Chalcocite is the most important and abundant secondary copper ore in the world with a rapid dissolution of copper in an acid-chloride environment. In this investigation, the methodology of surface optimization will be applied to evaluate the effect of three independent variables (time, concentration of sulfuric acid and chloride concentration) in the leaching of pure chalcocite to extract the copper with the objective of obtaining a quadratic model that allows us to predict the extraction of copper. The kinetics of copper dissolution in regard to the function of temperature is also analyzed. An ANOVA indicates that the linear variables with the greatest influence are time and the chloride concentration. Also, the concentration of chloride-time exerts a significant synergic effect in the quadratic model. The ANOVA indicates that the quadratic model is representative and the R2 value of 0.92 is valid. The highest copper extraction (67.75%) was obtained at 48 h leaching under conditions of 2 mol/L H2SO4 and 100 g/L chloride. The XRD analysis shows the formation of a stable and non-polluting residue; such as elemental sulfur (S0). This residue was obtained in a leaching time of 4 h at room temperature under conditions of 0.5 mol/L H2SO4 and 50 g/L Cl−.

Oxidized black copper ores are known for their difficulty in dissolving their components of interest through conventional methods. This is due to its non-crystalline and amorphous structure. Among these minerals, copper pitch and copper wad are of great interest because of their considerable concentrations of copper and manganese. Currently, these minerals are not incorporated into the extraction circuits or left untreated, whether in stock, leach pads, or waste. For the recovery of its main elements of interest (Cu and Mn), it is necessary to use reducing agents that dissolve the present MnO2, while allowing the recovery of Cu. In this research, the results for the dissolution of Mn and Cu from a black copper mineral are exposed, evaluating the reducing effect of NaCl for MnO2 through pre-treatment of agglomerate and curing, and subsequently leaching in standard condition with the use of a reducing agent (Fe2+). High concentrations of chloride in the agglomerate process and prolonged curing times would favor the reduction of MnO2, increasing the dissolution of Mn, while the addition of NaCl did not benefit Cu extractions. Under standard conditions, low Mn extractions were obtained, while in an acid-reducing medium, a significant dissolution of MnO2 was achieved, which supports the removal of Cu.

Manganese nodules are an attractive source of base metals and critical and rare elements and are required to meet a high demand of today’s industry. In previous studies, it has been shown that high concentrations of reducing agent (Fe) in the system are beneficial for the rapid extraction of manganese. However, it is necessary to optimize the operational parameters in order to maximize Mn recovery. In this study, a statistical analysis was carried out using factorial experimental design for the main parameters, including time, MnO2/Fe2O3 ratio, and H2SO4 concentration. After this, Mn recovery tests were carried out over time at different ratios of MnO2/Fe2O3 and H2SO4 concentrations, where the potential and pH of the system were measured. Finally, it is concluded that high concentrations of FeSO4 in the system allow operating in potential and pH ranges (−0.2 to 1.2 V and −1.8 to 0.1) that favor the formation of Fe2+ and Fe3+, which enable high extractions of Mn (73%) in short periods of time (5 to 20 min) operating with an optimum MnO2/Fe2O3 ratio of 1:3 and a concentration of 0.1 mol/L of H2SO4.

Purpose – Natural convection with heat transfer in porous media has been subject of extensive study in engineering due to its numerous applications. A case of particular interest is the Bénard-type flow.The paper aims to discuss this issue. Design/methodology/approach – Based on the network simulation method in order to solve this problem, a numerical model is proposed. Findings – Nusselt-Rayleigh correlation is determined for a broad range of Rayleigh, the dimensionless number that influences the solution, above and below the threshold which separates the conduction and convection pure mechanisms. Originality/value – Based on the network simulation method.

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When the governing equations of a problem are known, the non‐dimensionalization of these equations (applied in their classical form) is a useful and widely used method that can be used to identify the dimensionless groups that rule the solution. However, neither this technique nor dimensional analysis necessarily provides the most precise solution in terms of the sought numbers. The use of discrimination, a qualitative rather than quantitative extension of the non‐dimensionalization method, has demonstrated notable advantages over the classical method because it invariably provides a more precise set of dimensionless groups. The basis for the correct application of discrimination depends on a deep understanding of the phenomena involved in the problem, particularly in complex (coupled) problems. In this paper, discriminated non‐dimensionalization is applied to investigate a mixed convection problem in porous media, the Yusa problem. The derived discriminate groups are compared with those already known in the literature and deduced by classical methods. A number of scenarios are numerically solved to check the reliability of the discriminated groups in contrast with classical groups. Copyright © 2016 John Wiley & Sons, Ltd.

Density-driven flow and heat transport processes in 2-D porous media scenarios are governed by coupled, non-linear, partial differential equations that normally have to be solved numerically. In the present work, a model based on the network method simulation is designed and applied to simulate these processes, providing steady state patterns that demonstrate its computational power and reliability. The design is relatively simple and needs very few rules. Two applications in which heat is transported by natural convection in confined and saturated media are studied: slender boxes heated from below (a kind of Bénard problem) and partially heated horizontal plates in rectangular domains (the Elder problem). The streamfunction and temperature patterns show that the results are coherent with those of other authors: steady state patterns and heat transfer depend both on the Rayleigh number and on the characteristic Darcy velocity derived from the values of the hydrological, thermal and geometrical parameters of the problems.

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