Acid mine drainage (AMD) treatment: Neutralization and toxic elements removal with unmodiﬁed and modiﬁed limestone Evgenia Iakovleva a, *, Ermei Mäkilä b , Jarno Salonen b , Maciej Sitarz c , Shaobin Wang d , Mika Sillanpää a a LUT Chemtech, Department of Chemistry, Faculty of Technology, Lappeenranta University of Technology, Sammonkatu 12, FI-50130, Mikkeli, Finland b Laboratory of Industrial Physics, Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland c Department of Silicate Chemistry, Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Al Mickiewicza 30, 30-059 Krakow, Poland d Depatrment of Chemical Engineering, Curtin University, GPO Box U1987, Perth, WA 6845, Australia A R T I C L E I N F O Article history: Received 1 September 2014 Received in revised form 20 January 2015 Accepted 5 April 2015 Available online xxx Keywords: AMD treatment Mining wastewater Limestone Metal ions removal A B S T R A C T Limestones and their modiﬁcations from Nordkalk Corporation (Finland) ﬂotation ﬁnes (FF) and ﬁlter sand (FS) as potential adsorbents for AMD treatment and wastewater puriﬁcation from Cu, Fe, Zn and Ni ions were studied. Limestones were capable of binding signiﬁcant amounts of Cu and Fe from synthetic AMD solutions and wastewater, while unmodiﬁed limestones were not good for Zn and Ni removal. Two methods of surface area modiﬁcation were suggested. The ﬁrst one with 2 M solution of NaCl and the second one with wastewater from Norilsk Nickel Harjavalta. The structure of materials and their surface area were characterized by SEM, EDX, MIR spectroscopy and nitrogen adsorption methods. Optimal amount of adsorbents for different model and real solutions was found. Adsorption kinetics showed that the adsorption equilibrium was reached within approximately 8 h. The kinetic data ﬁts to a pseudo second order model with correlation coefﬁcients greater than 0.999. The adsorption capacity was the highest at solution pH range of 6–7. Langmuir, Toth and Sips models were used to ﬁt the adsorption isotherms. Based on the parameters calculated from models, the adsorption capacity decreased in the order of Cu > Fe > Zn > Ni for FF and Fe > Cu > Zn > Ni for FS. The research showed that the proposed modiﬁed limestones can be successfully used for AMD neutralization and removal of Cu(II), Fe(III), Zn(II) and Ni(II). ã 2015 Elsevier B.V. All rights reserved. 1. Introduction Each year global mining industry produces several billion tonnes of solid inorganic wastes or by-products, including liquid wastes through its mineral processing and metal production operations (Charbonier, 2001; Akcil and Koldas, 2006). Composition of solid and liquid wastes in mining varies greatly depending on the process, methods of enrichments and treatments of ores. Mine waters can be categorized into three groups according to their acid-base properties: acid mine drainage (AMD) with pH 6 and below, neutral mine drainage with pH 6 and above, and saline mine drainage with pH above 6 containing more than 1000 mg L 1 of carbonates (Wolkersdorfer, 2008). AMD is formed by the decomposition of pyrites (Wolkersdorfer, 2008 After hydrothermal deposits of copper, lead, zinc, tin, and other nonferrous/colored metals into pyrites, substantial amounts of them are sent to landﬁll as they are economically inefﬁcient to treat further. Process of pyrites decomposition is hazardous because of mining water acidiﬁcation and also because a large number of various toxic trace elements are released during the process, these are Ag, As, Bi, Cd, Co, Cu, Hg, Mo, Ni, Pb, Ru, Sb, Se, Sn, Te, and Zn (Abraitis et al., 2004; Chandra and Gerson, 2010; Deditius et al., 2011). The pyrite oxidation process has been extensively studied and can be summarized by the following reactions: FeS 2 þ 7 2 O 2 þ H 2 O ! Fe 2þ þ 2SO 2 4 þ 2H þ (1) FeS 2 þ 7 2 O 2 þ H 2 O ! Fe 3þ þ 1 2 H 2 O (2) * Corresponding author at: Laboratory of Green Chemistry, Department of Chemistry, Faculty of Technology, Lappeenranta University of Technology, Sammonkatu 12, FI-50130, Mikkeli, Finland. Tel.: +358 50 576 1177. E-mail addresses: evgenia.iakovleva@lut.ﬁ, evgenia.iakovleva@gmail.com (E. Iakovleva). http://dx.doi.org/10.1016/j.ecoleng.2015.04.046 0925-8574/ ã 2015 Elsevier B.V. All rights reserved. Ecological Engineering 81 (2015) 30–40 Contents lists available at ScienceDirect Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng