda-l ime-si l ica glass when melted a t 1350OC. percent Na2C03 and 1 6 weight percent CaC03 .

The g l a s s a d d i t i v e s used t o produce t h i s glass w e r e 24 weight

The proposed mercury capture method w a s a Na2S wash b o t t l e followed by a NaOH wash b o t t l e . The v o l a t i l i z e d mercury e n t e r e d t h e f i rs t wash b o t t l e through a bubbler and should have been converted t o HgzS, a very s t a b l e form of mercury. I f successfu l , no f u r t h e r t rea tment of t h e mercury would have been needed. However, a t t empt s t o cap tu re t h e v o l a t i l i z e d mercury i n a Na2S s o l u t i o n wash b o t t l e w e r e no t as success fu l as a n t i c i p a t e d . Maximum mercury captured w a s only about 2% of t h e mercury contained i n t h e feed. Ef fo r t s t hen s h i f t e d t o condensing t h e v o l a t i l i z e d mercury and t r e a t i n g it wi th a mercury s p e c i f i c r e s i n . This r e s i n w a s capable of captur ing t h e mercury and keeping it f r o m leaching out of t h e r e s i n when tested us ing t h e TCLP.

INTRODUCTION

The DOE has cha r t e red t h e Mixed Waste Focus A r e a (MWFA) t o i n v e s t i g a t e waste forms f o r LLMW. V i t r i f i c a t i o n o r high-temperature thermal t r e a t m e n t of t h e wastes i s a main focus of t h e KWA i n v e s t i g a t i o n s . The MWFA has funded the SRTC t o perform v i t r i f i c a t i o n and high-temperature thermal t rea tment s t u d i e s on LLMW. The SRTC's e f f o r t s have focused on t r e a t m e n t of LLMW sludges, so i l s , deb r i s , r e s i n s , and o t h e r s o l i d wastes.

A l a r g e focus of t h e e f f o r t s has been t reatment of s o i l s due t o t h e l a r g e volume of contaminated s o i l t h a t e x i s t s a t t h e SRS and o t h e r DOE sites. S o i l a t t h e SRS has been contaminated with both r a d i o a c t i v e and hazardous c o n s t i t u e n t s as a r e s u l t of a c c i d e n t a l s p i l l s and storage of l i q u i d wastes. but most have not and w i l l no t be u n t i l a t reatment method i s determined.

Some of t h e s e s o i l s have been exhumed and conta iner ized ,

A small amount of contaminated s o i l w a s exhumed a t t h e TNX p i l o t - p l a n t f a c i l i t y during r o u t i n e maintenance ope ra t ions . This s o i l w a s cha rac t e r i zed and found t o conta in e l eva ted l e v e l s of mercury. Two samples of t h i s s o i l w a s ob ta ined by SRTC f o r bench-scale v i t r i f i c a t i o n s t u d i e s . Previous s t u d i e s by SRTC had shown t h a t v i t r i f i c a t i o n of s o i l was a v i ab le option1 and t h a t v i t r i f i c a t i o n of fgas s y s t e m s could success fu l ly capture mercury.

For t h e mercury s o i l v i t r i f i c a t i o n v i a b i l i t y s t u d i e s a t t h e SRTC, bench- s c a l e s t u d i e s were performed with t h e t w o s o i l samples t o determine t h e necessary glass a d d i t i v e s f o r producing homogeneous g l a s s . T h e homogeneous g l a s s e s produced w e r e sub jec t ed t o leach t e s t i n g t o determine g l a s s d u r a b i l i t y , s i n c e it w a s important t o ensure t h a t t h e hazardous/radioact ive c o n s t i t u e n t s w e r e incorporated i n t h e g l a s s matr ix . Since t h e w a s t e contained mercury and mercury i s not incorporated i n t h e g l a s s matr ix , an offgas system had t o be i n s t a l l e d on t h e furnace . mercury, as w e l l as convert t h e mercury t o a stable f o r m .

The i n t e n t of t h i s system was t o c o l l e c t t h e vaporized

The composition of a sample of t h e TNX s o i l with less than TCLP l e v e l s of mercury w a s chemically c h a r a c t e r i z e d t o determine t h e chemical c o n s t i t u e n t s . and t h i s w a s confirmed by t h e chemical ana lyses . The chemical composition of t h e s o i l i s given i n Table 1 on an oxide basis. The previously determined t o t a l mercury i n t h e less than TCLP l i m i t sample w a s 1 . 9 2 ppm, while t h e high mercury sample contained 264 ppm t o t a l mercury.

I t w a s suspected t h a t t h e SRS s o i l contained mostly Si02

Previous bench-scale s t u d i e s with s imulated SRS s o i l had determined t h a t durable and homogeneous glasses could be made by us ing t h e soda-lime- s i l i ca t e r n a r y system. Waste loadings i n t h e s e g l a s s e s w e r e 55 and 58 w t % . The glass forming a d d i t i v e s used w e r e Na2C03 and CaC03, and a l l g l a s s e s w e r e melted a t 1150°C.1 Since t h e s e glasses w e r e made us ing simulated s o i l , bench-scale tests with a c t u a l s o i l had t o be performed t o determine t h e v a l i d i t y of t h e glass compositions.

TABLE 1 - TNX SOIL COMPOSITION

Wt% 3.534 0.016 0.014 0.146 0.001 0.052 0.007 0 .961 0.004 0.141 0.010 0.033 0.022 0.008 0.068 0.027

94.429 0.002 0.460 0.002 0 .051

LOW MERCURY SOIL EXPERIMENTS

I n order t o determine t h e a p p l i c a b i l i t y of t h e previously developed g l a s s compositions f o r a c t u a l SRS s o i l , two of t h e g l a s s compositions were selected f o r bench-scale t e s t i n g . A higher waste loading batch composition was a l s o der ived t o ensure t h a t t h e optimum waste loading had been found. The compositions t e s t e d on an a d d i t i v e b a s i s a r e shown i n Table 2 . Two a d d i t i o n a l batch compositions w e r e a l s o t e s t e d based on t h e r e s u l t s of t hese f i r s t bench-scale t r i a l s and t h e s e batch compositions a r e a l s o shown i n Table 2 .

TABLE 2 - LOW MERCURY SOIL BATCH COMPOSITIONS (WT%)

J s & d - I L - --- S o i l 58 55 60 80 60 CaC03 17 20 1 6 8 1 5

Na2C03 25 25 24 1 2 25

The batches l i s t e d i n Table 2 w e r e mixed using t h e low mercury s o i l sample and reagent grade chemicals. The batches w e r e then placed i n high p u r i t y alumina c r u c i b l e s and covered. Batches 1 - 3 w e r e melted a t 115OoC f o r 4 hours and v i s u a l l y examined a f te r a i r quenching. desc r ip t ion of t h e r e s u l t i n g product i s given i n Table 3. Since it appeared t h a t batch 3 more resembled homogeneous g l a s s than any of t h e o the r compositions, a higher w a s t e loading w a s t e s t e d as batch 4. This batch w a s melted a t 1175OC and i t s appearance is a l s o descr ibed i n Table 3 . As noted i n Table 3, some of t h e g l a s s e s appeared t o have some unreacted ma te r i a l around t h e c r u c i b l e edges, it was be l ieved t h a t t h i s

A

mater ia l was unreacted Si02. This was confirmed by Scanning Electron Microscopy (SEM). S ince t h e ma te r i a l w a s confirmed t o be S i O 2 , batch 3 was remelted a t 135OOC t o determine i f higher temperatures would f u l l y r e a c t t h e feed material. g l a s s w i t h only minimal unreacted p a r t i c l e s of S i O 2 . made t o diminish t h e formation of t h i s Si02 l a y e r by reducing t h e Ca0:NaaO r a t i o , s i n c e t h e presence of Na2O tends t o make Si02 more so lub le . This composition w a s ba tch 5 and w a s a l s o melted a t 135OOC. The appearance of t h e f i n a l product i s a l s o given i n Table 3.

This r e s u l t e d i n a very homogeneous looking Attempts w e r e also

TABLE 3 - PHYSICAL APPEARANCE OF BATCHES 1 - 5

Jwah-Xa Pescrintion 1 Mostly b lue g l a s s with some white l a y e r 2 Mostly white s o l i d with some b lue co lo r 3 Mostly b lue g l a s s with some s m a l l white

4 S o l i d i f i e d feed, not g l a s s 5

Since batch 3 produced t h e most homogeneous g l a s s , it w a s charac te r ized f o r chemical composition and phase assemblage. Durab i l i t y tes ts were a l s o performed using t h e PCT. The composition of t h e batch 3 g l a s s i s given i n Table 4 . T h e only s u b s t a n t i a l oxide components found i n t h e g l a s s were t h e Si02 and A1203 from t h e s o i l and Na20 and CaO from t h e g l a s s add i t ives . X-ray d i f f r a c t i o n (XRD) of t h e g l a s s i nd ica t ed t h a t t h e r e s u l t i n g g l a s s was amorphous. SEM analyses v e r i f i e d t h e amorphous s t a t e of t h e g l a s s , a s w e l l a s confirmed t h e presence of small amounts of unreacted Si02 a t t h e g l a s s su r face .

p a r t i c l e s

Greenish-blue g l a s s with some white p a r t i c l e s

TABLE 4 - OXIDE COMPOSITION OF GLASS 3

Qxide A 1 2 0 3 B203 BaO CaO CdO

C e 0 2 C r 2 0 3 ??e203

MnO N a 2 0 Nd203

N i O p205 PbO S io2 S r O

T i 0 2 ZnO

Z r 0 2

MgO

rn 3 . 6 0 1 0.016 0.009

12.672 0.001 0.030 0.007 0.750 0.082 0.016

11.876 0.014 0.008 ., 0.034 0.026

70.493 0.001 0.342 0.002 0.018

.I

I n o rde r t o determine t h e d u r a b i l i t y of t h e ba tch 3 glass, t h e PCT (ASTM C-1285-94) was performed. The PCT i s t h e s tandard t e s t used for determining t h e d u r a b i l i t y of High Level Waste (HLW) glasses and i s performed i n an a l k a l i n e environment. It i s a 7-day test performed a t 90°C i n ASTM type I w a t e r . The t e s t i s performed on 100-200 mesh glass p a r t i c l e s and t h e r e s u l t i n g leachate is analyzed fo r elemental concent ra t ions .2 These concent ra t ions are then normalized f o r t h e e l emen ta l glass c o n s t i t u e n t s .

A t p resent no PCT acceptance cri teria e x i s t fo r LLMW glasses. However, t h e acceptance c r i te r ia have been established f o r HLW glasses. The measured normalized releases f o r t h e Environmental Assessment (EA) glass, which is t h e benchmark fo r t h e Defense Waste Processing F a c i l i t y (DWPF) HLW g l a s s , are 3.922 g / L S i , 1 3 . 3 4 6 g/L N a , and 16.695 g / L B. The measured l eacha te pH i s 1 1 . 9 1 . 3 ba tch 3 glass w e r e 0.35 g /L S i , 5.90 g / L N a , and 0.88 g /L B. The measured pH w a s 11.85. Normalized PCT r e s u l t s for t h e ba t ch 3 glass were s i g n i f i c a n t l y less than t h e l i m i t s f o r S i and B, and t h e r e s u l t f o r N a w a s 2.5 t i m e s less. These r e s u l t s i n d i c a t e t h a t t h e r e s u l t i n g g l a s s product was a durable wasteform.

The normalized PCT r e s u l t s f o r

The TCLP was not performed on t h e g l a s s s i n c e no hazardous c o n s t i t u e n t s o t h e r than mercury w e r e p r e sen t i n t h e s o i l . Since it w a s known t h a t t h e mercury would v o l a t i l i z e dur ing v i t r i f i c a t i o n , no mercury should have remained i n t h e glass t o leach dur ing t h e TCLP.

ELEVATED MERCURY SOIL EXPERIMENTS

Before t h e t r e a t a b i l i t y s t u d i e s with t h e elevated mercury s o i l sample could be performed i n t h e bench-scale furnace, t h e o f fgas c o l l e c t i o n system had t o be f a b r i c a t e d and i n s t a l l e d . A d e t a i l e d drawing of t h e o f fgas s y s t e m f a b r i c a t e d i s contained i n Figure 1. The i n t e n t of t h e system was t o conta in a l l of t h e v o l a t i l e mercury i n t h e qua r t z l i n e s of t h e system. Using forced a i r on t h e seal of t h e c r u c i b l e and vacuum pressure on t h e end of t h e system l i n e , mercury w a s forced through t h e qua r t z tubing t o t h e f i rs t wash b o t t l e conta in ing Na2S. The vapors en te red through t h e d i p tube and w e r e bubbled i n t h e Na2S. Vapors from t h i s tube were forced through t h e NaOH wash b o t t l e by t h e vacuum a t t h e end of t h e l i n e . I n t h i s second bot t le , t h e s u l f u r i c acid gases generated from t h e first wash bo t t l e w e r e n e u t r a l i z e d by bubbling through t h e NaOH s o l u t i o n . A l l vapors generated from t h i s b o t t l e were vacuumed through a hood exhaust t h a t w a s i n l i n e with t h e bu i ld ing offgas system.

The offgas system w a s seated i n a Thermolyne furnace. For bench-scale v i t r i f i c a t i o n of t h e elevated mercury s o i l , batches w e r e hea ted i n a 50 mL platinum c r u c i b l e t o a minimum of 69OoC and then t h e f i n a l product w a s t r a n s f e r r e d t o an alumina c r u c i b l e and melted i n a Lindberg high temperature furnace a t 135OOC. Due t o chemical hood space c o n s t r a i n t s and t h e desire not t o d r i l l a 2 i nch ho le i n t h e Lindberg furnace, ba tches were hea ted us ing t h e Thermolyne furnace and t h e offgas system u n t i l temperatures s u b s t a n t i a l l y above t h e mercury vapor p o i n t were achieved.

c I II

f

L

Thermowell for - Offgas Temperature Measurement

Top Portion of the Primary

Containment Vessel

N a 2 S Wasl Bottle -

Air In Bottom Portion of the Primary Containment

Vessel

NaOH Wasl Bottle L

I Platinum Crucible

of Feed

FIGURE 1 - MERCURY COLLECTION -OFFGAS SYSTEM

Three approximately 50 g r a m batches of t h e s a m e batch composition tested with t h e l o w mercury s o i l (ba tch 3) w e r e mixed. These ba tches contained 60 w t % of t h e e l eva ted mercury s o i l , 1 6 w t % CaC03, and 2 4 w t % N a 2 C 0 3 . Three sepa ra t e t r ia l s w e r e performed with t h e s e feeds, with two of t h e batches of feed ( T r i a l 2 and 3 ) conta in ing 500 ppm of C s and C e as r ad ioac t ive su r roga te s . I n each t r i a l , t h e ba tch w a s p laced i n a platinum c ruc ib l e , which w a s placed i n s i d e t h e qua r t z containment v e s s e l . The i n n e r containment s e c t i o n w a s p laced d i r e c t l y on t h e c ruc ib l e , where it a c t u a l l y overlapped t h e c r u c i b l e t o p by about a 1 / 4 inch. The vacuum and a i r were started and then t h e furnace w a s t u rned on. The furnace w a s hea ted a t a rate of approximately 10°C/min u n t i l it reached t h e temperatures shown i n Table 5. Once a t temperature, t h e temperature w a s maintained f o r 2 hours . A f t e r t h e 2 hours, t h e furnace was turned off and t h e system w a s allowed t o cool. During t h e heat-up, maintain temperature, and cool-down cyc les , t h e temperature of t h e furnace and t h e thermocouple i n t h e o f fgas l i n e w e r e recorded. Maximum recorded o f fgas l i n e temperatures w e r e 269OC. Once t h e furnace had cooled, t h e a i r and vacuum s u p p l i e s w e r e tu rned o f f .

The amounts and concent ra t ions of t h e wash b o t t l e s o l u t i o n s are also contained i n Table 5 . T r i a l 3 contained a s t r o n g e r concent ra t ion of Na2S i n an at tempt t o cap tu re more of t h e mercury. Samples of t h e two wash b o t t l e s w e r e t aken so t h e chemical c o n s t i t u e n t s could be analyzed.

TABLE 5 - PARAMETERS FOR THE ELEVATED MERCURY TRIALS

al 1 2 3

- - 1075OC 90 ml-2.5% Na2S 7 O O O C 70 ml-2.5% N a 2 S 69OOC 70 ml-5.0% Na2S

lm&&d& 90 ml-5% NaOH 70 ml-5% NaOH 70 ml-5% NaOH

The platinum c r u c i b l e s of feed f r o m each t r i a l w e r e removed from t h e mercury c o l l e c t i o n system i n t h e Thermolyne furnace and p laced i n a programmable Lindberg furnace and hea ted t o 135OOC. A f t e r 4 hours a t temperature, t h e c r u c i b l e s w e r e removed f r o m t h e oven and t h e glasses were a i r quenched t o room temperature .

Glass Analvseg

Once t h e glasses had cooled, t h e y w e r e broken o u t of t h e c r u c i b l e f o r chemical composition, phase assemblage, and d u r a b i l i t y determinat ions. All glasses were blue-green i n appearance with s m a l l amounts of unreacted Si02 a t t h e s u r f a c e . D u r a b i l i t y w a s determined i n a l k a l i n e and a c i d i c condi t ions us ing t h e PCT2 and TCLP4, r e s p e c t i v e l y . r e s u l t s w e r e compared a g a i n s t t h e EA g l a s s accepted va lues f o r HLW3, while t h e TCLP r e s u l t s were compared t o t h e more r e s t r i c t i v e of t h e TCLP l i m i t s , Resource Conservation and Recovery A c t (RCRA) Land Disposal L i m i t s , o r t h e Universal Treatment Standards (UTS).

The PCT

The chemical composition of t h e g l a s s e s produced f r o m each t r i a l are contained i n Table 6 . Compositions w e r e f a i r l y c o n s i s t e n t between each t r i a l , with t h e except ion of t h e C s 2 0 and CeO2, s i n c e t h e s e w e r e no t added t o t h e ba tch for t h e f irst t r i a l . G l a s s ana lyses r e s u l t s i nd ica t ed t h a t most of t h e C s 2 0 and C e 0 2 w a s encapsulated i n t h e g l a s s , which w a s shown by a comparison of t h e f eed and glass ana lyses r e s u l t s . For t r i a l #2, more C s 2 0 w a s a c t u a l l y found i n t h e glass, which w a s probably due t o incomplete mixing i n t h e feed sample analyzed. HgO concent ra t ions i n t h e feed f o r each t r i a l w e r e 0.055, 0.077, and 0.015 w t % r e spec t ive ly . For t h e f i n a l glass products , t h e HgO l e v e l s w e r e a t t h e de t ec t ion l i m i t s and w e r e roughly t h e same i r r e l e v a n t of t h e feed concent ra t ion l e v e l s . This w a s expected s i n c e t h e mercury v o l a t i l i z e d from t h e feed. produced and t h e r e s u l t s i n d i c a t e d t h a t t h e condi t ions w e r e ox id i z ing (average r a t i o w a s 0 .0494) .

The Fe2+/Fe3+ r a t i o w a s also measured f o r t h e g l a s s e s

Phase assemblage w a s determined us ing XRD and SEM analyses . I n a l l cases, t h e g l a s s e s w e r e amorphous when analyzed by XRD. SEM a n a l y s i s of t h e glasses confirmed t h e presence of s m a l l amounts of unreacted Si02. This Si02 would l i k e l y be f u l l y reacted a t elevated temperatures o r i n a melter environment due t o t h e mixing t h a t occurs .

The PCT w a s performed on t h e glasses f r o m each t r i a l . Normalized releases w e r e equiva len t t o t h e releases fo r t h e low mercury s o i l g l a s ses , which were b e t t e r t han t h e HLW EA PCT l i m i t s 3 . Glasses from t h e second and t h i r d t r i a l had minimal releases fo r C e and C s , which were t h e r ad ioac t ive su r roga te s .

TABLE 6 - GLASS COMPOSITIONS FOR THE MERCURY TRIALS (Wt%)

Trial #1 Glass

3.889 0.014 0.007

12.894 0 . 0 0 1 0.026 0.040

N/A 0.744 0.009

0.004 0.076 0.005

19.662 0.012 0.050 0 . 0 7 1 0.02

62.156 0.008 0.238 0 . 0 0 1 0.070

N/A

Trial #2 Glass

5.698 0.019 0.032

14.329 0.001 0.065 0.303 0.149 1.926 0.008

N/A 0.061 0.172 0.046

16.500 0.038 0.087 0.049 0.112

60.127 0.007 0.235 0.007 0.045

THREE ELEVATED

Trial #3 Glass

4.180 0 - 0 1 3 0.006

10.174 0.006 0.025 0.015 0.107 0.806 0.009 0 . 3 5 1 0.004 0 . 0 7 1 0.019

17.699 0 . 2 3 1 0.032 0.095 0.032

64.570 0.002 0.185 0.004 0.057

The TCLP w a s performed on t h e s e glasses because of t h e e l eva ted l e v e l s of mercury i n t h e feed. A s expected, mercury leaching w a s less than t h e de t ec t ion l i m i t of 0.008 ppm.

The aqueous products contained i n t h e wash b o t t l e s af ter t h e t h r e e t r i a l s were analyzed f o r chemical con ten t . Each s o l u t i o n w a s analyzed using I C P t o determine t h e major c a t i o n concentrat ions, A t o m i c Absorption (AA) t o determine t h e C s content , Ion Chromatogrophy ( I C ) t o determine t h e major anions p re sen t , and cold vapor techniques w e r e used t o determine t h e mercury con ten t . The components of each wash b o t t l e are contained i n Table 7.

Resul t s presented i n Table 7 i n d i c a t e d t h a t t h e mercury w a s not s u f f i c i e n t l y being captured and converted t o Hg2S as a n t i c i p a t e d . Total mercury captured for t h e t r ia l s w e r e 0.03%, 1.97%, and 0.09%. The second t r i a l captured t h e most mercury and it w a s t h e only s o l u t i o n which changed c o l o r s . The s o l u t i o n i n t h e Na2S b o t t l e exh ib i t ed a blue- green co lo r by t h e end of t h e t r i a l . The h igher concent ra t ion of Na2S i n t h e wash b o t t l e i n t h e t h i r d t r i a l d i d not seem t o he lp capture t h e mercury. Even though t h e Na2S wash bo t t l e w a s no t effective i n

TABLE 7 - OFFGAS SOLUTION CONCENTRATIONS (ppm)

ComPonent H g cs C e C a Zn Z r N a Sn B P S i

F luor ide Nitrate N i t r i t e S u l f a t e Chloride

I n i t i a l pH F i n a l pH

Trial #1

0.0523 0.0309 N/A N/A N/A N/A 0.541 0.603 C0.030 <0.300 0.195 <O. 500 9827.1 30101 1.293 4.335 0.911 2.689 2.235 12.636 39.539 21.363 433 331 <30 30 <20 2.19 306 171 <4 <4 9.83 13.14 12.53 12.09

u s NaOH Trial

-2s 6.8864 0.9001 <1.820 2.528 14.208 <O. 455 4368.9 1.448 <0.364 1.006 24.495 <4 2.24 <20 817 11.3 9.87 11.78

#2 NaOH 3.9318 0.1335 <1.820 0.843 5.207 <O. 455 27412 <O. 637 0.665

<o. 910 10.356 <4 2.68 <2 0 331 <4

12.33 13.59

Trial Kazs 0.0288 0.4302 <1.820 1.573 <O. 273 <O. 455 8759.6 11.291 X0.364 5.968 66.007 <2 17.1 <10 <5 2.91 12.22 10.36

#3 NaOH 0.0643 0.0768 K1.820 <o. 091 <O. 273 <O. 455 29546 0.983 0.615 1.302 10.879 <2 7.79 15.1 <5 9.74 13.59 12.38

captur ing t h e mercury, t h e NaOH b o t t l e w a s success fu l i n scrubbing the a c i d gases generated from t h e first bo t t l e which i s i n d i c a t e d by t h e genera l decrease i n t h e pH and t h e cap tu re of s u l f a t e .

In o rde r t o more e f f i c i e n t l y cap tu re t h e v o l a t i l i z e d mercury, t h e wash b o t t l e s w e r e rep laced with a mercury condenser. The s a m e g l a s s formulations and melt ing schedules w e r e used from t h e earlier tes ts . The r e s u l t i n g product w a s a homogeneous and durable g l a s s , with PCT r e s u l t s similar t o t h e o t h e r e l eva ted mercury s o i l g l a s s e s . A l m o s t a l l of t h e v o l a t i l i z e d mercury w a s cap tured and condensed. A f t e r condensation of t h e mercury, it w a s t r e a t e d on a mercury s p e c i f i c ion exchange r e s i n . This r e s i n incorpora ted t h e mercury so it d i d not leach f r o m t h e r e s i n when sub jec t ed t o t h e TCLP.

CONCLUSIONS

Crucibles s t u d i e s with mercury contaminated SRS s o i l have shown t h a t t h e s o i l can be converted t o a durable , l each r e s i s t a n t glass w a s t e f o r m . Optimum waste loading w a s determined t o be 60 w t % wi th 24 w t % Na2C03 and 16 w t % CaC03 used as t h e glass forming a d d i t i v e s . Attempts t o cap tu re and convert t h e v o l a t i l i z e d mercury i n t o stable Hg2S w e r e no t as success fu l . Only 2% of t h e t o t a l mercury w a s captured i n t h e offgas system. However, it w a s shown t h a t by us ing convent ional condensers, mercury could be s u c c e s s f u l l y captured i n t h e o f fgas system and later converted t o a leach r e s i s t a n t form.

_I_ . . .

ACKNOWLEDGEMENTS

Funding f o r t h i s research and d e v e l o p m e n t w o r k w a s provided by the Department of E n e r g y - O f f i c e of Technology Development under t he auspices of t h e Mixed Waste Focus A r e a and Technical T a s k P l a n SR1-3-20- 0 4 and contract N o . DE-AC09-89SR18035 w i t h t h e U . S . Department of E n e r g y .

REFERENCES

1. C.A. CICERO, D . F . BICKFORD, and W.O. CREWS, " D e f i n i n g t h e G l a s s C o m p o s i t i o n L i m i t s f o r S R S C o n t a m i n a t e d Soi l s" , WSRC-MS-95-0184, Westinghouse Savannah R i v e r C o m p a n y ( A u g u s t 1 9 9 5 ) .

2 . C.M. JANTZEN, N .E . BIBLER, D.C. BEAM, and W.G. RAMSEY, " N u c l e a r Waste Product C o n s i s t e n c y T e s t (PCT) - V e r s i o n 7 . 0 , " WSRC-TR-90-539, R e v . 3, Westinghouse Savannah R i v e r Company , ( A p r i l 1 9 9 4 ) .

3. C.M. JANTZEN, N . E . BIBLER, D.C. BEAM, C . L . CRAWFORD, and M.A. PICKETT, " C h a r a c t e r i z a t i o n of t he D e f e n s e Waste Processing F a c i l i t y (DWPF) E n v i r o n m e n t a l A s s e s s m e n t (EA) G l a s s Standard R e f e r e n c e Material,

WSRC-TR-92-346, R e v . 1, Westinghouse Savannah R i v e r C o m p a n y ( June 1 9 9 3 ) .

4 . 4 0 CFR 2 6 1 A p p . 11, "Method 1131 T o x i c i t y C h a r a c t e r i s t i c L e a c h i n g Procedure ( T C L P ) , " pages 6 6 - 8 1 , R e v i s e d 7 / 1 / 9 1 .