Pritam Singh

Coal is commonly used as both fuel and reducing agent in producing synthetic rutile from ilmenite (FeTiO3) via the Becher process, which upgrades ilmenite to high-purity TiO2 (>88%). However, coal-based reduction generates significant carbon waste. This study investigated the effect of adding 1–5% w/w potassium hydroxide (KOH), sodium hydroxide (NaOH), and sodium tetraborate (borax) to coal during ilmenite reduction to improve metallisation and reduce carbon burn-off. Results showed that 1% w/w additives significantly increased metallisation to 96% (KOH), 95% (NaOH), and 93% (borax), compared to 80% without additives, while higher concentrations (3–5% w/w) decreased metallisation. Scanning electron microscopy (SEM)analysis showed cleaner particle surfaces and optimal metallisation at 1% w/w, whereas higher additive levels caused agglomeration or sintering due to elevated silica and alumina activity. Additive type also influenced TiO2 quality, with KOH enhancing TiO2 at low concentrations but causing negative effects at higher levels, while NaOH and borax reduced TiO2 quality via sodium-based compound formation. All additives reduced carbon burn-off, with KOH producing the greatest reduction. The iodine number of the carbon residue increased with higher additive concentrations, with KOH achieving 710 mg/g at 1% w/w and 900 mg/g at 5% w/w, making the residue suitable for water treatment. Overall, KOH is the most effective additive for producing high-quality synthetic rutile while minimising carbon waste.

Redox flow batteries (RFBs) are known for their exceptional attributes, including remarkable energy efficiency of up to 80%, an extended lifespan, safe operation, low environmental contamination concerns, sustainable recyclability, and easy scalability. One of their standout characteristics is the separation of electrolytes into two distinct tanks, isolating them from the electrochemical stack. This unique design allows for the separate design of energy capacity and power, offering a significantly higher level of adaptability and modularity compared to traditional technologies like lithium batteries. RFBs are also an improved technology for storing renewable energy in small or remote communities, benefiting from larger storage capacity, lower maintenance requirements, longer life, and more flexibility in scaling the battery system. However, flow batteries also have disadvantages compared to other energy storage technologies, including a lower energy density and the potential use of expensive or scarce materials. Despite these limitations, the potential benefits of flow batteries in terms of scalability, long cycle life, and cost effectiveness make them a key strategic technology for progressing to net zero. Specifically, in Australia, RFBs are good candidates for storing the increasingly large amount of energy generated from green sources such as photovoltaic panels and wind turbines. Additionally, the geographical distribution of the population around Australia makes large central energy storage economically and logistically difficult, but RFBs can offer a more locally tailored approach to overcome this. This review examines the status of RFBs and the viability of this technology for use in Australia.

The use of coal for ilmenite reduction to produce synthetic rutile is widespread in industry. However, the carbon dioxide emissions associated with coal combustion pose significant environmental concerns. Alternative reductants such as hydrogen have the potential to promote environmentally friendly production of green rutile. This study aimed to assess the technical feasibility of reducing an Australian secondary (weathered) ilmenite using hydrogen, focusing on the effects of reduction temperature and time. The ilmenite was composed of 65 % titanium dioxide, 29 % iron oxide, and 6 % impurities. Samples at each stage of the processing were analysed using X-ray fluorescence spectrometry (XRF) and scanning electron microscopy (SEM). The results revealed that both temperature and time impacted ilmenite reduction, with increasing values of both parameters leading to higher reduction percentages. The maximum reduction percentages were obtained for a reduction time of 240 min at all temperatures, and there was an increase from 62 % at 973 K to 99 % at 1273 K for this reduction time. A reduction percentage of 90 % was obtained at 1273 K with a holding time of 60 min. This study indicates that a minimum temperature of 1073 K is required to achieve a reduction exceeding 90 % for secondary ilmenite. The SEM analysis showed that fine, discrete, metallised iron particles were present on the surface of the reduced secondary ilmenite. The investigation into hydrogen as an alternative reductant demonstrated improved iron–titanium separation in acid leaching compared with the conventional reduction method using coal and resulted in green rutile products with titanium dioxide grades exceeding 96 %, and iron oxide content below 1 %.

The aim of lithium-ion battery (LiB) recyclers is to create a closed-loop process to recover and reuse all the material as secondary sources of material to manufacture new batteries. Global LiB recycling companies apply pyrometallurgy, hydrometallurgy, or direct recycling to meet this goal. Pyrometallurgy is very energy intensive, but hydrometallurgy requires a pretreatment process and a new version of direct recycling that shows more promise for automation would also require pretreatment. Currently, recycling companies appear to favor hydrometallurgy. This review summarizes the current state of development of the pretreatment process involving battery discharging and mechanical treatment series from the literature and its application in the industry, with particular attention on Asia Pacific recyclers. The key pretreatment steps of battery discharging and mechanical treatment are the focus of this review, but pretreatment of the black mass containing cathode material prior to leaching is also included. Discharging is important to reduce the risk of fire during mechanical treatment. An interesting finding is that despite promising laboratory results, there has been no reported commercial application of battery discharging using the submersion method in an electrolyte solution. An efficient mechanical treatment of discharged batteries is essential to remove the impurities which could adversely impact the subsequent LiB processing. Research into mechanical treatment should also include a method to evaluate the liberation of material. This review has highlighted a new potential flowchart for recycling of various cathode types of LiBs.

Copper smelting slag is a significant potential resource for cobalt and copper. The recovery of copper and cobalt from copper slag could significantly augment the supply of these metals, which are essential to facilitating the transition to green energy while simultaneously addressing environmental concerns regarding slag disposal. However, the complex mineral composition of copper slag poses an enormous challenge. This study investigated the mineralogical and chemical characteristics of copper slag, which are vital for devising the most effective processing techniques. XRD and FESEM-EDS were employed to examine the morphologies of copper slag before and after the reduction process. The effects of borax and charcoal (carbocatalytic) reduction on phase transformation were evaluated. The XRD analysis revealed that the primary phases in the copper slag were Fe2SiO4 and Fe3O4. The FESEM-EDS analysis verified the presence of these phases and yielded supplementary details regarding metal embedment in the Fe2SiO4, Fe3O4, and Cu phases. The carbocatalytic reduction process expedited the transformation of copper slag microstructures from crystalline dendritic to amorphous and metallic phases. Finally, leaching experiments demonstrated the potential benefits of carbocatalytic reduction by yielding high extractions of Cu, Co, and Fe.

The use of coal-derived activated carbon (AC) for water treatment applications demands more sustainable production methods, with chemical activation emerging as a promising alternative to thermal activation due to its higher AC quality, lower carbon burn-off, and higher yield. The study explored the effect of surface area, particle size and acid washing on the quality of AC derived from three seams of lower-rank Collie coal under the same activation conditions with potassium hydroxide (KOH). The quality of AC was determined by surface area and iodine number. The study demonstrates that Collie coal, suitable for AC production via KOH activation, yielded iodine numbers of 640 and 900 mg/g, with yields of 53 and 57 wt.%. Particle size influenced AC yield, with finer particle sizes yielding AC at 57–59 wt.%, whereas coarser ones yielded around 58–65 wt.%. SEM analysis shows the well-developed porous structure in Collie coal-derived activated carbons, with cleaner particles after acid washing. A positive correlation exists between coal surface area and AC iodine numbers, with higher values in coal samples correlating to increased iodine numbers in resulting AC. The regression model’s predicted values yield a coefficient of determination (R²) of 0.99.

Liberation of cathode materials (Co, Ni, Mn, Li) from spent lithium-ion batteries is essential to creating an acceptable leach feed in hydrometallurgical battery recycling. This study investigated the use of milled battery casing steel as the abrasive media in an attrition process, termed semi-autogenous attrition (SAA). The process aims to increase the liberation of the cathode materials, which are attached to other battery components, and also to release the agglomerated particles. The experimental parameters were pulp density, agitating speed and retention time. The performance of the SAA process was compared to wet sieving and attrition with agitation only. The optimum SAA conditions liberated 20% more cathode material to the <180 mm fraction and contained 90% Co with <2 wt% of contaminants (Al, Fe, and Cu). The results show that SAA can replace secondary milling. Moreover, the casing steel is a reliable abrasive media, which is already available in the system and easily separated from the cathode material. The casing steel can also be reused for multiple SAA.

Battery discharging prior to size reduction is an essential treatment in spent lithium-ion battery recycling to avoid the risk of fire and explosion. The main challenge for discharging the residual charges by immersion in an electrolyte solution is corrosion because of electrolysis reactions occurring at the battery terminals. This study investigated the discharging process of 18650 cylindrical lithium-ion batteries (LiBs) in NaCl and NaOH solutions and the generation of corrosion products, with the aim of developing a safe and clean discharging system for practical applications. The results show that water electrolysis is the primary reaction during battery immersion in either NaCl or NaOH solutions. Different forms of corrosion occur in each solution. Unlike the NaCl solution, which severely corroded the positive terminal of the battery, resulting in significant amount of solid residue, build-up of fluoride ions, and chlorine gas evolution, in the NaOH solution, a darkened surface of the negative terminal was the only obvious solid product, with no solid residue in the bulk solution, while oxygen gas was evolved. The NaOH solution was found to reduce battery capacity to a residual capacity range of 0–25 mAH after immersing batteries in the solution for 20 h. This value puts the battery in a safe condition for subsequent mechanical treatment. The results indicated that NaOH creates a clean discharging system and can potentially be reused.

Recovery of valuable metals from end-of-life cylindrical lithium-ion batteries (LiBs) by leaching using acetic acid in the presence of an organic reductant is a promising combination to overcome environmental concerns that arise from employing inorganic reagents. This study investigated the effect of using molasses as a reductant in acetic acid leaching of a mixture of cathode and anode materials (black mass) prepared using mechanical treatments from spent LiBs. The effects of temperature, solid/liquid ratio, stirring speed, and acid concentration on the leaching of target metals (Co, Ni, Mn, and Li), current collector metal foil elements (Al and Cu), and Fe from the battery casing, with and without reductant, were investigated to obtain the optimum leaching conditions. The effect of adding the molasses at the start of leaching and after 1 h of leaching was tested. Acid leaching without molasses extracted the target metals Li, Ni, Co, and Mn with an efficiency <35% for all leaching parameters. However, the Al and Fe extractions increased as the acid molarity increased. Molasses addition at the start of leaching increased the extraction of the target metals to >96% at temperatures >50 °C. This is likely due to oxidation of the reducing sugars in the molasses that reduced the insoluble Co(III), Ni(III), and Mn(IV) components to soluble Co(II), Ni(II), and Mn(II) species, respectively. The kinetics of Co extraction in the presence of molasses were analysed, which has indicated that the rate-determining step in the Co leaching process is the reduction of Co(III) on the surface of particles in the black mass. Excess molasses can precipitate out target metals, especially Co, due to the presence of oxalic acid in the molasses. The reducing effect precipitated Cu(II) to Cu2O, and could further reduce Co to metal, which suggests that leaching with the optimum dosage of acetic acid and molasses may selectively precipitate copper.

The mining industry faces a number of challenges that include rapid depletion of high-grade deposits, high energy cost for metal production, and growing environmental concerns associated with mining waste disposal. Copper slag is one of the mining wastes that is raising growing concern due to the huge volumes being produced and dumped annually worldwide. These huge quantities of slag not only cause environmental pollution and space problems for disposal, but they also waste valuable copper and cobalt. This is increasingly important due to the growing demand for these metals in emerging technologies, potentially resulting in a supply deficit from conventional mining production. To address these challenges, recycling and repurposing of copper slag waste using innovative technologies should be considered, creating a resource for a circular economy. This paper presents a review of copper slag production and its potential as a world resource for cobalt and copper metals. An overview of copper and cobalt production from ore reserves, and of global demand and supply risks for these metals is presented. The potential benefits of reprocessing copper slag waste using the circular economy model are discussed. This paper demonstrates that applying the circular economy principles to the copper slag waste has the potential to create additional economic value, improve the energy efficiency of the metal production, increase the supply of critical metals, and reduce the impacts of metal production on the environment.