Two-stage Oxidation Research Articles

Experimental study on the treatment of high COD metal degreasing cleaning wastewater by coagulation and two-stage Fenton oxidation

ABSTRACT In this study, based on the water quality characteristics of metal degreasing cleaning wastewater , wastewater treatment by coagulation combined with two-stage Fenton oxidation was proposed. The results showed that when the dosage of PAC was 5 g/L and the dosage of CPAM was 8 mg/L, with an initial pH of 8, rapid stirring at 350 rpm for 3 min followed by slow stirring at 200 rpm for 15 min, the optimal removal rate of chemical oxygen demand (COD) reached 74.08%. Primary Fenton oxidation is mainly aimed at decomposing macromolecular long-chain pollutants and removing some pollutants. The highest COD removal rate was achieved at 95.07% when the dosage of H2O2 was 4 mol/L, the dosage of FeSO4 was 40 g/L, the oxidation lasted for 60 min, the initial pH was 2, the effluent pH was 8, and the settling time was 90 min. The two-stage Fenton oxidation process provided further advanced treatment. With a reagent ratio of 1:0.5, the effluent COD concentration was reduced to 457 mg/L, meeting the third class standard of the `Integrated Wastewater Discharge Standard' (GB 8978 1996).

Catalytic conversion of soluble aniline into insoluble N-phenylphenazine for wastewater treatments

Aniline, a common pollutant in industrial wastewater, requires an effective treatment method with minimal chemical usage. In this study, a two-stage catalytic oligomerization process has been developed to address this issue by converting soluble aniline into insoluble oligomers for wastewater treatment. In the first stage, aniline is oxidized using hydrogen peroxide (H2O2) and a green catalyst, iron tetraamido macrocyclic ligand (Fe-TAML) to form aniline tetramers or pentamers. In the second stage, these oligoanilines undergo further oxidation with H2O2 alone at a higher temperature, resulting in the formation of N-phenylphenazine or its derivatives. These macrocyclic compounds precipitate from the wastewater due to π− π stacking, allowing easy separation through decantation or gravity filtration. After process optimization, only 3 mg/L of Fe-TAML and 2 g/L of H2O2 are required to treat 1 g/L of aniline, achieving a remarkable 96.8% aniline removal efficiency and a 62.5% precipitate yield. This two-stage oxidation approach shows promise for treating aniline and similar aromatic compounds in real industrial wastewater.

Structural-Change-Induced Two-Stage Redox Behavior of Pentacenebisquinodimethane with Tricolor Chromism.

Tricolor electrochromism was realized through the interconversion among the neutral (yellow), dicationic (green), and tetracationic (blue) states, even though only one kind of chromophore is generated upon oxidation. Both dicationic and tetracationic states were isolated as stable salts, and their different colors come from the effective inter-chromophore interaction only in the tetracationic state but not in the dicationic state. Despite the negligible Coulombic repulsion in the tetracationic state with four cyanine-type chromophores, pentacenebisquinodimethane undergoes stepwise two-stage two-electron oxidation when radical-stabilizing 5-(4-octyloxyphenyl)-2-thienyl groups are attached on the exomethylene bonds. A contribution from the biradical form only in the neutral state but not in the dicationic state is the reason for the observed negative cooperativity during the electrochemical oxidation.

Reducing Oxidation during Direct Metal Deposition Process: Effects on Ti6Al4V Microstructure and Mechanical Properties

The production of materials with a high affinity for oxidation using the direct metal deposition (DMD) process requires an extended process examination that goes beyond the usual, purely energetic consideration, with the aim of providing sufficient energy to melt the substrate and the powder material supplied. This is because the DMD process does not allow any conclusions to be drawn as to whether it and its respective selected parameters result in an oxidation critical process. To assess this, a superposition of the temperature field with the existing spatial oxygen concentration is required. This work uses this approach to develop an oxidation model that reduces oxidation during the DMD process. In addition to the numerical model, an analytical model is derived, with which the temperature of a material element can be calculated analytically and the resulting boundary oxygen concentration calculated using Fick’s 2nd law. The model also takes into account two-stage oxidation kinetics for Ti alloys. The effect of too high a travel speed (with the same specific energy of the other experiments) is shown visually in the numerical calculation of the temperature field. However, if the process model is taken into account, the components do fulfil the specified requirements. Finally, the effect of oxidation on the microstructure, microhardness, ultimate strength, yield strength and elongation at failure of Ti6Al4V structures produced using DMD is also investigated, and further supports our conclusions regarding the effectiveness of the proposed model.

Ultra-Dense Supported Ruthenium Oxide Clusters via Directed Ion Exchange for Efficient Valorization of 5-Hydroxymethylfurfural.

Maximizing the loadings of active centers without aggregation for a supported catalyst is a grand challenge but essential for achieving high gravimetric catalytic activity, especially toward multi-step reactions. The oxidation of 5-hydroxymethylfurfural (HMF), a key biomass-derived platform molecule, into 2,5-furandicarboxylic acid (FDCA), a promising alternative to polyester monomer, is such a multi-step reaction that involves 6 proton and electron transfers. This process often demands strong alkaline environment but also suffers from the alkali-driven polymerization side-reaction. Meanwhile, neutral media ameliorates the polymerization, but lacks efficient catalyst toward deep oxidation. Herein, we devised a strategy of creating ultra-dense supported Ru oxide clusters via directed ion exchange in a Co hydroxyanion (CoHA) support material. Pyrimidine ligands were first incorporated into the CoHA interlayers, and the subsequent evacuation of pyrimidines created porous channels for the directed ion exchange with the built-in anions in CoHA, which allowed the dense and mono-disperse functionalization of RuCl6 2- anions and their resulting Ru oxide clusters. These ultra-dense Ru oxide clusters not only enable high HMF electrooxidation currents under neutral conditions but also create microscopic channels in-between the clusters for the expedited re-adsorption and oxidation of intermediates toward highly oxidized product, such as 5-formyl-2-furoic acid (FFCA) and FDCA. A two-stage HMF oxidation process, consisting of ambient conversion of HMF into FFCA and FFCA oxidation into FDCA under 60 °C, was eventually developed to first achieve a high FDCA yield of 92.1 % under neutral media with significantly reduced polymerization.

Oxidation Mechanism and Surface Characterization of Pyrolytic Graphite in Simulated Air for Pyrochemical Reprocessing Application

Accidental air ingress into the containment chamber of pyrochemical reprocessing of spent nuclear fuels can cause severe oxidation of graphite components. Pyrolytic graphite (PyG) coating on conventional high-density graphite (HDG) is proposed for protection against oxidation, molten salt, and molten metal corrosion. The aim of the present study is to evaluate the thermal stability and kinetic parameters and propose a suitable oxidation mechanism of PyG under simulated air using thermogravimetry analysis (TGA). In dynamic oxidation, a linear increase in the oxidation onset, peak, and burnout temperature is observed for PyG synthesized at increasing pyrolysis temperature from 1200 to 2400°C except for 1400°C. The isothermal oxidation study showed a similar trend i.e., a decrease in the linear oxidation rate constant value for any given isotherm with increasing pyrolysis. The Arrhenius plot showed two-stage oxidation regimes operating between 600 to 1000°C. In regime-I, between 600 to ∼800°C controlled by surface chemical reaction kinetics, the activation energy is measured between 100-200 kJ.mol−1. The graphite-oxygen reaction initiates and propagates preferentially along the prismatic planes at the sample edges, where the dangling bonds of stacked graphite layer structures are exposed. In regime-II operating above ∼800°C, the surface reaction rate is infinitely faster, and the diffusional mass transport becomes a rate-limiting factor. In this regime, the graphite-oxygen initiates by pore formation on defective reactive sites on the bulk surface and propagates by pore-widening and pore-coalescence mechanism. The observed differences in the oxidation rates for different pyrolysis PyG attributed to its intrinsic material properties are investigated. This work provides new insights into the oxidation mechanism of the PyG during accidental air ingress in a pyrochemical reprocessing plant.

Applying bio-oxidation waste solution into two-stage oxidation process to enhance the bio-oxidation of pyrite: Insight on enhanced mechanism

Chemical oxidation that applies the bio-oxidation waste solution (BOS) as oxidation system, a simple and environmentally friendly method, can significantly enhance the bio-oxidation efficiency of pyrite (FeS2) in two-stage oxidation process. To clarify the dissolution process of pyrite and reveal the enhanced mechanism, the present study provided an in-depth analysis of oxidation results, physical and chemical changes on the pyrite surface during chemical oxidation. The microbial community structure and kinetic analysis were also performed for the bio-oxidation. Study indicated that the oxidation of Fe3+ resulted in the destruction of pyrite surface chemical structure and the reduction of particle size. The nitrogenous substances were also generated on pyrite surface. Kinetic analysis suggested that the dissolution rate of pyrite in bio-oxidation was mainly limited by interfacial chemical reaction step. Therefore, both physical and chemical factors caused by Fe3+ oxidation were conducive to accelerating the dissolution of pyrite. Additionally, releasing more Fe2+ as energy source and the generated nitrogenous substances as N or C source, greatly improved the microbial community structure and growth rate, thus leading to a rapid increase of oxidant-Fe3+ concentration. These factors greatly enhanced the dissolution kinetics of pyrite in bio-oxidation. As a result, the extraction levels of Fe and S elements for pyrite in two-stage oxidation process could reach 89.1 ± 1.5 % and 87.3 ± 1.2 %, respectively, which were significantly increased by 70.1 ± 0.2 % and 62.3 ± 0.1 % compared with the values in one-stage bio-oxidation process. These findings provide theoretical support for using BOS in the two-stage oxidation process for high‑sulfur refractory gold ores.

Exploring the oxidation behaviors of the Ti[sbnd]V[sbnd]Cr[sbnd]Mo high-entropy MAX at 800 °C for its self-lubricity

Given the unique nanolaminate structure, the MAX phase ceramics which are composed of alternatively stacked two-dimensional (2D) metal (M) carbides (X) and main group (A) atomic layers have shown promising properties at elevated temperatures. Recently, an excellent self-lubricating performance of a high-entropy (HE) (TiVCrMo)3AlC2 MAX is demonstrated at 800 °C in the air. However, the formation mechanism of a self-lubricative tribofilm is still waiting for clarified. In this work, the HE (TiVCrMo)3AlC2 MAX is synthesized and its oxidation behaviors are systematically evaluated at 800 °C in the air. A two-stage parabolic oxidation behavior is detected, which can be mainly ascribed to the volatilization of MoO3 species coupled with the thickening of the compound oxide scale. Meanwhile, the HE composition results in chemically complex phases including Rutile and vacancy-ordered TiO species in the oxide scale, which contribute to a higher ion diffusion rate for mass transportation. Consequently, the continued volatilization of MoO3 is beneficial for the enhanced lubricity and anti-wear performance of the (TiVCrMo)3AlC2 MAX at 800 °C.

Revealing a spontaneous two-stage process in femtosecond laser-induced fully-oxidized nanostructures

Femtosecond laser interactions with matter facilitate the creation of diverse structures on material surfaces, including laser induced periodic surface structures (LIPSS), ablation nanoparticles, sub-diffraction nanogrooves, and plasmonic nanostructures. In this study, we reveal a unique nanostructure on silicon induced by femtosecond laser irradiation, distinguished by its pea-shaped morphology. At the center of this nanostructure, a nano-slit is oriented perpendicular to the laser polarization. The nano-slit penetrates the pea-shaped nanostructure and an underlying layer with a depth of approximately 600 nm. Energy dispersive X-ray spectroscopy (EDS) analysis confirms that the nanostructure and the underlying layer consist entirely of silicon oxide. A spontaneous two-stage oxidation process is proposed to explain the formation mechanism of fully-oxidized nanostructures. The presence of nano-slits endows the oxide nanostructures with polarization sensitivity, which shows the potential in applications such as optical encryption and data storage. In addition, the spontaneous two-stage oxidation process allows for the maskless fabrication of oxide nanowires with a precision down to hundreds of nanometers, providing the flexibility to produce arbitrary nanostructures. This capability opens up new possibilities for manipulating light beams and enabling on-chip nano-glass printing.

Bioaugmentation using salt-tolerant bacteria in a dual-stage process for high-salinity wastewater treatment: Performance, microbial community, and salt-tolerance mechanism

To address the challenges of nitrogen removal and stability problems in biological treatment of high-salinity wastewater, a new technology based on salt-tolerant aerobic denitrifying (SAD) bacteria to strengthen the two-stage bio-contact oxidation reactor (TBOR) and moving bed biofilm reactor (MBBR) dual-stage process was proposed. The results showed that the NH4+-N removal rate of TBOR and TN removal rate of MBBR increased by 26.05 % and 15.90 %, respectively, after bioaugmentation with SAD bacteria at salinity of 5 %. The COD, NH4+-N and TN removal rates in real wastewater (at salinity of 4 ~ 5 %) treatment were 93.45 %, 97.57 % and 90.83 %, respectively. Microbial analysis showed that at salinity of 5 %, SAD bacteria Halomonas and Truepera were the main functional bacteria responsible for nitrogen removal. Microbial functional analysis and metabolic predictions further revealed that bioaugmentation enhanced the expression of the nir gene, thereby further promoting the process of dissimilatory nitrite reduction to ammonium (DNRA). Furthermore, bioaugmentation can also resist the external high-salinity environment by exporting Na+ extracellularly, promoting extracellular polymeric substances (EPS) secretion and amino acid metabolism. This study demonstrates that bioaugmentation with SAD bacteria is a suitable approach for nitrogen and carbon removal of high-salinity wastewater.

Investigation on the effect and growth mechanism of two-stage MAO coating

As a more popular surface treatment method, micro-arc oxidation technology can well solve the problems of insufficient strength and poor corrosion resistance of aluminum alloy surface. In this paper, a composite coating was obtained by using a two-stage micro-arc oxidation method different from the conventional micro-arc oxidation treatment, which solved the problem of incompatibility between the two types of electrolytes and obtained a coating with superior effect. The microscopic morphology and elemental composition were characterized by using Energy Dispersive Spectrometer (EDS)/X-ray Diffraction (XRD)/Scanning Electron Microscopy (SEM). The coating thickness was tested using a coating thickness gauge, its tribological properties were tested by friction experiments, and its corrosion resistance was tested by electrochemical corrosion tests. The results show that the coating has the advantages of large thickness, dense, good anti-wear performance, small friction coefficient and excellent corrosion resistance, which enhanced the performance of MAO coating and was an important guide for further work.

Insights into the enhanced activity and SO2 resistance of air oxidation treated Mn-Fe doped biochar catalyst in the low-temperature catalytic reduction of NOx with NH3

In this study, a sustainable two-stage air oxidation (TAO) was employed to prepare Fe modified MnOx-biochar catalyst (C-O2-MF-O2) instead of high temperature treatment and/or chemical activation for selective catalytic reduction of NO with NH3 (NH3-SCR). The collaborative effect of Fe modification and TAO on the physicochemical properties and catalytic performance of catalysts was systematically studied. Compared with counterpart catalysts treated with two-stage N2 (C-N2-MF-N2) or one-stage O2 (C-O2-MF-N2, C-N2-MF-O2), C-O2-MF-O2 showed obvious enhanced physicochemical properties (SBET, pore properties, high-valance metal ratio, chemisorption oxygen (Oα) content), superior catalytic performance, achieving 91.3% NO conversion with nearly 100% N2 selectivity at 150 °C, and much better H2O and SO2 resistance. It is worth noting that TAO facilitated the redox performance of MnOx after Fe modification to generate more dispersed high-valance metal (Mn4+ and Fe3+), thereby favoring the low-temperature SCR activity of the catalyst. Further, the in situ DRIFTS studies revealed TAO produced remarkable effects on the adsorption behaviors of NH3, NO and SO2, and the corresponding mechanisms of catalyst activity enhancement and SO2 resistance were proposed. Generally, TAO could be a favorable avenue to prepare catalysts with binary active metals for improving performance of NH3-SCR.

Responses of the microbial community and the production of extracellular polymeric substances to sulfamethazine shocks in a novel two-stage biological contact oxidation system.

The biological contact oxidation reactor is an effective technology for the treatment of antibiotic wastewater, but there has been little research investigating its performance on the sulfamethazine wastewater treatment. In this study, a novel two-stage biological contact oxidation reactor was used for the first time to explore the impact of sulfamethazine (SMZ) on the performance, microbial community, extracellular polymeric substances (EPS), and antibiotic-resistant genes (ARGs). The chemical oxygen demand (COD) and ammonia nitrogen (-N) removal efficiencies kept stable at 86.93% and 83.97% with 0.1-1 mg/L SMZ addition and were inhibited at 3 mg/L SMZ. The presence of SMZ could affect the production and chemical composition of EPS in the biofilm, especially for the pronounced increase in TB-PN yield in response against the threat of SMZ. Metagenomics sequencing demonstrated that SMZ could impact on the microbial community, a high abundance of Candidatus_Promineofilum, unclassified_c__Anaerolineae, and unclassified_c__Betaproteobacteria were positively correlated to SMZ, especially for Candidatus_Promineofilum. Candidatus_Promineofilum not only had the ability of EPS secretion, but also was significantly associated with the primary SMZ resistance genes of sul1 and sul2, which developed resistance against SMZ pressure through the mechanism of targeted gene changes, further provided a useful and easy-implement technology for sulfamethazine wastewater treatment.

Efficient Oxidative Desulfurization over [Mo8O26]4–-Based Hybrids: Phase Transfer Catalysis

Organic–inorganic hybrid materials [Rmim]4Mo8O26 (1-alkyl-3-methylimidazolium polyoxomolybdate, alkyl = n-C4H9, n-C6H13, and n-C8H17) were prepared, and various characterization techniques have proven the hybrids’ successful synthesis. Meanwhile, the oxidative desulfurization (ODS) performance of both model and real diesel has been evaluated with H2O2 as the oxidant and acetonitrile (MeCN) as the extractant. Notably, these catalysts, initially insoluble in MeCN solution, fulfill a H2O2-responsive phase transfer into the MeCN phase to improve the ODS performance, facilitating the S compound extraction to the MeCN phase. After the ODS reaction, the hybrids precipitated from the MeCN phase, completed the heterogeneous separation, and regenerated simply by drying. Hybrid materials [Omim]4Mo8O26 (1-octyl-3-methylimidazolium polyoxomolybdate) with the longest alkyl chain displayed the highest desulfurization efficiency, achieving 99.8% dibenzothiophene (DBT) removal at the optimum reaction conditions of 50 °C, O/S = 5, Mo/S = 1:1, and V(MeCN/diesel) = 1:5. Even for real diesel, the hybrid exhibited more than 97% sulfur removal in diesel with sulfur contents of 3000 μg/g through the two-stage extraction-coupled oxidation desulfurization (ECODS) process. High catalytic recycling capability has been manifested by no obvious decrease in ODS activity after five cycles. This extraction-promoted H2O2-responsive phase transfer catalysis guarantees a promising industrial ODS system, not only substantially improves the catalytic desulfurization activity but also shows superior recycling performance with a simple catalyst regeneration method.

Investigation on removal of multi-component volatile organic compounds in a two-stage plasma catalytic oxidation system - Comparison of X (X=Cu, Fe, Ce and La) doped Mn2O3 catalysts

Mn2O3-X catalysts (X = Cu, Fe, Ce and La) were prepared based on γ-Al2O3 for the mixture degradation of muti-component volatile organic compounds (VOCs) composed of toluene, acetone, and ethyl acetate. The catalysts were characterized, and the density functional theory (DFT) simulation of ozone adsorption on Mn2O3-X were carried out to investigate the influence of adsorption energy on catalytic performance. The results showed that the removal efficiency (RE) of each VOC component was similarly improved by Mn2O3-X catalysts, and the greatest increase in VOCs' removal efficiency was obtained (7.8% for toluene, 86.2% for acetone, and 82.5% for ethyl acetate) at a special input energy (SIE) of 700 J L−1 with Mn2O3–La catalyst. Characterization results demonstrated that Mn2O3–La catalyst had the highest content of low valence Mn elements and the greatest Oads/Olatt ratio, as well as the lowest reduction temperature. Mn2O3–La catalyst also presented superior catalytic effect in improving carbon balance (CB) and CO2 selectivity (SCO2). The CB and SCO2 were increased by 47.7% and 12.61% respectively with Mn2O3–La at a SIE of 400 J L−1 compared with that when only γ-Al2O3 was applied. The DFT simulation results of ozone adsorption on Mn2O3-X catalysts indicated that the adsorption energy of catalyst crystal was related to the catalytic performance of the catalyst. The Mn2O3–La/γ-Al2O3 catalyst, which had the highest absolute value of adsorption energy, presented the best performance in improving VOCs’ RE.

A synergistic platform enables co-oxidation of halogenated organic pollutants without input of organic primary substrate

While co-oxidation is widely used to biodegrade halogenated organic pollutants (HOPs), a considerable amount of organic primary substrate is required. Adding organic primary substrates increases the operating cost and also leads to extra carbon dioxide release. In this study, we evaluated a two-stage Reduction and Oxidation Synergistic Platform (ROSP), which integrated catalytic reductive dehalogenation with biological co-oxidation for HOPs removal. The ROSP was a combination of an H2-based membrane catalytic-film reactor (H2−MCfR) and an O2-based membrane biofilm reactor (O2−MBfR). 4-chlorophenol (4-CP) was used as a model HOP to evaluate the performance of ROSP. In the MCfR stage, zero-valent palladium nanoparticles (Pd0NPs) catalyzed reductive hydrodechlorination that converted 4-CP to phenol, with a conversion yield over 92%. In the MBfR stage, the phenol was oxidized and used as a primary substrate that supported the co-oxidation of residual 4-CP. Genomic DNA sequencing revealed that phenol produced from 4-CP reduction enriched bacteria having genes for functional enzymes for phenol biodegradation in the biofilm community. In the ROSP, over 99% of 60 mg/L 4-CP was removed and mineralized during continuous operation: Effluent 4-CP and chemical oxygen demand concentrations were below 0.1 and 3 mg/L, respectively. H2 was the only added electron donor to the ROSP, which means no extra carbon dioxide was produced by primary-substrate oxidation.

Thermal Atomic Layer Etching of MoS2 Using MoF6 and H2O.

Two-dimensional (2D) layered materials offer unique properties that make them attractive for continued scaling in electronic and optoelectronic device applications. Successful integration of 2D materials into semiconductor manufacturing requires high-volume and high-precision processes for deposition and etching. Several promising large-scale deposition approaches have been reported for a range of 2D materials, but fewer studies have reported removal processes. Thermal atomic layer etching (ALE) is a scalable processing technique that offers precise control over isotropic material removal. In this work, we report a thermal ALE process for molybdenum disulfide (MoS2). We show that MoF6 can be used as a fluorination source, which, when combined with alternating exposures of H2O, etches both amorphous and crystalline MoS2 films deposited by atomic layer deposition. To characterize the ALE process and understand the etching reaction mechanism, in situ quartz crystal microbalance (QCM), Fourier transform infrared (FTIR), and quadrupole mass spectrometry (QMS) experiments were performed. From temperature-dependent in situ QCM experiments, the mass change per cycle was -5.7 ng/cm2 at 150 °C and reached -270.6 ng/cm2 at 300 °C, nearly 50× greater. The temperature dependence followed Arrhenius behavior with an activation energy of 13 ± 1 kcal/mol. At 200 °C, QCM revealed a mass gain following exposure to MoF6 and a net mass loss after exposure to H2O. FTIR revealed the consumption of Mo-O species and formation of Mo-F and MoF x =O species following exposures of MoF6 and the reverse behavior following H2O exposures. QMS measurements, combined with thermodynamic calculations, supported the removal of Mo and S through the formation of volatile MoF2O2 and H2S byproducts. The proposed etching mechanism involves a two-stage oxidation of Mo through the ALE half-reactions. Etch rates of 0.5 Å/cycle for amorphous films and 0.2 Å/cycle for annealed films were measured by ex situ ellipsometry, X-ray reflectivity, and transmission electron microscopy. Precisely etching amorphous films and subsequently annealing them yielded crystalline, few-layer MoS2 thin films. This thermal MoS2 ALE process provides a new mechanism for fluorination-based ALE and offers a low-temperature approach for integrating amorphous and crystalline 2D MoS2 films into high-volume device manufacturing with tight thermal budgets.

Two-stage chemical-biological oxidation process for low-grade refractory gold concentrate with high arsenic and sulfur

In order to cost-effectively exploit and utilize the low-grade refractory gold ore resource with high arsenic and sulfur and reuse the ferric iron resources remained in the bio-oxidation waste solution, a two-stage oxidation process combining secondary high-temperature oxidation of the bio-oxidation solution with subsequent bio-oxidation was proposed for treating such resource. Scanning electron microscopy and laser particle sizer were used to analyze the oxidized residue, and the results demonstrated that the material surface was destroyed and the particle specific surface area was increased accordingly. Moreover, chemical analysis revealed that the nitrogen element content in concentrate was also increased greatly after oxidation. As a result, microbial adsorption behavior and growth rate were significantly improved and accelerated in the bio-oxidation stage. Specifically, 16S rRNA gene analysis indicated that the activity and proportion of iron-oxidized microorganism Leptospirillum genus in community was improved obviously after chemical oxidation. Therefore, the bio-oxidation efficiency of the concentrate was significantly increased in this stage. Consequently, the extraction levels of As, Fe and S elements in this process were 97.9 ± 0.9 %, 71.5 ± 4.8 % and 64.3 ± 1.6 % respectively, which were significant increased by 30.8 ± 0.8 %, 40.2 ± 1.6 % and 35.6 ± 3.8 % compared to the values in one-stage bio-oxidation. In the meantime, the gold and silver extraction yields by cyanidation in this process were increased from 61.5 ± 1.0 % and 58.1 ± 1.2 % of one-stage bio-oxidation process to 92.2 ± 1.2 % and 89.8 ± 2.8 %, respectively.

Strengthening Gold Extraction from Carbonaceous Gold Ore Based on Decarburization by Two-Stage Fluidized Oxidation Roasting

Oxidation roasting is one of the most effective methods to remove carbonaceous matter from carbonaceous gold ore. However, the consolidation of calcine is a common problem caused by a large amount of heat release during the oxidation roasting of gold ore with high carbon and sulfur content. In this study, a two-stage fluidized oxidation roasting method was developed to strengthen gold extraction. Pre-roasting was performed in a low oxygen environment for the mild combustion of carbonaceous matter, and then the pre-roasted product was subjected to secondary roasting followed by leaching. The results show that reducing the carbon content in the ore by pre-roasting can effectively lower the peak temperature inside the material. After the second-stage roasting, many cracks and pores were formed in silicates and carbonates, thus increasing the distribution of exposed gold from 28.95% to 88.01%. Finally, the extraction of gold increased from 4.55% to 86.10%. Overall, this study provides references for an efficient strategy for gold recovery from carbonaceous gold ores.

Using an innovative umbrella-shape membrane module to improve MBR for PN-ANAMMOX process.

Membrane fouling has been a key factor limiting the applications of membrane bioreactor (MBR). In this study, a novel umbrella-shape membrane module was applied to construct two MBRs for two-stage partial nitrification-anaerobic ammonia oxidation (PN-ANAMMOX) process. After 55days operation, the ANAMMOX process was started and the PN process was well controlled. Then, the ANAMMOX and PN process were successfully coupled to run the PN-ANAMMOX process. On 103days, the best nitrogen removing effect was achieved with the maximum nitrogen loading rate (NLR) of 0.4kgN·(m3·d)-1 and the corresponding maximum total nitrogen removal rate (TNRR) of 75.23%.The umbrella-shape membrane module in both reactors only needed to be cleaned once during the operation for 105days, indicating that the membrane module had better resistance to membrane fouling. The functional bacteria were cultivated in suspension state; moreover, the cell densities of ammonia oxidizing bacteria (AOB) and ANAMMOX bacteria (AnAOB) reached 58.32 × 1012 copies/g sludge and 28.39 × 1012 copies/g sludge. Their abundances reached 73.25% and 57.80% of the total bacteria, respectively. MBR improved by umbrella-shape membrane module could realize the rapid start-up of ANAMMOX process, effective control of PN process, and stable operation of PN-ANAMMOX process. This study provided a novel approach to control membrane fouling by optimizing the membrane module shape and widened applications of MBRs in PN-ANAMMOX process.