Spent Nickel Metal Hydride Batteries Research Articles

All-metal recovery from spent Ni-MH batteries based on electrolysis of sodium sulfate solution

A sustainable strategy for all-metal recycling from spent nickel metal hydride (Ni-MH) batteries was proposed, where H2SO4 and NaOH solutions by the electrolysis of Na2SO4 solution were used as the leaching agent and precipitation agent, respectively. The leaching of electrode materials was performed in mild condition, and more than 99% of the rare earths were firstly precipitated at pH 1.0 in the form of double sulphates, which were converted to hydroxides by reacting with NaOH. In the following purification steps, Al3+ and Fe3+ were deposited at pH 5.5, and Zn2+ and Mn2+ were extracted by saponified D2EHPA–kerosene from the leaching solution, and two hydroxide byproducts with industrial application were obtained. Ni2+ and Co2+ were precipitated at pH 9.5 with a total recovery rate of 97.5%. The recovery efficiency of Na2SO4 was up to 97% in total. This metal recovery approach produces considerable economic profit, without solid or liquid waste in the closed-loop process.

Selective Precipitation of Rare Earth Double Sulfate Salts from Industrial Ni–MH Battery Leachates: Impact of Downstream Processing on Product Quality

This work focuses on the recovery of rare earth elements (REEs = La, Ce, Nd, Pr) from spent nickel–metal hydride batteries by hydrometallurgical processing. The REEs were precipitated in the form of sodium-lanthanide double sulfate salts by adding Na2SO4 to a leach liquor prepared from industrially processed spent batteries. The objectives were to better understand the parameters driving the purity of the product and to identify the phases involved, as well as their crystallographic structure. The methodology included experiments performed in a 2 L reactor, thermodynamic calculations and product characterization. We confirmed that high REE precipitation yields (>95%) can be achieved under a wide range of hydrodynamic conditions. Furthermore, we demonstrated and quantified how appropriately washing the product allows for a significant reduction in nickel losses while maintaining control over REE product purity. Finally, using X-ray Diffraction analyses, it was established that REEs form a solid solution with a chemical formula (Na0.9K0.1)(La0.65Ce0.24Pr0.04Nd0.07)(SO4)2·H2O, which has not been reported so far.

Optimization of metals and rare earth elements leaching from spent Ni-MH batteries by response surface methodology

ABSTRACT The rechargeable battery market has almost doubled in 15 years. Regardless of the type of batteries, their limited lifespan means that sooner or later they will constitute a mass of waste whose management is problematic as their content is high in elements and metals of high economic interest, but also toxic to the environment. This project is to optimize the solubilization conditions for rare earth elements (REEs) and other metals from waste nickel-metal hydride (Ni-MH) batteries. The Ni-MH battery powder used contained the following main elements: Ni (548 g/kg), La (45 g/kg), Co (32 g/kg), Zn (22 g/kg), Nd (15 g/kg), Sm (12 g/kg), and Ce (11 g/kg). The metals were solubilized in the presence of sulfuric acid. Acid concentration, solids concentration, leaching time, and temperature were optimized using the Box–Behnken design methodology. The optimal conditions identified are an H2SO4 concentration of 2 M, a S:L ratio of 10% (w:v), a leaching temperature of 60°C and a reaction time of 90 min. These conditions make it possible to solubilize 81% Ni, 99% Co, and 70% REEs, while the mathematical model predicted 83% Ni, 100% Co, and 80% REEs respectively. The process was also operated in counter-current leaching mode with the optimal parameters. The high solubilized yields obtained after five loops for all metals, REE and the significant reduction of water consumption confirm that this process leaching can be apply for industrial application.

Upcycling of nickel oxide from spent Ni-MH batteries as ultra-high capacity and stable Li-based energy storage devices

Due to the rapid expansion of portable electronics and electric vehicles market, the projected demand of rechargeable batteries is huge and may lead to shortage of critical minerals, especially nickel (Ni) metal. In the present study, we upcycled NiO material from spent Nickel–Metal hydride batteries (Ni-MH) as electrodes in Li-ion battery (LIB) and supercapacitor. Intriguingly, recycled NiO was applied successfully to develop sustainable LiNi0.5Mn1.5O4 (LNMO) cathode, delivering the promising capacity. As the recovered NiO-anode in LIBs, the device exhibited ultrahigh capacity of 1248 mAh g−1 at 0.1C, exhibiting excellent rate capability and cycle life in traditional carbonate-based electrolyte. The full cell with NMC cathode gave a high discharged capacity of 137.4 mAh/g. Addition to conventional electrolyte, a safe and non-flammable diglyme electrolyte using recovered NiO was investigated under identical condition. The maximum reversible capacity of 642 mAh g−1 at 0.1C was achieved along with good rate performance. Likewise, the NiO-based supercapacitor electrode delivered a maximum capacitance of 106C g−1 at 0.5 A g−1. Hence, upcycling of abundant NiO waste as low-cost electrode materials from end-of-life batteries paves the way for future generation of Li-based energy storage devices and sustainable supply of critical minerals and clean environment.

Selective separation of lanthanide group in spent NiMH battery acidic leaching solutions

A novel selective separation of lanthanide group (Ln) known as rare earth elements (REEs) from acidic leaching solutions of spent nickel metal hydride (NiMH) batteries was examined using precipitation at low pH with disodium phosphate, Na2HPO4, as precipitation agent. The acidic leaching solutions containing lanthanides (La, Ce, and Nd) and base metals (Ni, Cd, Mn, Fe, Al, and Zn) were from spent NiMH batteries subject to subcritical water extraction (SWE) process using 0.5 mol/L of HCl, HNO3, and H2SO4 solution, respectively. The effects of important parameters such as the molar ratio of lanthanides to phosphate ions, Ln/P, to form precipitates of lanthanide phosphates (Ln(PO4)), pH and temperature were investigated. The recovery efficiency of lanthanides increased when decreasing Ln/P, while increased with increasing pH and temperature. The decrease in the concentration of Ln remaining in HCl and HNO3 leaching solutions was proportional to the decrease in the P concentration in leaching solutions, while different results were found in the leaching solution of H2SO4 due to the formation of another insoluble lanthanide mineral, double sulfate (NaLn(SO4)2·H2O). This separation process demonstrated that the high-purity lanthanide group including La, Ce, and Nd from spent NiMH batteries could be obtained simply by adding phosphate ions at low pH. It is efficient, effective, and selective for critical rare metals recovery from spent NiMH batteries.

A systematic analysis of the costs and environmental impacts of critical materials recovery from hybrid electric vehicle batteries in the U.S.

SummaryCritical materials such as rare earth underpin technologies needed for a decarbonized global economy. Recycling can mitigate the supply risks created by the increasing demand and net import dependence, and enable a circular economy for critical materials. In this study, we analyze the feasibility and life-cycle impacts of recovering critical materials from spent nickel metal hydride batteries from hybrid electric vehicles in the U.S., accounting for stocks, battery scrappage, and end-of-life reverse logistics, given uncertain future availability scenarios. Our results show that the total collection and recycling costs depend strongly on future battery availability, with marginal costs exceeding marginal revenues when the availability of spent batteries declines. We quantify the potential of recycling to reduce primary imports, as well as the accompanying climate change and resource impacts. We explore the underlying reverse logistics infrastructure required for battery recycling and evaluate strategies for reducing associated capital investment risk.

Efficient Recovery of Rare Earth Elements and Zinc from Spent Ni-Metal Hydride Batteries: Statistical Studies.

Considering how important rare earth elements (REEs) are for many different industries, it is important to separate them from other elements. An extractant that binds to REEs inexpensively and selectively even in the presence of interfering ions can be used to develop a useful separation method. This work was designed to recover REEs from spent nickel–metal hydride batteries using ammonium sulfate. The chemical composition of the Ni–MH batteries was examined. The operating leaching conditions of REE extraction from black powder were experimentally optimized. The optimal conditions for the dissolution of approximately 99.98% of REEs and almost all zinc were attained through use of a 300 g/L (NH4)2SO4 concentration after 180 min of leaching time and a 1:3 solid/liquid phase ratio at 120 °C. The kinetic data fit the chemical control model. The separation of total REEs and zinc was conducted under traditional conditions to produce both metal values in marketable forms. The work then shifted to separate cerium as an individual REE through acid baking with HCl, thus leaving pure cerium behind.

Recovery of rare earth elements from spent NiMH batteries using subcritical water extraction with citric acid

Spent nickel-metal hydride (NiMH) batteries contain high concentrations of rare earth elements (REEs), nickel (Ni), and cobalt (Co). Subcritical water extraction (SWE) process with citric acid as the leaching reagent was applied to spent NiMH batteries. The effects of acid concentration, solid to liquid ratio (S/L), reaction time, and reaction temperature were examined. Leaching efficiency increased with increasing acid concentration, reaction time and temperature, and decreased as S/L increased. Total of 90.85% of lanthanum (La), 88.84% of cerium (Ce), 90.85% of neodymium (Nd), 90.70% of Ni, and 91.62% of Co were leached out using 2.0 N of citric acid, S/L of 10 g/L, at 150 °C in 5 min. Selective precipitation of REEs was induced by the addition of diluted waste phosphoric acid (H3PO4) to the leaching solutions. At [H3PO4]:[REEs] of 10:1, pH 2.0, and 65 °C, 99.3% of La, 98.8% of Ce, and 99.0% of Nd were precipitated, which correspond to overall recovery of 90.2% of La, 87.8% of Ce, and 89.8% of Nd. The results showed that SWE using citric acid followed by selective precipitation with H3PO4 could effectively recover REEs from spent NiMH batteries.

Recovery of nickel, cobalt and rare-earth elements from spent nickel–metal-hydride battery: Laboratory tests and pilot trials

The recycling of nickel, cobalt and rare earths from spent nickel–metal-hydride batteries was investigated. Nickel and cobalt were recovered as a nickel–cobalt mixed sulfide, which can be used as an intermediate raw material in existing nickel refineries. Rare earths were recovered as double sulfates, which can be recycled into industrial materials. In the recovery of rare earths, yttrium, a heavy rare earth, could be precipitated and recovered by co-precipitation with a light rare-earth double sulfate, which was considered impossible by the double-sulfate precipitation method because of high solubility of yttrium double sulfate. On the other hand, the coprecipitation behavior of yttrium was found to be unstable at the pilot scale because the stirring force was weaker than that in the laboratory experiments. In this study, the optimum conditions for leaching, double-sulfate precipitation, and sulfide precipitation reactions were determined in a laboratory test and the good performance was demonstrated in a pilot test. Based on the results, the estimated metal yields were 87% nickel, 90% cobalt, 54% yttrium, 99% lanthanum and 99% cerium. The nickel and cobalt impurities in the double sulfate that were recovered by this process were 0.04% and 0.005%, respectively, and the rare-earth impurities in the nickel–cobalt mixed sulfide were low at 0.049% yttrium, 0.007% lanthanum and 0.003% cerium. This process combined with a precipitation method showed a high separation performance.

Recovery of Rare Earth Metals (REMs) from Nickel Metal Hydride Batteries of Electric Vehicles

Nickel metal hydride (NiMH) batteries are extensively used in the manufacturing of portable electronic devices as well as electric vehicles due to their specific properties including high energy density, precise volume, resistance to overcharge, etc. These NiMH batteries contain significant amounts of rare earth metals (REMs) along with Co and Ni which are discarded due to illegal dumping and improper recycling practices. In view of their strategic, economic, and industrial importance, and to mitigate the demand and supply gap of REMs and the limited availability of natural resources, it is necessary to explore secondary resources of REMs. Therefore, the present paper reports a feasible hydrometallurgical process flowsheet for the recovery of REMs and valuable metals from spent NiMH batteries. More than 90% dissolution of REMs (Nd, Ce and La) was achieved using 2 M H2SO4 at 75 °C in 60 min in the presence of 10% H2O2 (v/v). From the obtained leach liquor, the REMs, such as Nd and Ce, were recovered using 10% PC88A diluted in kerosene at eq. pH 1.5 and O/A ratio 1/1 in two stages of counter current extraction. La of 99% purity was selectively precipitated from the leach liquor in the pH range of 1.5 to 2.0, leaving Cu, Ni and Co in the filtrate. Further, Cu and Ni were extracted with LIX 84 at equilibrium pH 2.5 and 5, leaving Co in the raffinate. The developed process flow sheet is feasible and has potential for industrial exploitation after scale-up/pilot trails.

Selective recovery of rare earth elements (REEs) from spent NiMH batteries by two-stage acid leaching

The current study investigated selective recovery of rare earth elements (REEs) from spent nickel metal hydride (NiMH) batteries using two-stage acid leaching followed by precipitation at acidic pH. The first-stage conventional leaching using 2.5 M of waste phosphoric acid (H3PO4) at 25 °C for 60 min removed 60–100% heavy metals, such as Ni, Co, Zn and Cd, and converted more than 90% REEs into insoluble phosphate precipitates, REE(PO4). Subcritical water extraction (SWE) using mild concentration of sulfuric acid (H2SO4) in the second stage leached out all REEs. The leaching efficiency of REEs increased by increasing acid concentration, and 100% leaching efficiency of REEs, Ni, Co and Mn were achieved using 1 M of H2SO4, solid concentration of 20 g/L, at 125 °C for 30 min. As predicted by species distribution of metals at equilibrium, REEs in the leaching solution were selectively precipitated as NaREE(SO4)2·H2O at low pH (0.5–2) by the addition of NaOH solution, and separated from other metals (Ni, Co, Mn). Precipitation at pH 1 resulted in 82.59% of La, 90.75% of Ce, and 85.97% of Nd recovered as hexagonal rod crystals. This study provides an alternative process to selectively recover REEs from electronic waste (e-waste).

Process intensification for valuable metals leaching from spent NiMH batteries

Acid leaching is an essential unit in hydrometallurgy, yet it is time consuming and requires concentrated acids. Process intensification is examined for the leaching of valuable and rare earth elements (REEs), such as Ni, Co, La, Nd, and Ce, from spent nickel metal hydride (NiMH) batteries using subcritical water extraction (SWE) and microwave-assisted extraction (MAE). Results of SWE revealed that HCl performed better than H2SO4 and HNO3. Leaching efficiency increased as reaction temperature increased from 100 to 150°C, and it increased with HCl concentration. SWE was very effective using 0.5 N HCl, solid concentration of 20 g/L, initial pressure of 9.8 bar, 100°C for 5 min, and leaching efficiency of 99.85% for Ni, 91.72% for Co, 96.26% for La, 85.75% for Nd, and 84.37% for Ce was found, and the total energy consumption was 2,640 kJ. Leaching efficiency of MAE using 0.5 N HCl decreased slightly when heating rate increased from 30 to 70°C/min, and it increased as reaction time increased from 5 to 30 min. Compared with SWE and conventional leaching, MAE was the most energy-efficient, and total of 874.1 kJ was required to reach 85.93% for Ni, 77.60% for Co, 64.04% for La, 75.01% for Nd, and 57.17% for Ce, respectively under experimental conditions of 1 N of HCl, solid concentration of 20 g/L, 100°C for 5 min. Novel acid leaching methods showed promising potential for metals recovery from e-waste.

Leaching of rare earth elements and base metals from spent NiMH batteries using gluconate and its potential bio-oxidation products

Gluconate is known to mediate metal leaching. However, during bioleaching by e.g., Gluconobacter oxydans, gluconate can be oxidized to 2-ketogluconate and 5-ketogluconate. The impact of bio-oxidation of gluconate on metal leaching has not been investigated. Therefore, the aim of this study was to investigate leaching of rare earth elements (REEs) and base metals from spent nickel-metal-hydride (NiMH) batteries using gluconate, 2-ketogluconate and 5-ketogluconate. Batch leaching assays were conducted under controlled and uncontrolled pH conditions for 14 days using 60 mM of either the individual leaching agents or their various combinations. At target pH of 6.0 ± 0.1 and 9.0 ± 0.1 and without pH control, complexolysis was the dominating leaching mechanism and higher REE leaching efficiency was obtained with gluconate, while 5-ketogluconate enabled more efficient base metal leaching. At target pH of 3.0 ± 0.1, acidolysis dominated, and the base metal and REE leaching yields with all the tested leaching agents were higher than under the other studied pH conditions. The highest base metal and REE leaching yields (%) were obtained using gluconate at target pH of 3.0 ± 0.1 being 100.0 Mn, 90.3 Fe, 89.5 Co, 58.5 Ni, 24.0 Cu, 29.3 Zn and 56.1 total REEs. The obtained results are useful in optimization of heterotrophic bioleaching.

Impacts of Phosphorous Source on Organic Acid Production and Heterotrophic Bioleaching of Rare Earth Elements and Base Metals from Spent Nickel-Metal-Hydride Batteries

This study investigated heterotrophic bioleaching of rare earth elements (REEs) and base metals from spent nickel-metal-hydride (NiMH) batteries. Furthermore, the impacts of phosphorous source [Ca3(PO4)2, KH2PO4 and K2HPO4] and its concentration on organic acid production by Gluconobacter oxydans and Streptomyces pilosus were evaluated. Phosphorous source affected microbial acid production and metal leaching. Among the studied phosphorous sources, use of K2HPO4 resulted in highest organic acid production by both bacteria. Increasing K2HPO4 concentration from 2.7 to 27 mM enhanced pyruvic acid production by S. pilosus from 2.2 to 10.7 mM. However, no metal was leached from the spent NiMH batteries with S. pilosus using either one-step, two-step or spent-medium bioleaching. With G. oxydans, highest gluconic acid concentration of 45.0 mM was produced at the lowest K2HPO4 concentration of 2.7 mM. When using two-step bioleaching with G. oxydans, higher leaching efficiencies were obtained for base metals (88.0% vs. 68.0% Fe, 41.5% vs. 35.5% Co, 18.5% vs 16.5% Ni), while more REEs were leached using spent-medium bioleaching (9.0% vs. 6.0% total REEs). With both bioleaching methods, base metals leaching was faster than that of REEs. Surplus of phosphorous should be avoided in bioleaching cultures as precipitation especially with REEs is possible.Graphic

An alternative approach to reclaim spent nickel–metal hydride batteries

AbstractSpent nickel‐metal hydride (NiMH) batteries contained some valuable metals which are worthy of recovery. This study focuses on the reclamation of spent NiMH batteries using an alternative approach, thermal separation process (TSP). Spent NiMH batteries were mixed with cullet, limestone, and dolomite. The mixture was heated to 1,450°C and cooled to room temperature without forced convection. During the TSP, the output‐materials were divided into slag, ingot, and flue gas according to the boiling points and densities of metals. Results show that metals having a relatively low boiling points, such as Cd, Hg, Pb, and Zn, were mostly vaporized into flue gas. Among the metals retained in molten materials, Co, Cu, Fe, and Ni predominately went into the bottom layer and formed the ingot; on the contrary, Al, Ca, Mg, and Si stayed in the upper layer and formed slag. Therefore, the main components of slag were Si (316,000 mg/kg), Ca (289,000 mg/kg), and Mg (32,400 mg/kg) and the major crystalline phases were CaSiO3, CaMgSi2O6, and Ca2MgSi2O7. The slag was pended as non‐hazardous materials and could be reused as road pavement or building materials. The ingot had high levels of Ni (408,000 mg/kg), Fe (349,000 mg/kg), and Co (55,400 mg/kg) and could act as an additive in stainless steel manufacturing process.

Leaching Mechanisms of Industrial Powders of Spent Nickel Metal Hydride Batteries in a Pilot-Scale Reactor.

In view of a sustainable recycling process, the leaching mechanisms of nickel and rare-earth elements (REEs) contained within industrial samples of spent nickel metal hydride battery powders were investigated in HCl and H2 SO4 , under mild temperature (25-60 °C) and pH (3-5.5). First, in-depth characterization of the heterogeneous battery powder was carried out with powder XRD, SEM, electron probe microanalyzer wavelength-dispersive spectroscopy (EPMA-WDS) quantitative analyses of individual particles, and inductively coupled plasma optical emission spectrometry (ICP-OES) elemental analysis. An unusual result is the identification of particles that exhibit a core-shell structure, which is related to anode active mass aging mechanisms. Then, a leaching study in a 10 L pilot-scale reactor demonstrated the selective dissolution of REEs, with respect to nickel, at pH 3, which is attributed to 1) the kinetic inhibition of nickel metal dissolution, and 2) the specific core-shell structure of aged mischmetal particles. Furthermore, the use of H2 SO4 led to coprecipitation of lanthanide-alkali double sulfates and nickel salts.

Symmetric All-Quinone Aqueous Battery

Lithium-ion batteries continue to dominate portable electronics and electric vehicles markets for its high energy density/specific energy.1However, combustible electrolytes and expensive cathodes pose safety and cost concerns to consumers.2 Further cost reduction is expected to be limited after decades of development.3Next generation energy storage devices call for safe, cheap, resource-abundant and flexible batteries.2, 4 Rechargeable batteries with cost-effective redox active materials and aqueous electrolytes can potentially meet these requirements.5 Aqueous battery chemistries include lead-acid batteries, nickel-metal hydride aqueous batteries, and emerging aqueous lithium/sodium-ion batteries, but they all have their Achilles’ heels.6 - 12 Here we report a symmetric all-quinone aqueous battery based entirely on Earth-abundant elements that uses a naturally-occurring dye as the redox-active material in both positive and negative electrodes. We demonstrate a symmetric all-quinone cell with 1.04 V of open circuit voltage, 163 mAh/g of capacity, and 100 cycles at 10C with 100% of depth of discharge. The use of the same quinone in a symmetric setup expands the repertoire of inexpensive redox active materials for aqueous rechargeable batteries, and the simple cell design will enable optimizations toward safe, cheap, lightweight, and flexible electronics in the future. Natural abundance and cheap commercial source promise its low cost when produced at large scale. In addition, we demonstrate that other fused quinone derivatives can also be used for symmetric quinone-acid batteries. Further optimization of fused quinones with improved reduction potential and stability, and cell engineering of electrode composition and morphology can further improve the performance of the battery. References Zubi, G.; Dufo-López, R.; Carvalho, M.; Pasaoglu, G., The lithium-ion battery: State of the art and future perspectives. Renewable and Sustainable Energy Reviews 2018, 89, 292-308. Armand, M.; Tarascon, J. M., Building better batteries. Nature 2008, 451, 6. Hsieh, I.-Y. L.; Pan, M. S.; Chiang,Y.-M.; and Green, W. H. Learning only buys you so much: practical limits on battery price reduction Applied Energy 2019, 239, 218. Larcher, D.; Tarascon, J. M., Towards greener and more sustainable batteries for electrical energy storage. Nat. Chem. 2015, 7(1), 19-29. Beck, F.; Rüetschi, P., Rechargeable batteries with aqueous electrolytes. Electrochimica Acta 2000, 45, 16. Chen, H. Y.; Li, A. J.; Finlow, D. E., The lead and lead-acid battery industries during 2002 and 2007 in China. Journal of Power Sources 2009, 191(1), 22-27. van der Kuijp, T.; Huang, L.; Cherry, C. R., Health hazards of China's lead-acid battery industry: a review of its market drivers, production processes, and health impacts. Environmental Health 2013, 12(61), 10. Ruetschi, P., Aging mechanisms and service life of lead–acid batteries. Journal of Power Sources 2004, 127(1-2), 33-44. Zou, X., Kang, Zongxuan, Shu, Dong, Liao, Yuqing, Gong, Yibin, He, Chun, Hao, Junnan, Zhong, Yayun, Effects of carbon additives on the performance of negative electrode of lead-carbon battery. Electrochimica Acta 2015, 151, 89-98. Rodrigues, L. E. O. C.; Mansur, M. B., Hydrometallurgical separation of rare earth elements, cobalt and nickel from spent nickel–metal–hydride batteries. Journal of Power Sources 2010, 195(11), 3735-3741. Ying, T. K.; Gao, X. P.; Hu, W. K.; Wu, F.; Noréus, D., Studies on rechargeable NiMH batteries. Int. J. Hydrogen Energy 2006, 31(4), 525-530. Kim, H.; Hong, J.; Park, K. Y.; Kim, H.; Kim, S. W.; Kang, K., Aqueous rechargeable Li and Na ion batteries. Chem. Rev. 2014, 114(23), 11788-827. Figure 1

Synergistic Recovery of Valuable Metals from Spent Nickel–Metal Hydride Batteries and Lithium-Ion Batteries

This research presents a sustainable approach for the simultaneous recycling of spent lithium-ion batteries (LIBs) and nickel–metal hydride batteries (NiMHs). First, dissolution of LIBs and NiMHs w...

Two stage leaching process for selective metal extraction from spent nickel metal hydride batteries

In this study, a closed loop two-stage leaching process has been experimentally and theoretically established for the selective dissolution of metals from electrode material of spent Ni-MH batteries. In the first step, baking parameters, such as temperature, acid concentration, and duration were optimized as 300 °C, 2 mL H2SO4 for 1.5 g of cathode powder, 90 min. The thermodynamic feasibility of the process ascertained the spontaneous formation of water-soluble sulfates of nickel, zinc, and rare earth elements during the acid baking. Post-baking, a two-stage leaching was performed for leaching of different metals present in the baked material. In first stage leaching with water, 91.73% Ni, 94% Zn, 91% rare earth elements were extracted with a low recovery of 36.5% Co, 22.1% Fe, 23.5% Mn at 75 °C in 1 h. Owing to the low recovery of Co and Mn, 2nd stage leaching was performed using NaHSO3 in H2SO4 at 95 °C for 1 h, improving extraction to Co (55%) and Mn (74%). The overall recovery of the metals was found to be 98.2% Ni, 91.4% Co, 98% Zn, 97.8% Mn and 96% rare earth elements. The two-stage process (baking and leaching) outperforms direct sulfuric acid leaching of cathode powder due to lower acid consumption and its selectivity of metals.

Characterization of spent nickel–metal hydride batteries and a preliminary economic evaluation of the recovery processes

Valuable metal materials can be recovered from spent nickel–metal hydride (NiMH) batteries. However, little attention has been paid to the metal compositions of individual components of NiMH batteries, although this is important for the selection of the appropriate recycling process. In this study, NiMH batteries were manually disassembled to identify the components and to characterize the metals in each of these. A preliminary economic analysis was also conducted to evaluate the recovery of valuable metals from spent NiMH batteries using thermal melting versus simple mechanical separation. The results of this study show that metallic components account for more than 60% of battery weight. The contents of Ni, Fe, Co, and rare earth elements (REEs) (i.e., valuable metals of interest for recovery) in a single battery were 17.9%, 15.4%, 4.41%, and 17.3%, respectively. Most of the Fe was in the battery components of the steel cathode collector, cathode cap, and anode metal grid, while Ni (>90%) and Co (>90%) were mainly in the electrode active materials (anode and cathode metal powders). About 1.88 g of REEs (Ce, La, and Y) could be obtained from one spent NiMH battery. The estimated profits from recovering valuable metals from spent NiMH batteries by using thermal melting and mechanical processes are 2,329 and 2,531 USD/ton, respectively, when including a subsidy of 1,710 USD/ton. The findings of this study are very useful for further research related to technical and economic evaluations of the recovery of valuable metals from spent NiMH batteries. Implications: The spent nickel–metal hydride (NiMH) batteries were manually disassembled and their components were identified. The metals account for more than 60% of battery weight, when Ni, Fe, Co, and rare earth elements (REEs) were 17.9%, 15.4%, 4.41%, and 17.3%, respectively, in a single battery. The estimated profits of recovering valuable metals from NiMH batteries by using thermal melting and mechanical processing are 2,329 and 2,531 USD/ton, respectively, when including a subsidy of 1,710 USD/ton. These findings are very useful to develop or select the recovery methods of valuable metals from spent NiMH batteries.