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Copper oxide minerals composed of carbonates consume high quantities of leaching reagent. The present research proposes an alternative procedure for malachite leaching (Cu2CO3(OH)2) through the use of only compound, ammonium hydroxide (NH4OH). Preliminary studies were also carried out for the dissolution of malachite in an acid system. The variables evaluated were solution pH, stirring rate, temperature, NH4OH concentration, particle size, solid/liquid ratio and different ammonium reagents. The experiments were carried out in a stirred batch system with controlled temperatures and stirring rates. For the acid dissolution system, sulfuric acid consumption reached excessive values (986 kg H2SO4/ton of malachite), invalidating the dissolution in these common systems. On the other hand, for the ammoniacal system, there was no acid consumption and the results show that copper recovery was very high, reaching values of 84.1% for a concentration of 0.2 mol/dm3 of NH4OH and an experiment time of 7200 s. The theoretical/thermodynamic calculations indicate that the solution pH was a significant factor in maintaining the copper soluble as Cu(NH3)42+. This was validated by the experimental results and solid analysis by X-ray diffraction (XRD), from which the reaction mechanisms were obtained. A heterogeneous kinetic model was obtained from the diffusion model in a porous layer for particles that begin the reaction as nonporous but which become porous during the reaction as the original solid splits and cracks to form a highly porous structure. The reaction order for the NH4OH concentration was 3.2 and was inversely proportional to the square of the initial radius of the particle. The activation energy was calculated at 36.1 kJ/mol in the temperature range of 278 to 313 K.
Alvaro Aracena; Javiera Pino; Oscar Jerez. Mechanism and Kinetics of Malachite Dissolution in an NH4OH System. Metals 2020, 10, 833 .
AMA StyleAlvaro Aracena, Javiera Pino, Oscar Jerez. Mechanism and Kinetics of Malachite Dissolution in an NH4OH System. Metals. 2020; 10 (6):833.
Chicago/Turabian StyleAlvaro Aracena; Javiera Pino; Oscar Jerez. 2020. "Mechanism and Kinetics of Malachite Dissolution in an NH4OH System." Metals 10, no. 6: 833.
In pyrometallurgical processes refining copper, the main source of loss in the conversion stage is from slag. This paper reports on research work treating converter slag containing high percentages of copper (36 wt%) using ammonium hydroxide at room temperature. Variables analyzed are solution pH, agitation, temperature, NH4OH concentration and particle size. Results showed that the hydronium ion resulting from ammonium hydroxide dissociation was the main oxidant of copper compounds in slag, such as CuO, Cu2O and Cu, with the exception of CuFeO2. The particles contain a large amount of microcracks (porosity) in their refractory structure (analyzed by compositional image capture (BSE)). Thus, the diffusion of the leaching solution through the microcracks making contact with the copper oxides would be allowed. Leaching mechanisms were corroborated by X-ray diffraction and scanning electron microscopy analysis. Increasing temperature and NH4OH concentration while decreasing particle size obtained higher copper recoveries, reaching values of 84.8%. Under the same conditions, the main impurity (iron) was minimal (
Alvaro Aracena; Andrés Valencia; Oscar Jerez. Ammoniacal System Mechanisms for Leaching Copper from Converter Slag. Metals 2020, 10, 712 .
AMA StyleAlvaro Aracena, Andrés Valencia, Oscar Jerez. Ammoniacal System Mechanisms for Leaching Copper from Converter Slag. Metals. 2020; 10 (6):712.
Chicago/Turabian StyleAlvaro Aracena; Andrés Valencia; Oscar Jerez. 2020. "Ammoniacal System Mechanisms for Leaching Copper from Converter Slag." Metals 10, no. 6: 712.
Enargite ore (Cu3AsS4) is generally processed via pyrometallurgy, with high temperatures that release toxic arsenic (AsxOy) and sulfur (SOx) gases. In seeking alternatives that avoid production of noxious gases, this paper discusses batch leaching experiments of mineral mixtures of enargite and pyrite (Cu3AsS4 and FeS2), agitated under ammoniacal media (NH4OH) using sodium persulfate (Na2S2O8) as an oxidant. The results showed that almost complete leaching of enargite (98%) could be obtained due to the elimination of passivation (S°) by the action of the oxidant. With the help of a deep thermodynamic study and with DRX analysis, it was possible to establish the reaction mechanisms of dissolution of enargite with persulfate in an ammoniacal media. Leaching action selected for enargite, not affecting pyrite present. Enargite leaching can be represented under a heterogeneous kinetic model of reactant diffusion through a porous layer formed at reaction time. Orders of reaction 2.0 and 1.5, for persulfate and ammonium hydroxide concentrations, respectively, were established. Activation energy was calculated at 45.0 kJ/mol. Consecutive evaluations showed that metals present (Cu and As) could be precipitated with sodium sulfide and sodium hydrosulfide at 99% yields, thus generating a solution rich in ammonia that can be re-used in leaching.
A. Aracena; E. Rodríguez; O. Jerez. Enargite leaching under ammoniacal media with sodium persulfate and consecutive precipitation of As/Cu with Na2S/NaHS. Hydrometallurgy 2020, 192, 105290 .
AMA StyleA. Aracena, E. Rodríguez, O. Jerez. Enargite leaching under ammoniacal media with sodium persulfate and consecutive precipitation of As/Cu with Na2S/NaHS. Hydrometallurgy. 2020; 192 ():105290.
Chicago/Turabian StyleA. Aracena; E. Rodríguez; O. Jerez. 2020. "Enargite leaching under ammoniacal media with sodium persulfate and consecutive precipitation of As/Cu with Na2S/NaHS." Hydrometallurgy 192, no. : 105290.
Converter slags are by-products of pyrometallurgical processing of copper concentrates in Chile, which contain significant amounts of copper (close to 40.0% in the material considered here), converting them from a passive material (material that is not feasible to process) to an active material (it can be processed). This study analyses column leaching of converter slag with the use of ammonium hydroxide. A preliminary analysis was carried out on acid leaching (in an agitated system). Later, in ammonia medium, several variables were assessed, including particle size and NH4OH concentration, as well as different grades of acid purity to adjust the pH of the leaching solution. The experiments were carried out in 1.2 m high columns with a cross-section diameter of 7.5 × 10−2 m, using 2.0 kg of slag. The results show that using an acid system (i.e. ordinary leaching), reagent consumption reached 473.9 kg H2SO4/ton of slag, with copper recovery of only 50.8% and Fe recovery of over 67.0%. On the other hand, using an ammonia system, the recovery values reached 87.7% for Cu, with almost no impurities, with reagent consumption of 3.8 kg H2SO4/ton of slag. The working pH was 10.5. These recovery levels are due to the leaching of Cu2O and Cu° from the converter slag. When using an acid contaminated with impurities to adjust the pH, the copper extraction rate was increased. The impurities of antimony, bismuth and arsenic are not significant. The copper in pregnant solution (PLS) obtained was put into contact with NaSH to generate hydrated chalcanthite (CuSO4·5H2O) with a high grade of purity, while the remaining solution can be returned to the leaching stage due to its high level of ammonia content.
A. Aracena; F. Fernández; O. Jerez; A. Jaques. Converter slag leaching in ammonia medium/column system with subsequent crystallisation with NaSH. Hydrometallurgy 2019, 188, 31 -37.
AMA StyleA. Aracena, F. Fernández, O. Jerez, A. Jaques. Converter slag leaching in ammonia medium/column system with subsequent crystallisation with NaSH. Hydrometallurgy. 2019; 188 ():31-37.
Chicago/Turabian StyleA. Aracena; F. Fernández; O. Jerez; A. Jaques. 2019. "Converter slag leaching in ammonia medium/column system with subsequent crystallisation with NaSH." Hydrometallurgy 188, no. : 31-37.
Cuprite is a difficult oxide to leach under acidic conditions (for the maximum extraction of 50%). In this research, the feasibility of leaching cuprite in an ammoniacal medium was studied. The working conditions addressed here were the liquid/solid ratio (120:1–400:1 mL/g), stirring speed (0–950 r/min), temperature (10–45 °C) and NH4OH concentration (0.05–0.15 mol/L). In addition, different ammoniacal reagents (NH4F and (NH4)2SO4) were analyzed. The experiments were performed in a 2 L reactor with a heating mantle and a condenser. The most important results were that the maximum leaching rate was obtained at pH 10.5, 0.10 mol/L NH4OH, 45 °C, 4 h, 850 r/min and a liquid/solid ratio of 400:1, reaching a copper extraction rate of 82%. This result was related to the non-precipitation of copper in solution by the formation of copper tetra-amine. The liquid/solid ratio and stirring speed were essential for increasing the cuprite leaching. The maximum leaching rate was achieved at higher temperatures; however, significant copper leaching rate occurred at temperatures near the freezing point of water (17.9% over 4 h). Increasing NH4OH concentration and decreasing particle size increased the cuprite leaching rate. The two ammoniacal reagents (NH4F and (NH4)2SO4) had low extraction rate of copper compared with NH4OH. The kinetic model representing cuprite leaching was a chemical reaction on the surface. The order of the reaction with respect to the NH4OH concentration was 1.8, and it was inversely proportional to the radius of the ore particles. The calculated activation energy was 44.36 kJ/mol in the temperature range of 10–45 °C.
A. Aracena; F. Pérez; D. Carvajal. Leaching of cuprite through NH4OH in basic systems. Transactions of Nonferrous Metals Society of China 2018, 28, 2545 -2552.
AMA StyleA. Aracena, F. Pérez, D. Carvajal. Leaching of cuprite through NH4OH in basic systems. Transactions of Nonferrous Metals Society of China. 2018; 28 (12):2545-2552.
Chicago/Turabian StyleA. Aracena; F. Pérez; D. Carvajal. 2018. "Leaching of cuprite through NH4OH in basic systems." Transactions of Nonferrous Metals Society of China 28, no. 12: 2545-2552.
The dissolution kinetics of synthetic molybdite (MoO3) in a potassium hydroxide (KOH) medium was studied by varying the system temperature, KOH concentration, and particle size. Additionally, the effects of the stirring rate and different reagents such as barium hydroxide (Ba(OH)2), calcium hydroxide (Ca(OH)2), and sodium hydroxide (NaOH) were also evaluated. The experiments were performed in a reactor with controlled temperature and agitation. The results indicated that the dissolution reaction mechanism of molybdite generates potassium molybdate (K2MoO4) without intermediate compounds. Temperature (6–80 °C), KOH concentration (0.0005–0.025 mol/L), and particle size (5–40 μm) positively affected the dissolution of molybdite. The maximum Mo recovery was 67.5% in 0.25 h for 80 °C and 0.01 mol/L KOH. At the lowest temperature (6 °C), which is near the freezing point of water (0 °C), a substantial amount of Mo was recovered (17.8% in 45 min). The kinetics equation describing the molybdite dissolution in a KOH environment indicated that diffusion occurs through the porous layer. The activation energy was calculated to be 47.81 kJ/mol. A reaction order of 1.0 with respect to KOH concentration was obtained and was found to be inversely proportional to the squared particle size. The kinetics equation was obtained. The dissolution of molybdite resulting from the oxidation of a molybdenite concentrate (MoS2) led to a low molybdenum recovery, which was primarily caused by the consumption of KOH by impurities such as CaCO3 and Cr(MO4)3.
A. Aracena; A. Sanino; O. Jerez. Dissolution kinetics of molybdite in KOH media at different temperatures. Transactions of Nonferrous Metals Society of China 2018, 28, 177 -185.
AMA StyleA. Aracena, A. Sanino, O. Jerez. Dissolution kinetics of molybdite in KOH media at different temperatures. Transactions of Nonferrous Metals Society of China. 2018; 28 (1):177-185.
Chicago/Turabian StyleA. Aracena; A. Sanino; O. Jerez. 2018. "Dissolution kinetics of molybdite in KOH media at different temperatures." Transactions of Nonferrous Metals Society of China 28, no. 1: 177-185.