Browsing by Author "Figueroa, M"

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    Anode-support system for the direct electrorefining of cement copper .3. Pretreatment and process conditions to refine industrial cement
    (1997) Figueroa, M; Gana, R; Kattan, L; Mendez, S; Palma, L
    This paper describes the final part of a study on the utilization of a special anode-support system for the electrorefining of industrial cement copper produced by small mines. This type of cement is obtained from the leaching solutions of copper oxide minerals by precipitation with iron scrap. The cement is highly contaminated with iron, different metallic and non-metallic compounds and chloride. Therefore it is necessary to purify the cement copper before the electrorefining process. A two-stage method of purification is proposed, washing with water (pH4) to eliminate chloride and soluble species and magnetic removal of the metallic iron. A circular cell provided with an annular AISI-316 stainless steel mesh supporting the mass of cement copper was utilized. A vertical rotary cylinder of AISI-316 stainless steel was used as the cathode. As operating conditions, a solution of CuSO4 . 5H(2)O: 150 g dm(-3) and H2SO4: 50 g dm(-3), j(c): 5.0 A dm(-2), T: 40 degrees C, u: 60 rpm, were used. A cement copper of 85% purity was utilized. Under these recommended operating conditions it is possible to obtain copper sheets of good quality, meeting the ASTM B-11591 specification for commercial cathodes.
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    Electrochemical behaviour of chalcopyrite in the presence of silver and Sulfolobus bacteria
    (1998) Munoz, JA; Gomez, C; Ballester, A; Blazquez, ML; Gonzalez, F; Figueroa, M
    The electrochemical behaviour of massive chalcopyrite electrodes has been studied in an acid medium (pH 1.5) containing silver ions (0.02 g dm(-3) Ag+) and thermophilic bacteria (68 degrees C). Preliminary tests on particulate electrodes made from graphite, elemental sulfur and Ag2S were included to determine the electrochemical response of reactants (Ag+) and products (S degrees and Ag2S) associated with the dissolution of chalcopyrite in the presence of silver. Massive chalcopyrite electrodes under potential scan showed a dependence on the dissolution of the Ag2S film with both the time of contact with the silver solution and [Ag+]. As well as Ag2S, metallic silver was detected on the chalcopyrite surface. It has been demonstrated that Fe3+ and bacteria play an important role in the regeneration of the Ag2S film. The breakdown of this film is a requirement for the further dissolution of chalcopyrite. The bioleaching of chalcopyrite with thermophilic microorganisms in the presence of silver decreased the decomposition potential of the electrode and favoured its electrodissolution. Bioleaching treatment in the presence of silver ions for periods of time longer than two weeks did not improve the surface reactivity. However, in the initial stages of the process, the lower reactivity of the bioleached electrodes was probably related to a toxic effect of silver on the microorganisms.
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    Electrochemistry of chalcopyrite
    (ELSEVIER SCIENCE BV, 1996) Gomez, C; Figueroa, M; Munoz, J; Blazquez, ML; Ballester, A
    The electrochemical response of a massive chalcopyrite electrode at two different temperatures, 25 degrees C and 68 degrees C, were compared, The electrolyte used in the experiments was an acidic medium (0.4 g . l(-1) (NH4)(2)SO4, 0.5 g . l(-1) MgSO4 . 7H(2)O, 0.2 g . l(-1) K2HPO4 at pH = 2) which is suitable for the growth of the microorganisms involved in the bioleaching process, The chosen temperatures were optimum for the growth of the mesophilic (Thiobacillus ferrooxidans) and thermophilic (Sulfolobus) microorganisms. The experimental results at both temperatures were similar and confirmed that, during the anodic dissolution of chalcopyrite, a passive film is formed on the surface which restricts the oxidation reactions in the medium by diffusional control of the film, The different responses at the temperatures tested were due to the differing physical structure of the complex films of the electrochemically formed sulphides, polysulphides and elemental sulphur.
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    Use of quillaja saponins (Quillaja saponaria Molina) to control acid mist in copper electrowinning processes - Part 1. Laboratory scale evaluation
    (ELSEVIER SCIENCE BV, 2005) San Martin, RM; Otero, AF; Figueroa, M; Escobar, V; Cruz, A
    This work describes the use of extracts of the Chilean quillaja tree (Quillaja saponaria Molina) as alternative low cost surfactants for the control of acid mist in copper electrowinning (EW). Quillaja extracts contain triterpenoid saponins, which are natural surfactants traditionally used as foaming agents in food and beverages. Two commercial products with different degrees of purification were tested: QL 1000 (R) (non-refined product, 8.4% saponin content) and Mistop (R) (refined product, 16% saponin content). Laboratory experiments determined the effects of both products on electrolyte surface tension (ST), solvent extraction process (SX), current efficiency (CE) and cathode quality.