Galvanic Interaction Research Articles

Effects of pyrite on the flotation behavior and electrochemical interaction of different particle sizes of galena in the presence of diethyldithiocarbamate

ABSTRACT Lead is widely used metals and pyrite is usually associated with galena. In addition, galena is prone to super-crushing during the grinding process. In this study, the galvanic interaction between different particle sizes of galena and pyrite were studied by electrochemistry, adsorption test and flotation test, respectively. Adsorption tests and microflotation tests indicated the recovery of galena of different sizes in mixed ore was decreased 5%–15% compared with single galena flotation results. The results of electrochemical measurement pointed out that the presence of pyrite enhances the corrosion rate of galena, and the finer the galena particles were, the stronger the electrochemical corrosion effect with pyrite became.

Insight into the effect of galvanic interactions between sulfide minerals on the floatability and surface characteristics of pyrite

Insight into the effect of galvanic interactions between sulfide minerals on the floatability and surface characteristics of pyrite

Studies on the surface oxidation and its role in the flotation of mixed Cu-Ni sulfide ore

Surface oxidation has a significant influence on sulfides flotation. However, there is a little literature about the effect of surface oxidation in the flotation of mixed copper‑nickel sulfide (CuNi sulfide, mainly composed of pentlandite, chalcopyrite, pyrite and pyrrhotite). In this work, the effect of surface oxidation on the CuNi sulfide flotation was studied. Flotation results showed the surface oxidation had a stronger depression effect on CuNi sulfide flotation than that on the flotation of single pyrite and chalcopyrite mineral samples. XPS analysis results showed that the hydrophilic products sulfate and Fe/Ni oxide/hydroxide were generated on the oxidized CuNi sulfide surface, whereas no Cu oxide/hydroxide was found, indicating the occurrence of galvanic interaction, which might cause the stronger depression of oxidation on CuNi sulfide flotation. However, after the pretreatment of ultrasonic cleaning in HCl solution, the sulfate and iron hydroxide/oxide on CuNi sulfide surface decreased significantly, and then CuNi sulfide floatability was regained to some extent. Interestingly, adsorption results exhibited that the adsorption amounts of PBX on CuNi sulfide surface basically unchanged before and after oxidation, which might be caused by that chalcopyrite and pyrite were protected from oxidation as the cathode minerals in the galvanic interaction.

Recovery of valuable metals from spent mobile phone printed circuit boards using biochar in indirect bioleaching

Improving the bioleaching efficiency of metals from spent mobile phone printed circuit boards (PCBs) in a short time has been of major interest in recent years. In this paper, a novel cheap catalyst (oak wood biochar) was used to improve the copper and nickel bioleaching efficiency from spent mobile phone PCBs. The biochar was derived from oak wood through slow pyrolysis at a low temperature of 500 °C for 1h. The results of RSM optimization indicated that the optimum conditions to maximize copper and nickel recovery were 1.6 g/L biochar and 16 g/L pulp density. The findings indicated that compared to without the presence of biochar, the leach yields of copper and nickel were high. As much as 98% of copper and 82% of nickel were leached by indirect bioleaching under optimum conditions. The better performance in the presence of biochar is due to both galvanic interactions between biochar and solid waste. The biochemical characterization of bioleaching solution suggested that the high concentration of biochar (> 1.6 g/L) led to copper absorption by functional groups on the surface of biochar. Compared to chemical leaching, the bioleaching has better performance. Under optimum conditions, the copper and nickel recovery by indirect bioleaching was 36% and 64% more than that by chemical leaching. Also, it is found that biochar has a positive effect on the chemical leaching process. Therefore, in this paper, the function of biochar was elaborated not only in bio-hydrometallurgy but also in the hydrometallurgy process.

Microstructure and Electrochemistry of Al-Rich Primer

Al-rich primer (AlRP) is designed to be anodic relative to high strength Al alloys, so that it drives the mixed potential of Al alloy substrates (e.g. AA2024) into the cathodic region below the breakdown potentials of the Al alloys, preventing localized corrosion. The Al-rich primer (AlRP) under study is composed of spherical Al-Zn-In pigments in an epoxy binder. The 2D and 3D microstructure of the AlRP was studied using a combination of X-ray microscopy, plasma focus ion beam/scanning electron microscopy, and transmission electron microscopy techniques. The primer contained Al-Zn-In particles with various sizes ranging from tens of nanometers to microns, epoxy binder and a significant volume of voids. Potentiodynamic polarization testing was performed to measure the electrochemistry of the Al-Zn-In bulk alloy under neat primer in NaCl solution to simulate the environment which Al-Zn-In pigments are exposed to in the real primer. The bulk alloy under neat primer exhibited higher breakdown potential than the bare bulk alloy exposed to NaCl solution. The polarization curves of the bulk alloy under neat primer provide more accurate boundary conditions for modeling of the galvanic interaction between the AlRP and an alloy substrate. Galvanic corrosion between an AA2024 sample and Al-Zn-In bulk alloy was also studied using a zero resistance ammeter. A trivalent chromium process treatment on galvanic couples can protect AA2024 substrate from cathodic corrosion.Acknowledgements: this project is funded by the Office of Naval Research through the Small Business Innovation Research (SBIR) program. We thank Naval Air Systems Command (NAVAIR) for providing Al-rich primer samples. We acknowledge Dr. Mansoureh Norouzi Rad at Zeiss for 3D microstructure reconstruction on Al-rich primer using X-ray microscope, and Thermo Fisher Scientific for 3D microstructure reconstruction on Al-rich primer using Helios Plasma FIB/SEM. We appreciate Dr. Babu Viswanathan at OSU for STEM characterization, and Swagelok Center for Surface Analysis of Materials (SCSAM) at Case Western Reserve University for Ar ion polishing.

Modeling, Validation, and Application of Finite Element Models for the Galvanic Corrosion of Aluminum Alloy 6061-T6 Coupled to Non-Passivating and Passivating Alloys

Galvanic corrosion of aluminum alloys coupled to non-passivating and passivating alloys exposed in corrosive environments can cause severe corrosion damage in marine structures. The aim of this study is the development of a finite element model using COMSOL Multiphysics to predict the galvanic interaction of aluminum alloy AA6061-T6 coupled to noble materials.The numerical model is based on anodic dissolution kinetics of AA6061 and cathodic kinetics of Ti6Al4V, 316 stainless steel, and copper determined with potentiodynamic polarization. The model predicts that the cathodic material and the geometry of the galvanic couple both influence the corrosion rate of AA6061, and that the solution composition locally changes over time.In order to account for the time-dependent change in solution chemistry a thorough experimental investigation of the effect of pH and chloride ion (Cl-) concentration on the corrosion kinetics of AA6061 is presented using potentiodynamic polarization. Corrosion kinetics were obtained in sodium sulfate and sodium chloride solutions as a function of pH and chloride ion concentration and implemented in the numerical model.The validation of the model is in progress and will be compared to data of actual galvanic couples exposed in the laboratory and in different atmospheric environments. Acknowledgement: This material is based on research sponsored by the USAFA and University of Hawaii under agreement number FA7000-18-2-0004. The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon.

A new method to determine the synergistic effects of area ratio and microstructure on the galvanic corrosion of LAS A508/309 L/308 L SS dissimilar metals weld

The synergistic effects of area ratio and microstructure on the galvanic corrosion of A508/309 L/308 L dissimilar metals weld (DMW) are studied by a multi-analytical approach. It was demonstrated that decreasing the anode/cathode surface area ratio obviously enhances the corrosion rate of A508, both locally and globally. Deeper analyses of the AFM results enabled quantitative comparison of the corrosion behaviour of the different surface constituents. It was revealed that in the galvanic interaction of the DMW, the grain refined region corrodes most, followed by the partial grain refined region and base metal matrix of the A508, respectively. The electrochemical localization index (LI) estimation method and AFM analysis both confirmed the presence of a mixed (localized and uniform) corrosion phenomenon occurring on the surface of the A508 anode metal in the galvanic interaction of the dissimilar metals. Finally, the degree of synergism equation was utilized to describe the synergistic effects of anode/cathode area ratio and the microstructure of the samples on the galvanic corrosion of LAS A508/309L/308L SS DMW.

Surface chemistry of oxidised pyrite during grinding: EDTA extraction analysis

This paper investigates the surface chemistry of oxidised pyrite under two different grinding conditions (forged steel grinding media and 30% chrome steel grinding media with nitrogen gas flow) using the ethylene diamine-tetra acetic acid (EDTA) extraction technique. The measurement of EDTA extractable iron and dissolved total sulfur (DTS) in the solid and aqueous phase of the grinding slurry enables us to decouple the relative intensity of the pyrite oxidation and galvanic interactions in the mill. It is found that the galvanic interaction predominates in the mill when pyrite samples are ground with forged steel media in the presence of sufficient dissolved oxygen. While the oxidation of pyrite becomes the predominant reaction when the concentration of dissolved oxygen is low in the mill. However, the oxidation of pyrite predominates in the mill when pyrite samples are ground with 30% chrome steel media regardless of the concentration of dissolved oxygen. Reducing the level of dissolved oxygen in the mill (e.g., purging the system with nitrogen gas) or applying less electrochemically active grinding media (e.g., high chrome steel) can reduce the hydrophilic species on the pyrite surface during grinding (e.g., iron hydroxides/oxyhydroxides). Hence, it would be expected to consequently increase the floatability of pyrite.

Local Electrochemical Behavior of Friction Stir Welded Mg-Al-Mn Alloy Joints

Local scanning electrochemical microscopy (SECM), along with a scanning vibrating electrode technique (SVET), were used to spatially map anodic and cathodic regions in a complex assembly including a friction stir lap welded joint between two Mg-Al-Mn alloys, namely AM60 and AM30. The assembly investigated herein was comprised of the two base materials (AM60 and AM30) and a stir zone (SZ). The transitory electrochemical characteristics of the three regions were perceived from different electrochemical tests and have been correlated to their respective microstructures. Potentiometric and voltametric SECM performed on the assembly in 0.01 M NaCl revealed that during the first few minutes of exposure, AM60 and SZ regions act as dominant anodic regions in the assembly while after 2 h of exposure these regions transition to become cathodic relative to the AM30 region. Galvanic interaction between the different weld regions immersed in a significantly more conductive NaCl electrolyte was investigated by SVET. Under such conditions, filiform-like corrosion initiated, and propagated exclusively within the AM30 region, resulting in cathodic activation of the corroded surface. However, after approximately 5 h of exposure, the AM60 region preferentially dissolves following sufficient cathodic activation of the AM30 region.

PH evolution around the AZ31/Steel galvanic couple under gelled-electrolytes: A numerical and experimental study

This work presents an experimentally validated theoretical model for Mg alloy dissolution that accounts for transport phenomena. The galvanic interaction between AZ31 Mg alloy and low carbon steels in a solid electrolyte was simulated. The use of a solid agar-based electrolyte allowed to neglect the strong convective effects that are normally present during Mg alloy dissolution caused by copious hydrogen evolution. Furthermore, it allowed for a constant electrolyte thickness to be fixed. The gelled-electrolyte contained a pH indicator to permit a reliable visual tracking of the transient propagation of H+ and OH− ions during the electrochemical reaction.

Increase in gold dissolution in copper ammonia thiosulfate solution via cobalt surface modification

When gold was leached using copper ammonia thiosulfate solution, the dissolution rate of gold decreased as the leaching time increased. The dissolution of gold powder with 44 and 77 μm particles was studied，and the results indicated that the dissolution rate was not decreased by surface passivation or the decrease in copper concentration but by the changes of the electronic structure of the gold surface caused by the change in the exposed crystal surface. The transmission electron microscopy images of the gold powder revealed that the high-index (220) and (311) crystal surfaces almost disappeared during leaching. Furthermore, the surface of gold consisted mainly of the low-index (111) crystal surface during the later stages of leaching. Owing to the changes in crystal surface, the work function of the gold surface increased from 6.56 to 6.95 eV, and the increase in work function hindered the loss of electrons from the gold surface. When cobalt was used to modify the gold surface, the work function decreased from 6.56 to 5.99 eV. The leaching results indicated that the cobalt modification increased gold dissolution, and the gold leaching percentage was increased by 40% within 8 h. the tendency of gold to dissolve more easily after it underwent surface modification was confirmed by the apparent activation energy of the surface-modified being lower than that of the fresh gold powder, the formation of intermediate products of Co3O4 with high oxidation ability and the galvanic interaction between cobalt and gold electrodes. Dry-grind was applied for gold concentrate calcine and different contents of cobalt powder to study the possibility of industrial application of this effect. The results showed that only adding 50 mg cobalt to 100 g gold ores was beneficial to gold leaching

Actinide Drawdown From LiCl-KCl Eutectic Salt via Galvanic/chemical Reactions Using Rare Earth Metals

This study proposes a method of separating uranium (U) and minor actinides from rare earth (RE) elements in the LiCl-KCl salt system. Several RE metals were used to reduce UCl3 and MgCl2 from the eutectic LiCl-KCl salt systems. Five experiments were performed on drawdown U and plutonium (Pu) surrogate elements from RECl3-enriched LiCl-KCl salt systems at 773 K. Via the introduction of RE metals into the salt system, it was observed that the UCl3 concentration can be lowered below 100 ppm. In addition, UCl3 was reduced into a powdery form that easily settled at the bottom and was successfully collected by a salt distillation operation. When the RE metals come into contact with a metallic structure, a galvanic interaction occurs dominantly, seemingly accelerating the U recovery reaction. These results elucidate the development of an effective and simple process that selectively removes actinides from electrorefining salt, thus contributing to the minimization of the influx of actinides into the nuclear fuel waste stream.

Tribocorrosion of Ti6Al4V and NiCr Implant Alloys: Effect of Galvanic Interaction

Micromovements that occur in the joint between dental prostheses and implants can lead to wear-induced degradation. This process can be enhanced by corrosion in the oral environment influenced by the presence of solutions containing fluoride. Moreover, the eventual galvanic interactions between NiCr and Ti alloys can accelerate the wear-corrosion process. In this work, the tribocorrosion process of Ti6Al4V and NiCr alloys used in dental implant rehabilitations immersed in fluoride solutions at different pH values was investigated. The galvanic interaction effect between the alloys was also assessed. Tribocorrosion tests in corrosive media were performed with isolated Ti6Al4V and NiCr alloys, followed by testing with both alloys in contact. The media selected were based on fluoride concentrations and pH values that are possible to be found in oral environments. Analysis of the surfaces after the tribocorrosion tests was carried out using confocal laser microscopy. The wear profile and volume losses were determined by confocal measurements. It was concluded that the galvanic interaction between the alloys increased the tribocorrosion resistance of Ti6Al4V, compared with that of the isolated Ti6Al4V alloy. Ti6Al4V coupled with NiCr reduced the electrochemical potential decay during sliding. The increased resistance was explained by the electrochemical shift of the Ti6Al4V potential from active dissolution to the passive domain.

Dealloying-driven local corrosion by intermetallic constituent particles and dispersoids in aerospace aluminium alloys

Nanoscopic characterization of heterogeneous intermetallic particles (IMPs) which microstructurally and compositionally evolve during local corrosion is crucial in unravelling the mechanisms and sequence of initial and local corrosion events. Herein, we study site-specific initiation events focused on microscopic constituent intermetallic compounds and nanoscopic dispersoids in AA2024-T3 at the nanoscale using a combined quasi in-situ and ex-situ analytical TEM approach. Our findings show a dealloying-driven local corrosion initiation at the studied IMPs that have been considered as cathodic phases traditionally. Besides, local degradation which is a result of galvanic interactions between dealloyed regions of IMPs and their adjacent alloy matrix is largely governed by the intrinsic electrochemical instability of intermetallic compounds.

The effect of galvanic interaction between chalcopyrite and pyrite on the surface chemistry and collector adsorption: Flotation and DFT study

An investigation on the surface properties and collector adsorption was conducted after the galvanic interaction of chalcopyrite and pyrite in the flotation system. The surface compositions were studied through the metal ion dissolution test and X-ray photoelectron spectroscopy (XPS) characterization. The galvanic effect on flotation behavior was examined by the flotation test of mineral mixtures; the collector adsorption on the defect chalcopyrite surfaces was analyzed by DFT calculation. The results showed that the addition of pyrite enhanced copper ion dissolution from the chalcopyrite surface significantly. Adsorption of copper ion on the pyrite surface was observed by XPS analysis. Chalcopyrite surface showed a higher oxidation degree after contacting with pyrite as polysulfide and elemental sulfur appeared. Mineral recovery from flotation tests showed the galvanic effect caused lower selectivity of chalcopyrite and pyrite with SBX as a collector. DFT study revealed that the metal-deficient chalcopyrite surface does not facilitate collector adsorption with high adsorption energy. Therefore, pyrite is galvanically protected while the oxidation dissolution of chalcopyrite is enhanced in their galvanic cell. Lower chalcopyrite recovery from mineral mixtures was obtained due to surface defection and weaken collector adsorption.

Oil-Immersed Scanning Micropipette Contact Method Enabling Long-term Corrosion Mapping.

This work reports the development of an oil-immersed scanning micropipette contact method, a variant of the scanning micropipette contact method, where a thin layer of oil wets the investigated substrate. The oil-immersed scanning micropipette contact method significantly increases the droplet stability, allowing for prolonged mapping and the use of highly evaporative saline solutions regardless of ambient humidity levels. This systematic mapping technique was used to conduct a detailed investigation of localized corrosion taking place at the surface of an AA7075-T73 aluminum alloy in a 3.5 wt % NaCl electrolyte solution, which is typically challenging in the conventional scanning micropipette contact method. Maps of corrosion potentials and corrosion currents extracted from potentiodynamic polarization curves showed good correlations with the chemical composition of surface features and known galvanic interactions at the microscale level. This demonstrates the viability of the oil-immersed scanning micropipette contact method and opens up the avenue to mechanistic corrosion investigations at the microscale level using aqueous solutions that are prone to evaporation under noncontrolled humidity levels.

Bioleaching of Sulfide Concentrates with Different Copper and Zinc Contents and Evaluation of Bioleach Residue Grade

Bioleaching of sulfide concentrates with different copper and zinc contents using two cultures of acidophilic chemolithotrophic microorganisms, which were grown at 30 and 35°C, was studied. The average leaching rate of copper was shown to be directly dependent on the copper content in the concentrate. The leaching rate of zinc was found to depend not only on the zinc content but also on the copper content. At the same time, the specific leaching rate of copper varied insignificantly (28–45 mg/(g day)), while the change in the specific leaching rate of zinc was much more pronounced (107–319 mg/(g day)) and depended on the metal contents in the concentrates. Under all conditions of bioleaching, the specific rate of zinc extraction into the aqueous phase increased significantly with an increase in the copper content in the concentrates, which indicated galvanic interactions between sulfide minerals. The possibility of the obtainment of the copper concentrates containing negligible amounts of zinc after bioleaching of the concentrates, in which the content of copper exceeded that of zinc and was not less than 10%, was shown. Bioleaching of the concentrates containing more zinc than copper is impractical.

The influence of galvanic interaction on the dissolution and surface composition of galena and pyrite in flotation system

The dissolution behavior and surface composition of galena and pyrite in their coexisting flotation system were studied by metal ion releasing experiment and XPS analysis, to reveal the influence of galvanic interaction on their flotation. The results indicated that the dissolution of lead ions from galena surface was strongly enhanced in the presence of pyrite, significantly depending on the pyrite content. The dissolution of iron ions from pyrite surface was also enhanced in the presence of galena, but the effect of galena content was small. XPS analysis verified that the galvanic interaction enhanced the galena oxidation, leading to an increase in oxysulfide/hydroxide components on its surface. However, the galvanic interaction only had little impact on the pyrite oxidation, other than the migration and adsorption of lead ions. This work demonstrated that the galvanic interaction between galena and pyrite altered their surface components and increased the difficulty in flotation separation process.

Repurposing of nickeliferous pyrrhotite from mine tailings as magnetic adsorbent for the recovery of gold from chloride solution

The utilization and repurposing of waste materials from mining and minerals industry as low-cost adsorbents for valuable metals have received significant attention due to increasing drive for waste valorization, environmental protection and sustainable development. This study investigates the ability of magnetic nickeliferous pyrrhotite obtained from nickel sulphide mine tailings in Western Australia as adsorbent for gold (Au) from chloride solution. The influence of different variables, such as pH, contact time, initial Au concentration, and chloride (Cl–) concentrations on Au adsorption were examined. The use of magnetic adsorbents is considered as an emerging technology in the recovery of precious metals from aqueous solutions and offers a number of advantages related to ease of solid-liquid separation. The nickeliferrous pyrrhotite samples, composed of pyrrhotite (Fe(1-X)S, 65%), pentlandite ((Fe,Ni)9S8, 32%) and trace impurities of alumino-silicate minerals (3%), were collected manually using a permanent magnet, and were prepared by crushing and grinding to the desired particle size. Complete Au recovery (100%) was achieved after 15 min of contact time at acidic pH. It was also found that the magnetic adsorbent exhibited high loading capacity as evident by 100% Au recovery achieved even at higher initial Au concentrations and after eight times re-use of loaded particles. High Cl– concentration was observed to have a negative effect on Au uptake. The galvanic interaction between pentlandite and pyrrhotite as the possible mechanism for Au recovery is discussed. Repurposing nickeliferous pyrrhotite from mine wastes as magnetic adsorbent for Au offers a very attractive application for the material.

Protection Coordination of AC/DC Intersystem Faults in Hybrid Transmission Grids

The new characteristics and phenomena of hybrid AC/DC transmission grids challenge the conventional protection concepts. In hybrid AC/DC overhead line systems, AC and DC systems are located on the same support structure. As a result, electromagnetic and galvanic interactions between the AC- and the DC-line influence the AC-protection and the DC-control in a novel and complex way. This paper presents key findings and solutions from a current 400-kV-hybrid AC/DC overhead line project in Germany. The focus is on AC/DC intersystem faults, i.e. galvanic contact between DC and AC systems. Fault detection and fault response of the AC-protection and the DC-control as well as a proper AC/DC protection coordination are discussed. The paper illustrates the challenges of a secure and dependable fault clearing and indicates solution methods. The findings of this paper are based on EMT simulations with detailed PSCAD-models of the hybrid AC/DC overhead line and the VSC-converters. Laboratory protection tests have been conducted and confirmed the results.