Magnetite nanoparticles were synthesized using the green chemistry technique; ferric chloride was used as a precursor agent and Moringa oleifera extract was used as a stabilizer agent. A black powder, characteristic of magnetite, was obtained. X-ray diffraction was performed on the synthesis product and identified as magnetite (Fe₃O₄). Scanning electron microscopy characterization shows that nanoparticles have a spherical morphology, with sizes ranging from 15 nm to 35 nm. The synthesis of carbon nanotubes was carried out by the pyrolytic chemical deposition technique, from which multiwalled carbon nanotubes were obtained with diameters of 15–35 nm and of varied length. The decoration was carried out using the wet and sonification technique, where a non-homogeneous coating was obtained around the nanotubes. The thermal decomposition for both decorated and undecorated nanotubes presents two mass losses but with different slopes, where the activation energy for the decorated carbon nanotubes was 79.54 kJ/mol, which shows that the decoration gives more stability to the nanotubes since the activation energy of the undecorated nanotubes is 25.74 kJ/mol.

A prática mais comum para a disposição de rejeitos é a subaquática e vem se tornando um assunto cada vez mais importante e indispensável para a continuidade operacional das plantas mineradoras devido principalmente a aspectos como: ambientais, segurança, econômicos, etc. As técnicas de espessamento e filtragem se apresentam como alternativas atraentes para o desaguamento dos rejeitos quando comparada à disposição convencional, por diversos motivos, como por exemplo: reaproveitamento de água do processo, vida útil das barragens, segurança operacional e outros fatores que favorecem o gerenciamento de barragens. O objetivo principal deste trabalho é apresentar uma alternativa diferente às técnicas mencionadas através da utilização de polímeros desaguadores desenvolvidos recentemente. Foram avaliados em escala de laboratório: ensaios de espessamento contínuo, filtragem descontinua e aplicação de polímeros desaguadores em rejeitos. Os resultados apresentaram que é possível o uso desta alternativa tecnológica e permitiu estabelecer um comparativo das vantagens e desvantagens entre as outras técnicas mencionadas.

This study evaluates the use of seawater and continental water in tailings thickening and copper flotation at laboratory scale, focusing on water reuse in mining operations in arid regions. The tailings had a mean particle size of 10 µm, with 75% < 50 µm, and a specific weight of 2.64 g/cm³. Seawater contained significantly higher ion concentrations Na⁺ 10,741 ppm, Mg²⁺ 1245 ppm, and Ca²⁺ 556 ppm compared with continental water (187, 32, and 127 ppm, respectively), which negatively affected polymer performance. Sedimentation tests showed that the anionic polymer (A3) increased settling rates by 33 times with continental water at 40 g/t, while with seawater the increase was 31 times at 60 g/t. In column thickener tests, discharge solids reached 65% with continental water and 62% with seawater, representing an annual reduction of ~17,000 m³ of recovered water when seawater is used. Consistency tests indicated that achieving slump <20% required 75% solids with continental water and 77.5% with seawater. With dewatering polymers, doses of 200 g/t achieved ~70% solids and slump values near 50%, surpassing column thickener performance. Primary flotation results showed that recirculated and filtered seawater improved copper recovery by 3–5% compared with fresh seawater, due to partial removal of interfering ions. In contrast, recirculated and filtered continental water reduced recovery by 2–4%, likely because of residual polymer effects on mineral surfaces. These findings highlight the importance of polymer selection and dosage optimization to ensure efficient water recovery and sustainable flotation performance under varying water chemistries.

The final disposal of tailings in the form of paste is a technological alternative. The objective of the present study is to obtain knowledge and compare different operational conditions that are favorable to the production of paste with the fine tailings generated after final desliming stage, obtained from the processing of metallic and non-metallic ores. The sample tailings, despite having a specific weight and similar granulometry, presented different behaviors related to the formation of paste. The minerals calcite and dolomite were predominant in the phosphate tailings while in the manganese tailings, there were pyrolusite and kaolinite. The used column thickener with the best operational conditions found to obtain a maximum concentration of solids after 3 hours of continuous thickening: 55% (manganese tailing) and 70% (phosphate tailing), with values of yield stress around 100 Pa and 300 Pa respectively. This indicates that the pumping conditions are not the same. According to the slump and flume tests, it was possible to preliminary estimate the reduction of the disposal area and the recovery of process water considering the case of a final disposal paste.

A disposição de rejeitos como pasta possui várias vantagens em comparação às disposições convencionais, por exemplo: utiliza uma área menor, melhora a recuperação de água, maior segurança operacional das barragens, etc. Neste trabalho foram caracterizadas as pastas preparadas com rejeitos de manganês e fosfato. Na caracterização dos sólidos foram determinadas: análise granulométrica, determinação do peso específico e identificação das principais espécies mineralógicas. Nas pastas foram determinadas: altura de abatimento, ângulo de repouso (preliminar) e algumas propriedades reológicas (viscosidade e tensão de escoamento). Os principais resultados foram: i) Espécies mineralógicas predominantes no rejeito manganês (RM): Pirolusita e Caulinita, no rejeito fosfático (RF): Calcita e Dolomita; ii) O tamanho médio dos sólidos foram 6,23µm (RM) e 4,76µm (RF); iii) O RM e RF apresentam características de pasta desde 50% e 70% sólidos em massa respectivamente; iv) Foram atingidos ângulos de repouso superiores a 8° (RM) e 16° (RF); v) A viscosidade do RF foram superiores que o RM; vi) As tensões de escoamento do RM e RF aumentam exponencialmente desde 45% e 65% sólidos em massa respectivamente.

Mercury in jarosites is crucial for environmental management and metallurgy. These minerals can incorporate highly toxic heavy metals from mining waste into their structure. This study analyzes the decomposition of mercury jarosite in a Ca(OH)₂ medium, focusing on its topological, kinetic, and modeling characteristics. Topological analysis, XRD and SEM−EDS were performed. ICP−OES was used to analyze the mercury and sulfur ions diffusing from the mercury jarosite into the Ca(OH)₂ solution. The kinetic model that best fit the data was that of spherical particles of constant size with an unreacted core under chemical control. The XRD results did not show new crystallographic phases. SEM−EDS showed a partially decomposed particle indicating a halo and core. The experimental conditions included temperatures from 298.15 to 333.15 K, concentrations of 0.0071–0.23210 mol L⁻¹ Ca(OH)₂, particle diameters of 25–53 µm, and pH of 11.12–12.85. During the induction period, reaction orders of 1.04 and 0.44 were obtained, along with an activation energy of 77.580 kJ mol⁻¹. For the progressive conversion period, the reaction orders were 0.59 and 0.15, with an activation energy of 52.124 kJ mol⁻¹. The overall kinetic modeling showed favorable results, supporting the evolutionary process of the mercury jarosite decomposition reaction in an alkaline medium under different conditions. This allows prediction of when mercury could be released back into the environment in alkaline soils or lime barriers.