Copper and iron extraction from chalcopyrite by NaCl@MgCl2@urea: Synthesis of CuFe2O4 electrodes for supercapacitors

Abstract

This study was conducted in two sections. Initially, the effects of NaCl, MgCl2, and urea were investigated on extracting copper and iron from chalcopyrite. Subsequently, CuFe2O4-based electrodes for supercapacitors were synthesized using the extracted solution. The first phase revealed that 3 mol/L NaCl achieved the highest extraction performance, yielding 60% Cu and 23% Fe. MgCl2 at 1.5 mol/L extracted 52% Cu and 27% Fe, while a combination of 0.5 mol/L MgCl2 and 1.6 mol/L urea yielded 57% Cu and 20% Fe. Urea effectively reduced iron levels. CuFe2O4-based electrodes were then successfully synthesized via a hydrothermal method using a MgCl2-urea solution. Characterization studies confirmed CuFe2O4 formation with a 2D structure and 45−50 nm wall thickness on nickel foam. Electrochemical analysis showed a specific capacitance of 725 mF/cm² at 2 mA/cm2 current density, with energy and power densities of 12.3 mW·h/cm² and 175 mW/cm², respectively. These findings suggest that chalcopyrite has the potential for direct use in energy storage.

1. Introduction

Energy storage plays a critical role in ensuring the continuous availability of renewable energy sources [1 −3]. The most common energy storage devices are lithium-ion batteries and supercapacitors. Lithium-ion batteries, despite their high energy density, have a disadvantage due to their limited lifespan and losses during charge-discharge cycles [4, 5]. On the other hand, supercapacitors offer an advantage with their longer lifespan and fast charge-discharge capability [6].

Supercapacitors store energy by either adsorbing ions in the electrolyte onto the electrode surface or undergoing redox reactions, making it desirable for electrode materials to have both a high surface area and redox-active components [7 −9]. Therefore, compounds of metals like copper and iron are highly preferred due to their oxidizing/reducing properties. These metals are commonly sourced from ores such as pyrite and chalcopyrite [10, 11]. These copper and iron metals are extracted from these ores by extracting the acidic, basic, and salt components. However, the sulfur (S0) layer on the surface of chalcopyrite creates passivation, hindering the extraction of metals [12, 13].

In this context, TURAN and their colleagues attempted to overcome this by adding NaCl to the ammonium persulfate solution. They observed that the chloride ions in this solution disrupted sulfur passivation, resulting in copper and iron extraction efficiencies of 75% and 80% after 180 min duration, respectively [14]. VELÁSQUEZ-YÉVENES et al [15] treated chalcopyrite ore with high concentrations of acid and chloride ions, observing a 60% increase in copper extraction after a 20-day waiting period, with this increase continuing gradually with the waiting time. PETROVIC and their colleagues used hydrochloric acid and hydrogen peroxide to remove passivation. After an 80-min reaction period, they found that the maximum copper extraction rate was 33% with 0.5 mol/L HCl and 3.0 mol/L H2O2 at room temperature [16]. SolÍS-MARCIAL et al [17] argued that adding organic solvents to the solution is an effective method for removing the passivation layer. To achieve this, they employed various oxidants (H2O2, CuSO4, and O3) in an acidic solution and carried out chalcopyrite leaching at 40 ℃ in the presence of alcohols such as 2-propanol and hydrogen peroxide, determining an activation energy of 42 kJ/mol for copper dissolution. They also noted that above 40 ℃, peroxide degradation occurred, leading to a reduction in copper extraction. Additionally, they highlighted that methanol stabilized copper ions and prevented the formation of Cu2S2-6Cu2S. In all of these studies, the disruption of the passivation layer with secondary ions like oxidants has been successful in drawing copper and iron ions into the solution with primary components. Primary components such as salts like NaCl or MgCl2 are easily accessible, non-toxic, and cost-effective [18]. However, comparative analyses of different types of these salts are quite rare in the literature. On the other hand, sulfur is known to be removable with salts. Therefore, sulfur moving away from the surface can be captured by reacting with urea (CH4N2O) in the environment, converting it into thiourea (CH4N2S). This process may facilitate the transition of copper and iron into the solution.