A SEM study of the electro-reduction of strontium ion on Cu electrodes

M.D.L.A. CANGIANO; F. CORNACCHIULO; M.R. ESQUIVEL; A. AVALOS

CABA

Congreso; XV CIASEM CONGRESS; 2019

Asociación Argentina de Microscopía

The shale gas extraction via hydraulic fracture isa gas production method from non-traditional reservoirs [1]. The water management is, at least, a challengingissue because hydraulic fracture generates a large amount of wastewatercontaining different potentially toxic elements mixed in the waste. Amongthese, Ba and Sr ions are the most representative. Therefore, a valuable discussionshould be done on the separation methods, analysis of risks and strategies fortreatment. There is a large amount of different capture methods for these ions includingadsorption in fixed structures and chemical reduction [1]. Among these techniques, the electro-reduction isa candidate to capture and separate soluble ions such as that of strontium [2]. The electro-reduction method is speciallyappropriated for use in mobile devices operated by remote control. In this work, the reaction using Cu-Ni electrodesis followed by using scanning electron microscopy (SEM) and associatedtechniques. The samples are observed in a FEI-INSPECT S50 microscope operatedat 30 kV. The energy dispersive spectroscopy (EDS) measurements are done usingan Octane Pro Detector (EDAX). To perform this work, SEM is a key techniquebecause superficial study of the electrode is done to understand the kineticsof the capture of de divalent strontium ion. It is specially used to determinethe morphology and the habit and form related to the geometric crystallographyof the electrodes and the corresponding reaction products. These characteristicsare well described by SEM micro-images. The Figure 1.a shows a micro-image ofthe Cu cathode after the electro-reduction process for 30 min in a 0.1Mstrontium nitrate solution under a voltage of 24 V . The cathodic reactionproceeds with strontium reduction and hydrogen evolution. The star shapedstructure is Sr reduced on the surface. The bored sheet observed on the surfaceis Cu detached from the electrode. The remaining structure is the Cu cathode.The Figure 1 b. shows a SEM micro image of the anode. The reaction leads to theformation of parallelepiped protuberances of the Fm3m space group. Thesestructures relate to the sites where oxygen gas evolves during reaction. Noticethe difference on this morphology and that of the cathode. The global processis exothermic and proceeds with change of the pH from 7 to 12. The Figure 2shows SEM micrographs. The Figure 2a shows the starting Cu electrode. Noticethe former habit and forms of the Fm3m space group. The Figure 2 b shows theelectrode after reaction. Notice the Sr reduced on the surface. The EDSmeasurements are done to verify the elemental composition of the structures.The results presented shows that Sr reduction proceeds along to both anodic oxygenevolution and cathodic hydrogen formation, respectively. It indicates that theprocess is kinetically and thermodynamically possible. References:[1] Y Sun et. al. Environment International. 125 (2019), 452-469.[2] A. Vengosh et. al. Environ. Sci. Technol. 48 (2019) 8334-8348