Potential of calcium sulfoaluminate cements to immobilize ZnCl 2 -containing wastes

IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 1

Potential of calcium sulfoaluminate cements to immobilize ZnCl2-containing wastes

Stéphane BERGER 1, Céline CAU DIT COUMES 1, Patrick LE BESCOP 2, Denis DAMIDOT 3

1 CEA Marcoule, Laboratory for Waste Immobilization2 CEA Saclay, Laboratory for Concrete and Clay Investigation3 Ecole des Mines de Douai, Civil & Environmental Engineering Department


Overview

• Background

• Research objectives and experimental strategy

• Experimental results

• Conclusion, prospects and work plan


Cementation is a widely applied process for the conditioning of LLW and ILW radioactive wastes

ProcessProcess

simple inexpensive

Calcium silicate Calcium silicate cementscements

easy supply good mechanical strength compatibility with aqueous wastes good self-shielding high alkalinity precipitation of many radionuclides

Encapsulated ion exchange resins

Cemented waste introducedinto a container

500 µm

BUT…

Some waste components may chemically react with cement phases or mixing water

Possible reduction in the quality of the solidified waste form

1. Background


Incineration of technological wastesincluding neoprene and P.V.C

Ashes with substantial amounts of soluble ZnCl2

Ex: Zn content = 29.5% by massSoluble Zn concentration in a suspension

(L/S 2.5 mL/g) = 22.4 g/L (0.34 mol/L)

Deleterious effects on Portland cement• setting is strongly delayed and can be inhibited at high zinc chloride loadings (Arliguie 1985)• hydration and hardening are slowed down (Ortego 1989).

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Time (h)

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ture

rise

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Cau

-dit-

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mes

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al,

ICC

C 2

007

> 4 days

Portland Cement with 0,1 mol/L ZnCl2

Portland Cement without ZnCl2

< 24 h

Precipitation of β2-Zn(OH)2 or Zn2Ca(OH)6.2H2O over the cement

grains has been postulated to explain the delay in cement hydration

(Arliguie 1985).

1. Background


How to deal with adverse cement waste – interactions ?

1. Background

Treatment of the waste in order to convert interfering species into compounds stable in cement

(a) Precipitation as hopeite (Zn3PO4.2H2O) by addition of withocklite(b) Precipitation as a silicate form (hemimorphite 2ZnO.SiO2.H2O, metasilicate ZnSiO3 or orthosilicate Zn2SiO4) by addition of sodium silicate

(c) Precipitation as calcium hydroxyzincate (CaZn2(OH)6.2H2O) by addition of calcium hydroxide

- (a) and (b) too slow at 25 or 60°C for an industrial application (Drouin, 1994)- (c) max. (Zn/Cement) ratio : 3.4%- Complexity and cost of the process increased

BUT :

To select a binder which would show an improved compatibility with the waste, such as

a calcium sulfoaluminate cement


Calcination at 1300-1350°C

clinker cement

Gypsum (from 0 to 30%)

Co-grinding

Manufacturing process of calcium sulfoaluminate cements

Advantages of CSA cements as compared to OPC :

reduced energy consumption during manufacturing

low CO2 emission during manufacturing

high-early strength development

Limestone, claybauxitegypsum

(industrial residues)

1. Background

0.50.52.63.16.61671QuartzCSPericlaseC12A7C3FTC2SC4A3S

Minerals (% weight)

0.50.52.63.16.61671QuartzCSPericlaseC12A7C3FTC2SC4A3S

Minerals (% weight)Composition of the clinker used in this study :


Two main features of CSA cement hydration

1. Background

Hydrates repartition depends on the amount of gypsum

mixed with the clinker

0102030405060708090

100

% gypsum

% h

ydra

tes

Mod

ified

from

Gla

sser

and

al,

CC

R 2

001

AH3

Ettringite

Calcium monosulfoaluminatehydrate

CSHGypsum

Rapid heat production

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0 10 20 30 40Time (h)

Tem

pera

ture

(°C

)

Portland cement

CSA cementsemi-adiabatic Langavant calorimetry

Both influences of temperature and gypsum content have to be studied


Overview

• Background



• Conclusion

• Prospects and work plan


2. Research objectives and experimental strategy

Objectives : - to assess the potential of CSA cement to immobilize ZnCl2-containing wastes- to progress in the understanding of CSA cement hydration

Investigation of the influence of three parameters

the gypsum content of the cement

the thermal evolution of the solidified waste form

the ZnCl2 concentration of the mixing solution

on the rate of hydration and products formed

the properties of the solidified waste forms (porosity, mechanical strength, dimensional variations, evolution under leaching)


2. Research objectives and experimental strategyCement prepared by mixing clinker with variable gypsum contents

(from 0 to 35 %)

Mixing solution

demineralized water + possible dissolution of a ZnII salt ([Zn2+]max = 0.5 mol/L)

2 kinds of materials

Mortars (W/C = 0.55, S/C = 3)

29-0285 (I) - Strat lingite, syn - Ca2Al2SiO7·8H2O - Y: 32.73 % - d x by: 1. - W L: 1 .5406 - Hexagonal (Rh) -

46 -1045 (*) - Quartz , syn - SiO2 - Y: 49.88 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 4.91344 - b 4.91344 05 -0586 (*) - Calcite , syn - CaCO3 - Y: 43.64 % - d x by: 1. - WL: 1.5406 - Hexagonal (Rh) - a 4.98900 - b 4Operations: Y Scale Add 20 | Smooth 0.105 | Strip kAlpha2 0.500 | Importc:\michel\bpHT1p.RAW - File: bpHT 1p .RAW - Type: 2Th /Th locked - Start: 10 .000 ° - End: 60.000 ° - Step: Operations: Y Scale Add 20 | Y Scale Mul 0 .333 | Smooth 0.105 | Strip kAlpha2 0.500 | ImportCendres Volan tes - File: Cv.raw - Type: 2Th /Th locked - Start: 10.000 ° - End: 60.000 ° - Step: 0.020 ° - SteOperations: Y Scale Mul 0.333 | Smooth 0.105 | Strip kAlpha2 0.500 | Importmétakaolin - Fi le: mk.RAW - T ype: 2Th/Th locked - Start: 10.000 ° - End : 60.000 ° - Step: 0.020 ° - Step tim

Lin

(Cou

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2-Theta - Scale11 20 30 40 50 60

XRD DSC / TGA SEM

Langavant calorimetry Dimensional stability Mechanical strength

Pastes (W/C = 0.55)


2. Research objectives and experimental strategy

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Tem

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20°C curing

semi-adiabatic curing

After elaboration, the samples were either cured in a sealed plastic bag at 20°Cor submitted to a thermal cycle in an oven.

Thermal cycles: temperature profiles defined from the temperature evolution of mortars under semi-adiabatic conditions and applied on investigated samples to reproduce the temperature rise and decrease which may occur in a massive structure during cement hydration

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temperature profile applied to the paste

Temp. in paste

Temp. in mortar

20% gypsum, 0.5 mol/L ZnCl2

Temperature profiles were defined by interpolating in 20-40 segments the curves recorded on mortars.

Some corrections were required to keep the inner temperature of the

paste near that of the mortar under semi-adiabatic curing.


Overview

• Background



• Conclusion



3. Experimental results3.1 Hydration of reference materials : influence of the gypsum content

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0%2% 1%3%

5%7%

10%

MortarsNo ZnCl2 additionGypsum: 0-10%



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0%2% 1%3%

5%7%

10%


Two effects were observed when the gypsum content increased from 0 to 10%:• the induction period decreased strongly, especially at low gypsum contents,



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Two effects were observed when the gypsum content increased from 0 to 10%:• the induction period decreased strongly, especially at low gypsum contents,• the cumulated heat output was reduced when the gypsum content exceeded 5%.


3. Experimental results

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Beyond a gypsum content of 10%, heat output and induction period did not vary anymore.


3.1 Hydration of reference materials : influence of the gypsum content



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yee

limite

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Without gypsum: • yeelimite started to react much later, in agreement with the long induction period

previously observed. • Yeelimite was almost totally depleted at 24 h while with gypsum, 10 to 20% were

still unreacted.

(based on XRD relative peak areas)

3.1 Hydration of reference materials : influence of the gypsum content


3. Experimental results3.1 Hydration of reference materials : products formed

What about the influence of the thermal cycle ?

- Precipitation of calcium monosulfoaluminate hydrate promoted by a low gypsum content and by the thermal cycle.- CAH10 destabilized by an increase in the gypsum content and/or temperature.

2-Theta - Scale

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M

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CAH 10

CAH 10

2 Theta scale2-Theta - Scale

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2 Theta scale

Gypsum = 0%

- Curing at 20°C- Thermal cycle

2-Theta - Scale

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MA

A


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E

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E

E

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MA

A

2 Theta scale

Gypsum = 10%


Time = 24 hCement pastesNo ZnCl2 addition

E: C3A.3CS.H32M: C3A.CS.H12Y: C4A3SA: AH3

E: C3A.3CS.H32M: C3A.CS.H12Y: C4A3SA: AH3


3. Experimental results3.1 Hydration of reference materials : products formed

What about the influence of the thermal cycle ?

2-Theta - Scale

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E

E E

E

EG

M +

E

E

GEE

2-Theta - Scale

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

E

E E

E

EG

M +

E

E

GEE

2 Theta scale

With a gypsum content > 20%, the thermal cycle had no significant effect on the mineralogy: gypsum stabilized ettringite in spite of the temperature increase.

Gypsum = 20%


Time = 24 hCement pastesNo ZnCl2 addition


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Gypsum = 35%


E: C3A.3CS.H32M: C3A.CS.H12G: CSH2Y: C4A3SA: AH3

E: C3A.3CS.H32M: C3A.CS.H12G: CSH2Y: C4A3SA: AH3


3. Experimental results3.2 Hydration of ZnCl2-containing materials

• A retardation was observed, especially with a gyspum-free cement, but its magnitude was much smaller than that recorded with OPC.

• Setting inhibition was never observed: setting occurred in less than 2h with gypsum, and in less than 24h without it.

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0.5 mol/l



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CaCl2

ZnCl2

Zn(NO3)2

Ca(NO3)2

CaSO4ZnSO4

acceleration Zn2+ > Ca2+ delay

Salt concentration : 0.5 mol/l

0% gypsumH2O

Temperature of the mixing solution: 20°C

What about the influence of the zinc cation ?



What about the influence of the Zinc counter-ion ?

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CaCl2

Zn(NO3)2

CaSO4

acceleration SO42- >> 2 NO3

- > 2 Cl- delaySalt concentration : 0.5 mol/l

Chloride anions strongly slowed down hydration but zinc cations accelerated it!

Temperature of the mixing solution: 20°C

ZnSO4

Ca(NO3)2

ZnCl2

0% gypsumH2O



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H2O ZnCl2

CaCl2

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H2O ZnCl2

CaCl2

20% gypsum

With gypsum in the binder, similar rates of hydration with CaCl2 and ZnCl2 solutions.



AFm phases

Calcium monosulfoaluminate hydrate : C3A.CaSO4.12H2O

Friedel’s salt : C3A.CaCl2.12H2O

Kuzel’s salt : C3A.1/2CaSO4.1/2CaCl2.12H2O

3.2 Hydration of ZnCl2-containing materials : products formed at early age


3. Experimental results3.2 Hydration of ZnCl2-containing materials : products formed at early age

Hydrates formed (7 d) 0% gypsum

Curing at 20°C CAH10 (+)

Calcium monosulfoaluminate hydrate (++) Ettringite (+) Gibbsite (tr)

Thermal cycle Calcium monosulfoaluminate hydrate (+++) Gibbsite (+)

Without ZnClWithout ZnCl22

- Destabilization of CAH10

- Precipitation of calcium monosulfoaluminate hydrate favoured instead of ettringite

Hydrates formed (7 d) 0% gypsum

Curing at 20°C

CAH10 (tr)

Calcium monosulfoaluminate hydrate (+) Friedel’s salt (+) Kuzel’s salt (++)

Ettringite (++) Gibbsite (tr)

Thermal cycle

Calcium monosulfoaluminate hydrate (++) Friedel’s salt (+) Kuzel’s salt (++)

Ettringite (+) Gibbsite (+)

With ZnClWith ZnCl22

- Destabilization of CAH10

- Precipitation of calcium monosulfoaluminate hydrate favoured instead of ettringite- No influence on the Friedel’s and Kuzel’s salts


3. Experimental results3.2 Hydration of ZnCl2-containing materials : products formed

Hydrates formed 0% gypsum 20% gypsum

Curing at 20°C CAH10 (+)

Calcium monosulfoaluminate hydrate (++) Ettringite (+) Gibbsite (tr)

Calcium monosulfoaluminate hydrate (tr) Ettringite (+++)

Gibbsite (tr)

Thermal cycle Calcium monosulfoaluminate hydrate (+++) Gibbsite (+)


Gibbsite (+)

Without ZnClWithout ZnCl22

Almost no influence on the stability of ettringite

Hydrates formed 0% gypsum 20% gypsum

Curing at 20°C

CAH10 (tr) Friedel’s salt (+) Kuzel’s salt (++) Ettringite (++) Gibbsite (tr)


Gibbsite (tr)

Thermal cycle

Calcium monosulfoaluminate hydrate (++) Friedel’s salt (+) Kuzel’s salt (++)

Ettringite (+) Gibbsite (+)


Friedel’s salt (++) Gibbsite (+)

With ZnClWith ZnCl22

Precipitation of Friedel’s salt



Where are the zinc cations?



Experimental device

constant temperature (20°C) and pH stirring and injection of N2 into the cells to avoid carbonation samples protected from lateral attack by polymer coating renewal of the solution at regular intervals, in connection with the quantity of added HNO3

N2 gas

pH regulator

pH meterAutomatic supplying

pump

Thermoregulated water

Nitric acid0.5 M

Reactor

Leaching by pure water at fixed pH (7) and temperature (20°C)

4 months of leaching – 22 renewals : [Zn] in the leachates below 0.1 mg/L (detection limit of the ICP method)

Zinc is well insolubilized

3.2 Hydration of ZnCl2-containing materials : products formed



Investigation of simplified systems

Ettringite + ZnCl2 solution

Partial conversion of ettringite into CaZn2(OH)6.2H2O

No clear evidence of Zn insertion into ettringite

Calcium monosulfoaluminate hydrate + ZnCl2 solution

Total conversion into ettringite + Friedel’s salt + CaZn2(OH)6.2H2O + Zn4Al2(OH)12CO3.xH2O

No clear evidence of Zn insertion into ettringite or Friedel’s salt

Friedel’s salt

Complementary work is needed


3. Experimental results3.3 Properties of hardened mortars : porosity

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0% 10% 20%Gypsum content

Tota

l por

osity

( %)

Curing at 20°C, [ZnCl2] = 0M

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25


Tota

l por

osity

(%)

28 days 90 days

Total porosity increased with the gypsum content.



28 days 90 days

Curing at 20°C, [ZnCl2] = 0M Thermal cycle, [ZnCl2] = 0M

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25


Tota

l por

osity

( %)

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Tota

l por

osity

(%)

No significant influence of the thermal cycle on the total porosity



Curing at 20°C, [ZnCl2] = 0M Thermal cycle, [ZnCl2] = 0M Thermal cycle, [ZnCl2] = 0.5M

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l por

osity

( %)

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l por

osity

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Adding ZnCl2 slightly decreased the porosity of gypsum-free mortars.


3. Experimental results3.3 Properties of hardened mortars : compressive strength

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0 20 40 60 80 100 120 140 160 180Time (days)

Rc (

MPa

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Gypsum : 0% 10% 20%

Mixing solution = waterNo thermal cycle

gypsum addition (10, 20%) decrease in the

compressive strength

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60

0 40 80 120 160 200 240 280 320 360Time (days)

Rc (

MPa

)

Gypsum : 0% 10% 20%

Mixing solution = waterThermal cycle

Thermal cycle strength loss without gypsum only


3. Experimental results3.3 Properties of hardened mortars : compressive strength

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Time (days)

Rc (

MPa

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20% gypsum – ZnCl2

0% gypsum – ZnCl2

20% gypsum – H2O

0% gypsum – H2O

Mixing solution = water or ZnCl2 0.5 MThermal cycle

ZnCl2 addition strength increase, especially with gypsum (20%)


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Leng

th c

hang

e (µ

m/m

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0% gypsum

0% gypsum - thermal cycle

10% gypsum


20% gypsum


3. Experimental results3.3 Properties of hardened mortars : length change under wet curing

Swelling was increased by the thermal cycle for a gypsum-free cement only

Mixing solution = water


3. Experimental results3.3 Properties of hardened mortars : length change under wet curing

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th c

hang

e (µ

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0% gypsum - H2O

0% Gypsum - ZnCl2

20% gypsum - H2O

20% Gypsum - ZnCl2

Swelling was increased by ZnCl2 for a gypsum-free cement only

Mixing solution = water or ZnCl2 0.5 MThermal cycle


Overview

• Background



• Conclusion



4. Conclusions

CSA cements showed a much better compatibility with zinc chloride than OPC: hydration was slightly slowed down but setting inhibition was never observed, even at high Zn concentrations (0.5 mol/L).

Adding a 20% gypsum content to cement was beneficial in the presence of Zn II ions increase in the compressive strength decrease in expansion under wet-curing stabilization of ettringite, even at high temperature (80°C)

Chloride anions induced a strong retardation of a gypsum-free cement, but this effect was balanced by the accelerating effect of zinc cations and sulfate anions.

In the presence of zinc chloride, the mineralogy observations revealed the precipitation of chloro-AFm phases such as Kuzel’s and Friedel’s salts.

The thermal history of the samples proved to be a key parameter since a temperature rise accelerated the rate of hydration and modified the nature of the hydrates, particularly with a low gypsum content.


5. Prospects and work plan

Task Year 1 Year 2 Year 3 Investigation of CSA hydration by : ZnCl2-containing solutions B(OH)4

- -containing solutions Investigation of Zn-containing hydrates: AFt and AFm phases Hydrotalcite-like phases

Investigation of the durability of solidified waste forms (leaching by pure water)

CSA cements+ ZnCl2

Characterization of: - the mineralogy of older samples- the microstructure of hardened cement pastes as a function of various parameters (hydration degree, compositions of cement and mixing solution, temperature)

Investigation of leaching by pure water (experiments under way):- analysis of the degraded solid and leachates- modelling of leaching using a reactive transport model

CSA cements+ B(OH)4

-Investigation of the influence of B(OH)4

- ions on the hydration process of CSA cements

Potential of calcium sulfoaluminate cements to immobilize ZnCl 2 -containing wastes

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Transcript of Potential of calcium sulfoaluminate cements to immobilize ZnCl 2 -containing wastes