The enrichment and transformation mechanism of Pb and Cu in suspension magnetization roasting and magnetic separation from iron tailings.

Magnetic iron concentrate (MIC) and nonmagnetic tailings (NT) are obtained from magnetization roasting of iron tailings (IT). MIC containing Pb adversely affects blast furnace ironmaking, while Cu in NT poses leaching risks. This study utilizes fast pyrolysis-suspension magnetization roasting to recover iron from IT. The enrichment of Pb, Cu, and the phase transformation mechanism of Cu in the process of suspension magnetization roasting and magnetic separation were clarified. Results show 96.13 % of Cu in IT is in limonite and 47.23 % of Pb is associated with iron. At 750 °C, with 10 % dosage of biomass pyrolysis and 10 min roasting, Pb, Cu and Fe contents in MIC are 0.96, 2.14 and 3.17 times that of NT. Increasing roasting temperature enhances Cu associated with iron enrichment into the MIC, while oxidation of free copper oxide associated with iron forms magnetic copper ferrite. Increased pyrolyzed biomass leads to over-reduction of magnetite associated with Cu to FeO associated with Cu, promoting magnetic copper ferrite decomposition into FeO and free copper oxide. This research holds significant importance in controlling the quality of MIC and the storage risk of IT, and provides theoretical guidance for the regulation and recovery of valuable metals in subsequent processes.

Recovery of iron from iron tailings by suspension magnetization roasting with biomass-derived pyrolytic gas.

A major industrial solid waste, iron tailings occupy a large area and pose long-term pollution risks. The pyrolysis gas of biomass was used as reducing agent to suspension magnetize and roast iron tailings to recover iron in this study. The process conditions, phase transformation and microstructure evolution of the iron tailings, pyrolysis gas production, and reaction regulations were investigated to explain the mechanism of iron recovery by suspension magnetization roasting (SMR) under the action of biomass pyrolysis gas. These studies were conducted using X-ray diffraction, scanning electron microscopy, vibrating sample magnetometer, thermo-gravimetric and differential scanning calorimetry, brunauer-emmett-teller specific surface area, and gas chromatography. The results showed that, after the grinding-magnetic separation process, the iron recovery rate was 93.32 %; the iron grade of the iron concentrate was 61.50 %. The optimal process conditions were determined as follows: fast pyrolysis temperature of 600 °C, SMR temperature of 700 °C, biomass dosage of 10 %, and SMR time of 4-5 min. The formation of Fe3O4 from the surface to the interior of the particles during the reduction process, and formation of pores and cracks led to an increase in the specific surface area. The SMR temperature not only improved the heat and mass transfer effect in the reduction process but also generated more CO and H2 through the reverse reaction of methanation, which work together to increase the saturation magnetisation of the unit sample. This method can be used to efficiently recover high quality iron from refractory iron ores.

Biomass waste as a clean reductant for iron recovery of iron tailings by magnetization roasting.

The magnetization roasting with coal as primary reductants adds cost and causes environmental pollution. Therefore, it is of great importance to investigate the biomass application as a reductant for magnetization roasting to recover iron from low-utilization iron tailings for emission mitigation and green utilization. This study systematically investigated the impact of biomass (pyrolysis gas from agricultural and forestry waste) as a reductant on the conversion of iron tailings to magnetite in magnetization roasting. Additionally, the thermal decomposition of biomass, phase transformation and microstructure evolution of iron tailings were analyzed by TG, XRD, BET, and other methods to elucidate the conversion mechanism for facilitating magnetized hematite in iron tailings with biomass-derived gas. The results showed that woody biomass was a more appropriate reductant for magnetization roasting; 650 °C was the optimal temperature for the complete transformation of hematite to magnetite by reduction roasting with biomass waste. Through magnetic separation, the concentrate with an iron grade of 62.04% and iron recovery of 95.29% was obtained, and the saturation magnetization was enhanced from 0.60 emu/g to 58.03 emu/g of iron tailings. During the magnetization roasting, CO and H2 generated from biomass reduced the hematite in tailings particles from interior to exterior, forming a loose structure with rich microfissures, facilitating the subsequent separation operations. This study offers a novel reference for applying biomass to exploit hematite minerals and shows the potential of biomass for energy savings and emission reduction in the utilization of iron tailing resources.

Treatment of a simulated sludge by ultrasonic zero-valent iron/EDTA/Air process: Interferences of inorganic salts in polyaromatic hydrocarbon removal.

Understanding the occurrence states of persistent organic pollutants such as polycyclic aromatic hydrocarbons (PAHs) in textile dyeing sludge is the key to their further treatment and disposal. Here, the effects of inorganic salts (silicate, sulfate, phosphate, hydroxide, and iron salts) that were typically rich in textile dyeing sludge on PAH adsorption by sludge and PAH degradation by an ultrasound (US) combined zero-valent iron/EDTA/Air (ZEA) system were studied in a simulated sludge system. The results showed that the simulated sludge containing inorganic salts had a larger specific surface area, which was beneficial for the adsorption of PAHs. More low-ring PAHs were adsorbed on the surface of the particles in the simulated sludge because of the inorganic salts, which was conducive to low-ring PAHs degradation by US/ZEA. The PAH removal rates were increased by 15.37% and 11.19%, respectively, in the presence of SiO32- and HPO42-. The yield of hydroxyl radicals (OH) was increased by 42.39% and 66.25% by SiO32- and HPO42-, respectively. The reason was that the oxidation of the ligand ([FeⅡ(EDTA)]) formed by ethylenediaminetetraacetic acid (EDTA) and divalent iron was promoted by SiO32- and HPO42-. The formation of OH in the US/ZEA system was inhibited by the corrosion inhibition of SO42- on zero-valent iron (ZVI), the reaction of ferric salt with EDTA, and the reaction of Mg(OH)2 with the ligand ([FeIII(EDTA)]). This work provides an essential theoretical insight into the role of the inorganic components of sludge in the removal of PAHs by advanced oxidation processes.

Sono-advanced Fenton-like degradation of aromatic amines in textile dyeing sludge: efficiency and mechanisms.

In this paper, a novel strategy integrating ultrasound (US) with a Fenton-like (zero-valent iron/EDTA/air, ZEA) process was proposed for the removal of the refractory and carcinogenic aromatic amines (AAs) in textile dyeing sludge for the first time. The operating condition was optimized as 1.08 W/cm3 ultrasonic density, 15 g/L ZVI, and 1.0 mM EDTA, which could reach degradation efficiencies of 51.79% in US, 72.88% in ZEA, and 92.40% in US/ZEA system after 90-min reaction. Quenching experiments showed that electron transfer reactions generated by the iron ligands in ZEA brought about various reactive oxidative species (ROS), in which Fe (IV), O2˙-, and ˙OH dominated the degradation. US induced sludge disintegration by ultrasonic shear, proven by particle size decrease and supernatant organic matter upsurge, which helps ROS contact with those pollutants in the sludge cavities. Besides, US facilitated the iron redox cycle for oxygen activation by promoting the corrosion of ZVI and stripping considerable ferric ions from sludge iron oxides which were verified by SEM, XRF, and XPS. Graphical abstract.

Formation of lead ferrites for immobilizing hazardous lead into iron-rich ceramic matrix.

A strategy of immobilizing lead in the framework of ferrite-ceramic matrix, to reduce its environmental hazard was explored in this study. The mechanisms of incorporating lead into lead ferrites (δ-phase (2PbO·Fe2O3), γ-phase (PbO·(2-2.5)Fe2O3) and ß-phase (PbO·(5-6)Fe2O3)) was revealed by observing the phase transformation in the products. The δ-phase was dominantly formed at low temperature of 700-800 °C at Pb/Fe of 1/1-1/3. The significant growth of γ-phase was observed at 750-850 °C and Pb/Fe of 1/4-1/7. The ß-phase substantially formed at 900-1000 °C with Pb/Fe of 1/7-1/12. The transformation of δ-phase to γ-phase and/or ß-phase indicated the destruction of δ-phase unit and reconstruction of γ-phase and ß-phase units during sintering process. However, the transformation of γ-phase into ß-phase suggested a structure conversion process, local structural changes arose as a consequence of the addition of Fe2O3. When comparing the leaching ability of δ-, γ- and ß-phase, the results showed the superiority of ß-phase for lead immobilization over the longer leaching period.

Inhibitory effect of cadmium(II) ion on anodic electrochemically active biofilms performance in bioelectrochemical systems.

Cadmium(II) ion can affect the anode performance of bioelectrochemical systems (BES); however, how the presence of Cd2+ affect the extracellular electron transfer of anodic electrochemically active biofilms (EABs), the microbial viability and species composition of microorganism on the anode remain poorly understood. Here, we investigated the inhibitory effect of Cd2+ at different concentrations on the electrochemical performance and the biofilm community in mixed-culture enriched BES. The electrochemical performance of the BES was not inhibited at 2 mg L-1 Cd2+, while higher concentrations of 5-20 mg L-1 resulted in the decrease in the maximum power density, with 0.34 ±â€¯0.01 W m-2 at 5 mg L-1, 0.28 ±â€¯0.01 W m-2 at 10 mg L-1, and 0.17 ±â€¯0 W m-2 at 20 mg L-1, respectively. When adding 30 mg/L Cd2+, there was almost no power output. The decline of the power output was possibly ascribed to the suppressed viability and the change of species richness as evident from confocal laser scanning microscopy and microbial community analysis. Cyclic voltammogram and electrochemical impedance spectroscopy revealed that high concentration of Cd2+ exceeding 5 mg L-1 can inhibit the secretion of outer membrane cytochromes, thus reducing the electron transfer between the EABs and the anode surface. Analysis of bacterial structures showed a decrease in Geobacter accompanied by an increase in Stenotrophomonas and Azospira in response to Cd2+ at 10 and 20 mg L-1. This study added to the in-depth analysis of the inhibition of Cd2+ on EABs, and provided new insights into the removing Cd2+ and organics simultaneously in BES.

Removal of polycyclic aromatic hydrocarbons (PAHs) from textile dyeing sludge by ultrasound combined zero-valent iron/EDTA/Air system.

This paper proposes a combined ultrasound (US) and zero-valent iron/EDTA/Air (ZEA) system to remove polycyclic aromatic hydrocarbons (PAHs) from textile dyeing sludge. The removal efficiencies of 16 PAHs using ZEA, US/Air (air injected into the US process), and US/ZEA treatments were investigated, together with the effects of various operating parameters. The enhanced mechanisms of US and the role of reactive oxygen species (ROS) in removing PAHs in the US/ZEA system were explored. Results showed that only 42.5% and 32.9% of ∑16 PAHs were removed by ZEA and US/Air treatments respectively, whereas 70.1% were removed by US/ZEA treatment, (with favorable operating conditions of 2.0 mM EDTA, 15 g/L ZVI, and 1.08 w/cm3 ultrasonic density). The US/ZEA system could be used with a wide pH range. US led to synergistic improvement of PAHs removal in the ZEA system by enhancing sludge disintegration to release PAHs and promoting ZVI corrosion and oxygen activation. In the US/ZEA system, PAHs could be degraded by ROS (namely OH, O2-/HO2, and Fe(IV)) and adsorbed by ZVI, during which the ROS made the predominant contribution. This study provides important insights into the application of a US/ZEA system to remove PAHs from sludge.

Combined ultrasound with Fenton treatment for the degradation of carcinogenic polycyclic aromatic hydrocarbons in textile dying sludge.

To develop an effective method to remove the toxic and carcinogenic polycyclic aromatic hydrocarbons (CPAHs) from textile dyeing sludge, five CPAHs were selected to investigate the degradation efficiencies using ultrasound combined with Fenton process (US/Fenton). The results showed that the synergistic effect of the US/Fenton process on the degradation of CPAHs in textile dyeing sludge was significant with the synergy degree of 30.4. During the US/Fenton process, low ultrasonic density showed significant advantage in degrading the CPAHs in textile dyeing sludge. Key reaction parameters on CPAHs degradation were optimized by the central composite design as followed: H2O2 concentration of 152 mmol/L, ultrasonic density of 408 W/L, pH value of 3.7, the molar ratio of H2O2 to Fe2+ of 1.3 and reaction time of 43 min. Under the optimal conditions of the US/Fenton process, the degradation efficiencies of five CPAHs were obtained as 81.23% (benzo[a]pyrene) to 84.98% (benz[a]anthracene), and the benzo[a]pyrene equivalent (BaPeq) concentrations of five CPAHs declined by 81.22-85.19%, which indicated the high potency of US/Fenton process for removing toxic CPAHs from textile dyeing sludge.

Enhanced bioelectricity generation and azo dye treatment in a reversible photo-bioelectrochemical cell by using novel anthraquinone-2,6-disulfonate (AQDS)/MnOx-doped polypyrrole film electrodes.

A novel anthraquinone-2,6-disulfonate/MnOx-doped polypyrrole film (AQDS/Mn/PPy) electrode was prepared by one-step electropolymerization method and was used to improve performance of a reversible photo-bioelectrochemical cell (RPBEC). The RPBEC was operated in polarity reversion depended on dark/light reaction of alga Chlorella vulgaris by which sequential decolorization of azo dye and mineralization of decolorization products coupled with bioelectricity generation can be achieved. The results showed that formation of uniform AQDS/Mn/PPy film significantly enhanced electroactive surface area and electrocatalytic activity of carbon electrode. The RPBEC with AQDS/Mn/PPy electrodes demonstrated 77% increases in maximum power and 73% increases in Congo red decolorization rate before polarity reversion, and 198% increases in maximum power and 138% increases in decolorization products mineralization rate after polarity reversion, respectively, compared to the RPBEC with bare electrode. This was resulted from simultaneous dynamics improvement in half-reaction rate of anode and photo-biocathode due to enhanced electron transfer and algal-bacterial biofilm formation.

Effect of K2FeO4/US treatment on textile dyeing sludge disintegration and dewaterability.

The effect of potassium ferrate/ultrasonic (K2FeO4/US) treatment on the physicochemical features of textile dyeing sludge was studied. The soluble chemical oxygen demand (SCOD), deoxyribonucleic acid (DNA), sludge volume index (SVI), sludge viscosity, capillary suction time (CST) and particle size were measured to understand the observed changes in the sludge physicochemical features. The results showed that the combined K2FeO4/US treatment presented great advantages for disrupting the sludge floc structure over K2FeO4 or ultrasonic treatments alone. The optimal parameters of sludge disintegration were found to be a K2FeO4 treatment time of 60 min, a K2FeO4 dosage of 0.5936 g/g SS, an ultrasonic time of 15 min and an ultrasonic intensity of 0.72 W/mL. The initial median diameter of the sludge particles was 15.24 µm, and this value decreased by 35.89%. The CST was initially 59.6 s and increased by 231%, whereas the SVI was 97.78 mL/g and decreased by 25.89%. Scanning electron microscope (SEM) images indicated that the sludge surface was irregular and loose with a large amount of channels or voids during K2FeO4/US treatment. K2FeO4/US treatment synergistically enhanced the sludge solubilization and reached 668.67 mg/L SCOD, which is 31.81% greater than the additive value obtained with K2FeO4 treatment alone (215.95 mg/L) or with ultrasonic treatment alone (240 mg/L).

Effect of different sulfides on cadmium distribution during sludge combustion based on experimental and thermodynamic calculation approaches.

The effects of sulfur compounds on the migration of a semi-volatile heavy metal (cadmium) during sludge incineration were investigated with two methods, i.e., experiments in a tubular furnace reactor and thermodynamic equilibrium calculations. The representative typical sludge with and without the addition of sulfur compounds was incinerated at 850 °C. The partitioning of Cd among the solid phase (bottom ash) and gas phase (fly ash and flue gas) was quantified. The results indicate that sulfur compounds in the elemental form and a reduced state could stabilize Cd in the form of CdS, aluminosilicate minerals, and polymetallic sulfides, whereas sulfur in the oxidized forms slightly increases Cd volatilization during incineration. For Cd solidification points, the inhibition effect on the volatilization of Cd is as follows: S > Na2SO4 > Na2S. Chemical equilibrium calculations indicate that sulfur binds with Cd and alters Cd speciation at low temperatures (<950 K). Furthermore, SiO2- and Al2O3-containing minerals can function as sorbents stabilizing Cd as condensed phase solids (CdSiO4 and CdAl2O4) according to the results of equilibrium calculations. These findings provide useful information for understanding the partitioning of Cd and thus facilitate the development of strategies to control Cd volatilization during sludge incineration.

Levels, composition profiles and risk assessment of polycyclic aromatic hydrocarbons (PAHs) in sludge from ten textile dyeing plants.

As components of synthetic dyes, polycyclic aromatic hydrocarbons (PAHs) are present as contaminants in textile dyeing sludge due to the recalcitrance in wastewater treatment process, which may pose a threat to environment in the process of sludge disposal. In order to evaluate PAHs in textile dyeing sludge, comprehensive investigation comprising 10 textile dyeing plants was undertaken. Levels, composition profiles and risk assessment of 16 EPA-priority PAHs were analyzed in this study. The total concentrations of 16 PAHs (∑16 PAHs) varied from 1463 ± 177 ng g(-1) to 16,714 ± 1,507 ng g(-1) with a mean value of 6386 ng g(-1). The composition profiles of PAHs were characterized by 3- and 4-ring PAHs, among which phenanthrene, anthracene and fluoranthene were the most dominant components. The mean benzo[a]pyrene equivalent (BaPeq) concentration of ∑16 PAHs in textile dyeing sludge was 423 ng g(-1), which was 2-3 times higher than concentrations reported for urban soil. According to ecological risk assessment, the levels of PAHs in the textile dyeing sludge may cause a significant risk to soil ecosystem after landfill or dumping on soil.

Characterization and environmental risk assessment of heavy metals found in fly ashes from waste filter bags obtained from a Chinese steel plant.

The environmental risk of exposure to six heavy metals (Cu, Pb, Zn, Cr, Ni, and Cd) found in fly ashes from waste filter bags obtained from a steel plant was estimated based on the mineralogical compositions, total concentrations and speciation of the metals in the fly ashes. The results indicated that the fly ashes mainly consisted of hematite, magnetite, cyanite, spinel, coesite and amorphous materials. The concentrations of Zn and Pb were much higher than that of other materials. After Zn and Pb, Ni was present in the highest concentration, followed by Cu, Cr and Cd. Each heavy metal was distributed differently in fly ashes. The levels of Zn, Cd and Pb in the active fraction were very high, and ranged from 64.83 to 81.96%, 34.48 to 82.4% and 6.92 to 79.65% respectively, while Cu, Cr and Ni were mainly present in the residual fraction. The risk assessment code (RAC) values of fly ashes showed that the Zn and Cd present in the H3 sample presented a very high risk, with RAC values greater than 50%. The Cu present in the H3 sample, Cd in the H2 sample and Zn in the H4 and H5 samples presented a high risk. The Pb present in the H2 sample, Cd in the H4 sample, Ni in the H1 and H5 samples, and Zn in the H1 sample presented a medium risk. A low risk was presented by the Cu present in the H1, H2, H4 and H5 samples, the Pb in the H1, H3 and H5 samples, the Cd in the H1 and H5 samples, and the Ni in the H2 sample. No risk was presented by Cr in any sample.

[Determination of metals in waste bag filter of steel works by microwave digestion-flame atomic absorption spectrometry].

A method of microwave digestion technique-flame atomic absorption spectrometry was proposed to determine the total contents of Cu, Zn, Pb, Cd, Cr and Ni in five different kinds of waste bag filters from a steel plant. The digestion effects of the six acid systems on the heavy metals digestion were studied for the first time. The relative standard deviation (RSD) of the method was between 1.02% and 9.35%, and the recovery rates obtained by standard addition method ranged from 87.7% to 105.6%. The results indicated that the proposed method exhibited the advantages of simplicity, speediness, accuracy and repeatability, and it was suitable for determining the metal elements of the waste bag filter. The results also showed that different digestion systems should be used according to different waste bag filters. The waste bag filter samples from different production processes had different metal elements content. The Pb and Zn were the highest in the waste bag filters, while the Cu, Ni, Cd and Cr were relatively lower. These determination results provided the scientific data for further treatment and disposal of the waste bag filter.