Contents lists available at ScienceDirect Desalination journal homepage: www.elsevier.com/locate/desal Investigation of the hydrogen evolution phenomenon on CaCO 3 precipitation in artificial seawater Milad Piri, Reza Arefinia ⁎ Chemical Engineering Department, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad, Iran ARTICLE INFO Keywords: Deposition Hydrogen evolution Calcium carbonate Cathodic potential ABSTRACT Precipitation of CaCO 3 , as the most important part of scales, causes a serious problem in industrial equipment such as pipelines and desalination plants. The effect of the hydrogen evolution phenomenon on the electro- chemical precipitation was studied through varying different factors including cathodic potential (CP), bi- carbonate concentration, and solution temperature. The application of CP from -0.8 V SCE to -1.2 V SCE , an increase in bicarbonate concentration and temperature elevation from 25 °C to 45 °C led to the increase of scaling time (t s ) and residual current density (i r ). In all cases, it was indisputably found that the hydrogen evolution phenomenon had a predominant effect on the calcium carbonate precipitation. The surface analyses by means of scanning electron microscopy (SEM) showed formation of crystals in two defined forms of calcite and aragonite. Moreover, the energy dispersive spectroscopy (EDS) technique confirmed the formation of CaCO 3 crystals. 1. Introduction Many activities have been performed to reduce the precipitation phenomenon [1,2]. Formation of mineral scales on the internal wall of heat exchangers, boilers, cooling water systems, and desalination plants reduces the tube's diameter, causes significant decrease in heat transfer efficiency and may be occasionally lead to the shutdown of the in- dustrial plant [3,4]. Cathodic protection is an effective method to reduce the corrosion process in desalination unites. However, one major problem associated with cathodic protection is that it can lead to the formation of mineral scales known as “calcareous deposits” whose major constituent is cal- cium carbonate (CaCO 3 )[5,6]. Mineral scales, mainly as CaCO 3, may cause serious problems such as pitting corrosion or failure in the structural metal of equipment [7]. To evaluate the precipitation process, the experiments must be run in conditions similar to the actual operating system conditions. However, this takes a lot of time [8]. Therefore, certain procedures of scaling study have been based on the acceleration of calcareous pre- cipitation. Among them, some are chemical using materials such as sodium hydroxide and sodium carbonate [9], whereas some others are electrochemical techniques such as chronoelectrogravimetry, im- pedancemetry and chronoamperometry [6,10–13]. Electrochemical precipitation occurs in a very thin layer on the electrode surface, con- trary to chemical precipitation that occurs in the whole solution [14]. Indeed, electrochemical methods are based on the increase of the interfacial pH of the metal caused by oxygen and water reduction re- actions as a result of the application of cathodic potential (CP). Then, the concentration of carbonate ions increases according to the following reaction [15]: + → + − − − HCO OH CO HO 3 3 2 2 (1) Afterward, the increase of carbonate concentration induces the CaCO 3 scaling as [7,15]: + → − + CO Ca CaCO 3 2 2 3 (s) (2) The influence of different parameters such as seawater composition [2,5,6,11,16,17], flow rate of solution [18–23], pH of solution (pH s ) [21] and solution temperature [6,11,17,21,22] have been studied on the formation and characteristics of calcareous scales. However, mainly due to the various compositions of seawater solution used and sub- strates considered, some contradictory results and conclusions have been reported [11]. It is well known that calcium carbonate is the major constituent of scales and understanding its deposition mechanism is very important. Barchiche et al. proposed that in the absence of Mg 2+ , calcium carbonate deposits in two crystalline forms: calcite and ara- gonite on gold [2]. Benslimane et al. studied the inhibition effect of Zn 2+ on CaCO 3 precipitation in a synthetic CalcoCarbonically pure (CCP) solution [12]. Some other researchers have investigated the calcareous scaling in artificial seawater based on standard ASTM D1141 [5,11]. In these works, the mechanism of CaCO 3 precipitation is af- fected by the contribution of other types of scales such as Mg(OH) 2 [2] https://doi.org/10.1016/j.desal.2018.05.018 Received 30 January 2018; Received in revised form 8 May 2018; Accepted 22 May 2018 ⁎ Corresponding author at: Chemical Engineering Department, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad, Iran. E-mail address: arefinia@um.ac.ir (R. Arefinia). Desalination 444 (2018) 142–150 Available online 28 May 2018 0011-9164/ © 2018 Elsevier B.V. All rights reserved. T