The use of the emulsion liquid membrane technique to remove copper ions from aqueous systems using statistical experimental design Hao Ma, Ozan Kökkılıç, Kristian E. Waters ⇑ Department of Mining and Materials Engineering, McGill University, 3610 University, Montreal, Quebec H3A 0C5, Canada article info Article history: Received 15 August 2016 Revised 13 October 2016 Accepted 17 October 2016 Available online xxxx Keywords: Mine waste Emulsion liquid membrane Copper extraction ELM abstract Process water from mineral processing plants may contain a significant amount of dissolved metal ions, which may be recycled as process water, or discharged into the environment as effluent. If they are dis- charged into the environment they may cause significant problems for the local flora and fauna. One method of removing metal ions from aqueous systems, which has generated considerable interest over recent years, is the emulsion liquid membrane (ELM) technique, which incorporates solvent extraction and stripping. This work details the use of design of experiments applied to an ELM process for removing copper ions from a dilute aqueous solution. Initially, a fractional factorial design was used to screen out the most important factors; this was followed by a central composite design to obtain optimal operating conditions. The extraction percentage of copper was obtained as more than 99% under these conditions. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Every year a huge volume of waste water is discharged by the mining, metallurgy and smelting industries; these waste streams may contain significant amounts of heavy metal ions (Wan Ngah and Hanafiah, 2008; Fu and Wang, 2011). These metals ions should be recovered for both environmental and economic considerations. Thus, the removal of heavy metal ions from waste water has been an important topic for the past several decades. For waste streams released by the mining industry, acid mine drainage (AMD) is con- sidered to be the biggest problem (Akcil and Koldas, 2006; Johnson and Hallberg, 2005). There have been various ways for recovering heavy metal ions, the most commonly used methods being ion-exchange (IX) (Kang, 2004; Alyüz and Veli, 2009), adsorption (Jusoh et al., 2007; Bhattacharyya and Gupta, 2008; Babel and Kurniawan, 2003), sol- vent extraction and chemical precipitation (Ku and Jung, 2001; Huisman et al., 2006; Özverdi and Erdem, 2006). However, when facing AMD, these methods have some disadvantages. The concen- tration of heavy metal ions found in the drainage is usually less than 500 ppm (Kentish and Stevens, 2001), and a significant amount of reagents are usually required for treating such large scale waterbodies. Thus an effective way for extracting low concentration of heavy metal ions and requiring fairly lower cost must be developed. One potentially effective method of recovering these heavy metal ions is the emulsion liquid membrane (ELM) technique (Kislik, 2009; Draxler et al., 1988; Ooi et al., 2015). This technique was introduced by Li in 1968 and has been researched ever since (Li, 1971; Li et al., 2011; Garti, 1997; Valenzuela et al., 2005, 2009; Yasser and Ibrahim, 2012; Kumbasar, 2010; Draxler and Marr, 1986). It works by forming a primary water in oil (W/O) emulsion as the first step in which the internal phase con- tains the stripping acid, and the oil phase contains the surfactant and metal extractant. The primary W/O emulsion is then sent for treatment with a solution containing heavy metal ions, and emul- sion liquid membrane globules are formed during this process. In this project, the ELM globules are water (H 2 SO 4 liquor) in an oil phase (copper extractant & surfactant in kerosene) in water (CuSO 4 solution) emulsions. The interfaces between water and oil phases are termed liquid membranes. The copper ions are extracted by the copper extractant in the oil phase and further stripped into the internal H 2 SO 4 droplets. A schematic representation of extrac- tion of copper ions using ELM technique is shown in Fig. 1. The copper extractant is represented by HA, and CuA 2 repre- sents the copper-extractant complex (Garti, 1997; Valenzuela et al., 2005). Copper ions will be extracted, stripped and concen- trated at the same time (Valenzuela et al., 2005, 2009; Yasser and Ibrahim, 2012). After extraction, the water phase (effluent) will be sent for further treatment such as acid neutralization prior being discharged into environment; the emulsion phase will be sent for de-emulsification such as electrostatic coalescence (Sastre et al., 1998). The de-emulsification process will separate http://dx.doi.org/10.1016/j.mineng.2016.10.014 0892-6875/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: kristian.waters@mcgill.ca (K.E. Waters). Minerals Engineering xxx (2016) xxx–xxx Contents lists available at ScienceDirect Minerals Engineering journal homepage: www.elsevier.com/locate/mineng Please cite this article in press as: Ma, H., et al. The use of the emulsion liquid membrane technique to remove copper ions from aqueous systems using statistical experimental design. Miner. Eng. (2016), http://dx.doi.org/10.1016/j.mineng.2016.10.014