Abstract Laterite ores, which represent around two-thirds of nickel reserves, became an important source of nickel and cobalt metals. The objective of the present study was to investigate the efficiency of a hybrid route to extract nickel and cobalt present in a laterite ore sample which was not commercially attractive to be processed through the current routes. The process efficiency was investigated through the application of different test conditions, such as roast temperature, ore sample comminution, and moisture. Chemical analysis by atomic absorption was used to quantify the metals. The solid phase’s identification and characterization were accomplished by X-ray diffraction and Scanning Electron Microscopy. The Rietveld Method was used for the mineral’s phase quantification. In terms of nickel and cobalt extractions, the most favorable condition was: particle size smaller than 38 µm, 50% sulfuric acid (wt.%), and 10% moisture (wt.%), which permitted nickel, cobalt, magnesium, and iron recoveries of 84.5%, 92.0%, and 93.0%, 27.0% respectively. These results indicate the successful application of the route. In addition, it was found that chlorite, chromite, hematite, and goethite were identified as the main nickel and cobalt carriers present in the process residue.

Waste printed circuit boards (WPCB) residues were mechanically processed to concentrate their metal content aiming to reduce costs of the subsequent recovery of copper, tin, and lead. A fully dry route was proposed to avoid the generation of liquid effluents that would require additional treatment. Firstly, 10.7% of the residue was segregated by magnetic separation; the remaining nonmagnetic fraction was comminuted and sieved. Ceramic and polymer materials (1/3 of the total weight) concentrated in the finer and the coarser size fractions, while metallic materials (2/3 of the total weight) concentrated in the intermediate size fraction (90.7, 94.5, and 95.6% of the total copper, tin, and lead contained in the milled WPCB, respectively). The fractions between 0.3-1.20 mm were submitted to gravity separation using a zig-zag air classifier; enrichment of copper (from 43±11% to 68±5%), tin (from 10±3% to 17±1%), and lead (from 4±1% to 6.4±0.5%) were obtained.

RESUMO A oxidação da superfície da pirita é um problema sério na indústria de mineração, uma vez que diminui a sua hidrofobicidade dificultando a flotação desse mineral ou levando a um consumo elevado de coletor. Neste estudo, os produtos da reação entre os íons Fe2+ e HS-, formados na superfície da pirita oxidada e da hematita, foram estudados. As condições para a formação de uma camada hidrofóbica na superfície desses minerais também foram investigadas. Avaliou-se a influência do pH das soluções de hidrossulfeto de sódio (NaHS) para atingir uma condição de Eh-pH adequada para a formação de compostos de enxofre hidrofóbicos nas superfícies minerais. Medidas de ângulo de contato, difração de raios-X (DRX), microscopia eletrônica de varredura/espectroscopia de energia dispersiva (MEV/EDS) e espectroscopia Raman foram as técnicas analíticas empregadas para se verificar a natureza dos produtos formados na superfície desses minerais. Essas análises permitiram a identificação de cristais de enxofre elementar sobre a superfície da hematita e da pirita oxidada, após o condicionamento das amostras em meio redutor, e o melhor resultado foi obtido com condicionamento em pH 8,0 durante 96 horas com solução de NaHS 0,3 M para as duas amostras analisadas.

ABSTRACT The pyrite surface oxidation is a serious problem in the mining industry, since it decreases its hydrophobicity turning it difficult to float or leading to a high collector consumption. In this study, the products of the reaction between the Fe2+ and HS-, formed on the surface of oxidized pyrite and hematite, were studied. The conditions for the formation of a hydrophobic layer on the surface of these minerals were also investigated. The pH influence of sodium hydrosulphide (NaHS) solutions was evaluated in order to achieve a suitable Eh-pH condition for the formation of hydrophobic sulfur compounds on mineral surfaces. Measurements of contact angle, X-ray diffraction (XRD), scanning electron microscopy/dispersive energy spectroscopy (SEM/EDS) and Raman spectroscopy were the analytical techniques used to verify the nature of the products formed on the surface of those minerals. The formation of elemental sulfur crystals on the hematite and oxidized pyrite surfaces was identified after the conditioning in a reducing medium, and the best result was obtained at pH 8.0 during 96 hours with a 0.3 M NaHS solution for the two samples analyzed.

In this paper the influence of calcination temperature on the corrosion resistance of a Ti/SnO2-Sb electrode prepared according to Pechini's method and its efficiency for phenol oxidation in chloride medium were investigated. When calcination was performed at 600 °C tin distribution throughout the film was more uniform, providing a more homogeneous film structure. Electrolysis of a 0.34 mol.L-1 NaCl solution containing 100 mg.L-1 phenol at 10 mA.cm-2 for 30 minutes lead to corrosion of the electrodes calcined at 400 and 500 °C, whereas the one calcined at 600 °C remained practically unchanged, indicating that the coating structure, which is dependent of calcination temperature, plays an important role on the structural integrity of electrode material. Phenol concentration was reduced in 90% with the Ti/SnO2-Sb electrode calcined at 600 °C after 60 minutes of electrolysis at 10 mA.cm-2.

Eletrólitos cianídricos, apesar de sua alta toxicidade, são amplamente empregados pelas indústrias de eletrorrecobrimento devido à qualidade dos depósitos metálicos obtidos. No caso dos depósitos de cobre sobre aço-carbono, após algum tempo de operação contínua, o teor de impurezas, especialmente o de carbonatos alcança valores indesejáveis, prejudicando a qualidade do depósito metálico e tornando, portanto, o banho inadequado. Dessa forma, é gerado um efluente denominado sangria que requer tratamento para descarte seguro. Nesse trabalho foi avaliada a possibilidade de se recuperar eletroliticamente o cobre dessa solução de modo a se reutilizar o cobre contido e simultaneamente destruir parte do cianeto, diminuindo a carga tóxica do efluente. Recuperações de cobre em torno de 99,9% e oxidação de 99% do cianeto foram obtidas após cinco horas de eletrólise a 50°C com uma densidade de corrente de 9,4A/cm², a partir de um litro de efluente contendo 26g/L de cobre e 27g/L de cianeto total.

Despite their toxicity, cyanide electrolytes are widely used by electroplating industries due the high quality of the metallic deposits. In the copper deposition on mild steel, after relatively long periods of continuous operation the build up of impurities, especially carbonates, reach undesirable values, decreasing the deposit quality and turning the solution unsuitable for its purpose. Then, a waste solution known as bleed, which requires treatment for a safe discard, is generated. In this paper, the possibility of simultaneous copper electrowinning and cyanide oxidation from this effluent, decreasing its hazardousness was evaluated. Copper recoveries around 99.9% and oxidation of 99% of the cyanide were achieved, from an effluent containing 26g/L of copper and 27g/L of cyanide after a five-hour electrolysis at 50° C with a current density of 9.4 A/cm².

O ouro é encontrado freqüentemente na natureza associado a sulfetos, como pirita e arsenopirita. Geralmente, tais sulfetos são concentrados por flotação para posterior tratamento hidrometalúrgico. A flotabilidade dos sulfetos minerais depende do balanço hidrofílico/hidrofóbico, que é induzido, respectivamente, pelos produtos de oxidação formados nas superfícies minerais e pelo processo de adsorção do coletor, que, por sua vez, não pode ser completamente interrompido pela presença da camada de produtos de oxidação. No presente trabalho, foram tomadas medidas de potencial de repouso de pirita e de arsenopirita, indicando que tais minerais, após adição de solução de H2O2 10 % v/v a 1 mL/min, são oxidados a Fe(OH)3 e FeOOH, respectivamente. As voltametrias cíclicas indicaram que, tanto para a pirita, quanto para a arsenopirita, as espécies responsáveis por conferir hidrofobicidade aos sulfetos (xantato férrico e dixantógeno, respectivamente) se formam em potenciais mais elevados, na presença de produtos de oxidação em suas superfícies. Medidas de potencial de repouso indicaram que a pirita sofre oxidação com formação de Fe(OH)3, entretanto, ao ser interligada à arsenopirita, torna-se catodicamente protegida e, portanto, menos suscetível à oxidação. Quando nitrogênio foi borbulhado na solução, o potencial de repouso da arsenopirita, ao ser interligada à pirita, atingiu valores mais elevados, sugerindo que nessa interação ela se comporta anodicamente.

Gold is frequently found in nature associated with sulfides, as pyrite and arsenopyrite. Usually, these sulfides are concentrated by flotation and submitted to posterior hydrometallurgical treatment. The flotability of the sulfide minerals depends on the hydrophilic/hydrophobic balance, which is induced respectively by the oxidation products formed on the minerals surface and by the collector adsorption that can not be completely interrupted by the presence of oxidation products. In the present work, rest potentials measurements for pyrite and arsenopyrite indicated that after the addition of hydrogen peroxide solution 10 % v/v in a 1 mL/min rate, these minerals were oxidized to Fe(OH)3 and FeOOH, respectively. Cyclic voltammetries indicated that ferric xanthate and dixanthogen are the species responsible for the hydrophobicity of pyrite and arsenopyrite respectively. Furthermore, the minerals oxidation leads to the formation of those species at more elevated potentials. Rest potentials measurements indicated that the formation of Fe(OH)3 on the pyrite surface due its oxidation is inhibited when this mineral is connected to arsenopyrite. The rest potential of arsenopyrite in the presence of nitrogen bubbling is more elevated when connected to pyrite, indicating its anodic behavior.

Embora o cianeto seja um reagente amplamente empregado na lixiviação de metais preciosos e no acabamento superficial de certos metais, sua elevada toxicidade faz com que o uso de tecnologias eficientes no tratamento dos efluentes desses processos seja primordial. Existem diversas técnicas disponíveis para o tratamento de efluentes industriais contendo cianeto, contudo os métodos mais empregados baseiam-se na oxidação química do cianeto a uma espécie menos tóxica, o cianato, que se hidrolisa produzindo os íons amônio e bicarbonato, além de uma lama contendo hidróxidos de metais pesados, quando presentes no efluente. Entre as técnicas mais recentes para o tratamento de efluentes contendo cianeto, a oxidação eletroquímica apresenta algumas vantagens, como a possibilidade de recuperação dos metais complexados pelo cianeto, além de não necessitar de reagentes químicos adicionais, sendo perfeitamente capaz de atender às exigências dos órgãos ambientais. Esse trabalho apresenta uma comparação entre os diversos processos de tratamento de efluentes contendo cianeto, com ênfase no processo eletroquímico, e também uma revisão sobre estado atual dessa tecnologia.

Although cyanide is widely employed for leaching precious metals and electroplating certain metals, its high toxicity demands efficient technologies to treat the wastewater generated by these processes. There are a number of available techniques for the treatment of industrial aqueous cyanide-bearing effluents. However, the most employed method is based on its chemical oxidation to the less toxic cyanate which is hydrolyzed to ammonium and bicarbonate ions. The heavy metal complexes, when present in the effluent, will form a sludge composed of hydroxides. Among the most recent techniques for the treatment of effluents containing cyanide, electrochemical oxidation presents some advantages, such as: possible metal recovery from the cyano-complexes, no need for further chemicals additions, compliance to environmental agencies directives. This paper presents a comparison among several processes for treating the aforementioned effluents, with emphasis on the electrochemical process, which is briefly reviewed.

Neste artigo, o potencial no qual a depressão da galena ocorre, é relacionado com a formação de compostos hidrofílicos em sua superfície. São propostas reações com base em voltametria cíclica, dados termodinâmicos e análises por espectroscopia de fotoelétrons. Variáveis eletroquímicas, tais como o potencial de oxirredução, apresentam boas perspectivas para a flotação seletiva da galena e esfalerita, pois numa dada faixa de potencial, a superfície da galena, ao contrário da esfalerita, se torna hidrofílica, conforme mostraram as medidas de ângulo de contato e testes de microflotação.

In this article, the potential at which galena depression occurs is related to the formation of hydrophilic compounds on its surface. Reactions are proposed based on analyses by cyclic voltammetry, thermodynamic data, and X-ray photoelectron spectroscopy (XPS). Electrochemical variables, such as the redox potential, present good perspectives for selectivity in the flotation of galena and sphalerite, because in a given range of potentials, the galena surface becomes hydrophilic, as shown by measurements of the contact angle and floatability tests.