Giorgio Lollino

Andrea Manconi
Fausto Guzzetti
Martin Culshaw
Peter Bobrowsky
Fabio Luino
Editors

Engineering Geology
for Society and
Territory – Volume 5
Urban Geology, Sustainable Planning
and Landscape Exploitation
 Production of Lightweight Aggregates
from Phosphate Washing Plant Sludge 11
Emna Fakhfakh, Imen Khiari, Walid Hajjaji, Mounir Medhioub,
Fernando Rocha, Alberto López-Galindo, and Fakher Jamoussi

Abstract
In this study, we assessed the potentialities of using the phosphate washing by-products as row
materials for the production of lightweight aggregates. Sludge samples from different washing
plants have been physic-chemically characterized. Slurries were dried, milled and shaped into
spherical pellets. These raw aggregates were sintered for 5 min in the laboratory kiln at
different temperatures between 1,120 and 1,180 °C. The bloating potential of the lightweight
aggregates as well as the effect of the firing temperatures on their properties (expansion,
apparent density, water absorption and compressive strength) were assessed. The mineral-
ogical data shows that the collected sludge samples are mainly composed of carbonates,
francolite, clinoptilolite, quartz and feldspars; smectite, palygorskite and sepiolite are also
present as clayey fractions. Chemically, the samples exhibited significant amount of SiO2,
CaO, and P2O5. When sintered, the aggregates expand; this expansion results from the
concomitant reaction of gas release and viscous phase formation. The produced lightweight
aggregates revealed acceptable technological properties with apparent density values often
lower than 0.9 g/cm3. Moreover, good expansion (60 % in volume) and water absorption
(close to 10 %) were obtained. These results are encouraging and allow considering the
studied sludge as promising material for the production of lightweight aggregates.

Keywords
Lightweight aggregate Phosphate Sludge Expansion Tunisia

11.1 Introduction

Lightweight aggregates (LWAs) are granular and porous

materials with a loose bulk density lower than 1200 kg/m3
E. Fakhfakh (&)
I. Khiari
W. Hajjaji
F. Jamoussi (1. 20 g/cm3) or with a particle density lower than 2,000 kg/
Laboratoire de valorisation des matériaux utiles, CNRSM, BP 73, m3 (2.00 g/cm3) (UNE-EN-13055-1 2003). They can be
8027, Soliman, Tunisia produced from natural materials such as clays, shale, slates
e-mail: efakhfakh@yahoo.com (Dahab 1980; Dahab and Champetier 1984; Decleer and
M. Medhioub Viaene 1993; Fragoulis et al. 2004; Fakhfakh et al. 2007), or
Département des Sciences de la Terre, Faculte des Sciences de volcanic rocks (Riley 1951; De ‘Gennaro et al. 2004). LWAs
Sfax, 3018, Sfax, Tunisia
can also be produced from waste materials (Liaw et al. 1998;
F. Rocha González corrochano et al. 2009) or industrial by-products
Geobiotec & Dep. Geociencias, Universidade de Aveiro,
3810-193, Aveiro, Portugal (Verma et al. 1998; Baykal and Doven 2000; Ducman et al.
2002; Huang et al. 2007; González corrochano et al. 2009)
A. López-Galindo
Andalusian Institute of Earth Sciences (IACT), CSIC-University which can constitute an environmental alternative.
of Granada, Avda. Palmeras 4, Armilla, Granada, Spain

G. Lollino et al. (eds.), Engineering Geology for Society and Territory – Volume 5, 59
DOI: 10.1007/978-3-319-09048-1_11, © Springer International Publishing Switzerland 2015
60 E. Fakhfakh et al.

Table 11.1 Mineralogical composition of the studied samples

Samples Sm Pal Sep Ill Fra Clino Qz Gyp Cal Dol Fel Hal
RLM4 6 21 9 0 24 6 3 1 20 2 8 0
RLK 26 16 5 0 9 6 0 0 28 5 5 0
RLR 25 19 0 9 11 2 1 0 23 7 3 0
RLMD 10 29 12 0 10 3 1 2 22 8 0 3
Sm smectite; Pal palygorskite; Sep sepiolite; Ill illite; Fra francolite; Clino clinoptilolite; Qz quartz; Gyp gypsum; Cal calcite; Dol dolomite; Fel
feldspars; Hal halite

The production of LWAs is performed by heating at high Apparent density (AD, expressed in g/cm3) was calcu-
temperature materials that are able to bloat, i.e. materials lated as W/V ratio, where W is the weight of the expanded
which develop simultaneously gases and viscous phase that aggregates and V is their volume measured by the method of
could entrap the released gases (Riley 1951). sand dislocation.
LWAs are mainly used as constituents in concrete and Compressive strength (S) is given by Li et al. (2000):
various building materials due to their typical properties of

good thermal and acoustic insulation as well as their good S ¼ ð2:8PcÞ= pX 2
fire resistance. They can also be used as filter media for
bacterial (Ausland et al. 2002) or metallic ion removal. The Where X is the distance between loading points (sphere
porous and inert properties of these materials make them diameter) and Pc is the fracture load occurring rupture.
highly suitable for agriculture application such as hydro- Fracture force of a single aggregate (expressed in N) was
ponic cultivation (Dahab 1980). measured in an EZ 50 LLOYD traction- compression
The phosphate washing plants in Tunisia led to a huge machine.
accumulation of by-products discarded in waste ponds. These Water absorption (WA) was estimated after 24 h of
wastes are considered hazardous materials. The alternative of immersion in distilled water, and expressed in percentage
recycling them would offer a suitable environmental solution. weight:
The aim of this study is to recycle the sludge produced by
the phosphate washing plants, in order to obtain a usable WA ¼ 100  ðWs  WÞ=W;
materiel such as LWAs.
where Ws is the water-saturated weight, and W the original
weight.
11.2 Materials and Methods Expansion (E) was expressed as diameter changes after
firing, following the equation:
Samples from the sludge generated from the phosphate
E ¼ 100  ðd2  d1Þ=d1;
washing process have been collected from different phos-
phate washing plants: M’dhilla (RLMD), Metlaoui (RLM4), where d1 and d2 are the diameters of the balls before and
Kef Eddour (RLK) and Redeyef (RLR). The characterization after firing, respectively.
of these materials involved mineralogical analysis using a
Philips X’Pert X-ray diffractometer equipped with Cu-Ka
radiation and chemical analysis by X-ray fluorescence 11.3 Results and Discussion
(XRF), using an Axios Wavelength Dispersive XRF spec-
trometer. The loss on ignition was estimated from measuring 11.3.1 Characterisation of Raw Materials
the loss of weight of a 10 g sample first dried in a 110 °C
oven, and then calcined at 1000°. The grain size distribution The mineral composition of the phosphate-washing plant’
was determined by a micromeritics Sedigraph 5100. sludge (RLM4, RLK, RLR and RLMD) revealed that clay
Small pellets (7–9 mm in diameter) were shaped by hand minerals are an essential component (36, 47, 53 and 51 %
from fresh wet paste of powdered sludge, air-dried at room respectively) of these materials. Palygorskite, smectite and
temperature for several days, and then heated. The dried sepiolite are the main minerals of the clayey phases
balls were submitted to the firing temperatures ranging from (Table 11.1). Francolite (fluorapatite carbonate) which is the
1,120 up to 1,180 °C, during 5 min. The following proper- typical phosphate mineral ranges from 9 to 24 %, and calcite
ties were determined on the bloated balls: varies between 20 and 28 %. Clinoptilolite, dolomite, quartz
11 Production of Lightweight Aggregates 61

Table 11.2 Chemical composition of the studied samples

Sample SiO2 Al2O3 Fe2O3 P2O5 CaO MgO Na2O K2O SO3 TiO2 LOI Fl Si/Fl
RLM4 31.8 6.9 2 11.8 23.3 2.3 1 0.8 3.1 0.2 16.8 29.4 1.1
RLK 33.3 7.5 2 9.8 21 2.4 0.9 1 3.2 0.3 18.6 27.3 1.2
RLR 30.4 7.7 2.4 11.2 23.4 2.4 0.5 1.3 2.7 0.3 17.7 30 1.0
RLMD 21,9 5.5 2.1 6.4 18.5 2.9 12.7 0.4 1.8 0.2 27.6 36.6 0.6
Fl Fluxing. Si/Fl SiO2/fluxing (CaO, MgO, Fe2O3, Na2O and K2O)

120 RLM4 SiO2

100
Cumulative mass (%)

RLK
80

60
RLR
RLK RLM4
40 RLR
RLMD RLMD
20

0
1000 100 10 1 0,1 Limits of
Cougny
Equivalent spherical diametre (µm) Al2O3 Fluxing elements
(1990)

Fig. 11.1 Grain size distribution curves of the studied samples Fig. 11.2 Ternary diagram showing the area of bloating mineral
according to Riley (1951)

and feldspar contents are relatively low and halite is only

present in RLMD. and the bursting of RLMD pellets during firing process
Chemical analysis (Table 11.2) showed that SiO2, Al2O3, should be related to the fineness of this material (Fakhfakh
P2O5 and CaO are the main constituents of the raw materials. et al. 2007) and presumably to the presence of halite which
This result is consistent with mineralogical composition form a superficial layer.
since SiO2 and Al2O3 contents relate principally to clay According to the mineralogical and chemical data, the
minerals, P2O5 to francolite and CaO to carbonate minerals. gases developed during swelling could originate from the
The high value in P2O5 should be related to another unde- fluxes (calcite, dolomite and/or iron derivatives), the struc-
tected phase in the XRD patterns. High Na2O (12. 7 %) tural water of the clay minerals and from francolite which
detected in RLMD are mainly related to the presence of decomposition produce CO2 and F2. These gazes have to be
halite in this sludge. trapped by a viscous phase thus allowing the expansion of
Grain size analysis showed that RLMD is finer material the pellets.
compared to the other sludge samples, with an important
clay fraction (<2 μm) of 86.5 % (Fig. 11.1).
11.3.3 Expanded Products Characterization

11.3.2 Expansion LWAs produced from RLM4, RLK and RLR sludge showed
uniform expansion and spherical shape for firing tempera-
The chemical data of the raw materials (recalculated to tures of 1120–1160 °C. At 1180 °C LWAs are flattened
100 %) were plotted on the SiO2—Al2O3 -fluxing elements (RLM4) or fused (RLR and RLK). Their mantles are yellow
(CaO + MgO + Fe2O3 + Na2O + K2O) diagram (Riley (Fig. 11.3) due to the presence of francolite, while their cores
1951). All the sludge samples are located outside the “area are blackish.
of bloating” (Fig. 11.2): they have high fluxing element The expansion, that expresses the volume change of
contents (27–37 %) and low Si/fluxing ratio (<2, see LWAs, increases with temperature (Fig. 11.4a). The value of
Table 11.2). Hence they were thought to have low viscosity, −3 % recorded for RLR is due to the shrinkage of these pellets,
meaning they cannot trap a significant amount of gas and thus at 1,120 °C the softening doesn’t occur yet. The apparent
thus are prevented from swelling during firing (Riley 1951; density of the fabricated LWAs decreases with temperature
De’Gennaro et al. 2004). This was proven wrong with the (Fig. 11.4b). At 1,120 °C the values are >1 g/cm3, however at
experimental results since bloating occurred for the sludge 1,160 °C they are <0.5 g/cm3. It is clear that apparent density
materials RLM4, RLR, and RLK. The absence of bloating and expansion move in opposite. In fact, it has been reported
62 E. Fakhfakh et al.

Fig. 11.3 External appearance

and surface texture of LWA
fabricated from RLK at 1,120–
1,160 °C

Fig. 11.4 Effect of heating (a) RLM4 RLK RLR (b) RLM4 RLK RLR

Apparent density (g/cm3)

temperature on the expansion (a), 70 1,4
apparent density (b), water 60 1,2
Expansion (%)

absorption (c) and compressive 50 1

strength (d) of the fabricated 40
0,8
LWAs 30
0,6
20
10 0,4
0 0,2
-10 0
1110 1120 1130 1140 1150 1160 1170 1110 1120 1130 1140 1150 1160 1170
Temperature (°C) Temperature (°C)

(c) (d)

Compressive strength (MPa)

RLM4 RLK RLR RLM4 RLK RLR
16 4,5
Water absorption (%)

4
14
3,5
12
3
10 2,5
8 2
6 1,5
4 1
2 0,5
0 0
1110 1120 1130 1140 1150 1160 1170 1110 1120 1130 1140 1150 1160 1170
Temperature (°C) Temperature (°C)

that these two properties are related to each other and to the strength decreases when temperature increases. This is due to
LWAs pore size (Fakhfakh et al. 2007). the increase of the pore sizes which become much large and
As shown in Fig. 11.4c, the behavior of fabricated LWAs less abundant when temperature rises from 1,120 to 1,160 °C.
with respect to water is the same. When the temperature The highest value of 4.08 MPa obtained for RLR at 1,120 °C
increases between 1,120 and 1,140 °C water absorption corresponds to non bloated pellets (E: −3 %).
decreases. This is due to the formation of a viscous phase
able to seal the fractures occurred at 1,120 °C (see Fig. 11.3).
When the temperature increases to 1,150 °C the viscous 11.4 Conclusion
phase becomes liquid enough to entrap more gas. Therefore,
the porosity develops further, promoting the increase of In this study, the sludge samples taken from phosphate
water absorption. Beyond 1,150 °C, the decrease of WA is washing plants were investigated regarding their possible
due to the vitrification of the surface of LWAs which use in the production of LWAs. The laboratory results have
opposes a high WA. It has been reported that water proved that these materials are able to bloat, although they
absorption rate below 10 % indicates that the surface of the don’t fulfill chemical requirements (Riley 1951). The bloated
LWAs has been well vitrified (Huang et al. 2007). pellets have an apparent density of 0.3−1.23 g/cm3, a water
Strength of LWAs is an important parameter for their absorption percentage in the range of 4–14 % and a com-
classification. It is affected by factors, such as the density and pressive strength values between 0.04 and 4.08 MPa.
shape of the aggregates, the size and distribution of the pores, Phosphate washing plant sludge can be a promising raw
the densification effect due to sintering, the glassy phase and material for the production of LWAs. Even though, from a
the nature of the newly formed phases (Decleer and Viane technological consideration, these LWAs do not show high
1993; Fakhfakh et al. 2007; Chang et al. 2007; González performances in terms of compressive strength, they could
corrochano et al. 2009). Figure 11.4d shows that Compressive be used when only insulating properties are required.
11 Production of Lightweight Aggregates 63

References Fakhfakh E, Hajjaji W, Medhioub M, Rocha F, Lopez-Galindo A, Setti

M, Kooli F, Zargouni F, Jamoussi F (2007) Effect of sand addition
on production of lightweight aggregates from Tunisian smectite-rich
Ausland G, Stevik TK, Hanssen J, Køhler JC, Jensessen PD (2002) clayey rocks. Appl Clay Sci 35:228–237
Intermittent filtration of wastewater-removal of fecal coliforms and Fragoulis D, Stamatakis G, Chaniotakis E, Columbus G (2004)
fecal streptococci. Water Res 36:3507–3516 Characterization of lightweight aggregates produced with clayey
Baykal G, Doven AG (2000) Utilization of fly ash by pelletization diatomite rocks originated from Greece. Mater Charact 53:307–316
process; theory, application areas and research results. Resour González corrochano B, Alonso Azcarate J, Rodas M (2009) Charac-
Conserv Recycl 30:59–77 terization of lightweight aggregates manufactured from washing
Chang FC, Lo SL, Lee MY, Ko CH, Lin JD, Huang SC, Wang CF aggregate sludge and fly ash. Resour Conserv Recycl 53:571–581
(2007) Leachability of metals from sludge-based artificial light- Huang SC, Chang FC, Lo SL, Lee MY, Wang CF, Lin JD (2007)
weight aggregate. J Hazard Mater 146:98–105 Production of lightweight aggregate from mining residues, heavy
Dahab AS (1980)”Les argiles expansibles: caractérisation minéralog- metal sludge, and incinerator fly ash. J Hazard Mater 144:52–58
ique et chimique. Expansion statique: application à la culture sans Li Y, Wu D, Zhang J, Chang L, Frang Z, Shi Y (2000) Mesurement and
sol. PhD thesis, University of Nancy statistics of single pellet mecanical strength of differently shaped
Dahab AS, Champetier Y (1984) Recherches sur les argiles égyptiennes catalysts. Powder Technol 113:176–184
pour la production de granulats legers. Bull Int Assoc Eng Geol Liaw CT, Chang HL, Hsu WC, Huang CR (1998) A novel method to
30:361–365 reuse paper sludge and co- generation ashes from paper mill.
Decleer J, Viaene W (1993) Rupelian Boom clay as raw material for J Hazard Mater 58:93–102
expanded clay manufacturing. Appl Clay Sci 8:111–128 Riley CM (1951) Relation of chemical properties to the bloating of
De’Gennaro R, Capelletti P, Cerri G, de’ Gennaro M, Dondi, M, clays. J Am Ceram Soc 34:121–128
Langella A (2004) Zeolitic tuffs as raw materials for lightweight UNE-EN-13055-1 (2003) Aridos ligeros. Parte 1 : Aridos ligeros para
aggregates. Appl Clay Sci 25:71–81 hormigon, mortero e inyectado
Ducman V, Mladenovič A, Šuput JS (2002) Lightwheight aggregate Verma CL, Handa SK, Jain SK, Yadav RK (1998) Techno- commercial
based on waste glass and its alcai-silica reactivity. Cem Concr Res perspective study for sintered fly ash light-weight aggregates in
32:223–226 India. Constr Build Mater 12:341–346