Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman Review Hazardous aluminum dross characterization and recycling strategies: A critical review Mostafa Mahinroosta a , Ali Allahverdi a,b,* a Research Laboratory of Inorganic Chemical Process Technologies, School of Chemical Engineering, Iran University of Science and Technology, Narmak 1684613114, Tehran, Iran b Cement Research Center, Iran University of Science and Technology, Narmak 1684613114, Tehran, Iran ARTICLE INFO Keywords: Aluminum dross Waste recycling Waste treatment Hazardous waste Recovery ABSTRACT By finding appropriate recycling approaches, the volume of wastes, corresponding disposal cost, and the pol- lution of environment could be diminished. Also, such promising approaches can result in the conservation of natural sources and economic benefits. Aluminum dross as a hazardous solid waste in aluminum production industries has caused serious environmental and public health challenges. Various methods have been in- troduced for management, utilization, and recycling of the waste. The present review describes, firstly, different types of aluminum dross, their environmental and health hazards, composition, and production process and then focuses on the direct and indirect recycling approaches and recovery strategies. 1. Introduction In general, industrial production is accompanied by issues such as generation of waste and depletion of natural resources as well. Industrial wastes accumulate over time bringing about critical en- vironmental and public health detriments (Xiao et al., 2005). One of the most important and strategic industries producing hazardous wastes, is the aluminum production industry. Aluminum as the third most abundant element in the earth cannot be found as a free element in nature (Abdulkadir et al., 2015). Aluminum is the second most widely used metal after iron. It is a lightweight, conductive, easily paintable, malleable, corrosion resistant, non-magnetic, water/smell-proof, and easily alloyable metal with a high reducing power. It also has a low density (∼2.70 g/cm 3 ) and low melting temperature (∼933 K) (Gil, 2005; Tsakiridis et al., 2013). These characteristics have made this metal as a widely applicable material in the aerospace, building ar- chitecture and marine industries (Tsakiridis et al., 2013). In 1886, Charles Martin Hall and Paul L.T. Héroult invented industrial electro- lytic process for the production of aluminum from aluminum oxide (alumina). In this process, alumina is digested in an electrolytic bath containing cryolite (chemical name: sodium hexafluoroaluminate). An electric current of about 150,000 amperes passes through the electro- lyte (Tsakiridis et al., 2013). During the process, oxygen moves toward the anode and reacts with the graphite electrode. Finally, the aluminum is generated in the cathode. The overall reaction is as follows (Gil, 2005): 2Al 2 O 3 +3C→4Al+3CO 2 (1) Compared to other materials, aluminum production is an energy- intensive industry (Abdulkadir et al., 2015) that shows the greatest difference in energy between primary and secondary production (about 174–186 MJ/kg for primary production, compared to 10–20 MJ/kg for secondary production) (Green, 2007). The reason for the much less energy consumed by the secondary Al production is that its raw feed is Al scraps and primary metallic Al (Tsakiridis et al., 2013). Therefore, today, aluminum is manufactured by means of two different pathways: the primary Al production from the alumina extracted from bauxite ore and the secondary Al production from Al scraps and used aluminum products (foils, extrusion, turnings) (Tsakiridis et al., 2013). Table 1 shows a comparison of the primary and secondary processes of alu- minum production. According to the data given in Table 1, primary Al production requires much more energy and water consumption than secondary Al production. Also, primary Al production releases sig- nificant atmospheric emissions and solid wastes compared to secondary Al production. The manufacturing process of alumina from bauxite was proposed by K.J. Bayer. In this process, bauxite, along with sodium hydroxide is heated at high pressure (∼30 atm) and temperatures between 373 and 593 K resulting in sodium aluminate solution in accordance with the following reaction: https://doi.org/10.1016/j.jenvman.2018.06.068 Received 17 February 2018; Received in revised form 21 May 2018; Accepted 20 June 2018 * Corresponding author. Research laboratory of Inorganic Chemical Process Technologies, School of Chemical Engineering, Iran University of Science and Technology, Narmak 1684613114, Tehran, Iran. E-mail addresses: m_mahinroosta@chemeng.iust.ac.ir (M. Mahinroosta), ali.allahverdi@iust.ac.ir (A. Allahverdi). Journal of Environmental Management 223 (2018) 452–468 0301-4797/ © 2018 Elsevier Ltd. All rights reserved. T