Isabel Lázaro

The use of carbon paste electrodes with non-conducting binder for the study of minerals: Chalcopyrite

A pulverized chalcopyrite mixture with graphite and silicon was subjected to electrochemical studies and found to have similar behaviour to that of chalcopyrite massive electrodes, with the advantage of excellent reproducibility, since the problems of polishing deficiency, fracture and lack of homogeneity that solid electrodes present, are avoided. From voltammetric studies of these carbon paste-chalcopyrite electrodes in H2S04, HN03 and HCl media, it has been established that the reduction process is limited by the diffusion of protons to the interface. This study also shows that the increase of chloride ion concentration energetically favours the chalcopyrite reduction process, allowing for the separation of the processes of formation of chalcocite and bomite. On the other hand, this study also shows a reversible oxidation of the bomite and chalcocite obtained in the previous chalcopyrite reduction.

Electrochemical oxidation of arsenopyrite in acidic media

Abstract Arsenopyrite (FeAsS) is a common sulfide mineral in base metals and precious metals ores and concentrates. The treatment of these kinds of ores involves frequently an oxidation step to improve metal recoveries. The study of the mechanisms occurring during the arsenopyrite oxidation is then necessary to optimize industrial processes, like bioleaching of arsenopyrite-bearing concentrates using autotrophic acidophilic bacteria. In this work, an electrochemical approach was used to study the arsenopyrite oxidation in acidic media. Cyclic voltammetry and chronoamperometry techniques were performed using a carbon paste electrode (CPE) and an acidic growth medium as electrolyte solution. This electrochemical study allows to determine that the oxidation of arsenopyrite in an acidic growth medium is performed in two steps. The first step corresponds to the initial surface oxidation of arsenopyrite to produce realgar (As 2 S 2 ) and ferrous ions in solution ( E V SCE ). During the second step, a catalytic oxidation of these interfacial products appears to solubilize finally H 3 AsO 4 and ferric ions ( E > 0.55 V SCE ). The presence of elemental sulfur on the arsenopyrite surface was not detected in this study. This fact is associated to the potential zone where this electrochemical study was performed. However, the study here reported allows to have some advances in the understanding of the arsenopyrite oxidation in acidic media.

EC treatment for reuse of tissue paper wastewater: Aspects that affect energy consumption

The need for more rational use of water also calls for more efficient usage. An example is the production of tissue paper, where large amounts of water are discharged into the drain because its turbidity does not allow for recirculation. While this is a serious problem, even worse is the fact that the quality of such wastewater makes it difficult not only to recirculate but also to discharge due to environmental law restrictions. In this paper, electrocoagulation is proposed as a suitable technology to meet standards of water discharge, and even better, as a treatment option for removal of turbidity. Since energy consumption has been a drawback for EC applications, relevant aspects that contribute to increase it such as cell voltage and current density have been reviewed. For this purpose a systematic micro-electrolysis study combined with macro-electrolysis experiments have provided evidence that shows it is possible to achieve a turbidity removal of 92% with an energy consumption of 0.68 kWh/m(3). Thus, the results presented in this paper support the use of EC to obtain water of acceptable quality for reuse in the tissue paper industry.

Surface characterization of arsenopyrite in acidic medium by triangular scan voltammetry on carbon paste electrodes

Abstract To optimize the industrial processes involving chemical or biological oxidation of arsenopyrite and to control acid rock drainage it is necessary to perform a precise characterization of the mineral surfaces. In this work we have demonstrated that a voltammetric study with carbon paste electrodes (CPE) provide a possible alternative method to allow a rough characterization of the arsenopyrite surface. By these means the presence of sulfur or FeAsO 4 passive layers on the surface is shown, when arsenopyrite is previously oxidized by either chemical, biological and biological assisted methods. The presence of sulfur or FeAsO 4 was confirmed by XRD and IRD surface determinations. On the other hand the heterogeneity of the precipitates formed during the previous oxidation process was detected by CPE-mineral voltammetry studies. These observations were confirmed by SEM photomicrographs of the surface treated arsenopyrite.

Electrochemical Study of Orpiment ( As2 S 3 ) and Realgar ( As2 S 2 ) in Acidic Medium

Electrochemical characterizations of high purity natural crystals of orpiment (As 2 S 3 ) and realgar (AS 2 S 2 ) were performed in the presence of a bacteria-free, acidic bacterial growth medium for Thiobacillus ferrooxidans, name M2. A carbon-paste electrode (CPE), composed of a mixture of pure mineral grains with graphite powder and silicon oil as a binder, was used for the experiments. Reproducibility of the mineral surfaces was assured by monitoring the open-circuit potential (OCP) of the initial CPE-mineral-electrolyte interface. The voltammetric study revealed that the oxidation processes for both of these arsenic-bearing minerals involves two steps: an initial oxidation of the sulfide mineral to H 3 AsO 8 and HSO 4 - , followed by the oxidation of H 3 AsO 3 to H 3 AsO 4 . The reduction processes for the two minerals, however, differ. While the reduction of orpiment occurs in a dual step process, for realgar, the process is achieved in a single step.

Avoiding a Voltage Sag Detection Stage for a Single-Phase Multilevel Rectifier by Using Control Theory Considering Physical Limitations of the System

The use of control theory in power electronics applications is aimed toward several objectives, which include, obtaining a good dynamic response, stabilizing in an operation point, regulation of state variable, reference tracking, rejecting of disturbances and robustness against parametric variations. It is also possible to eliminate stages that represent computational effort via control theory without loss of the main desirable characteristics. However, it should be considered the physical limitations of the topology given that even with sophisticated controllers they cannot achieve the established objectives if these limitations are exceeded. This paper aims at highlighting the importance of physical limitations of a single-phase multilevel rectifier (SPMR) using a nonlinear controller, an aspect not considered in previous works published by the authors. Thus, the design here presented is based on input–output linearization via feedback combined with a generalized PI controller. These controllers are used because they allow avoiding a voltage sag detection stage without changing the main characteristics of the topology. The procedure to reproduce these results is shown and the feasibility of the method is demonstrated by simulation and experimental results in a 1 kVA SPMR prototype.

A Rotating Disc Electrochemical Dual Autoclave for the Study of Electrochemistry and Leaching at High Temperature and Pressure

A study of the pressure acid leaching of chalcopyrite was performed using a unique rotating disc electrochemical dual autoclave. The autoclave permits electrochemical and leaching experiments to be conducted up to 200 °C using a chalcopyrite rotating disc electrode. The paper describes in detail the design of the dual autoclave, which consists of a separate pre-heater and reactor. This eliminates heat-up effects, and allows either leaching or electrochemical investigations to be commenced at the correct temperature. The mixed potential measurements and voltammograms of chalcopyrite at 150 °C indicate that pressure acid leaching in a solution containing 0.1 M iron(III) will occur quite rapidly. In comparison, when using 120 psi partial pressure of oxygen, the mixed potential is in the so-called prewave region, and hence slow leaching would be expected.

Electrochemical and spectroscopic study of interfacial interactions between chalcopyrite and typical flotation process reagents

Comparative voltammetry and differential double-layer capacitance studies were performed to evaluate interfacial interactions between chalcopyrite (CuFeS2) and n-isopropyl xanthate (X) in the presence of ammonium bisulfite/39wt% SO2 and caustic starch at different pH values. Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, contact angle measurements, and microflotation tests were used to establish the type and extent of xanthate adsorption as well as the species involved under different mineral surface conditions in this study. The results demonstrate that the species that favor a greater hydrophobicity of chalcopyrite are primarily CuX and S0, whereas oxides and hydroxides of Cu and Fe as well as an excess of starch decrease the hydrophobicity. A conditioning of the mineral surface with ammonium bisulfite/39wt% SO2 at pH 6 promotes the activation of surface and enhances the xanthate adsorption. However, this effect is diminished at pH ≥ 8, when an excess of starch is added during the preconditioning step.

An Overview of Reclaimed Wastewater Reuse in Gold Heap Leaching

ABSTRACT The intensive use of groundwater by the gold mining industry is an important sustainability concern, especially in arid and semiarid regions where groundwater is a scarce resource. Alternatives, such as water reuse, treatment and recycling, have been implemented to overcome this issue. The potential use of reclaimed wastewater in gold heap leaching, without decreasing the process efficiency, has not yet been considered. Hence, this review focuses on the physicochemical, biological, and chemical features (organic matter, microbial loads, metal ions, and anions) of reclaimed wastewater that may limit its use in gold heap leaching.

Processing Methodology Based on ASTER Data for Mapping Mine Waste Dumps in a Semiarid Polysulphide Mine District

Abstract. The aim of this work is to present a simple, economic, and efficient methodology based on the use of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data to map areas of mining waste composed of heterogeneous mineral mixtures. This methodology has been applied to the District of Santa María de la Paz, Mexico, to detect different mineral phases that have been previously characterized. The methodology consists of techniques such as band ratioing, Normalized Difference Tailings Index (NDTI), and Spectral Angle Mapper (SAM) classification. Experimentation with the SAM classification has established a minimum threshold of 0.08 radians for the mapping of mining waste and tailings impoundments. The results of this analysis indicate that the different techniques applied to ASTER images do not show the same level of accuracy for all waste dumps. In this study, the best technique for mapping the different mine wastes is the ferrous iron ratio, which features an overall accuracy of 93.25 % and a kappa coefficient of 0.86. The accuracy of the results suggest that the proposed methodology can be used in the detection of mine waste in mining districts that have not been fully characterized, especially in countries with a large amount of abandoned mining waste.