Estudio experimental de los parámetros que influyen en el equilibrio químico del electrolito del refino de cobre de Atlantic Copper

Abstract

The present research work entitled "Study of the chemical equilibrium in the copper refining electrolyte", carried out over four years, is the result of the collaboration between Atlantic Copper SLU and the University of Huelva. The work is based on three lines of research. In the first one, the stability of As, Sb and Fe and their oxidation states in the industrial copper electrolyte of Atlantic Copper SLU have been studied. For this, different parameters of conservation of the sample have been considered, such as dilution, acidification, temperature and storage period. The determination of As and Sb species has been performed by coupling high performance liquid chromatography, hydride generation and atomic fluorescence spectroscopy (HPLC-HG-AFS), while Fe species have been determined by molecular absorption spectroscopy in the visible region. The results indicated that the species As(V) is the predominant compared to As(III), Sb(III) compared to Sb(V) and Fe(III) compared to Fe(III). Under the optimized conservation conditions, As and Sb species were more stable than Fe, which must be analysed on the first day of sampling, while Sb and As can be analysed during the 15 or 28 days, respectively, after sample collection without observing changes in the oxidation states or in the total content. In the second line of research, the elimination of Sb species from the industrial copper electrolyte has been studied on a laboratory scale and in the Atlantic Copper SLU industrial plant for Sb/Bi removal. The removal procedure consisted of a pre-treatment based on the use of copper shavings followed by a treatment in ion exchange columns. In addition, the evolution of the Sb, As and Fe species in the electrolyte has been studied before and after the start-up of the industrial plant for the elimination of Sb/Bi, installed in 2018. Both on a laboratory scale and in the industrial plant, it was possible to eliminate close to all of the Sb(III) in the industrial electrolyte, and to reduce the concentration of Sb(V) by half, without affecting the content and oxidation states of As and Fe. The entry into operation of the industrial plant for the elimination of Sb/Bi has meant a reduction of the content of Sb in the electrolyte of ca. 45%. Regarding the last line of research, the precipitation equilibrium diagrams of BiAsO4 and SbAsO4 in synthetic and industrial electrolyte have been obtained. In the case of BiAsO4, Bi and As spiking experiments have been carried out in the electrolyte, based on the determination of the concentrations of these impurities in solution of the industrial electrolyte by means of inductively coupled plasma atomic emission spectrometry (ICP-AES), and in changes in the turbidity of the synthetic and industrial electrolyte due to the precipitation of BiAsO4. Furthermore, the chemical composition of the precipitate formed has been confirmed by X-ray diffraction (XRD). Similarly, in the case of the SbAsO4 precipitation line, Sb and As spiking experiments have been carried out by means of turbidity measurements in both electrolytes. In the equilibrium diagrams of BiAsO4 and SbAsO4 has confirmed that the industrial electrolyte is more stable than the synthetic electrolyte. The industrial electrolyte spiking results indicated that the electrorefining process can operate under supersaturated conditions of Bi, As and Sb, with respect to the theoretical precipitation line calculated from thermodynamic parameters. In this way, no precipitation occurs and ensuring a proper performance of the copper refining process.