Electrochemical sensors applied to pyrometallurgical obtaining of copper

LUCILA P. MENDEZ DE LEO; SANCHEZ-LOREDO M GUADALUPE; GRACIELA A. GONZÁLEZ; PEDRE IGNACIO; F ERNANDO BATTAGLINI

Bath

Congreso; ESEAC 2016 16TH International Conference on Electroanalysis; 2016

ESEAC

Copper is an important metal present in many aspects of our dailylife, for example in wires, coins, paints and plumbing. For its winning andpurification, additives such as ethyl xanthate and thiourea are used indifferent parts of the pyrometallurgical process.Xanthates are used as collectors in the processing of sulphideminerals (chalcopyrite, covellite, etc.). They exert their flotation functionby adsorbing on the surface of the mineral. The typical concentration inflotation cells goes from 10-5 to 10-3 M, and monitoring the concentration isnecessary for process control. From the environmental point of view, it is alsoimportant to measure their concentration in effluents.Thiourea is used for the electro-purification of copper. A typicalbath 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 obtainhigh quality copper deposits, it is important to maintain its concentrationbetween these values. Thiourea is also toxic: it interferes with the metabolismof carbohydrates, inhibits the nitrification of soils and is potentiallycarcinogenic and allergenic.For the reasons exposed above, it is desirable to develop simple andeconomic methods for the determination of these compounds. In this work, wepresent electrochemical sensors for direct monitoring of ethyl xanthate andthiourea in their typical industrial matrices. The devices are based ondisposable graphite electrodes obtained by screen-printing, modified with alayer of a polymeric matrix (Polyallilamine, PAA and sodium dodecyl sulphate,SDS) containing nanomaterials.For the determination of xanthate, we used electrodes modified withPAA with and without CdS nanoparticles embedded in it. Electrochemicalimpedance spectroscopy (EIS) measurements were made on artificial flotationbaths. For EIS measurements a sinusoidal potential modulation of ±10 mVamplitude in the 1 Hz?10 kHz frequency range, spaced logarithmically (9 perdecade), was superimposed onto the formal potential of the redox probeFe(CN)63-/Fe(CN)64-, 530 mV versus Ag/AgCl. The results were analyzed byfitting the experimental impedance data to an electrical equivalent circuitmodel. It was found that the charge transfer resistance was linear withconcentration. In the case of thiourea,the electrodes were modified with the polymeric matrix containing silvernanoparticles. The sensors were exposed to different TU artificial industrialbath solutions, including typical additives, in which voltammetric and squarewave voltammetric measurements were performed showing different sensitivity andlinear range. With the objective of finding out which of the reportedmechanisms was taking place in our particular conditions, measurements byPM-IRRAS were performed. For voltammetric determinations, the scanned range ofpotentials was between 0.8 and 1.5 V vs. Ag/AgCl reference electrode, at a scanrate of 10 mV/s and in SWV measurements the used frecuency was 25 Hz, the stepvoltage 5 mV and the amplitude 20 mV. The proposed systemsprovide simple and robust measurement tools for the direct monitoring ofthiourea and xanthates, in pyrometallurgical processes, in a suitableconcentrations range for reconditioning of baths and reducing its environmentalimpact.