Study of Low-Frequency Electrochemical Leaching of Sulfide Copper-Zinc Concentrates As

STUDY OF LOW-FREQUENCY ELECTROCHEMICAL LEACHING OF SULFIDE COPPER-ZINC CONCENTRATES AS AN EXAMPLE

V. B. Fetisov, L. D. Kirr , V. S. Tsvetkov, K. S. Mitrofanov, S. V. Rassokhin, S. I. Noritzin*, K.Yu. Shunyaev*

Ural State University of Economy, Ekaterinburg, Russia

* Institute of Metallurgy, Ural Division RAS, Ekaterinburg, Russia

Hydrometallurgical processes are widely used in nonferrous metallurgy for extraction of gold, silver, platinoids, copper, zinc, nickel, cobalt, aluminum, uranium, and refractory, chemically stable, rare, scattered, and rare-earth elements. They have some advantages over pyrometallurgical processes, including more selective extraction of metals, processing of raw materials, which are lean in main components, and hard-milling ores, and preparation of selective concentrates.

Hydrometallurgists have a wide spectrum of extraction methods – chemical, hydrolytic, sorption, extraction, crystallization, electrochemical, autoclave, etc. techniques – providing a high extraction of pure metals and their salts. Furthermore, hydrometallurgical plants ensure smaller dust and gas emissions to the environment.

Sulfides of copper, zinc, nickel, cobalt and other metals in sulfide concentrates or mattes are dissolved in acid solutions only in the presence of oxygen, which acts as an oxidizer. This process is slow in ordinary conditions. It is intensified in practice by two means:

1. Preliminary oxidizing roasting of ores or concentrates for conversion of metal sulfides to oxides (the latter dissolve much easier). A byproduct of this treatment is sulfuric acid, which is used for leaching of the cinder.

2. Dissolution of sulfides from concentrates in autoclaves at an elevated temperature (above 100 °C) and a high air or oxygen pressure.

In this paper we propose an original method for intensification of dissolution of sulfides in acid solutions using low-frequency electric currents.

The subject of study was a copper-zinc concentrate containing (weight %) 3.9% copper, 39.65% zinc and 14.8% iron as determined by the chemical analysis. Sulfides were leached from the concentrate in a reactor made of a chemically resistant material. Two semi-cylindrical lead electrodes and a mechanical agitator were fitted inside the reactor. Current parameters (the frequency and the signal shape) were preset by a specially designed power current converter. Comparative experiments were performed in three leaching regimes:

- purely chemical dissolution;

- application of a direct current;

- application of a low-frequency current (8 Hz) at the mean current strength of 5 A.

Other parameters of the process, including the ratio between the solid and liquid (5% solution of sulfuric acid in water) phases (1:5), the temperature (50-55 °C) and the process duration (60 min), were the same in all the regimes. In the first leaching regime the necessary temperature was maintained by an external heat source. The chemical analysis was performed using the atomic absorption method on a "Hitachi" analyzer.

Results of the chemical analysis of the formed solutions are given in the Table.

The numerals in brackets denote the amount of elements (weight %) passed into the solution from the concentrate.

Let us take purely chemical leaching, which provides an almost uniform dissolution of sulfides (cf. the yield in %), as the reference in the analysis of the tabulated data. Application of an external electric field influenced differently the sulfide leaching rate depending on the metal type and current characteristics. For example, electrochemical dissolution of the copper

Table. Concentration of main elements (Cu, Zn, Fe) in solutions after 60-min leaching of a copper-zinc concentrate in different regimes

sulfide (independently of the nature of the applied current) was much slower than chemical leaching. In other words, given the aforementioned parameters, the current retarded passage of copper ions into the electrolyte solution. However, the iron sulfide dissolved twice as fast as in the reference regime in the same conditions. Of special interest was the response of the zinc sulfide to the experimental conditions. It follows from the Table that the direct current with the chosen parameters had little effect on Zn leaching. On the other hand, the low-frequency current (8 Hz) considerably intensified dissolution of this element. Summing up it may be stated that in the given experimental conditions the low-frequency current suppressed the Cu dissolution reaction, accelerated a little dissolution of Fe, and considerably intensified leaching of Zn.

One may reasonably think that elements can be extracted selectively already during leaching of polymetallic concentrates by adjusting the current parameters.

This study was supported in part by the grants "Leading scientific schools" No. НШ-468.2003.3; НШ-1997.2003.3.

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