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

1. Potential of calcium sulfoaluminate cements to immobilize ZnCl2-containing wastes Stéphane BERGER 1, Céline CAU DIT COUMES1, Patrick LE BESCOP 2, Denis DAMIDOT 3 1 CEA Marcoule, Laboratory for Waste Immobilization 2 CEA Saclay, Laboratory for Concrete and Clay Investigation 3 Ecole des Mines de Douai, Civil & Environmental Engineering Department

2. Overview • Background • Research objectives and experimental strategy • Experimental results • Conclusion, prospects and work plan

3. Calcium silicate cements Process  easy supply  good mechanical strength  compatibility with aqueous wastes  good self-shielding  high alkalinity  precipitation of many radionuclides  simple  inexpensive Encapsulated ion exchange resins Cemented waste introduced into a container 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 Cementation is a widely applied process for the conditioning of LLW and ILW radioactive wastes 500 µm

4. 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). Portland Cement without ZnCl2 Portland Cement with 0,1 mol/L ZnCl2 From Cau-dit-Coumes and al, ICCC 2007 < 24 h > 4 days 1. Background Incineration of technological wastes including neoprene and P.V.C Ashes with substantial amounts of soluble ZnCl2 Ex: Zn content = 29.5% by mass Soluble Zn concentration in a suspension (L/S 2.5 mL/g) = 22.4 g/L (0.34 mol/L) 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).

5.  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 BUT : - (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  To select a binder which would show an improved compatibility with the waste, such as a calcium sulfoaluminate cement 1. Background How to deal with adverse cement waste – interactions ?

6. Composition of the clinker used in this study : • Advantages of CSA cements as compared to OPC : •  reduced energy consumption during manufacturing • low CO2 emission during manufacturing • high-early strength development 1. Background Manufacturing process of calcium sulfoaluminate cements Calcination at 1300-1350°C Limestone, clay bauxite gypsum (industrial residues) Co-grinding clinker cement Gypsum (from 0 to 30%)

7. Rapid heat production AH3 Calcium monosulfoaluminatehydrate Ettringite Modified from Glasser and al, CCR 2001 semi-adiabatic Langavant calorimetry CSA cement Gypsum CSH Portland cement  Both influences of temperature and gypsum content have to be studied 1. Background Two main features of CSA cement hydration Hydrates repartition depends on the amount of gypsum mixed with the clinker

8. Overview • Background • Research objectives and experimental strategy • Experimental results • Conclusion • Prospects and work plan

9. Investigation of the influence of three parameters the gypsum content of the cement the ZnCl2 concentration of the mixing solution the thermal evolution of the solidified waste form 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 strategy • Objectives : • to assess the potential of CSA cement to immobilize ZnCl2-containing wastes • - to progress in the understanding of CSA cement hydration

10. 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) Langavant calorimetry Dimensional stability Mechanical strength Pastes (W/C = 0.55) XRD DSC / TGA SEM 2. Research objectives and experimental strategy prepared by mixing clinker with variable gypsum contents (from 0 to 35 %) Cement

11. semi-adiabatic curing 20°C curing Temp. in paste 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. Temp. in mortar temperature profile applied to the paste 20% gypsum, 0.5 mol/L ZnCl2 2. Research objectives and experimental strategy After elaboration, the samples were either cured in a sealed plastic bag at 20°C or 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

12. Overview • Background • Research objectives and experimental strategy • Experimental results • Conclusion • Prospects and work plan

13. 5% 7% 10% 1% 0% 3% 2% 3. Experimental results 3.1 Hydration of reference materials : influence of the gypsum content Mortars No ZnCl2 addition Gypsum: 0-10%

14. 5% 7% 10% 1% 0% 3% 2% 3. Experimental results 3.1 Hydration of reference materials : influence of the gypsum content Mortars No ZnCl2 addition Gypsum: 0-10% • Two effects were observed when the gypsum content increased from 0 to 10%: • the induction period decreased strongly, especially at low gypsum contents,

15. 5% 7% 10% 1% 0% 3% 2% 3. Experimental results 3.1 Hydration of reference materials : influence of the gypsum content Mortars No ZnCl2 addition Gypsum: 0-10% • 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%.

16. 0% 10% 35% 20% 3. Experimental results 3.1 Hydration of reference materials : influence of the gypsum content Mortars No ZnCl2 addition Gypsum: 10-35% Beyond a gypsum content of 10%, heat output and induction period did not vary anymore.

17. 3. Experimental results 3.1 Hydration of reference materials : influence of the gypsum content (based on XRD relative peak areas) • 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.

18. Gypsum = 10% - Curing at 20°C - Thermal cycle 3. Experimental results 3.1 Hydration of reference materials : products formed What about the influence of the thermal cycle ? Gypsum = 0% Time = 24 h Cement pastes No ZnCl2 addition - Curing at 20°C - 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.

19. Gypsum = 35% - Curing at 20°C - Thermal cycle 3. Experimental results 3.1 Hydration of reference materials : products formed What about the influence of the thermal cycle ? Gypsum = 20% Time = 24 h Cement pastes No ZnCl2 addition - Curing at 20°C - Thermal cycle 2 Theta scale 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.

20. 3. Experimental results 3.2 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.

21. 3. Experimental results 3.2 Hydration of ZnCl2-containing materials What about the influence of the zinc cation ? CaSO4 ZnSO4 0% gypsum H2O ZnCl2 CaCl2 Zn(NO3)2 Temperature of the mixing solution: 20°C Salt concentration : 0.5 mol/l Ca(NO3)2 acceleration Zn2+ > Ca2+delay

22. 3. Experimental results 3.2 Hydration of ZnCl2-containing materials What about the influence of the Zinc counter-ion ? ZnSO4 CaSO4 Ca(NO3)2 Zn(NO3)2 0% gypsum H2O CaCl2 ZnCl2 Temperature of the mixing solution: 20°C acceleration SO42- >> 2 NO3- >2 Cl-delay Salt concentration : 0.5 mol/l Chloride anions strongly slowed down hydration but zinc cations accelerated it!

23. 3. Experimental results 3.2 Hydration of ZnCl2-containing materials 20% gypsum With gypsum in the binder, similar rates of hydration with CaCl2 and ZnCl2 solutions.

24. 3. Experimental results 3.2 Hydration of ZnCl2-containing materials : products formed at early age AFm phases Calcium monosulfoaluminate hydrate : C3A.CaSO4.12H2O C3A.CaCl2.12H2O Friedel’s salt : Kuzel’s salt : C3A.1/2CaSO4.1/2CaCl2.12H2O

25. With ZnCl2 • Destabilization of CAH10 • Precipitation of calcium • monosulfoaluminate hydrate favoured • instead of ettringite • - No influence on the Friedel’s and Kuzel’s salts 3. Experimental results 3.2 Hydration of ZnCl2-containing materials : products formed at early age Without ZnCl2 • Destabilization of CAH10 • Precipitation of calcium • monosulfoaluminate hydrate favoured • instead of ettringite

26. With ZnCl2 Precipitation of Friedel’s salt 3. Experimental results 3.2 Hydration of ZnCl2-containing materials : products formed Without ZnCl2 Almost no influence on the stability of ettringite

27. 3. Experimental results 3.2 Hydration of ZnCl2-containing materials : products formed Where are the zinc cations?

28. Nitric acid 0.5 M Thermoregulated water Automatic supplying pump pH meter pH regulator 4 months of leaching – 22 renewals : [Zn] in the leachates below 0.1 mg/L (detection limit of the ICP method) Reactor  Zinc is well insolubilized 3. Experimental results 3.2 Hydration of ZnCl2-containing materials : products formed Leaching by pure water at fixed pH (7) and temperature (20°C) Experimental device N2 gas • 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

29. 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 3. Experimental results 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  Complementary work is needed

30. 3. Experimental results 3.3 Properties of hardened mortars : porosity 28 days 90 days 25 25 20 20 15 15 Total porosity( %) Total porosity (%) 10 10 5 5 0 0 0% 10% 20% 0% 10% 20% Gypsum content Gypsum content Curing at 20°C, [ZnCl2] = 0M  Total porosity increased with the gypsum content.

31. 3. Experimental results 3.3 Properties of hardened mortars : porosity 28 days 90 days 25 25 20 20 15 15 Total porosity( %) Total porosity (%) 10 10 5 5 0 0 0% 10% 20% 0% 10% 20% Gypsum content Gypsum content Thermal cycle, [ZnCl2] = 0M Curing at 20°C, [ZnCl2] = 0M  No significant influence of the thermal cycle on the total porosity

32. 3. Experimental results 3.3 Properties of hardened mortars : porosity 28 days 90 days 25 25 20 20 15 15 Total porosity( %) Total porosity (%) 10 10 5 5 0 0 0% 10% 20% 0% 10% 20% Gypsum content Gypsum content Thermal cycle, [ZnCl2] = 0M Thermal cycle, [ZnCl2] = 0.5M Curing at 20°C, [ZnCl2] = 0M  Adding ZnCl2 slightly decreased the porosity of gypsum-free mortars.

33. 60 50 Mixing solution = water Thermal cycle 40 Rc (MPa) 30 20 Thermal cycle  strength loss without gypsum only Gypsum : 0% 10% 20% 10 0 0 40 80 120 160 200 240 280 320 360 Time (days) 3. Experimental results 3.3 Properties of hardened mortars : compressive strength 60 50 Mixing solution = water No thermal cycle 40 Rc (MPa) 30 gypsum addition (10, 20%)  decrease in the compressive strength 20 10 Gypsum : 0% 10% 20% 0 0 20 40 60 80 100 120 140 160 180 Time (days)

34. 60 50 40 30 Rc (MPa) 20 0% gypsum – ZnCl2 0% gypsum – H2O 10 20% gypsum – H2O 20% gypsum – ZnCl2 0 0 40 80 120 160 200 240 280 320 360 Time (days) 3. Experimental results 3.3 Properties of hardened mortars : compressive strength Mixing solution = water or ZnCl2 0.5 M Thermal cycle ZnCl2 addition  strength increase, especially with gypsum (20%)

35. 3. Experimental results 3.3 Properties of hardened mortars : length change under wet curing Mixing solution = water  Swelling was increased by the thermal cycle for a gypsum-free cement only

36. 3. Experimental results 3.3 Properties of hardened mortars : length change under wet curing Mixing solution = water or ZnCl2 0.5 M Thermal cycle  Swelling was increased by ZnCl2 for a gypsum-free cement only

37. Overview • Background • Research objectives and experimental strategy • Experimental results • Conclusion • Prospects and work plan

38. 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 ZnII 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.

39. CSA cements + B(OH)4- Investigation of the influence of B(OH)4- ions on the hydration process of CSA cements 5. Prospects and work plan • 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 + ZnCl2