A SEM Study Of the Electro-Reduction Of Strontium Ion On Cu Electrodes

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

CABA

Congreso; XV CIASEM CONGRESS; 2019

Asociación Argentina de Microscopia - Sociedad Interamicana de Microscopia

The shale gas extraction via hydraulic fracture is a gas production method from non-traditionalreservoirs 1. The water management is, at least, a challenging issue because hydraulic fracturegenerates a large amount of wastewater containing different potentially toxic elements mixed in thewaste. Among these, Ba and Sr ions are the most representative. Therefore, a valuable discussionshould be done on the separation methods, analysis of risks and strategies for treatment. There is alarge amount of different capture methods for these ions including adsorption in fixed structures andchemical reduction 1. Among these techniques, the electro-reduction is a candidate to capture andseparate 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 electrodes is followed by using scanning electron microscopy(SEM) and associated techniques. The samples are observed in a FEI-INSPECT S50 microscopeoperated at 30 kV. The energy dispersive spectroscopy (EDS) measurements are done using an OctanePro Detector (EDAX). To perform this work, SEM is a key technique because superficial study of theelectrode is done to understand the kinetics of the capture of de divalent strontium ion. It is speciallyused to determine the morphology and the habit and form related to the geometric crystallography ofthe electrodes and the corresponding reaction products.These characteristics are well described by SEM micro-images. The Figure 1.a shows a micro-imageof the Cu cathode after the electro-reduction process for 30 min in a 0.1M strontium nitrate solutionunder a voltage of 24 V . The cathodic reaction proceeds with strontium reduction and hydrogenevolution. The star shaped structure is Sr reduced on the surface. The bored sheet observed on thesurface is 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 the formation of parallelepipedprotuberances of the Fm3m space group. These structures relate to the sites where oxygen gas evolvesduring reaction. Notice the 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 2 shows SEMmicrographs. The Figure 2a shows the starting Cu electrode. Notice the former habit and forms of theFm3m space group. The Figure 2 b shows the electrode after reaction. Notice the Sr reduced on thesurface. The EDS measurements are done to verify the elemental composition of the structures. Theresults presented shows that Sr reduction proceeds along to both anodic oxygen evolution and cathodichydrogen formation, respectively. It indicates that the process is kinetically and thermodynamicallypossible.References:[1] Y Sun et. al. Environm. Intern. 125 (2019), p 452.[2] A. Vengosh et. al. Environ. Sci. Technol. 48 (2019), p. 8334.