Pongsiri Julapong

The growing volume of end-of-life lithium-ion batteries (LIBs) is necessitating the development of physical separation processes that recover electrode materials while reducing downstream recycling burdens. This systematic review and bibliometric analysis examined LIB flotation research published from 2016 to 2025. Scopus and Web of Science (WoS) databases were searched, and items were screened using predefined eligibility criteria following the PRISMA guidelines 2020, yielding 79 eligible publications. These studies were classified into (i) collector-free (n = 9), (ii) non-ionic (n = 62), (iii) ionic (n = 6), and (iv) unspecified-reagent systems (n = 2). Pretreatment has been reported as an essential step for improved liberation and surface accessibility, as well as better control of aggregation and aqueous chemistry. Collector-free flotation was effective when graphite retained sufficient hydrophobicity, but selectivity was constrained by residual binders, ultrafine entrainment, particle aggregation, and solution chemistry. Meanwhile, non-ionic hydrocarbon collectors dominated the literature, primarily enhancing graphite floatability rather than imparting intrinsic selectivity against cathode active materials. In addition, flotation performance depended strongly on pretreatment, collector dispersion, frother behavior, reagent sequence, hydrodynamics, and circuit configuration. In contrast, ionic collectors were less studied and were used mainly for copper–aluminum separation and differential flotation of blended cathode materials. Unspecified-reagent systems integrated flotation with direct recycling and graphite regeneration, but incomplete reporting limited comparison. Across all regimes, feed heterogeneity and surface condition strongly governed separation efficiency. Finally, a universally superior collector regime was not found because reagent selection strongly depended on feed characteristics and the intended separation objective, product requirements, and extent of process integration.

Rare earth minerals, the primary sources of 17 rare earth elements, are crucial for advanced technologies. Efficient separation of monazite and xenotime from their associated mineral, zircon, is essential due to their unique properties. This study focuses on the selective flotation of monazite, xenotime, and zircon using a novel ionic liquid collector, tetraoctylammonium di(2-ethylhexyl) phosphate (TOA-DEHP), without the addition of depressants. The flotation behavior of high-purity single minerals was investigated in a Hallimond tube under varying TOA-DEHP concentrations, pH levels, and temperatures. The results indicate that the optimal conditions for separation occur at pH 9 and 60 °C. Subsequently, the flotation of an artificial mixture of the three minerals was evaluated in a mechanical flotation system under these optimized conditions. The separation results revealed that monazite predominantly remained in the tailing product with a recovery of 42.0%, leading to an increase in total light rare earth oxide content to 51.5% compared to the feed. Xenotime was primarily recovered in the froth product of the second stage with a recovery of 54.1%, increasing the total heavy rare earth oxide content to 31.7% relative to the feed. The adsorption mechanism of TOA-DEHP on each mineral surface was analyzed using Fourier transform infrared spectroscopy (FT-IR). The results suggest that TOA-DEHP adsorbs onto monazite via physisorption, which becomes reversible at 60 °C, while xenotime and zircon exhibit chemisorption, as evidenced by the detection of P─O─C vibrational peaks of anionic moieties in FT-IR spectra.

The exposure of microplastics (MPs) to ultraviolet (UV) light in the environment can affect their flotation behavior and removal efficiency. This study investigated the effects of UVC irradiation on the physical and surface characteristics of polypropylene (PP), polyethylene (PE), acrylonitrile butadiene styrene (ABS), polystyrene (PS), polyethylene terephthalate (PET), and polyvinyl chloride (PVC), and evaluated their removal using agglomeration–micro-flotation. MPs were irradiated with UVC for 7 days, and they were characterized using particle size distribution analysis, CIE L*a*b* color analysis, and contact angle measurements. Flotation experiments were conducted using kerosene as a hydrophobic bridging liquid. The results showed that UVC irradiation induced polymer-dependent changes, including fragmentation, apparent shape-related changes, and redistribution behavior, resulting in changes in particle size distribution. Surface discoloration and reduced contact angle were also observed after UV exposure, suggesting photooxidative surface modification and increased surface hydrophilicity. These surface modifications reduced flotation performance at low kerosene dosages, particularly for PET and PVC. However, increasing kerosene dosage improved removal efficiency by enhancing agglomeration and particle–bubble attachment. The results indicated that agglomeration–micro-flotation is a promising approach for removing UV-aged MPs and provided insights into the influence of UV-induced surface modifications on flotation behavior.

This study investigates the modification and application of natural, micro-scale magnetite (Fe₃O₄)—an iron oxide mineral and one of the most abundant iron ores in the world—as a magnetic carrier for removing six common types of microplastics (MPs) from water: polypropylene (PP), polyethylene (PE), acrylonitrile butadiene styrene (ABS), polystyrene (PS), polyethylene terephthalate (PET), and polyvinyl chloride (PVC). Hexadecyltrimethoxysilane (HDTMS) was employed as a surfactant to modify the naturally hydrophilic magnetite, transforming it into a hydrophobic material. The characterization of magnetite treated with HDTMS for 0, 6, 12, 24, and 48 h was performed using a scanning electron microscope with energy-dispersive X-ray spectroscopy (SEM-EDS) and Fourier transform infrared spectroscopy (FT-IR). The results showed HDTMS sorption on the surface of natural magnetite, confirming successful surface modification. Carrier magnetic separation was then performed to remove PP, PE, ABS, PS, PET, and PVC using surface-modified, natural magnetite in two size fractions: +38–75 µm (fine-sized) and +75–150 µm (coarse-sized). Improved performance was observed with longer HDTMS treatment of magnetite, while greater than 90% MP removal was achieved using fine-sized, surface-modified, natural magnetite. These results suggest that surface modification enhanced the heterogenous interactions between magnetite and MPs via hydrophobic-hydrophobic interactions, leading to efficient MP removal via carrier magnetic separation.

The use of washing machines to wash textiles gradually breaks down synthetic fibers like polyethylene terephthalate (PET) or polyester (PES) in diverse clothing materials, a process that is growing in notoriety because it generates microplastics (MPs). In this study, we investigated the emission of microfibers, including both microplastic fibers (MPFs) and natural fibers (MFs), from top-loading washing machines. Our investigation focused on four popular textiles with prevalent weave structures (plain, satin, and twill): (i) PES, (ii) tetron cotton (TC), (iii) chief value cotton (CVC), and (iv) cotton (CO) fabrics. This study also examined the effects of textile weight and detergent dosage on MF emissions. After washing, MFs were collected through filtration, and their concentrations were determined using micro-Fourier Transform Interferometry (μFTIR). The results showed varying concentrations of MFs in the washing effluent depending on the type of textile. Specifically, CVC exhibited the highest emission at 4022 particles/L, followed by TC, PES, and CO at 2844 particles/L, 2382 particles/L, and 2279 particles/L, respectively. The hydrophobic nature of PES makes this type of textile prone to rapid degradation in detergent-rich environments, leading to high MF emissions. Additionally, the mechanical properties of textiles, such as tensile and bending strengths, may play a crucial role in the generation of MFs in washing machines. Textiles made of CO with twill weaves demonstrated superior strength and correlated with lower emissions of MFs. In comparison, textiles made of CVC and satin weave exhibited lower mechanical properties, which could explain their high emissions of MFs. Finally, the MF emissions of textiles composed of PES and TC, which are plain weaved, could be attributed to their intermediate mechanical properties compared with those of CVC and CO.

Material recycling and thermal treatment are the two most common recycling methods employed for plastic waste management. Thermal treatment for energy recovery is more widely applied compared with material recycling because the latter requires a high efficiency of separation and a high purity of products. Unfortunately, certain plastics like polyvinyl chloride (PVC) are unsuitable for thermal treatment because they contain additives like chloride (Cl⁻) that have adverse effects on refractory materials used in boilers. As a result of this, mixed plastic wastes containing PVC generally end up in landfills. PVC-bearing mixed plastics, however, remain valuable resources as championed by the United Nation Sustainable Development Goals (UN-SDGs): Goal 12 “Responsible production and consumption”, and their recycling after the removal of PVC is important. In this paper, recent studies (2012–2021) related to the separation of PVC from other types of plastics were systematically reviewed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A total of 66 articles were selected, reviewed, and summarized. The results showed that various separation technologies conventionally applied to mineral processing—selective comminution, gravity separation, magnetic separation, electrical separation, and flotation—have been studied for PVC separation, and the majority of these works (>60%) focused on flotation. In addition, more advanced technologies including sorting and density-surface-based separation were introduced between 2019 and 2021.

Rare earth minerals (REMs) contain rare earth elements (REEs) that are important in modern technologies due to their unique magnetic, phosphorescent, and catalytic properties. However, REMs are not only non-renewable resources but also non-uniformly distributed on the Earth’s crust, so the processing of REE-bearing secondary resources via recycling is one potential route to ensure the long-term sustainability of REE supply. Flotation—a method that separates materials based on differences in their surface wettability—is a process applied for both mineral processing and recycling of REEs, especially when the particles are fine and/or a high-purity product is required. In this review, studies about rare earth flotation from 2012 to 2021 were systematically reviewed using the PRISMA guideline. It was found that most REM flotation research works focused on finding better collectors and depressants while, for recycling, studies on advanced flotation techniques like froth flotation, ion flotation, solvent sublation, electroflotation, and adsorbing colloid flotation with an emphasis on the recovery of dissolved REEs from aqueous solutions dominated.

Microplastics (MPs), defined as plastics with diameters between 1 and 5000 µm, are problematic pollutants in the environment, but their removal is challenging because of their minute size. One promising approach for their removal is flotation because MPs are inherently hydrophobic. However, the very small particle size of MPs lowers the probability of MPs-bubble collision and attachment that in turn affects the efficiency of the process. To address this challenge, we propose the use of agglomeration-flotation, a technique using kerosene as a bridging liquid to enlarge the particle sizes of MPs and make them amenable to flotation. In this study, the effects of kerosene dosage on particle size enlargement and floatability of six types of MPs with 100–1000 µm size fractions were investigated. The results showed that MPs with lower density compared with water could easily float in water without bubble attachment and particle agglomeration required. So, the effects of agglomeration on removal were negligible. In contrast, agglomeration using kerosene enhanced the floatability of MPs with high-density plastics. Moreover, image analysis was used to determine the agglomerated MPs’ particle size. The results indicate that kerosene could agglomerate the MPs and enhanced the removal of MPs by agglomeration-flotation.