To investigate the effect of nitrogen on the photoluminescence properties of carbon quantum dots (CO Ds), N-doped carbon quantum dots (N-CQDs)were synthesized by one-step hydrothermal treatment using biomass tar as the carbon precursor.As an inevitable organic pollutant,the unsaturated bonds in biomass tar,such as carboxylic acids,aldehydes,and aromatics,are favorable for formation of the graphitic carbon lattice.The obtained N-CQDs are spherical with an average particle size of 2.64nm and the crystal lattice spacing is 0.25nm,corresponding to the (100)facet of graphitic carbon.The N-CQDs emit bright blue photoluminescence under 365nm ultraviolet light,and they have excellent water solubility and stability with a high quantum yield of 26.1%.Coordination between the functional groups on the N-CQD surface and Fe^3+ ions is promoted because of the improved electronic properties and surface chemical reactivity caused by N atoms,leading to a significant fluorescence quenching effect of the N-CQDs in the presence of Fe^3+ions with high selectivity and sensitivity.There is a linear relationship between In (Fo/F)and the Fe^3+ concentration in the N-CQD concentration range 0.06-1400μmol/L with a detection limit of 60nmol/L, showing that the N-CQ.Ds have great potential as a fluorescent probe for Fe^3+detection.
Xiangyi DengYali FengHaoran LiZhuwei DuQing TengHongjun Wang
Bacillus mucilaginosus was used in pretreatment ofpyrolusite to facilitate the flotation removal of quartz from pyrolusite minerals. Quartz was activated by B. mucilaginosus, whereas pyrolusite was unaffected at pH 7 with laurylamine as collector. Flotation recovery of pyrolusite with B. mucilaginosus pretreatment is 73.62%, slightly lower than that of the process without biopretreament, namely 74.70%. The grade of concentrate of recovered pyrolusite is 19.44%, 2.18% higher than that of the recovered pyrolusite without B. mucilaginosus pretreatment （17.26%）. The results of FTIR and SEM showed that no bacteria were adsorbed on the surface of quartz or pyrolusite, indicating that the better selectivity and collectability of flotation resulted from bacterial byproducts. And interaction of bacterial byproducts such as extracellular bacterial polysaccharide, extracellular bacterial protein and acetic acid, on minerals were studied by FTIR and adsorption.
The acid bio-leaching process of vanadium extraction from clay vanadium water-leached residue was studied and the effect of the performance of iron transformation was investigated.Acidithiobacillus ferrooxidans affects the dissolution of vanadium through the catalytic effect on Fe^3+/Fe^2+couple and material exchange.The passivation of iron settling correlates with ferrous ion content in bio-leaching solution.In medium containing A.ferrooxidans and Fe(Ⅲ),the increment in Fe(Ⅱ)concentration leads to the formation of jarosite,generating a decline in vanadium extraction efficiency.Analysis of cyclic voltammetry shows that Fe(Ⅱ)ion is apt to be oxidized and translated into precipitate by A.ferrooxidans,which strongly adsorbed to the surface of the residue.Fe(Ⅲ)ion promotes the vanadium extraction due to its oxidizing activity.Admixing A.ferrooxidans to Fe(Ⅲ)medium elevates the reduction of low valence state vanadium and facilitates the exchange of substance between minerals and solution.This motivates 3.8%and 21.8%increments in recovery ratio and leaching rate of vanadium compared to the Fe(Ⅲ)exclusive use,respectively.Moreover,Fe(Ⅱ)ion impacts vanadium extraction slightly in sterile medium but negatively influences vanadium leaching in the presence of bacteria.
Based on the fluidized roasting reduction technology of low-grade pyrolusite coupling with pretreatment of stone coal, the manganese reduction efficiency was investigated and technical conditions were optimized. It is found that the optimum manganese reduction efficiency can be up to 98.97% under the conditions that the mass ratio of stone coal to pyrolusite is 3：1, the roasting temperature of stone coal is 1000℃, the roasting temperature of pyrolusite is 800℃, and the roasting time is 2 h. Other low-grade pyrolusite ores in China from Guangxi, Hunan, and Guizhou Provinces were tested and all these minerals responded well, giving -99% manganese reduction efficiency. Meanwhile, the reduction kinetic model has been established. It is confirmed that the reduction process is controlled by the interface chemical reaction. The apparent activation energy is 36.397 kJ/mol.
Ya-li FengZhen-lei CaiHao-ran LiZhu-wei DuXin-wei Liu
A novel method of extracting valuable metals from Ti-bearing blast furnace slag(TBBF slag)via pressure pyrolysis of recyclable ammonium sulfate(AS)−acid leaching process was proposed.The results show that when pressurized roasting at an AS-to-slag mass ratio 3:1 and 370℃for 90 min,the extraction rates of titanium,aluminum and magnesium reached 94.5%,91.9%and 97.4%,respectively.The acid leaching solution was subjected to re-crystallization in a boiling state to obtain a titanium product having a TiO2 content of 94.1%.The above crystallization mother liquor was adjusted to pH=6 and pH≥12.2,respectively,and then qualified Al2O3 and MgO products were obtained.The analysis through XRD and SEM−EDS proves that the main phases in roasted samples were NH4AlSO4,CaSO4 and TiOSO4.The thermodynamic analysis presents that the main minerals of perovskite,spinel and diopside in raw ore could spontaneously react with the intermediate produced by AS under optimal conditions.
In the present paper,the experimental method and computational fluid dynamics(CFD)method were used to investigate the effect of gas distributors with different orifice sizes and orifice pitches on fluidization characteristics in a gas-solid fluidized bed.The Euler-Euler two fluid model(TFM)approach based on the kinetic theory of granular flow(KTGF)and the standard k-epsilon turbulence model was employed in the numerical simulation by using ANSYS Fluent 15.0.The results showed that the orifice size and the orifice pitch of gas distributor had a significant influence on the flow characteristics in the gas-solid fluidized bed.With a decreasing orifice size and orifice pitch of gas distributor having the same opening area,the distributor pressure drop,the initial bubble size,and the height of dead zone just above the distributor were decreased,and the bed pressure drop was increased more than that of the larger orifice size and orifice pitch of distributors,the distribution of solid volume fraction was also more homogeneous for the smaller orifice size.
