Cleaner production techniques in the Peruvian mining sector based on ISO 14001 audits

El sector minero es uno de los de más rápido crecimiento en el Perú y actualmente es responsable de más del 50% de las exportaciones totales peruanas donde más del 30% de la inversión directa extranjera ha sido colocada. Asimismo, es el sector más regulado en el Perú debido a la presión que ejercen diversos grupos de interés. Debido a ello, entre otras razones, muchas empresas mineras decidieron lograr la certi-ficación ISO 14001. Este estudio presenta evidencia a partir de once auditorias ambientales referidas a la norma ISO 14001 y efectuadas a cuatro empresas mineras y siete subcontratistas mineras dedicadas a la labor de exploración, explotación y extracción. Se encontraron desviaciones significativas relacionadas con los controles operativos que conducían a impactos medioambientales negativos. Desafortunadamen-te la respuesta más común a estas desviaciones fue la adopción de tecnologías que buscan remediar el daño ambiental efectuado (end-of-pipe) en lugar de tecnologías de producción mas limpia. Finalmente,algunas tecnologías de producción más limpia son sugeridas para las empresas que operan en el sector minero en el Perú.The mining sector accounts for more than 50% of the Peruvian total exports and it is the fastest growing industry in Peru where more than 30% of the foreign direct in-vestment has been allocated. Furthermore, it is the most regulated sector in Peru, so it faces, more than ever, pressure from regulators as well as stakeholders. Given this situation, several mining related companies decided to comply with the ISO 14001 standard. In this study one presents findings from ISO 14001 environmental audits performed to 11 mining related companies (4 mining companies and 7 mining sub-contractors dedicated to blasting, exploration and extraction). One finds several deviations related to operational controls that lead to negative environmental impacts. Unfortunately, the most common response to these deviations was the adoption of end-of-pipe technologies instead of cleaner production techniques. Hence, one also suggests some cleaner production techniques that could be adopted in order to cope with these deviations

Charge Transfer mechanism in the Surface Enhanced Raman Scattering of 2,2'-bipyridine recorded on a silver electrode

Nowadays, Surface Enhanced Raman Spectroscopy (SERS) has become a powerful technique to investigate the electronic structure of surface-molecule hybrid systems due to the huge enhancement of the Raman signal. It is established that the origin of this enhancement has two main contributions; the electromagnetic (EM), related to surface plasmons, and the chemical mechanism, due to resonant charge transfer (CT) processes between the adsorbate and the metal. With the aim to investigate the SERS-CT of bipyridine and to identify charge transfer process, the spectra were recorded on silver electrode by using three different wavelengths (473, 532 and 785 nm) in a range from 0.0 up to -1.4 V electrode potential. The electrode potential was modelled in the calculations with atomic silver wires of different size and charge attached to the BPy molecule (AgnBPyq, with q = 0 for n = 2 and q = ±1 for n = 3, 5, 7) and were computed with Density Functional Theory (DFT). Although BPy shows a trans conformation in solution, a cis conformation was chosen for its chelating properties. The results indicate that the intensification of the ~1550 cm-1 band at negative potentials is due the Franck-Condon factors related to the resonant CT process from the metal to the BPy molecule.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Resistencia a la compresión axial del concreto F’C=210 y 280 KG/CM², al reemplazar agregado con origen de roca volcánica de la cantera El Balcón, provincia de San Pablo – Cajamarca, 2022

En la provincia de San Pablo, a partir del crecimiento demográfico, se evidencia un incremento de la construcción de edificaciones usando concreto; sin embargo, dichas edificaciones se ven afectadas por la escasa disponibilidad de agregados, por lo que recurren a zonas aledañas. Por otro lado, cerca de la ciudad existe la cantera El Balcón, del cual solo se extrae piedra grande para cimientos y aún no cuenta con estudios para usar su agregado en concreto. Se confirmó que el material extraído es de origen volcánico mediante un estudio petrográfico; es así que, la presente investigación tiene como objetivo determinar la resistencia a la compresión axial del concreto, reemplazando agregado de cerro con origen de roca volcánica, para un diseño f’c=210 y 280 kg/cm². Para ello, se realizaron ensayos físico-mecánicos a los agregados (de río y roca volcánica), diseños de mezcla, especímenes de concreto y ensayos de resistencia a la compresión axial. El concreto con roca volcánica, para un diseño f¨c=210 kg/cm², alcanzó 331.22 kg/cm² (28 días); para un diseño f¨c=280 kg/cm² obtuvo 384.57 kg/cm² (28 días). Su resistencia aumenta un 50.95% y 33.23% en relación con la muestra patrón, para un diseño 210 y 280 kg/cm² respectivamente; siendo un agregado apto para su uso en concreto

Voltage selection of physisorbed or chemisorbed 4-cyanobenzoate on a nanostructured silver electrode and the dual electronic structure of charged metal-molecule hybrids.

Applied electric potentials tune SERS wavenumbers due to vibrational Stark effect, but some modes of 4CNB- show two differentiated regions, being redshifted at more negative potentials than the potential of zero charge of the electrode but remain unshifted at positive potentials. DFT calculations have been carried out for a model where 4CNB- is linked through the carboxylate [Agnq-OOC(4CNB-)]q-1 or the nitrile [Agnq-NC(4CNB-)]q-1 to stick-like silver clusters [Agn]q with different densities of charge (qeff =q/n). The comparison between calculated and experimental wavenumber shifts points out that 4CNB- is always adsorbed through the carboxylate. The dual behaviour of the wavenumbers is due to the existence of two types of electronic structure of the metal-molecule hybrid. Physisorbed (P-hybrid, repulsive) or chemisorbed (C-hybrid, attractive) surface complexes are selected by the sign of the surface excess of charge of the electrode. The electronic structure of weakly bonded P-hybrid is very sensitive to the voltage and their wavenumbers are continuously shifted, while the wavenumbers of the strong C-hybrid remain almost unshifted. This result proves the dual nature of the electronic structure of molecules bonded to charged metal electrodes or nanoparticles which can be responsible of the qualitative changes observed in electrochemical or molecular electronics experiments.Junta de Andalucía/FEDER (UMA18-FEDERJA-049 and P18-RT-4592

Sensing Bisphenol A by Means of Surface-Enhanced Raman Spectroscopy and DFT Calculations to Elucidate the Enhancement Mechanism That Dominates the Spectrum

Surface-Enhanced Raman Spectroscopy (SERS) was employed as a spectroscopic tool to detect Bisphenol A (BPA), a building block in polycarbonate and epoxy resins or an additive in other polymer plastics like PVC, which has an endocrine disruptor effect. Silver nanoparticles (AgNPs) synthesized by using different reducing agents such as hydroxylamine (Ag@HX), citrate (Ag@Cit), borohydride (Ag@BH), and β-cyclodextrin (Ag@βCD) were employed, aiming to select the best standard SERS substrate. The lowest limit of quantification was reached at a concentration of 0.01 mM (2.3 μg/mL) of a sonicated aqueous solution by using Ag@Cit NPs and identifying two enhanced bands recorded at about 350 and 460 cm−1. In order to gain insight into the nature of the enhanced bands, and therefore into which mechanism governs the SERS signal, electrochemical spectra recorded at different electrode potentials were acquired and TD-DFT calculations were applied to a neutral silver complex of BPA, Ag2-BPA, and to its monohydroxylated chemical specie, Ag2-BPA(OH), which is present in sonicated solution. The calculated electronic structure and the resonance Raman spectra point out that a surface plasmon-like resonance inside the silver cluster dominates the SERS spectrum corresponding to the physisorbed BPA(OH) species, a charge transfer enhancement mechanism or an intramolecular resonance transition localized in the phenolic framework was then discardedThis research was funded by Junta de Andalucía/FEDER (UMA18-FEDERJA-049 and P18-RT-4592). Partial funding for open access charge: Universidad de Málag

Comparative study of different theoretical approaches for modeling the dependence of the SERS vibrational wavenumbers on the electrode potential

Surface-enhanced Raman scattering (SERS) is a powerful technique to study the electronic structure of charged metal-molecule interfaces, which are relevant in many fields like electrochemistry, heterogeneous catalysis or molecular electronics. When electrochemical SERS experiments are carried out two main features are observed: a selective enhancement of the intensity of some bands and a shift of the vibrational wavenumbers. Both characteristics are very often dependent on the applied electrode potential. The first of them has been widely discussed and is related to different SERS enhancement mechanisms,1,2 while the second one reflects changes of the electronic structure of the adsorbate in the ground electronic state. The theoretical modelling of the effect of the electrode potential in electronic structure calculations is a challenge due to the large number of factors to be considered such as the adsorption on a particular site of the metal surface, the way to take into account the role of the electrode potential on the calculations or the electrolyte or solvent effects. In this work we discuss two different approaches to compute the wavenumber dependence of the vibrational modes of pyridine adsorbed on silver at different electrode potentials (Figure 1). On the one hand, the effect of the electrode potential has been modelled by means of simple linear metal-pyridine complexes3 [AgnPy]q where the metal cluster has variable size (n) and charge (q) what allows for defining the qeff = q/n parameter, which quantifies the mean density of charge of the cluster (Figure 1A). On the other hand, an external electric dipole field has been applied on the [Ag2Py]0 neutral complex as an alternative model for simulating the effect of the electrode potential (Figure 1B). The calculations were performed using Density Functional Theory (DFT) and several variables have been considered like the level of theory, solvent effects and the size or shape of the metal cluster.Universidad de Málaga. Campus de Excelencia Internacional Andalucia Tech

Selection rules of surface-enhanced Raman scattering: the role of the out-of-plane vibrations

The electromagnetic/plasmonic (SERS-PL) and the chemical (usually involving resonant photoinduced metal-adsorbate (M-A) charge transfer processes (SERS-CT:M-A+hn-->M+-A-)) mechanisms are recognized as the two main contributions to the enhancement of a particular band in a SERS record. The key problem is to know which mechanism dominates the spectrum and to apply the corresponding selection rules. Many spectra have been analyzed according to the so-called “SERS propensity rules” of the PL mechanism. In this way, it would be possible to get information about the perpendicular/parallel orientation of the adsorbate on the nanoparticle if in-plane/out-of-plane vibrations of planar aromatic molecules show relative enhancement. The SERS of pyridazine (Pdz) on a silver electrode (Figure 1) is a very special case where the relative intensities are tuned by the electrode potential. Three different types of spectra are recorded showing no selective intensification (0 V) or in-plane (-0.5 V) and out-of-plane (-0.75 V) enhancements. The relative activity of both in-plane (8a and 19b modes) and out-of-plane (16b mode) vibrations can be explained under the same resonant SERS-CT chemical mechanism due to Franck-Condon factors related to differences between the equilibrium geometries (A1 vibrations, DQ≠0) and gradients (B1 vibrations, Dn≠0 and DQ≠0), respectively, of the potential energy surfaces of the involved ground and photoinduced CT electronic states. Therefore, it is not necessary to resort to any change in the orientation of the adsorbate, which is the standard explanation based on the propensity rules of the SERS-PL mechanism. This conclusion is supported on the basis of electronic structure calculations of the properties of Ag2-Pdz clusters in the ground (S0;A1) and excited states with CT characteristics (CT0;A2 and CT1;B1).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech