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Journal of Environmental Management 101 (2012) 7e12

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Journal of Environmental Management j o ur n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j e n v m a n

Recycling of sugarcane bagasse ash waste in the production of clay bricks K.C.P. Faria, R.F. Gurgel, J.N.F. Holanda* Northern Fluminense State University, Laboratory of Advanced Materials, Group of Ceramic Materials, Av. Alberto Lamego 2000, 28013-602 Campos dos Goytacazes-RJ, Brazil

a r t i c l e i n f o

a b s t r a c t

Article history: Received 14 April 2011 Received in revised form 18 November 2011 Accepted 9 January 2012 Available online 2 March 2012

This work investigates the recycling of sugarcane bagasse ash waste as a method to provide raw material for clay brick bodies, through replacement of natural clay by up 20 wt.%. Initially, the waste sample was characterized by its chemical composition, X-ray diffraction, differential thermal analysis, particle size, morphology and pollution potential. Clay bricks pieces were prepared, and then tested, so as to determine their technological properties (e.g., linear shrinkage, water absorption, apparent density, and tensile strength). The sintered microstructure was evaluated by scanning electron microscopy (SEM). It was found that the sugarcane bagasse ash waste is mainly composed by crystalline silica particles. The test results indicate that the sugarcane bagasse ash waste could be used as a filler in clay bricks, thus enhancing the possibility of its reuse in a safe and sustainable way. Ó 2012 Elsevier Ltd. All rights reserved.

Keywords: Sugarcane bagasse ash Waste Recycling Clay bricks

1. Introduction Sugarcane, a grog in the same family of bamboo, is used as the main raw material for both sugar and ethanol industries. Brazil is the world’s largest producer of sugar and ethanol from sugarcane, being also the only country worldwide to develop a program for the production of ethanol as an automobile fuel (Teixeira et al., 2008). In 2009, Brazil produced about 34.6 million tons of sugar and 25.8 billion liters of ethanol (CONAB, 2009). Currently, more than 90% of new light cars built in Brazil use the flex-fuel technology for vehicles (ethanol and/or gasoline). Nevertheless, the sugarcane industry produces large amounts of sugarcane bagasse. In general, the sugarcane bagasse is used by the plants for energy co-generation (FIESP, 2001). As a result, this industry produces large amounts of sugarcane bagasse ashes. Sugarcane bagasse ash is considered a non-biodegradable solid waste material. Brazilian sugarcane industry generates a considerable amount of sugarcane bagasse ash, that is estimated in about 2.5 million tons per year (Cordeiro, 2006). However, Brazilian sugarcane industry is still booming, so that the levels of such sugarcane bagasse ash waste are expected to continuously increase. Traditionally, sugarcane bagasse ash in Brazil has been mainly disposed of as soil fertilizer (Freitas, 2005). In view of its environmental impact, such a way of disposal is far from being the most suitable one. In addition, Brazil is now enacting more regulations on environmental matters, such as those relating to solid waste disposal, so that the

development of economically viable recycling technology for sugarcane bagasse ash waste acquires a growing relevance. Sugarcane bagasse ash

In the context of recycling, the present study focuses on the incorporation of sugarcane bagasse ash waste into clay bricks for civil construction. Although the ceramic industry is highly promising for the final disposal of solid wastes, little is known about reuse of sugarcane bagasse ash waste in clay ceramics (Faria, 2011). The reason for such a lack of data in this area relates to the fact that sugarcane bagasse ashes are mainly produced in developing countries. Anyway, as Brazilian flex-fuel technology for vehicles has aroused great interest from international investors, being likely to be adopted worldwide, an increasing volume of sugarcane bagasse ash waste will have to be produced.

2. Materials and methods * Corresponding author. Tel.: þ55 22 2731 6108; fax: þ55 22 2726 1533. E-mail address: [email protected] (J.N.F. Holanda). 0301-4797/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvman.2012.01.032

Common clay and a dry sugarcane bagasse ash waste in form of powder were selected as raw materials. The ash waste was

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collected from a sugarcane plant located in south-eastern Brazil (Campos dos Goytacazes-RJ). Selected mixtures containing 0, 5, 10, 15 and 20 wt.% waste were prepared (Table 1). The mineralogical composition of the clay powder used as reference is mainly constituted by kaolinite, being also composed by quartz, gibbsite, and goethite as accessory minerals. The chemical composition of the waste sample was determined by using energy-dispersive X-ray spectrometer (EDX 700; Shimadzu). The loss on ignition (LOI) was determined according to LOI ¼ (Wd  Wc)/Wd  100, where Wd is the weight of the dry sample at 110  C, and Wc is the weight of the calcined sample at 1000 C during 2 h. Mineralogical analysis was performed by X-ray diffraction using monochromatic Cu-Ka radiation at a scanning speed of 1.5  (2 q) min1 in a conventional diffractometer (XRD e 7000; Shimadzu). The crystalline phases were identified by comparing the intensities and positions of the Bragg peaks with those listed in the JCPDS-ICDD cards. The morphology of the powder particles was observed by scanning electron microscopy (SEM SSX-550, Shimadzu). The particle size distribution was determined by a combination of sieving and sedimentation procedures, according to NBR 7181 (ABNT, 1984). The plasticity of the waste sample was determined according to the Atterberg method. The content of organic matter has also been determined in accordance with WalkleyeBlack method. Differential thermal analysis (DTA) of the waste sample was performed within the 25e1150 C temperature range, by using a heating rate of 10  C/min under air atmosphere. The pollution potential of sugarcane bagasse ash waste sample was determined by leaching (acetic acid buffer solution (0.5 M) at pH 5.0 for 18 h) and solubilization tests in aqueous media, according to the NBR 10005 (ABNT, 2004a) and NBR 10006 (ABNT, 2004b) Brazilian standards. The concentrations of elements present in the leaching and solubilization extracts were determined. The concentrations obtained were then compared to the maximum concentrations of elements predicted by the NBR 10004 Brazilian standard (ABNT, 2004c). The raw materials (Table 1) were mixed and homogenized by using a cylindrical mixer during 30 min, and then sieved until the fraction passing in a 42 mesh (355 m m ASTM) screen. The moisture content was adjusted to 7% (moisture mass/dry mass), which is within the range used in the ceramic industry. The cylindrical specimens (f ¼ 25 mm) were prepared on a laboratory scale by uniaxial pressing at 21 MPa, and dried at 110 C for 24 h. The green pieces formed were fired at 1000 C (24 h cold to cold). The firing step was carried out in an electrical kiln. Heating and cooling rates have been controlled. The following technological properties of the clay bricks have been determined in accordance with standardized procedures: linear shrinkage, water absorption, apparent density, and tensile strength. Linear shrinkage values upon drying and sintering were evaluated from the variation of the diameter of the cylindrical specimens (ASTM,1997). Water absorption values were determined from weight differences between the as-sintered and water satured pieces (immersed in boiling water for 2 h) (ASTM, 1994). The apparent density was determined by the Archimedes method (ASTM, 1994). The mechanical strength of the sintered pieces was

Table 1 The proportions of the mixtures for the formulations (wt.%). Formulation

Clay

Sugarcane bagasse ash

K0 W K5 W K10 W K15 W K20 W

100 95 90 85 80

0 5 10 15 20

Fig. 1. X-ray diffraction pattern of the sugarcane bagasse ash waste.

determined in terms of tensile strength because the sample size (cylindrical disk with diameter of 25 mm). The tensile strength of the sintered pieces obtained by the diametral compressive method (Fett, 1998; Chen et al., 2001) was determined by using a universal testing machine (model DL100/100 kN, EMIC). The crossbar speed was hold at 0.5 mm/min for all tests. Scanning electron microscopy operating at 15 kV was used to examine gold-coated fracture surfaces of clay bricks pieces fired at 1000 C. 3. Results and discussion The X-ray diffraction pattern of sugarcane bagasse ash waste is shown in Fig. 1. The following crystalline phases were found: quartz (SiO2), cristobalite (SiO 2), potassium carbonate (K2 CO3), hydrated calcium phosphate (Ca 3 (PO 4)2 $H2O), primary mullite (3Al 2O3 $2SiO2) and hematite (Fe 2O3 ), with predominance of quartz. The ash waste sample’s chemical composition, as well as its loss on ignition, are provided by Table 2. According to said data, the ash waste sample contains a large amount of silica (61.59%), and to a lesser extent alumina (Al 2 O3), calcium oxide (CaO), iron oxide (Fe 2 O3), and potassium oxide (K 2O). This result is consistent with the X-ray diffraction data (Fig. 1). Loss on ignition (LOI) implied in high weight loss of about 9.78%, and is mainly attributed to the presence of organic matter in the waste sample. In fact, the percentage of organic matter found in the waste sample corresponded to 10.32%. When compared to data disclosed by the literature (Teixeira et al., 2008), the sugarcane bagasse ash waste employed in this work uses to have less silica. This result may be Table 2 Chemical composition of the sugarcane bagasse ash waste (wt.%). SiO2 Al2 O3 Fe2 O3 TiO2 CaO MgO MnO K2O P 2O 5 SO3 LOI at 1000  C

61.59 5.92 7.36 1.46 5.00 1.17 0.10 6.22 0.98 0.42 9.78

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Fig. 4. DTA curve for the sugarcane bagasse ash waste.

Fig. 2. Particle size distribution of the sugarcane bagasse ash waste.

probably related to the differences of soils where sugarcane grows, as well as to other factors, such as fertilization methods and soil management. The particle size distribution curve of the sugarcane bagasse ash waste sample is shown in Fig. 2. The results revealed that the sample presented a wide range of particles sizes. It has 0.7 wt.% clay (63 m m). This result is in accordance with the presence of a high content of silica particles in the ash waste sample. Morphological aspects of the waste particles observed by scanning electron microscopy are shown in Fig. 3. It can be seen that the waste sample is rich in angular-shaped particles, which are probably silica ones, and also contains a huge amount of long cylindrical porous plates of sugarcane bagasse not burnt. In addition, a wide particle size range can be observed, in accordance with the particle size data (Fig. 2). Various tests were performed to determine the plastic properties of the waste sample. However, the non-cohesive nature of this solid waste material jeopardized the success of said evaluations. Thus, in terms of soil mechanical, the sugarcane bagasse ash waste can be classified as a non-plastic material (Faria, 2011). DTA curve of the sugarcane bagasse ash waste sample (Fig. 4) shows an endothermic valley around 45 C, which is associated to

the removal of physically adsorbed water on the waste powder particles. The small exothermic peak around 330 C hereby disclosed is mainly due to the dehydration of calcium phosphate, and to the combustion of volatile substances. However, at 525  C, an intense exothermic peak was observed. This thermal event is mainly related to the decomposition of organic matter. In addition, the endothermic valley related to polymorphic transformation of aeb quartz should have been probably overlapped. The ecotoxicity of sugarcane bagasse ash waste was evaluated through leaching and solubilization tests, as shown in Tables 3 and 4. As observed at Table 3, the sugarcane bagasse ash waste presented concentrations of Ag, As, Ba, Cd, Cr (total), Hg and Hg below the maximum limits accepted by NBR 10004 standard. This result indicates that the waste sample can be considered as a nonhazardous solid waste material. Solubilization tests for the waste sample, as shown in Table 4, also presented values below the maximum limits accepted by the NBR 10004 standard. Thus, according to NBR 10004 standard, the sugarcane bagasse ash waste used in this study can be classified as an inert waste material (class IIB). The great relevance of such a result arises from the fact that inert solid wastes are more favorable for recycling in the ceramic industry. The quality of clay brick pieces obtained with up to 20 wt.% sugarcane bagasse ash waste after firing at 1000  C was determined on the basis of their technological properties (linear shrinkage, water absorption, apparent density, and tensile strength). The pieces with 0 wt.% sugarcane bagasse ash waste (sample KW0, 100% brick kaolinitic clay) were considered as reference pieces. As may be observed, all clay brick pieces exhibited low firing shrinkage, varying within a range from 2.0 to 2.8% (Fig. 5), considered to be within the safety limits for industrial production of clay bricks. In this case, the sintering was dominated by particleto-particle contact, especially of metakaolinite platelets (Milheiro et al., 2005). The linear shrinkage was found to decrease, as the waste content increased up to 20 wt.%. This effect is related to the waste sample composition, rich in crystalline silica, which is a non-plastic component and, as such, behaves as a filler material and decreases the plasticity of the clay/ash waste mixes. Table 3 1 Results of the leaching test for the sugarcane bagasse ash waste (mg L ).

Fig. 3. Morphology of the sugarcane bagasse ash waste powder particles.

Elements

Brazilian limits

Sugarcane bagasse ash

Ag As Ba Cd Cr (total) Hg Pb

5.0 1.0 70.0 0.5 5.0 0.1 1.0...