1. CRETE 2014 4th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
STABILIZATION/SOLIDIFICATION OF INCINERATOR FLY ASH BY MEANS OF CEMENTITIOUS COLD-BONDING PELLETIZATION
Raffaele Cioffi; Francesco Colangelo; Francesco Messina
Department of Engineering
University Parthenope of Naples
R.U.- INSTM – National Interuniversity Consortium of Materials Science and Technology
ITALY

2. ARTIFICIAL AGGREGATE PRODUCTION
CRETE th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
ARTIFICIAL AGGREGATE PRODUCTION
Sustainable development and environmental impact due to increasing demand for natural resources in civil engineering:
UEPG ("Union Européenne des Producteurs de Granulats") Annual Review the average consumption of aggregates in Europe is 5.5 tonnes/capita
Partial replacement of natural aggregates with artificial ones:
artificial aggregate of improved technological and leaching properties can be manufactured from re-processed wastes
specific treatments can be of different type depending on the nature of the waste and on the characteristics of the desired product
artificial aggregates can be manufactured by means of two types of processes: cement-based granulation and high temperature sintering

3. Cement-based granulation processes:
CRETE th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Cement-based granulation processes:
have not been deeply studied yet
Suitability for the manufacture of artificial aggregates is undoubtedly worthy of consideration:
treatment of wastes (often hazardous) largely relies on cement-based stabilization/solidification processes which allow safer disposal and/or material recovery for the manufacture of building materials
application has economical and environmental advantages due to the reduced energy requirement (process carried out at ordinary temperature) and the lack of secondary pollution (no gaseous emission is involved)

4. Aarding Lightweight Granulates BV (ND)
CRETE th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Aarding Lightweight Granulates BV (ND)

5. Raw wastes Cold-bonding pelletization
CRETE th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Raw wastes
Cold-bonding
pelletization

6. CRETE 2014 4th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Roadmap for utilising alternative materials in Manufactured
Aggregates

7. CRETE 2014 4th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece

8. CRETE 2014 4th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece

9. Chemical and Physical Characterization of Raw Wastes
CRETE th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Chemical and Physical Characterization of Raw Wastes
Two MSWI Fly Ash samples
Manufacture of Artificial Aggregates
Cold-bond pelletization
Characterization of Artificial Aggregates
grading; density, WAC, crushing resistance, mechanical degradation
Preparation and Characterization of Concrete
Physical and mechanical properties of concrete

10. Selection of waste CRETE 2014 4th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Selection of waste
Two fly ash samples from an incineration plant (Melfi-PZ) in which municipal, hospital and industrial wastes are treated.
The plant is equipped with rotary and stoker furnaces and fly ash samples from both furnaces have been individually employed

11. CRETE 2014 4th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
MSWI fly ash pre-washing treatment
The whole ash sample was divided in two halves and one of them was water washed with a 4:1 liquid to solid ratio
The recovered liquid (after filtering) was contacted to the second ash sample half to carry out the second step of the water washing pre-treatment
Each step is conducted with a 4:1 liquid to solid ratio to avoid the difficulties due to a too thick liquid-solid system
The overall operating liquid to solid ratio is 2:1, for the sake of process economy
F. Colangelo et al Soluble salt removal from MSWI fly ash and its stabilization for safer disposal and recovery as road basement material Waste Management, 32, 6, 2012,1179–1185

12. Fly Ash chemical composition, wt%
CRETE th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Fly Ash chemical composition, wt%
Component
Ash origin
Rotary furnace
Stoker furnace
Al2O3
7.61
3.89
Na2O
3.36
2.62
K2O
3.85
2.32
SO3
9.12
7.12
CaO
32.11
41.23
Fe2O3
2.03
1.02
MgO
3.24
1.69
MnO2
0.56
0.11
P2O5
1.12
0.53
TiO2
1.85
0.42
SiO2
7.93
11.06
Cl-
3.92
1.41
Cu, mg/kg
4927
2261
Cd, “ 62 23
Pb, “
3621
1720
Zn, “
4643
2645
Fly ash from the rotary furnace incinerator has higher content of polluting metals as a consequence of the different feed.
Rotary furnace incinerator is fed with wastes from industrial processes.
Stoker furnace incinerator is fed with municipal wastes.

13. Fly Ash leaching behaviour
CRETE th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Fly Ash leaching behaviour
A = Rotary furnace
B = Stoker furnace
Cd = 5
Zn = 3000
Pb = 50
Cu = 50
Limits (µg/l) Ministerial Decree 5/4/2006 n.186

14. Fly ashs particle size distribution
CRETE th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Fly ashs particle size distribution
Size fraction, m
Ash origin
Rotary furnace
Stoker furnace
<1
0.21
1.81
1–10
8.46
14.02
10–20
19.98
12.22
20–45
44.04
21.49
45–80
20.28
19.76
80–120
5.31
14.13
>120
1.72
16.57
Differences between the two ash samples:
resulting volume weighted mean diameter is 36.6 m for the rotary furnace incinerator ash sample and 64.4 m for the stoker furnace incinerator ash sample.

15. Granulation apparatus
CRETE th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Granulation apparatus
The granulator is equipped with a rotating and tilting plate.
The rotating speed and the tilting angle can be adjusted between wide limits.
In the experiments, the settings were 35, 45 and 55 rpm for the rotating speed and 50° for the tilting angle.
Mixed solids have been slowly and continuously poured into the granulator plate.

16. Manufacture of granules
CRETE th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Manufacture of granules
Initial granulation phase:
rotating speed was in the range rpm to favour the formation of small granules nuclei
Second granulation phase:
neither solid mix nor water were added
rotating speed was adjusted to 55 rpm
small granules coalesce and compact by the expulsion of part of the water employed in the initial phase

17. Pelletization industrial plant
CRETE th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Pelletization industrial plant
Rotary
And
Tilting
Granulator
Plate
Feeding
Sliding
Belt
Intensive mixers

18. Granules composition CRETE 2014 4th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Granules composition
System
Ash origin
Binder type
Water/Solids
Rotary furnace
Stoker furnace
CEM
Lime
CFA
R70C 70 - 30
0.25
S70C
0.41
R70L
S70L
0.36
R60LA 60 15 25
0.32
S60LA
0.39
R50LA 50 20
0.35
S50LA
0.40
All the systems were submitted to a second granulation step in which a 1:1 cement/coal fly ash binder was used in amount equal to 40% of granules weight.
In the following, these systems are distinguished by placing the + sign at the end of each label.

19. CRETE 2014 4th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Grading and curing
Aggregates of 4–12 mm and 12–20 mm in size have been stored and cured
First curing phase:
24 hours in a climatic chamber at 40°C and 95% RH
Second curing phase:
14-day at room temperature and 100% RH

20. CRETE 2014 4th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Density is greater for the smaller size fraction:
during the final compacting phase of granulation, water is more easily expelled in the case of smaller granules.
Ash origin has no significant effect on granules density:
despite the greater water requirement in the granules manufacture starting from stoker furnace incinerator ash.
Higher density is obtained when cement is used in the granules manufacture instead of lime.
Granules can be classified as lightweight aggregate: densities are lower than the limit of 1600 kg/m3 and, particularly, 4-12 mm size aggregates show an average density of about 1050 kg/m3

21. CRETE 2014 4th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
WAC is clearly affected by the size of the fraction under consideration: higher values are found for the mm fraction..
In comparison to commercial lightweight aggregate:
granules tested in this study lay within a range whose limits are lower.
WAC ranges between 10 and 16% for commercial artificial aggregate and between % for one-step granulation and % in the case of two-step granulation, for granules manufactured in this study.

22. CRETE 2014 4th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
As in the case of commercial alternatives, crushing strength of our lightweight aggregates relies in the range of 2-6 MPa.

23. A B C CRETE 2014 4th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Microstructural analysis has been carried out in order to evaluate the influence of the second pelletization step on physical and mechanical properties.
Interface between the core and the outer shell can favor the release of heavy metals and so lower the benefits of a pure binder external layer. Figure 5 shows the interface zone between the external layer and the waste matrix.
Figure A: inner matrix which is more porous than outer shell (Figure C) due to high waste content.
Figure B shows the interface between the two phases, revealing that double-step pelletization process enable to obtain an improved microstructure in order to reduce leaching and enhance physico-mechanical performance. A B C

24. CRETE 2014 4th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Mechanical degradation resistance, represented by Los Angeles coefficient values, shows a similar trend to that of crushing strength.
According to UNI EN 13242: 2008 (Italian-European standard “Aggregates for unbound and hydraulically bound materials for use in civil engineering work and road construction”), all the produced aggregates can be classified LA50 category, except for R70L , R70L+, S70L and S70L+ which can be instead classified as LA60.

25. CRETE 2014 4th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
System
Cd, g/L
Limit=5
Zn, mg/L
Limit=3
Pb, g/L
Limit=50
Cu, g/L
Time, days pH 3 14 28
R70C
3.07
3.89
4.13
2.13
2.49
2.71
12.8
15.3
21.2
27.1
32.2
38.4
11.08
R70C+
1.24
1.81
1.93
0.67
0.79
0.91
3.25
4.47
4.92
10.4
12.3
15.7
10.47
R70L
6.34
7.76
8.11
3.62
4.31
4.87
47.1
54.5
68.8
41.3
59.5
68.7
10.97
R70L+
1.02
1.68
1.85
0.92
1.09
3.15
3.74
13.4
16.2
19.5
10.24
R60LA
3.19
3.92
4.23
2.31
2.38
2.93
12.6
17.3
19.1
24.3
26.9
29.8
11.03
R60LA+
1.05
1.78
1.89
0.58
0.73
0.78
3.31
4.32
4.67
9.12
9.87
11.4
10.15
R50LA
3.56
4.62
4.91
2.21
2.48
2.83
13.3
14.9
20.3
23.2
28.1
31.7
11.14
R50LA+
1.08
1.77
0.61
0.70
0.86
3.18
3.76
4.15
10.5
13.6
15.2
10.92
UNI 10802: 2004 (EN : 2002) leaching test carried out on the size fraction mm of the granules manufactured starting from the rotary furnace incinerator ash.
According to Italian regulation, only the cumulative release value after 3 days is to be taken into account for comparison with the limit fixed for each metal.
The compliance leaching test employed for the granules was extended to 14 and 28 days to have a better understanding of the long term leaching behaviour of the granules.

26. CRETE 2014 4th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Consideration on artificial aggregates leaching behaviour
Size fraction 4-12 mm has been excluded from this test because the granules have shown better physical properties (higher density, lower porosity).
Samples obtained from stoker furnace incinerator ash have not been tested for leaching behavior.:
Granules based on this ash proved to have better physical and technological properties in relation to civil engineering applications.
Stoker furnace incinerator ash is poorer of heavy metals of environmental concern than rotary furnace incinerator ash.
Metal release is also affected by the type of binder. In fact, cement-based granules containing 70% ash behave better than the corresponding lime-based ones. This is quite an expected result, as physico-mechanical properties of the granules based on lime alone as binder revealed to be of the worst rank.
Effect of MSWI Fly Ash content on leaching behaviour does not seem significant at least in the composition range investigated.
Release at times longer than 3 days (14 and 28 days) increases over that at 3 days but to a limited extent, this is a very positive result in view of long-term behaviour in civil applications.

27. Concrete mixtures composition
CRETE th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Concrete mixtures composition
Components [kg/m3]
R70C
R70C+
S70C
S70C+
R60LA
R60LA+
S60LA
S60LA+
R50LA
R50LA+
S50LA
S50LA+
CEM I 42.5R
350
Water
175
S:AA*
3:4
Adm. [l/m3]
7.1
6.2
6.3
5.4
6.8
5.9
6.0
5.1
6.1
5.7
5.3
*S:AA represents sand to coarse artificial aggregates ratio

28. Concrete density CRETE 2014 4th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Concrete density
UNI EN 206-1: 2006 (Italian-European standard “Concrete - Part 1: Specification, performance, production and conformity”)
Concretes containing R70C, R70C+, S70C and S70C+ aggregates belong to density class D2,0 while the remaining one belong to D1,8 class.

29. Concrete compressive strength
CRETE th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Concrete compressive strength
Unconfined compressive strength of cubic specimens ranged from 15 to 35 MPa, revealing that middle range performance building elements could be obtained.

30. CRETE 2014 4th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
CONCLUSIONS
Ash from municipal, hospital and industrial solid wastes incinerator can be successfully employed up to 70% content in the production of artificial aggregate by means cold-bonding pelletization
Different binders can be used for the production of the granules, but only cement and coal fly ash/lime systems give satisfactory technological properties. Lime alone proved to be unsuitable as granules binder
Fly ash samples coming from stoker furnae incinerators was able to give granules of better technological properties
Influence of aggregates size on physical and mechanical properties is in line with other literature studies
In the majority of the cases tested, the release of heavy metals was below the limits fixed by Italian law for civil engineering applications. Exceptions to this have only been observed when lime alone is used as a binder for the production of the granules

31. Work in progress CRETE 2014 4th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
CONCLUSIONS
All the relevant granules properties, mainly compressive strength and leaching behavior, improve when the granules are produced via a two-step pelletization process. This was an expected result and the quantitative effect of the second pelletization step was evaluated
Depending on process parameters (type of binder, granules composition, type of pelletization etc.),it is possible to produce artificial aggregates of satisfactory physico-mechanical properties for concrete of middle range performances
Work in progress
The potential issues related to durability of concrete containing this particular kind of artificial aggregates will be discussed in future studies. After further investigations, these artificial aggregates could be proposed for the production of cementitious composites, bricks, lightweight panels etc.

32. for your kind attention….
CRETE th International Conference on
Industrial and Hazardous Waste Management
2-5 September Chania, Crete, Greece
Thank you very much
for your kind attention….