Development of a rapid measurement of current efficiency in the electrowinning of zinc J McGinnity, M Nicol ⁎, Z Zainol, A Ang School of Engineering and Information Technology, Murdoch University, Perth, WA 6150, Australia abstract article info Article history: Received 17 October 2016 Received in revised form 20 December 2016 Accepted 29 January 2017 Available online 01 February 2017 A method for the rapid measurement of current efficiency for the deposition of zinc by a computer controlled an- odic stripping technique has been successfully developed and evaluated in the laboratory and in a zinc tankhouse. This method provides rapid measurement of the efficiency within about 3 min from 1 to 2 L of electrolyte at a fixed temperature. Minimum preparation time is involved as the pure lead wire cathode surface can be easily renewed by simply cutting the coated wire to expose a new surface. Reproducible results have been achieved which compare very favourably with those obtained by longer term conventional methods. It has been demonstrated that the technique can also prove to be useful as a convenient method for the study of cathode morphology and for the nature of the potential/time transients during nucleation and growth of zinc de- posits under various conditions. Thus, the effects of the concentrations of various impurities such as selenium, an- timony and cobalt on the current efficiency and the morphology of the zinc deposits have been studied. The effects of the addition of additives such as glue and gelatine have similarly been evaluated. The results have been shown to be consistent with published data. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Approximately 11 million tonnes per year of zinc are produced around the world (Hassall and Roberts, 2010) and it is expected to con- tinue growing at 2–3% per year. About 85–90% of the total is produced by electrowinning. Generally, the electrowinning of zinc is carried out in an electrolyte containing about 60 g/L of zinc and 170 g/L of H 2 SO 4 with aluminium cathodes and anodes made of a lead-silver alloy. The deposition process is known to be accompanied by the reduc- tion of protons with the evolution of hydrogen. The corresponding anodic reaction is the oxidation of water with oxygen evolution. Zn 2þ þ 2e ¼ Zn E° ¼ -0:76 V ð1Þ 2H þ þ 2e ¼ H 2 E° ¼ 0V ð2Þ 2H 2 O ¼ O 2 þ 4H þ þ 4e E° ¼ 1:23 V ð3Þ The relative rates of Reactions (1) and particularly (2) are known to be extremely sensitive to the impurities present in the electrolyte (Bestetti et al., 2001; de Souza and Tenorio, 2002; Dhak et al., 2011; Guillaume et al., 2007; Ivanov, 2004; Ivanov and Stefanov, 2002; Recendiz et al., 2007; Tripathy et al., 2004). Even though the electrolytic processing of zinc has been widely established and practiced for many years, there continues to be various problems related to the current ef- ficiency of the cathodic process. Zinc producers often use the current ef- ficiency as a key performance indicator given its importance in determining the overall energy consumption. Theoretically, 1.6 kWh is required to deposit 1 kg of zinc but typical energy consumption for zinc electrowinning in current industrial practice is 3.25–3.40 kWh/kg of zinc with 85–95% current efficiency (Huang et al., 2010; Parada and Asselin, 2009). It is not unusual to experience periods of low current ef- ficiency (as low as 75%) at various times in most tankhouses. The primary source of low current efficiency is the presence of cer- tain metal impurities which enhance the rate of Reaction (2) (Gabe, 1997). In addition, the presence of some organic compounds in the feed solution has also been reported (Majuste et al., 2015) to have an ef- fect on the cathode current efficiency. In order to counteract the harmful effects of the impurities, various organic additives are added to the electrolyte to inhibit the hydrogen evolution reaction and promote a smoother surface morphology of the cathodes. Numerous researchers have studied various additives and their effect on the current efficiency (Das et al., 1996; Das et al., 1997; de Souza and Tenorio, 2002; Dhak et al., 2011; Guillaume et al., 2007; Ivanov, 2004; Ivanov and Stefanov, 2002; Majuste et al., 2015; Merrin et al., 1997; Stefanov and Ivanov, 2002; Tripathy et al., 1997; Tripathy et al., 1998a; Tripathy et al., 1998b; Tripathy et al., 1999a; Tripathy et Hydrometallurgy 169 (2017) 173–182 ⁎ Corresponding author. E-mail address: m.nicol@murdoch.edu.au (M. Nicol). http://dx.doi.org/10.1016/j.hydromet.2017.01.009 0304-386X/© 2017 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Hydrometallurgy journal homepage: www.elsevier.com/locate/hydromet