Search

The reported CNCo-Fe3O4/ZIS heterojunction catalysts exhibit excellent photocatalytic water splitting and long-term stability under visible-light irradiation, indicating their great potential in improvement of the greenhouse effect.

To improve the magnesia removal effect of collophane and increase the P2O5 grade of phosphorus concentrate, the fatty acid collector mixed with sodium dodecyl sulfate (SDS) was used as the compound collector in reverse flotation for magnesia removal in acid system. Solution surface tension measurement, Zeta potential test and infrared spectrum analysis were conducted to analyze the intensified effect of compound collector for dolomite removal. The results showed that under the conditions of grinding fineness -0.074 mm accounted for 89.8%, sulfuric acid dosage 12.0 kg/t, phosphoric acid dosage 3.0 kg/t, SDS compound proportion 3%, collector dosage 1.0 kg/t, the P2O5 grade of concentrate is increased from 25.7% to 29.94%. SDS can reduce the surface tension of slurry, which is conducive to the formation and stability of flotation foam. Zeta potential became negative due to the compound collector adsorbed on the mineral surface. Moreover, the -CH2 antisymmetric stretching vibration peak originated from fatty acid and SDS were detected after the interaction of collectors with dolomite. The compound collector was effectively adsorbed on the surface of dolomite, enhancing the magnesium removal effect of collophane.

Significant amounts of foam generated during the production of phosphoric acid would severely occupy the head space in the reactors, thereby reducing output capacity dramatically. Here, we first proposed a green and clean approach based on Fenton oxidation theory to mitigate the generation of foam. The effect of H2O2 dosage, FeSO4 dosage, and pH value on the defoaming performance were investigated systematically. Moreover, the defoaming performance between Fenton oxidation process and traditional defoamer were compared and the defoaming mechanism was described with the help of XRD analyses. The results obtained from the Fenton oxidation process demonstrate that the use of H2O2 in conjunction with FeSO4 are beneficial to mitigating the foam generation, and the defoaming performance is positively correlated to the dosage. Furthermore, Fenton oxidation process outperforms than that of traditional defoamer in terms of reducing foam generation. The defoaming mechanism is ascribed to the fact that the organic substrates existing on the phosphate concentrate surface could be completely decomposed and the soluble carbonate minerals were prone to being dissolved during the regulation of pH value, thereby inhibiting the production of CO2 gas. This work is helpful in providing guidance for utilizing a green and clean approach based on advanced oxidation theory to mitigate the foam generation during the wet phosphoric acid process. More importantly, it provides a theoretical basis for optimizing this type of processing methods.

Abstact Facilitating photogenerated carriers separation as well as broadening visible-light driven range play important roles in enhancing photocatalytic activity of catalysts. The hierarchical heterostructured photocatalysts have attracted increasing attention due to unique structure and high photocatalytic performance in photocatalytic applications. Here, the hierarchical Ti3C2Tx MXene/ZnIn2S4 heterostructures were successfully synthesized by a simple one-step method, which can serve as an efficient catalyst for photocatalytic reduction of potassium dichromate (Cr(VI)) and degradation Methyl orange (MO) under visible light. The few-layered MXene acts as a charge carrier, enhancing the catalytic activity of the zinc indium sulfide (ZnIn2S4) by promoting the carrier transport and the redox reactions. The strong interactions between ZnIn2S4 and the MXene are beneficial to the high utilization of solar energy, enhanced charge separation ability, excellent photocatalytic capability and stability. The hierarchical Ti3C2Tx MXene/ZnIn2S4 heterostructures exhibit promising photocatalytic ability for Cr(VI) reduction and MO degradation with high degradation rate of 93.4% and 96.9% within 45 min under simulated visible-light irradiation, respectively. This work provides a novel design idea for fabricating the hierarchical heterostructured materials to solve the environmental pollution problems.

Few literatures pay emphasis on investigating the use of anionic and cationic’s combined collector in flotation separation. In this work, we evaluated the effectiveness of a new combined collector for the separation of collophanite, dolomite, and quartz using isooctyl ether phosphate (AEP) and octadecylamine polyoxyethylene ether (AC1810). To explain the flotation phenomenon, we use zeta potential, surface tension, and molecular dynamics simulation. Experimental results demonstrate that when the mass ratio of AEP and AC1810 was 1:3 and the total collector concentration was 72 mg/L at a neutral pH, a concentrate containing 36.28 wt% P2O5 was obtained from a feed sample containing 19.6 wt% P2O5, indicating a recovery rate of 78.83%. Results from a zeta potential analysis indicate that more AEP was adsorbed onto dolomite rather than collophanite, while AC1810 was adsorbed onto quartz. The molecular dynamics simulation revealed that AEP and AC1810 were not solely physically adsorbed onto the dolomite and quartz surfaces. Specific chemical adsorption also occurred on the exterior of the dolomite, which could selectively adsorb substances onto its surfaces.

In this work, the hydrophobic agglomeration of apatite fines induced by sodium oleate in aqueous solutions has been investigated through the measurement of agglomeration degree and fractal dimension. The results showed that the agglomeration degree of apatite fines and agglomerates morphology was strongly depended on sodium oleate concentration, pH, stirring speed and time. Better agglomeration degree and more regular agglomerates were achieved at sodium oleate concentration of 5 × 10−5 mol/L under neutral condition. The critical stirring speed for agglomerates rupture was 1000 rev/min, above which, prolonged stirring time would cause breakage and restructure of the agglomerates after a certain stirring time, resulting in lower agglomeration degree and more regular agglomerates. The agglomeration degree of apatite fines could be greatly enhanced with the addition of emulsified kerosene, but only if the apatite surface was hydrophobic enough. Keywords: Hydrophobic agglomeration, Apatite fines, Agglomeration degree, Fractal dimension, Sodium oleate

In this work, HPAA (2-Hydroxyphosphonoacetic Acid) was explored as a novel sphalerite depressant for the selective flotation of sphalerite and galena. The depression performances and mechanisms were investigated through micro-flotation tests and various characterization techniques. Micro-flotation tests showed that HPAA selectively inhibited sphalerite but barely affected the flotation of galena at board pH range in Sodium Isobutyl Xanthate system (SIBX). Zeta potential, Fourier Transform Infrared Spectrometer (FTIR) and XPS results suggested that HPAA was tended to adsorb on sphalerite surface chemically in the form of a six-membered chelating ring through the complexation of PO3-2 and COO– with Zn atoms on sphalerite surface. Moreover, SIBX could substitute HPAA from galena surface while almost didn’t influence the adsorption of HPAA on sphalerite surface, which rendered galena surface hydrophobic and sphalerite surface hydrophilic. HPAA had potential application prospect because of the good selectivity and environmental compatibility.

In this work, xanthan gum (XG) was exploited as a novel dolomite depressant in the flotation separation of apatite from dolomite in sodium oleate system. The flotation performances and adsorption mechanism of XG towards apatite and dolomite were studied through flotation tests, adsorption capacity measurements, micro-heat tests, atoms density calculations and surface characterizations. Flotation results revealed that XG exhibited strong depression effect on dolomite but barely influenced the flotation of apatite. The results of zeta potential, infrared spectroscopy analysis, adsorption capacity measurements and micro-heat tests proved that XG trended to adsorb on dolomite other than apatite, which hindered the adsorption of NaOL on dolomite and rendered the surface hydrophilic. Atom density calculations indicated that the preferential adsorption of XG on dolomite was due to much more dense and active Ca sites on dolomite surface than that of apatite. XPS results suggested that XG was strongly adsorbed on dolomite surface by means of chelation between COOH or OH groups within XG and Ca sites on dolomite, while it was weakly adsorbed on apatite by hydrogen bonding between OH groups within XG and F atoms on apatite surface.

Sulfuric acid (H 2 SO 4 ) is widely used as a depressant in the flotation of phosphorus minerals, usually in large dosages. This study used microflotation, flotation of the actual ore, X-ray photoelectron spectroscopy (XPS) analyses, reaction thermodynamic analyses and adsorption experiments, to examine the effect of citric acid (H 3 Cit) and a combined depressant (H 2 SO 4 /H 3 Cit) on collophanite ore flotation. H 2 SO 4 and H 3 Cit both exhibit selective depressive effects on apatite when they are used individually as depressants. When combined, the added H 3 Cit greatly reduced H 2 SO 4 dosages above 30% and produced better flotation results. Closed-circuit reverse flotation results for tests on the actual ore also confirmed this. Mechanism analyses demonstrated that H 3 Cit adsorbs onto apatite surface via a chemical chelating reaction with Ca 2+ . H 3 Cit is selectively and largely adsorbed onto apatite, thus selectively depressing it. Compared with SO 4 2– , the reactions of Cit 3− and Ca 2+ are thermodynamically favored at pH 5.5–13.0. Therefore H 3 Cit manifested a stronger inhibitive effect than H 2 SO 4 and significantly reduced the required H 2 SO 4 dosage. A rough economic evaluation suggests that the combined depressant exhibits economic advantages and shows potential for industrial application.

Reverse flotation is an effective method for separating apatite from gangue minerals (such as dolomite) in collophanite ore. However, collophanite ore flotation using traditional fatty acid collectors is uneconomical because of the relatively high cost of the raw materials. In this work, saponified gutter oil fatty acid (GOFA) was used as the collector, and its effect on collophanite ore flotation and the mechanism of adsorption were studied. The results showed that Ca 2 + is the active site for reaction with GOFA and initiates apatite flotation. The dissolution of Ca 2 + from dolomite was found to be thermodynamically more favorable than that from apatite, and the relative abundance of Ca 2 + enhanced the reaction of dolomite with GOFA. XPS analysis revealed that the interaction between GOFA and magnesium on the dolomite surface strengthened chemisorption. As magnesium is a major constituent of dolomite, but not of apatite, GOFA was selectively chemisorbed onto the dolomite surface. Closed-circuit reverse flotation tests using GOFA as the collector resulted in an excellent concentrate with 28.46 wt% P 2 O 5 and 0.65 wt% MgO, corresponding to a P 2 O 5 recovery of 87.2%. GOFA was demonstrated to exhibit outstanding selectivity for dolomite in the reverse flotation of collophanite ore. The use of GOFA as an environment-friendly, cost-effective, and selective collector is expected to provide new insights into low-cost collophanite ore flotation.

Potassium and phosphate were extracted at low temperature by acid hydrolysis process to decompose a new type of associated phosphorus and potassium ore. The main factors affecting the dissolution rate were investigated, such as grinding fineness, the amount of sulfuric acid and fluoride salt, reaction time and temperature, etc. Meanwhile, the effects of various factors on the formation of soluble potassium and phosphate were also discussed. The reaction products and residues were determined by X-ray diffraction (XRD), scanning electron microscopic (SEM) analysis and other means. The results showed that the dissolution rates of potassium and phosphorus were 70wt% and 93.7wt%, respectively, under the conditions of a grain size of 95.64wt% lessthan 0.074 mm, 9.78 g•g-1 sulfuric acid, 0.5 g•g-1 ammonium fluoride, 160 °C and a reaction time of 2 h. The thermodynamic and chemical reaction mechanism was revealed that the primary reaction could be completed spontaneously in a temperature range of 298-433 K. The increase of reaction temperature had an important influence on ion exchange reaction, which was more conducive to the spontaneous process. The research will open up a new way for efficient use of potassium ore resources.

The Acinetobacter sp. strain M isolated from a contaminated soil sample in Jiangsu Province of China was found to be able to degrade perfluorooctane sulfonamide (PFOSA) effectively. Fluoride anion (F- ) released from PFOSA degradation was detected by ion chromatography, and showed positive correlation to the growth curve of Acinetobacter sp. strain M. The PFOSA degradation efficiency of strain M was approximately 27 %, as assessed by GC analysis. It was shown that enzymes localized outside of cells of Acinetobacter sp. strain M catalyzed the degradation of PFOSA. This further indicates a possibly new (multi-step/pathway) mechanism for PFOSA degradation. It revealed that the extracellular enzyme of the Acinetobacter strain M preferentially cleaves carbon-carbon and carbon-fluorine bonds instead of destroying the carbon-sulfur bond. The growth condition for Acinetobacter sp. strain M was optimized at 30 °C and pH 7.0 in the presence of 2000 mg L-1 of PFOSA and 0.5 % (v/v) of Tween-20. The optimal PFOSA degradation time was found to be 12 h, with a degradation efficiency of 76 % by extracellular enzymes in strain M as determined by GC analysis. The result may provide potential applications for biodegradition of perfluoro organic compounds, such as derivatives of perfluorooctane (C8).

Rutile (TiO2), ilmenite (FeTiO3) and titanite (CaTiSiO5) are considered as the most important titanium minerals, particularly rutile, is believed to be the principal source because of its high added value of products. The conventional methods used for concentrating rutile include gravity, magnetic, electrostatic separation or their combination among others. Besides physical separation approaches, selective flotation attracts massive attention due to its remarkable efficiency for separation of rutile with analogous physic-chemical characteristics. A comprehensive review of rutile flotation in terms of its surface chemical properties, effects of slimes on rutile flotation as well as the flotation reagents which have been employed is presented. Additionally, perspectives for further future investigations based on the analysis of the previous work are provided.

In this study, a novel TiO2-graphene modified epoxy resin employed as coatings for ordinary Portland cement (OPC) concrete was for the first time fabricated with three different dosages. It was found that the TiO2-graphene could be dispersed homogeneously in the epoxy resin matrix without reducing interfacial bonding strengths between coatings and OPC concrete substrates. Moreover, with the aid of certain dosages of TiO2-graphene nanofiller (0.3 % and 0.5 %), both the impermeability towards water and chloride of the OPC concrete reflected by capillary sorptivity and chloride penetration respectively was greatly improved compared to the pure epoxy resin coated concrete or concrete substrate without coatings. In contrast, 1.0 % dosage led to higher water and chloride permeability than the concrete coated by pure epoxy resin coating. Thus, within the range of considered dosages, it seems that 0.5 % dosage achieved the best coating performance evidenced by the lowest capillary sorptivity and chloride permeability, overcoming the disadvantages of 0.3 % (not enough) and 1.0 % (noticeable agglomerations). In addition, TiO2-graphene addition seems to have no significant impact on the gas permeability of the epoxy resin coated OPC concrete. Overall, the cost-effective fabrication method and improved impermeability of OPC concrete coated by the epoxy resin which is enhanced by the TiO2-graphene nano-composite create more opportunities for epoxy resin being utilised as surface coatings for cementitious binders.

Three-dimensional (3D) photocatalytic heterostructures have attracted intense interest, due to their interlayer synergy and high quantum yield. Bismuth oxyiodide (BiOI) is considered as a useful semiconductor material due to its narrow bandgap, good visible-light absorption and tendency to form anisotropic heterostructures. Herein, we propose a facile design strategy for structure-controlled nano-flower-like BiOI/MoS2 microspheres with uniform size and enhanced capacity to photodegrade tetracycline (TC) and methyl orange (MO). These 3D BiOI/MoS2 microspheres were outstanding catalysts of visible-light-driven contaminant degradation, as shown by their ability to degrade TC and MO three times and four times faster, respectively, than pure BiOI. This excellent photocatalytic performance of 3D BiOI/MoS2 microspheres is attributable to synergistic effects resulting from their unique defect-rich structure, specifically the loading of MoS2 onto the surface of defect-rich BiOI suppressing recombination of photogenerated electron–hole pairs. Moreover, the abundant active edge-sites and unique physicochemical properties of MoS2 nanosheets enables them to inhibit photogenerated electron–hole recombination. In this study, a novel route for synthesis of structure-controlled nano-flower-like BiOI/MoS2 microspheres was developed, which will increase the application of these useful materials for addressing environmental pollution. An important direction in future research will be to develop large-scale, controllable synthesis and interfacial microstructural control of these heterostructured photocatalysts.

Few literatures pay emphasis on investigating the effect brought out by metal ions on flotation in the case of cationic collector. In this work, the effect of Al(Ⅲ) and Fe(Ⅲ) on rutile floatability using dodecylamine polyxyethylene ether (AC1203) as collector was evaluated. In addition to the flotation tests, zeta potential measurements, solution chemistry calculation, surface tension measurement and XPS analysis were conducted to elucidate the detailed depression mechanism. The results indicate that the floatability of rutile seriously inhibited by Al(Ⅲ) and Fe(Ⅲ), and the depression effect of Al(Ⅲ) is much stronger than that of Fe(Ⅲ). Moreover, on the basis of zeta potential and solution chemistry calculation tests, Al(OH)3 and Fe(OH)3 precipitates are believed to be the principal components that act with rutile surface, and the preferential adsorption of Al(OH)3 precipitate could further deteriorate the interaction of collector with rutile. It is worth mentioning that Al(Ⅲ) and Fe(Ⅲ) are capable of acting with AC1203 to form complexes, consequently affecting the flotation environment. Furthermore, XPS analysis reveals that Fe(OH)3 precipitate tend to adsorb on rutile surface through physical interaction, while Al(OH)3 precipitate could react with Os and bridging O on rutile surface to form Ti-O-Al bonds, resulting in less active Ti sites for collector adsorption.

There is little scientific agreement on the way sodium fluorosilicate (SF) depresses gangue minerals, resulting in a stagnation into in-depth research. Here, we describe a new explanation hoping to advance this step of development. In this study, flotation of rutile from almandine was investigated using SF as the depressant and Styryl phosphonic acid (SPA) as the collector. The study was performed through the measurements of zeta potential, contact angle, and X-ray photoelectron spectroscopy (XPS), in addition to the micro-flotation of single minerals and artificially mixed minerals. The experimental results demonstrated that SF acting in the form of SiF62− at pH 5–6 was a highly selective depressant on almandine, rather than on rutile, leading to a high selectivity for the flotation of rutile. The XPS results revealed a strong interaction between F and active Fe sites on almandine surface, reducing adsorption sites for collector, thereby strongly depressing the flotation of almandine.

The effects of Ca2+, Mg2+, Al3+, and Fe3+ on the flotation behaviors of apatite, dolomite and quartz were investigated through a micro-flotation test, and the influence of calcium ions on the flotation of these minerals was further elucidated by solution chemistry study, zeta potential measurement, and X-ray photoelectron spectroscopy (XPS) analyses. The results indicate that an appropriate amount of Ca2+ and Mg2+ can improve the floatability of apatite but had a negligible effect on the flotation performance of dolomite, whereas Al3+, Fe3+, and excessive amounts of Ca2+ decreased the recovery of apatite and dolomite. The studied metal cations can activate quartz at a particular pH. It can be inferred from solution chemistry and zeta potential measurement that the influence of metal ions on the flotation of different minerals should be attributed to the adsorption of various hydrolysis species on the mineral surfaces. XPS analyses reveal that calcium ions can enhance the adsorption of anionic collector on apatite and quartz surfaces, and there are no apparent changes to be observed on the surface of dolomite in the absence and presence of calcium ions at a concentration of 2.5 × 10−3 M, which was in good agreement with the micro-flotation results.

The mid-low grade sedimentary phosphate ore, abundant in silicate and carbonate gangue minerals, exhibits a poor processability. It is conventionally enriched using high temperature flotation to remove silicate gangues with fatty acid as a collector. Cottonseed oil has been proved to be an efficient collector for achieving ambient temperature flotation of the sedimentary phosphate ore used in this study. Flotation kinetics was investigated to ascertain the excellent collecting performance of cottonseed oil, as compared with oleic acid, and the phosphate flotation fitted well with the first-order flotation model. Based on the analysis of flotation reagent effect on the direct flotation process using the response surface methodology (RSM), a closed circuit of direct-reverse flotation for stepwise removing silicate and carbonate gangues from the sedimentary phosphate ore was established. Consequently, a required high quality of phosphate concentrate containing 30.16% P2O5 was obtained, with a recovery of 90.90%. Scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) of the flotation products confirmed that the majority of silicate and carbonate gangues were effectively removed from the concentrate products.