Flotability and flotation separation of polymer materials modulated by wetting agents

Enhanced flotation removal of polystyrene nanoplastics by chitosan modification: Performance and mechanism

Nanoplastics are difficult to remove from water using conventional flotation processes due to their stability and resistance to biodegradation. Here, polystyrene nanoplastics (PSNPs) were selected as the object of study. In addition, chitosan (CTS), an environmentally friendly natural cationic polymer, was selected to modify the air flotation process to improve the separation of PSNPs using air flotation. Adding chitosan effectively enhanced the removal of PSNPs using air flotation from 3.1 % to 96.7 %. The residual concentration decreased from 9.69 mg/L to 0.33 mg/L. Removal of PSNPs by CTS-modified air flotation was maintained at 92.8 % even when the air flotation time was significantly shortened. The zeta potential alterations demonstrated robust electrostatic attraction within the CTS-modified air flotation process. The contact angle measurements indicated that incorporating CTS could enhance the hydrophobic interaction between bubbles and PSNPs. PSNPs particles around 100 nm agglomerated to form floating flocs with a particle size of more than 4500 nm. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) images confirmed the presence of tight adhesion between PSNPs and CTS, indicating the presence of bridging adsorption during the process. The major PSNPs removal mechanisms included electrostatic attraction, enhancement of hydrophobicity, and bridging adsorption. Increasing the aeration volume could improve the removal rate, but this improvement was finite. Weakly acidic and low ionic strength conditions favored PSNPs removal. The CTS-modified air flotation process showed great potential for PSNPs removal from real water bodies.

A Complete Guide to Extraction Methods of Microplastics from Complex Environmental Matrices

Sustainable development is a big global challenge for the 21st century. In recent years, a class of emerging contaminants known as microplastics (MPs) has been identified as a significant pollutant with the potential to harm ecosystems. These small plastic particles have been found in every compartment of the planet, with aquatic habitats serving as the ultimate sink. The challenge to extract MPs from different environmental matrices is a tangible and imperative issue. One of the primary specialties of research in environmental chemistry is the development of simple, rapid, low-cost, sensitive, and selective analytical methods for the extraction and identification of MPs in the environment. The present review describes the developments in MP extraction methods from complex environmental matrices. All existing methodologies (new, old, and proof-of-concept) are discussed and evaluated for their potential usefulness to extract MPs from various biotic and abiotic matrices for the sake of progress and innovation. This study concludes by addressing the current challenges and outlining future research objectives aimed at combating MP pollution. Additionally, a set of recommendations is provided to assist researchers in selecting appropriate analytical techniques for obtaining accurate results. To facilitate this process, a proposed roadmap for MP extraction is presented, considering the specific environmental compartments under investigation. By following this roadmap, researchers can enhance their understanding of MP pollution and contribute to effective mitigation strategies.

Separation of plastic wastes using froth flotation - An overview

Despite various initiatives and efforts, plastic solid waste (PSW) has become a major global problem due to decades of relentless use of plastics. Since non-biodegradable plastics can persist in the environment for hundreds of years, threatening animal and human life, discarding them into the environment is not a viable option. Plastic recycling is a critical research area that requires urgent attention since less than 10% of the seven billion tons of globally generated plastic waste has been recycled so far. With recent technological developments, it is now possible to recycle many types of PSW using a variety of methods. This review provides an overview of the froth flotation technology that is currently being researched for PSW recycling. Fundamental working principles, the current state of the development, and limitations of this technique are reviewed. It is suggested that froth flotation with continuous development has tremendous potential to result in a more efficient and environmentally friendly approach to PSW recycling.

Improving the Separation of PS and ABS Plastics Using Modified Induced Air Flotation with a Mixing Device

A dramatic increase in plastic waste has resulted in a strong need to increase plastic recycling accordingly. A selective flotation has been highlighted due to its outstanding efficiency for the separation of mixed plastics with analogous physicochemical characteristics. In this study, the effects of design and operational factors on the bubble’s hydrodynamic and mixing parameters in induced air flotation (IAF) with a mixing device were investigated through a design of experiment method (DOE) analysis for improving the plastic separation efficiency (i.e., PS and ABS). As a result of DOE analysis, the increase in the induced air tube diameter together with the rotational speed could generate a smaller bubble size. This led to the enhancement of the ratio of interfacial area to velocity gradient (a/G), which was interestingly found to be a significant factor affecting plastic recovery apart from the chemical agents. It demonstrates that operating IAF with a mixing device at a greater a/G ratio improved the plastic separation performance. These findings suggest that operating an IAF process with a mixing device at suitable a/G conditions could be a promising technique for separating plastic wastes, which have similar physicochemical characteristics as PS and ABS.

Assessing the effectiveness of microplastic extraction methods on fishmeal with different properties

Microplastic presence in fishmeal is an emerging research area because of its potential to enter food chains, and the importance of fishmeal within global food security. However, fishmeal is a complex medium dependant on fish composition. This study measured properties (organics, carbonates, protein and density) of five fishmeal types (trimmings, sardine and anchovy, krill, tuna and salmon), sourced from locations worldwide (Norway, South America, Antarctica, Spain and Scotland). Microplastic recovery rates were compared for existing methodologies using sodium chloride overflows and potassium hydroxide digestions and then compared to newly developed methods. These methods included dispersants and calcium chloride density separations which were developed and designed to be environmentally conscious and affordable, which we argue should become an international standard approach for researchers. A calcium chloride overflow with dispersant and potassium hydroxide digestion provided the highest recovery rate in sardine and anchovy fishmeal (66.3%). Positive correlations with recovery rate were found with protein content, and negative correlations with organic content. Low recovery rates found here suggest microplastics in fishmeal reported in the literature are underestimated. With complex media such as fishmeal, attention must be paid to variation between types and composition when choosing methods and interpreting results.

Is froth flotation a potential scheme for microplastics removal? Analysis on flotation kinetics and surface characteristics

Increasing microplastics (MPs) cause significant threats to the ecosystem and society. The tremendous advances concerning the sources, occurrence, chemical behavior, toxicology, and ecological effects contribute to the emerging MPs removal. Based on the intrinsic hydrophobicity of MPs, froth flotation can remove MPs from water environments via bubble attachment on hydrophobic surfaces. This study comprehensively investigated plastic, aqueous, and operating variables in the flotation removal of polyethylene terephthalate (PET) and polystyrene (PS) MPs, assisted by numerous bench-scale experiments and a first-order model with rectangular distribution of floatability. Froth flotation performed better to remove MPs with higher density, larger size, and lower concentration. K⁺ (0-50 mM), Na⁺ (0-150 mM), and Ca²⁺ (0-10 mM) did not affect the flotation recovery of MPs. MPs particles could be thoroughly removed by froth flotation when humic acid (HA) and Al³⁺ concentrations were less than 30 mg/L and 0.05 mM, respectively. 100% of MPs could be removed at a rapid flotation rate under aeration volume of 5.4 mL/min and frother dosage of 28 mg/L. Non-covalent interactions and near-surface water film might favor the adhesion of hydrophilic species and obstruct the flotation removal of MPs. The froth flotation-based MPs removal had potential application in multiple flow systems due to its simplicity and continuity.

Separation of hazardous polyvinyl chloride from waste plastics by flotation assisted with surface modification of ammonium persulfate: Process and mechanism

Plastic separation becomes an effective method to improve the plastic recycling by concentrating a single component from complex plastic mixtures. Based on advanced oxidation process, surface modification assisted by ammonium persulfate ((NH₄)₂S₂O₈) was applied to selectively wet plastic surface, achieving the separation of hazardous polyvinyl chloride (PVC) from acrylonitrile butadiene styrene (ABS), polystyrene (PS), and polycarbonate (PC) in forth flotation. The mechanisms were investigated through contact angle, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), as well as scanning electron microscope (SEM). The floatability of PS, PC, and ABS reduces owing to the introduction of carbonyl (O = CO), hydroxyl (-OH), and amide (O = C-NH₂) on plastic surfaces, which is the result of the oxidation by sulfate radical (SO₄^∙-) and the hydrolysis of nitrile group (CN) and butadiene (CC). Then, available reaction equations of ABS, PS, and PC were established to supplement the mechanisms of surface modification. The optimal conditions for flotation separation of PVC are (NH₄)₂S₂O₈ concentration 0.2 M, temperature 70 °C, pretreatment time 30 min, pH 10, flotation time 4 min, terpineol dosage 20 mg/L, and particle size 3-4 mm. The recovery and purity of PVC reach 100 % and 99.7 ± 0.2 % respectively, favoring the reuse of separated waste plastic.

Separation of polyvinylchloride and acrylonitrile-butadiene-styrene combining advanced oxidation by S2O82-/Fe2+ system and flotation

A combining technology of advanced oxidation by S₂O₈^2-/Fe²⁺ system and flotation was proposed for separating polyvinyl chloride (PVC) and acrylonitrile butadiene styrene (ABS). In this research, sodium persulfate was activated by heating and ferrous ions. The separation efficiency of PVC/ABS oxidized by S₂O₈^2-/Fe²⁺ was higher than that by sodium persulfate. The mechanism of this process was investigated through contact angle, Fourier transform infrared spectroscopy (FT-IR) inductively coupled plasma (ICP), nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS). The floatability of ABS reduced owing to the introduction of oxygen-containing functional groups such as carbonyl (OCO) and hydroxyl (OH), which was a result of oxidation by sulfate radicals (SO₄^·-). The optimal conditions for separating PVC and ABS were: Na₂S₂O₈ concentration 0.1 M, molar ratio (S₂O₈^2-/Fe²⁺) 200, treatment time 10 min, flotation time 4 min, frother concentration 14.7 mg L^-1 and airflow rate 6.8 mL min^-1. Novel kinetics of pretreatment time and flotation were proposed and researched in this work. The max rate constant of PVC/ABS flotation was 0.64 min^-1. In addition, the pretreatment solution can be reused for three times with superior performance. The recovery and purity of PVC reached 100% and 99.7%, respectively. According to reasonable evaluation, the combination of S₂O₈^2-/Fe²⁺ advanced oxidation and flotation is a practical and efficient technology for separating PVC and ABS.

Evaluation of ground calcite/water heavy media cyclone suspensions for production of residual plastic concentrates

Viable recycled residual plastic (RP) product(s) must be of sufficient quality to be reusable as a plastic or source of hydrocarbons or fuel. The varied composition and large volumes of such wastes usually requires a low cost, high through-put recycling method(s) to eliminate contaminants. Cyclone separation of plastics by density is proposed as a potential method of achieving separations of specific types of plastics. Three ground calcite separation medias of different grain size distributions were tested in a cylindrical cyclone to evaluate density separations at 1.09, 1.18 and 1.27 g/cm³. The differences in separation recoveries obtained with these medias by density offsets produced due to displacement of separation media solid particles within the cyclone caused by centrifugal settling is evaluated. The separation density at which 50% of the material of that density is recovered was found to increase from 0.010 to 0.026 g/cm³ as the separation media density increased from 1.09 to 1.27 g/cm³. All separation medias were found to have significantly low Ep₉₅values of 0.012-0.033 g/cm³. It is also demonstrated that the presence of an excess content of <10 µm calcite media particles (>75%) resulted in reduced separation efficiencies. It is shown that the optimum separations were achieved when the media density offset was 0.03-0.04 g/cm³. It is shown that effective heavy media cyclone separations of RP denser than 1.0 g/cm³ can produce three sets of mixed plastics containing: PS and ABS/SAN at densities of >1.0-1.09 g/cm³; PC, PMMA at a density of 1.09-1.18 g/cm³; and PVC and PET at a density of >1.27 g/cm³.

Study of the physicochemical effects on the separation of the non-metallic fraction from printed circuit boards by inverse flotation

Recycling printed circuit boards using green technology is increasingly important due to the metals these contain and the environmental care that must be taken when separating the different materials. Inverse flotation is a process that can be considered a Green Technology, which separates metallic from non-metallic fractions. The degree of separation depends on how much material is adhered to air bubbles. The contact angle measurement allows to determine, in an easy way, whether the flotation process will occur or not and thus establish a material as hydrophobic or not. With the material directly obtained from the milling process, it was found that the contact angle of the non-metallic fraction-liquid-air system increases as temperature increases. In the same way, the increments in concentration of frother in the liquid increase the contact angle of the non-metallic fraction-liquid-air system. 10ppm of Methyl Isobutyl Carbinol provides the highest contact angle as well as the highest material charging in the bubble.

A novel process for separation of polycarbonate, polyvinyl chloride and polymethyl methacrylate waste plastics by froth flotation

A novel process was proposed for separation of ternary waste plastics by froth flotation. Pretreatment of plastics with potassium permanganate (KMnO₄) solution was conducted to aid flotation separation of polycarbonate (PC), polyvinyl chloride (PVC) and polymethyl methacrylate (PMMA) plastics. The effect of pretreatment parameters including KMnO₄ concentration, treatment time, temperature and stirring rate on flotation recovery were investigated by single factor experiments. Surface treatment with KMnO₄ changes selectively the flotation behavior of PC, PVC and PMMA, enabling separation of the plastics by froth flotation. Mechanism of surface treatment was studied by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray photoelectron spectrum (XPS). Effect of frother concentration and flotation time on flotation behavior of plastic mixtures was further studied for flotation separation. The optimized conditions for separation of PC are KMnO₄ concentration 2mmolL^-1, treatment time 10min, temperature 60°C, stirring rate 300rpm, flotation time 1min and frother concentration 17.5mgL^-1. Under optimum conditions, PVC and PMMA mixtures are also separated efficiently by froth flotation associated with KMnO₄ treatment. The purity of PC, PVC and PMMA is up to 100%, 98.41% and 98.68%, while the recovery reaches 96.82%, 98.71% and 98.38%, respectively. Economic analysis manifests remarkable profits of the developed process. Reusing KMnO₄ solution is feasible, enabling the process greener.

Separation of plastics by froth flotation. The role of size, shape and density of the particles

Over the last few years, new methods for plastic separation in mining have been developed. Froth flotation is one of these techniques, which is based on hydrophobicity differences between particles. Unlike minerals, most of the plastics are naturally hydrophobic, thus requiring the addition of chemicals that promote the selective wettability of one of its components, for a flotation separation. The floatability of six granulated post-consumer plastic - Polystyrene (PS), Polymethyl methacrylate (PMMA), Polyethylene Terephthalate (PET-S, PET-D) and Polyvinyl Chloride (PVC-M, PVC-D) - in the presence of tannic acid (wetting agent), and the performance of the flotation separation of five bi-component plastic mixtures - PS/PMMA, PS/PET-S, PS/PET-D, PS/PVC-M and PS/PVC-D - were evaluated. Moreover, the effect of the contact angle, density, size and shape of the particles was also analysed. Results showed that all plastics were naturally hydrophobic, with PS exhibiting the highest floatability. The contact angle and the flotation recovery of six plastics decreased with increasing tannic acid concentration, occurring depression of plastics at very low concentrations. Floatability differed also with the size and shape of plastic particles. For regular-shaped plastics (PS, PMMA and PVC-D) floatability decreased with the increase of particle size, while for lamellar-shaped particles (PET-D) floatability was slightly greater for coarser particles. Thus, plastic particles with small size, lamellar shape and low density present a greater floatability. The quality of separation varied with the mixture type, depending not only on the plastics hydrophobicity, but also on the size, density and shape of the particles, i.e. the particle weight. Flotation separation of plastics can be enhanced by differences in hydrophobicity. In addition, flotation separation improves if the most hydrophobic plastic, that floats, has a lamellar shape and lower density and if the most hydrophilic plastic, that sinks, has a regular shape and higher density. The results obtained show that froth flotation is a potential method for plastics separation, in particular for plastics with particle size greater than 2.0mm.

Investigation on an innovative technology for wet separation of plastic wastes

This paper presents an original device for the separation of plastic polymers from mixtures. Due to the combination of a characteristic flow pattern developing within the apparatus and density, shape and size differences among two or more polymers, this device allows their separation into two products, one collected within the instrument and the other one expelled through its outlet ducts. Experimental tests have been conducted to investigate the effectiveness of the apparatus, using two geometric arrangements, nine hydraulic configurations and three selections of polymers at three stages of a material life cycle. Tests with samples composed of a single typology of polymer have been used to understand the interaction between the particles and the carrying fluid within the apparatus in different hydraulic configurations and geometric arrangements. Multi-material tests are essential to simulate the real conditions in an industrial recycling plant. The separation results have been evaluated in terms of grade and recovery of a useful material. Under the proper hydraulic configurations, the experimentation showed that it is possible to produce an almost pure concentrate of Polyethylene Terephthalate (PET) from a mixture of 85% PET and 15% Polycarbonate (PC) (concentrate grade and recovery equal to 99.5% and 95.1%) and a mixture of 85% PET and 15% Polyvinyl Chloride (PVC) (concentrate grade and recovery equal to 97.9% and 100.0%). It is further demonstrated that almost pure concentrates of PVC and PC can be produced from a mixture of 85% PVC and 15% PC (PVC grade and recovery equal to 99.9% and 99.7%) and a mixture of 85% PC and 15% PVC (PC grade and recovery equal to 99.0% and 99.5%).

Flotation separation of waste plastics for recycling-A review

The sharp increase of plastic wastes results in great social and environmental pressures, and recycling, as an effective way currently available to reduce the negative impacts of plastic wastes, represents one of the most dynamic areas in the plastics industry today. Froth flotation is a promising method to solve the key problem of recycling process, namely separation of plastic mixtures. This review surveys recent literature on plastics flotation, focusing on specific features compared to ores flotation, strategies, methods and principles, flotation equipments, and current challenges. In terms of separation methods, plastics flotation is divided into gamma flotation, adsorption of reagents, surface modification and physical regulation.

Separation of polyethylene terephthalate from municipal waste plastics by froth flotation for recycling industry

Recycling is an effective way to manage plastic wastes and receives considerable attention. Since plastic mixtures are difficult to recycle because of their intrinsic characteristics, separation of mixed plastics is the key problem for recycling. Separation of polyethylene terephthalate (PET) from municipal waste plastics (MWP) by froth flotation combined with alkaline pretreatment was investigated for recycling industry. The effect of process variables was estimated by L9 (3(4)) orthogonal array of experiments and single factor experiments. The optimum conditions of alkaline pretreatment are 10 wt% sodium hydroxide, 20 min and 70°C. After alkaline pretreatment under optimum conditions, flotation separation PET from acrylonitrile-butadiene-styrene, polystyrene, polycarbonate or polyvinyl chloride was achieved with high purity and efficiency. The purity of PET is up to 98.46% and the recovery is above 92.47%. A flow sheet of separation PET from MWP by a combination of froth flotation and sink float separation was designed. This study facilitates industrial application of plastics flotation and provides technical insights into recycling of waste plastics.

Separation of polycarbonate and acrylonitrile-butadiene-styrene waste plastics by froth flotation combined with ammonia pretreatment

The objective of this research is flotation separation of polycarbonate (PC) and acrylonitrile-butadiene-styrene (ABS) waste plastics combined with ammonia pretreatment. The PC and ABS plastics show similar hydrophobicity, and ammonia treatment changes selectively floatability of PC plastic while ABS is insensitive to ammonia treatment. The contact angle measurement indicates the dropping of flotation recovery of PC is ascribed to a decline of contact angle. X-ray photoelectron spectroscopy demonstrates reactions occur on PC surface, which makes PC surface more hydrophilic. Separation of PC and ABS waste plastics was conducted based on the flotation behavior of single plastic. At different temperatures, PC and ABS mixtures were separated efficiently through froth flotation with ammonia pretreatment for different time (13 min at 23 °C, 18 min at 18 °C and 30 min at 23 °C). For both PC and ABS, the purity and recovery is more than 95.31% and 95.35%, respectively; the purity of PC and ABS is up to 99.72% and 99.23%, respectively. PC and ABS mixtures with different particle sizes were separated effectively, implying that ammonia treatment possesses superior applicability.