•Surface treatment with Fenton was developed for flotation separation of waste plastics.•Surface treatment changes selectively the floatability of ABS surface.•Mechanism of surface treatment was studied by FT-IR and XPS analysis.•Plastic mixtures with different particle sizes and mass fractions were separated effectively.Surface treatment with Fenton was applied to flotation separation of acrylonitrile-butadienestyrene (ABS) and polyvinylchloride (PVC). After treatment, the floatability of ABS has a dramatic decrease, while the floatability of PVC is not affected. Fourier transform infrared spectroscopy (FT-IR) spectra and X-ray photoelectron spectroscopy (XPS) spectra were recorded to ascertain the mechanism of Fenton treatment. FT-IR and XPS analysis confirms that the introduction of oxygen-containing group occurs on the surface of ABS. The optimum conditions are molar ration (H2O2:Fe2+) 10000, H2O2 concentration 0.4 M/L, pH 5.8, treatment time 2 min and temperature 25 °C, frother concentration 15 mg/L and flotation time 3 min. Particle sizes and mixing ratios were also investigated. Plastic mixtures of ABS and PVC with different particle sizes and mixing ratios can be effectively separated. The purity of ABS and PVC are up to 100% and 99.78%, respectively; the recovery of ABS and PVC are up to 99.89% and 100%, respectively. A practical, environmentally friendly and effective reagent, namely Fenton, was originally applied to surface treatment of ABS and PVC waste plastics for flotation separation of their mixtures.Download high-res image (227KB)Download full-size image

•A novel method was proposed for separation of PVC by froth flotation.•Calcium hypochlorite treatment improves selectively surface wettablity.•Mechanism of surface treatment was examined by SEM, FTIR and XPS.•Binary plastics with different particle sizes were separated effectively.•Separation of PVC from mixed plastic wastes was obtained.A novel method, calcium hypochlorite (CHC) treatment, was proposed for separation of hazardous poly(vinyl chloride) (PVC) plastic from mixed plastic wastes (MPWs) by froth flotation. Flotation behavior of single plastic indicates that PVC can be separated from poly(ethylene terephthalate) (PET), poly(acrylonitrile-co-butadiene-co-styrene) (ABS), polystyrene (PS), polycarbonate (PC) and poly(methyl methacrylate) (PMMA) by froth flotation combined with CHC treatment. Mechanism of CHC treatment was examined by contact angle measurement, scanning electron microscopy, Fourier transform infrared and X-ray photoelectron spectroscopy. Under the optimum conditions, separation of PVC from binary plastics with different particle sizes is achieved efficiently. The purity of PC, ABS, PMMA, PS and PET is greater than 96.8%, 98.5%, 98.8%, 97.4% and 96.3%, respectively. Separation of PVC from multi-plastics was further conducted by two-stage flotation. PVC can be separated efficiently from MPWs with residue content of 0.37%. Additionally, reusing CHC solution is practical. This work indicates that separation of hazardous PVC from MPWs is effective by froth flotation.Download high-res image (138KB)Download full-size image

•KMnO4 treatment changes selectively flotation behavior of PC, PVC and PMMA plastics.•Ternary waste plastics are separated efficiently by froth flotation.•Recycling of KMnO4 solutions is conducted to make the process green.•A novel process is proposed for separation of 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 2 mmol L−1, treatment time 10 min, temperature 60 °C, stirring rate 300 rpm, flotation time 1 min and frother concentration 17.5 mg L−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.Download high-res image (230KB)Download full-size image

•Fenton treatment was developed for flotation separation of PVC from plastic mixtures.•Fenton treatment selectively decreased the floatability of PC and PS plastic.•FT-IR confirmed the introduction of oxygen-containing group on PC and PS surface.•The purity and the recovery of PVC were up to 99.26% and 100.00% respectively.The generation of waste plastics has been radically promoted by large-scale consumption and rapid upgrading of plastic products in the last decades, which brings serious threats to environment and management. Combined with Fenton treatment, froth flotation was evaluated to separate polyvinyl chloride (PVC) from waste plastics for recycling. The floatability of polystyrene (PS) and polycarbonate (PC) has a dramatic decrease after Fenton treatment, while the floatability of PVC is not affected. Contact angle, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were conducted to ascertain the mechanism of Fenton treatment. The reduction of PS and PC floatability is attributed to the increase of surface wettability confirmed by contact angle measurement. FT-IR and XPS analysis confirmed that hydrophilic oxygen-containing groups were introduced on PC and PS surface. SEM images indicated that Fenton treatment considerably increased the surface roughness of PC and PS. With respect to flotation separation PVC from plastic mixtures, optimum conditions are molar ratio (H2O2/Fe2+) 7500, H2O2 concentration 0.2 M/L, treatment 2 min, temperature 25 °C, pH 5.8, frother concentration 15 mg/L and flotation time 4 min. Particle size, mass fractions and reuse of plant effluent were also investigated. After Fenton treatment under optimum conditions, floatation separation of PVC from plastic mixtures was accomplished with high purity and recovery. The purity and the recovery of PVC are up to 99.26% and 100% respectively. The purity and the recovery of other plastics are up to 100% and 97.20% respectively. Consequently, flotation combined with Fenton treatment is a simple, environmental friendly and cost-effective method for separation of PVC from plastic mixtures.Download high-res image (225KB)Download full-size image

Coal-based active carbon was prepared and used as electrodes of electric double-layer capacitors (EDLCs). The performance of EDLCs using active carbon electrodes with different pore structure was studied, including cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. With an increase of sodium hydrate/coal ratio, the pore structure of active carbon is greatly improved, resulting in larger double-layer capacitance. The capacitance of asymmetric EDLC is up to 65.98 F/g. Moreover, it is found that different pore structure of active carbon is necessary for positive and negative electrodes. Asymmetric EDLC not only exhibits high capacitance but also shows excellent charge-discharge performance, suggesting that it is very suitable and promising to design electrode materials for supercapacitors.

•Succinylation of camphor leaf was conducted for sorption of Pb(II) ion.•The adsorbent was characterized by COD, FTIR, XRD and SEM.•Sorption process follows pseudo-second order model and Langmuir model.•The removal rate and sorption capacity reach 99.98% and 185.2 mg g−1.•Ion exchange mechanism was determined in the sorption process.Camphor leaf from a native everygreen tree (Cinnamomum camphora) widely distributed in southwestern part of China is locally available waste in China. A novel biosorbent (SCLP) was prepared by modification camphor leaf with succinic anhydride for Pb (II) removal. SCLP was characterized by Fourier transform infrared spectrum (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Chemical modification reduces negative effects on the treated water, and it introduces carboxyl groups on the surface, improving the sorption capacity. Sorption of Pb (II) ions was evaluated at different SCLP dose, pH, contact time and initial concentration. Sorption equilibrium and kinetics were investigated by sorption isotherms and kinetic models. Sorption of Pb (II) onto SCLP follows pseudo-second order kinetics and Langmuir model. Ion exchange plays an important role for Pb (II) uptake onto SCLP. The removal rate and sorption capacity is up to 99.98% and 185.2 mg g−1. It is anticipated that camphor leaf would find important application in purification Pb (II) from wastewaters, owing to the advantages of high efficiency, low cost and environmental friendliness.

A hydrometallurgical process was developed for recycling pharmaceutical blisters. Leaching aluminum from pharmaceutical blisters using sodium hydroxide (NaOH) solutions was investigated with respect to leaching behaviors and kinetics. A L9 (34) orthogonal design of experiments suggests that the most significant factor is NaOH concentration followed by temperature and leaching time. Factorial experiments demonstrate that the leaching rate of aluminum increases with increasing of the factors. The optimum conditions are temperature of 70 °C, leaching time of 20 min, NaOH concentration of 1.25 mol/L, liquid-to-solid mass ratio of 15:1 and agitation speed of 400 r/min. Under optimum conditions, the leaching rate is up to 100%, implying that aluminum and polyvinyl chloride (PVC) plastic in pharmaceutical blisters are separated completely. Kinetics of leaching aluminum is best described by the product layer diffusion control model, and the activation energy is calculated to be 19.26 kJ/mol.

Wetting behavior and wetting mechanism of wetting agents on low-energy surface (LES) are well investigated in this paper. Four wetting agents, namely Lignin sulfonate, Tannic acid, Methylcellulose and Triton X-100, were involved in our study. Wetting behavior was well examined through discussion of surface energy of LES, interfacial interaction and zeta potential of polymer resins. Experimental results demonstrate that adsorption of wetting agents changes the surface energy parameters of LES; interfacial free energy between wetting agent molecule and LES exhibits hydrophobic attraction between them fails to be the dominant driving force of adsorption; the effect of wetting agent on zeta potential of polymer illustrates electrostatic force is not the major factor of interfacial interaction between wetting agent molecule and LES. Based on wetting action of wetting agents, we discussed wetting mechanism of wetting agents on LES in detail, and an adsorption model was proposed. Adsorption of wetting agent on LES is achieved through hydration shell taken as mesophase, namely, hydrophobic attraction between LES and water molecule results in the formation of hydration shell, and wetting agents molecules approach to hydration shell under the effect of Lifshitz–van der Waals attraction and they adsorb on hydration shell through hydrogen bond. In terms of post-consumer plastics composed of polymer and additives, apart from hydrophobic attraction and hydrogen bond, wetting action depends also on chelating ability between wetting agent molecule and additive ions due to the chemical adsorption between wetting agent and additives. In addition, wetting ability, adsorption and selective desorption of wetting agents are well examined.Adsorption of wetting agents on low-energy surface is achieved through hydration shell taken as mesophase.Highlights► Adsorption of wetting agents changes the surface energy parameters of low-energy surface (LES). ► Hydrophobic attraction between LES and wetting agents and electrostatic force are not the major reasons of adsorption. ► An adsorption model is proposed. ► Wetting ability, adsorption intensity and desorption of wetting agent are investigated.

Recycling of printed circuit board (PCB) is an important subject and to which increasing attention is paid, both in treatment of waste as well as recovery of valuable material terms. Precede physical and mechanical method, a good liberation is the premise to further separation. In this study, two-step crushing process is employed, and standard sieve is applied to screen crushed material to different size fractions, moreover, the liberation situation and particles shape in different size are observed. Then metal of the PCB is separated by physical methods, including pneumatic separation, electrostatic separation and magnetic separation, and major metal contents are characterized by inductively coupled plasma emission spectrometry (ICP-AES). Results show that the metal and nonmetal particles of PCB are dissociated completely under the crush size 0.6 mm; metal is mainly enriched in the four size fractions between 0.15 and 1.25 mm; relatively, pneumatic separation is suitable for 0.6–0.9 mm size fraction, while the electrostatic separation is suitable for three size fractions that are 0.15–0.3 mm, 0.3–0.6 mm and 0.9–1.25 mm. The whole process that involves crushing, electrostatic and magnetic separation has formed a closed cycle that can return material and provide salable product.Highlights► Metal and nonmetal particles have been completely dissociated for the crushed PCB material in diameter that is smaller than 0.6 mm. ► Metal in PCB can be separated by physical method that involves crushing, electrostatic and magnetic separation. ► Copper grade does can be achieved to more than 71% by single electrostatic or electrostatic, magnetic combined separation.

•A simple and practical method was developed for separation of waste plastics.•Surface modification increases selectively the wettability of PVC.•Mechanism of surface modification may be due to oxidization reactions.•Flotation separation of PVC and PET was obtained efficiently.•A flotation process was designed for flotation separation of PVC and PET plastics.Surface modification with potassium permanganate (KMnO4) solution was developed for separation of polyvinyl chloride (PVC) and polyethylene terephthalate (PET) waste plastics. The floatability of PVC decreases with increasing of KMnO4 concentration, treatment time, temperature and stirring rate, while that of PET is unaffected. Fourier transform infrared (FT-IR) analysis confirms that mechanism of surface modification may be due to oxidization reactions occurred on PVC surface. The optimum conditions are KMnO4 concentration 1.25 mM/L, treatment time 50 min, temperature 60 °C, stirring rate 300 r/min, frother concentration 17.5 g/L and flotation time 1 min. PVC and PET with different particle sizes were separated efficiently through two-stage flotation. Additionally, after ultrasonic assisted surface modification, separation of PVC and PET with different mass ratios was obtained efficiently through one-stage flotation. The purity and the recovery of the obtained products after flotation separation are up to 99.30% and 99.73%, respectively. A flotation process was designed for flotation separation of PVC and PET plastics combined with surface modification. This study provides technical insights into physical separation of plastic wastes for recycling industry.Graphical abstractSurface modification with KMnO4 solutions increased the wettability of PVC plastic, while PET was unaffected. A process was developed for flotation separation of PVC and PET waste plastics combined with surface modification.Download high-res image (168KB)Download full-size image

Interfacial interactions involving Van der Waals force, hydrophobic attractive force and hydration exclusive force were investigated in this paper. The interfacial interactive free energy of a series of interfaces occurring between minerals, water, collectors and bubble was calculated. The results show that a Van der Waals attractive force and a hydrophobic attractive force exist between each mineral and water interface. The hydrophobic attractive force between molybdenite and water is markedly weaker than the hydrophobic attractive force between gangue and water. The hydrophobic attractive force between collector molecules and water is the main driving force that causes the collectors to become dispersed in the pulp. The strong hydrophobic attractive force between molybdenite and the bubble interface is the basic reason for the natural floatability of molybdenite. The Van der Waals force between molybdenite and the collectors is attractive in water solution, but it is not the cause of the main force between them. The main force that results in the collection effect is a hydrophobic attractive force caused by the Lewis acid-base interaction at the molybdenite surface. A floatation experiment shows that the adsorption intensity of the collector on the molybdenite surface is not the crucial factor for molybdenite floatation. Rather, the dispersing capability of the collector in the water phase and its selectivity for the various minerals in the floatation system are more important.

•Flotation separation of plastics was reviewed including principles, methods and challenges.•The specific features of plastics flotation are presented compared to ores flotation.•Four methods were classified in terms of plastics flotation.•The problems that hinder the application of plastics flotation are put forward.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.

•Boiling treatment was developed to aid plastic separation.•Surface rearrangement of polymer made surface of boiling treated ABS hydrophilic.•Flotation separation of ABS and PS was achieved efficiently.A new physical method, namely boiling treatment, was developed to aid flotation separation of acrylonitrile–butadiene–styrene (ABS) and polystyrene (PS) plastics. Boiling treatment was shown to be effective in producing a hydrophilic surface on ABS plastic. Fourier Transform Infrared analysis was conducted to investigate the mechanism of boiling treatment of ABS. Surface rearrangement of polymer may be responsible for surface change of boiling treated ABS, and the selective influence of boiling treatment on the floatability of boiling treated plastics may be attributed to the difference in the molecular mobility of polymer chains. The effects of flotation time, frother concentration and particle size on flotation behavior of simple plastic were investigated. Based on flotation behavior of simple plastic, flotation separation of boiling treatment ABS and PS with different particle sizes was achieved efficiently. The purity of ABS and PS was up to 99.78% and 95.80%, respectively; the recovery of ABS and PS was up to 95.81% and 99.82%, respectively. Boiling treatment promotes the industrial application of plastics flotation and facilitates plastic recycling.Graphical abstractAs shown in the figure above, surface rearrangement of polymer made surface of boiling treated ABS hydrophilic. Flotation separation of ABS and PS plastics was achieved efficiently combined with boiling treatment.Download full-size image

The aim of this research was to separate waste plastics acrylonitrile butadiene styrene (ABS) and polystyrene (PS) by dissolved air flotation in a self-designed dissolved air flotation apparatus. The effects of wetting agents, frother, conditioning time and flotation time on flotation behavior of waste plastics ABS (w-ABS) and PS (w-PS) were investigated and the optimized separation conditions were obtained. The results showed that when using 25 mg L−1 tannic acid, 5 mg L−1 terpineol, 15 min conditioning time and 15 min flotation time, mixtures of w-ABS and w-PS were separated successfully by dissolved air flotation in two stages, the results revealed that the purity and recovery rate of w-PS in the floated products were 90.12% and 97.45%, respectively, and the purity and recovery rate of w-ABS in the depressed products were 97.24% and 89.38%, respectively. Based on the studies of wetting mechanism of plastic flotation, it is found that the electrostatic force and hydrophobic attraction cannot be the main factor of the interaction between wetting agent molecules and plastic particles, which can be completed through water molecules as a mesophase, and a hydrogen bonding adsorption model with hydration shell as a mesophase was proposed.Highlights► The dissolved-air flotation is applied on separation of waste plastics. ► The depressing ability of TA on waste plastics is higher than that of LS. ► Increasing conditioning time benefits the adsorption of wetting agent. ► W-ABS and w-PS could be separated by dissolved-air flotation using 25 mg L−1 TA. ► A hydrogen bonding adsorption model with hydration shell as a mesophase is proposed.

•Factors of NaOH treatment were studied by orthogonal and single factor experiments.•Mechanism of alkaline treatment for facilitating flotation was manifested.•Flotation separation of PET was achieved with high purity and efficiency.•A flow sheet of purification PET from MWP was designed.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 (34) 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.

•The properties of wetting agents were investigated.•Adsorption of wetting agents changes wetting behavior of polymer resins.•Flotability of polymer materials modulated by wetting agents was studied.•The wetting ability is lignin sulfonate > tannic acid > methylcellulose > triton X-100.•Flotation separation of plastic mixtures was achieved by using wetting agents.The surface free energy, surface tension and contact angles were performed to investigate the properties of wetting agents. Adsorption of wetting agents changes wetting behavior of polymer resins. Flotability of polymer materials modulated by wetting agents was studied, and wetting agents change significantly flotability of polymer materials. The flotability decreases with increasing the concentration of wetting agents, and the wetting ability is lignin sulfonate (LS) > tannic acid (TA) > methylcellulose (MC) > triton X-100 (TX-100) (from strong to weak). There is significant difference in the flotability between polymer resins and plastics due to the presence of additives in the plastics. Flotation separation of two-component and multicomponent plastics was conducted based on the flotability modulated by wetting agents. The two-component mixtures can be efficiently separated using proper wetting agent through simple flotation flowsheet. The multicomponent plastic mixtures can be separated efficiently through multi-stage flotation using TA and LS as wetting agents, and the purity of separated component was above 94%, and the recovery was more than 93%.Flotability of polymer materials modulated by wetting agents was studied, and wetting agents change significantly flotability of polymer materials. Flotation separation of plastic mixtures was conducted based the flotability modulated by wetting agents. The multicomponent plastic mixtures can be efficiently separated through multi-stage flotation using TA and LS as wetting agents, and the purity of separated component was above 94%, and the recovery was more than 93%.Download full-size image

•The EDLVO profiles were calculated to examine interparticle interactions.•The dominant force between plastic particles is hydrophobic attraction.•Selective adsorption of wetting agents improves flotation separation of plastics.•Increasing the polarity of solid surface reduces hydrophobic attraction.Plastics flotation used for recycling of plastic wastes receives increasing attention for its industrial application. In order to study the mechanism of plastics flotation, the interfacial interactions between plastic particles in flotation system were investigated through calculation of Lifshitz–van der Waals (LW) function, Lewis acid–base (AB) Gibbs function, and the extended Derjaguin–Landau–Verwey–Overbeek potential energy profiles. The results showed that van der Waals force between plastic particles is attraction force in flotation system. The large hydrophobic attraction, caused by the AB Gibbs function, is the dominant interparticle force. Wetting agents present significant effects on the interfacial interactions between plastic particles. It is found that adsorption of wetting agents promotes dispersion of plastic particles and decreases the floatability. Pneumatic flotation may improve the recovery and purity of separated plastics through selective adsorption of wetting agents on plastic surface. The relationships between hydrophobic attraction and surface properties were also examined. It is revealed that there exists a three-order polynomial relationship between the AB Gibbs function and Lewis base component. Our finding provides some insights into mechanism of plastics flotation.

•Ammonia treatment changes selectively floatability of PC.•The effects of ammonia on PC were investigated through contact angle and XPS.•Reactions between ammonia and PC surface make PC more hydrophilic.•PC and ABS mixtures with different particle sizes were separated effectively.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.

•The flotation tests of various polymer materials were conducted modulated by frothers.•Three-category low-energy surface was defined based on the hydrophile index of polymer materials.•A model of adsorption of frother molecules was proposed.•Floatability of polymer materials modulated by frothers is investigated and discussed.Flotation tests of 35 polymer materials were carried out to investigate their floatability modulated by frothers. Results of flotation tests demonstrated that polymer resins and soft PVC showed high floatability, floatability of hard PVC plastics was relatively low and was related to the frothers, and there exists significant difference in the floatability of different post-consumer plastics. Flotation rate of post-consumer plastics varies from 0% to 100%. Furthermore, three-category low-energy surface (LES) was defined based on the hydrophile index of the materials involved in this paper, and an adsorption model was proposed to explain the results of flotation and to discuss the floatability of polymer materials modulated by frothers. Frother molecules are prone to adsorb on the surface of bubble rather than LES at relatively low concentration, bubble adsorbed by frother molecules is prone to approach first-category LES rather than third-category LES, and the structure of liquid film is formed on the first-category LES at large concentration. Floatability of polymer materials modulated by frothers is further discussed: frothers increase the floatability of the first-category LES but decrease the floatability of the third-category LES, while the floatability of the second-category LES is related to the type of frothers.

Neutral oils like kerosene, diesel, transformer and rapeseed oil were used as collectors or bridging reagents in conventional flotation and oil agglomeration flotation (OAF) process, and a promising OAF process has been developed for the recycling of ultrafine molybdenite resources from the waste tailings. The average size of collected particles (d50p), agglomerates (d50a) and their distribution of the froth concentrate were determined by laser particle size analyzer or sieve analysis. Conventional flotation froth cannot catch the ultrafine particles, so it is an ineffective process to recover molybdenum metal in the waste tailings, while OAF has some advantages to recover fine minerals. And the best result was obtained from transformer oil due to its appropriate length of carbon chain, kinematic viscosity and cyclical structure. The oil amount plays a very important role on average size of the particles, with the increase of transformer oil from 2.0 to 13.8 kg/t, d50a increases from 0.15 to 0.68 mm and d50p decreases from 9.06 to 2.05 μm. This finding suggests the bigger the d50a, the smaller the d50p, and the higher the recovery of molybdenite.The appropriate conditions for recovering ultrafine molybdenite were determined as follows: dosage of frother: 0.5 kg/t, natural pH: 6.2, stirring time: 3 min, and stirring intensity:400–600 r/min. Lastly, the closed cycle test and industrial application in the producing scale of 500 t/d were carried out, and result shows 95% molybdenum was recovered with a satisfied grade of 22.62%.Graphical abstractThe mean diameter of agglomerates (d50a) increased from 0.15 to 0.68 mm when the dosage of oil increased from 2.0 to 13.8 kg/t. At the same time, the mean diameter of collected molybdenite particles (d50p) decreased from 9.06 to 2.05 μm with the increase of the transformer oil amount. Accordingly, it can be conjectured the bigger the d50a, the smaller the d50p, and the higher the molybdenum recovery.Download full-size imageHighlights► Conventional flotation is an ineffective process in recovery of ultrafine molybdenite. ► The mean particle size of concentrate using transformer oil as bridging is 2.05 μm. ► The bigger the d50a, the smaller the d50p, and the higher the molybdenum recovery. ► Oil agglomeration flotation has achieved good results under industrial scale.