Electrochemical sensors applied to pyrometallurgical obtaining of copper

LUCILA MÉNDEZ DE LEO; IGNACIO PEDRE; MARÍA GUADALUPE SÁNCHEZ-LOREDO; FERNANDO BATTAGLINI; GRACIELA A. GONZÁLEZ

Bath

Conferencia; 16th International Conference on Electroanalysis; 2016

University of the West of England

Copper is an important metal present in many aspects of our daily life, for example in wires, coins, paints and plumbing. For its winning and purification, additives such as ethyl xanthate and thiourea are used in different parts of the pyrometallurgical process.Xanthates are used as collectors in the processing of sulphide minerals (chalcopyrite, covellite, etc.). They exert their flotation function by adsorbing on the surface of the mineral [1]. The typical concentration in flotation cells goes from 10-5 to 10-3 M, and monitoring the concentration is necessary for process control. From the environmental point of view, it is also important to measure their concentration in effluents.Thiourea is used for the electro-purification of copper. A typical bath of a copper refinery contains CuSO4 0.65 M, H2SO4 1.8 M, Avitone® and glue (3 mg/l each), and thiourea in a concentration between 3 and 10 mg/L. To obtain high quality copper deposits, it is important to maintain its concentration between these values. Thiourea is also toxic: it interferes with the metabolism of carbohydrates, inhibits the nitrification of soils and is potentially carcinogenic and allergenic [2-4].For the reasons exposed above, it is desirable to develop simple and economic methods for the determination of these compounds. In this work, we present electrochemical sensors for direct monitoring of ethyl xanthate and thiourea in their typical industrial matrices. The devices are based on disposable graphite electrodes obtained by screen-printing, modified with a layer of a polymeric matrix (Polyallilamine, PAA and sodium dodecyl sulphate, SDS) containing nanomaterials.For the determination of xanthate, we used electrodes modified with PAA with and without CdS nanoparticles embedded in it. Electrochemical impedance spectroscopy (EIS) measurements were made on artificial flotation baths. For EIS measurements a sinusoidal potential modulation of ±10 mV amplitude in the 1 Hz?10 kHz frequency range, spaced logarithmically (9 per decade), was superimposed onto the formal potential of the redox probe Fe(CN)63-/Fe(CN)64-, 530 mV versus Ag/AgCl. The results were analyzed by fitting the experimental impedance data to an electrical equivalent circuit model. It was found that the charge transfer resistance was linear with concentration.In the case of thiourea, the electrodes were modified with the polymeric matrix containing silver nanoparticles. The sensors were exposed to different TU artificial industrial bath solutions, including typical additives, in which voltammetric and square wave voltammetric measurements were performed showing different sensitivity and linear range. With the objective of finding out which of the reported mechanisms was taking place in our particular conditions, measurements by PM-IRRAS were performed. For voltammetric determinations, the scanned range of potentials was between 0.8 and 1.5 V vs. Ag/AgCl reference electrode, at a scan rate of 10 mV/s and in SWV measurements the used frecuency was 25 Hz, the step voltage 5 mV and the amplitude 20 mV.The proposed systems provide simple and robust measurement tools for the direct monitoring of thiourea and xanthates, in pyrometallurgical processes, in a suitable concentrations range for reconditioning of baths and reducing its environmental impact.References[1] Talanta 33, 10, pp 801-806, 1986[2] J. Anal. Chem. 60 (2005) 514?517[3] Analyst 136 (2011) 5256?5260[4] J. Appl. Electrochem. 36(2006) 1075?1081