Molten Salt Medium Research Articles

Dynamic simulation and control strategy development of molten salt steam generation system for coal-fired power plant flexible retrofit

The coal-fired power plant (CFPP) coupled with the molten salt thermal energy storage system is a potential way to improve its flexibility and peak-shaving ability. The steam generation system (SGS) is a suitable choice to convert the feed water into hot steam by using the heat from the molten salt. In this paper, the schematic of an SGS coupled with the CFPP is presented. A dynamic model of the SGS basing lump parameter method is established and validated to investigate its dynamic response characteristics. Five different disturbance experiments including feed water inlet parameters, molten salt inlet parameters and medium pressure steam valve, are conducted and analyzed. The dynamic response curves of molten salt and steam are obtained. Moreover, the load adjustment process of SGS with three different load changing rates (3 %, 6 %, 10 % Pe/min) under the rated conditions is compared and its influence on the SGS is analyzed. The temperature changing rates in the thick-wall components of SGS are within 2 °C/min which meets the safe operating standard. Based on the above results, the three elements control strategy with excellent robustness for the SGS safety operation is proposed and demonstrated. The results show that the response time for the SGS load regulation process and the water level fluctuation have been significantly improved as the three elements control strategy is imposed. The water level can be stabilized in 200 s with tiny fluctuation when the SGS loads down 10 % thermal load with 10 % Pe/min load changing rate. These results could provide useful references for the design and control strategy making of the CFPP coupled with the molten salt thermal energy storage system.

Lignin pyrolysis assisted by molten salt medium: Evolution behavior of volatiles and biochar structure

This study focuses on the use of a molten salt reaction medium (NaCl-KCl-LiCl) in the lignin pyrolysis process to modify the pyrolysis volatiles and biochar structure. The effect of pyrolysis reaction temperature (300°C, 400°C, 500°C, and 600°C) and lignin/molten salt mass ratios (3:1, 1:1, 1:3 and 1:5) on the evolution behavior of volatiles and biochar structure was explored. The pyrolysis products were determined using GS-MS, CO2 adsorption-desorption analyses, SEM, elemental analysis, proximate analysis, Raman, XRD, and TG/DTG analysis. Results indicated that the introduction of molten salt can enhance the lignin depolymerization, leading to the production of phenolic precursors. Moreover, the metal cation (Na+, K+ and Li+) of molten salt can in-situ induce the modification of biochar structure with high porosity. The lower sulfur content in biochar was attributed to the immobilize function of molten salt. The evolution behaviour of volatiles and biochar structure during molten salt-assisted lignin pyrolysis was proposed. This study can serve as a benchmark for the high-value recycling of industrial lignin waste.

Hot corrosion behavior of selective laser melted TiC/GT D222 nickel-based composite in 75% Na2SO4 and 25% K2SO4 molten salt medium at 900°C

PurposeThis paper aims to investigate the differences in hot corrosion behavior of the GTD222 superalloy and TiC/GTD222 composite in a mixed salt of 75% Na2SO4 and 25% K2SO4 at 900°C.Design/methodology/approachThe GTD222 superalloy and TiC/GTD222 nickel-based composite were prepared using selective laser melting (SLM). Subsequently, the hot corrosion behavior of the two alloys was systematically investigated in a salt mixture consisting of 75% Na2SO4 and 25% K2SO4 (Wt.%) at 900°C.FindingsThe TiC/GTD222 composite exhibited better hot corrosion resistance compared to the GTD222 superalloy. First, the addition of alloying elements led to the formation of a protective oxide film on the TiC/GTD222 composites 20 h before hot corrosion. Second, TiC/GTD222 composite corrosion surface has a higher Ti content, after 100 h of hot corrosion, the composite corrosion surface Ti content of 10.8% is more than two times the GTD222 alloy 4% Ti. The Ti and Cr oxides are tightly bonded, effectively resisting the erosion of corrosive elements.Originality/valueThe hot corrosion behavior of GTD222 superalloy and TiC/GTD222 composites prepared by SLM in a mixed salt of 75% Na2SO4 and 25% K2SO4 was studied for the first time. This study provides insights into the design of high-temperature alloys resistant to hot corrosion.

Efficient photocatalytic H2O2 production and photodegradation of RhB over K-doped g-C3N4/ZnO S-scheme heterojunction

Designing efficient dual-functional catalysts for photocatalytic oxygen reduction to produce hydrogen peroxide (H2O2) and photodegradation of dye pollutants is challenging. In this work, we designed and fabricated an S-scheme heterojunction (g-C3N4/ZnO composite photocatalyst) via one-pot calcination of a mixture of ZIF-8 and melamine in the KCl/LiCl molten salt medium. The KCN/ZnO composite produced 4.72 mM of H2O2 within 90 min under illumination (with AM 1.5 filter), which is almost 1.3 and 7.8 times than that produced over KCN and ZnO, respectively. Simultaneously, the KCN/ZnO also showed excellent photodegradation performance for the dye pollutants (Rhodamine B, RhB), with a removal rate of 92 % within 2 h. The apparent degradation rate constant of RhB over KCN/ZnO was approximately 5–8 times that of KCN and ZnO. In the photocatalytic process, photo-generated holes and superoxide radicals are the main active species. Oxygen (O2) was mainly reduced to produce H2O2 via a two-electron (2e−) pathway with superoxide radicals as intermediates and the 2e− oxygen reduction reaction selectivity of KCN/ZnO was close to 69.82 %. Photo-generated holes are mainly responsible for the degradation of RhB. Compared with pure KCN and ZnO, the enhanced photocatalytic activity of the KCN/ZnO composite is mainly attributed to the following aspects: 1) larger specific surface area and pore volume is beneficial to expose more active sites; 2) stronger light harvesting ability and red-shifted absorption edge bestow the compound a stronger light utilization efficiency; 3) the construction of S-scheme heterostructure between KCN and ZnO improve the photogenerated electron-hole pairs separation ability and bestow photogenerated carriers a higher redox potential.

Overview of corrosion behaviour of ceramic materials in molten salt environments

This study reviewed previous studies between the years 2015 and 2021 on how ceramic materials degraded in the presence of molten salt environments. The processes of corrosion resistance of various ceramic compositions subjected to various molten salt compositions and temperatures were also scrutinized. The results offer important new insights into the variables affecting ceramics' corrosion behaviour and the production of corrosion products. The reported result reveals that the ceramic material with the composition (Sm0.5Sc0.5)2Zr2O7 performed better than that of Sm2Zr2O7 in terms of hot corrosion resistance in molten salt (V2O5 + Na2SO4). It has also been reported that corrosion behaviour is influenced by particle size. Notably, zirconia (n-YSZ) with nanoscale grain sizes was more susceptible to hot corrosion, which was explained by increased specific surface areas. On the other hand, sintering and additives have been found to enhance corrosion resistance. The Y-Y2Si2O7 ceramic's resistance to corrosion in (V2O5 + Na2SO4) molten salt was enhanced by the addition of alumina. The results of these investigations help us understand how corrosion works and what influences ceramic materials' susceptibility to deterioration in molten salt media. This information can direct the creation of more corrosive-resistant ceramic materials for use in high-temperature environments or molten salt-based energy systems, among other corrosive uses.

Design and Simulations of Solar-Based Hydrogen Production System via Methane Decomposition

A solar-based hydrogen production system is analyzed and studied with the intention of optimizing the parameters involved in oil refining industry and the environment of the United Arab Emirates. Methane decomposition in molten salt media using a concentrated solar power system was adopted, since the temperature range required in the system design is achievable with this method. The System Advisor Model software was used in this study with three cases to optimize the system using the levelized cost of heat concept. In Case 1, a levelized cost of heat of 9.32 ¢/kWh was achieved using an optimized system with a CSP-RTUVR-2014 receiver and a Luz LS-3 collector. The design of Cases 1 and 2 exhibited pressure drops along the system of just 10 bar, significantly lower than the 50 bar of Case 3. Similarly, designs of Cases 1 and 2 resulted in maximum receiver thermal losses of around 7 MW, whereas Case 3 yielded 14 MW loss. Analysis of the best-suited molten salt option showed that HITEC solar salt was better than HITEC XL and standard HITEC. A regression analysis was carried out to examine the pressure drop responses since it is a key variable affecting the integrity of the solar system. It was observed that the receiver mass flow rate is the main contributing cause of pressure drop. Through careful operator control of receiver mass flow rate, premature failures of the solar system caused by the pressure drop can be avoided.

Enhanced service performances of in-situ Mg-Sialon/MgAl2O4 folding structure in low carbon Al2O3–C refractories: Phase reconfiguration of nano-MgSiN2

The utilization of in-situ ceramic combination effectively addressed the issue of weak bonding at the interface in low carbon Al2O3–C refractories, enhancing the material service performances. In this study, nano-MgSiN2 synthesized from molten salt was utilized for incorporation of Al2O3–C refractories, as well as in assessment of mechanical properties, thermal shock stability, oxidation resistance and corrosion resistance. The findings demonstrate that the molten salt medium can lower synthesis temperature and decrease particle size of nano-MgSiN2. In addition, nano-MgSiN2 undergone phase reconfiguration at 1500 °C to form Mg(g) and Si3N4(s). The folding structure Mg-Sialon/MgAl2O4 were formed through phase reconfiguration of Mg(g) and Si3N4(s). This change enhanced interfacial bonding strength of Mg-Sialon/Al2O3 and MgAl2O4/Al2O3. The mechanical properties and thermal shock stability of refractories were enhanced by novel reconfiguration technology, resulting in CCS value of 176.9 MPa. Simultaneously, Mg-Sialon transformation facilitated the interconnection of the oxide layer, enhancing oxidation resistance and corrosion resistance.

Direct Tungsten Extraction from Scheelite in a Molten Salt Media

Direct Tungsten Extraction from Scheelite in a Molten Salt Media

Enhanced CO2 capture and reverse water gas shift reaction using CaO in NaCl-CaCl2 molten salt medium

This study introduces an Integrated Carbon Capture and Utilisation-Reverse Water Gas Shift (ICCU-RWGS) approach, a novel method for in situ CO2 adsorption and conversion, leveraging the synergistic effects of CaO within a NaCl-CaCl2 molten salt blend to enhance CO2 capture and conversion efficiency. Building upon this foundation, we optimize CaO concentration and operating temperature to maximize CO2 uptake and conversion performance. The research focuses on integrating CaO with a NaCl-CaCl2 molten salt blend (mass ratio 4:6) to improve CO2 sorption and conversion performance. Findings show significant enhancements in CO2 uptake and CO yield with the presence of molten salt compared to systems without it. The optimal operating temperature and CaO concentration are identified for maximum CO yield. Characterisation techniques like in-situ infrared spectroscopy, XRD, and SEM provide insights into the behavior of CaO in the molten salt, revealing the solubility of the partial carbonate formed from CO2 and CaO, dispersion of CaO particles, and their morphological characteristics. Overall, the study demonstrates the potential of CaO-molten salt integration in improving ICCU-RWGS process efficiency and contributes to the development of more effective and sustainable ICCU technologies.

Kinetics of electrochemical Eu3+ to Eu2+ reduction in aqueous media

All lanthanides have a stable trivalent oxidation state, but some of them can also occur in the divalent or tetravalent state. Europium is well-known for its divalent oxidation state, which has been investigated in aqueous, organic, and molten salt media. In contrast to other lanthanides, Eu3+ can be easily reduced (Eo=−0.34 V vs. SHE) via chemical, electrochemical or photochemical routes, and Eu2+ is quite stable in a variety of electrolytes, including nitrate salts. To date, the kinetics of the Eu3+/Eu2+ reduction reaction has been investigated only by polarography and chronopotentiometry, most often in perchlorate medium. In this study, the kinetics of the Eu3+/Eu2+ couple were analysed in nitrate, chloride and perchlorate media by cyclic voltammetry and linear sweep voltammetry with a rotating disk electrode (RDE). The diffusion coefficient, charge transfer coefficient and rate constants were calculated based on the Levich and Koutecký-Levich analysis and Tafel plot to gain insight in the electrochemical process and the influence of the electrolyte type on it. Given the pre-existing characterization of this redox couple in perchlorate medium, it is selected as a reference system to both compare the kinetic parameters and to validate whether the methodology can be applied to other electrolytes. The Eu3+ reduction reaction was found to be quasi-reversible in these electrolytes and the calculated kinetic parameters are in line with the previously reported values.

Multiple‐dimensioned defect engineering for graphite felt electrode of vanadium redox flow battery

AbstractThe scarcity of wettability, insufficient active sites, and low surface area of graphite felt (GF) have long been suppressing the performance of vanadium redox flow batteries (VRFBs). Herein, an ultra‐homogeneous multiple‐dimensioned defect, including nano‐scale etching and atomic‐scale N, O co‐doping, was used to modify GF by the molten salt system. NH4Cl and KClO3 were added simultaneously to the system to obtain porous N/O co‐doped electrode (GF/ON), where KClO3 was used to ultra‐homogeneously etch, and O‐functionalize electrode, and NH4Cl was used as N dopant, respectively. GF/ON presents better electrochemical catalysis for VO2+/VO2+ and V3+/V2+ reactions than only O‐functionalized electrodes (GF/O) and GF. The enhanced electrochemical properties are attributed to an increase in active sites, surface area, and wettability, as well as the synergistic effect of N and O, which is also supported by the density functional theory calculations. Further, the cell using GF/ON shows higher discharge capacity, energy efficiency, and stability for cycling performance than the pristine cell at 140 mA cm−2 for 200 cycles. Moreover, the energy efficiency of the modified cell is increased by 9.7% from 55.2% for the pristine cell at 260 mA cm−2. Such an ultra‐homogeneous etching with N and O co‐doping through “boiling” molten salt medium provides an effective and practical application potential way to prepare superior electrodes for VRFB.

Prussian blue analogues-derived 2D NiCo@C bimetals grown on g-C3N4 as photocatalysts for hydrogen evolution

The development of highly active and stable cocatalysts using earth-abundant transition metals to replace noble metals is important for the application of photocatalytic hydrogen production technology. In this study, two-dimensional (2D) carbon-encapsulated NiCo bimetallic nanosheets (NiCo@C) was designed for the first time as a new co-catalyst to synergistically combine with graphitic carbon nitride (g-C3N4) and promote its hydrogen evolution. The NiCo@C cocatalysts were using an innovative molten salt method by using nickel hexacyanocobaltate Ni3[Co(CN)6]2 (Ni-Co PBA) nanocubes as precursor. The Ni-Co PBA nanocubes undergo dissolution growth and salt templating processes to form bimetallic 2D nanosheets during charring in molten salt media, and combine with 2D g-C3N4 to form NiCo@C/g-C3N4 photocatalyst. The optimized NiCo@C/g-C3N4 photocatalyst significantly improved the H2 evolution activity, and the H2 evolution rate reached 3791.07 μmol·g−1·h−1, which was 5 times higher than that of the particle CoNi/g-C3N4 (636.89 μmol·g−1·h−1). The H2 evolution activity was also comparable to that of the photocatalytic activity of 1.0% Pt/g-C3N4 system, indicating that the earth-abundant NiCo@C can replace noble metal as a cocatalyst to significantly enhance the photocatalytic performance of 2D photocatalysts. The conversion of three-dimensional Ni-Co PBA into carbon-coated 2D metal nanosheets by molten salt-assisted pyrolysis provides a feasible approach to explore the synthesis and design of efficient and robust non-precious metal catalysts.

Ternary molten salt-assisted lignin pyrolysis for the co-production of monophenols and value-added carbon materials

In this paper, the ternary molten salt (Li2CO3-Na2CO3-K2CO3) was introduced into the lignin pyrolysis process for the co-production of monophenols and value-added carbon materials. The effect of lignin/molten salt ratios (i.e., 3:1, 1:1, and 1:3) on lignin pyrolysis behaviour was investigated herein. The pyrolytic products were characterized by gas chromatography–mass spectrometry, ultimate analyses, scanning electron microscopy, nitrogen adsorption analyses, and Raman analyses. Results showed that molten salt media can promote the conversion of bulky phenolic oligomers into mono-phenols by enhancing the cracking and deoxygenation reactions. P-type phenols (49.76 %) were produced when the lignin/molten salt mass ratio was 1:3. The porosity and aromaticity of biochar were regulated in-situ using molten salt. The possible catalytic effect of molten salt on lignin pyrolysis was proposed. This study provides a case reference for lignin waste resource utilization.

Activity gradient mass transport accelerated corrosion of stainless steel in molten salt

Advanced energy systems based on molten salt technologies have gained increasing interest, and their design and construction are likely going to involve the use of materials of dissimilar chemistries. With dissimilar materials being used, galvanic coupling induced corrosion acceleration is one of the mechanisms believed to be an issue for the deployment of molten salt systems. However, non-galvanic interaction mechanisms such as activity gradient mass transport have also been theorized to represent a potential challenge. Unfortunately, the two effects have often been compounded in the literature, such that it is still unclear which degradation mechanisms are at play in these systems. In the following study, electrochemical measurements are used to predict the effect that galvanic coupling would have on dissimilar materials submerged in the same molten salt medium. Dissimilar material salt exposure tests are then performed to investigate whether galvanic coupling or activity gradient driven processes account for the levels of materials degradation observed. These separate effect electrochemical and corrosion experiments uniquely elucidate the degradation mechanisms in dissimilar materials systems.

Molten Salts‐Driven Discovery of a Polar Mixed‐Anion 3D Framework at the Nanoscale: Zn4Si2O7Cl2, Charge Transport and Photoelectrocatalytic Water Splitting

AbstractMixed‐anion compounds widen the chemical space of attainable materials compared to single anionic compounds, but the exploration of their structural diversity is limited by common synthetic paths. Especially, oxychlorides rely mainly on layered structures, which suffer from low stability during photo(electro)catalytic processes. Herein we report a strategy to design a new polar 3D tetrahedral framework with composition Zn4Si2O7Cl2. We use a molten salt medium to enable low temperature crystallization of nanowires of this new compound, by relying on tetrahedral building units present in the melt to build the connectivity of the oxychloride. These units are combined with silicon‐based connectors from a non‐oxidic Zintl phase to enable precise tuning of the oxygen content. This structure brings high chemical and thermal stability, as well as strongly anisotropic hole mobility along the polar axis. These features, associated with the ability to adjust the transport properties by doping, enable to tune water splitting properties for photoelectrocatalytic H2 evolution and water oxidation. This work then paves the way to a new family of mixed‐anion solids

Molten Salts-Driven Discovery of a Polar Mixed-Anion 3D framework at the nanoscale: Zn4Si2O7Cl2, Charge Transport and Photoelectrocatalytic Water Splitting.

Mixed-anion compounds widen the chemical space of attainable materials compared to single anionic compounds, but the exploration of their structural diversity is limited by common synthetic paths. Especially, oxychlorides rely mainly on layered structures, which suffer from low stability during photo(electro)catalytic processes. Herein we report a strategy to design a new polar 3D tetrahedral framework with composition Zn4Si2O7Cl2. We use a molten salt medium to enable low temperature crystallization of nanowires of this new compound, by relying on tetrahedral building units present in the melt to build the connectivity of the oxychloride. These units are combined with silicon-based connectors from a non-oxidic Zintl phase to enable precise tuning of the oxygen content. This structure brings high chemical and thermal stability, as well as strongly anisotropic hole mobility along the polar axis. These features, associated with the ability to adjust the transport properties by doping, enable to tune water splitting properties for photoelectrocatalytic H2 evolution and water oxidation. This work then paves the way to a new family of mixed-anion solids.

Pyrolysis of LignoBoost lignin in ZnCl2-KCl-NaCl molten salt media: Insights into process-pyrolysis oil yield and composition relations

Depolymerization of lignin by pyrolysis has been identified as a viable route to produce renewable fuels and biobased platform chemicals. Herein we report the pyrolysis of LignoBoost lignin in a molten salt consisting of ZnCl2-KCl-NaCl (60:20:20 mol ratio) in a g-scale reactor set-up with a focus on the liquid phase yields and composition. The effects of relevant process parameters such as temperature (250–450 °C), reaction time (10–50 min), and N2 flow rate (10–30 mL min−1) on the product yields were elucidated using design of experiments. The highest bio-oil yield was 47.1 wt% (450 °C, 10 min) and the yield of organics in the bio-oil at this condition was 24 wt% (on lignin intake), the remainder being water. The latter is considerably higher than found for an experiment at similar conditions without salt (16 wt%). Temperature and reaction time were shown to have the largest effects on bio-oil yield. Prolonged reaction times resulted in higher amounts of gas phase components (H2, CO2) and water, and a reduced amount of solid products. Statistical analyses and validation experiments showed that the experimental product yields are in good agreement with the predicted values from the model. The properties and molecular composition of the liquid products were determined using various analytical techniques and reveal that the presence of a molten salt during pyrolysis has a positive influence on the composition of the liquid phase like a higher level of depolymerization and higher selectivity to aromatic and phenolic monomers compared to thermal pyrolysis.

One step molten salt synthesis of nickel nanoparticles incorporated on graphene sheets as non-precious and an effective electrocatalyst for methanol oxidation

Fabricating electrocatalysts based on metal nanoparticles (NPs)/carbon nanomaterials by a facile and cost-effective method have attracted serious attention in the past several years to expand their applications. This study aimed to prepare an effective electrocatalyst based on nickel nanoparticles decorated graphene sheets (NiNPs@Gr) by molten salt synthesis method and to clarify its advantages compared to the calcination method without molten salt. The microscopic characterization revealed that the calcination of nickel/carbon precursors in the molten salt medium resulted in nickel NPs supported on graphene sheets, whereas produce NPs with larger sizes supported on porous carbon without molten salt. X-ray diffraction analysis showed that the catalysts prepared by the molten salt method (NiNPs@Gr-S1 and NiNPs@Gr-S2) resulted in nickel NPs with a mixture of crystalline structures (face-centered cubic and hexagonal close-packed). The electrocatalytic activity of NiNPs@Gr-S1 and NiNPs@Gr-S2 toward methanol oxidation was higher than that of the NiNPs@C catalyst prepared without molten salt. The maximum peak current density of NiNPs@C, NiNPs @Gr-S1, and NiNPs @Gr-S2 are 30, 80, and 81.5 mA/cm2, respectively. Moreover, electrocatalysts derived from molten salt synthesis demonstrated significantly increased electrocatalytic stability. These results emphasize the synthesis of graphene nanosheet-supported Ni NPs in a single step without any additional chemicals, which makes such a strategy promising in trust acquisition for investors in large-scale production of NiNPs@Gr.

Sparging-based fission gas separation technology for molten salt reactor

Thorium molten salt reactor is one of the GEN-IV Molten Salt Reactors currently developed in China. The online removal of fission gases like Xenon and Krypton is a crucial technique to achieve high burnup of the liquid nuclear fuel. One of the promising candidates for practical application is the bubble sparging method, where tiny bubbles are first introduced into the liquid fuel, then the fission gases migrate to the carrier bubbles by interfacial mass transfer, and finally, a gas–liquid separator is used to remove the carrier bubbles along with the absorbed fission gases from the liquid. A thorough understanding of the mechanism and accurate modeling for the three sub-processes mentioned-above, namely bubble generation, mass transfer, and gas–liquid separation, are necessary for quantitative control of the fission gas removal performance.As for the bubble injection, the microbubble generating approach based on turbulent fragmentation mechanism is proposed, the predicting model of bubble diameter and the design criterion of bubble generator were established, constructing a generation and control technology of microbubbles for molten salt medium. For the mass transfer process, a novel numerical method simulating the interfacial migration of dissolved gases in bubbly flow is developed. Besides, a compact gas–liquid reactor with enhanced mass transfer efficiency applied to nuclear installations is proposed. In terms of the separation of bubbles, the separation length and stability of the swirling flow gas–liquid separator are investigated, and a solution of gas–liquid separation with ultra-high separation efficiency under extremely low gas fraction conditions is proposed. The feasibility and efficiency of the fission gas separation technology integrating all three procedures have been evaluated experimentally, providing a solid foundation for the future online post-processing of both off-gas and liquid fuel.

Electrochemical Deposition with Redox Replacement of Lanthanum with Uranium in Molten LiCl-KCl

Electrochemical recovery of dilute concentrations of actinides from spent nuclear fuel would reduce the longevity of storing high-level nuclear waste. Electrochemical deposition with redox replacement (EDRR) is used in a molten salt medium for the selective electrochemical recovery of uranium in the presence of excess concentrations of lanthanum. In each EDRR cycle, after a short electrodeposition pulse, the deposited lanthanum is spontaneously replaced by uranium at open circuit. After repeated cycles, uranium metal was obtained on a tungsten electrode immersed in a LiCl-KCl melt that contained 1 wt% lanthanum chloride—0.15 wt% uranium (IV) chloride. Scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS) analysis revealed uranium particles approximately 0.5−1 μm with well-defined rectangular shapes; and with 20–60 times more uranium recovered on the surface of the electrode than lanthanum.