Nanometric particles of high economic value in coal fire region: Opportunities for social improvement Luis F.O. Silva a, * , Tito J. Crissien a, b , Ismael L. Schneider a ,  Erika P. Blanco a , Carlos H. Sampaio b, c a Department of Civil and Environmental. Universidad de la Costa, CUC, Calle 58 # 55e66, Barranquilla, Atl antico, Colombia b Universidade Federal do Rio Grande do Sul, Escola de Engenharia, Departamento de Metalurgia, Centro de Tecnologia, Av. Bento Gonc alves, 9500. Bairro Agronomia, Porto Alegre, RS, Brazil c Departament d’Enginyeria Minera, Industrial i TIC, Serra Húnter Prof., Universitat Polit ecnica de Catalunya Barcelona Tech, Av. Bases de Manresa 61e63, Manresa, 08242, Barcelona, Spain article info Article history: Received 26 November 2019 Received in revised form 15 January 2020 Accepted 6 February 2020 Available online 10 February 2020 Handling Editor: Cecilia Maria Villas B^ oas de Almeida Keywords: Rare earth elements Carbon nanotubes Spontaneous coal combustion Advanced analytical approach Colombian coals abstract Spontaneous coal combustion in the La Guajira coals was studied for the presence of carbon nanophases (e.g., carbon nanotubes), occurrence of rare earth elements (REEs) in them, and the probable mechanisms for concentration of these rare compounds. For this purpose, various techniques such as scanning electron microscopy (SEM), Field-emission SEM, transmission electron microscopy (TEM), high- resolution TEM, and focused ion beam (FIB) were used. The development and alteration of the nano- particles by geo-processes during the early modification periods of coal combustion were explored. Certain types of carbon nanophases and REE compounds may constitute nanominerals and ultra-fine particles accumulated in the coal peat. Assemblages of these nanophases (crystalline and amorphous compounds), predominantly the clay-monazite relationship and its connection to tonsteins in the coal combustion zones in the east region of the coal mines studied in this work, indicate that the coal area was subjected to REE concentration. The carbon nanophases contained several potential hazardous el- ements (PHEs), including, arsenic, bromine, cadmium, chlorine, fluorine, mercury, and other PHEs. While carbon nanotubes have been known to be produced from spontaneous combustion of coal of varying ranks, the present work is the first report on the naturally occurring REEs and carbon nanophases in the Colombian coal mining area. © 2020 Elsevier Ltd. All rights reserved. 1. Introduction Globally, coal mining and subsequent coal fires are responsible for air, soil and water (e.g. gases, sulfuric acid, hazardous inorganic elements, polycyclic aromatic hydrocarbons) pollution involving, in part, a large amount of particulate matter which affects human health (Zheng et al., 2019; Hower et al., 2013; Ribeiro et al., 2010; Oliveira et al., 2019a, b, d, 2018a, b, 2017 , 2014; Gasparotto et al., 2018; Landim et al., 2018; Schneider et al., 2016). The Interna- tional Agency for Research on Cancer (IARC), an agency operating under the World Health Organization (WHO), has cataloged out- door air contaminants as the principal (Group 1) carcinogens affecting health (IARC, 2013). In addition to the many man-made threats to the atmosphere, self-combustion of coal also needs further scientific exploration (Kríbek et al., 2017; Garcia et al., 2014; Agudelo-Casta~ neda et al., 2016; Agudelo-Casta~ neda et al., 2017). The heterogeneity of a coal fire requires a more interdisciplinary approach to its local and global assessments (Dias et al., 2014a,b). The coal-burning area studied in this work is located in the Department of La Guajira in northeastern Colombia between the areas of Albania, Barrancas, and Hatonuevo (Oliveira et al., 2019b). It is a combination of Wayúu ethnic settlements, a smaller Afro- Colombian population and rustic farming societies. On the other hand, rare earth elements (REEs) and carbon nanoparticles (CNPs) are vital to the modern society as they are used in high-tech industry and a variety of consumer goods such as computers, cell phones, catalysis, fluorescent lighting, permanent magnets, medical devices and advanced defense technology (Dai et al., 2016). However, there is a sharp discrepancy between the high demand for and low production of REEs due to the limited * Corresponding author. E-mail address: felipeqma@hotmail.com (L.F.O. Silva). Contents lists available at ScienceDirect Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro https://doi.org/10.1016/j.jclepro.2020.120480 0959-6526/© 2020 Elsevier Ltd. All rights reserved. Journal of Cleaner Production 256 (2020) 120480