Hydrometallurgical detoxification and recycling of electric arc furnace dust

Electric arc furnace dust(EAFD)is a hazardous waste but can also be a potential secondary resource for valuable metals,such as Zn and Fe.Given the increased awareness of carbon emission reduction,energy conservation,and environmental protection,hydrometallurgical technologies for the detoxification and resource use of EAFD have been developing rapidly.This work summarizes the generation mechanisms,compositions,and characteristics of EAFD and presents a critical review of various hydrometallurgical treatment methods for EAFD,e.g.,acid leaching,alkaline leaching,salt leaching,and pretreatment–enhanced leaching methods.Simultaneously,the phase transformation mechanisms of zinc-containing components in acid and alkali solutions and pretreatment processes are expounded.Finally,two novel combined methods,i.e.,oxygen pressure sulfuric acid leaching combined with composite catalyst preparation,and synergistic roasting of EAFD and municipal solid waste incineration fly ash combined with alkaline leaching,are proposed,which can provide future development directions to completely recycling EAFD by recovering valuable metals and using zinc residue.

Enhanced photocatalytic performance of iron oxides@HTCC fabricated from zinc extraction tailings for methylene blue degradation:Investigation of the photocatalytic mechanism

Photocatalytic processes are efficient methods to solve water contamination problems,especially considering dyeing wastewater disposal.However,high-efficiency photocatalysts are usually very expensive and have the risk of heavy metal pollution.Recently,an iron oxides@hydrothermal carbonation carbon(HTCC)heterogeneous catalyst was prepared by our group through co-hydrothermal treatment of carbohydrates and zinc extraction tailings of converter dust.Herein,the catalytic performance of the iron oxides@HTCC was verified by a nonbiodegradable dye,methylene blue(MB),and the catalytic mechanism was deduced from theoretical simulations and spectroscopic measurements.The iron oxides@HTCC showed an excellent synergy between photocatalysis and Fenton-like reactions.Under visible-light illumination,the iron oxides@HTCC could be excited to generate electrons and holes,reacting with H_(2)O_(2)to produce·OH radicals to oxidize and decompose organic pollutants.The removal efficiency of methylene blue over iron oxides@HTCC at 140 min was 2.86 times that of HTCC.The enhanced catalytic performance was attributed to the advantages of iron oxides modification:(1)promoting the excitation induced by photons;(2)improving the charge transfer.Furthermore,the iron oxides@HTCC showed high catalytic activity in a wide pH value range of 2.3-10.4,and the MB removal efficiency remained higher than 95% after the iron oxides@HTCC was recycled 4 times.The magnetically recyclable iron oxides@HTCC may provide a solution for the treatment of wastewater from the textile industry.

Durable poly(binaphthyl-co-p-terphenyl piperidinium)-based anion exchange membranes with dual side chains

Building well-developed ion-conductive highways is highly desirable for anion exchange membranes(AEMs).Grafting side chain is a highly effective approach for constructing a well-defined phaseseparated morphological structure and forming unblocked ion pathways in AEMs for fast ion transport.Fluorination of side chains can further enhance phase separation due to the superhydrophobic nature of fluorine groups.However,their electronic effect on the alkaline stability of side chains and membranes is rarely reported.Here,fluorine-containing and fluorine-free side chains are introduced into the polyaromatic backbone in proper configuration to investigate the impact of the fluorine terminal group on the stability of the side chains and membrane properties.The poly(binaphthyl-co-p-terphenyl piperidinium)AEM(QBNp TP)has the highest molecular weight and most dimensional stability due to its favorable backbone arrangement among ortho-and meta-terphenyl based AEMs.Importantly,by introducing both a fluorinated piperidinium side chain and a hexane chain into the p-terphenyl-based backbone,the prepared AEM(QBNp TP-QFC)presents an enhanced conductivity(150.6 m S cm^(-1))and a constrained swelling at 80℃.The electronic effect of fluorinated side chains is contemplated by experiments and simulations.The results demonstrate that the presence of strong electro-withdrawing fluorine groups weakens the electronic cloud of adjacent C atoms,increasing OH^(-)attack on the C atom and improving the stability of piperidinium cations.Hence QBNp TP-QFC possesses a robust alkaline stability at 80℃(95.3%conductivity retention after testing in 2 M Na OH for 2160 h).An excellent peak power density of 1.44 W cm^(-2)and a remarkable durability at 80℃(4.5%voltage loss after 100 h)can be observed.

Effects of internals and distributors on the distribution and growth of bubbles in the conventional gas-solid fluidized bed

The effects of internals and gas distributors on the local dynamics of the bubbles in the conventional gas-solid fluidized bed were studied.Mesh-type internals with different opening areas(50%,70%and 90%)and different arrangements(two-layer and four-layer);and a sintered plate with a smaller pore size(1μm)and a perforated plate with a larger pore size as distributors were investigated.Differential pressure drops and local solids holdups were measured under various superficial gas velocities to compare the performances of the different types of internals and distributors.The instantaneous solids holdup signals from the optical fibre probe were used to further examine the local bubble dynamics in detail.Smaller bubbles were found,with the installation of internals or using the sintered plate,resulting in lower pressure drops and a higher bed expansion.Internals with reduced opening area or distributor with smaller pore size further leads to a higher changeover rate between the bubbles and dense phase,both axially and radially,and hence a better gas-solid contacting and an earlier transition to the turbulent flow regime of the bed.

Characterization of countercurrent liquid-upward and solid-downward fluidized system

Acting as an operating mode of fluidization,the flow characteristics of a countercurrent liquid–solid fluidized bed(CCLSFB)were experimentally investigated using a Plexiglas column of 1.5 m in height.Countercurrent liquid-upward and solid-downward fluidization was achieved under a limited solid flowrate before flooding occurred.The“flooding”phenomena and the flooding velocity were identified by measuring the variations in pressure drop in the axial direction of the column.Two different methods were used to quantify the flooding point that led to the instability of the system.Axial solids holdup profiles were also obtained from the pressure drop data along the column and the influences of device structure and operating conditions on the solids holdup were also studied.Seven types of particles with different diameters and densities were used.An agreement was found between the experimental results and the mathematic prediction derived from the Richardson–Zaki equation on the data of the solids holdup.

Nitrogen distribution in the products from the hydrothermal liquefaction of Chlorella sp. and Spirulina sp.

The high contents of nitrogen-containing organic compounds in biocrude obtained from hydrothermal liquefaction of microalgae are one of the most concerned issues on the applications and environment.In the project,Chlorella sp.and Spirulina sp.were selected as raw materials to investigate the influence of different reaction conditions(i.e.,reaction temperature,residence time,solid loading rate)on the distribution of nitrogen in the oil phase and aqueous phase.Three main forms of nitrogen-containing organic compounds including nitrogen-heterocyclic compounds,amide,and amine were detected in biocrudes.The contents of nitrogen-heterocyclic compounds decreased with temperature while amide kept increasing.The effect of residence time on the components of nitrogen-containing organic compounds was similar with that of temperature.However,the influence of solid loading rate was insignificant.Moreover,it was also found that the differences of amino acids in the protein components in the two microalgae might affect the nitrogen distribution in products.For example,nitrogen in basic amino acids of Spirulina sp.preferred to go into the aqueous phase comparing with the nitrogen in neutral amino acids of Chlorella sp.In summary,a brief reaction map was proposed to describe the nitrogen pathway during microalgae hydrothermal liquefaction.

Local solids flow structure in a countercurrent liquid-upward and solids-downward fluidized bed(CCLSFB)system

The local solids holdup and local particle velocity in a Countercurrent Liquid-upward and Solids-downward Fluidized Bed(CCLSFB)were investigated in details using optical fiber probes with two different models in a Plexiglas column of 1.5 m in height and 7.0 cm in inner diameter.A new flow regime map including fluidized bed,transition,and flooding regimes was established.The axial solids holdup distribution is almost uniform at low liquid velocity and/or solids flowrate and becomes less uniform with higher solids holdup at the top of the column after the operating liquid velocity is reaching the flooding velocity.The radial solids holdup profile is also nearly flat with a slightly lower solids holdup in the near-wall region at low liquid velocity and solids flowrate but becomes nonuniform as the operating liquid velocity approaches the flooding velocity.Two equations were also proposed to correlate radial local solids holdups.The descending particle velocity in CCLSFB increases with the decrease of the liquid velocity and the increase of the solids flowrate.A generally uniform particle velocity distribution was found in the axial direction,as well as in the radial direction except for a small decrease near the wall.These results on the local solids flow structure would provide basic information and theoretical supports for the design and industrial application of CCLSFB.

A modified wake model in bubble-induced three-phase inverse fluidized bed(BIFB)

A modified wake model was proposed for the newly developed bubble-induced three-phase inverse fluidized bed(BIFB),by combining the generalized wake model and the gas-perturbed liquid model.On the basis of the modified wake model,the solids and liquid holdups and the complete fluidization gas velocity in BIFB system have been successfully predicted with two established correlations.The predictions achieved very good agreements with the experimental data.