Sustainable technologies for the recycling and upcycling of precious metals from e-waste.

E-waste is the fastest growing solid waste in the world. Each year, over 50 million tonnes of e-waste are produced, with its rate increasing by 3-5 % annually. Currently, only 17 % of e-waste is properly recycled, leaving the majority managed unsustainably, thereby causing detrimental environmental and economic effects. Cleaner e-waste management technologies are essential to address this urgent and rapidly expanding issue. Precious metals within e-waste significantly contribute to recycling revenues. In this paper, we review state-of-the-art technologies for sustainable recycling and upcycling of these metals from e-waste, including cleaner extractive metallurgy, solution purification technologies, and direct synthesis of green nanomaterials. We also discuss the potential impacts and constraints of these technologies and provide recommendations for improving and implementing both existing and prospective technologies.

A review on the recycling of spent lithium iron phosphate batteries.

Lithium iron phosphate (LFP) batteries have gained widespread recognition for their exceptional thermal stability, remarkable cycling performance, non-toxic attributes, and cost-effectiveness. However, the increased adoption of LFP batteries has led to a surge in spent LFP battery disposal. Improper handling of waste LFP batteries could result in adverse consequences, including environmental degradation and the mismanagement of valuable secondary resources. This paper presents a comprehensive examination of waste LFP battery treatment methods, encompassing a holistic analysis of their recycling impact across five dimensions: resources, energy, environment, economy, and society. The recycling of waste LFP batteries is not only crucial for reducing the environmental pollution caused by hazardous components but also enables the valuable components to be efficiently recycled, promoting resource utilization. This, in turn, benefits the sustainable development of the energy industry, contributes to economic gains, stimulates social development, and enhances employment rates. Therefore, the recycling of discarded LFP batteries is both essential and inevitable. In addition, the roles and responsibilities of various stakeholders, including governments, corporations, and communities, in the realm of waste LFP battery recycling are also scrutinized, underscoring their pivotal engagement and collaboration. Notably, this paper concentrates on surveying the current research status and technological advancements within the waste LFP battery lifecycle, and juxtaposes their respective merits and drawbacks, thus furnishing a comprehensive evaluation and foresight for future progress.

Direct selective leaching of lithium from industrial-grade black mass of waste lithium-ion batteries containing LiFePO4 cathodes.

Demand for lithium-ion batteries (LIBs) is projected to maintain unprecedented acceleration for decades, towards satisfying international climate and source objectives. LIB wastes pose a threat to the environment, but also may be considered a strategic, high-grade resource. Yet, recycling the black mass of waste LIBs, which contains plastic, C, Li, Fe, Ni, Co, Mn, Cu, and Al, is very complex. Herein, the direct selective leaching of Li from the industrial-grade black mass powder of waste LIBs is proposed for the first time. Results demonstrated that the leaching efficiency of Li is shown to exceed 97%, while other metals remain below 1%. The mechanism of selective leaching was also investigated in this study. Under the experimental conditions, Fe is not leached out and remains in the form of solid FePO4. As for other impurity metal elements, they are removed from the solution due to the alkaline environment of the post-leaching solution and the adsorption effect of the anodic carbon. Furthermore, the alkaline post-leaching solution can avoid the neutralizing stage before the precipitation of lithium salts. This highly efficient and Li-selective leaching strategy offers a broadly applicable approach to reclaiming critical energy minerals from the black mass of wasted LIBs.

Adsorption of sulfur on Lanxess Lewatit® AF 5 resin during the acidic albion leaching process for chalcopyrite.

Elemental sulfur is one of the major byproducts of the acidic Albion leaching process for chalcopyrite. It is a challenging component in the leach solution as it impedes gold recovery from the residue. Lanxess Lewatit® AF 5 (AF 5) is a microporous carbon-based resin, which is being investigated for the removal of elemental sulfur during this leaching process. In the current research, a series of leaching experiments were performed as a function of temperature, agitation speed and concentrate to AF 5 ratio. Using these results, the adsorption isotherms, the kinetics and the thermodynamics of sulfur removal were studied. One hundred percent of the elemental sulfur could be adsorbed by the AF 5 resin from the acidic Albion leaching process for chalcopyrite. Adsorption isotherms at various temperatures were determined using the Langmuir and Freundlich models. The maximum sorption capacity of AF 5 at 95 °C was 488 mg/g. The kinetic data were fitted to pseudo-first order (PFO) and pseudo-second order (PSO) models and it was shown that the PFO model was best suited to describe the results. The rapid kinetics of sulfur adsorption were attributed to the open pore structure of the AF 5. The Gibbs free energy, enthalpy and entropy of sulfur adsorption by AF 5 were determined as follows: ΔGads o = -1.9 kJ/mol, ΔHads o = -9.1 kJ/mol, and ΔSads o = -0.1 kJ/(mol K). The negative free energy and enthalpy changes demonstrated that the adsorption of elemental sulfur was both spontaneous and exothermic over the temperature range studied.

Thermal treatment of Lanxess Lewatit® AF 5 resin used in the atmospheric chalcopyrite leaching process: Regeneration and sulfur recovery.

Elemental sulfur is a key component in the acidic Albion chalcopyrite atmospheric leaching process and is a challenging issue in the residue. It has been proposed to use Lanxess Lewatit® AF 5 (AF 5) catalyst during the leaching of copper concentrates in the acidic Albion leach process, to eliminate the elemental sulfur from the leach residue. When using AF 5 during leaching, the copper and the iron recoveries were above 95% and 80%, respectively. The AF 5 collected 100% of the elemental sulfur and for a 1:1 ratio of AF 5 to concentrate, the loaded AF 5 gained 12.3 wt% sulfur after the first acidic Albion leach test and contained 24.3 wt% sulfur after two leaching tests. In this study, the optimum conditions for the removal of sulfur from the catalyst were investigated using a high temperature process in a laboratory tube furnace. The results indicated that the maximum desulfurization of 90.1% was achieved at 550 °C after 10 min. The regenerated AF 5 could be reused for several chalcopyrite leaching-AF 5 cycles. For the recycled AF 5, the sulfur absorption decreased by only 1.0% while the recoveries of copper and iron were not affected. The kinetic study showed that the activation energy for AF 5 desulfurization was 164.5 kJ/mol.

Efficient Gold Recovery from Cyanide Solution Using Magnetic Activated Carbon.

Activated carbon has been used for gold recovery in the gold mining industry commercially for decades. The high specific surface area and porosity, good affinity to aurocyanide ions, and abundant resources make activated carbon an efficient and economical material for the adsorption of aurocyanide. However, the separation of activated carbon from the slurry is usually a challenge, and the adsorption rate of activated carbon is limited by the coarse particle size. Herein, a simple and sustainable way to recover gold from cyanide solution using magnetic activated carbon synthesized via a solvothermal method has been developed. The synthesized magnetic activated carbon possesses good magnetism (44.57 emu/g) and specific surface area equal to 249.7 m2/g. The magnetic activated carbon showed 99.1% recovery efficiency of gold from 10 mg/L solution within 5 h, which is much faster compared to the commercial granular activated carbon, and the magnetic activated carbon can be easily separated from the solution with an external magnet. The adsorption ability of this magnetic activated carbon has been tested under different conditions in the cyanide solution, the adsorption isotherm and kinetics are also investigated. The magnetic activated carbon was also recycled in the adsorption-desorption tests and showed good reusability.

Gold Leaching from an Oxide Ore Using Thiocyanate as a Lixiviant: Process Optimization and Kinetics.

Thiocyanate (SCN-) is a promising alternative to cyanide as a lixiviant for gold extraction and is 1000 times less toxic than cyanide. In this study, the following leaching parameters were tested to optimize the gold recovery for the first time from an oxide ore using the response surface methodology: initial thiocyanate concentration (10-500 mM), initial Fe3+ concentration (10-500 mM), and pulp density (10-50% w/v). The maximum gold recovery (96%) was achieved with 500 mM thiocyanate, 100 mM Fe3+, and 50% pulp density at 25 °C and pH = 2 for 24 h. A kinetic study on the optimum leaching condition showed that it followed the shrinking core model, in which the rate-controlling mechanism was the diffusion process. These results are discussed in the context of the published literature.

Leaching characteristics and stability assessment of sequestered arsenic in flue dust based glass.

Arsenic (As), a toxicant, present in flue dust, tailings, and mine drainages generated from mineral processing and smelting processes represents high environmental risk due to its high mobility. Around 42-50% As is found in flue dust in the form of As2O3. The vitrification of As results in the formation of stable inert glass material and supposed to reduce the risk of As release to the environment. In this study, a glass material produced by vitrification of As bearing flue dust via DST GlassLock™ Process was received from Dundee Sustainable Technologies, Canada and was subjected for As stability assessment using United States Environmental Protection Agency (EPA) leaching methods-1311,1312,1313,1314,1315 and 1316. The released arsenic concentration was found to be less than the recommended TCLP hazardous waste limit for arsenic i.e., 5 mg/L in most of the test conditions. The experimental data were analyzed using LeachXS Lite™, a data management software that showed the goodness of the DST GlassLock™ Process for As stabilization and safe landfill deposition of the resulting product.

Toward Sustainable Solution for Biooxidation of Waste and Refractory Materials Using Neutrophilic and Alkaliphilic Microorganisms-A Review.

The significant increase in economic concern and environmental restrictions has resulted in increasing interest in biotechnological solutions. The application of acidophilic, sulfur-oxidizing microorganisms in biomining and in the treatment of waste matrices has been extensively explored. However, to surmount the current challenges encountered by the industrial use of acidophiles, there is an opportunity for neutrophilic and alkaliphilic microorganisms to be comprehensively considered for the biooxidation of refractory sulfide materials. This review, for the first time, provides a detailed study of neutrophiles and alkaliphiles that have potential for oxidizing sulfur-containing wastes and sulfide refractory ores to recover entrapped metals especially gold in a sustainable manner. The study illustrates the applicability of neutrophilic and alkaliphilic microorganisms to provide better and sustainable alternatives for the recovery of metals from wastes from various sources as well as refractory materials. The microorganisms summarized in this review have been successfully used in oxidizing different sulfide sources by achieving high oxidizing efficiencies (>80%) in numerous technologies. The fundamentals of biooxidation along with possible mechanisms involved in the biooxidation have been discussed in detail.

Hydrothermal Monodisperse Microspherulite Pyrite: Novel Synthesis Process and Electrochemical Study of Its Oxidation.

A simple one-step hydrothermal method was developed to synthesize pyrite (FeS2) sheet- and bulklike pyrite mineral. The Fe/S molar ratio determines the phase of FeS2, including pyrite and marcasite. The reaction temperature and time are key factors to regulate the structure, morphology, and size of pyrite. Scanning electron and transmission electron microscopy showed the formation of monodisperse microspherulite within 1 h reaction time, and the particles aggregated to large irregular polyhedron particles with increasing reaction time up to 4 h. Electrochemical oxidation tests demonstrated that their electrochemical activity significantly decreased with increasing synthesis time. At an elevated temperature of 200 °C, bulk pyrite was obtained after a 24 h reaction time, which could have promising applications in hydrothermal pyrite ore oxidation research.

Green catalytic process for in situ oxidation of Arsenic(III) in concentrated streams using activated carbon and oxygen gas.

Arsenic(III) oxidation is a critical pre-treatment step for overall arsenic immobilization in concentrated industrial arsenic streams. Activated carbon (AC) catalysis is a green, economical and efficient method to oxidize As(III) from waters with high arsenic concentration prior to its removal through precipitation or adsorption. This research investigates AC-catalyzed oxidation process for oxidizing aqueous solutions of As(III) and proposed the possible reaction pathway. Batch tests were performed and efficient oxidation of 2.0 g/L acidic As(III) solution have been induced on AC surfaces in the presence of oxygen. The in-situ formation of reactive oxygen species on carbon surfaces and arsenic adsorption onto AC play important roles in As(III) oxidation. The kinetics of adsorption and catalyzed oxidation has been studied and the samples were characterized using ICP-OES, Zeta potential, TEM coupled with EDX and XPS techniques. A systematic reaction pathway was proposed, and reusability of AC has confirmed the economic viability of the proposed green process. This study offers a promising and facile solution for As(III) oxidation from waste water, mining and metal industrial waste streams under ambient conditions for arsenic immobilization.

In-situ oxidative arsenic precipitation as scorodite during carbon catalyzed enargite leaching process.

This study explores the in-situ precipitation of scorodite (FeAsO4.2H2O) during the atmospheric enargite leaching in acid chloride media. The temperature, oxygen sparging rate and the different fractions of the catalyst and ferric ions were the effective parameters on the scorodite precipitation process. Crystalline scorodite was precipitated out of the leach solution in the absence of seed at temperatures above 80 °C where the ratio of both AF5 to concentrate and activated carbon (AC) to concentrate were 1:1. The minimal dosage of ferric ions to form the scorodite residue was 5 g/L. Seed addition facilitated the scorodite precipitation process where the primary scorodite particles precipitated after 6 h of enargite leaching. Via this process it was shown that the residual concertation of arsenic in the pregnant leach solution can be reduced as low as 50 mg/L. A series of the toxicity characteristic leaching procedure (TCLP) tests on the generated scorodite exhibited a low arsenic release ranging from 0.2 to 0.7 mg/L, showing an acceptable stability of the scorodite in the residue.

Cytogenetic study of the genus Cousinia ( Asteraceae, section Serratuloideae ) in Iran

Meiotic studies of ploidy level, chromosome paring and chiasma frequency were performed on 11 Cousinia (Asteraceae) species of the section Serratuloideae. The diploid number of the species studied was 2n = 2x = 24 and 26 so these species possess two different basic numbers (x = 12 or 13), a phenomenon common to other sections of the genus. The chromosome numbers of 9 species are reported here for the first time. When the 2n = 24 and 2n = 26 species were subjected to cluster analysis based on relative meiotic characters two different clusters were formed indicating their distinctness. Our data support the results obtained from morphometry, anatomy, pollen morphology and molecular studies of the genus Cousinia.