Pourbaix Research Articles

Insights into the Electrochemical Oxidation and Reduction of Nickel Oxide Surfaces.

Surface oxidation/reduction processes, driven by varying electrochemical potentials, can substantially impact catalyst effectiveness and, consequently, electrolyzer performance. This study combines theoretical and experimental approaches to explore the surface redox behavior of nickel oxides, which are cost-effective and efficient catalysts for many electrochemical reactions. Surface Pourbaix diagrams for three different phases of nickel oxides, i.e., nickel hydroxide (Ni(OH)2), nickel oxyhydroxide (NiOOH), and nickel dioxide (NiO2), were constructed using density functional theory-based simulations. Various experimental methods, including cyclic voltammetry, in situ Raman spectroscopy, and electrochemical titration, were employed to probe the surface redox processes of nickel oxide thin films. Our findings indicate that the ABAB stacking sequence of Ni(OH)2 lacks stability under oxidizing conditions to host the surface oxidation (deprotonation) events, while the AABBCC stacking sequence of NiOOH is energetically favorable due to the presence of interlayer hydrogen bonding. Rapid charge transfer facilitated by interlayer hydrogen bonding accounts for the higher reactivity of partially oxidized/reduced NiOOH (001) surfaces compared to Ni(OH)2 (001) and NiO2 (001) surfaces with the same stoichiometry, where interlayer hydrogen bonding is absent. Insights presented in this work can offer guidelines for optimizing operational conditions and tailoring the surface structures and oxidation states of nickel oxides to enhance performance in applications such as electrocatalysis and supercapacitors.

The Catalytic Mechanism of a Highly Active Cobalt Chlorin Complex for Photocatalytic Water Oxidation.

Highly active catalysts for electrocatalytic and photocatalytic water oxidation are strongly demanded to realize artificial photosynthesis. A cobalt complex with a chlorin derivative ligand (CoII(Ch)) exhibited high activity for electrocatalytic water oxidation with an overpotential of 0.45 V at pH 9.0. Spectroelectrochemistry (UV-vis) unveiled the formation of two intermediates by successive one-electron oxidations. Also, the Pourbaix diagram depicted by the pH dependence of redox potentials indicated that the water oxidation proceeded after the oxidation of both the central cobalt ion and chlorin ligand with proton-coupled electron transfer (PCET). Then, the photocatalytic activity of CoII(Ch) was examined for water oxidation using [RuII(bpy)3]2+ (bpy: 2,2'-bipyridine) and S2O82- as a photosensitizer and a sacrificial electron acceptor, respectively. The turnover number, turnover frequency, and oxygen yield reached as high as 980, 5.2 s-1, and 98%, respectively, under optimized conditions. The O2-evolution rates increased in proportion to the square of the catalyst concentration in the reaction solution, suggesting that the formation of the O-O bond regarded as the rate-determining step of water oxidation proceeded by the interaction of two metal centers (I2M) mechanism in which two molecules of high-valent metal oxo or oxyl radical species react with each other.

PH Dependence of Noble Metals Dissolution: Iridium

Iridium's stability and catalytic properties make it indispensable in a wide range of electrochemical applications including water electrolysis, yet its dissolution behavior across varying pH conditions remains poorly understood. This study addresses this gap by employing online inductively coupled plasma mass spectrometry (ICP-MS) to monitor iridium dissolution across a pH range of 1 to 12.7 under both pre-OER and OER conditions. An electrochemical protocol consisting of potential scans and holds is designed to track how potential and time affect Ir dissolution. In the pre-OER region, iridium shows consistent qualitative dissolution behavior across pH levels, although the extent of anodic and cathodic dissolution depends on the electrolyte. To explain this dependence, the thermodynamics of Ir in aqueous media, as revealed by the Pourbaix diagram, electrochemical profiles representing oxidation / reduction processes, and adsorption of electrolyte species are considered. During potential scans, kinetic effects from native oxides and phosphate adsorption lead to the absence of anodic dissolution, while prolonged holds at higher pH result in increased anodic dissolution, likely due to IrO42− formation. Iridium's cathodic dissolution is observed in all studied protocols. It decreases from acidic to neutral pH, in line with the stability window of Ir3+ ionic species in the Pourbaix diagram, and surprisingly increases in highly alkaline conditions again, suggesting the existence of species not reflected on the diagram. In the OER region, iridium remains stable in acidic to neutral conditions, with stability decreasing under alkaline conditions. Two distinct dissolution mechanisms are proposed based on pH: in acidic environments, H2O primarily acts as the reactant, leading to Ir³⁺ formation, while above pH 9, OH− becomes the main reactant, contributing to IrO42− formation and reduced stability. Under neutral conditions, buffers play a key role in maintaining local pH and supporting consistent OER rates, especially when the buffer's pKa aligns with the solution's pH. These findings improve our understanding of iridium dissolution mechanisms and support the development of more stable and cost-effective iridium-based catalysts for various electrochemical technologies.

Halogen Thermochemistry Assessed with Density Functional Theory: Systematic Errors, Swift Corrections and Effects on Electrochemistry.

Despite its sizable errors, density functional theory (DFT) is extensively used to evaluate thermochemical properties of gases, liquids and their interfaces with solids. As numerous halogen-containing compounds appear as reactants, products and/or electrolytes in electrochemical reactions, and ionic effects are currently an active area of research, it is important to evaluate the accuracy of DFT for halogen thermochemistry. Herein, we assess the formation energies of interhalogens, hydrogen halides, diatomic and atomic halogens and their ions using six widespread functionals at the GGA, meta-GGA and hybrid levels. We observe that DFT errors with respect to experiments are correlated with the electronegativity of the species and there are systematic trends across functionals, such that swift corrections were devised. Specifically, the average of the mean absolute errors for the six functionals decreased from 0.19 eV before the corrections to 0.08 eV after them. Besides, the overall maximum absolute error (MAX) decreased from 0.76 to 0.44 eV and the average of the MAXs decreased from 0.51 to 0.24 eV. Finally, we illustrate the qualitative and quantitative impact of gas-phase errors on the predictions of surface Pourbaix diagrams.

Using machine learning towards enhancement of electrochemical activity in OER/ORR half-reactions of MXene cathode materials for Li-air batteries

Metal-air batteries are the target of the ever-growing interest as considering as the new “lead” technology among the most promising electrochemical energy storage solutions. The projected energy density of lithium-air batteries considered in this study exceeds current commercial lithium-ion batteries by more than three times. In this study, we consider the characteristics of MXenes, 2D layered phases with such attractive characteristics as a high specific surface area with the numerous active reaction centers, mechanical strength, the diverse functional characteristics and the perspectives of scalability of their production, which are of importance for the practical realization of Li-air batteries of different architecture. The formation of the phases of complex content and structure inherent to pseudomorphism at the interface, as it is actual for the objects of our study, allows one to conclude that it is necessary to consider the processes that occur at the interfaces of lithium-air battery cathodes in direct relation to the cathode material used. Machine learning methods were involved in model development for (i) MXenes predicting the electrochemical phase diagrams, Pourbaix diagrams, which circumscribe the stability window of MXenes of certain composition formed with synthesis-defined terminations as a function of pH and USHE for single and double MXenes and (ii) the elastic characteristics of MAX phases, precursors of MXenes, to assess the commensurability of the interface of MXene cathode materials and Li2O2 phase as well as the prospects of using target MXene compositions combined with the solid electrolyte materials of different families for employing in all-solid-state Li-air batteries. The obtained models demonstrate high predictive performance that argue on the possibility to use them for rational screening of new phases with desired functional characteristics.

Enhance the Proportion of Fe3+ in NiFe-Layered Double Hydroxides by utilizing Citric Acid to Improve the Efficiency and Durability of the Oxygen Evolution Reaction.

NiFe-layered double hydroxides (NiFe-LDH) are a type of catalyst known for their exceptional catalytic performance during the oxygen evolution reaction (OER). In this study, citric acid was incorporated into the synthesis process of NiFe-LDH, resulting in the NiFe-LDH-CA catalyst with superior OER performance. The catalytic efficacy was evaluated using linear sweep voltammetry (LSV), which demonstrated a significant reduction in the overpotential for OER from 320 mV to 240 mV at a current density of 100 mA cm-2. X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) indicate that the distribution of nickel valence states showed no significant difference between two samples. However, the NiFe-LDH-CA exhibits a markedly higher proportion of Fe3+ ions in its iron content. In-situ Raman spectroscopes reveal that Fe3+ broadens the redox potential of nickel and Pourbaix diagrams indicate that higher Fe3+ levels could facilitate the interaction with oxygen active sites. Based on the analysis of test data, we propose a hypothesis that the high proportion of Fe3+ in catalysts may accelerate the oxygen evolution process by modulating the redox potential of nickel and engaging with reactive oxygen species. This provides valuable insights into how to improve the reaction rate of nickel-based catalysts.

Uncovering the electrochemical stability and corrosion reaction pathway of Mg (0001) surface: Insight from first-principles calculation

An understanding of the anomalously enhanced hydrogen evolution reaction (HER) of magnesium (Mg) under anodic polarisation in aqueous corrosion is paramount for a predictive theory of its corrosion and metal electrocatalysis. Previous theoretical and experimental studies have proposed that sub-surface hydride phases play a role in this behaviour but the underlying atomic mechanisms remain unclear. By constructing theoretical surface Pourbaix diagrams, based on density functional theory (DFT) calculations, we have identified the atomic structure of a sub-surface hydride phase on the Mg (0001) surface that remains electrochemically stable under significant anodic overpotentials across a wide pH range. Specifically, this stability persists up to 0.38 VSHE under mildly alkaline conditions (e.g., pH = 8), thus providing thermodynamic support for the proposed hydride-enhanced HER under anodic conditions. Reaction barrier analysis establishes that the proposed sub-surface hydride phase could promote anodic HER via a Heyrovsky pathway, based on hydrogen outward diffusion, with an energy barrier of 1.54 eV as the rate-limiting step, showing an anodic characteristic and significantly favouring external anodic polarisation. Furthermore, we have established that the surface adsorption condition, contingent on both the pH and potential, significantly influences the mechanism and kinetics of the initial corrosion of Mg.

Optimization of Copper-Ammonia-Sulfate Electrolyte for Maximizing Cu(I):Cu(II) Ratio Using pH and Copper Solubility

An investigation has been carried out to understand the solution chemistry of the Cu-NH−-SO4−2 system, focusing on the effect of pH on the solubility of copper in the solution and maximizing the Cu(I):Cu(II) ratio. A Pourbaix diagram for the Cu-N-S system has also been created using the HSC Chemistry software for a wide range of Cu-NH3 species, unlike most other studies that focused only on Cu(NH3)42+ and Cu(NH3)52+ (Cu(II)) as the dominant species. The Pourbaix diagram demonstrated that the Cu(I) exists as Cu(NH3)2+, while the Cu(II) species are present in the system as Cu(NH3)42+ and Cu(NH3)52+, depending upon the Eh and pH of the solution. Copper precipitation was observed in the electrolyte at pH values less than 8.0, and the precipitation behavior increased as the pH became acidic. The highest Cu(I):Cu(II) ratio was observed at higher pH values of 10.05 due to the higher solubility of copper at higher alkaline pH. The maximum Cu(II) concentration can be achieved at 4.0 M NH4OH and 0.76 M (NH4)2SO4. In the case of low pH, the highest Cu(I):Cu(II) ratio obtained was 0.91 against the 4.0 M and 0.25 M concentrations of NH4OH and (NH4)2SO4, respectively. Meanwhile, at high pH, the maximum Cu(I):Cu(II) ratio was 15.11 against the 0.25 M (NH4)2SO4 and 4.0 M NH4OH. Furthermore, the low pH experiments showed the equilibrium constant (K) K < 1, and the high pH experiments demonstrated K > 1, which justified the lower and higher copper concentrations in the solution, respectively.

Iron bed accelerator for discharging cylindrical NCA battery in salt solution

This study examines the iron bed accelerator for discharging cylindrical NCA batteries in salt solution. The use of Li-ion batteries has increased due to the rise of e-mobility in computers, cell phones, and electric vehicles. Recycling Li-ion batteries for raw material in lithium-ion battery production is increasingly important as the revolution unfolds. When disposing of, transporting, and recycling the battery, it is important to crush it to separate the black mass, plastic, and metal components. However, there is a potential explosion risk due to the remaining voltage in the battery. In recycling, the discharge step is significant. The research aimed to test a new method for discharging cylinder batteries using saltwater and an iron bed. Higher NaCl content increases pH and lowers electrochemical potential for water electrolysis. This unique combination enables the battery to discharge at a high rate. In 6 hours, the battery discharged in a 20 wt.% salt solution with 99.6% efficiency. The battery discharge efficiency decreased when exposed to 25 wt% and 30 wt% salt solutions, attributed to reduced water electrolysis intensity. According to the results of various experiments, it has been observed that as the temperature of the salt solution rises, there is a slight increase in the rate of battery discharge; however, no significant difference has been observed. This article talks about how batteries are discharged. It shows the electrochemical reaction using the Eh-pH diagram for Fe-Na-Cl. It also has a schematic diagram that shows the process and a chemical analysis of the precipitate that forms during the discharge test.

Analysis of Corrosion Potential of Zn, Ni, and Zn-Ni Alloy Using Ab Initio Calculations Supported by Experimental Thermodynamics Data

The purpose of this study is to investigate the corrosion properties of Zn, Ni, and Zn - Ni alloy using density functional theory (DFT). DFT can assist in predicting the thermodynamic properties of challenging compounds such as metals, alloys, and transition metal oxides. In the present work, DFT is used to predict Zn, Ni, and Zn - Ni alloy phase diagram. The Hubbard correction (U) and dispersion correction (D) are used to minimize the inherent error associated with the DFT. We studied the crystal structure, electronic structures, and thermodynamic energies of Zn and Ni compounds using the generalized gradient approximation (GGA) density functional employing Perdew–Burke–Ernzerhof (PBE). We have developed the corresponding Pourbaix diagram of Zn, Ni, and their alloy to compare the performance of density functional theory with the experimental observations. The corrosion behavior of various alloys including Zn11Ni2,ZnNi,ZnNi3 are compared and discussed. This can be useful for predicting the corrosion-resistant properties of these alloys.

Investigation of Metal-H2O Systems at Elevated Temperatures: Part II. SnO2(s) Solubility Data and New Sn Pourbaix Diagrams at 298.15 K and 358.15 K

Abstract The Zircaloy alloy system (1.2–1.7 wt.% Sn) provides an excellent basis to study the effect of temperature on Pourbaix diagrams, as Zircaloy fuel rods in a CANadian Deuterium UraniumTM (CANDU) reactor are exposed to an aqueous phase coolant in the range 250 °C (523.15 K) to 310 °C (583.15 K). In addition to its presence in Zircaloy, much of the thermochemical data for tin, particularly for the aqueous species, is unavailable or uncorroborated. This paper presents tin Pourbaix diagrams at 85 °C (358.15 K) alongside the reconstructed 25 °C (298.15 K) diagram. Solid-aqueous phase SnO2 equilibria were used to determine thermochemical data for tin +IV species in a batch vessel with in situ pH measurement. Solubilities were used to calculate the Gibbs energies of Sn complexes. The SnOH3+ and Sn(OH)5− species were incorporated into the 25 °C and 85 °C diagrams.

Investigation of Metal–H2O Systems at Elevated Temperatures: Part I. Development of a Solubility Apparatus Specialized for Super-Ambient Conditions

Abstract Metals used in aqueous environments where high temperatures and pressures are present are susceptible to corrosion. This is the case for nuclear power plants, especially CANDUTM reactors, where the liquid water systems can reach over 300 °C at pressures well above 101.325 kPa (1 atm). In such situations, failure to control corrosion has economic and safety consequences. To extend corrosion modeling tools, such as Pourbaix diagrams, to harsh aqueous conditions, there is a need for experimental thermochemical data performed at elevated temperatures. This is particularly true for metal and alloy systems where such information is unavailable or unreliable. A relatively simple approach to obtaining temperature dependent thermodynamic properties is the investigation of solid–liquid phase, or solubility, equilibria. However, this requires specially designed instrumentation that can withstand harsh temperatures and extreme pH conditions, while providing accurate data. In this work, an apparatus developed for super-ambient highly acidic and alkaline solubility experiments is presented. Solubility measurements were made in the zinc oxide system, which has been extensively studied. Using these equilibrium data and comparing to the literature, allowed the instrumentation and analysis process to be validated. In situ pH measurements using a constant volume, batch reactor system are described along with a brief presentation of the ZnO dissolution equilibria results at 85 °C (358.15 K).

A new iron recovery and dephosphorization approach from unroasted high‐phosphorus oolitic hematite ore via a facile chemical beneficiation process

AbstractDespite the abundance of scientific reports on the treatment of oolitic hematite, it still constitutes a global challenge. The distinctive oolitic structure within the ore is regarded as the primary factor causing the difficulty in the beneficiation of oolitic hematite ore. The objective of this study is to devise an effective approach to tackle the issue of beneficiation of oolitic hematite ore, thereby facilitating the utilization of oolitic hematite ore, which is widely abundant worldwide. Based on the Pourbaix diagram (Eh‐pH) of the Al‐Si‐H2O system, an alkaline leaching process for eliminating impurities from unroasted oolitic hematite using NaOH solution as the leaching agent was proposed. The optimal parameters were determined as a temperature of 250°C, a NaOH concentration of 16 mol/L, a liquid‐to‐solid ratio of 4 mL/g, and a reaction time of approximately 2 h. Around 54% of phosphorus (P), 21% of Al2O3, and 61% of SiO2 can be preliminarily removed from unroasted oolitic hematite ore. Through further dephosphorization with dilute sulfuric acid at room temperature, a high‐quality Fe concentrate with 63.3% Fe, 0.04% P, and a Fe recovery rate of 96% was obtained. The alkali can be readily regenerated by adding lime to the leaching solution, and the regenerated alkali has a leaching effect comparable to that of the fresh leaching solution. The recycling and utilization of alkaline leaching agents minimize production costs to the greatest extent possible. Mechanical studies have discovered that intact oolites undergo complete dissociation under alkaline leaching, enabling the leaching solution to permeate into the particles and thereby deeply eliminate impurities. The novel method has accomplished efficient processing of oolitic hematite and a reasonable control of production costs during processing, which is significant for expanding the reserves of iron ore resources.

Electrochemical stability of biodegradable Zn-Cu alloys through machine-learning accelerated high-throughput discovery.

Zn-Cu alloys have attracted great attention as biodegradable alloys owing to their excellent mechanical properties and biocompatibility, with corrosion characteristics being crucial for their suitability for biomedical applications. However, the unresolved identification of intermetallic compounds in Zn-Cu alloys affecting corrosion and the complexity of the application environment hamper the understanding of their electrochemical behavior. Utilizing high-throughput first-principles calculations and machine-learning accelerated evolutionary algorithms for screening the most stable compounds in Zn-Cu systems, a dataset encompassing the formation energy of 2033 compounds is generated. It reveals that most of the experimentally reported Zn-Cu compounds can be replicated, especially the structure of R32 CuZn5 is first discovered which possesses the lowest formation energy of -0.050 eV per atom. Furthermore, the simulated X-ray diffraction pattern matches perfectly with the experimental ones. By formulating 342 potential electrochemical reactions based on the binary compounds, the Pourbaix diagrams for Zn-Cu alloys are constructed to clarify the fundamental competition between different phases and ions. The calculated equilibrium potential of CuZn5 is higher than that of Zn through the forward reaction Zn + CuZn5 ⇌ CuZn5 + Zn2+ + 2e-, resulting in microcell formation owing to the stronger charge density localization in Zn compared to CuZn5. The presence of chlorine accelerates the corrosion of Zn through the reaction Zn + CuZn5 + 6Cl- + 6H2O ⇌ Cu + 6ZnOHCl + 6H+ + 12e-, where the formation of ZnOHCl disrupts the ZnO passive film and expands the corrosion pH range from 9.2 to 8.8. Our findings reveal an accurate quantitative corrosion mechanism for Zn-Cu alloys, providing an effective pathway to investigate the corrosion resistance of biodegradable alloys.

Electrowinning for Room-Temperature Ironmaking: Mapping the Electrochemical Aqueous Iron Interface.

A promising route toward room-temperature ironmaking is electrowinning, where iron ore dissolution is coupled with cation electrodeposition to grow pure iron. However, poor faradaic efficiencies against the hydrogen evolution reaction (HER) is a major bottleneck. To develop a mechanistic picture of this technology, we conduct a first-principles thermodynamic analysis of the Fe110 aqueous electrochemical interface. Constructing a surface Pourbaix diagram, we predict that the iron surface will always drive toward adsorbate coverage. We calculate theoretical overpotentials for terrace and step sites and predict that growth at the step sites are likely to dominate. Investigating the hydrogen surface phases, we model several hydrogen absorption mechanisms, all of which are predicted to be endothermic. Additionally, for HER we identify step sites as being more reactive than on the terrace and with competitive limiting potentials to iron plating. The results presented here further motivate electrolyte design toward HER suppression.

Investigation of metal-H2O systems at elevated temperatures: Part III. solubility data and new Zr Pourbaix diagrams at 298.15 K and 373.15 K.

Abstract The fuel bundles in coolant systems of CANDUTM reactors operate between 533 to 583 K (260 to 310°C). Given these extreme conditions and because of its neutronic properties, zirconium and Zircaloy-4 are used in these applications which require corrosion resistance at elevated temperatures. However, thermodynamic and hydrolysis properties of aqueous zirconium species have not been measured above standard conditions, making prediction using standard thermodynamic tools, such as the Pourbaix (E-pH) diagram difficult. This lack of information is addressed through solubility measurements and the development of elevated temperature Pourbaix diagrams for zirconium and Zircaloy-4. These Pourbaix diagrams of zirconium and a multi-element diagram (Sn, Zr, Cr) of Zircaloy-4 were developed at 373.15 K (100°C) and are presented in this work. Solubility measurements were made using a batch-style pressure vessel and concentration measurements were made using ICP-OES and ICP-MS, for zirconium and Zircaloy-4, respectively. For Zr(OH)6(2-); Zr(OH)4 (aq); Zr(OH)3+; and Zr(OH)2(2+) the Gibbs energy of formation (ΔG(°f,373.15 K)°) were found to be: -2177.4±8.5 kJ/mol, -1704.9±1.5 kJ/mol, -1808.8±8.9 kJ/mol, and -1095.1±2.7 kJ/mol, respectively.

Operando Insights on the Degradation Mechanisms of Rhenium‐Doped and Undoped Molybdenum Disulfide Nanocatalysts During Hydrogen Evolution Reaction and Open‐Circuit Conditions

AbstractMolybdenum disulfide (MoS2) nanostructures are promising catalysts for proton‐exchange‐membrane (PEM) electrolyzers to replace expensive noble metals. Their large‐scale application demands high activity for the hydrogen evolution reaction (HER) as well as robust durability. Doping is commonly applied to enhance the HER activity of MoS2‐based nanocatalysts, but the effect of dopants on the electrochemical and structural stability is yet to be discussed. Herein, operando electrochemical measurements to the structural evolution of the materials down to the nanometric scale are correlated by identical location electron microscopy and spectroscopy. The range of stable operation for MoS2 nanocatalysts with and without rhenium doping is experimentally defined. The responsible degradation mechanisms at first electrolyte contact, open circuit stabilization, and HER conditions are experimentally identified and confirmed with the calculated Pourbaix diagram of Re‐doped MoS2. Doping MoS2‐based nanocatalysts is validated as a promising strategy for continuing the improvement of high‐performance and durable PEM electrolyzers.

An acid-tolerant metal-organic framework for industrial CO2 electrolysis using a proton exchange membrane

Industrial CO2 electrolysis via electrochemical CO2 reduction has achieved progress in alkaline solutions, while the same reaction in acidic solution remains challenging because of severe hydrogen evolution side reactions, acid corrosion, and low target product selectivity. Herein, an industrial acidic CO2 electrolysis to pure HCOOH system is realized in a proton-exchange-membrane electrolyzer using an acid-tolerant Bi-based metal-organic framework guided by a Pourbaix diagram. Significantly, the Faradaic efficiency of HCOOH synthesis reaches 95.10% at a large current density of 400 mA/cm2 with a high CO2 single-pass conversion efficiency of 64.91%. Moreover, the proton-exchange-membrane device also achieves an industrial-level current density of 250 mA/cm2 under a relatively low voltage of 3.5 V for up to 100 h with a Faradaic efficiency of 93.5% for HCOOH production, which corresponds to an energy consumption of 200.65 kWh/kmol, production rate of 12.1 mmol/m2/s, and an energy conversion efficiency of 38.2%. These results will greatly aid the contemporary research moving toward commercial implementation and success of CO2 electrolysis technology.

Selective removal of iron from sulfuric acid leaching solution of aerospace magnetic material scraps by jarosite process

Aerospace magnetic material scraps are abundant in cobalt and nickel. Sulfuric acid leaching process is an efficient method for extracting them. But it is a non-selective process, a significant amount of iron dissolves in the solution. This study focuses on the selective removal of iron from this solution using the jarosite process. Eh-pH diagram of K-S-Fe-H2O system was established. Based on thermodynamic analysis, H2O2 is used to oxidize Fe2+ into Fe3+, achieving efficient and selective removal of iron from the solution containing cobalt and nickel. The optimal conditions are as follows: temperature 95°C, K2SO4 dosage coefficient 1.5, seed dosage 10 g/L, time 90 min, pH 1.76, and endpoint pH controlled at approximately 3. Under these conditions, the iron removal efficiency is above 99%, while the loss ratios of cobalt and nickel are below 2%. The product is characterized by XRD and SEM-EDS. Results indicate that the product is jarosite ((K,H3O)Fe3(SO4)2(OH)6), exhibiting an ellipsoid structure with the mean particle size in the range of 0.2–5.0 μm. Temperature, pH value and seed dosage significantly affect reaction rate, particle size and crystallinity, and K2SO4 dosage mainly affects reaction rate and the morphology of jarosite. The jarosite crystallization kinetics can be described by the Avrami equation, with an Avrami index (n) of approximately 2.5 and the apparent activation energy of 42.68 kJ/mol.

Leaching behavior of Cu, Zn, Fe and Pb from polymetallic tailings

ABSTRACT Copper tailings are a common byproduct of copper production, containing high levels of heavy metals which are released into the environment. Conventional methods have historically prioritized copper recovery, and often overlooking the leaching of other valuable elements. However, the rising demand for nonferrous metals necessitates understanding their leaching behavior from copper tailings. This study examined the atmospheric leaching of Cu, Fe, Pb, Zn, and CuO from a polymetallic tailing ore. Leaching recoveries of 63.5% for Cu, 97.5% for CuO, 1% for Fe, and 100% for Zn were achieved under the optimum conditions of 0.5 M sulfuric acid concentration, 25% solids percentage, 65°C, stirring speed of 100rpm, particle size of 75 µm within 30 minutes. Results indicated that the dissolution of oxide minerals such as CuO and ZnO was significant; however, copper sulfides need oxidant to be dissolved. In this condition, iron oxides and silicates were partially reacted by sulfuric acid, and Pb-bearing minerals formed lead sulfate. The presence of iron and lead-bearing minerals in the leaching residue was confirmed by XRF, XRD, and SEM analyses, and was in agreement with the information displayed in the Eh-pH diagrams.