Galvanostatic Electrolysis Research Articles

Electrochemical Drawdown of U3+ and Ce3+ in Molten LiCl-KCl Using a Liquid Cadmium Cathode

Abstract The electrorefining of spent nuclear fuels is a key step to recover uranium and transuranium on separated cathodes. However, the electrolyte salts become contaminated with fission products after batches of electrorefining, and therefore the two unit processes for the drawdown of actinide and lanthanide are suggested before treatment of the contaminated salts. We investigated the electrochemical drawdown of U3+, Ce3+, and U3+ from Ce3+ in molten LiCl-KCl electrolyte using a liquid cadmium cathode (LCC) at 773 K. The drawdown mechanism of U3+ and Ce3+ was determined by cyclic voltammograms and calculating the equilibrium potential. After galvanostatic electrolysis, high recovery yields were obtained for the drawdown of U3+ and Ce3+, but the current efficiency of Ce3+ was at least twice as high as that of U3+ due to the cyclic electrolysis of U3+/U4+. Despite significant underpotential deposition of Ce3+ in the LCC, an exceptional separation factor for Ce relative to U reached 84.67 ± 17.13, which was attributed to the formed pure uranium products hindering the subsequent deposition of Ce3+. Moreover, pure uranium products and Ce-Cd intermetallic compounds were characterized by X-ray diffraction and scanning electron microscope coupled with energy dispersive X-ray spectroscopy.

Direct Synthesis of Ti-Al Compound Powders by Electrolysis in Molten LiCl-KCl

The deposition potential difference between Ti and Al is only 70 mV. The deposition reaction of Ti-Al compound happens at the potentials slightly higher than that of metallic Ti and Al. Through galvanostatic electrolysis of mixture solution of Al and Ti ions, all kinds of titanium aluminides can be directly synthesized. The composition of the product compound can be selected through adjusting the combination of Ti and Al ions in the electrolyte.

A novel process for producing Al-Si alloy utilizing aluminum-silicon oxide extracted from coal fly ash

As a kind of solid waste rich in aluminum and silicon resources, the comprehensive utilization of coal fly ash (CFA) will be of great significance to reduce environmental pollution and improve economic benefits. This work proposed a facile and environmentally friendly cleaning process for producing Al-Si alloy by molten salt electrolysis from CFA extract, aluminum-silicon oxide (ASO). The dissolution behavior and dissolution reaction mechanism of ASO were studied by high temperature visual dissolution experiment, thermodynamics analysis and phase analysis. Due to the chemical reaction between ASO and cryolite-based melt, ASO powder dissolves rapidly in melt and the dissolution rate of ASO is not determined by the phase compositions but by the mass ratio of Al2O3/SiO2. For replenishing the oxide concentration in the electrolyte as quick as possible, the proper mass ratio of Al2O3/SiO2 is in the range of 0.75–7.5. The electrochemical co-reduction behavior of Si (IV) and Al (III) ions on the W electrode was performed by cyclic voltammetry and square wave voltammetry. The results indicated that the reduction of Si (IV) ion in the melt was a two-step irreversible process. Hypoeutectic Al-Si alloy and eutectic Al-Si alloy were prepared by galvanostatic electrolysis using ASO as raw material. This innovative technology can realize high-value recycling of CFA resources and low carbon emission, low energy consumption production of Al-Si alloy.

Electricity-driven dealkalization of bauxite residue based on thermodynamics, kinetics, and mineral transformation.

High alkalinity content of bauxite residue is a major factor that hinders resource reutilization and pollutes the environment. Although acid neutralization is a direct and effective method, the amount of acid and secondary waste of sodium salt are still difficult problems to solve. Herein, we innovatively integrated an electric field into the acid neutralization dealkalization of bauxite residue and analyzed the dealkalization behavior by thermodynamics, kinetics, and mineral transformation. The results show that the pH of the anode chamber was maintained at the acidic levels of 3-6 after 30min of galvanostatic electrolysis, and bauxite residue can realize dealkalization by acid neutralization. In the anode chamber, Na+ was released into the leachate via the reactions of Na3Al3Si3O12 and the removal of encapsulated soluble alkali. The stainless steel wire mesh anode exhibited its superiority and decreased the Na2O content in bauxite residue from 9.48 to 3.13% through convective mass transfer driven by the electric field and steady-state diffusion under stirring. This research provides a promising method for the electricity-driven dealkalization of bauxite residue, thus facilitating the development of multifield coupling theory and the application of electric fields in the alumina industry.

Formation of Be13Ln intermetallics by codeposition of Be and Ln from molten NaF-BeF2-LnF3 (Ln = Pr, Nd, Gd)

The electrodeposition of Be and Ln from NaF-BeF2-LnF3 (Ln = Pr, Nd, Gd) molten salts on various electrodes, including W, Mo, Ni, Cu, and brass (70 %Cu-30 %Zn alloy), is systematically investigated using cyclic voltammetry (CV), stripping chronopotentiometry (SCP), square wave voltammetry (SWV), chrono-amperometry (CA), galvanostatic electrolysis, and microanalytical analysis of the deposits. Underpotential deposition (UPD) of Be is observed on all electrodes, while UPD of Ln is selectively observed on certain electrodes like Ni, Cu, and brass. Furthermore, the codeposition of Be and Ln is observed on all electrodes at a potential between −0.090 to −0.190 V vs Eeq,Be(II)/Be. SEM-EDS and XRD analysis confirm the intermetallic compound Be13Ln as the predominant phase in the deposits. The current–time transient behavior indicates a 3D instantaneous nucleation for Be electrodeposition, followed by a progressive nucleation process for the codeposition of Be-Gd on the W electrode. The standard Gibbs free energy of various Be-containing intermetallics is calculated based on the determined standard potentials. A novel strategy for Ln separation from BeF2-based molten salt is proposed based on the insights gained from this study.

Electrochemical Oxidative Cross-Coupling Reactions of Ketene Dithioacetals and Dichalcogenides to Construct C−Se/C−S Bonds

A green protocol for construction of C−Se bonds from ketene dithioacetals and diselenides through direct electrochemical oxidative cross-coupling has been developed. This reaction was carried out in an undivided cell system with NaBF4 as the electrolyte and CH3CN as the solvent through galvanostatic electrolysis. A series of substituted ketene dithioacetals and diselenides were tolerant and the desired tetrasubstituted alkenyl selenides were obtained in moderate to excellent yields. In addition, construction of C−S bond from ketene dithioacetals and disulfides through electrochemical method in the presence of KI was also successfully realized. It exhibited high efficiency and broad functional group tolerance.

Electrochemical Analysis of an Electrolyte-Supported Solid Oxide Cell-Based MK35x Stack during Long-Term Electrolysis Operation

The currently ongoing scale-up of high-temperature solid oxide electrolysis (SOEL) requires an understanding of the underlying dominant degradation mechanisms to enable continuous progress in increasing stack durability. In the present study, the degradation behavior of SOEL stacks of the type “MK35x” with chromium-iron-yttrium (CFY) interconnects and electrolyte-supported cells (ESC) developed at Fraunhofer IKTS was investigated. For this purpose, the initial electrochemical performance of a 10-cell stack was characterized in various operating conditions in both fuel cell and electrolysis mode. Degradation was evaluated during galvanostatic steady-state steam electrolysis operation for more than 3000 h at an oxygen side outlet temperature of 816 °C and a current density of −0.6 A cm−2 and showed an average voltage evolution rate of −0.3%/kh demonstrating high stability. Initial and final characterization at the part load operating point at −0.39 A cm−2 and 800 °C led to the determination of a positive overall degradation rate of 0.4%/kh showing a considerable impact of the operating conditions on the degradation rate. By means of electrochemical impedance spectroscopy analysis it was shown that the stack’s ohmic resistance increased whereas the polarization resistance decreased most likely due to an enhancement in LSMM’/ScSZ oxygen electrode performance.

Electrochemical Oxidative Ring‐Opening Reactions of 2H‐Indazoles with Alcohols to Obtain Ortho‐alkoxycarbonylated Azobenzenes

AbstractA strategy for synthesis of azo‐derived compounds by electrochemical oxidative ring‐opening reactions of 2H‐indazoles with alcohols is reported. The reactions are carried out under galvanostatic electrolysis conditions in an undivided cell without the use of transition metal catalysts. On the basis of cyclic voltammetry and control experiments, a plausible mechanism for this ring‐opening reaction involving the radical pathway is proposed. Furthermore, various 2H‐indazoles and alcohols are suitable in this system, giving the desired ortho‐alkoxycarbonylated azobenzenes in 9–84% yields.

Electrochemistry of Uranium on Liquid Cadmium Electrode in LiCl-KCl Eutectic

This work presents the electrochemical study of LiCl-KCl-UCl3 solutions at the temperature range 673–823 K on inert and reactive electrodes, i.e. W and Cd, respectively. On inert electrode, U(III) ions were reduced to metallic uranium through one step and the mechanism of the cathode reaction was irreversible. The diffusion coefficients of U(III) ions in molten chloride eutectic and liquid cadmium were calculated. On reactive electrode, U(III) ions were reduced with depolarization and were accompanied by the formation of intermetallic compound UCd11. The reactions of the cathodic deposition and anodic dissolution of the U-Cd alloy were studied and the conditions of the alloy formation via galvanostatic electrolysis were found. The solubility and the activity of uranium in liquid cadmium were determined.

Theoretical Understanding of Effects of Operating Modes on the Performance Durability of Solid Oxide Cells: A Comparison between Potentiostatic and Galvanostatic Operations

In solid oxide cells (SOCs), the choice between galvanostatic (constant current) and potentiostatic (constant voltage) modes does not significantly affect the performance of SOCs as long as the cell components remain unchanged and intact. However, the degradation of cell components, which leads to changes in electrochemical and physical properties of the cell, elevates the importance of the selected operating mode. This paper aims to investigate the effects of galvanostatic and potentiostatic operating modes on the evolving properties of SOCs and their subsequent influence on performance durability. Employing non-equilibrium thermodynamic analysis, a crucial approach for understanding the degradation phenomena within an active electrochemical system, this study aims to provide in-depth insights into how these operating modes affect the longevity and efficacy of SOCs. Key findings include: In cases where oxygen electrode (OE) degradation is accelerated by higher partial pressure of oxygen ( pO2 ), operating under constant voltage electrolysis can mitigate the high pO2 at the OE|electrolyte (OE|EL) interface. Conversely, if OE degradation occurs more rapidly under a lower pO2, constant current electrolysis is more effective in suppressing degradation by achieving a high pO2 at the OE|EL interface. For degradation of the fuel electrode (FE) due to higher pO2, constant current electrolysis is beneficial for more stable performance, which helps maintain low pO2 at the FE|EL interface. When FE degradation is accelerated by lower pO2, constant voltage electrolysis can avert low pO2 at the FE|EL interface. In practical scenarios, more complex degradation mechanisms come into play, especially when pO2 significantly deviates from initial conditions. Degradation in one electrode can influence pO2 in the other electrode, a phenomenon more pronounced in potentiostatic than in galvanostatic electrolysis.

Electrodeposition of Silicon Fibers from KI–KF–KCl–K2SiF6 Melt and Their Electrochemical Performance during Lithiation/Delithiation

The possibility of using Si-based anodes in lithium-ion batteries is actively investigated due to the increased lithium capacity of silicon. The paper reports the preparation of submicron silicon fibers on glassy carbon in the KI–KF–KCl–K2SiF6 melt at 720 °C. For this purpose, the parameters of silicon electrodeposition in the form of fibers were determined using cyclic voltammetry, and experimental samples of ordered silicon fibers with an average diameter from 0.1 to 0.3 μm were obtained under galvanostatic electrolysis conditions. Using the obtained silicon fibers, anode half-cells of a lithium-ion battery were fabricated, and its electrochemical performance under multiple lithiations and delithiations was studied. By means of voltametric studies, it is observed that charging and discharging the anode based on the obtained silicon fibers occurs at potentials from 0.2 to 0.05 V and from 0.2 to 0.5 V, respectively. A change in discharge capacity from 520 to 200 mAh g−1 during the first 50 charge/discharge cycles at a charge current of 0.1 C and a Coulombic efficiency of 98–100% was shown. The possibility of charging silicon-based anode samples at charging currents up to 2 C was also noted; the discharge capacity ranged from 25 to 250 mAh g−1.

Effect of the Substrate Materials in the Fabrication of an Electrode Based on Mixed Nickel‐Iron Oxide Electrocatalyst

AbstractThe effect of different substrate materials in the fabrication of an electrode intended for use in the water oxidation reaction is investigated. The electrocatalyst is nickel‐iron oxide (NiFeOx) which is deposited by chronoamperometry on nickel, iron, titanium, and stainless steel substrates. The process of electrodeposition is optimized to achieve the lowest overpotential for the water oxidation reaction. The four electrodes are characterized by scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS), and glow‐discharge optical emission spectroscopy (GDOES) to describe the effect of the substrate on the nature of the electrocatalyst layer. Electrochemical tests in 1 m NaOH are applied on the four electrodes to assess the stability and the retention of the electrocatalytic properties of the whole electrode. All electrodes show similar overpotential of ≈0.3 V at 10 mA cm−2 implying that the substrate do not affect the electrocatalytic activity of the NiFeOx. After use, the overpotential increases in a range of 30–50 mV for nickel, iron, and titanium substrates, while stainless steel retains the lowest overpotential with an increase of 10 mV. This limited variation can be the effect of smaller NiFeOx nanoparticles compared to other substrates. XPS analysis reveals that after galvanostatic electrolysis, the oxidation state of Fe shifts slightly from Fe(II) to Fe(III), likely Fe3O4 and Fe2O3, while NiO/Ni2O3 change partially to Ni(OH)2.

Electrochemical formation and characterization of Ni-Sc intermetallic compounds in LiF-CaF2 eutectic melt

The present investigation aimed to examine the cathodic behavior of Sc(III) on a reactive nickel electrode within a fluoride molten salt system. The electrochemical formation process of Ni-Sc alloy in LiF-CaF2 eutectic melt was investigated using cyclic voltammetry and square wave voltammetry electrochemical techniques. The formation of Ni-Sc intermetallic compounds induces a depolarization phenomenon, hence promoting the underpotential deposition of scandium onto the Ni electrode. The standard Gibbs free energy of formation for Ni-Sc intermetallic compounds were calculated by the use of open-circuit chronopotentiometry measurements. Furthermore, Ni-Sc alloys were fabricated via potentiostatic and galvanostatic electrolysis methods and subsequently characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The results indicated that a sequential emergence of Ni5Sc, Ni2Sc, and combined NiSc+NiSc2 intermetallic compounds escalates as the cathodic polarization potential. Multifarious Ni-Sc intermetallic compounds can be synthesized by controlling the electrolysis conditions, providing new insights for the preparation of Ni-Sc alloy and establishing a theoretical foundation for the synthesis of Ni-Sc intermediate alloy for solid-state reactive cathodes.

Rapid and efficient extraction of cerium by forming Al-Ce alloys in LiCl-KCl molten salts

The extraction of lanthanides in spent fuel reprocessing plays a key role in the development of nuclear energy. In this work, the extraction of the typical fissionable cerium elements has been studied by electrolytic co-reduction of Al(III) and Ce(III) in LiCl-KCl-CeCl3 molten salts assisted by KAlCl4. The electrochemical behavior of the reduction of Al(III) and Ce(III) on a molybdenum electrode was studied by cyclic voltammetry (CV), square wave voltammetry (SWV), and open circuit chronopotentiometry (OCP), and specific peaks of five Al-Ce intermetallic compounds were detected. After 2.7 h of galvanostatic electrolysis at a current density of 0.064 A cm-2, the extraction efficiency and current efficiency of Ce(III) reached 99.9 % and 91.3 % respectively. Potentiostatic electrolysis is slightly more efficient, with 99.9 % Ce(III) extraction in 3.5 h at a current efficiency of 97.8 %. The products of electrolysis are rod-shaped alloys (Al11Ce3, Al3Ce, Al2Ce), and the molten salts purified by electrolytic separation are free of impurity signals and can be reused for electrolytic refining.

Electrolytic Reduction of CO2 Using Perovskite-Type La-Based Oxide Anodes in Chloride Molten Salts

CO2 decomposition in molten salt is an attractive process as a new method for achieving carbon neutrality, for which the development of inert anodes and electrolytic bath suitable for CO2 decomposition is essential. Previous studies mostly investigated the electrode material but did not investigate the relationship between the electrolysis bath and electrode reaction. The effects of the electrolytic bath on anode reaction and the development of inert anode material with high current density were investigated in this study. Electrolytic bath of LiCl–CaCl2 and NaCl–CaCl2 with similar oxide solubilities were compared, finding that LiCl–CaCl2 melts exhibited higher oxidation current density in cyclic voltammetry and more stable potential transition in galvanostatic electrolysis. Among the five anodes with a perovskite-type La-based oxide were investigated, La0.6Sr0.4CoO3−δ showed the highest electrical conductivity and the largest increase in oxidation current density. CO2 decomposition tests were performed in LiCl–CaCl2 with CaO and CaCO3 added as a CO2 source at 873 K using La0.6Sr0.4CoO3−δ anode. Only C and O2 were recovered from CO2 by electrolysis test. The current efficiencies were 78.3% and 54.4%, respectively. The La0.6Sr0.4CoO3−δ anode exhibited excellent corrosion resistance, demonstrating its potential as a promising inert anode for CO2 decomposition.

Reductive cyclodimerization of chalcones: exploring the "self-adaptability" of galvanostatic electrosynthesis.

The "self-adaptability" of galvanostatic electrolysis was shown to assist a multistage unprecedented chemo- and diastereoselective electrochemically promoted cyclodimerization of chalcones. The process, all involving the reductive events, delivered densely functionalized cyclopentanes featuring five contiguous stereocenters (25 examples, yields of up to 95%, dr values up to >20 : 1). Dedicated and combined experimental as well as electrochemical investigation revealed the key role of a dynamic kinetic resolution of the aldol intermediate for the reaction mechanism.

Numerical study on inclusion collision, coalescence and removal in an extra-thick slab continuous casting mold with M-EMS

Surface flaw detection is one of the main problems of extra-thick slab. In practice, it is considered that the application of mold electromagnetic stirring (M-EMS) is an effective means to reduce the inclusions located at the subsurface of thick slab. The present study conducted numerical studies on the inclusion transports in an extra-thick slab continuous casting mold with the effects of M-EMS. The influences of M-EMS on the inclusion collision, coalescence and removal were revealed. The predicted results indicate that the majority of inclusions entering the mold are smaller than 20 µm. The application of M-EMS promotes the collision, aggregation, and flotation of these inclusions. When the inclusions entering the mold are larger than 30 µm, the flotation removal of inclusions significantly increases, and the collision and aggregation among inclusions decreases accordingly. Furthermore, the predicted results show that inclusions larger than 200 µm in size are unlikely to follow the downward flow into the lower region of the mold, with the primary removal location concentrated near the nozzle. Large-size inclusions have been quantitatively extracted from samples with and without M-EMS using galvanostatic electrolysis method. The results indicate that the inclusions of various sizes in the slab surface layer are reduced when M-EMS is employed. Notably, inclusions sized 50–150 µm show the most significant reduction, with their mass density decreasing from 38.17 mg/10 kg to 15.11 mg/10 kg. This demonstrates a substantial reduction in large-size inclusions on the slab surface layer following the introduction of M-EMS in the mold.

Electrolytic Reduction of UO2 Microspheres Synthesized Via Internal Gelation Method

Pyroprocessing is the combination of process steps to extract and recycle actinides from fission products in spent nuclear fuels in high-temperature molten salt media. Pyroprocessing has been studied extensively over the past decades. One of the key sub-processes is the electrolytic reduction of uranium oxides. The electrolytic reduction process originated from the FFC Cambridge process, an approach for electrochemically reducing titanium dioxide into titanium metal in molten CaCl2. In the electrolytic reduction of uranium oxides, the uranium oxide feed is applied as the cathode in LiCl-Li2O molten salt electrolyte at 650°C. LiCl appears more promising than conventional CaCl2 owing to the lower melting point (878 K), and higher decomposition voltage (3.46 V at 923 K). Additionally, Li2O is expected to speed up the reduction via an additional chemical reduction pathway with the participation of Li metal, and prevents the direct dissolution of the Pt anode.This work aims to study the morphology effect of the oxide feed on the reduction kinetics and the incorporation of impurities during the electrolytic reduction process. The electrolytic reduction of UO2 is carried out on sintered UO2 pellets, as well as various UO2 microspheres synthesized via internal gelation. The introduction of uranium oxide microspheres holds several advantages. The spheres provide a higher surface area, which is expected to improve the overall reduction efficiency of uranium oxide during electrolysis. In addition, it is easier to handle the feed during loading and unloading of the cathode basket compared to powder feeds.The potentiostatic and galvanostatic electrolysis of UO2 is performed, and the comparison between the electrolytic reduction of UO2 pellets and microspheres is investigated. The SEM micrographs in figure 1show the morphology change of a UO2 pellet to uranium metals particles. A significant morphology change between the flat surface of the sintered UO2 feed and the reduced U particles is observed at the surface. Further characterization is performed using XRD and TGA to identify the products of the electrolytic reduction process qualitatively and quantitatively. Results show that galvanostatic electrolysis shows a better reduction efficiency compared to potentiostatic electrolysis, applied both below and above the Li formation onset potential. Overall, there is barely un-reacted UO2 visible in the XRD patterns of the reduced feed after galvanostatic electrolysis. U metal and UO are identified in the XRD patterns depending on electrolysis parameters. The presence of UO can be as an intermediate of UO2 reduction during electrolysis, which is a rare compound to be reported in literature. Overall, the reduction of microspheres does improve the overall reduction efficiency compared to the conventional pellet feeds. Figure 1

Electrocoagulation using aluminum electrodes as a sustainable and economic method for the removal of kinetic hydrate inhibitor (polyvinyl pyrrolidone) from produced wastewaters

Electrocoagulation is a water treatment technology capable to remove a variety of organic pollutants from water. It is advantageous compared to chemical coagulation due to the controlled dissolution of coagulants by regulating the current density and pH. In this work, the removal of kinetic hydrate inhibitor (KHI) (polyvinyl pyrrolidone, PVP) from water by electrocoagulation using Al electrodes was investigated. The effects of several experimental conditions including the nature of the supporting electrolyte, the current density, and the initial pH value on the electrochemical dissolution of aluminum was evaluated. The findings of the experiments revealed that both chemical and electrochemical dissolution play important roles in the generation of hydroxo-aluminum species. Corrosion studies demonstrated that the presence of chloride ions in water promotes aluminum dissolving via pitting corrosion, whereas the presence of phosphate ions inhibits aluminum corrosion by the deposition of a thick passive layer of aluminum hydroxide/phosphate on the metal surface. The theoretical and experimental amounts of aluminum, increase linearly with increasing specific electrical charge for Q< 2.5 Ah/L, which correlates well with Faraday's Law. The removal of KHI from 0.1M NaCl aqueous solutions by electrocoagulation using aluminum electrodes achieved high removal efficiency in terms of total organic carbon (TOC) up to 95%. TOC decay during galvanostatic electrolysis confirmed the removal of KHI molecules by Al-electrocoagulation at different current densities and pH conditions. The primary mechanism involved in eliminating KHI from water by electrocoagulation using Al electrodes includes mainly the adsorption of PVP molecules on the surface of Al(OH)3 flocs and their enmeshment inside the solid coagulants.

Ti/Ti4O7 Anodes for Efficient Electrodeposition of Manganese Metal and Anode Slime Generation Reduction.

Preventing lead-based anodes from causing high-energy consumption, lead pollution, and harmful anode slime emission is a major challenge for the current electrolytic manganese metal industry. In this work, a Ti4O7-coated titanium electrode was used as anode material (Ti/Ti4O7 anode) in manganese electrowinning process for the first time and compared with a lead-based anode (Pb anode). The Ti/Ti4O7 anode was used for galvanostatic electrolysis; the cathodic current efficiency improved by 3.22% and energy consumption decreased by 7.82%. During 8 h of electrolysis, it reduced 90.42% solution anode slime and 72.80% plate anode slime formation. Anode product characterization and electrochemical tests indicated that the Ti/Ti4O7 anode possesses good oxygen evolution activity, and γ-MnO2 has a positive catalytic effect on oxygen evolution reaction (OER), which inhibited anode Mn2+ oxidation reaction and reduced the formation of anode slime. In addition, the low charge-transfer resistance, high diffusion resistance, and dense MnO2 layer of the anode blocked the diffusion path of Mn3+ in the system and inhibited the formation of anode slime. The Ti/Ti4O7 anode exhibits excellent electrochemical performance, which provides a new idea for the selection of novel anodes, energy savings and emission reduction, and the establishment of a new mode of clean production in the electrolytic manganese metal industry.