The electrocatalytic reduction of 0.5 M nitrate in 1 M HClO 4 over carbon-supported palladium nanoparticles ͑mean size 10.5 nm͒ was studied with differential electrochemical mass spectrometry ͑DEMS͒ as a function of reaction temperature between 0 and 55°C. The palladium nanoparticles are active for the electrocatalytic reduction of nitrate as evidenced by the detection of N 2 O and NO in DEMS. NO is produced during the anodic scan between 0.8 and 1.0 V vs reversible hydrogen electrode ͑RHE͒ and also during the cathodic scan between 0.3 and 0.0 V vs RHE. In contrast, N 2 O is only produced during the cathodic scan between 0.4 and 0.0 V vs RHE. While the reduction of NO 3 − to NO and N 2 O during the cathodic scan occurs only at significant overpotentials, the required overpotential decreases with increasing temperature. The potential dependencies of the apparent activation energies for the cathodic NO and N 2 O production indicate that at potentials above 0.1 and 0.075 V vs RHE, the respective kinetics of NO and N 2 O evolution are primarily determined by the potential. At potentials below 0.1 and 0.075 V vs RHE, respectively, the apparent activation energies for the evolution of NO and N 2 O are largely potential independent.

not Available.

RESUMOO cobre é um dos metais de maior interesse econômico. Cerca de 70% deste metal é encontrado na natureza na forma de calcopirita (CuFeS2), entretanto com um teor relativamente baixo. Dessa forma, existe um grande interesse no desenvolvimento de alternativas para otimizar processos que visem sua extração e purificação. Tendo em vista essa relevância, o presente artigo realiza um estudo bibliográfico do elemento químico ABSTRACTCopper is one of the metals of greatest economic interest. About 70% of this metal is found in nature in the form of chalcopyrite (CuFeS2), however with a relatively low content. Thus, there is great interest in the development of alternatives to optimize processes aimed at their extraction and purification. In view of this relevance, this article performs a bibliographical study of the chemical element copper, predominantly chalcopyrite, showing how the extraction can be carried out and which factors contribute to the real solution and somehow influence the extraction efficiency, especially the competitiveness of other ions present in the medium in complex with the extractor, evidencing the importance of pH control during the extraction process. Copper is a metal of great interest to the metallurgical industry due to its high ductility, malleability, thermal and electrical conductivity, and corrosion resistance The hydrometallurgical process for copper recovery is generally applied to the extraction of low grade minerals through the leaching operation, which can be enhanced by promoting the growth of naturally occurring bacteria and can accelerate the oxidation process. Conventional solvent extraction processes try to maximize the contact area between two phases for mass transfer to occur. However, these processes have some disadvantages such as the formation of stable emulsions and foams, which makes phase separation difficult, and consequently the extraction and/or purification of the product of interest. emerging and promising unit operation to replace the separation process by solvent extraction

"...Cansado de deitar-se na luz do sol De ficar em casa observando a chuva Você é jovem e a vida é longa Há tempo de viver o hoje E depois, um dia você descobrirá Que dez anos ficaram para trás Ninguém te disse quando correr Você perdeu o tiro de partida..."