Removal of strontium by electrocoagulation using stainless steel and aluminum electrodes Z.V.P. Murthy ⁎, Snehal Parmar Department of Chemical Engineering, Sardar Vallabhbhai National Institute of Technology Surat, Surat – 395 007, Gujarat, India abstract article info Article history: Received 19 June 2011 Received in revised form 25 August 2011 Accepted 26 August 2011 Available online 21 September 2011 Keywords: Electrocoagulation Strontium Stainless steel electrode Aluminum electrode In the present work, removal of strontium (up to 100 mg/L) from synthetic wastewater by electrocoagulation has been studied. Stainless steel and aluminum electrodes have been used and removal efficiencies have been compared with respect to electrocoagulation time, current density, amount of electrolyte added, solution pH, distance between electrodes, temperature and initial concentration of strontium. Preliminary operating cost estimation has been found out for both electrode materials. The strontium removal data has been used to find adsorption kinetics using pseudo-first-order and pseudo-second-order adsorption kinetics models. Results show that the optimum operating variables values are 50 min of process time, 8 mA/cm 2 current density and solution pH 5 for which around 93% and 77% removal efficiency was achieved with using stainless steel and aluminum electrodes, respectively. Pseudo-second-order kinetic model fitted the data better than the pseudo-first-order model. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Strontium is one of the rare earth elements present in very low concentration in earth's crust and due to its high reactivity rarely found in pure form but occurs in the form of minerals like strontianite (SrCO 3 ) and celestite (SrSO 4 ). Strontium contains many isotopes from which 90 Sr and 85 Sr are radioactive and used as fuel in nuclear reac- tors [1]. Apart from these radioactive isotopes, strontium contains four non-radioactive stable isotopes. 87 Sr and its compounds like strontianite and celestite are widely used in the manufacturing of X-ray absorbing glass for cathode ray tubes, removal of lead from zinc sulphate solution in the electrolytic zinc process, electro-ceramic and oxide superconductors, oxygen eliminator in electron tubes, glass for color television. Strontium ion is considered as little toxic and it is due to concerned anion. We can consider the effect of strontium on environment based on its chemical form [2]. Therefore, it is desired to remove strontium and its compounds from wastewater as much as possible. For radioactive 90 Sr and its compounds, it is desired to bring the concentration in the wastewater to less than or equal to 8 pCi/L (equivalent to 5.67 × 10 -11 mg/L) before discharge, but prac- tically it is very difficult to achieve this target [3]. The methods reported on the removal of Sr(II) from aqueous wastewaters are adsorption using montmoritlonite and zeolite [1], adsorption using activated carbon [2], supported liquid membranes with strip dispersion [3] and complexation-nanofiltration [4]. These methods are efficient but require extra cost in terms of addition of ex- ternal chemical compounds and/or application of high pressure. In the last couple of years, electrocoagulation has shown its useful- ness for the treatment of water as well as wastewater. Electrocoagu- lation is efficient for the treatment of wastewaters containing metal ions, like Zn(II), Cu(II), Ni(II), Ag(I), Cr(VI) [5]; Hg(II) [6]; In(III) [7]; As(III) [8];B [9] and heavy metals from metal plating effluent [10]. We can use variety of electrodes for the treatment of wastewater, which are iron or steel, aluminum, magnesium or combination of them [11]. The possible reactions which occur during the electrocoa- gulation process are [12–14]: At the anode: M s ðÞ →M aq ð Þ nþ þ ne - ð1Þ 2H 2 O→4H þ þ O 2 þ 4e - ð2Þ At the cathode: M aq ð Þ nþ þ ne - →M s ðÞ ð3Þ 2H 2 O l ðÞ þ 2e - →H 2g ðÞ þ 2OH - ð4Þ Here M is the material used as electrode and n is the number of elec- trons. During the electrocoagulation process metal hydroxides, poly- hydroxides and/or polyhydroxymetallic compounds of the electrode material will be generated. These materials contain strong affinity for dispersed particles and counter ions, which results in coagulation [12]. Desalination 282 (2011) 63–67 ⁎ Corresponding author. Tel.: +91 261 2201648/2201642; fax: +91 261 2227334. E-mail addresses: zvpm2000@yahoo.com, zvpm@ched.svnit.ac.in (Z.V.P. Murthy). 0011-9164/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2011.08.058 Contents lists available at SciVerse ScienceDirect Desalination journal homepage: www.elsevier.com/locate/desal