Lithium-ion batteries (LIBs) are dangerous to recycle, as they pose a fire hazard when cut and contain various chemical hazards. If recycled safely, LIBs provide a rich secondary source for metals such as lithium and cobalt, while reducing the environmental impact of end-of-life LIBs. Discharging the spent LIBs in a 5 wt.% NaCl electrolyte at room temperature enables their safe dismantling. A sludge was observed to form during the LIB discharging, with a composition of 34.9 wt.% Fe, 35 wt.% O, 17.7 wt.% Al, 6.2 wt.% C, and 4.2 wt.% Na. The average electrolytic solution composition after the first discharge cycle contained only 12.6 mg/L Fe, 4.5 mg/L Li, 2.5 mg/L Mn, and trace amounts of Ni and Co. Separating the active cathode powder from the aluminum cathode with a 10 wt.% NaOH leach produced an aqueous filtrate with an Al metal purity of 99.7%. The leach composition consisted of 9558 mg/L Al, 13 mg/L Li, 8.7 mg/L Co, and trace amounts of Mn and Ni. The hydrometallurgical sample preparation processes in this study enables the production of a pure black mass with less than 0.05 wt.% Co, 0.2 wt.% Li, 0.02 wt.% Mn, and 0.02 wt.% Ni losses from the active cathode material.

Microplastics are accumulated in coastal regions due to human activity. Although limited data from beach surveys show an increase in microplastics in marine habitats, continuous monitoring is required on microplastics loading and distribution in the marine environment. In this study, CFD numerical simulations using VOF and Airy wave models coupled with DPM were carried out to investigate the effects of various variables on microplastics motion and distribution in a simulated coastal marine environment. PET, PU, and PP microplastic particles were released from the oceanside to investigate the effects of microplastic type, size, and shape with two different ocean–water flow velocities and temperature conditions. Particle position data from their tracking were used to determine the effect of each variable on the spatial distribution of particles. The quantitative analysis of vertical and horizontal distribution of microplastics particles revealed that, with low water velocity, most of the large denser spherical PET and PU microplastics would sink towards the bottom and settle at the ocean floor, while most of the small non-spherical particles would float near the surface and travel towards the shoreline. For lighter PP microplastics, larger spherical particles would float more readily than denser spherical ones. Large spherical and smaller non-spherical PP particles travel farthest reporting to the shoreline. Increasing the oceanwater velocity altered the distribution patterns in which lighter PP particles, almost independent of shape and size, travel swiftly to the shoreline together with smaller non-spherical denser microplastics. Lastly, the simulation results revealed that the oceanwater temperature did not play any significant role in the spatial distribution of microplastic particles.

Rare earth elements (REEs) have been identified as valuable and critical raw materials, vital for numerous technologies and applications. With the increasing demand for and supply gap in REEs, many research studies have focused on alternative sources of REEs. This study involved an elemental and mineralogical characterisation of discarded coal from a coal plant and coal fly ash (CFA) from a power station in South Africa for REE presence. XRD results revealed that the discard coal sample consisted mainly of kaolinite, pyrite, siderite, quartz, calcite, gypsum, and muscovite, whereas CFA contained abundant glassy amorphous phases, alumina silicates, quartz, gypsum, calcite, and minute levels of muscovite and hematite. SEM-EDAX showed REE-carrying grains containing phosphorus in both discard coal and CFA samples. This was followed by investigating the leaching potential of REEs using hydrochloric acid from discard coal and CFA. This research’s potential impact is possibly providing a new and sustainable source of REEs. For that purpose, multiple batch leaching tests were performed to investigate the effects of temperature and acid concentration on the leaching efficiencies of REEs from discard coal and CFA. The experimental results indicated that temperature strongly influences REE leaching efficiency, while acid concentration has a lesser impact. This study identifies the best leaching conditions for the total REE recovery as 1 M HCl and 80 °C for discard coal and CFA.

This study investigated the performance of citric acid as lixiviant for cathode material from end-of-life lithium-ion batteries (LIBs). Black mass containing 84.2 wt% MNC (LiNi_0.45Mn_0.4Co_0.15O₂) and 15.8 wt% LCO (LiCoO₂) material was leached at solid-to-liquid ratios of 20, 50, and 100 g/L. Leaching with 1.5 M citric acid, 2 vol.% H₂O₂, and a solid-to-liquid ratio of 20 g/L at 95 °C extracted 90% Co, 95% Li, 94% Mn, and 94% Ni within 20 min. At the highest solid/liquid ratio of 100 g/L with 1.5 M citric acid, 10 vol.% H₂O₂, and 95 °C, 84% Al, 84% Co, 87% Li, 86% Mn, and 96% Ni were leached after 40 min, producing a leach solution containing 0.68 g/L Al, 20.0 g/L Co, 6.0 g/L Li, 13.6 g/L Mn, and 19.3 g/L Ni. Using stepwise addition of H₂O₂, instead of initial bulk addition, did not significantly improve the leaching efficiency but did reduce the required leaching time. Temperature control of the reactor was also more manageable with stepwise addition of H₂O₂ and evolution of gas was less vigorous. It was observed that the leaching efficiencies of Co, Li, and Mn decreased slightly at solid/liquid ratios of 50 g/L and 100 g/L, while the leaching of Ni increased slightly. The solution leached at 20 g/L could be stored for 6 weeks without any spontaneous precipitation. However, solutions leached at 50 g/L and 100 g/L showed changes in concentration after 1 month’s storage, suggesting that processes that have a large material throughput and use high solid-to-liquid ratios around 100 g/L must ensure that the solutions are not stored for extended periods of time.

Lithium-ion battery (LIB) recycling has received continued interest in recent years due to its benefits, which include reducing the environmental impact of spent LIBs and providing a secondary source of valuable metals, such as Li, Co, and Ni. This paper characterized the Li separation with D2EHPA from citrate media as a function of pH and identified the optimal overall Li separation at a pH of 5.5. The Li separation was optimized at a pH of 5.5, with which it was concluded that 23 vol.% D2EHPA and an O/A ratio of 4 provided the best Li separation, for which 66.1% Li was extracted with 26.9% residual Mn, 6.8% Co, and 7.7% Ni in a single stage. The formation of a reversible hydrophobic third phase was identified during Li extraction at a pH of 5.5 or greater. Investigation of the third phase revealed that more than 99% of the Li, Co, and Ni were extracted to the third phase, while more than 69% of the Mn was extracted to the organic phase. STEM images of the third phase revealed a honeycomb-like structure, which was hypothesized to be a 2D mesoporous film caused by the insolubility of the organometallic complexes in the aqueous and organic phase.

Hydrogen production via microbial photofermentation shows great promise as a method for sustainable hydrogen production; however, operating costs associated with photofermentative hydrogen production need to be reduced. Costs can be reduced using a passive circulation system like the thermosiphon photobioreactor, and by operating it under natural sunlight. In this study, an automated system was implemented to investigate the effect of diurnal light cycles on the hydrogen productivity and growth of Rhodopseudomonas palustris and on the operation of a thermosiphon photobioreactor, under controlled conditions. Diurnal light cycles, simulating daylight times, were found to reduce hydrogen production in the thermosiphon photobioreactor demonstrating a low maximum production rate of 0.015 mol m⁻³ h⁻¹ (± 0.002 mol m⁻³ h⁻¹) as compared to 0.180 mol m⁻³ h⁻¹ (± 0.0003 mol m⁻³ h⁻¹) under continuous illumination. Glycerol consumption as well as hydrogen yield also decreased under diurnal light cycles. Nonetheless, hydrogen production in a thermosiphon photobioreactor under outdoor conditions was demonstrated as possible avenue for further investigation.