A novel process for the coupling treatment of coal gangue and red mud is reported. Red mud containing 23.4% Al2O3, 19.1% SiO2, and 9.4% Na2O by weight was used as the blended ingredients of coal gangue for alumina extraction. Calcination of coal gangue with the addition of Na2CO3 at 850 °C could obtain more than 90% of Al2O3 extraction. Nevertheless, the high consumption of Na2CO3 is equivalent to the same weight amount of coal gangue. Both nepheline and sodium aluminum silicate formed during the process have the molecular structure of NaAlSiO4. The 1:1:1 of the theory molar ratio of Na, Al, and Si suggested that the minimum consumption of Na2CO3 might be obtained at the optimal Al/Si molar ratio of 1:1. Red mud with an Al/Si molar ratio of 1.44 mixed with coal gangue with a ratio of 0.64 was used to extract alumina. The results showed that red mud could adjust the Al/Si molar ratio of coal gangue to an appropriate value and Na2O in red mud was also used to partly substitute for Na2CO3 required for coal gangue activation, which consequently decreased the consumption of Na2CO3 from 100% to 12.1–20.5%.

Flotation continues to be a major technique for the production of potash from low grade, complex systems containing a variety of ores and ions. The specific ion effects on the behavior of the flotation collector in the KCl flotation system becomes important to the interpretation of the flotation mechanism. In this work, specific ion effects on the turbidity, surface tension and aggregation behavior of the common collector in KCl flotation, octadecylamine hydrochloride (ODA), have been investigated. The results from turbidity and surface tension studies of ODA solutions show that both cations and anions can affect the colloidal properties of ODA. Molecular dynamics simulations show that the binding that energy barrier between ODA headgroups and anions is principally responsible for the specific anion effect of γCAC of ODA solutions. In addition, the ion effect on the ODA aggregation particle size was also studied by using transmission electron micrographs (TEM) and dynamic light scattering. The data reveal that the presence of salt ions can induce the formation of larger ODA colloidal particles, on which the cation effect is more significant. This work provides detailed information of specific ion effect on colloidal properties of ODA, which may promote a further understanding of the flotation mechanism and help to improve the flotation of KCl from brine sources.

•Poly-silicic-cation coagulants were prepared for bio-treated coking wastewater.•PAFSiC demonstrates the highest bio-refractory organics removal efficiency.•PASiC and PFSiC have specific interactions with different organic components.•The superiority of PAFSiC is due to the synergetic effect of aluminum and iron.•Floc structure is important for capture, adsorption and enmeshment of the organics.Poly-silicic-cation coagulants are increasingly being used to remove the bio-refractory organic compounds from industrial wastewaters, yet the research on the interactions between the coagulants and organics remains limited. In this study, three composite coagulant poly-aluminum-silicate-chloride (PASiC), poly-ferric-silicate-chloride (PFSiC) and poly-aluminum-ferric-silicate-chloride (PAFSiC) were prepared and examined as tertiary-treatment coagulants for coking wastewater. Excitation-emission fluorescence (EEM) spectra and gas chromatograph/mass spectroscopy (GC/MS) were applied to characterize composition of the organics, and the floc characteristics were monitored using a laser diffraction particle size analyzer and a particle vision system. The results show that a board range of organics including microbial metabolites, fulvic acid and humic acid-like fluorophores and polymeric aromatic hydrocarbons, can be removed by PAFSiC. This is attributed to the synergetic removal of organic compounds by aluminum and iron based poly-silicic salts. Compared with PASiC and PFSiC, the resultant flocs of PAFSiC have the moderate size and porous inner structure, with more branch-like units but less agglomeration. The structure is favorable for capture, adsorption and enmeshment of the bio-refractory organic compounds from the bio-treated coking wastewater. This study indicates that the organic removal is closely related to floc characteristics and PAFSiC can be used as an effective and promising coagulant for tertiary-treatment of coking wastewater.Download high-res image (211KB)Download full-size image

•A horizontal rich/lean burner and polygonal tangential fired furnace were studied.•Factors influencing the flow in the horizontal fuel-rich/lean burner were studied.•The polygonal tangential air system enhances the multi-scale staged combustion.•The retrofit of power plant boilers demonstrated this burner reduced NOx by 56%.Large quantities of low-volatile coal are utilized in power plants throughout China. With increasingly stringent environmental regulations, it is important to develop and deploy low-NOx combustion technologies for pulverized coal boilers burning low-volatile coal. The objective of this study was to investigate a novel decoupling combustion system for low-volatile coal via experiments and computational fluid dynamics (CFD). The combustion system includes horizontal fuel-rich/lean low-NOx burners (LNB) and the associated air distribution system for a polygonal tangentially fired boiler (PTFB). The effects of coal particle diameter and coal feeding rate on the gas/particle flow characteristics of the burner, and the cold state aerodynamic field of the PTFB were analyzed in detail. The structural design of the LNB results in advantageous gas/particle flow characteristics and the PTFB improved the distribution of the flow field. The CFD models and simulation results were validated by comparing with those of cold experiments data. The simulation results demonstrated that this low-NOx combustion technology enhances staged combustion at different scales, which can reduce NOx generation significantly. In the industrial application on a 300 MW pulverized coal boiler, installation of the LNBs improved the stability of low-volatile coal combustion and reduced NOx emissions significantly. These research findings provide valuable guidance to the design of low-NOx combustion system for pulverized coal boilers using low volatile coal.

•A reaction mechanism of kaolinite calcined with sodium carbonate is proposed.•The mechanism relies on the combination change of different oxygen coordination.•Pauling's electrostatic valence rule limits the arrangement of [AlO4] and [SiO4].Thermal decomposition, phase transformation and microstructure change for the mixture of kaolinite and sodium carbonate (Na2CO3) calcined at different temperatures were studied through experimental investigation and theoretical analysis. Thermo-gravimetric and differential scanning calorimetric coupled with mass spectrometer (TG-DSC/MS) were utilized to determine the reaction temperature of kaolinite and Na2CO3. The calcinated products at different temperatures were characterized by X-ray diffraction (XRD), magic angle spinning nuclear magnetic resonance (MAS-NMR) and Fourier transform infrared (FT-IR). The results showed that the solid-state reaction between kaolinite and Na2CO3 mainly occurred within the temperature of 300–850 °C. During the calcining process, kaolinite was decomposed and transformed into meta-kaolin (MK), low-temperature carnegieite (L-phase), nepheline and zeolite in turn, which can be interpreted in terms of the combination change of different oxygen coordination. With the increase of temperature, the [AlO6] octahedron in kaolinite gradually transformed into the [AlO4] tetrahedron in MK by dehydroxylation, and the bridging oxygen between [AlO4] and [SiO4] layers together with the bridging oxygen in [AlO4] layer and [SiO4] layer were broken with the participation of Na2CO3. Subsequently, the obtained individual [AlO4] and [SiO4] tetrahedrons alternately recombined and formed an anion frame-like structure by sharing the oxygen atom owing to the limitation of Pauling's electrostatic valence rule. In order to further maintain the charge neutrality and structural stability, Na+ ions were filled in the anion frame-like structure of L-phase, nepheline and zeolite. This research is of some theoretical significance for the Na2CO3-assisted thermal activation of kaolinite and kaolinite-based solid wastes.

•Anion effects on ODA adsorption characteristics were studied by SFVS and MDS.•Anions penetrate and disturb the ODA monolayer.•The larger the anion the greater the disruption of the ODA monolayer.•With the exception of sulfate, H-bonding of water increases with anion addition.The spread of collector molecules on bubble surfaces in salt solution is a fundamental phenomenon in the froth flotation of soluble salts, such as KCl, and consideration of ionic effects on adsorption behavior and packing of collector molecules at the air/solution interface is appropriate for study. In this work, specific anion effects on the adsorption and packing of one common collector (octadecylamine hydrochloride, ODA) at the air/water interface were investigated by employing a combination of surface pressure measurements, sum frequency vibrational spectroscopy (SFVS) and molecular dynamics simulations (MDS). The results from experiments and MDS showed that the addition of external anions disturbs the arrangement of ODA molecules due to the penetration of these anions from the water subphase into the ODA monolayer at the air/water interface. During monolayer compression, the penetrated anions might be driven back to the water subphase by electrostatic forces and the added compression force. These anions could screen the charge of NH3 groups resulting in a reduction of the minimum area of the ODA molecule (Amin) for the solid phase state of the monolayer. With the exception of the sulfate anion, the added anions increase hydrogen bonding of interfacial water molecules at the air/water interface. These results allow for a better understanding of the anionic effect on adsorption and packing of ODA molecules at the air/water interface, and might therefore provide new insights into froth flotation of soluble salts and should help to improve soluble salt flotation technology.Download high-res image (201KB)Download full-size imageA combination of SFVS and MDS techniques was employed to reveal the molecular characteristics of ODA adsorption at the air/water interface.

•The interaction between probes and CN in solution was studied in detailed.•Probe 1 can be applied in bioimaging.•The detection limit is as low as 10−8M.In this work two novel fluorescent imaging materials for CN with twin binding groups (1 and 2) have been synthesized and fully characterized by standard analytical tools and spectroscopic techniques. The selectivity of 1 and 2 has been explored in aqueous solution, and the resulting turn-on fluorescence response toward CN among different anions was studied. The cyanide ion adduct was characterized using NMR and mass spectroscopy and detection mechanism was further confirmed to be the nucleophilic attack of the indolium group of probe by CN, which induces a turn-on fluorescence change. NMR and mass spectra indicate nucleophilic addition of CN to indolium group is reversible in ionization process. For the practical application of the sensors, 1 could be used for fluorescence-microscopic imaging of CN in biological applications.Based on the nucleophilic attack of the indolium group by CN under mild conditions, we herein report two new fluorescent probe which features a rapid signal response time, a good linearity range and a low detection limit. The potential application of this new fluorescent probe was demonstrated by fluorescent imaging of CN in living cells.

•Adsorption kinetics and isotherm of ODA at KCl crystal surface are studied.•The effects of bubbling and temperature are discussed systematically.•Micro-flotation tests are conducted to support the adsorption behaviors.•Results could develop the design of process and facilities of KCl flotation.Understanding the adsorption process of collectors and the interaction between bubbles and mineral particles during KCl froth flotation are still weaknesses in our interpretation of the mechanism of flotation. In this study, we investigated in detail the adsorption kinetics and adsorption isotherm of a commonly used collector, octadecylamine hydrochloride (ODA), at the surface of KCl crystals. The effects of bubbling and temperature are discussed systematically. Our results indicated that the adsorption of ODA onto the surface of KCl crystals can be facilitated by bubbles, and that the adsorption kinetics of this process can be interpreted according to a pseudo-second order model. Both the Langmuir and Freundlich isotherm models were found to fit the adsorption isotherm of ODA on KCl crystal surface inappropriately, implying that the adsorption of ODA upon KCl crystal surfaces is a more complex process than typical monolayer, or multilayer, adsorption. This might be because the adsorption of ODA on KCl crystal surfaces takes place through an aggregated intermediate, rather than through the direct interaction of dispersed molecules. We note that the quantity of ODA adsorbed at 0 °C increased markedly with increasing numbers of bubbles. Micro-flotation tests suggested that increasing the gas flow rate effectively improved flotation recovery at 0 °C, consistent with the adsorption behavior. These results provide complementary information on the adsorption behavior of ODA at the surface of KCl crystals and on the effect of bubbles during froth flotation, which could help to design new flotation process and improve flotation recovery of KCl at low temperatures.Download high-res image (124KB)Download full-size imageThe presence of bubbles can facilitate the adsorption of ODA on KCl surface due to the formation of bubble-collector-KCl crystal structure in the froth flotation.

The combustion characteristics of coal sludge were investigated with thermogravimetric analysis at different heating rates (10, 20, 30, 40 °C min−1). The influences of heating rates on the combustion behavior of coal sludge were studied. The research found that the value of general combustion parameters for Taiyuan coal sludge (TY) is the lowest, for Shuozhou coal sludge (SZ) is the highest, and for Jincheng coal sludge (JC) is in middle at any heating rate. The experimental results indicated that a higher heating rate is useful for the combustion performance of coal sludge in this study. Kinetic parameters of the coal sludge samples were evaluated with the Ozawa–Flynn–Wall (OFW) and distributed activation energy model (DAEM) method. The activation energy values obtained from the DAEM method are a little lower than the ones obtained from the OFW method for every kind of coal sludge. The activation energy values of JC were 119.62 and 113.63 kJ mol−1 obtained by OFW and DAEM methods, respectively, and were lower than corresponding values of TY and SZ. Higher amounts of alkaline metal (Na and K), alkaline earth metals (Ca and Mg), Fe and Ti in JC may play a major role in lowering the activation energy values. The present results have important significance for understanding the characteristics of combustion of coal sludge.

•The effect of ultrasound on morphology of precipitated CaCO3 was investigated.•Ultrasound makes CaCO3 crystals smaller in nucleation or early growth stages.•Pretreatment and post-treatment by ultrasound cause diverse morphologies.•Effects of NH3 and CO2 on morphology are opposite to those of ultrasound and Na+.•Crystals may be square, spheroidal, ellipsoidal, pisciform, hexagonal, etc.Micron-grade calcium carbonate (CaCO3) crystals are by-products in the preparation of (NH4)2SO4 fertilizer using CaSO4·2H2O, NH3, and CO2. Since ultrasound can make crystals smaller and their morphology quite complex, the morphological change rules need to be studied to make meaningful use of them. In the present work, the morphologies of CaCO3 crystals precipitated from the ultrasound CaSO4-NH3-CO2-H2O system were analyzed in different conditions. It was found that ultrasound can make the crystals smaller in nucleation or the early growth stage, or it can make the shapes diversified and dispersed by influencing the solution property and in the aging process. In an ultrasound environment, crystals may be square, spheroidal, ellipsoidal, pisciform (spindle), hexagonal, carambola-like, or scattered particles. High-concentrations of NH3 and CO2 facilitate CaCO3 crystals becoming smooth balls, while high-intensity ultrasound and a high-concentration of foreign Na+ ions help to turn CaCO3 into tiny square particles or a clustered aggregate of tiny particles with rough surfaces.

•A novel process of alumina extraction from coal fly ash has been proposed.•The consumption of Na2CO3 decreased significantly by the process.•The alumina dissolution could reach 87% at the lower consumption of Na2CO3.•The process realizes the high value and high efficiency utilization of CFA.Alumina extraction from coal fly ash (CFA) by Na2CO3 activation-acid leaching method could make Al2O3 and SiO2 in CFA achieve high value utilization simultaneously, which shows wide application prospects. The large consumption of Na2CO3, however, limits its industrial application. A novel process of alumina extraction from coal fly ash by “Pre-desilicating—Na2CO3 activation—acid leaching” has been proposed in this work. By this process, the consumption of Na2CO3 decreased significantly thanks to the adjustment of Al/Si molar ratio in the raw materials. The effects of pre-desilication conditions on the dissolution of SiO2 in coal fly ash, the effect of the novel process on the consumption of Na2CO3 and the phase transformations and the alumina dissolutions at various consumption of Na2CO3 were investigated. The results showed that the dissolution of SiO2 reached 37.3% at 20% (by weight) of NaOH concentration, 1 mL/g of liquid to solid ratio, 100 °C and 2.0 h, when the Al/Si molar ratio in coal fly ash could be raised to 1.21 from 0.81. The mixed coal fly ash with an Al/Si molar ratio of 1 could be obtained by mixing desilicated and the as-received coal fly ash. The dissolution of Al2O3 of the mixed coal fly ash reached ~ 87% at the Na/Al molar ratio of 1. The consumption of Na2CO3 decreased obviously and the reduction percentage reached 53.1% at Na/Al molar ratio of 1.0 after undergoing the pre-desilication process compared with the Na2CO3 direct activation process. This work could provide a novel thought for the utilization of coal fly ash with high value and high efficiency.

•Mechanical grinding greatly improved the alumina extraction from coal gangue.•Kaolinite in coal gangue still maintained the SiOAlVI structure without calcination.•An amorphous metakaolinite with SiOAlIV structure was formed with calcination.•Grinding before calcination made the amorphous transformation more completely.Coal gangue, a type of kaolinite clay in coal measures, is one of the largest categories of solid industrial wastes in China. Alumina extraction from coal gangue could offer an alternative to bauxite as a source of alumina. Mechanically modification by grinding is an effective activation method to improve alumina recovery from coal gangue. The effect of grinding on coal gangue, however, had not been investigated systematically. Present understanding regarding the effects of grinding on coal gangue is still restricted to that on kaolinite. Furthermore, the differences in the inherent mechanisms between grinding and thermal activation on coal gangue have not been investigated so far. This study aimed to clarify the differences among them. Changes in particle size, surface area, and morphology were followed by means of laser particle size analysis, nitrogen adsorption/desorption isotherms, and scanning electron microscopy (SEM). Possible modifications of the chemical structure, mineral phase and thermal behavior were monitored using X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Infrared analysis (IR), and Thermogravimetry (TG). The results showed that the alumina dissolution from coal gangue increased with longer grinding time. Grinding followed by calcination further improved the alumina extraction. After the calcined coal gangue was ground for 20 h, the alumina extraction reached ~ 95%. The results of XRD, XPS, and IR analysis implied that grinding produced defects in the coal gangue kaolinite; however the main kaolinite layer structure (SiOAlVI) were unaffected in the absence of calcination. In this case, the improved activity might be due to reduced particle size, increased surface area, and aluminum enrichment at the surface. The primary structure of kaolinite in coal gangue was destroyed by calcination after grinding, and kaolinite was altered to amorphous metakaolinite with SiOAlIV structure, which facilitated alumina extraction.SEM images of coal gangue particles after 20 h grinding.

•The Fe(III) extraction using undiluted Aliquat 336 is fast and highly efficient.•Undiluted ILs have higher Fe(III) loading capacity than conventional extractants.•The regeneration and recycling of undiluted ILs have been demonstrated.•The high purity AlCl3·6H2O was obtained from CMW based on Fe(III) removal using ILs.This study reported an environmentally benign approach to iron(III) extraction using undiluted Aliquat 336. This technique was then applied for iron(III) removal from coal mining waste (CMW) hydrochloric acid leach liquor to produce high purity aluminum chloride. The extraction behavior, loading capacity, selectivity, and stripping of iron(III) were investigated within synthetic solutions and compared with those obtained from Cyphos IL 101. The results showed that iron(III) can be quantitatively extracted using Aliquat 336 with high efficiency and high selectivity against aluminum(III), calcium(II), magnesium(II) and potassium(I). The maximum loading capacity of iron(III) in Aliquat 336 was 100.7 g L−1, which is higher than that in Cyphos IL 101. Iron can be more effectively stripped from Aliquat 336 rather than Cyphos IL 101 when using 0.5 M H2SO4 as the stripping solution. The regeneration of the IL phase and their reuse in subsequent extractions of iron from CMW leach liquor were further examined. The extraction efficiency of iron(III) decreased after Aliquat 336 and Cyphos IL 101 had been recycled for six and three cycles, respectively. High purity AlCl3·6H2O crystals were prepared under vacuum evaporation from the raffinate after iron removal, where the iron content in the AlCl3·6H2O crystals was less than 0.005%.

•Colloidal properties of ODA in different saturated salt solutions were studied in detail.•Effect of temperature was considered for all the systems.•Turbidity and surface activity were discussed systematically.•Contact angle indicates the effect of ions on the adsorption of ODA on KCl crystal surface.Froth flotation is still an efficient technique for KCl production from low grade and complex systems containing various ions. In this work, the colloidal properties of one common collector, octadecylamine hydrochloride (ODA), in different saturated salt solutions at different temperature are investigated systematically. The results show that the turbidity of salt solutions increased substantially with the concentration of ODA increasing and the ODA colloidal particles aggregate seriously in the presence of MgCl2. Compared with ODA aqueous solutions, the surface activity and the critical aggregate concentration (CAC) of ODA became lower in saturated salt solutions. With the increase of MgCl2 percentage, the CAC values of ODA solution decreased gradually, while the CAC value of KCl-MgCl2 saturated solution was the lowest. The temperature has a great influence on the turbidity and surface activity of ODA aqueous solution, however, the effect is slight in saturated salt solutions. In addition, the salt solutions with MgCl2 result in lower contact angle on KCl crystal surface indicating that the adsorption of ODA molecules can be inhibited in the salt solutions with MgCl2.

A novel molecule, 3,6-bis(dimesitylboryl)-9-(4-(1,2,2-triphenylvinyl)phenyl)-9H-carbazole (DTPC), was synthesized by introducing two dimesitylboron groups and one tetraphenylethene group to the 3-position, 6-position, and 9-position of carbazole, respectively. The structure of DTPC was fully characterized by proton nuclear magnetic resonance spectroscopy, mass spectrometry, and elemental analysis. The thermal, electrochemical, and photophysical properties of DTPC were studied by thermogravimetry in conjunction with electrochemistry, UV–vis absorption spectroscopy and fluorescence spectroscopy. The results reveal that DTPC has excellent aggregation-induced emission properties. The multilayer electroluminescent device fabricated by using DTPC as light-emitting layer emits the blue light (λmax 489 nm) with CIE coordinates (0.17, 0.29) and shows good electroluminescent performances with the turn-on voltage of 5.7 V, maximum luminance of 5709 cd/m2 (at 15 V) and maximum luminance efficiency of 4.31 cd/A (at 8.2 V).A novel compound based on tetraphenylethene, carbazole and dimesitylboron moieties with aggregation-induced emission (AIE) properties was synthesized and utilized as a highly efficient blue light-emitting material in OLEDs.

•The kerosene emulsion was used as collector for water insoluble mineral flotation.•The stability was tested using water and KCl saturated solution as aqueous phase.•A highly stabilized emulsion tends to form in the KCl saturated solution.The removal of slimes (water-insoluble minerals) from high slime-containing potash ores from Qinghai Province, PRC, was investigated using flotation. A higher slime flotation recovery was obtained when a surfactant (polyoxyethylene fatty acid ester)–kerosene water emulsion was used as the collector. The stabilities of the kerosene/aqueous emulsions in water and in KCl saturated solution were tested to understand the mechanism of the desliming flotation process. The results showed that the phase separation of the emulsion was pronounced at low surfactant concentration. Microscopic observation of the emulsion microstructure indicated that the droplets were spherical with the exception of samples with low surfactant concentration and that the droplet size increased with decreasing surfactant concentration. The emulsion droplets in the KCl saturated solution were smaller than those in pure water. Additionally, the emulsion was easier to stabilize in KCl because of the higher surface activity in KCl saturated solution; therefore, this emulsion can be used as a collector in desliming flotation.

•AlCl3⋅6H2O recovered from the acid leaching liquors of coal gangue using concentrated hydrochloric inpouring.•Low temperature (<45 °C) and high volume ratio of HCl to liquor (>2.25) are beneficial to the recovery of AlCl3⋅6H2O.•The effect of the recycled crystallized liquor on the comprehensive dissolution of alumina is negligible.•The remained Al and impurities in crystallized liquor had a significant effect on the quality of AlCl3⋅6H2O.Alumina extraction from coal gangue is hopeful to solve the stockpile and pollution problems of it in China. The impurities such as Fe, Ca, K and Mg in coal gangue would be dissolved in the acid leaching liquor in the process of alumina extraction using hydrochloric acid leaching, resulting in the difficulty in the separation of Aluminum. AlCl3⋅6H2O recovery from the recycled AlCl3-containing acid leaching liquor of coal gangue by concentrated hydrochloric acid inpouring was discussed in this paper. It showed that the saturated AlCl3 solution or leaching liquor presented high recovery and the maximum reached more than 80% at <45 °C. The recovery increased with increasing the volume of concentrated HCl. It reached >85% of the maximum crystallization at the volume ratio of concentrated HCl to the solution exceeding 2.25. The effect of the recycled crystallized liquor on the comprehensive dissolution of alumina is negligible. The contents of Al and levels of impurities such as Fe, Ca, K and Mg in the leaching liquor increased with the cycles, which had a significant effect on the recovery and quality of AlCl3⋅6H2O. The recovery of AlCl3⋅6H2O decreased gradually with the cycles and it decreased to 59.5% after 10th cycle. The contents of AlCl3⋅6H2O in crystals decreased since the levels of impurities in it increased with the cycles, which would limit the cycle times of the crystallized liquor.

In this study, iron(III) extraction from acidic chloride solutions using undiluted trihexyltetradecylphosphonium chloride (Cyphos IL 101) was carried out in a liquid–liquid extraction process. The extraction behaviors under various HCl, chloride, and iron(III) concentrations; selectivity; and extraction isotherm of iron(III) were investigated. It was found that iron(III) was extracted fast and efficiently in a wide chloride concentration range. The highly selective separation of iron(III) from aluminum(III), calcium(II), magnesium(II), and potassium(I) in acidic chloride solutions was achieved with a separation factor of Fe(III) over Al(III) at 11 000 from a 3 M HCl solution. The maximum loading capacity of iron(III) reached 83.2 g·L–1 with a molar ratio of 0.91 for Fe(III)/Cyphos IL 101. Effective stripping of the loaded iron(III) was achieved with a 0.5 M H2SO4 solution. The iron-chloro complexes in both aqueous phase and Cyphos IL 101 phase were characterized using spectroscopic techniques. Ultraviolet–visible and Raman spectra confirmed that iron(III) formed a series of iron-chloro complexes in acidic chloride solutions, while present solely in the form of tetrachloroferrate complex ([FeCl4]−) in the Cyphos IL 101 phase. An extraction mechanism was proposed in which both FeCl3 ion association and [FeCl4]− anion exchange with the chloride anion of Cyphos IL 101 play the key role during iron(III) extraction.

Two novel indolo[3,2-b]carbazole derivatives, 5,11-di(4′-dimesitylboronphenyl)indolo[3,2-b]carbazole (DDBICZ) and 2,8-dimesitylboron-5,11-di(4′-dimesitylboronphenyl)indolo[3,2-b]carbazole (DDDBICZ), were synthesized by introducing two dimesitylboron groups and/or four dimesitylboron groups (as electron-acceptors) into the indolo[3,2-b]carbazole moiety (as an electron-donor). The structures of these two compounds were fully characterized by elemental analysis, mass spectrometry and proton nuclear magnetic resonance spectroscopy methods. Their thermal properties were studied by thermogravimetric analysis and differential scanning calorimetry. Their electrochemical and photophysical properties were studied by electrochemical methods, UV-vis absorption spectroscopy and fluorescence spectroscopy. The charge-transporting properties of DDBICZ and DDDBICZ were studied by fabricating single carrier devices using them as charge-transporting layers. The results reveal that DDBICZ and DDDBICZ have high thermal stability (the decomposition temperature of DDBICZ = 201 °C and the decomposition temperature of DDDBICZ = 210 °C) and good electrochemical and electron-transporting properties. Moreover, in order to examine the electroluminescent properties of DDBICZ and DDDBICZ, Device A and Device B were fabricated by using them as light-emitting layers, respectively. The turn-on voltage, maximum luminance and maximum luminance efficiency of Device A are 6.1 V, 5634 cd m−2 and 2.96 cd A−1, whereas those of Device B are 3.6 V, 1363 cd m−2 and 2.88 cd A−1.

•A novel asymmetric indolo[3,2-b]carbazole compound was synthesized.•The compound contains benzothiazole and diphenylamino moieties.•The compound has strong intramolecular charge transfer character.•The compound can be served as an excellent hole-transporting material in OLEDs.A novel asymmetric donor–π-donor–π-acceptor compound, 2-benzothiazolyl-8-diphenylamino-5,11-dihexylindolo[3,2-b]carbazole (BDDAICZ), has been successfully synthesized by introducing a benzothiazole moiety (as an electron-acceptor) and a diphenylamino moiety (as an electron-donor) to 2-position and 8-position of indolo[3,2-b]carbazole moiety (as a skeleton and an electron-donor), and characterized by elemental analysis, 1H NMR, 13C NMR and MS. The thermal, electrochemical properties of BDDAICZ were characterized by thermogravimetric analysis combined with electrochemistry. The absorption and emission spectra of BDDAICZ was experimentally determined in several solvents and computed using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The calculated absorption and emission wavelengths are coincident with the measured data. The ionization potential (IP), the electron affinity (EA) and reorganization energy of BDDAICZ were also investigated using density functional theory (DFT). Charge-transporting properties of BDDAICZ were characterized by OLEDs devices fabricated by using it as charge-transport layers. The results show that BDDAICZ has excellent thermal stability, electrochemical stability and hole-transporting properties, indicating its potential application as a hole-transporting material in OLEDs devices.Graphical abstract

•MDS was used to study interfacial water structure at KCl crystal surfaces.•MDS of brine and brine/KCl crystals was used to determine effect of temperature.•At low temperature MDS, water molecules increased order at a KCl crystal surface.•Low temperature might change KCl from water ‘structure breaker’ to ‘structure maker’.The low flotation recovery of sylvite from salt lakes at low temperatures has dogged the cryogenic producer for many years. Interfacial water structure at sylvite crystal surfaces has been considered as one noticeable aspect on interpreting the selected KCl collection during flotation, and so the microscopic structure of the water membrane over KCl crystal surfaces at low temperatures was modeled through the use of molecular dynamics methods. In our simulation, the properties of the water membrane adjacent to KCl crystal surface, such as molecular mobility, water structure and preferred molecular orientation, were compared to the results for an otherwise identical system at higher temperatures or in saturated KCl solutions in the absence of a KCl crystal. In our simulation, hydrogen atoms approached the KCl crystal surface more closely, and the mobility of water molecules was more restricted compared to results for saturated KCl solutions. When the temperature decreased, the mobility of water molecules decreased, the number of hydrogen bonds made by the water molecules in the membranes was reduced and the molecules exhibited greater order than in other systems we studied. It was proposed that the property of KCl salt may change from water ‘structure breaker’ to ‘structure maker’ when temperature decreases. These results may provide complementary information which cannot be obtained from experiments on the research of flotation at low temperature directly.Download high-res image (105KB)Download full-size image

•Pb was the main pollution source in greenhouse soils and vegetables.•Cd had larger enrichment ability, especially in leaf vegetables.•Transfer factors: leaf vegetables ≥ fruit vegetables > tuber vegetables.•Leaf and fruit vegetables had higher HI than tube types.Heavy metal pollution in greenhouse vegetable production system is a growing concern for public health. In this study, 87 soil and 72 vegetable samples were collected from greenhouse vegetable production systems in Shanxi province, Northern China, aiming to evaluate the accumulation characteristics and potential risk of heavy metals in soil-vegetable system under greenhouse condition. The results showed that Cd and Pb concentrations in 72.4% and 35.5% of the soil samples were higher, while all of As, Cr, Ni, Cu, Zn samples were lower than the Grade II value in Environmental Quality Standard for Soils (GB15618-1995). Nearly 99% of the total amount Pb existed in the form of residual and could not be absorbed by vegetables. The proportions of As, Cd, Zn in ionic form, bound to carbonates and the exchangeable fraction were 6.21, 13.71, and 13.47% respectively, and were relatively higher than other metals (Cr, Cu, Ni, Pb). The transfer factors (TF) of As, Cr, Ni, Pb were found to be higher in leaf and fruit vegetables than that in tuber vegetables. With a relatively low total concentration and high proportion of available form in soils, Cd showed relatively larger TF in three kinds of vegetables than other metals. The concentrations of Cr, Ni and Pb in three kinds of greenhouse vegetables exceeded the limit in national food safety standards. Especially, Ni in leaf and fruit vegetables showed significantly higher hazard quotient (HQ) than that in tube vegetables. Overall, leaf and fruit vegetables had a relatively higher hazard index (HI) than tube types, and exceeded 1, suggesting that there was larger potential health risk by ingestion of heavy metals through fruit and leaf vegetables. Thus, in order to avoid human body health endangered by heavy metals through the food chain, appropriate management measures should be implemented in greenhouse cultivation, especially tuber vegetables be cultivated instead of leaf and fruit types.

•Time-varying properties of gypsum have remarkable effect on wastewater coagulation.•Ripening is a mechanism for affecting the dispersion of gypsum/kaolinite particles.•Ostwald ripening equations were embedded into the extended DLVO model.•Four stages of potential variation happen in the ripening and coagulation process.Besides the well-known mechanism of compressed double electric layer, this paper quantitatively found that the time-varying properties of gypsum particles play an important role on coagulation of kaolinite loaded wastewater. The Ostwald ripening equations were embedded into the DLVO model, based on which we investigated how the size and ξ potential of gypsum particles and the interaction energy between gypsum and kaolinite particles work as a function of time. Four stages were presented when gypsum particles were added into water: the trends in size were smaller, larger, constant and smaller whereas the ξ potential absolute values increased, decreased and remained constant, respectively. The electrostatic and the total potentials between gypsum and kaolinite particles decreased first, followed by an increase–decrease fluctuation as time passed. According to the potential changing, the biggest coagulation tendency happens when the gypsum particles have been put into water for 6–7 min, but it is not stable until the water soaking time reaches 30 min. This deduction was confirmed by the pilot sedimentation test of wastewater with gypsum as a coagulant. Furthermore, the network structures formed by fine ripening gypsum particles were observed and the flocculation effect was confirmed to be another part of the co-sedimentation mechanisms.Download high-res image (126KB)Download full-size image

•We discussed the activation effect of Na2CO3 on coal gangue.•Na2CO3 react with aluminosilicates in coal gangue to form nepheline at 600~900 °C.•Na2CO3 improved the dissolution of Al2O3 and made SiO2 enriched in the residue.•Na2CO3 facilitate the decomposition of AlO6 and SiO4 network in coal gangue.The effect of Na2CO3 additive on the activation of coal gangue for alumina extraction was investigated. The discussion on the action mechanisms was performed by the means of TG-DSC, XRD and XRF. The results showed that the calcined coal gangue with the addition of Na2CO3 improved the alumina extraction significantly. At the calcination temperatures of 800–900 °C with Na2CO3 to coal gangue weight ratios of 0.8–1, the alumina extractions of > 90% were obtained. There were reactions between Na2CO3 and coal gangue during the calcination to form nepheline, which improved the dissolution of Al2O3 in acid and enriched SiO2 concentration in the residue during the acid leaching process. Na2CO3 could attack AlO6 and SiO4 network in coal gangue owing to the compensation charge effect, and therefore facilitate the decomposition of coal gangue.

•Water structure influence on the flotation of sulfate salts.•FTIR shows that K2SO4 is a water structure breaker and MgSO4 is a structure maker.•Flotation of arcanite, a structure beaker, can be float by DAH and SDS collectors.•Flotation of epsomite, a structure maker, can not be achieved by DAH and SDS.The flotation chemistry of soluble salts has been studied for many decades. In this work, the flotation behavior of arcanite (K2SO4) and epsomite (MgSO4·7H2O) with both the cationic collector, dodecylamine hydrochloride (DAH), and the anionic collector, sodium dodecyl-sufate (SDS), has been studied. The results show that K2SO4 can be floated with both the cationic and anionic collectors at natural pH. In contrast, MgSO4·7H2O cannot be floated by either collector. The results indicate that the flotation response of these salts cannot be explained based on surface charge considerations. It is now known that interfacial water structure has been found to be a significant factor in the explanation of soluble salt flotation.In this regard, the water structure of K2SO4 and MgSO4 solutions was investigated by FTIR-transmission and FTIR-ATR methods which are useful to detect changes in water structure as influenced by dissolved salts. FTIR transmission spectra suggest that MgSO4 is a water structure making salt, while it is expected that K2SO4 is a structure breaker, although such an expectation is not confirmed from FTIR transmission spectra due to the low solubility of K2SO4.In this regard, FTIR-ATR measurements can also be used to determine the influence of dissolved salts on water structure. After subtraction of the O–H band spectrum of salt solutions from that of pure water, the change in the “ice-like” water structure as influenced by the dissolved salt (K2SO4 and MgSO4) can be observed even in solutions of K2SO4 at low concentrations. In summary, the results from FTIR spectroscopy of solutions show that K2SO4 is a water structure breaker, while MgSO4 is a water structure maker. This conclusion is further confirmed from a macroscopic view point by viscosity measurements. Again for these sulfate salts flotation is achieved with DAH and SDS as collectors if the salt is a water structure breaker.