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Preliminary Studies of Tank Fill Materials

for Radioactive Waste Management at

Hanford and Savannah River

Authors: Ms.Gaelle Belot, Drs. Yun Bao and Michael W. Grutzeck

The Pennsylvania State University

University Park, PA 16802

Prepared under the auspices of Grant No. DE-FG02-05ER63966-

January 30, 2006

Introduction

The U.S. Department of Energy has been working on ways to reduce/eliminate its

inventory of radioactive waste. It is planning to process all of its waste and dispose of it as a

solid in an appropriate national repository or on-site engineered land fill. It is currently in the

process of cleaning up two major sites: Savannah River and Hanford. These sites collectively are

the custodians of 80 million gallons of radioactive waste stored in million gallon underground

tanks. The majority of this waste has been in storage for 50 years so that it is relatively low

activity waste. For the most part the waste consists a highly alkaline liquid (supernate) and a

small amount of insoluble sludge which has settled to the bottom of the tank. Because of the

potential hazards associated with leaks, the DOE is actively converting the liquid waste and the

sludge into solid waste forms. Vitrification of the sludge is underway at Savannah River and a

glass melter is being built at Hanford. The supernate is extremely voluminous and it would be

impossible to convert it to glass in a timely fashion using the existing/proposed melters. Thus

alternates have been adopted by Savannah River (solidification of a Cs/Sr-free supernate with a

blended pozzolanic Portland cement to form Saltcrete) and are being evaluated by Hanford (bulk

vitrification in a disposable melter) in order to speed up the clean up process.

As the clean up continues and finally ends, the DOE will have an inventory of empty

underground tanks to deal with. Washington and South Carolina both require that the tanks be

filled with some type of cementitious solid that will prevent subsidence once the tanks rust away.

The current choice of tank fill material is a variant of a basic Portland cement concrete. Concrete

is one of the World’s most ubiquitous materials, having been used to fill almost every and any

underground opening including oil wells, gasoline tanks, oil tanks, subway tunnels, water wells,

and abandoned mines. But as is the case with all materials some applications are better suited for

its use than others. DOE’s waste tanks will contain traces of radioactive substances that are

tightly cemented to the bottom and edges of the tanks. These are usually insoluble sodium

silicates, sodium salts and sludge that can not be removed using tank washing techniques.

Legislation has been passed by Washington State that will allow contractors to dispose of this

waste in situ in the tank. This waste is called residual waste. It is well known that Portland

cement is unable to host alkalis and therefore Portland cement concrete would not “protect” the

environment from residual materials after tanks have rusted away. In this case it is proposed that

an alternate concrete based on a hydroceramic binder (metakaolin/fly ash plus NaOH would be a

better choice.

The proposed hydroceramic concrete can be mixed and placed much the same as Portland

cement concrete, but in addition to filling space the hydroceramic concrete also has the ability to

absorb/chemically attract the remaining sludge and the soluble alkaline/alkaline earth ions

present in the empty tanks. The work reported below, provides a summary of preliminary work

undertaken in order to explore the potential of formulating hydroceramic equivalent concretes

that set up at room temperature and at the same time contain zeolites that able to adsorb and react

with residual waste ions. Three tasks are summarized: formulation of binders able to set up at

room temperature, the development and testing of two equivalent concretes, and the ability of

selected formulations to cation exchange with dilute CsCl solutions.

Formulations

Zeolites are a group of minerals that have a microporous crystalline structure. They

consist of networks of hydrous sodium aluminum silicates that typically enclose cations such as

sodium, potassium and/or calcium that are able to engage in cation exchange with a variety of

monovalent and divalent cations many of which are toxic. Zeolites are commonly found in

nature as hard well cemented deposits, but they can also be synthesized

(http://www.bza.org/zeolites.html) usually in the form of a very fine powder. What is tricky in

the current application is the requirement that the tank fill material form a hard concrete-like

substance that will set up in the tank and form a stable monolith and at the same time to be able

to adsorb residuals immediately or in the future when the tank has rusted away.

Previous Work

Hydroceramics have been developed as part of the current DOE grant. Here we try to

reformulate these to set up at room temperature. Two accelerators were evaluated: sodium

silicate (PQ Type D) and a Class C fly ash/dry FGD (flue gas desulfurization) material from

Xcel’s Sherco plant. In addition two conventional starting materials heretofore used in all of our

work were also used: Class F fly ash from the Ft. Martin power plant (part of Allegheny Energy)

and metakaolin produced in-house from Troy clay mined near Troy Idaho. The nominal

composition of metakaolin clay and Class F fly ash is: Al2Si2O7. The metakaolin was made from

kaolin clay by firing it in a rotary kiln at 700°C for a few hours. The Class F fly ash consists of

very fine spherical particles of partially devitrified glass derived from the combustion of

bituminous coal. Both contain a high level of silica which is ultimately responsible for stronger

chemical bonds. Moreover, working with fly ash and/or metakaolin produces less carbon dioxide

vis à vis Portland cement which is ultimately beneficial for the environment. In addition to fly

ash and metakaolinite, concentrated sodium hydroxide solutions and/or sodium silicate and/or

Class C FGD were also used to create an alkali medium which activated the chemical process.

Chemical analyses of the starting materials are given in Table 1.

Table 1. Chemical Composition of Starting Materials (wt%)

Oxide Ft. Martin Sherco Troy metakaolin

Al2O3 13.5 13.8 36.6

B2O3 0.03 0.37 nd

BaO 0.05 0.48 0.04

CaO 3.73 30 0.82

Fe2O3 14.5 4.82 1.57

K2O 1.32 0.71 0.67

MgO 0.37 2.85 0.26

MnO 0.03 0.10 0.01

Na2O 0.78 1.92 0.07

SiO2 60 30 54.6

SrO 0.07 0.58 0.01

TiO2 1.47 0.76 1.30

Sulfite as SO2 <0.01 4.43 nd Sulfate as SO3 0.97 4.64 nd

LOI (90°C) nd nd 2.07

Total 98.0 98.3 98.0

Nd=not determined

Methods

Different mixtures of metakaolin, Class F and Class C FGD1 fly ash and sodium

hydroxide were prepared and placed in 2 inch cube molds. Metakaolin was mixed with fly ash at

different ratios. Class F fly ash from the Ft. Martin power plant (25, 40, 50, 60 and 75 weight %)

1 FGD: Flue Gas Desulfurization product. The Class C fly ash is calcium rich and is used to “scrub” the fine gases of

power plants burning.

was dry blended with metakaolin (75, 60, 50, 40 and 25 weight %). Class F fly ash was also

blended with Class C FGD fly ash from the Sherco power plant at a 1 to 1 ratio. Sodium

hydroxide with a molarity of 5 or 8, sometimes 15 M was added to the metakaolin and the fly

ash in a Hobart mixer and mixed until the mixture resembled a barely/not pourable thick putty-

like paste. Sodium silicate or sodium aluminate was sometimes added to the mixture to study and

analyze their effects on reactivity and the resulting compressive strength and amount of zeolite in

the mixtures. These samples were cured in the molds covered with a glass plate of thickness of

about 1 cm either at room temperature or at 40°C. The copper molds were placed in shallow

plastic containers fitted with air-tight covers. Water was poured around the copper molds to

maintain saturated (~100%) relative humidity. These conditions were used to simulate the

environment in which the tank fill materials would be exposed to in the empty radioactive waste

tanks. Tables 2-5 summarize the different mixtures that were made.

Table 2. Formulas Used for Samples made from 07/19/05 to 08/11/05

*Sherco ash is from Northern States Power’s Sherburne Co. Unit 3 generating station.. **Ft Martin Class F ash is from Allegheny Energy’s Ft Martin generating station. ***Returns are previously formulated samples that were not cured. They are a considerable source of savings. ****The number indicates which samples were recycled


Date mix was made 08/25/05 08/25/05 08/26/05 08/30/05 08/31/05 08/31/05 09/02/05

Wt% fly ash 50 50 50 100 100 100 75

Sherco fly ash (g)* 500g 500g - - 600g 600g -

Ft Martin fly ash (g)** - - 600g 1410.3g 600g 600g 900g

Troy metakaolin (g) 500g 500g 600g -- -- -- 300g

NaOH (g) & molarity 598.2 15 446 8 605 8 539.5 8 594.9 5 676 8 577.7 8

Sodium silicate (g) -

Sodium aluminate (g) -

Quartz sand (g) -

Phillipsite (g) -

Water (g) -

Returns (g)*** -

Comments**** very thick mix

hardened quickly

very slow curing

mix hardened

*Same as Table 2.

Date mix was made 07/19/05 07/21/05 07/21/05 07/26/05 08/08/05 08/10/05 08/11/05

Wt% fly ash

Sherco fly ash (g)* - - - - - - -

Ft Martin fly ash** - - - - - - -

Troy metakaolin (g) 900 800 360 700 630 855 855

NaOH (g) & molarity 837.9 12 710.3 10 772.1 533.9 10 480.5 10 796 12 796 12

Sodium Silicate (g) 100 200 - 300 270 95 95


Quartz sand (g) 1100

Phillipsite (g) 100

Water (g) 117.7 155.4 83.9 11.8

Returns (g)*** 50 50

Comments**** 071905#2 071905#2


Date mix was made 09/07/05 09/08/05 09/12/05 09/12/05 09/15/05 09/15/05 09/20/05

Wt% fly ash 50 60 40 40 25 12500 60

Sherco fly ash (g)* -- -- -- - -- -- -

Ft Martin fly ash (g)** 600 720 480 480 300 300 720

Troy metakaolin (g) 600g 480g 720g 720g 900g 900g 480g

NaOH (g) & molarity 711.5 8 671.8 8 763.2 8 719.7 5 849 5 879.8 8 660.7 5

Sodium silicate (g) -


Quartz sand (g) -

Phillipsite (g) -

Water (g) -

Returns (g)*** -

Comments**** *Same as Table 2. Table 5. Formulas Used for Samples made from 10/03/05 to 10/14/05

Date mix was made 10/03/05 10/05/05 10/14/05 10/14/05

% fly ash 75 50 50 50

Sherco fly ash (g)* -- -- -- -

Ft Martin fly ash (g)** 975g 600g 600g 600g

Troy metakaolin (g) 315g 540g 540g 600g

NaOH (g) & molarity 624.3 5 677.7 5 674 5 781.6 8

Sodium silicate (g) 60g -

Sodium aluminate (g) 60 60

Quartz sand (g) -

Phillipsite (g) -

Water (g) -

Returns (g)*** -

Comments**** substituted 60 mk by na-

silicate

substituted 60 mk by na-

aluminate

mk increased to 600 from

540 *Same as Table 2.

Their compressive strengths were tested at 7 day intervals up to three times. Their mass

was also recorded in order to monitor the rate at which water would evaporate from the samples.

The samples were examined using X-ray diffraction in order to evaluate the quantity of zeolites

that formed in each sample. Those samples with the highest compressive strength that also

contained some crystalline zeolites were made again, but this time they were cast in 1x1x11.5

inch bar molds in order to measure the expansion or contraction of the mixture after curing. The

length comparator as described in ASTM-C 490 was used for that purpose.

Results The tables below represent a summary of the data obtained during the study. Tables 6

through 12 summarize the compressive strength and the mass obtained for the samples analyzed

for tank fill materials purposes as a function of time and curing temperature. Tables 6-9 present

the findings in chronologic order and therefore closely parallel the mixes reported earlier as per

their mixing date. Tables 10-12 have been tabulated using these same data, but now are arranged

as a function of the type of fly ash used (Ft. Martin Figures 10-11) and Sherco (Figure 12) plus

the molarity of NaOH used as mixing solution. In each case samples were mixed in a Hobart-

type mixer, molded in 2” cube molds, demolded when hard (time varied from one to more than 7

days), and then cured for additional periods of time at room temperature (RT) or 40°C.

Table 6- Compressive Strength and Weight obtained by Date (08/25/05 to 08/31/05)

*Samples were covered with a glass plate and cured in covered plastic containers. It is assumed that the RH ~ 100.

Table 7- Compressive strength and Weight obtained- by Date (09/02/05 to 09/12/05)

Formulation ID 9/2/2005 9/7/2005 9/8/2005 9/12/2005 9/12/2005

Wt% fly ash 75 50 60 40 40

Ft Martin fly ash (g) 900 600 720 480 480

Troy metakaolin (g) 300 600 480 720 720

NaOH (g) & molarity 577.7 8M 711.5 8M 671.8 8M 763.2 8M 719.7 5M

Curing conditions* RT 40°C RT 40°C RT 40°C RT 40°C RT 40°C

cured 2 days hard hard hard hard soft soft soft soft soft soft

Sample mass (g) 246.2 245.6 242.3 208.6

Sample density (g/cm

3) 1.88 1.87 1.85 1.59

Force (lbs) 260 2720 520 1860

Compressive strength (psi) 65 680 130 465

cured 7 days hard hard hard hard hard hard hard hard hard hard

Sample mass (g) 244 208.5 240.4 202.1 241.2 234 240.5 189.3 222.5 189.3

Density g/cm3 1.86 1.59 1.83 1.54 1.84 1.78 1.83 1.44 1.70 1.44

Force(lbs) 500 6000 740 3440 400 4180 700 1140 240 120

Compressive strength (psi) 125 1500 185 860 100 1045 175 285 60 30


Sample mass (g) 243.3 233.6 237.8 235.1 242.3 206.1 240.4 191.7 228 172.7


3) 1.86 1.78 1.81 1.79 1.85 1.57 1.83 1.46 1.74 1.32

Formulation ID 8/25/2005 8/25/2006 8/26/2005 8/31/2005 8/31/2005

Wt% fly ash 50 50 50 100 100

Sherco fly ash (g) 500g 500 600 600 600

Ft Martin fly ash (g) -- -- -- 600 600

Troy metakaolin (g) 500 500 600 -- --

NaOH (g) 598.2 15 M 446 8 M 605 8 M 676 8 M 594.9 5 M



Sample mass (g) 252 252 248.4 206.8 238.3 243.2 242.4 241.78 239.28 240.13


3) 1.92 1.92 1.89 1.58 1.82 1.86 1.85 1.84 1.83 1.83

Force (lbs) 5840 13500 1180 12840 620 5680 540 1340 2600 5240



Sample mass (g) 252.56 246.62 251.34 223.72 248.83 234.02 248.74 241.32 242.11 241.34


3) 1.93 1.88 1.92 1.71 1.90 1.79 1.90 1.84 1.85 1.84

Force(lbs) 16420 18130 2000 14240 990 12900 620 8150 3880 5460

Compressive strength (psi) 4105 4532.5 500 3560 247.5 3225 155 2037.5 970 1365


Sample mass (g) 253 248.1 251.8 209.7 252.2 228.5 248.9 237.8 241.3 235.3


3) 1.93 1.89 1.92 1.60 1.92 1.74 1.90 1.81 1.84 1.79

Force (lbs) 18820 17220 2600 12340 1180 13700 2640 11860 6740 10050

Compressive strength (psi) 4705 4305 650 3085 295 3425 660 2965 1685 2512.5

Force (lbs) 2760 4070 1070 3160 780 8710 920 760 180 60

Compressive strength (psi) 690 1017.5 267.5 790 195 2177.5 230 190 45 15

cured 28 days NA** NA NA NA hard hard hard hard hard hard

Sample mass (g) 245.5 219.1 240.2 235 228.1 225.7


3) 1.87 1.67 1.83 1.79 1.74 1.74

Force 6240 10440 1420 1580 280 180

Compressive strength (psi) 1560 2610 355 395 70 45


**NA indicates that no samples were tested under these conditions.

Table 8- Compressive Strength and Weight obtained- by Date (09/15/05 to 10/03/05)

Formulation ID 9/15/05 9/15/05 9/20/05 10/03/05

Wt% fly ash 25 25 60 75

Ft Martin fly ash (g) 300 FM 300 FM 720 FM 975 FM

Troy metakaolin (g) 900 900 480 315

NaOH (g) 849g 5M 879.8g 8M 660.7g 5M 624.3g 5M

Sodium silicate (g) -- -- -- --

Curing conditions* RT 40°C RT 40°C RT 40°C RT 40°C

cured 2 days soft soft soft soft soft soft soft soft

Sample Mass (g)


3)

Force (lbs)

Compressive strength (psi)

cured 7 days soft hard hard hard soft soft soft soft

Sample mass (g) 197.3 235.8 223.5


3) 1.50 1.80 1.70

Force(lbs) 140 600 1400

Compressive strength (psi) 35 150 350

cured 14 days soft hard hard hard hard hard soft soft

Sample mass (g) 199.03 231.93 199.44 232.9 232.1


3) 1.52 1.77 1.52 1.78 1.77

Force (lbs) 1120 760 1070 100 540

Compressive strength (psi) 280 190 267.5 25 135

cured 28 days hard hard hard hard hard hard hard hard

Sample mass (g) 221.2 163.41 232.5 164.8 234.1 189 241.5 185.2


3) 1.69 1.25 1.78 1.26 1.79 1.44 1.84 1.41

Force (lbs) 160 120 1160 180 200 600 170 2000

Compressive strength (psi) 40 30 290 45 50 150 42.5 500

cured 35 days NA** NA NA NA hard hard

Sample mass of (g) 242.9 205.5


3) 1.86 1.57

Force (lbs) 940 1420

Compressive strength (psi) 235 355

cured 49 days hard hard

Sample mass of (g) 236.8 187.2

Sample density 1.81 1.43

(g/cm3)

Force (lbs) 380 540




Table 9- Compressive Strength and Weight obtained- by Date (10/03/05 to 10/14/05)

Formulation ID 10/03/05 10/05/05 10/14/2005 10/14/2005

Wt% fly ash (%) 75 50 50 50

Ft Martin fly ash (g) 975 600 600 600


NaOH (g) & molarity 624.3 5M 677.7 5M 674 5M 781.6 8M

Sodium aluminate (g)* -- -- 60 60

Sodium silicate (g)** -- 60 -- --

Curing conditions*** RT 40°C RT 40°C RT 40°C RT 40°C


Sample mass (g)

Sample density of (g/cm

3)

Force (lbs)

Compressive strength(psi)


Sample mass (g)


3)

Force(lbs)

Compressive strength(psi)

cured 17 days soft soft hard hard hard hard hard hard

Sample Mass (g) 233.5 234.5 233.1 218 233.2 230.8


3) 1.78 1.79 1.78 1.66 1.78 1.76

Force(lbs) 180 300 50 630 2960 8790

Compressive strength(psi) 45 75 12.5 157.5 740 2197.5

cured 28 days hard hard hard hard hard cracked hard hard

Sample mass (g) 241.5 185.2 235.12 183.57 229.7 237.9 218.3


3) 1.84 1.41 1.8 1.4 1.75 1.82 1.67

Force(lbs) 170 2000 160 350 940 2800 9510

Compressive strength(psi) 42.5 500 40 87.5 235 700 2377.5

cured 35 days hard hard hard hard NA**** NA NA NA

Sample mass (g) 242.9 205.5 210 238.9


3) 1.86 1.57 1.6 1.82

Force(lbs) 940 1420 140 420


After 50 days cracked cracked weaker weaker

*Liquid sodium silicate from PQ Corporation-----

**Reagent grade NaAlO2

***Samples were covered with a glass plate and cured in covered plastic containers. It is assumed that the RH ~100.

****NA indicates that no samples were tested under these conditions.

After 14 days of curing, the compressive strength for the samples (Figures 10-12) was

observed to fall between 190 and 2000 psi, between 30 and 150 psi, and between 2000 and 4700

psi when samples were made with 8M NaOH, 5M NaOH and Sherco fly ash, respectively. The

mass of the samples were recorded and were observed to range from 200 to 240 grams.

Table 10. Comparison of Samples Based on the Percentage of Fort Martin Fly Ash (8M NaOH)

Formulation ID 9/15/2005 9/13/2005 9/7/2005 9/8/2005 9/2/2005

Wt% fly ash 25 40 50 60 75


Troy metakaolin (g) 900 720 600 480 300

NaOH (g) & molarity 879.8 763.2 711.5 671.8 577.7


cured 2 days soft soft soft soft hard hard soft soft hard hard

Sample mass of (g) 242.3 208.6 246.2 245.6


3) 1.85 1.59 1.88 1.87

Force (lbs) 520 1860 260 2720



Sample Mass (g) 235.8 223.5 240.52 189.29 240.48 202.1 241.2 234 244 208.5


3) 1.80 1.70 1.83 1.44 1.83 1.54 1.84 1.78 1.86 1.59

Force (lbs) 600 1400 700 1140 740 3440 400 4180 500 6000



Sample mass of (g) 231.93 199.44 240.4 191.7 237.8 235.1 242.3 206.1 243.33 233.65


3) 1.77 1.52 1.83 1.46 1.81 1.79 1.85 1.57 1.86 1.78

force(lbs) 760 1070 920 760 1070 3160 780 8710 2760 4070

Compressive strength (psi) 190 267.5 230 190 267.5 790 195 2177.5 690 1017.5

cured 28 days NA** NA hard hard NA NA hard hard NA NA

Sample mass (g) 240.2 235 245.5 219.1


3) 1.83 1.79 1.87 1.67

Force 1420 1580 6240 10440




Table 11. Comparison of Samples Based on the Percentage of Fort Martin fly ash (5M NaOH)

Formulation ID 9/15/2005 9/12/2005 9/20/2005 10/3/2005

Wt% fly ash 25 40 60 75

Ft Martin fly ash (g) 300 480 720 975


NaOH (g) & molarity 849 719.7 660.7 624.3

Curing conditions* RT 40°C RT 40°C RT 40°C RT 40°C


Sample mass (g)

Sample density (g/cm3)

Force (lbs)

Compressive strength (psi)

cured 7 days soft hard hard hard soft soft soft soft

Sample mass (g) 197.3 222.5 189.29


3) 1.50 1.70 1.44

Force(lbs) 140 240 120

Compressive strength (psi) 35 60 30

cured 14 days soft hard hard hard hard hard soft soft

Sample mass (g) 199.03 228 172.7 232.9 232.1

Sample density (g/cm3) 1.52 1.74 1.32 1.78 1.77

Force (lbs) 1120 180 60 100 540

Compressive strength (psi) 280 45 15 25 135

cured 28 days hard hard hard hard hard hard hard hard

Sample mass (g) 221.2 163.41 228.1 225.7 234.1 189 241.5 185.2

Sample density (g/cm3) 1.69 1.25 1.74 1.74 1.79 1.44 1.84 1.41

Force (lbs) 160 120 280 180 200 600 170 2000

Compressive strength (psi) 40 30 70 45 50 150 42.5 500

cured 35 days NA** NA NA NA hard hard

Sample mass (g) 242.9 205.5

Sample density (g/cm3) 1.86 1.57

Force (lbs) 940 1420


cured 49 days hard*** hard***

Sample mass (g) 236.8 187.2

Sample density (g/cm3) 1.81 1.43

Force (lbs) 380 540




Table 12. Comparison of Samples Based on the Percentage of Sherco fly ash

Formulation ID 8/25/2005 8/25/2006 8/20/2005 8/31/2005 8/31/2005

Wt% fly ash 50 50 50 100 100


Sherco fly ash (g) -- -- -- 600 600

Troy metakaolin (g) 500 500 600 -- --

NaOH (g) & molarity 598.2 15 M 446 8 M 605 8 M 676 8 M 594.9 5 M



Sample mass (g) 252 252 248.4 206.8 238.3 243.2 242.4 241.78 239.28 240.13


3) 1.92 1.92 1.89 1.58 1.82 1.86 1.85 1.84 1.83 1.83

Force (lbs) 5840 13500 1180 12840 620 5680 540 1340 2600 5240



Sample mass(g) 252.6 246.6 251.3 223.7 248.8 234.0 248.7 241.3 242.1 241.3


3) 1.93 1.88 1.92 1.71 1.90 1.79 1.90 1.84 1.85 1.84

Force(lbs) 16420 18130 2000 14240 990 12900 620 8150 3880 5460

Compressive strength (psi) 4105 4532.5 500 3560 247.5 3225 155 2037.5 970 1365


Mass of sample(g) 253 248.1 251.8 209.7 252.2 228.5 248.9 237.8 241.3 235.3


3) 1.93 1.89 1.92 1.60 1.92 1.74 1.90 1.81 1.84 1.79

Force (lbs) 18820 17220 2600 12340 1180 13700 2640 11860 6740 10050

Compressive strength (psi) 4705 4305 650 3085 295 3425 660 2965 1685 2512.5


X-ray Diffraction Results

Generally, the X-ray diffraction patterns for the samples revealed that zeolites were

forming in a small percentage of the samples. However, those samples made with 8 molar versus

4 molar NaOH were stronger and contained more zeolites. The zeolites in these samples were

either faujasite-like, having a variant of the general formula (Na2CaMg3.5)[Al7Si17O48]·32H2O, or

a variant on Zeolite A having a composition similar to Na12Al12Si12O48·27H2O. In addition to

zeolites other compounds such as hydroxysodalite (Na8[AlSiO4]6(OH)2) formed early in the

hydration process. Residual quartz (SiO2) and mullite (3Al2O3·2SiO2) were also present in most

cases. The glass in the fly ash was the most reactive substance present. The alkalinity was not

high enough in most cases to consume the quartz and mullite. The X-ray diffraction patterns for

our “best mixes” are reproduced as Figures 12 through 18 below.

Sherco Samples

The sample made on August 26th

, 2005, consisted of 600g of Class C Sherco FGD fly ash,

600g of Troy metakaolinite and 605g of 8M NaOH. It was X-rayed after 14 days of curing at

room temperature. See Figure 12. The X-ray pattern revealed that it contained quartz, which is

an impurity present in the fly ash which did not react. It also contained a fair amount of

portlandite (Ca(OH)2). It contained an insignificant amount of sodium aluminum silicate hydrate

(a zeolite with a Zeolite A structure) and calcium aluminum oxide carbonate hydrate (a

cementitious phase normally associated with hydration of calcium aluminate cements). The

pronounced “hump” in the pattern (black curve at bottom) suggests that the majority of the

glassy portion of the fly ash did not react under these conditions. The total counts are also very

low, again suggesting little if any reaction. There is, however, a noted bimodality to the X-ray

amorphous hump. The glass itself usually has a median value of approximately 21-28°2θ. The

development of a second hump at 31°2θ indicates the formation of complex silicate structures

associated with Portland cements (calcium aluminate hydrate, a.k.a. C-S-H). The X-ray of a

August 26th

companion sample cured at 40°C after 14 days (see Figure 13) revealed that it also

contained quartz. However reactivity was a bit more advanced at the higher temperature. The

sample also contained a faujasite-like zeolite. Although neither of the two samples developed

very much crystallinity, they were among the strongest formulations tested so far.

Ft Martin Samples

The sample made on September 2nd

was composed of 75% Class F Ft. Martin fly ash

(900 g), 25% Troy metakaolinite (300 g) and 578 g 8M NaOH. The sample was mixed and cured

at RT and 40°C. After 7 days of curing at room temperature it was X-rayed. The X- ray

diffraction pattern of the RT sample revealed that it contained only quartz and mullite; both are

impurities found in fly ash which had not reacted (Figure 14). It contained little else, i.e. no

zeolites. The plot also shows that the fly ash had not reacted completely because the sample still

contains a large amount of quartz and mullite and there is still a big amorphous hump due to the

presence of glassy material (black curve at bottom of the graph).

Figure 12- X-ray of sample made on August 26

th, 2005 after 14 days of curing at room temperature.

Q=quartz, P=portlandite, CAH=4CaO·Al2O3·12H2O·7CO2, SAS = sodium aluminum silicate hydrate

Figure 13- X-ray of sample made on August 26

th, 2005 after 14 days of curing at 40

oC.

Q=quartz, F= faujasite

CAH P

CAH

P

Q

SAS

Q

Q

F

F

Figure 14- X-ray of sample made on September 2nd

, 2005 after 7 days of curing at room temperature.

Q=quartz, M= mullite, F= faujasite

Figure 15- x-ray of sample made on September 2

nd, 2005 after 7 days of curing at 40

oC.

Q=quartz, M=mullite, HS=hydroxysodalite.

Q

M Q

M

M M

M

M

M

M M FQ

M

HS

M

M

M

HS

Figure 16- X-ray of sample made on September 2

nd, 2005 after 14 days of curing at 40

oC.

Q= quartz, M= mullite, A=zeolite A, F=faujasite

The X-ray pattern taken for the sample after 7 days of curing at 40°C showed the

presence of quartz and mullite. It contained what seems to be a small amount of hydroxysodalite

(Na6Al6Si6O24·8H2O) (Figure 15). The 40°C sample was decidedly stronger, albeit not noticeably

different in phase composition from its RT cured counterpart. However, after 14 days, the X-ray

pattern for the sample cured at 40°C showed even a higher percentage of zeolite in addition to

the presence of quartz and mullite. It contained a large amount of faujasite as well as zeolite A.

(Figure 16). It is interesting that the initially formed hydroxysodalite has been replaced by a

combination of faujasite-like and zeolite A structured zeolites at 14 days.

The sample made on September 7th

was composed of 50% Fort Martin fly ash (600 g),

50% Troy metakaolinite (600 g) and 712 g 8M NaOH. It was cured at RT and 40°C and was X-

rayed after 14 days of curing at 40oC. The X-ray pattern (Figure 17) revealed that it contained

quartz as well as mullite mixed with an abundance of zeolites having the Zeolite A and faujasite

structure.

The sample made on September 8th

, was composed of 60% Fort Martin fly ash (720 g),

40% Troy metakaolinite (480 g) and 672 g 8M NaOH. After curing at 40°C for 7 days it was X-

rayed. The X-ray pattern showed that it contained some zeolite in addition to quartz (see Figure

18). This sample also was among the strongest. There is a notable hump but both zeolites are

also very well crystallized.

M

F

M

M

M

M

F

F F F F

F

A

A A

FF

F

A A A

A

A



oC.

F=faujasite/zeolite X, Q= quartz, M= mullite, A=zeolite A



oC

F=faujasite, Q= quartz, A=zeolite A

Q

F

M

M M

M

M

A

Q

A

M

F

F

F F

FF

Q

Discussion

The tables in the result section summarize the results obtained, the compressive strength

measured, the mass and the density computed for each of the samples prepared for the tank fill

materials study. Generally, no direct correlation was found between the density calculated and

the compressive strength of the samples. However, it was evident that the compressive strength

of the samples were relatively strong based on the amount of fly ash used, its type, i.e. Class C

Sherco or Class F Fort Martin, and the ratio fly ash to other components such as Troy metakaolin

used to prepare the samples. Also, the curing temperature determined how quickly the samples

would reach a certain level of compressive strength. The molarity of the sodium hydroxide had

also an effect on the strength. Higher molarities often led to higher degrees of crystallinity and

strength.

Samples made with 5M NaOH

Cube samples were made from Fort Martin fly ash, metakaolinite and 5M sodium

hydroxide (NaOH). See Table 11. In general, the samples cured at 40°C were stronger than the

ones cured at room temperature when tested at the same age. The samples containing 75% of

Fort Martin fly ash that were cured at 40°C were the strongest with a compressive strength of

500 psi. However, a steady increase in compressive strength over time was not observed for

these samples. Instead, after 28 days, they became weaker: e.g. after 35 days the observed

compressive strength was 355 psi and the samples broke on their own accord after 50 days of

curing. Expansion was clearly active in these samples. In general, samples made with 5M NaOH

didn’t reach strength higher than 150 psi after 28 days. These data are summarized in Figures 19

and 20 given below and again in Figure 21 where all the data are represented on a single plot.

Given these results it seems prudent to select the 75wt% Ft. Martin fly ash/25wt% metakaolin

sample as the one most likely to provide strength and performance needed once scaled up to a

concrete.

Figure 19- Comparison of samples based on the Figure 20- Comparison of samples based on the

percentage of Class F fly ash cured at RT (5M NaOH) percentage of Class F fly ash cured at 40C (5M NaOH)

Another sample made on 10/05/05 containing a 50:50 mix of Ft. Martin fly ash:Troy

metakaolin with 60g of sodium silicate as a replacement for 60 g of metakaolin was mixed and

tested as the sample above. Sodium silicate often accelerates a sample’s rate of hardening. In this

instance performance suffered rather than improved. After curing for 14 days, the samples had

compressive strengths of 45 and 75 psi. However, the samples cured at room temperature got

weaker in general while the ones cured at 40°C got stronger and reached up to 105 psi at 35 days.

See Figure 22. However, all of the samples got weaker after 50 days

Comparison of samples based on

percentage of Class F Fort Martin fly ash

cured at room temperature (5M NaOH)

0

50

100

150

200

250

0 7 14 21 28 35

Time (days)

Co

mp

ressiv

e

Str

en

gth

(p

si)

25% classF RT

40% classF RT

60% classF RT

75% classF RT

Comparison of samples based on the

percentage of Class F Fort Martin fly

ash cured at 40C (5M NaOH)

0

200

400

600

0 7 14 21 28 35

Time (days)

Co

mp

ressiv

e

Str

en

gth

(p

si)

25% classF40C

40% classF 40C

60% classF 40C

75% classF 40C


percentage of Class F Fort Martin fly

ash (5M NaOH)

0

200

400

600

7 14 28 35

Time (days)

Com

pre

ssiv

e

Str

ength

(psi) 25% classF RT

25% classF40C

40% classF RT

40% classF 40C

60% classF RT

60% classF 40C

75% classF RT

75% classF 40C

Figure 21- Summary of CS behavior of samples based on the percentage of Class F fly ash cured at room

temperature and 40°C (5M NaOH)

Figure 22- Graph of samples containing sodium silicate cured at room temperature and 40C (5M NaOH).

In a similar vein, the samples containing 60 g sodium aluminate (NaAlO2), a replacement

for 60 g metakaolinite, mixed with 5 M sodium hydroxide reached a compressive strength of

157.5 psi after 7 days when cured at 40°C while the ones cured at room temperature reached

only 12.5 psi. However, the samples cured at 40°C cracked while the ones cured at room

Samples containing sodium silicate cured

at room temperature and at 40C (5M

NaOH)

020406080

100120

14 28 35

Time (days)

Co

mp

ressiv

e

Str

en

gth

(p

si)

50% Class F RT

50% Class F 40C

temperature reached 235 psi after 28 days. Results suggest that neither additive (silicate or

aluminate) helped very much in changing the longer term behavior of samples made with 5M

NaOH.

Samples made with 8M NaOH

The tank fill materials study also included samples made with 8M NaOH instead of 5M

NaOH. Most of these samples showed a steady increase in compressive strength over time with

the exception of the samples cured at 40°C for 7 days. Strengths for all samples decreased with

the sole exception of the 60 wt% fly ash sample. In both cases, the 60 wt% fly ash samples cured

at RT or 40°C were the strongest. After 28 days, their compressive strengths were observed to be

2610 psi and 1560 psi for samples cured at 40°C and room temperature, respectively. In general,

samples made of 8M NaOH did not have a compressive strength lower than 190 psi at 14 days of

curing. All samples cured for 14 days and longer contained faujasite and Zeolite A.

Samples containing sodium aluminate

Some of these samples were also made with sodium aluminate in addition of Ft Martin

fly ash, metakaolinite and sodium hydroxide to study how sodium aluminate would affect the

strength and also the content in zeolite of the samples. Whereas the samples made with 5M

NaOH cracked after 21 days of curing in a 40°C environment and the highest strength reached

by the samples was 235 psi at room temperature, samples made with 8M NaOH were in general

stronger than the ones made with 5M, with strength of 700 and 2377.5 psi for the ones cured at

room temperature and at 40°C respectively.

Figure 23- Comparison of samples based on the Figure 24- Comparison of samples based on the

percentage of Class F fly ash cured at room percentage of Class F fly ash cured at

temperature (8M NaOH) 40oC (8M NaOH)

Samples made with Sherco fly ash

The samples made of Sherco fly ash instead of Fort Martin fly ash had the strongest

compressive strengths of all the samples tested. The reason is the superior ability that Sherco fly

ash has to react with components more thoroughly. Indeed, the study showed that these samples

were quickly cured. The lowest strength observed was 295 psi after 14 days of cure for the



cured at room temperature (8M NaOH)

0

500

1000

1500

2000

2 7 14 28

Time (days)

Co

mp

ress

ive

Str

en

gth

(p

si) 25% classF RT

40% classF RT

50% classF RT

60% classF RT

75% classF RT


percentage of Class F fly ash cured at

40C (8M NaOH)

0

1000

2000

3000

0 10 20 30

Time (days)

Co

mp

res

siv

e

Str

en

gth

(p

si)

25% classF40C

40% classF 40C

50% classF 40C

60% classF 40C

75% classF 40C



(8M NaOH)

0

1000

2000

3000

0 7 14 21 28

Time (days)

Co

mp

res

siv

e

Str

en

gth

(p

si)

25% classF RT

25% classF40C

40% classF RT

40% classF 40C

50% classF RT

50% classF 40C

60% classF RT

60% classF 40C

75% classF RT

75% classF 40C

Figure 25- Summary of CS behavior of samples based on the percentage of Class F fly ash at RT and 40°C

(8M NaOH)

samples made of Sherco fly ash and Troy metakaolinite in a 1 to 1 ratio mixed with 8M NaOH

(Figure 27). The highest strength reached was 4705 psi when 8M NaOH was replaced by 15M

NaOH in the formulation of the samples (Figure 26). Samples made of Sherco fly ash and Fort

Martin fly ash in a 1 to 1 ratio mixed with 8M NaOH reached a compressive strength of 2965 psi

when cured at 40°C. The lowest strength observed was about 660 psi. Once again all the data are

compared and contrasted in Figure 28.

Figure 26- Compressive strength of samples Figure 27. Compressive strength of samples

Containing Sherco fly ash and 15M NaOH containing Sherco fly ash and 8M NaOH

Samples containing Class C Sherco fly

ash and 15M NaOH (RT and 40C)

0

1000

2000

3000

4000

5000

0 7 14

Time (days)

Co

mp

res

siv

e

Str

en

gth

(p

si)

50% classC/MK(15M)RT

50% classC/MK(15M)40C

Samples containing Class C Sherco fly

ash and 8M NaOH

0

1000

2000

3000

4000

0 7 14

Time (days)

Co

mp

res

siv

e

Str

en

gth

(p

si)

50% classC/MK(8M)RT

50% classC/MK(8M) 40C

Samples containing 50/50 Class F/Class C fly ash (5M

and 8M NaOH)

0

1000

2000

3000

4000

0 7 14

Time (days)

Co

mp

res

siv

e

Str

en

gth

(p

si) 50% classF/classC

(8M) RT

50% classF/classC(8M) 40C

50% classF/classC(5M) RT

50% classF/classC(5M) 40C

Figure 28- Compressive strength of samples containing 50/50 Sherco/Fort Martin fly ash

(5M and 8M NaOH)

Samples containing sodium silicate cured at room

temperature and at 40C (8M NaOH)

0

500

1000

1500

2000

2500

0 10 20 30

Time (days)

Co

mp

ressiv

e

Str

en

gth

(p

si)

50% Class F RT

50% Class F 40C

Figure 19. Graph of samples containing sodium silicate cured at room temperature

and at 40C (8M NaOH)

X-ray results

Despite their high compressive strength, samples made of Sherco fly ash instead of Ft

Martin fly ash contained an insignificant amount of zeolite. This is sharp contrast with a similar

sample made from 75% Ft Martin fly ash and 25% metakaolinite. By the 14th

day of its curing

process, the sample made on September 2nd

contained a significant amount of zeolite. The

sample made on September 8th

, was composed of 60% Fort Martin fly ash, 40% metakaolinite

and 8M NaOH, was X-rayed after 7 days of curing at 40oC and also showed the presence of

zeolite.

Conclusions

The study that was conducted showed that it was possible to make grout like equivalents

that could be mixed and placed much like Portland cement based materials without actually

using Portland cement. The mixtures are based on the chemistry of zeolite formation. In this

instance the NaOH used to liquefy the dry materials reacts with the glassy portion of the Class F

and C fly ash to form precursor zeolites. With time these precursors tend to crystallize and form

zeolites. The process tends to occur without any notable change to the sample’s outward

appearance. However, in some cases the samples expanded and self cracked. These were

predominately samples made with 5M NaOH which tended to be the weaker samples anyway.

Samples made with 8 M NaOH and 15M NaOH tended to be stable and strengthen with time.

The initiation of microcracks tend to cause the sample to suffer retrograde strength development,

i.e. the samples made with 5M NaOH are not reliable since after a peak at 14 days or so, the

compressive strength would go down as the samples would get weaker and more brittle. In

general, the samples made with Sherco fly ash and metakaolin mixed with 15M NaOH and cured

at RT were the strongest ones, but they earned this position without the development of very

much crystalline zeolite. A priori this would suggest that the samples were more typically

portland cement-like and did not have the capacity to absorb residual radioactive ions left in the

tank. However, the samples containing Ft Martin fly ash and metakaolin in a 50:50 or 60:40 ratio

in addition to 8M NaOH were the most reliable, they tended to exhibit a steady increase in

compressive strength with time. They had an adequate content of zeolites and reached an

adequate compressive strength for tank fill materials purposes. The samples composed of 75% Ft

Martin fly ash, 25% metakaolinite and the ones composed of 60% Fort Martin fly ash, 40%

metakaolinite in addition to 8M NaOH contained a decent amount and zeolite and also had a

good compressive strength after 14 days of curing. The final set of formulation of note were

those consisting of 50:50 wt% mixtures of Sherco and Ft. Martin fly ashes mixed with 5 and 8M

NaOH and cured at RT. These developed reasonably good strengths. They increased without

signs of weakening.

A few additional experiments were carried out at this point in time. A series of cation

exchange reactions in which powdered samples of some of the best tank fill material were

suspended in solutions containing CsCl and initial attempts to make concrete-like equivalents of

the better samples by mixing them with quartz sand and limestone aggregate were carried out.

The results of these experiments were generally positive.

Cation Exchange

Three of the better performing mixtures were remixed and cured at RT and 40°C for 7

days. These were ground to a powder and 100 mg of each powder were placed in 20 mL solution

on a shaking table for 7 days. Then they were analyzed for Na and Cs and Kd values were

calculated. The formulations and cation exchange data are given in Table 13. The best

performing mixture was the Ft Martin-metakaolin formulation, followed by the Sherco-

metakaolin formulation. The least adsorptive were the two fly ash sample (Sherco-Ft Martin).

Compressive strength of Concrete cylinders made with best formulations

Compressive strengths were measured on three concrete samples made with a Ft. Martin

fly ash-sodium silicate-NaOH solution, a Sherco sample and a Ft. Martin-metakaolin sample.

They were cast in large cylinder molds and cured in air at RT for ~2 months. The plastc sleeves

were removed and the strengths determined. The results were promising. The Ft Martin/Na-

silicate/NaOH sample was weak (did not work), the Sherco and Ft Martin samples were strong.

Of these, the Ft Martin-metakaolin sample was the best.

Table13. Cation exchange behavior of three best mixtures cured at RT and 40°C for 7 days

Sample Tested Cs % adsorption = Kd (Cs) Na

mg/L (A0-Af)/A0 mL/mg mg/L

P24-0 Stock solution [0.0002 N CsCl dissolved in 0.02N NaCl] 26.7 -- -- 440

P24-1 50:50 Ft. Martin and Sherco fly ashes mixed with 8 M NaOH cured at 40°C 7 days 21.0 21.3% 5.4% 640

P24-2

50:50 Ft. Martin and Sherco fly ashes mixed with 8 M NaOH cured at RT 7 days 19.2 28.1% 7.8% 650

P24-3

50:50 Ft. Martin fly ash and metakaolin mixed with 8 M NaOH cured at 40°C 7 days 10.7 59.9% 29.9% 490

P24-4

50:50 Ft. Martin fly ash and metakaolin mixed with 8 M NaOH cured at RT 7 days 11.6 56.6% 26.0% 490

P24-5

50:50 Sherco fly ash and metakaolin mixed with 8 M NaOH cured at 40°C 7 days 16.1 39.7% 13.2% 640

P24-6

50:50 Sherco fly ash and metakaolin mixed with 8 M NaOH cured at RT 7 days 14.2 46.8% 17.6% 620

P24-7

50:50 Sherco fly ash and metakaolin mixed with 15 M NaOH cured at 40°C 7 days 19.7 26.2% 7.1% 670

Future work

Follow up work should concentrate on refining and improving 50:50 60:40 Class F Fort

Martin fly ash: metakaolinite mixed with 8M NaOH mixture as a concrete. Follow up should

also focus on improving the Sherco formulation. Finally, the combination of Sherco and Ft

Martin showed promise, but the cation exchange capacity was among the lowest. Improvements

on the amount of zeolite present could be made by either: increasing the percentage of Ft Martin

or by including some metakaolin in the formulation.

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