Ricardo I. Jeldres’s research while affiliated with University of Antofagasta and other places

Black coppers are mineraloids with a high content of Cu and Mn. These have an amorphous crystalline structure that makes them refractory to conventional leaching processes. For this reason, these mineral resources are not incorporated in industrial leaching heap processes and are taken to dumps. In the present study, an agglomerate pretreatment process incorporating NaCl is evaluated, and a curing stage, followed by acid-reducing leaching for Cu and Mn dissolution from a high-grade black copper mineral. For this, an experimental design was developed both to evaluate the impact of the dependent variables on the response, to generate analytical models that represent the copper and manganese recoveries under the set of sampled conditions. The models indicate that the curing time and the NaCl concentration have a primary effect on the recovery of both elements. In contrast, the optimization model suggests that the optimal operating levels are reached at relatively high levels of time (>130 h) and of NaCl concentration (>22 kg/t).

In this study, weak acid in the curing and leaching stages of copper ore was incorporated, and we analyzed its effect on the dissolution of copper and final impurities. The weak acid corresponds to a wastewater effluent from sulfuric acid plants produced in the gas treatment of copper smelting processes. This effluent is basically water with high acidity (pH-value low at 1), which contains several toxic elements and some valuable metals. The results indicated that there is no positive or negative effect on the incorporation of the weak acid in the curing stage, while the case of the leaching stage is favored. Toxicity characteristic leaching procedure (TCLP) and synthetic precipitation leaching procedure (SPLP) toxicity tests were performed on the solid leaching residues, determining that they accomplish the stability ranges of the impurities (Pb, Cd, Hg, Cr, Ba, Se, As, and Ag).

Based on the results obtained from a previous study investigating the dissolution of Mn from marine nodules with the use of sulfuric acid and foundry slag, a second series of experiments was carried out using tailings produced from slag flotation. The proposed approach takes advantage of the Fe present in magnetite contained in these tailings and is believed to be cost efficient. The surface optimization methodology was used to evaluate the independent variables of time, particle size and sulfuric acid concentration in the Mn solution. Other tests evaluated the effect of agitation speed and the MnO2/Fe2O3 ratio in an acid medium. The highest Mn extraction rate of 77% was obtained with MnO2/Fe2O3 ratio of 0.5, concentration of 1 mol/L of H2SO4, particle size of -47 + 38 μm, and 40 min of leaching. It is concluded that higher rates of Mn extraction were obtained when tailings instead of slag were used, while future research needs to focus on the determination of the optimum Fe2O3/MnO2 ratio to improve dissolution of Mn from marine nodules.

The authors wish to make the following corrections to this paper [1]: We worked at a temperature of 60 • C for all the tests carried out in which FeS 2 was added as a reducing agent, whereas in the other experiments, other added Fe reducing agents were worked at room temperature (25 • C). This affects the results presented in Table 5 (results when working with FeS2), Figures 4a and 6a. By accident and through carelessness, we did not indicate this important detail in the work methodology. For this reason, we must correct it for the readers, otherwise the reproduction of the results of our experiments will not be possible due to incorrect working parameters. However, we confirm that this error does not affect the conclusions of the manuscript. We must indicate that it is unlikely that the following series of reactions that were presented in the document could occur at room temperature: 3FeS 2 + 4H 2 SO 4 = 3FeSO 4 + 4H 2 O + 7S (1) 6FeSO 4 + 4H 2 SO 4 = 3Fe 2 (SO 4) 3 + 4H 2 O + S (2) 2FeS 2 + 4H 2 SO 4 = Fe 2 (SO 4) 3 + 4H 2 O + 5S (3) 15MnO 2 + 2FeS 2 + 14H 2 SO 4 = Fe 2 (SO 4) 3 + 15MnSO 4 + 14H 2 O (4) We will update the article and the original version will remain available on the article webpage.

Covellite is a secondary copper sulfide, and it is not abundant. There are few investigations on this mineral in spite of it being formed during the leaching of chalcocite or digenite; the other investigations on covellite are with the use of mineraloids, copper concentrates, and synthetic covellite. The present investigation applied the surface optimization methodology using a central composite face design to evaluate the effect of leaching time, chloride concentration, and sulfuric acid concentration on the level of copper extraction from covellite (84.3% of purity). Copper is dissolved from a sample of pure covellite without the application of temperature or pressure; the importance of its purity is that the behavior of the parameters is analyzed, isolating the impurities that affect leaching. The chloride came from NaCl, and it was effectuated in a size range from –150 to +106 μm. An ANOVA indicated that the leaching time and chloride concentration have the most significant influence, while the copper extraction was independent of sulfuric acid concentration. The experimental data were described by a highly representative quadratic model obtained by linear regression (R² = 0.99).

Studying the dissolution of chalcocite allows to understand the behavior of the most abundant secondary sulfide ore in copper deposits, while digenite (Cu1.8S) and other intermediate sulfides (Cu2−xS) are often associated with chalcocite. The most common mechanism of dissolution is by two stages, and chloride ions benefit the kinetics of dissolution. In this study, a pure chalcocite mineral (99.9% according to XRD (X-Ray Diffraction) analysis) is leached in chloride media using NaCl and wastewater as the sources of chloride. Magnetic leaching tests are performed at 65, 75, and 95 °C, using a particle size between −150 and + 106 μm. Chloride concentration and leaching time are the main variables. A substantial dissolution of chalcocite was obtained with 0.5 M H2SO4, 100 g/L of chloride and a leaching time of 3 h. The apparent activation energy (Ea) derived from the slopes of the Arrhenius plots was 36 kJ/mol. The XRD analysis proves the presence of elemental sulfur (S⁰) as the main component in the leaching residue. No significant differences in copper extraction were detected when using 100 g/L of chloride ion or wastewater (39 g/L).

The marine nodules are an attractive alternative source for the extraction of manganese due to the scarcity of high-grade metals on the surface. In the present investigation, working parameters (Fe 2 O 3 /MnO 2 ratio and sulfuric acid concentration) were optimized for the dissolution of Mn from marine nodules using foundry slags. Finally, it is concluded that the optimum MnO 2 /Fe 2 O 3 proportion is 1/2, while the optimum concentration of H 2 SO 4 is 0.3 mol/L for a leaching time of 20 minutes achieving solutions of 70% Mn. ARTICLE HISTORY