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Graphical abstract Abstract Conversion of solid wastes into biochar for removal of toxic heavy metals provides a cleaner method for waste management and benefits environmental protection. Ultrasound-assisted alkali activation of biochar prepared by pyrolysis of camphor leaves (Cinnamomum camphora) was used as sorbent (AABC) for Pb(II) sorption. The biochar was characterized by XPS, FTIR, XRD and SEM. Ultrasound-assisted alkali activation results in more surface groups, larger surface area and pore volume, contributing to larger sorption capacity of AABC. AABC shows larger sorption rate than biochar (BC) without alkali activation. Chemisorption between surface groups and Pb(II) ions is verified by the pseudo-second order kinetics. Langmuir isotherm suggests that the maximum monolayer sorption capacity of Pb(II) onto AABC is 98.33 mg g−1, 2.5 times higher than BC and comparable to reported biochar. Ultrasound-assisted alkali activation provides a promising method for improving sorption capacity of biochar in terms of heavy metals sorption. [ABSTRACT FROM AUTHOR]

The wettability of floc has a large effect on the selective flocculation flotation process of fine coal separation. The changes of thermodynamic characterization of coal and kaolinite have been investigated by Washburn dynamic method and Fourier transform infrared spectroscopy (FTIR) before and after the adsorption of anionic polyacrylamide. Lipophilic hydrophilic ratio (LHR), surface free energy, and its components were calculated by Washburn equation combined with Van Oss–Chaudhury–Good theory according to the wetting curves of coal and kaolinite samples wetted by n-hexane, α-bromonaphthalene, formamide, and water. After PAM A401 adsorption, the peaks of hydrophilic functional groups of coal (the amide group, free-NH2, secondary amide N–H, C–N) were increased, while the peaks of the hydrophobic functional group, including methyl (-CH3) and methylene (–CH2–), was decreased. The LHR value of coal decreased from 9.23 to 7.28. The polar components of coal were increased, the non-polar components were decreased, and the surface free energy was increased from 39.92 to 40.43 mN m−1. The coal surface became more hydrophilic. For kaolinite, both hydrophilic and hydrophobic functional groups were increased, while its LHR values increased from 1.44 to 1.65. The polar component was decreased from 58.27 to 55.05 mN m−2. Results of FTIR were corresponding to the surface property. [ABSTRACT FROM AUTHOR]

In order to remove aluminum ions in bauxite processing wastewater, two natural clay minerals (bentonite and kaolin) were used as adsorbents. The adsorption behaviors including kinetics and isotherms were studied at much broader pH range, higher temperature, and higher Al(III) concentration by batch experiments. The adsorption mechanisms were investigated by optical microscope, zeta potential testing, and XRD analysis. The results show that Al(III) adsorption is strongly pH dependent and increases clearly with increasing pH. The pseudo-second-order kinetic model can best describe the adsorption process, and the intra-particle diffusion was not the sole rate-controlling step. The Langmuir–Freundlich model can fit best the adsorption equilibrium data, and the maximum capacities of Al(III) adsorbed on bentonite and kaolin reach to 8.52 mg g–1and 0.58 mg g–1, respectively, at 35°C. Thermodynamic studies display that the adsorption of Al(III) onto clay minerals is non-spontaneous. The adsorption of Al(III) onto bentonite is endothermic and causes an increase in the entropy, while kaolin is exothermic and causes a decrease in the entropy. The interaction mechanisms of Al(III) with bentonite and kaolin involve electrostatic attraction, cation exchange, surface complex, and precipitation. Bentonite as adsorbent has more potential to remove Al(III) than kaolin. [ABSTRACT FROM PUBLISHER]

In order to improve the separation efficiency of fine oil droplets from oily wastewater, a new process utilizing coal adsorption and column flotation has been developed. In this work, anthracite from Jincheng, China was used as an adsorbent for oil removal from wastewater. The effects of adsorption time, coal particle size distribution, the value of pH, and the oil concentration in wastewater on the adsorption capacity of anthracite were investigated by static experiments. A novel device named a cyclone-static microbubble flotation column was developed for the separation of oily wastewater, which combines the conventional hydrocyclone with a conventional flotation column. Coal adsorption-column flotation tests were carried out and scaled-up from a lab-scale (1 m3/day), to a pilot scale (30 m3/day), and to a full-scale (2000 m3/day) unit. Different operating parameters, such as coal dosage, feed rate, circulation pressure, and gas flow rate were studied. In full-scale tests of 2000 m3/day, oil removal of 97.70% with the treated effluent containing an oil concentration of 23.39 mg/L was obtained. [ABSTRACT FROM AUTHOR]

In practical celestite flotation, iron contamination is commonly found on celestite surfaces. The effect of ferric ions on celestite flotation was assessed by a combination of ion release experiments, DFT calculation, X-ray photoelectron spectroscopy (XPS) analysis, adsorption isotherm study, and flotation experiments in this work. The ion release experiments showed that the associated limonite released ferric ions to solution. According to DFT calculation and surface complexation theory, we found that ≡SrOH0 and ≡SO4H0 are primary functional groups on celestite surface in aqueous environments. The XPS analysis and adsorption isotherm study revealed that ferric ions mainly adsorbed on celestite surface by complexing with two oxygen atoms of surface ≡SrOH0 groups to form ≡Sr–O–Fe–OH precipitates. Flotation results showed that ferric ions strongly depressed celestite flotation. Combined with the change in surface properties determined by XPS, it can be concluded that the adsorption of ferric ions on celestite surface decreased adsorption sites for the collector, and hence, led to depression on celestite flotation. [ABSTRACT FROM AUTHOR]

Ca2+, Mg2+, Sr2+ and Fe3+ were found to be commonly released into bastnaesite flotation pulp from minerals with relatively high concentrations. The influence and corresponding mechanism of Ca2+, Mg2+, Sr2+, Fe3+ and Al3+, on bastnaesite flotation, have been studied by micro flotation tests, induction time measurements, adsorption measurements and solution chemistry analysis. It was found that all aforementioned metal ions depressed bastnaesite flotation. The order of depression ability was Fe3+ > Al3+ > Mg2+ > Sr2+ > Ca2+ and the depression ability changed along with pH. The depression was mainly attributed to the adsorption of metals ions, which hindered collector adsorption. The species diagrams of metal ions changed along with pH, consequently changing the adsorption of metal ions on mineral surfaces, and therefore leading to different influences on flotation. [ABSTRACT FROM AUTHOR]

Ti 3 C 2 MXenes were constructed via different strategies using HF-forming etchants or HF as etchants and were subsequently modified through alkalization to replace –F with O-containing terminal functional groups. Various analytical techniques were used to fully characterize all fabricated materials for confirming the formation of species with the desired morphologies and properties. ML-Ti 3 C 2 , etched with HF, presented a multilayered structure that made it resemble an accordion, while DL-Ti 3 C 2 , prepared using HF-forming etchants, was not completely etched, with some amounts of the parent compound's Al remaining in unformed vague laminated structures. ML-Ti 3 C 2 alkalization yielded ML-Ti 3 C 2 (OH) 2 , which was characterized by large amounts of O-containing functional groups and greatly enhanced porosity compared with that of ML-Ti 3 C 2. Methylene blue (MB) adsorption and photocatalytic degradation tests were then conducted to evaluate the functionalities of ML-Ti 3 C 2 (OH) 2 by putting it into direct application instead of being used as catalyst promoters. ML-Ti 3 C 2 (OH) 2 achieved adsorption–desorption equilibrium using MB in the dark within 30 min and 81.2% of MB was then selectively degraded over 120 min under simulated visible light irradiation. A possible degradation mechanism was proposed on the basis of the results of radical quenching experiments. This study offers a unique mechanism for directly applying MXene to the adsorption–photocatalytic degradation of organics in wastewater. For Preparation and regulation of two-dimensional Ti 3 C 2 T x MXene for enhanced adsorption-photocatalytic degradation of organic dyes in wastewater. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • The hardness of hydroxyl group on the mineral surface affects the interaction between metal ions and mineral surface. • The hydroxyl groups on the cassiterite surface are less hard-base, while on the quartz surface are high hard-base. • The oxygen on the quartz surface has stronger localization, and it has no electron migration ability. • The oxygen on the cassiterite surface has stronger delocalization and stronger electron migration ability. • Pb2+ can more strongly interplay with cassiterite than quartz resulting in selective flotation of cassiterite from quartz. Current research has trouble explaining the selective flotation mechanism realized by metal ions, which hinders the advancement of effective flotation techniques. In this work, the selective activation flotation of cassiterite from quartz with Pb2+ is taken as an example to illustrate the pivotal roles of surface hydroxyls in selective flotation. Accordingly, flotation, adsorption amount, and X-ray photoelectron spectroscopy (XPS) measurements and systematic first-principles calculations have been used to investigate the roles of hydroxyl groups on the selective adsorption of Pb2+. The obtained flotation, adsorption amount, and XPS test results consistently show that the Pb2+ can more strongly interplay with cassiterite than quartz resulting in selective flotation of cassiterite from quartz. The electron localization functional results illustrate that the electron localization of oxygen of Si-O bonds is stronger than the Sn-O bond resulting in the weaker electron migration ability (high hardness) of oxygen atoms of quartz than oxygen atoms of cassiterite. This makes the cassiterite surface hydroxyl groups less hard than quartz. Further crystal orbital Hamilton population and partial density of states show that the Pb2+ interacts with the oxygen atoms on cassiterite forming chemical bonds before and after the adsorption of benzohydroxamic acid (BHA). On the other hand, the interaction of Pb2+ with quartz is physical in the presence of BHA. The strong adsorption of Pb2+ on cassiterite makes it easier for BHA adsorption which accounts for the selective flotation of cassiterite from quartz. This work sheds new light on establishing a consistent and dependable theory that the hardness of surface hydroxyls is the original factor affecting the selective adsorption of metal ions on oxide mineral surfaces. [ABSTRACT FROM AUTHOR]

The proposed mechanism model for oxalic acid pretreatment of diaspore and kaolinite surfaces. [Display omitted] • Oxalic acid was first introduced to pretreat the diasporic bauxite. • Surface pretreatment increased the flotation of diaspore from bauxite. • Oxalic acid exposed and increased the Al O bonds on diaspore surface. • Oxalic acid dissolved more Al on kaolinite surface than diaspore. Surface pretreatment on minerals prior to flotation was proved to increase the selectivity of separation process. Organic acid pretreatment of low-grade diasporic-bauxite was conducted, and the effects of oxalic acid on bauxite flotation were investigated in this work. The oxalic acid pretreatment mechanisms were studied by adsorption measurements, zeta potential testing, XPS analysis, and ICP analysis. The flotation results showed that the oxalic acid treatment could significantly improve Al 2 O 3 recovery from 75.39% to 81.88% and decrease SiO 2 recovery from 53.26% to 47.30%. The adsorption capacity of diaspore for sodium oleate (NaOL) increased by 8.50%, while that of kaolinite decreased by 11.72%. XPS analysis revealed that oxalic acid treatment improved the relative contents of unsaturated Al at diaspore surface beneficial to the adsorption of NaOL. While the relative content of Al at kaolinite surface was decreased due to the Al dissolution revealed by ICP results. Zeta potential analysis indicated that oxalic acid changed the surface property of minerals favorable for the selective adsorption of NaOL on diaspore surface rather than kaolinite surface. These findings provided a promising direction for surface pretreatment of low-grade bauxite using oxalic acid for the improvement of the flotation desilication. [ABSTRACT FROM AUTHOR]

[Display omitted] • A target bio-adsorbent for gallium was assembled through imprinting technology. • The gallium imprinted material has an upgraded adsorption performance. • Coexisting metal ions have little effect on gallium adsorption on this material. • This material can be applied to a wide range of gallium ions. • Bio-sorbent prepared from waste persimmon-peel can recover gallium ions from water. A gallium ion-imprinted material (Ga-IIP-PP) was fabricated from persimmon peel using persimmon tannin as a functional monomer. Thereafter, it was applied for the selective adsorption of Ga ions from aqueous solutions containing other metal ions. The sorbent morphology and surface characterization data confirmed the successful loading of a gallium-imprinted layer onto the waste persimmon peel. The imprinted material exhibited a relatively smooth structure with few wrinkles, a negatively charged surface, and a low number of hydroxyl surface functional groups. The results of adsorption experiments revealed that Ga-IIP-PP could be applied in a wide range of Ga concentrations, while its highest adsorption capacity of 128 mg/g and adsorption rate of 0.0081 min−1 were achieved at pH = 3. Moreover, the synthesized Ga-IIP-PP exhibited high selectivity toward Ga ions even in binary systems with similar competitive ions. Finally, Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy were performed to elucidate the adsorption mechanism of Ga ions onto the Ga-IIP-PP surface, which primarily involved electrostatic adsorption and the cation exchange between the H+ ions of OH/ COOH groups and Ga ions. This work demonstrates that the bio-sorbent prepared from waste persimmon peel is a promising adsorbent for recovering Ga ions from aqueous solutions. [ABSTRACT FROM AUTHOR]

• Imidazolium ionic liquid was impregnated onto fumed silica at room temperature. • Ionic liquid could alter the charge characteristics of fumed silica and as active groups for adsorption. • IFS exhibited a high adsorption capacity along with a rapid adsorption rate. • IFS demonstrated excellent reusability. Butyl xanthate (BX) usually serve as an available collector in the sulfide mineral flotation. However, it will cause severe pollution and be harmful for living beings when discharged together with beneficiation wastewater. Adsorption, affected by sorbents structure to a great extent, is an effective strategy to treat BX-bearing wastewater. In this paper, ionic liquid-loaded fumed silica (IFS) generated by a simple process was acted as an adsorbent for removing BX from aqueous solution. The ratio of IL loaded onto silicon was about 40 %. The N elements existing in the structure of adsorbents suggested IL loaded onto silica surface successfully. The specific surface area of IFS was 65.25 m2/g, which was smaller than original material. And the total pore volume decreased from 36.75 to 15.22 cm3 g−1 after modification. Different from the virginal silica barely adsorbing BX, ionic liquid (IL) loaded silica had large uptake capacity up to 202.84 mg/g under the combined effect of functional groups modified in the silica particle and the porous structure of nanomaterial. The adsorption kinetics and isotherms are followed with the pseudo-second-order model and Langmuir model, respectively. And the functional groups, charge of adsorbent were analyzed to reveal approaching mechanism. This paper provides an alternative for xanthate and other organic contaminants treatment. [ABSTRACT FROM AUTHOR]

In low-rank coal (LRC) mixed collectors, little attention has been paid to the structure-activity relationship of different carboxylic acids. In this study, the application effect and adsorption mechanism of the mixed collector composed of dodecane (D) and carboxylic acid with different carbon chain lengths (n-valeric acid (VA), n-decanoic acid (DA), myristic acid (MA)) for LRC were explored by using sum-frequency vibration spectroscopy (SFG) and molecular dynamics simulation (MD). SFG measured the groups orientation angle on the LRC surface treated with the mixed collector, revealing that during the interfacial assembly process of mixed collector molecules, D molecules and the main molecular axes of DA molecules with similar carbon chain length tend to be adsorbed parallel to the LRC surface. The MD results showed that adding D-DA could weaken the hydrogen bonding between the LRC surface and interfacial water to the greatest extent, thereby improving every component's diffusion ability. [Display omitted] • First time to use SFG and MD to study the adsorption and assembly of mixed collectors. • SFG strength calculation illustrated the overall interface adsorption conformation. • MD revealed the dynamic properties and the damage degree of the hydrogen bond network. • Note: SFG (Sum-frequency vibration spectroscopy); MD (Molecular dynamics simulation). [ABSTRACT FROM AUTHOR]

L-cysteine (Lcys) induced the self-assembly of montmorillonite nanosheets (MMTNS), creating a three-dimensional structured adsorbent with high adsorption capacity for Pb(II). Lcys was grafted onto the edge of MMTNS by hydrogen-bonding and then formed disulfide bonds (–S–S–) under the oxidation of H 2 O 2 to form MMTNS-Lcys adsorbent. This technique maintains the exposed adsorption sites of MMTNS and resolves the challenge of nanosheet separation from water. MMTNS-Lcys possessed a large specific surface area (73.95 m2 g−1) and pore volume (0.1124 cm3 g−1), exhibiting outstanding adsorption performance for Pb(II), The adsorption process is consistent with the Pseudo-first-order kinetic and Langmuir isotherm models, indicating the monolayer adsorption of Pb(II) on the homogeneous surface of the MMTNS-Lcys adsorbent, with a maximum adsorption capacity of 46.92 mg/g (C 0 = 80 mg/L, M = 0.5 g/L, T = 25 °C, pH = 6). These findings offer valuable insights for the design and development of future adsorbent materials. [Display omitted] • Self-assembly of MMTNS solves the challenge of separating nanosheets from water. • Self-assembly of MMTNS protects the exposed adsorption sites. • MMTNS-Lcys adsorbent possesses a large and loosely layered structure. • The layered structure of MMTNS-Lcys adsorbent achieves efficient adsorption of lead. [ABSTRACT FROM AUTHOR]

[Display omitted] • Better flotation and attachment behavior of fine molybdenite were achieved using CTD. • Abundant of aromatic compounds in the CTD were exacted from coal tar. • Aromatic compounds were preferentially adsorbed on the (1 0 0) plane of molybdenite. • Larger adsorption amounts of CTD were responsible for superior flotation efficiency. With the depletion of high-grade molybdenum (Mo) deposits, it is more pressing to separate the low-grade deposits effectively due to the large demand for Mo. However, traditional hydrocarbon oil collectors such as kerosene suffered low collecting capacity for low-grade ores because of the fine disseminated nature and crystal anisotropy of molybdenite. In this study, the effect of a compound collector prepared from coal tar and dodecane (CTD) on the flotation of fine molybdenite was investigated by micro-flotation experiments, bubble-particle attachment tests, gas chromatography-mass spectrometry (GC–MS), density functional theory (DFT) calculations, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and contact angle measurements. The results of micro-flotation experiments demonstrated that CTD improved the flotation recovery of fine molybdenite dramatically compared with dodecane and kerosene, the fine particles pretreated with CTD had a better affinity for bubbles, and a stronger mineralization efficiency was achieved than that with dodecane as the improvement of the surface coverage and attachment rate constant. The results of GC–MS, FTIR, and DFT calculations indicated that there were plenty of compounds with benzene rings in the CTD, especially for phenanthrene and naphthalene, which showed a stronger interaction on the (1 0 0) plane of molybdenite than dodecane, thereby proving a stronger affinity for hydrophilic planes. The results of XPS analysis depicted that more adsorption amounts were achieved on molybdenite by CTD than that of dodecane, and contact angle test results further demonstrated that the effect of CTD was stronger than dodecane in improving the hydrophobicity of fine molybdenite particles. In general, the compound collector (CTD) is beneficial to the improvement of attachment rate of molybdenite particles to bubble and hydrophobicity of molybdenite particles, which improves the flotation recovery of fine molybdenite. The extract from coal tar had more affinity for the (1 0 0) plane of molybdenite compared to the (0 0 1) plane through DFT calculations. The finding has important reference value and guiding significance for the future research on collectors for fine molybdenite flotation. [ABSTRACT FROM AUTHOR]

Effects of the modified starch in the flotation of the refractory iron ore. [Display omitted] • Amino radical was introduced in starch to improve flocculation and depression properties. • Modified starch exhibited an excellent depression effect on hematite. • Modified starch is beneficial to the attachment of siderite to quartz. • Modified starch is a promising regulator for refractory iron ore separation. Starch was modified by introducing amino radicals to solve the problem of poor selectivity during flotation. Changes in the flocculation and depression properties of starch after introducing amino radicals were compared in carbonate-containing iron ore flotation. Differences in adsorption between corn starch and modified starch were determined through zeta potential measurements, X-ray photoelectron spectroscopy (XPS) analyses, and molecular simulations. The flocculating effects of corn starch and modified starch were explored by the particle dynamics analysis and an in situ scanning electron microscopy (SEM) method. Amino radical can enhance the adsorption of modified starch on quartz via enhanced electrostatic forces. Both corn starch and modified starch exhibit excellent flocculating effects on fine siderite. However, siderite flocs formed with modified starch tend to attach to the quartz. Modified starch is a promising regulator for improving the grade by scarifying recovery in the flotation of refractory carbonate-containing iron ore. [ABSTRACT FROM AUTHOR]

• Psyllium seed gum (PSG) used as depressant in flotation process for the first time. • The PSG has excellently selective depression effect on calcite. • Flotation separation of fluorite from calcite can be achieved with PSG. • The chemisorption dominates the interaction of PSG with calcite. Separating fluorite and calcite through flotation is difficult due to their similar Ca2+ sites on the adsorption surface of collectors. Psyllium seed gum, a reagent naturally derived from psyllium seed, was used for the first time as an efficient depressant in the flotation separation of fluorite and calcite. Micro-flotation experiments showed that psyllium seed gum had a strong depressing effect on calcite at a wide pH range (8–12). Calcite recovery was significantly and sharply reduced from 97.38% to less than 10% in the presence of psyllium seed gum at pH 9.0. By contrast, fluorite recovery was slightly affected by psyllium seed gum and maintained above 90%. FTIR analysis, XPS analysis, and adsorption test were conducted to determine the selective depression mechanism of psyllium seed gum on these two minerals, and the results show the adsorption effect and capacity of psyllium seed gum were stronger and higher on the calcite surface than on the fluorite surface. Owing to the high electronegativity and powerful electron-gaining ability of CO 3 2−, many electron clouds moved from the hydroxyl groups of psyllium seed gum to the Ca, C, and O elements on the calcite surface. A large amount of psyllium seed gum was chemisorbed on the calcite surface by reacting with Ca2+ site and preventing NaOl adsorption. On the contrary, psyllium seed gum barely affected NaOl adsorption on the fluorite surface. In this case, the efficient flotation separation of fluorite from calcite is realized. [ABSTRACT FROM AUTHOR]