Sugarcane Bagasse Ash as a Potential Quartz Replacement inRed Ceramic

Silvio Rainho Teixeira,w Agda Eunice de Souza, Gleyson Tadeu de Almeida Santos, andAngel Fidel Vilche Pena

Departamento de Fısica, Quımica e Biologia, Universidade Estadual Paulista-UNESP, Presidente Prudente–SP, Brazil

Alvaro Gil Miguel

Usina Alto Alegre, Presidente Prudente–SP, Brazil

Sugarcane bagasse ash (SCBA) is an industrial waste that con-tains silicon and aluminum oxides as the major components andiron, calcium, magnesium, and potassium oxides as the mainminor components. In this paper, SCBA from one Brazilianfactory was characterized and tested for its influence on the ce-ramic properties of clay/ash ceramic probes. Prismatic probeswere pressed (18 MPa) using a ceramic mass mixed with 0%,5%, 8%, and 10% ash. The probes were fired at temperaturesbetween 8001 and 12001C. X-ray diffraction, X-ray fluores-cence, thermal analysis (differential thermal analysis, thermo-gravimetric analysis/differential thermogravimetric analysis),and tests for texture (particle-size analysis), flexural strength,and linear shrinkage were carried out to characterize the sam-ples. The results showed that the amount of ash to be incorpo-rated will depend on mainly the composition of clay but also ash,and indicated that the clay used in this work can incorporate upto 10% weight of ash to produce solid bricks. The results alsoshowed an improvement in ceramic/ash properties up to sinter-ing temperatures higher than 10001C.

I. Introduction

NOWADAYS, many scientists worldwide are studying wastesfor recycling or for reuse to make useful products. Numer-

ous silicate-based wastes have been studied for reuse in theceramic industry. Recently,1 a review was published showingthat considerable knowledge and expertise has been accumulat-ed in the process of transforming silicate waste into useful glass–ceramic products. Although numerous types of waste have beenstudied, sugarcane bagasse ash (SCBA) has been overlooked,probably because this residue is more common in developingcountries that produce sugar and alcohol from sugarcane. Brazilis the world’s largest producer of alcohol and sugar fromsugarcane. In addition, it is the only country in the world thathas an extensive alternative program for automobile fuel. TheBrazilian PROALCOOL program completed its 30th birthdayin 2005. The new technology of flex–fuel (alcohol and/or gaso-line) vehicles revived the program, and today more than 80% ofthe new cars built in the country use this system. There are atleast three reasons favoring alcohol as an automobile fuel: thecrude oil market has a poor outlook, alcohol is a renewableresource, and alcohol as a fuel produces very little environmen-tal pollution. Many countries have expressed interest in this

program and there is a worldwide tendency of stepping up al-cohol consumption for fuel.

Pressed sugarcane bagasse is burned by factories to producesteam and electricity. The combustion yields ashes (bottom andfly ashes) containing high amounts of charcoal and silicon ox-ides as the major components. Aluminum, calcium, iron, andmagnesium oxides are the main minor components. The fly ashcontains more charcoal than the bottom ash and is sieved toseparate thick charcoal from inorganic materials, which is con-centrated in the thinner fraction. Approximately 30% by weightof the dry ash is charcoal and 70% is inorganic material, withsilica as the major phase. Two years ago, it was estimated that1.2 million tons of ash were produced by the Brazilian sugar/alcohol industry. The charcoal in the fly ash can be separatedfrom the inorganic fraction and can be used to produce charcoalbriquettes,2 and the ash has many applications: cement replace-ment (pozzolanic) material,3–12 adsorbent of heavy metals,13 andnonplastic material (filler) in ceramic materials.14–19

There are some discrepancies in the results published on thepozzolanic activity of sugarcane ashes for reuse in concrete andin lime–pozzolana binders. These discrepant results may be dueto the reactivity of the ash, which depends on its compositionand on several factors involved in the burning process, such asthe temperature, time, environment, and cooling rate as well aschemical activation.3 Although some studies have found thatSCBA is amorphous, the majority of the works cited indicatethat SCBA is composed mainly of crystalline quartz, impairingits pozzolanic activity. In recent works, Freitas9 and Frias andVillar-Cocina4 showed that SCBA needs to be calcinated to beactive and can be classified as a pozzolanic material. Also,Ganesan et al.20 showed that SCBA burned at 6501C andground (o46 mm) is a better substitute than other mineraladmixtures for durable concrete structures.

The raw material for the manufacture of conventional ceram-ics has different combinations of clay, silt, and sand fractionsdepending on the final desired product.21 Its composition ismore complex than traditional porcelain, which is a triaxialbody composed of plastic material (clays), a fluxing agent(generally feldspar, used to reduce the firing temperature), andquartz. In the red ceramic industry, two or more natural mate-rials are generally mixed to prepare the ceramic mass with thedesired properties. In some cases, fluxing and/or nonplasticmaterials (e.g., quartz) can be used to improve the sinteringprocess and the final ceramic properties. The wide compositionrange of clays used for manufacturing red ceramic makes themgood receptors of residues. The possibility to recycle waste ma-terials in red ceramic is nowadays an advantageous reality inenvironmental protection and in saving raw materials. SCBA iswidely available in many developing countries, and in Brazilsome research has been ongoing to take advantage of this.

In this work, SCBA was characterized and its use in replacingquartz to produce red ceramic was evaluated.

C. Jantzen—contributing editor

Presented at the Annual Meeting of The Brazilian Ceramic Society (50o CongressoBrasileiro de Ceramica), Blumenau, SC, Brazil, May 22–25, 2006 (Paper 19-14).

This work was partially supported by FAPESP.wAuthor to whom correspondence should be addressed. e-mail: rainho@fct.unesp.br

Manuscript No. 23211. Received May 15, 2007; approved October 31, 2007.

Journal

J. Am. Ceram. Soc., 91 [6] 1883–1887 (2008)

DOI: 10.1111/j.1551-2916.2007.02212.x

r 2008 The American Ceramic Society

1883

II. Experimental Procedure

SCBA was collected from boilers (bottom ash) at ‘‘Usina AltoAlegre,’’ a company in Presidente Prudente-SP, Brazil. The sam-ples were sieved (o0.5 mm) and coarser particles were rejected.Fine charcoal was separated from the inorganic material with anair jet. This ash was milled (6 h) with water in a ball mill toprovide a grain-size distribution compatible with that of theclay. After drying in an oven (1001C), the sample did not showclumping due to the high concentration of quartz and was sievedto o88 mm (170 mesh).

The clay sample was a ceramic mass used to produce roof tilesand was obtained from the company ‘‘Ceramica Romana’’ inPresidente Epitacio-SP, Brazil. This clay showed a grain-sizedistribution with more than 97% of the particles beingo88 mm.The concentrations of the clay, sand, and silt fractions were de-termined using the pipette method.22

The chemical composition of the ash and clay was determinedby the X-ray fluorescence (XRF) method (Model EDX 700,Shimadzu Scientific Instruments, Tokyo, Japan). The ash andclay crystalline phases were identified by X-ray diffraction(XRD, Model D/MAX-2100/PC, Rigaku Corporation, Osaka,Japan). Differential thermal analysis (DTA, Model TA-1600,TA Instruments, New Castle, DE) and thermogravimetric anal-ysis (TGA, Model TG-209, NETZSCH Instruments, Burling-ton, MA) were also used to characterize these materials.

Prismatic probes (60 mm� 20 mm�B5 mm) were pressed(18 MPa) using a ceramic mass for roof tile production mixedwith 0%, 5%, 8%, and 10% ash. The probes were fired (8001,9001, 10001, 1100, and 12001C) in a laboratory electric kiln at aheating rate of 101C/min. The flexural strength (FS) (threepoints) and linear shrinkage (LS) of the sintered probes weredetermined using a Model DL 2000 apparatus (EMIC Equip-amentos e Sistemas de Ensaio, Parana, Brazil) and a caliper.

III. Results and Discussion

(1) Characterization

The chemical compositions (XRF) of SCBA from different plac-es and the SCBA and clay used in the present work are sum-marized in Table I. A comparison of the chemical compositionsof SCBA with the literature data8–10,12,17,18 shows that there aredifferences among them due to differences in soil where the sug-arcane was grown. The ashes have a very high silica concentra-tion and contain aluminum, iron, alkaline, and alkaline earthoxides as minor components. The SCBA–XRD patterns for thetwo types of ash were similar, with quartz as the major phase(Fig. 1). The chemical analysis (Table I) of SCBA used in thiswork shows that it possesses more silica than the others found inthe literature, thereby resulting in different diffractograms witha predominance of quartz.

The clay showed a typical composition of kaolinitic material,with a high iron concentration, confirmed by the XRD patternsof an oriented specimen on a glass slide23,24 (Fig. 2). In this

pattern, the clay was saturated with potassium (KCl, 3.15 A)and it contained kaolinite (7.22 and 3.58 A) as the major phase.Mica (10.01 and 4.99 A), quartz (4.26 and 3.34 A), gibbsite (4.85A), goethite (4.18 A), lepidocrocite (6.30A), and probablymontmorillonite (B12.5 A), a 2:1 clay mineral are the minorphases.25 This mineralogical composition is common to claysfrom this region.26,27 Mica and gibbsite increase the K and Alconcentrations in the sample, respectively. Titanium, iron, phos-phorus, and other compounds act as nucleating agents in glass–ceramic formation. The combination of some of these nucleatingoxides promotes the formation of small crystals of spinel, whichin turn act as nucleating sites for the main crystal phase (e.g.,, apyroxene). The alkaline and alkaline earth oxides act as fluxingagents, which lower the melting temperature and the viscosity,aiding the crystallization process.1 Thus, their concentrations inthe ceramic mass are important for the sintering process.

The texture analysis of the clayed material (sand, silt, and clayfractions: 24.1%, 17.6%, and 58.3%) showed that it has a highclay concentration and consequently high plasticity, which mayresult in many difficulties during the production (extrusion,drying, and firing) process (Table II).21 To reduce material plas-ticity, a sandy material is generally mixed with it. SCBA can beused as a sandy material with the advantage of containing somefluxing oxides.

The clay thermogravimetric (TGA and DTG) curve (Fig. 3)confirms its kaolinitc nature (loss of hydroxyls near 5001C) andthe presence of hydroxides (loss of hydroxyls near 3001C) in theclay, as was observed in the XRD pattern of the clay fraction(gibbsite, goethite, and lepidocrocite).25

The ash DTA thermal patterns (Fig. 4) show two low-inten-sity ranges (probably some aluminum silicate from the kaolinminerals family) and the characteristic peak of a3b quartztransformation, confirming the predominance of this crystalline

Table I. Chemical Composition of Clay and Several SCBA by XRF

Oxides Clay SCBA Borlini and colleagues17,18 Zardo et al.8 Freitas9w Paya et al.12z Martirena et al.10

SiO2 51.48 85.58 77.5 77.3 83.1/65.7 59.87 72.74Al2O3 36.00 5.25 4.7 5.4 5.1/13.8 20.69 5.26Fe2O3 8.43 1.31 3.8 8.1 2.6/4.1 5.76 3.92CaO 0.31 2.08 2.3 1.6 1.9/3.5 3.36 7.99MgO — 1.09 3.0 1.4 — 1.87 2.78Na2O — — — — — 1.13 0.84K2O 1.57 3.46 5.4 4.0 4.5/8.1 1.37 3.47TiO2 1.95 0.32 0.3 2.2 — — 0.32MnO 0.11 0.08 0.3 — — — —P2O5 — 0.54 2.3 — — — 1.59

wTwo ash samples from two different factories. zAccording to the authors, the higher aluminum concentration is probably due to the addition of coal to bagasse for

combustion. SCBA, sugarcane bagasse ash; XRF, X-ray fluorescence.

Fig. 1. X-ray diffraction pattern of the ash (Q–quartz).

1884 Journal of the American Ceramic Society—Teixeira et al. Vol. 91, No. 6

silicate in SCBA. No peak was observed up to 12001C. All theanalytical results confirmed quartz as being the principal com-ponent of SCBA, indicating that under these conditions, this ashshould show low pozzolanic activity. Burned sugarcane bagasseshows a lower concentration of quartz and produces slightlyless ash than that of rice, which produces an amorphous ashwith high pozzolanic activity when burned at low temperatures(o8001C).28

(2) Technological Properties of the Sintered Probes

LS (Fig. 5) of the clay/ash mixture was lower than that of theclay. The ash improved LS due to its high concentration ofcrystalline silica (quartz), which lowers the sample plasticity(clay concentration). This was an expected result observed inother studies.14,17–19 At temperatures higher than 10001C, it canbe observed that there was an inversion in the curves and LSincreased faster for the clay/ash material than for the clay. Thisresult indicates the formation of liquid phases due to the fluxingagents, which are in higher concentrations in the ash than in theclay, and that lower the melting temperature. This behavior isalso observed in the variation of FS with temperature (Fig. 6)and also in water absorption (o20%) and apparent porosity (o35%).29 Although the clay did not show any variation of FSabove 10001C, samples with 8% and 10% of incorporated ashexhibited a continuous increase in FS with temperature. At theseash concentrations, this effect is not enough to overcome thebehavior imposed by the clay composition. Although the vari-ation of data as seen from the standard errors does not showsignificant differences in the properties with ash concentration,the data indicate a tendency toward worse technological prop-erties with a higher ash concentration. Between 9001 and12001C, the FS showed better results for ash concentrations of5% and 8% compared with 10%. At 8001 and 12001C, therewere no differences in FS and LS for the three ash concentra-tions. In the former case, this occurs because nothing significantoccurs at those temperatures, and the latter case is explained by

liquid-phase formation at all ash concentrations. On studyingthe influence of SCBA in the substitution for fluxes (feldspar andtalc), Borlini et al.16 concluded that the ash did not act as afluxing agent in the compositions studied, at 12001C, and itsincorporation into the ceramic mass improved only the LS.Borlini et al.18 also observed that there were no significant

Fig. 2. X-ray diffraction pattern of the potassium-saturated clay (M,mica; K, kaolinite; L, lepidocrocite; Gi, gibbsite; Go, goethite; Q, quartz;and KCl).

Table II. Ideal Granulometric Composition of the RedCeramic Products21

Red ceramic products

Granulometric composition (%)

r2 mm 2–20 mm �20 mm

(A) High quality products 40–50 20–40 20–30(B) Roofing tiles 30–40 20–50 20–40(C) Hollow bricks 20–30 20–55 20–50(D) Solid bricks 15–20 20–55 25–55 Fig. 5. Linear shrinkage to the ceramic mass with different ash

concentrations.

Fig. 3. Thermogravimetric and differential thermogravimetric curvesfor the clay sample.

Fig. 4. Differential thermal analysis curve of the sugarcane bagasse ash.

June 2008 SCBA: A Quartz Replacement in Red Ceramic 1885

changes in the physical and mechanical properties of the redceramic in which ash has been incorporated. Meanwhile, theyobserved large microstructural differences when 20% ash wasincorporated in comparison with the other compositions stud-ied, due to the substantial formation of a liquid phase at 12001C.In other works,17,19 it was observed that ash incorporation had adetrimental effect on the mechanical strength of specimens firedat 9701C and concluded that low addition (o5%) of ash did nothave a significantly detrimental effect. As a general rule, allworks conclude that due to the high concentration of quartz inthe SCBA, it behaves as a filler material reducing the ceramicmass plasticity at firing temperatures up to 12001C. This willimprove its workability and the production process (extrusion,drying, and firing).

It is difficult to compare the data because the compositions ofashes and mainly the clays used to incorporate the ashes aredifferent and the clay composition has a strong influence on theresults. Therefore, the amount of ash that can be incorporatedwill depend on the nature of the clay utilized as the matrix. Forthe clay used in this work, incorporation up to 10% of ash al-lows its utilization for the manufacture of solid bricks.

These results suggest future work with higher ash concentra-tions incorporated into the clay. Moreover, the SCBA compo-sition also suggests that it could be used as a component in themanufacture of glass, glass ceramics, and porous ceramics (forfiltering).

IV. Summary

The ash resulting from the burning of sugarcane bagassehas a very high quartz concentration and low concentrationsof fluxing oxides. The ash composition is variable and dependson the place where the sugarcane is produced. Although theconcentration of fluxing agents (K, Na, Ca, Mg) is low, it ishigher than that in clay, and the data show an improvement inthe ceramic/ash properties with regard to sintering temperatureshigher than 10001C.

The amount of ash to be incorporated will depend on the ashand mainly, the clay composition. The results indicate that theclay used in this work can incorporate up to 10% by weight ofash to produce bricks.

SCBA has a composition that indicates that it can be used ina triaxial ceramic composition (clay, SCBA, fluxing agent) insubstitution to quartz and that it has the potential to be used tomake other practical glass-based products. In addition to theindustrial utility of this silicate waste, there are many environ-mental benefits to be gained from its recycling.

Acknowledgments

The authors thank Dra. Deyse I. dos Santo, and Dra. Elisabete A. A. Rubo forX-ray data; and Usina Alto Alegre for the ashes and information about the ashproduction. Dr. A. Leyva assisted with the English editing of the manuscript.

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