Contents lists available at ScienceDirect Journal of Water Process Engineering journal homepage: www.elsevier.com/locate/jwpe Investigation of the parameters afecting the treatment of mining waters by electrocoagulation Maria A. Mamelkina a, ⁎ , Fedor Vasilyev a , Ritva Tuunila a , Mika Sillanpää b , Antti Häkkinen a a LUT University, School of Engineering Science, 53850, Lappeenranta, Finland b LUT University, School of Engineering Science, 50130, Mikkeli, Finland ARTICLE INFO Keywords: Sulfate Response surface method Mining waters Electrochemical treatment ABSTRACT Recently electrochemical methods have been studied as an alternative to conventional methods to treat in- dustrial and municipal waters. One such water, the mining water, has been mainly treated previously by elec- trocoagulation (EC) to remove metals. Few studies have been performed on the removal of sulfate, nitrate and cyanide from mining waters. In this paper, results from 39 lab-scale experiments on the elimination of sulfate by electrocoagulation with iron electrodes are presented. Signifcance of parameters afecting the removal of sulfate by EC was studied using response surface methodology (RSM). Also, results from kinetic studies and comparison of synthetic and real mining waters are reported. According to kinetics studies, it was suggested that both physical and chemical mechanisms are involved in sulfate removal. At the same test conditions, sulfate removal from both synthetic and real mining waters followed the same pattern. The study concludes that the most signifcant parameters in sulfate removal are initial sulfate concentration and applied current when initial pH was insignifcant in batch operation. From a technology development perspective, this study enhances knowl- edge about the signifcance of process parameters and their interactions as well as allows further scale-up of the process 1. Introduction Electrochemical water treatment is mainly represented by electro- chemical oxidation and reduction, electrocoagulation, electrofotation and electrodialysis [1]. Among others, electrocoagulation (EC) is a promising technique for the removal of various contaminants, such as dyes [2], toxic metals [3–5], natural organic matter [6–8], arsenic [9,10], fuoride [11–13], cyanide [14], sulfate [15–17], nitrate [18] and other anions [19]. Currently, at laboratory scale, electrocoagula- tion has been successfully applied to treat water streams from oil [20], tannery [21], textile [22,23], paper [24,25] and food productions [26,27], mining [15,28,29] and polishing operations [30,31] as well as from municipal waters [32,33]. Some studies report that a potential application of EC could be the removal of toxic metals, sulfate and ni- trate removal from mining waters at diferent stages of mining opera- tions [15,28,29]. Electrocoagulation of mining waters can be considered to be suc- cessful when contaminants are removed from water and destroyed or made less soluble with the application of the reacted and excited state [34]. Possible mechanisms of contaminants removal can be coagula- tion, precipitation, enmeshment, complexation, adsorption or charge neutralization of particles [35,36]. The removal mechanisms depend on the water composition, pH as well as Redox-potential [37–39]. Another signifcant factor afecting the removal mechanisms and electro- coagulation process is the electrode material that mainly infuences the coagulation efciency and process costs [40]. However, electrode material and subsequently the predominant species formed are not the only parameters afecting the electro- coagulation process. Hence, reactor design, applied current, operating time, presence of other contaminants, pH, temperature as well as the combination of factors may afect the process performance signifcantly [36,41–43]. To study the signifcance and possible contribution of factors and their interactions to the process performance, detailed re- search should be conducted. Incorrect combination of factors and misunderstanding their infuence on each other may lead to the failures of the process. Thus, at the beginning of the process development and its upcoming implementation, it is necessary to gain information about the parameters afecting the process. For instance, reactor design gen- erally infuences the mixing and settling characteristics, bubble pass and fotation efciency. Applied current mainly afects anodic dis- solution, system lifetime, unit size, coagulant dosage and bubble gen- eration. Removal rate and energy consumption depend on operating https://doi.org/10.1016/j.jwpe.2019.100929 Received 29 April 2019; Received in revised form 16 August 2019; Accepted 23 August 2019 ⁎ Corresponding author at: PO Box 20 FI-53851 Lappeenranta, Finland. E-mail address: maria.mamelkina@lut.f (M.A. Mamelkina). Journal of Water Process Engineering 32 (2019) 100929 2214-7144/ © 2019 Elsevier Ltd. All rights reserved. T