Chemosphere 81 (2010) 633–638

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Chemosphere

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Technical Note

Recycling of ash from mezcal industry: A renewable source of lime

L. Chávez-Guerrero a,c,⇑, J. Flores b, B.I Kharissov a,d

a Department of Nanotechnology, PIIT Monterrey, C.P. 66600, Apodaca, Centre of Innovation Research and Development on Engineering and Technology,Universidad Autónoma de Nuevo León (UANL), Nuevo León, Mexicob División de Ciencias Ambientales, Camino a la presa San José 2055, C.P. 78216, Instituto Potosino de Investigación Científica y Tecnológica, San Luis Potosí, Mexicoc Facultad de Ingeniería Mecánica y Eléctrica, Cd. Universitaria s/n, C.P. 66450, Universidad Autónoma de Nuevo León, Nuevo León, Mexicod Facultad de Ciencias Químicas, Cd. Universitaria s/n, C.P. 66450, Universidad Autónoma de Nuevo León, Nuevo León, Mexico

a r t i c l e i n f o a b s t r a c t

Article history:Received 9 February 2010Received in revised form 19 August 2010Accepted 20 August 2010

Keywords:AgaveMezcalAshLimeArid land

0045-6535/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.chemosphere.2010.08.042

⇑ Corresponding author at: Facultad de IngenieríUniversitaria s/n, C.P. 66450, Universidad AutónomaMexico. Tel./fax: +52 81 13404000.

E-mail address: leonardo.chavezgr@uanl.edu.mx (L

Agave bagasse is a byproduct generated in the mezcal industry. Normally it is burned to reduce its vol-ume, then a byproduct is generated in the form of residual ash, which can contaminate the water in riversand lakes near the production places called ‘‘mezcaleras”. This report details measurements of the AgaveSalmiana fiber transformation after the burning process. The wasted ash was heated at 950 �C, and thenhydrolyzed. The compounds were indentified using the X-ray diffraction. The images obtained by scan-ning electron microscope showed all the morphological transformations of the lime through the wholeprocess. Thermal, elemental and morphological characterization of the agave bagasse were done. Exper-iments showed that 16% of ash was produced in the burning process of agave bagasse (450 �C), and 66% ofthe ash remains after heating (950 �C) in the form of calcium oxide. The results show an importantrenewable source of calcium compounds, due to the high production of agave based beverages in México.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Agave has been used by man for 10 000 years, it was used as asource of food and the fibers were used as footwear (Kuttruff et al.,1998). These days Agave is used to produce primarily the alcoholicbeverages mezcal and tequila, as well as aguardiente, aguamiel andother products such as food and candies (Harshberger, 1897;Iñiguez-Covarrubias et al., 2001; Dalton, 2005; De León-Rodríguezet al., 2006). By mezcal we mean an alcoholic beverage obtainedusing Agave angustifolia Haw, Agave esperrima Jacobi, Agave weberiCela, Agave potatorum Zucc, or Agave Salmiana (Norma OficialMexicana, 1994; De León-Rodríguez et al., 2006; Michel-Cuelloet al., 2008; Martínez-Aguilar and Peña-Álvarez, 2009). The pro-duction of mezcal is of high importance in México, especially forcommunities where it is the only source of income. It is known that15–33 kg of agave are needed to produce 1 L of mezcal. The makingof mezcal produces a byproduct or waste (bagasse) representingabout 40% of the total weight of agave used to produce the alco-holic beverage on a wet weight basis (Iñiguez-Covarrubias et al.,2001). The wasted fibers are used for informal applications, suchas animal feeding or papermaking (Idarraga et al., 1999). Thebyproduct or bagasse is normally burned to reduce its volume, pro-

ll rights reserved.

a Mecánica y Eléctrica, Cd.de Nuevo León, Nuevo León,

. Chávez-Guerrero).

ducing large quantities of ash, which is a hazardous pollutant forhumans, animals, and the environment around the factory, espe-cially for rivers and water corps that can be easily contaminated.Tequila production in the first 6 months of the 2008 was 8254 Lper month, this information is given in order to have an idea ofthe mezcal production and consequently the huge amount of ba-gasse and ash produced (INEGI, 2008).

Calcium is required for structural roles in the cell wall andmembranes, this divalent cation is taken up by roots from the soilsolution (White and Broadley, 2003). It is known that needle-likecalcium oxalate crystals are found in all tissues of agave plants(Salinas et al., 2001). Crystals are sharpened at both ends (raph-ides) with length of 30–500 lm. Calcium oxalate is a commonbiomineral in plants, it appears in monohydrate (whewellite) ordi-hydrated (weddelite) form. Among the biological function ofthe crystals, they play an important role in physical protection (de-fense mechanism) against herbivores animals (Demiray, 2007).

Due to their optimum adaptation, the agave plants (and theirbyproducts) can be used to generate fuel, food, and chemicals,using arid lands with unfavorable conditions for the productionof other crops (Hinman, 1984; Jordan et al., 2007). There have beenlots of works being done in the area of ash usage, mainly in the ce-ment, glass and steel industries which can be an incentive to pro-pose new ash sources from industrial byproducts. (Stout et al.,1997; Renedo and Fernandez, 2002; Rostami and Brendley, 2003;Katayama, 2004; Oner et al., 2005; Sakai et al., 2005; Mahmoudkhaniet al., 2007; Mymrin and Correa, 2007). Commonly, the CaCO3 is

634 L. Chávez-Guerrero et al. / Chemosphere 81 (2010) 633–638

extracted from rocks, which are heated to expulse the CO2 in orderto obtain the CaO. These rocks are not a renewable source ofcalcium carbonate, so it is desirable to find alternative sourcesand methods to provide the industry with this important product(Hinman, 1984; Stout et al., 1997; Katayama, 2004; Sakai et al.,2005; Jordan et al., 2007; Mymrin and Correa, 2007). An importantpoint to consider is that for every 1000 kg of CaCO3, 560 kg of CaOare produced along with 440 kg of CO2, which is a pollutant relatedto global warming (Ragauskas et al., 2006).

In this paper, ash from the mezcal industry as a new source oflime is investigated. The objectives are to minimize pollution(ash), and to propose an alternative way to obtain chemical com-pounds using renewable feedstocks produced in arid lands (agave).

2. Materials and methods

2.1. Thermal analysis of the bagasse

The bagasse was collected direct from the mezcal factory IPIÑAS.A de C.V. in San Luis Potosí, México. A Thermolyne 48000 furnacewas used to heat the bagasse (450 �C) to obtain ash (ASH-450). Theash was sieved to obtain a powder less than 1.5 mm in size, using aUSA Standard test sieve No. 12 (1.7 � 1.7 cm2). The sample consist-ing of 10 g of ASH-450 was placed in the alumina (Al2O3) crucibleand then into the furnace, 30 samples were used to ensure repro-ducibility. Then, the ash was heated from 25 to 950 �C and the tem-perature was kept for 2 h to expulse the water, CO2 and volatilecompounds in the material. This sample was termed ASH-950.After that, the sample ASH-950 was loaded in de-ionized water.The mixture was stirred for 2 h at 25 �C. The sample was dried at100 �C for 5 h in order to eliminate the moisture. De-ionized waterwas used in all the reactions. This hydrated sample was termedASH-950–H2O. Baggase (4 mg) were tested in a Thermo gravimet-ric analyzer (TGA) Thermo Cahn modelo Versatherm, with temper-ature range of 25–1000 �C and heating rate of 10 �C min�1 in N2

atmosphere.

2.2. Imaging of the samples

The samples were glued to aluminium holders, sputter-coatedwith gold (Cressington Sputter Coater 108 auto) using 40 A for20 s under argon atmosphere for scanning electron microscope(SEM) studies. The morphology and composition (qualitatively)of the samples were determined by SEM (FEI XL 30 SFEG with anenergy dispersive X-ray microanalysis system, standard-less anal-ysis) with acceleration energy of 15 kV. X-ray powder diffractionspatterns were obtained with Cu Ka radiation (k = 1.5406 Å) in aD8 Advance Bruker powder diffractometer. The diffractogram pat-terns were ranged from 2h = 10� to 90�. Atomic Force Microscope

Fig. 1. TGA/DTA data showing the loss weight versus the temperature of thebagasse.

(AFM) images were taken with a Jeol JSPM-5200 Scanning ProbeMicroscope in order to investigate the morphological changes atthe nanoscale.

3. Results and discussion

3.1. Thermogravimetric analysis

The weight loss shown by the bagasse (450 �C) in the burningprocess was 84 ± 2% which means that 16% of ash was produced.

Fig. 2. X-ray diffractogram patterns that correspond with: (a) CaO, (b) Ca(OH)2 and(c) CaCO3.

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The remaining weight of the ash after heating at 950 �C was of66 ± 0.6%, thus about 34% of the initial weight of the ash wasconverted into CO2 and other products. These results can be cor-roborated with the TGA analysis showed in Fig. 1. Theoreticalcalculations show that decomposition of CaCO3 into CaO and CO2

is only 56% and 44% respectively. The experimental results showed10% more residue than the theoretical value, it can be explainedbecause the ash has other elements, mainly silicon as it can be seenin Fig. 3b.

The DTA curve of the bagasse in Fig. 1 presented three mass losssteps. The first step up to 200 �C is related to the alcohols andmoisture elimination. The peak at 303 �C represents the releaseof organic compounds like fats, waxes, etc. The third step at397 �C shows the emission of CO2 due the decomposition of lignin,hemicellulose and cellulose.

For 1 L of mezcal about 24 kg of agave are needed, during theprocess 9.6 kg (40%) of bagasse are generated which produces1.5 kg (16%) of ash. Then, for every liter of mezcal produced about1.5 kg of ash are generated, which can become an environmentalproblem in the areas surrounding the mezcal factories.

3.2. X-ray diffraction

X-ray diffraction was used to determine the crystal nature ofthe samples. The ASH-450 sample had a crystal structure corre-

Fig. 3. Morphology of the sample ASH-450 (a) and its composition presented inatomic percentage (b).

sponding to the calcium carbonate, this is shown in Fig. 2c. After2 h of permanence inside a furnace at 950 �C (ASH-950), the ashwas chemically transformed into a different phase, the lime orCaO, which is shown in the diffractogram in Fig. 2a. Finally thesample ASH-950–H2O was analyzed to obtain the diffractionshown in Fig. 2b. All the diffraction patterns were compared withthe database of the diffractometer in order to corroborate the exis-tence of the compounds mentioned before. These results showedthe presence of CaCO3, CaO and Ca(OH)2; these chemical com-

Fig. 4. SEM image of a fiber with rectangular shape contained in the ASH-450 (a).Zoom image that shows the fiber surface (b), and ASH-450 composition in atomicpercentage (c).

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pounds can be recycled and used in a wide range of applications indifferent kind of industries.

This renewable source of calcium-based compounds has energysaving advantages, mainly in the extraction and grind process com-pared with the traditional methods, although total energy forburning is same. The most important advantage is the ecologicalone, because the emissions released in the production process willnot increase the CO2, because plants previously took the CO2 fromthe environment.

Fig. 5. SEM image showing the sample ASH-950 where the permanence of the fibershape can be observed (a). It is clear that the surface had a change due the deliveryof different compounds and that the surface appears to have more particles (b). Theatomic composition qualitatively showed that CaO is present on the sample (c).

3.3. Scanning electron microscope (SEM)

In Fig. 3a, a SEM image shows the ASH-450 morphology, whereit is shown that fibers of different sizes and thickness persistedafter the burning process. In Fig. 3b, the ash composition estimatedby EDS is reported as atomic percentage (at.%). The main compo-nents are C, O and Ca, while Fe, Mg, Al, P, Si and K are in minorquantity.

Fig. 4a shows a SEM image with only one fiber in a rectangularshape, while in Fig. 4b it is possible to observe the detail over the

Fig. 6. SEM Image of the sample ASH-950–H2O (a and b), the crystals formed duringthe hydrated process can be seen. The composition in (c) confirms the existence ofCa(OH)2.

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fiber surface. The ratio between Ca, C and O in the CaCO3 formula is1:1:3 respectively, which can be corroborated in the Fig. 4c, wheremeasuring of atomic percentage (at.%) showed a ratio Ca:C:O of21:26:52. The differences can be attributed to elemental carbonor residues from the combustion process (soot). Fig. 4b shows par-ticles with sizes in the range of the nanoscale up to �200 nm,which is the burning process result of the organic fibers, resultingin microparticles of CaCO3.

Fig. 5a shows a SEM image of ASH-950, where it can be seenthat one fiber preserved the rectangular shape after the heatingprocess (950 �C). The appearance in Fig. 5b exhibits more poresor holes over the structure compared with Fig. 4b, due the total lossof CO2 during the heating treatment. In Fig. 5c the elemental com-position of the ASH-950 is shown, where it can be qualitativelyproved that the ash became a different compound. The atomic ratioin lime is 1:1 which can be corroborated in the atomic percentage(at%) in Fig. 5c, with a Ca/O ratio of about 46:47. Here, the atomicrelation becomes more accurate because of the heating process(950 �C), where the carbon was expulsed as CO and CO2.

Fig. 6a shows a SEM image of ASH-950–H2O where the mor-phology can be examined at high magnifications. It exhibits arather different appearance compared with the ASH-450 andASH-950 structure. Figs. 6a and b show a hexagonal tubular struc-

Fig. 7. In (a) a 3D AFM image of the ASH-950–H2O is shown, while in (b) themorphology of the surface and the size of the particles can be seen.

ture which corresponds to hydrated lime. Fig. 6c shows the atomiccomposition of the sample, where the Ca/O ratio is 29:60, with thisdata the existence of Ca(OH)2 can be corroborated. These resultswere in concordance with the X-ray analysis previously shown,thus providing a visual map of the ash through all the chemicalchanges.

3.4. Atomic force microscope

3.4.1. Morphological analysisThe presence of crystals in ASH-950–H2O is quite obvious, but

also other smaller structures were observed in Fig. 6a and b, whereparticles less than 1 lm in size with irregular form can be seen.Using the AFM, the structure can be elucidated with more detailin a three dimensional way at nanometric resolution. Fig. 7a showsa 3D image with 10 � 10 lm in size, where the morphology of theASH-950–H2O can be observed. In Fig. 7b an image of the samearea is shown but in 2D where semispherical structures less than1 lm in diameter are solved. The hydrated lime can be used in pro-cesses such catalysis or as bactericide (Gomes et al., 2006; Yücelet al., 2007), where the surface plays an important roll due thereactivity of the material.

4. Conclusions

This paper deals with the bagasse produced in the mezcalindustry, which can be recycled from this process to generate dif-ferent products in a sustainable way.

(1) We conclude that for every liter of mezcal 1.5 kg of ash aregenerated.

(2) The products obtained and characterized were calcium car-bonate, lime and hydrated lime. Calcium carbonate isobtained after the burning process of the bagasse (ash), thiscompound is supposed to have been transformed from acommon biomineral (calcium oxalate) in agave plants as aresult of burning. The X-ray analysis proved the existenceof the different compounds and their transformation.

(3) Using SEM and AFM the appearance of the different materi-als were observed where microcrystals and irregular parti-cles less than 1 lm were found.

(4) The development of this work in a bigger scale can generatean important feedstock for different industries; this can beachieved growing plants like agave in semi-arid and aban-doned lands, creating with this new income sources (andjobs) for the people living in and around these areas.

The process presented on this report has positive impacts, duethe zero emissions to the total CO2 into the environment and be-cause it helps to minimize the contaminants (ash) near factories(mezcaleras).

Acknowledgements

This work was supported by the Universidad Autónoma deNuevo León (FIME-UANL) and the Consejo Nacional de Ciencia yTecnología (CONACyT) through the Project 92991. To Grisel R.,Daniel R, Ferdinando L., Hugo M., Patricia Slater, and the IPICyT.

References

Dalton, R., 2005. Alcohol and science. Saving the agave. Nature 438, 1070–1071.De León-Rodríguez, A., González-Hernández, L., Barba de la Rosa, A.P., Escalante-

Minakata, P., López, M.G., 2006. Characterization of volatile compounds ofmezcal, an ethnic alcoholic beverage obtained from Agave salmiana. J. Agric.Food Chem. 54, 1337–1341.

638 L. Chávez-Guerrero et al. / Chemosphere 81 (2010) 633–638

Demiray, H., 2007. Calcium oxalate crystals of some crateagus (Rosaceae) speciesgrowing in Aegean region. Biologia 62, 46–50.

Gomes, B.P.F.A., Vianna, M.E., Sena, N.T., Zaia, A.A., Ferraz, C.C.R., de Souza Filho, F.J.,2006. In vitro evaluation of the antimicrobial activity of calcium hydroxidecombined with chlorhexidine gel used as intracanal medicament. Oral Surg.Oral Med. O. 102, 544–550.

Harshberger, J.W., 1897. A botanical excursion to Mexico. Science 6, 569–572.Hinman, C.W., 1984. New crops for arid lands. Science 225, 1445–1448.Idarraga, G., Ramos, J., Zuniga, V., Sahin, T., Young, R.A., 1999. Pulp and paper from

blue agave waste from tequila production. J. Agric. Food Chem. 47, 4450–4455.INEGI 2008. National Institute of Statistics and Geography. Bebidas destiladas de

agave/tequila/volumen, México. Access 12/17/2009. <http://dgcnesyp.inegi.org.mx/cgi-win/bdieintsi.exe/>.

Iñiguez-Covarrubias, G., Langue, S.E., Rowell, R.M., 2001. Utilization of byproductsfrom the tequila industry: part 1: agave bagasse as a raw material for animalfeeding and fiber board production. Bioresour. Technol. 77, 25–32.

Jordan, N., Boody, G., Broussard, W., Glover, J.D., Keeney, D., McCown, B.H., McIsaac,G., Muller, M., Murray, H., Neal, J., Pansing, C., Turner, R.E., Warner, K., Wyse, D.,2007. Environment: sustainable development of the agricultural Bio-Economy.Science 316, 1570–1571.

Katayama, T., 2004. How to identify carbonate rock reactions in concrete. Mater.Charact. 53, 85–104.

Kuttruff, J.T., Gail DeHart, S., O’Brien, M.J., 1998. 7500 Years of prehistoric footwearfrom Arnold research cave, Missouri. Science 281, 72–75.

Mahmoudkhani, M., Richards, T., Theliander, H., 2007. Sustainable use of biofuel byrecycling ash to forest: treatment of biofuel ash. Environ. Sci. Technol. 41, 4118–4123.

Martínez-Aguilar, J.F., Peña-Álvarez, A., 2009. Characterization of five typical agaveplants used to produce mezcal through their simple lipid composition analysisby gas chromatography. J. Agric. Food Chem. 57, 1933–1939.

Michel-Cuello, C., Juárez-Flores, B.I., Aguirre-Rivera, J.R., Pinos-Rodríguez, J.M., 2008.Quantitative characterization of nonstructural carbohydrates of mezcal agave(Agave salmiana Otto ex Salm-Dick). J. Agric. Food Chem. 56, 5753–5757.

Mymrin, V., Correa, S.M., 2007. New construction material from concreteproduction and demolition wastes and lime production waste. Constr. Build.Mater. 21, 578–582.

NORMA Oficial Mexicana NOM-070-SCFI-1994, Bebidas alcohólicas-Mezcal-Especificaciones. Access 02/09/2010. <http://www.economia.gob.mx/work/normas/noms/1997/070-scfi.pdf>.

Oner, A., Akyuz, S., Yildiz, R., 2005. An experimental study on strength developmentof concrete containing fly ash and optimum usage of fly ash in concrete. Cem.Concr. Res. 35, 1165–1171.

Ragauskas, A.J., Williams, C.K., Davison, B.H., Britovsek, G., Cairney, J., Eckert, C.A.,Frederick, W.J., Hallett, J.P., Leak, D.J., Liotta, C.L., Mielenz, J.R., Murphy, R.,Templer, R., Tschaplinski, T., 2006. The path forward for biofuels andbiomaterials. Science 311, 484–489.

Renedo, M.J., Fernandez, J., 2002. Preparation, characterization, and calciumutilization of fly ash/Ca(OH)2 sorbents for dry desulfurization at lowtemperature. Ind. Eng. Chem. Res. 41, 2412–2417.

Rostami, H., Brendley, W., 2003. Alkali ash material: a novel fly ash-based cement.Environ. Sci. Technol. 37, 3454–3457.

Sakai, E., Miyahara, S., Ohsawa, S., Lee, S.H., Daimon, M., 2005. Hydration of fly ashcement. Cem. Concr. Res. 35, 1135–1140.

Salinas, M.L., Ogura, T., Soffchi, L., 2001. Irritant contact dermatitis caused byneedle-like calcium oxalate crystals, raphides in Agave tequilana among workersin tequila distilleries and agave plantations. Contact Dermatitis 44, 94–96.

Stout, W.L., Daily, M.R., Nickeson, T.L., Svendsen, R.L., Thompson, G.P., 1997.Agricultural uses of alkaline fluidized bed combustion ash: case studies. Fuel 76,767–769.

White, P.J., Broadley, M.R., 2003. Calcium in plants. Ann. Bot. 92, 487–511.Yücel, A.C., Aksoy, A., Ertas, E., Güvenç, D., 2007. The pH changes of calcium

hydroxide mixed with six different vehicles. Oral Surg. Oral Med. O. 103, 712–717.