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Clinker at El Cerrejón Coal Mine, Colombia
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CHAPTER 5
Clinker at El Cerrejón Coal Mine, Colombia: Characteristics and Potential Uses
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CHAPTER CONTENTS Clinker at El Cerrejón Coal Mine, Colombia Introduction Photo Tour References and Additional Reading WWW Addresses
Highly brecciated rock of the Cogollo Formation, collected from the hanging wall of the Cerrejón thrust fault. The sample contains coarse fragments of clinker (red) and its nonthermally altered calcareous protolith along with bivalve shells (square). From Quintero et al., 2009.
Coal and Peat Fires: A Global Perspective Edited by Glenn B. Stracher, Anupma Prakash, and Ellina V. Sokol © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/B978-0-444-59412-9.00005-3
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Clinker at El Cerrejón Coal Mine, Colombia Jhon A. Quintero Carlos A. Ríos Glenn B. Stracher
Introduction El Cerrejón Coal Mine is a group of open-cast pits located in the La Guajira peninsula in the northern part of Colombia; bordered on the east by Venezuela. The open-pit mines are administratively distributed in the Cerrejón northern zone (CNZ), Cerrejón central zone (CCZ), and Cerrejón southern zone (CSZ). El Cerrejón is an integrated mining operation that extracts and commercializes low-rank bituminous coal from the Upper Paleocene Cerrejón Formation. Sedimentary rocks in the Cerrejón Formation were thermally altered after the late Paleocene as a consequence of the spontaneous combustion of coal seams in the formation (Quintero et al., 2009). The altered rock now includes pyrometamorphic rock called clinker. In addition, coal that burned is reduced to a thin layer of ash. In Colombia, clinker and the coal seams ignited by spontaneous combustion are studied in little detail, and the only reported occurrences are at El Cerrejón. Álvarez and Gómez (1986) studied the petrological characteristics of thermally altered rocks due to coal combustion in El Cerrejón. Locally, temperatures were high enough to partially melt ash from previously burned coal and rocks above coal seams, converting the rocks into paralavas of basaltic composition. Candela and Quintero (2004) mapped clinker within an approximately 690 km2 area of El Cerrejón and modeled its structural relationship to other rocks at depth. More recent studies of the clinker include its petrographic, physical, and chemical characteristics and proposals for its use (Ríos, 2008; Ríos and Williams, 2008; Ríos et al., 2008; Quintero et al., 2009; Sandoval et al., 2009; Henao et al., 2010; Perea and Rincon, 2010). In this chapter, we summarize such studies. Geologic Setting The Cerrejón Formation, exposed in the Cesar-Rancheria basin (Montes et al., 2010), consists of middle to late Paleocene shales, argillaceous sandstones, sandstones, coal seams of economic interest, and combustion altered rocks that vary from slightly baked to completely fused. The sedimentary sequence of the Cerrejón Formation was affected by late Paleocene faulting associated with the Rancheria and Cerrejón faults and by late Paleocene folding in the Tabaco fold zone (Quintero et al., 2009). According to Quintero et al. (2009), clinker at El Cerrejón Coal Mine occurs in the following open pits: Palotal 10 (CSZ), Tipiala (CSZ), 100 (CSZ), Patilla (CSZ), Tabaco High dip (CNZ), Tabaco extension (CNZ), and La Puente (CNZ). The clinker outcrops over an area of 2.9 × 106 m2, and its volume is 1.4 × 108 m3 (Quintero et al., 2009). It was produced during the complete combustion of 6.4 Mt (26.4 × 106 J/kg) of coal; outcrops in irregular patterns as wedge-shaped bodies up to 100 m thick. Clinker outcrops pinch at depths of up to 448 m down dip along the coal seam (Candela and Quintero, 2004). The clinker occurs in structurally complex zones and is well developed along the Ranchería fault (Quintero et al., 2009). A connection between faulting, folding, and spontaneous combustion has not been established. However, combustion can sometimes be influenced by faults and folds that serve as conduits for transmitting oxygen to coal seams. These seams may self-ignite because of exothermic-oxidation reactions involving minerals, such as pyrite, in the coal (Stracher and Taylor, 2004). Self ignition may also occur when coal is exposed to oxygen because of lowering of the water table (Quintero et al., 2009).
Clinker at El Cerrejón Coal Mine, Colombia: Characteristics and Potential Uses
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Clinker at El Cerrejón is easily recognized in the field because of its red to red-brown color that varies in intensity, although it also exhibits shades of black, gray, green, cream, and white. All of these colors contrast with the black hue of the Cerrejón Formation coals. The clinker is compact and highly fractured, and has a fine-grained to sandy texture. The red to red-brown color is due to the presence of hematite. The clinker consists of a complex mixture of amorphous and crystalline-inorganic phases. It contains relict-inorganic materials derived from shales, argillaceous sandstones, and gray sandstones interbedded with the burnt coal. Fossil plant remains and relict sedimentary structures, such as bedding, occur. In contrast to other locations where clinker occurs such as Utah, Colorado, and the Powder River Basin in the United States (Stracher et al., 2005, 2007; Heffern et al., 2007), the clinker at El Cerrejón does not occur in topographically steep areas. There are no current reports about active coal fires in El Cerrejón Coal Mine, but some of the fires that occurred were ignited by spontaneous combustion associated with mining activities that exposed coal to oxidation, especially in open-pit walls. Natural spontaneous combustion, as is evident from field relations, took place either after or before deformation, such as the Cerrejón and Samán thrust faults, respectively (Quintero et al., 2009). According to Quintero et al. (2009), periods of spontaneous combustion also occurred during previous arid-climatic times in the Cesar-Ranchería Valley when coal, formerly in the phreatic zone, was exposed as the water table dropped. Petrologic Characteristics and Quantitative Analysis of Clinker Clinker includes a variety of pyrometamorphic rocks that vary in the degree of thermal alteration, as is evident from their texture, original composition, and stratigraphic and structural positions in the burn area (Henao et al., 2010). Clinker varieties identified by Henao et al. (2010) include those with baked sandstone or claystone, tigerstripe, vesicular, and brecciated textures (Figure CCM 5). The clinker usually has the texture of baked sandstone or claystone (Figures CCM 5a and 5b, respectively), the latter resembling building brick characterized by its reddishorange color due to intense oxidation. The baked claystone may be interlayered with relict sedimentary bedding, all arranged in a millimeter-size, tiger-stripe pattern (Figure CCM 5c). Figure CCM 5d illustrates a variety of clinker texturally similar to slag, and has a vesicular or spongy texture. Brecciated zones along faults clearly demonstrate that spontaneous combustion occurred before faulting because the breccias contain mixtures of clinker, unburnt rock, and coal (Figures CCM 5e and CCM 5f). Sandoval et al. (2009) using X-ray analyses, determined that the clinker at El Cerrejón is comprised mainly of quartz and its tridymite polymorph (up to 34.4%), mullite (14.2%), montmorillonite (4.0%), hematite (up to 2.4%), traces of rutile and its anatase polymorph, and traces of ilmenite, cordierite, and kaolinite. Henao et al. (2010) demonstrated by X-ray diffraction studies of clinker from El Cerrejón that the Rietveld method is a powerful tool for the quantitative analysis of phases in polycrystalline samples. Potential Uses of Clinker Industrial Applications Clinker has a number of industrial applications (Hoffman, 1996; Ríos and Williams, 2008). It is used as an aggregate on dirt roads, as well as for grading mining roads, for reclamation and stabilization purposes, and for constructing dam foundations. Recycling clinker could save the coal industry millions of dollars per year by reducing landfill costs. This is because by reducing the amount of clinker in mine tailings, less waste has to be transported to and deposited in landfills. Landfills cost taxpayers millions of dollars to clean up and monitor, and this will likely continue for many years to come (Eco·cycle, 2011). More in-depth studies about the disposal of clinker and the after-effects of doing so may provide valuable data on the environmental impacts of doing so. El Cerrejón has rehabilitation and conservation projects in the areas of biodiversity, energy management, greenhouse gas emissions, air quality, wastewater treatment and dumping, and recycling (Cerrejón, 2011). Synthetic Zeolites Several research teams have studied zeolites synthesized from clinker. Ríos and Williams (2008), Ríos et al. (2008), and Sandoval et al. (2009) synthesized zeolites from clinker by hydrothermal alkaline activation (Figure CCM 6) and also by alkaline fusion, prior to hydrothermal reaction. Experimental results indicate that alkaline activation, NaOH or KOH concentrations, and time have a strong effect on the type and degree of crystallinity of the synthesized zeolites. Low-silica, sodium, and potassium zeolitic materials synthesized by these authors include phillipsite, sodalite, cancrinite, chabazite, zeolite K-F, faujasite, and zeolite Linde Type A.
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Clinker-based zeolites synthesized under well-optimized experimental conditions could be used for environmental waste treatment (Ríos, 2008; Ríos et al., 2008). Geopolymers Geopolymers, a term first used by Davidovits (1991), are more commonly known as inorganic polymers (Duxson et al., 2007). Geopolymer refers to materials with the ability to transform, polycondense, and, like “polymers,” rapidly acquire a shape at low temperatures. These materials include alkali-bounded ceramics, hydroceramics, and alkali-activated cements. Pacheco-Torgal et al. (2007, 2008, 2009), Caballero and Sánchez (2009), and Perea and Rincon (2010) investigated the use of mining waste to form geopolymers. Perea and Rincon (2010) showed that when clinker reacted with the addition of an activator solution (sodium silicate and sodium hydroxide), a geopolymer could be produced with a compressive strength similar to that of Portland cement. When synthesized at higher temperatures, the compressive strength and durability of the geopolymer increased. The formation of geopolymers, through a process called geopolymerization, occurs in response to complicated heterogeneous reactions that occur between a solid rich in aluminum-silicate oxides and an alkali-metal silicate solution, under highly alkaline conditions (Panias and Giannopoulou, 2006). Geopolymerization is regarded as the analogue of zeolite synthesis because the chemistry involved is similar, although the resulting products are different in composition and structure (Komnitsas and Zaharaki, 2007). Geopolymerization is thought to involve four steps that proceed simultaneously, as a result of which the steps are impossible to distinguish (Xu and Van Deventer, 2000): (1) Dissolution of Si and Al from the solid aluminumsilicate in the strong alkaline aqueous solution; (2) formation of Si and/or Si-Al oligomers in the aqueous phase; (3) polycondensation of oligomers to form a three-dimensional aluminosilicate framework; and (4) bonding of the undissolved solid particles into the geopolymer framework and hardening of the entire material (geopolymeric system). Geopolymers exhibit unique physical and chemical properties that make them suitable for use in diverse applications. These include precast structures and nonstructural elements; concrete pavements and products; containment and immobilization of toxic, hazardous, and radioactive waste; advanced structural tooling and refractory ceramics; and fire-resistant composites used in buildings, airplanes, shipbuilding, racing cars, and the nuclear power industry (Komnitsas and Zaharaki, 2007). The utilization of minerals and industrial waste for geopolymerization as well as for immobilizing toxic metals has been investigated extensively by researchers, including Van Jaarsveld et al. (2000) and Xu and Van Deventer (2000, 2002).
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Photo Tour
Figure CCM 1. Location of Colombia, South America, and the La Guajira peninsula in the Caribbean region of Colombia (inset, upper left). The rectangular box in the larger illustration of the peninsula is where El Cerrejón Coal Mine occurs. Map from Quintero et al., 2009, with modifications by Martha M. Barreto, 2009; permission from Elsevier.
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Figure CCM 2. Spontaneous combustion of seam 145 in the Tabaco High Dip, pit (upper-left photo). Note the sulfur (yellow) deposits at the top of the pit. These are from gas exhaled at surficial vents. A walkie-talkie is visible near the center of this photo. A bottle (center of red circles) was inserted upside down in the culm bank at the top of the pit. Once removed (bottom left photo), sulfur and other minerals were found on the outside of the bottle and adjacent rock, but none were visible on the inside. The green circles in the two photos on the right enclose a gas vent encrusted with sulfur and creosote that nucleated adjacent to the opening. At elevated temperatures, heat energy released from the burning coal converts waste rock in the culm bank into pyrometamorphic rock called clinker. Photos by Camilo Montes (bottom right) and Jhon A. Quintero, 2007.
Figure CCM 3. Evidence for coal-bed fires in the north wall of the Tabaco High Dip open-cast mining pit (Cerrejón North Zone) includes coal, clinker of different colors and unknown age, and white ash (upper left photo) in El Cerrejón Coal Mine. From Quintero et al., 2009, with modifications by Carlos A. Ríos, 2011; permission from Elsevier.
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Figure CCM 4. Clinker of unknown age formed during the spontaneous combustion of coal beds in the south wall of pit 100 in the CSZ El Cerrejón Coal Mine. Note variations in the red color of the clinker and its displacement along faults. From Henao et al., 2010, with modifications by Carlos A. Ríos and Glenn B. Stracher, 2011; permission of Earth Science Research Journal. Photos by Wilson Mendoza, 2002.
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(a)
(b)
(c)
(d)
(e)
(f)
Figure CCM 5. Specimens illustrating varieties of clinker and their textural and structural—features discussed in the text. From Henao et al., 2010; permission of Earth Science Research Journal. Photo by Andrew Brook, 2007.
Clinker at El Cerrejón Coal Mine, Colombia: Characteristics and Potential Uses
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(b)
(c)
(d)
(e)
(f)
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Figure CCM 6. Scanning electron microscope (SEM) images of zeolite phases synthesized from alkaline hydrothermal treatment of clinker from El Cerrejón Coal Mine. The zeolites include sodalite (SOD), phillipsite (PHI), chabazite (CHA), edingtonite (EDI), faujasite (FAU), and analcime (ANA). The zeolites observed by SEM depict the following features: (a) “ball of yarn” morphology in sodalite, (b) prismatic crystals of phillipsite, (c) relict faujasite after replacement by sodalite, (d) analcime crystals with trapezohedral morphology, (e) intergrowth of phacolitic chabazite and prismatic edingtonite, exhibiting a bow tie-like aggregate, and (f) octahedral faujasite crystals and bladed crystals of sodalite. From Carlos A. Ríos, 2008. SEM microphotographs by Barbara Hodson, 2007.
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Figure CCM 7. X-ray diffraction (XRD) pattern and a SEM image of clinker from El Cerrejón Coal Mine. The phases identified in the clinker include quartz (Qtz), hematite (Hem), and muscovite (Ms). Figures by Carlos A. Rios, 2008 (XRD) and Barbara Hodson (SEM), 2008. From Carlos A. Rios, 2008.
References and Additional Reading Álvarez, R., Gómez, C., 1986. Para-lavas basálticas y metamorfitas generadas por combustión espontánea de mantos de carbón, Formación Cerrejón, Colombia: Bogotá DC, Colombia. Geología Norandina (10), 3–9. Caballero, E., Sánchez, W., 2009. Síntesis de nuevos cementos geopoliméricos a partir de subproductos del proceso de extraccion de oro en la Mina La Baja, Distrito de California: Santander, Tesis de pregrado. Universidad Industrial de Santander, Escuela de Geología, Bucaramanga, p. 95. Candela, S.A., Quintero, J.A., 2004. Cartografía de las zonas de clinker en las áreas de minería de la mina el Cerrejón. Tesis de pregrado, Universidad Industrial de Santander, Escuela de Geología, Bucaramanga, Albania, La Guajira, p. 90. Cerrejón, 2011. Minería responsible. http://www.cerrejoncoal.com (accessed February 2011). Davidovits, J., 1991. Geopolymers: Inorganic polymeric new materials. Journal of Thermal Analysis 37, 1633–1656. Duxson, P., Fernández-Jiménez, A., Provis, J.L., Lukey, G.C., Palomo, A., Van Deventer, J.S.J., 2007. Geopolymer technology: The current state of the art. Journal of Materials Science 42 (9), 2917–2933. Eco·cycle, 2011. Recycling and Environmental Facts. http://www.ecocycle.org/tidbits/index.cfm (accessed February 2011). Heffern, E.L., Reiners, P.W., Naeser, C.W., Coates, D.A., 2007. Geochronology of clinker and implications for evolution of the Powder River Basin landscape. In: Stracher, G.B. (Ed.), Geology of Coal Fires: Case Studies from Around the World: Reviews in Engineering Geology, XVIII, Geological Society of America, pp. 155–175. Henao, J.A., Carreño, A.M., Quintero, J.A., Candela, S.Á, Ríos, C.A., Ramos, M.A., Pinilla, J.A., 2010. Petrography and application of the Rietveld method to the quantitative analysis of phases of natural clinker generated by coal spontaneous combustion. Earth Sciences Research Journal 14 (1), 17–29. Hoffman, G.K., 1996. Natural clinker: The red dog of aggregates in the Southwest. In: Austin, G.S., Hoffman, G.K., Barker, J.M., Zidek, J., Gilson, N. (Eds.), Proceedings of the 31st Forum on the Geology of Industrial Minerals, Bureau of Geology and Mineral Resources Bulletin, 154. The Borderland Forum, New Mexico, pp. 187–196.
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Komnitsas, K., Zaharaki, D., 2007. Geopolymerisation: A review and prospects for the minerals industry. Minerals Engineering 20 (14), 1261–1277. Montes, C., Guzman, G., Bayona, G., Cardona, A., Valencia, V., Jaramillo, C., 2010. Clockwise rotation of the Santa Marta massif and simultaneous Paleogene to Neogene deformation of the Plato-San Jorge and CesarRanchería basins. Journal of South American Earth Sciences 29 (4), 832–848. Pacheco-Torgal, F., Castro-Gomes, J., Jalali, S., 2007. Investigations about the effect of aggregates on strength and microstructure of geopolymeric mine waste mud binders. Cement and Concrete Research 37 (6), 933–941. Pacheco-Torgal, F., Castro-Gomes, J., Jalali, S., 2008. Properties of tungsten mine waste geopolymeric binder. Construction and Building Materials 22 (6), 1201–1211. Pacheco-Torgal, F., Castro-Gomes, J., Jalali, S., 2009. Tungsten mine waste geopolymeric binder: Preliminary hydration products investigations. Construction and Building Materials 23 (1), 200–209. Panias, D., Giannopoulou, I.P., 2006. Development of inorganic polymeric materials based on fired coal fly ash. Acta Metallurgica Slovaca 12, 321–327. Perea, G., Rincon, H., 2010. Residuos generados por la autocombustión del carbón como materias primas en la preparación de materiales geopoliméricos para promover el desarrollo de procesos industriales ambientalmente óptimos: Tesis de pregrado. Universidad Industrial de Santander, Escuela de Geología, Bucaramanga, p. 85. Quintero, J.A., Candela, S.A., Ríos, C.A., Montes, C., Uribe, C., 2009. Spontaneous combustion of the Upper Paleocene Cerrejón Formation coal and generation of clinker in La Guajira Peninsula (Caribbean Region of Colombia). International Journal of Coal Geology 80 (3–4), 196–210. Ríos, C.A., 2008. Synthesis of zeolites from geological materials and industrial wastes for potential application in environmental problems, Ph.D. Thesis School of Applied Sciences, University of Wolverhampton, England, p. 233. Ríos, C.A., Williams, C.D., 2008. Synthesis of zeolitic materials from natural clinker: A new alternative for recycling coal combustion by-products. Fuel 87 (12), 2482–2492. Ríos, C.A., Williams, C.D., Roberts, C.L., 2008. Removal of heavy metals from acid mine drainage (AMD) using coal fly ash, natural clinker, and synthetic zeolites. Journal of Hazardous Materials 156 (1–3), 23–35. Sandoval, M.V., Henao, J.A., Ríos, C.A., Williams, C.D., Apperley, D.C., 2009. Synthesis and characterization of zeotype ANA framework by hydrothermal reaction of natural clinker. Fuel 88 (2), 272–281. Stracher, G.B., Lindsley-Griffin, N., Griffin, J.R., Renner, S., Schroeder, P., Viellenave, J.H., Masalehdani, M.N.-N., Kuenzer, C., 2007. Revisiting the South Cañon Number 1 Coal Mine fire during a geologic excursion from Denver to Glenwood Springs, Colorado. In: Raynolds, R.G. (Ed.), Roaming the Rocky Mountains and Environs: Geological Field Trips, Geological Society of America Field Guide, 10, pp. 101–110. Stracher, G.B., Tabet, D.E., Anderson, P.B., Pone, J.D.N., 2005. Utah’s state rock and the Emery Coalfield: Geology, mining history, and natural burning coal beds. In: Pederson, J., Dehler, C.M. (Eds.), Interior Western United States, Geological Society of America Field Guide, 6, pp. 199–210. Stracher, G.B., Taylor, T.P., 2004. Coal fires burning out of control around the world: Thermodynamic recipe for environmental catastrophe. In: Stracher, G.B. (Ed.), Coal Fires Burning around the World: A Global Issue: International Journal of Coal Geology 59 (1–2), pp. 7–17. Van Jaarsveld, J.G.S., Lucky, G.C., Van Deventer, J.S.J., 2000. The stabilization of mine tailings by reactive geopolymerization. In: Griffiths, P., Spry, A. (Eds.), Proceedings of the MINPREX 2000 International Congress on Mineral and Processing and Extractive Metallurgy, The Australian Institute of Mining and Metallurgy, Melbourne, Australia, pp. 363–371. Xu, H., Van Deventer, J.S.J., 2000. The geopolymerization of alumino-silicate minerals. International Journal of Mineral Processing 59 (3), 247–266. Xu, H., Van Deventer, J.S.J., 2002. Geopolymerization of multiple minerals. Minerals Engineering 15 (12), 1131–1139.
WWW Addresses (1) Cerrejón http://www.cerrejoncoal.com (2) Clinker http://geoinfo.nmt.edu/staff/hoffman/Clinker/Clinker.html http://geology.utah.gov/surreynotes/geosights/coal_Clinker.html http://www.dmr.nd.gov/ndgs/ndnotes/ndn13_html
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(3) Construction Aggregate http://www.wsgs.uwyo.edu/Topics/IndustrialMinerals/aggregate.aspx (4) Eco·Cycle http://www.ecocycle.org (5) Geopolymer Institute http://www.geopolymer.org (6) Geopolymers: Building Blocks of the Future http://www.csiro.au/science/Geopolymers-Overview.html (7) Geopolymers http://www.geopolymer.org/science/introduction http://en.wikipedia.org/wiki/Geopolymers (8) Geopolymers: Structures, Processing, Properties, and Industrial Applications http://www.woodheadpublishing.com/en/book.aspx?bookID=1502
CHAPTER 5
Clinker at El Cerrejón Coal Mine, Colombia: Characteristics and Potential Uses
◆
CHAPTER CONTENTS Clinker at El Cerrejón Coal Mine, Colombia Introduction Photo Tour References and Additional Reading WWW Addresses
Highly brecciated rock of the Cogollo Formation, collected from the hanging wall of the Cerrejón thrust fault. The sample contains coarse fragments of clinker (red) and its nonthermally altered calcareous protolith along with bivalve shells (square). From Quintero et al., 2009.
Coal and Peat Fires: A Global Perspective Edited by Glenn B. Stracher, Anupma Prakash, and Ellina V. Sokol © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/B978-0-444-59412-9.00005-3
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Clinker at El Cerrejón Coal Mine, Colombia Jhon A. Quintero Carlos A. Ríos Glenn B. Stracher
Introduction El Cerrejón Coal Mine is a group of open-cast pits located in the La Guajira peninsula in the northern part of Colombia; bordered on the east by Venezuela. The open-pit mines are administratively distributed in the Cerrejón northern zone (CNZ), Cerrejón central zone (CCZ), and Cerrejón southern zone (CSZ). El Cerrejón is an integrated mining operation that extracts and commercializes low-rank bituminous coal from the Upper Paleocene Cerrejón Formation. Sedimentary rocks in the Cerrejón Formation were thermally altered after the late Paleocene as a consequence of the spontaneous combustion of coal seams in the formation (Quintero et al., 2009). The altered rock now includes pyrometamorphic rock called clinker. In addition, coal that burned is reduced to a thin layer of ash. In Colombia, clinker and the coal seams ignited by spontaneous combustion are studied in little detail, and the only reported occurrences are at El Cerrejón. Álvarez and Gómez (1986) studied the petrological characteristics of thermally altered rocks due to coal combustion in El Cerrejón. Locally, temperatures were high enough to partially melt ash from previously burned coal and rocks above coal seams, converting the rocks into paralavas of basaltic composition. Candela and Quintero (2004) mapped clinker within an approximately 690 km2 area of El Cerrejón and modeled its structural relationship to other rocks at depth. More recent studies of the clinker include its petrographic, physical, and chemical characteristics and proposals for its use (Ríos, 2008; Ríos and Williams, 2008; Ríos et al., 2008; Quintero et al., 2009; Sandoval et al., 2009; Henao et al., 2010; Perea and Rincon, 2010). In this chapter, we summarize such studies. Geologic Setting The Cerrejón Formation, exposed in the Cesar-Rancheria basin (Montes et al., 2010), consists of middle to late Paleocene shales, argillaceous sandstones, sandstones, coal seams of economic interest, and combustion altered rocks that vary from slightly baked to completely fused. The sedimentary sequence of the Cerrejón Formation was affected by late Paleocene faulting associated with the Rancheria and Cerrejón faults and by late Paleocene folding in the Tabaco fold zone (Quintero et al., 2009). According to Quintero et al. (2009), clinker at El Cerrejón Coal Mine occurs in the following open pits: Palotal 10 (CSZ), Tipiala (CSZ), 100 (CSZ), Patilla (CSZ), Tabaco High dip (CNZ), Tabaco extension (CNZ), and La Puente (CNZ). The clinker outcrops over an area of 2.9 × 106 m2, and its volume is 1.4 × 108 m3 (Quintero et al., 2009). It was produced during the complete combustion of 6.4 Mt (26.4 × 106 J/kg) of coal; outcrops in irregular patterns as wedge-shaped bodies up to 100 m thick. Clinker outcrops pinch at depths of up to 448 m down dip along the coal seam (Candela and Quintero, 2004). The clinker occurs in structurally complex zones and is well developed along the Ranchería fault (Quintero et al., 2009). A connection between faulting, folding, and spontaneous combustion has not been established. However, combustion can sometimes be influenced by faults and folds that serve as conduits for transmitting oxygen to coal seams. These seams may self-ignite because of exothermic-oxidation reactions involving minerals, such as pyrite, in the coal (Stracher and Taylor, 2004). Self ignition may also occur when coal is exposed to oxygen because of lowering of the water table (Quintero et al., 2009).
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Clinker at El Cerrejón is easily recognized in the field because of its red to red-brown color that varies in intensity, although it also exhibits shades of black, gray, green, cream, and white. All of these colors contrast with the black hue of the Cerrejón Formation coals. The clinker is compact and highly fractured, and has a fine-grained to sandy texture. The red to red-brown color is due to the presence of hematite. The clinker consists of a complex mixture of amorphous and crystalline-inorganic phases. It contains relict-inorganic materials derived from shales, argillaceous sandstones, and gray sandstones interbedded with the burnt coal. Fossil plant remains and relict sedimentary structures, such as bedding, occur. In contrast to other locations where clinker occurs such as Utah, Colorado, and the Powder River Basin in the United States (Stracher et al., 2005, 2007; Heffern et al., 2007), the clinker at El Cerrejón does not occur in topographically steep areas. There are no current reports about active coal fires in El Cerrejón Coal Mine, but some of the fires that occurred were ignited by spontaneous combustion associated with mining activities that exposed coal to oxidation, especially in open-pit walls. Natural spontaneous combustion, as is evident from field relations, took place either after or before deformation, such as the Cerrejón and Samán thrust faults, respectively (Quintero et al., 2009). According to Quintero et al. (2009), periods of spontaneous combustion also occurred during previous arid-climatic times in the Cesar-Ranchería Valley when coal, formerly in the phreatic zone, was exposed as the water table dropped. Petrologic Characteristics and Quantitative Analysis of Clinker Clinker includes a variety of pyrometamorphic rocks that vary in the degree of thermal alteration, as is evident from their texture, original composition, and stratigraphic and structural positions in the burn area (Henao et al., 2010). Clinker varieties identified by Henao et al. (2010) include those with baked sandstone or claystone, tigerstripe, vesicular, and brecciated textures (Figure CCM 5). The clinker usually has the texture of baked sandstone or claystone (Figures CCM 5a and 5b, respectively), the latter resembling building brick characterized by its reddishorange color due to intense oxidation. The baked claystone may be interlayered with relict sedimentary bedding, all arranged in a millimeter-size, tiger-stripe pattern (Figure CCM 5c). Figure CCM 5d illustrates a variety of clinker texturally similar to slag, and has a vesicular or spongy texture. Brecciated zones along faults clearly demonstrate that spontaneous combustion occurred before faulting because the breccias contain mixtures of clinker, unburnt rock, and coal (Figures CCM 5e and CCM 5f). Sandoval et al. (2009) using X-ray analyses, determined that the clinker at El Cerrejón is comprised mainly of quartz and its tridymite polymorph (up to 34.4%), mullite (14.2%), montmorillonite (4.0%), hematite (up to 2.4%), traces of rutile and its anatase polymorph, and traces of ilmenite, cordierite, and kaolinite. Henao et al. (2010) demonstrated by X-ray diffraction studies of clinker from El Cerrejón that the Rietveld method is a powerful tool for the quantitative analysis of phases in polycrystalline samples. Potential Uses of Clinker Industrial Applications Clinker has a number of industrial applications (Hoffman, 1996; Ríos and Williams, 2008). It is used as an aggregate on dirt roads, as well as for grading mining roads, for reclamation and stabilization purposes, and for constructing dam foundations. Recycling clinker could save the coal industry millions of dollars per year by reducing landfill costs. This is because by reducing the amount of clinker in mine tailings, less waste has to be transported to and deposited in landfills. Landfills cost taxpayers millions of dollars to clean up and monitor, and this will likely continue for many years to come (Eco·cycle, 2011). More in-depth studies about the disposal of clinker and the after-effects of doing so may provide valuable data on the environmental impacts of doing so. El Cerrejón has rehabilitation and conservation projects in the areas of biodiversity, energy management, greenhouse gas emissions, air quality, wastewater treatment and dumping, and recycling (Cerrejón, 2011). Synthetic Zeolites Several research teams have studied zeolites synthesized from clinker. Ríos and Williams (2008), Ríos et al. (2008), and Sandoval et al. (2009) synthesized zeolites from clinker by hydrothermal alkaline activation (Figure CCM 6) and also by alkaline fusion, prior to hydrothermal reaction. Experimental results indicate that alkaline activation, NaOH or KOH concentrations, and time have a strong effect on the type and degree of crystallinity of the synthesized zeolites. Low-silica, sodium, and potassium zeolitic materials synthesized by these authors include phillipsite, sodalite, cancrinite, chabazite, zeolite K-F, faujasite, and zeolite Linde Type A.
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Clinker-based zeolites synthesized under well-optimized experimental conditions could be used for environmental waste treatment (Ríos, 2008; Ríos et al., 2008). Geopolymers Geopolymers, a term first used by Davidovits (1991), are more commonly known as inorganic polymers (Duxson et al., 2007). Geopolymer refers to materials with the ability to transform, polycondense, and, like “polymers,” rapidly acquire a shape at low temperatures. These materials include alkali-bounded ceramics, hydroceramics, and alkali-activated cements. Pacheco-Torgal et al. (2007, 2008, 2009), Caballero and Sánchez (2009), and Perea and Rincon (2010) investigated the use of mining waste to form geopolymers. Perea and Rincon (2010) showed that when clinker reacted with the addition of an activator solution (sodium silicate and sodium hydroxide), a geopolymer could be produced with a compressive strength similar to that of Portland cement. When synthesized at higher temperatures, the compressive strength and durability of the geopolymer increased. The formation of geopolymers, through a process called geopolymerization, occurs in response to complicated heterogeneous reactions that occur between a solid rich in aluminum-silicate oxides and an alkali-metal silicate solution, under highly alkaline conditions (Panias and Giannopoulou, 2006). Geopolymerization is regarded as the analogue of zeolite synthesis because the chemistry involved is similar, although the resulting products are different in composition and structure (Komnitsas and Zaharaki, 2007). Geopolymerization is thought to involve four steps that proceed simultaneously, as a result of which the steps are impossible to distinguish (Xu and Van Deventer, 2000): (1) Dissolution of Si and Al from the solid aluminumsilicate in the strong alkaline aqueous solution; (2) formation of Si and/or Si-Al oligomers in the aqueous phase; (3) polycondensation of oligomers to form a three-dimensional aluminosilicate framework; and (4) bonding of the undissolved solid particles into the geopolymer framework and hardening of the entire material (geopolymeric system). Geopolymers exhibit unique physical and chemical properties that make them suitable for use in diverse applications. These include precast structures and nonstructural elements; concrete pavements and products; containment and immobilization of toxic, hazardous, and radioactive waste; advanced structural tooling and refractory ceramics; and fire-resistant composites used in buildings, airplanes, shipbuilding, racing cars, and the nuclear power industry (Komnitsas and Zaharaki, 2007). The utilization of minerals and industrial waste for geopolymerization as well as for immobilizing toxic metals has been investigated extensively by researchers, including Van Jaarsveld et al. (2000) and Xu and Van Deventer (2000, 2002).
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Photo Tour
Figure CCM 1. Location of Colombia, South America, and the La Guajira peninsula in the Caribbean region of Colombia (inset, upper left). The rectangular box in the larger illustration of the peninsula is where El Cerrejón Coal Mine occurs. Map from Quintero et al., 2009, with modifications by Martha M. Barreto, 2009; permission from Elsevier.
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Figure CCM 2. Spontaneous combustion of seam 145 in the Tabaco High Dip, pit (upper-left photo). Note the sulfur (yellow) deposits at the top of the pit. These are from gas exhaled at surficial vents. A walkie-talkie is visible near the center of this photo. A bottle (center of red circles) was inserted upside down in the culm bank at the top of the pit. Once removed (bottom left photo), sulfur and other minerals were found on the outside of the bottle and adjacent rock, but none were visible on the inside. The green circles in the two photos on the right enclose a gas vent encrusted with sulfur and creosote that nucleated adjacent to the opening. At elevated temperatures, heat energy released from the burning coal converts waste rock in the culm bank into pyrometamorphic rock called clinker. Photos by Camilo Montes (bottom right) and Jhon A. Quintero, 2007.
Figure CCM 3. Evidence for coal-bed fires in the north wall of the Tabaco High Dip open-cast mining pit (Cerrejón North Zone) includes coal, clinker of different colors and unknown age, and white ash (upper left photo) in El Cerrejón Coal Mine. From Quintero et al., 2009, with modifications by Carlos A. Ríos, 2011; permission from Elsevier.
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Figure CCM 4. Clinker of unknown age formed during the spontaneous combustion of coal beds in the south wall of pit 100 in the CSZ El Cerrejón Coal Mine. Note variations in the red color of the clinker and its displacement along faults. From Henao et al., 2010, with modifications by Carlos A. Ríos and Glenn B. Stracher, 2011; permission of Earth Science Research Journal. Photos by Wilson Mendoza, 2002.
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Figure CCM 5. Specimens illustrating varieties of clinker and their textural and structural—features discussed in the text. From Henao et al., 2010; permission of Earth Science Research Journal. Photo by Andrew Brook, 2007.
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Figure CCM 6. Scanning electron microscope (SEM) images of zeolite phases synthesized from alkaline hydrothermal treatment of clinker from El Cerrejón Coal Mine. The zeolites include sodalite (SOD), phillipsite (PHI), chabazite (CHA), edingtonite (EDI), faujasite (FAU), and analcime (ANA). The zeolites observed by SEM depict the following features: (a) “ball of yarn” morphology in sodalite, (b) prismatic crystals of phillipsite, (c) relict faujasite after replacement by sodalite, (d) analcime crystals with trapezohedral morphology, (e) intergrowth of phacolitic chabazite and prismatic edingtonite, exhibiting a bow tie-like aggregate, and (f) octahedral faujasite crystals and bladed crystals of sodalite. From Carlos A. Ríos, 2008. SEM microphotographs by Barbara Hodson, 2007.
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Figure CCM 7. X-ray diffraction (XRD) pattern and a SEM image of clinker from El Cerrejón Coal Mine. The phases identified in the clinker include quartz (Qtz), hematite (Hem), and muscovite (Ms). Figures by Carlos A. Rios, 2008 (XRD) and Barbara Hodson (SEM), 2008. From Carlos A. Rios, 2008.
References and Additional Reading Álvarez, R., Gómez, C., 1986. Para-lavas basálticas y metamorfitas generadas por combustión espontánea de mantos de carbón, Formación Cerrejón, Colombia: Bogotá DC, Colombia. Geología Norandina (10), 3–9. Caballero, E., Sánchez, W., 2009. Síntesis de nuevos cementos geopoliméricos a partir de subproductos del proceso de extraccion de oro en la Mina La Baja, Distrito de California: Santander, Tesis de pregrado. Universidad Industrial de Santander, Escuela de Geología, Bucaramanga, p. 95. Candela, S.A., Quintero, J.A., 2004. Cartografía de las zonas de clinker en las áreas de minería de la mina el Cerrejón. Tesis de pregrado, Universidad Industrial de Santander, Escuela de Geología, Bucaramanga, Albania, La Guajira, p. 90. Cerrejón, 2011. Minería responsible. http://www.cerrejoncoal.com (accessed February 2011). Davidovits, J., 1991. Geopolymers: Inorganic polymeric new materials. Journal of Thermal Analysis 37, 1633–1656. Duxson, P., Fernández-Jiménez, A., Provis, J.L., Lukey, G.C., Palomo, A., Van Deventer, J.S.J., 2007. Geopolymer technology: The current state of the art. Journal of Materials Science 42 (9), 2917–2933. Eco·cycle, 2011. Recycling and Environmental Facts. http://www.ecocycle.org/tidbits/index.cfm (accessed February 2011). Heffern, E.L., Reiners, P.W., Naeser, C.W., Coates, D.A., 2007. Geochronology of clinker and implications for evolution of the Powder River Basin landscape. In: Stracher, G.B. (Ed.), Geology of Coal Fires: Case Studies from Around the World: Reviews in Engineering Geology, XVIII, Geological Society of America, pp. 155–175. Henao, J.A., Carreño, A.M., Quintero, J.A., Candela, S.Á, Ríos, C.A., Ramos, M.A., Pinilla, J.A., 2010. Petrography and application of the Rietveld method to the quantitative analysis of phases of natural clinker generated by coal spontaneous combustion. Earth Sciences Research Journal 14 (1), 17–29. Hoffman, G.K., 1996. Natural clinker: The red dog of aggregates in the Southwest. In: Austin, G.S., Hoffman, G.K., Barker, J.M., Zidek, J., Gilson, N. (Eds.), Proceedings of the 31st Forum on the Geology of Industrial Minerals, Bureau of Geology and Mineral Resources Bulletin, 154. The Borderland Forum, New Mexico, pp. 187–196.
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Komnitsas, K., Zaharaki, D., 2007. Geopolymerisation: A review and prospects for the minerals industry. Minerals Engineering 20 (14), 1261–1277. Montes, C., Guzman, G., Bayona, G., Cardona, A., Valencia, V., Jaramillo, C., 2010. Clockwise rotation of the Santa Marta massif and simultaneous Paleogene to Neogene deformation of the Plato-San Jorge and CesarRanchería basins. Journal of South American Earth Sciences 29 (4), 832–848. Pacheco-Torgal, F., Castro-Gomes, J., Jalali, S., 2007. Investigations about the effect of aggregates on strength and microstructure of geopolymeric mine waste mud binders. Cement and Concrete Research 37 (6), 933–941. Pacheco-Torgal, F., Castro-Gomes, J., Jalali, S., 2008. Properties of tungsten mine waste geopolymeric binder. Construction and Building Materials 22 (6), 1201–1211. Pacheco-Torgal, F., Castro-Gomes, J., Jalali, S., 2009. Tungsten mine waste geopolymeric binder: Preliminary hydration products investigations. Construction and Building Materials 23 (1), 200–209. Panias, D., Giannopoulou, I.P., 2006. Development of inorganic polymeric materials based on fired coal fly ash. Acta Metallurgica Slovaca 12, 321–327. Perea, G., Rincon, H., 2010. Residuos generados por la autocombustión del carbón como materias primas en la preparación de materiales geopoliméricos para promover el desarrollo de procesos industriales ambientalmente óptimos: Tesis de pregrado. Universidad Industrial de Santander, Escuela de Geología, Bucaramanga, p. 85. Quintero, J.A., Candela, S.A., Ríos, C.A., Montes, C., Uribe, C., 2009. Spontaneous combustion of the Upper Paleocene Cerrejón Formation coal and generation of clinker in La Guajira Peninsula (Caribbean Region of Colombia). International Journal of Coal Geology 80 (3–4), 196–210. Ríos, C.A., 2008. Synthesis of zeolites from geological materials and industrial wastes for potential application in environmental problems, Ph.D. Thesis School of Applied Sciences, University of Wolverhampton, England, p. 233. Ríos, C.A., Williams, C.D., 2008. Synthesis of zeolitic materials from natural clinker: A new alternative for recycling coal combustion by-products. Fuel 87 (12), 2482–2492. Ríos, C.A., Williams, C.D., Roberts, C.L., 2008. Removal of heavy metals from acid mine drainage (AMD) using coal fly ash, natural clinker, and synthetic zeolites. Journal of Hazardous Materials 156 (1–3), 23–35. Sandoval, M.V., Henao, J.A., Ríos, C.A., Williams, C.D., Apperley, D.C., 2009. Synthesis and characterization of zeotype ANA framework by hydrothermal reaction of natural clinker. Fuel 88 (2), 272–281. Stracher, G.B., Lindsley-Griffin, N., Griffin, J.R., Renner, S., Schroeder, P., Viellenave, J.H., Masalehdani, M.N.-N., Kuenzer, C., 2007. Revisiting the South Cañon Number 1 Coal Mine fire during a geologic excursion from Denver to Glenwood Springs, Colorado. In: Raynolds, R.G. (Ed.), Roaming the Rocky Mountains and Environs: Geological Field Trips, Geological Society of America Field Guide, 10, pp. 101–110. Stracher, G.B., Tabet, D.E., Anderson, P.B., Pone, J.D.N., 2005. Utah’s state rock and the Emery Coalfield: Geology, mining history, and natural burning coal beds. In: Pederson, J., Dehler, C.M. (Eds.), Interior Western United States, Geological Society of America Field Guide, 6, pp. 199–210. Stracher, G.B., Taylor, T.P., 2004. Coal fires burning out of control around the world: Thermodynamic recipe for environmental catastrophe. In: Stracher, G.B. (Ed.), Coal Fires Burning around the World: A Global Issue: International Journal of Coal Geology 59 (1–2), pp. 7–17. Van Jaarsveld, J.G.S., Lucky, G.C., Van Deventer, J.S.J., 2000. The stabilization of mine tailings by reactive geopolymerization. In: Griffiths, P., Spry, A. (Eds.), Proceedings of the MINPREX 2000 International Congress on Mineral and Processing and Extractive Metallurgy, The Australian Institute of Mining and Metallurgy, Melbourne, Australia, pp. 363–371. Xu, H., Van Deventer, J.S.J., 2000. The geopolymerization of alumino-silicate minerals. International Journal of Mineral Processing 59 (3), 247–266. Xu, H., Van Deventer, J.S.J., 2002. Geopolymerization of multiple minerals. Minerals Engineering 15 (12), 1131–1139.
WWW Addresses (1) Cerrejón http://www.cerrejoncoal.com (2) Clinker http://geoinfo.nmt.edu/staff/hoffman/Clinker/Clinker.html http://geology.utah.gov/surreynotes/geosights/coal_Clinker.html http://www.dmr.nd.gov/ndgs/ndnotes/ndn13_html
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(3) Construction Aggregate http://www.wsgs.uwyo.edu/Topics/IndustrialMinerals/aggregate.aspx (4) Eco·Cycle http://www.ecocycle.org (5) Geopolymer Institute http://www.geopolymer.org (6) Geopolymers: Building Blocks of the Future http://www.csiro.au/science/Geopolymers-Overview.html (7) Geopolymers http://www.geopolymer.org/science/introduction http://en.wikipedia.org/wiki/Geopolymers (8) Geopolymers: Structures, Processing, Properties, and Industrial Applications http://www.woodheadpublishing.com/en/book.aspx?bookID=1502