Fabrication of Ag3PO4/TiO2@molecular sieve (MS) ternary composites with remarkably enhanced visible light-responded photocatalytic activity and mechanism insight

In this study, Ag3PO4/TiO2@molecular sieve (MS) ternary composites were fabricated via in-situ deposition and hydrothermal growth method for photocatalytic degradation of formaldehyde and sodium isobutyl xanthate (SIBX) under visible light irradiation. XRD, PL, UV-vis, UPS, SEM-EDS and XPS techniques were adopted to characterize the composite. The results show that the MS material was indexed as zeolite P and Ag3PO4/TiO2 hybrid structure could improve the absorption of visible light and greatly inhibit the recombination of photogenerated charge carriers by introducing 3 times TiO2. After evaluating the photocatalytic activity and kinetics model, it is found that photocatalytic activity is consistent with the apparent first-order kinetic model. The Ag3PO4/TiO2-3@MS ternary composite under visible light irradiation appears the highest removal rate with 97.9% of formaldehyde and 96.7% of SIBX, respectively. Furthermore, the reusability of the photocatalyst was investigated by successive reuse. After five reuses, the removal rates reached 97.3% and 94.6% within 105 min for formaldehyde and SIBX, respectively. At last, the proposed mechanism of the photocatalytic reaction and the degradation mutes of formaldehyde and SIBX were systematically discussed

Removal of chemical oxygen demand (COD) and heavy metals by catalytic ozonation-microbial fuel cell and Acidithiobacillus ferrooxidans leaching in flotation wastewater (FW)

A catalytic ozonation-microbial fuel cell and Acidithiobacillus ferrooxidans leaching process was used in treating flotation wastewater to remove chemical oxygen demand (COD) and heavy metals in this study. The results indicated that when adding 1 g/L of manganese/modified activated carbon catalyst and 1.5 g/min ozone flow, the COD could be degraded from 2,043.67 mg/L to 711.4 mg/L. After that, the COD could continue decreasing down to 72.56 mg/L through an air-cathode single chamber microbial fuel cell (SCMFCs), coated with 0.4 mg/cm(2) platinum catalyst, after 15 days. Meanwhile, the maximum voltages and the ultimate power density of the SCMFCs reached 378.96 mV and 7,608.35 mW/m(2), respectively. For filter residue, when 1.2 g/L Fe3+, 10% (m/v) filter residue, and 10% Acidithiobacillus ferrooxidans were added, the copper leaching rate could reach 92.69% after 7 days if the pH values were adjusted to 1.9. Furthermore, the other heavy metals were also decreased to a level lower than the pollution control standard (Chinese standard GB3838-2002). The leaching parameters in terms of pH, redox potential, and cyclic voltammetry showed that the addition of an appropriate concentration of Fe3+ to the leaching systems was beneficial to copper dissolution

Efficient separation of vanadium, titanium, and iron from vanadium-bearing titanomagnetite by pressurized pyrolysis of ammonium chloride-acid leaching-solvent extraction process

A novel process featuring pressurized pyrolysis of ammonium chloride-acid leaching-solvent extraction was carried out to separate vanadium, titanium, and iron from vanadium-bearing titanomagnetite (VBT). Then vanadium and iron existed in the form of ammonium polyvanadate ((NH4)(2)V6O16) and ammonium jarosite (NH4Fe3(SO4)(2)(OH)(6)) after precipitation from the water phase and the raffinate, while titanium remained in the acid leaching tailings. When pyrolysis temperature of 320 degrees C, pyrolysis time of 2 h, and the mass ratio of NH4Cl to slag of 1.5 followed by leaching in 61.7 g/L HCl solution, the extraction rates of vanadium, titanium, and iron reached 95.1%, 1.2%, and 92.5%, respectively. The analysis through XRD and SEM-EDS proves that the main phases of the roasted sample were attributed to FeCl2 and FeCl3, indicating pressurized pyrolysis of ammonium chloride could promote the capture of more vanadium by generated ferric/ferrous chloride in situ. The concentration of vanadium and iron was enriched to 17.8 g/L and 10.6 g/L through the N-235 solvent extraction-Na2SO4 washing-Na2CO3 stripping processes, which could produce V2O5 with a purity of 99.93% by roasting (NH4)(2)V6O16 and ammonium jarosite with excellent crystal faces. Additionally, the TiO2 concentration reached 184.2 g/L using 80 wt% sulfuric acid for the acid leaching residue, which could be used as the raw material to production of TiO2 pigment. Moreover, the mechanism of the reaction of NH4Cl with valuable metal in the closed environment has been systematically studied

<p>New understanding of extraction and separation of vanadium(IV), iron and titanium using iron powder induction-leaching and P204-P507 synergistic extraction</p>

Herein, we investigated the induced-leaching behavior of hematite by iron powder after ammonium sulfate roasting vanadium titanomagnetite concentrate and develop a P204-P507 synergistic extraction method for separation of vanadium(IV), iron and titanium. The results showed that the effective selective separation of vanadium, iron and titanium could be obtained in which 97.39 % V and 88.62% Fe were dissolved into the solution and over 91.76% Ti was remained in leaching residue after leaching at 0.5 M H2SO4, 110 ?& nbsp;for 1 h, then added 10% iron powder and continue to leaching for 2 h. Tafel polarization curve and impedance spectroscopy both proved that iron powder could reduce the chemical reaction resistance and accelerate the ion transfer rate in the leachate. Based on the speciation analysis by Medusa software, the speciation distribution of vanadium, iron and titanium in the sulfuric acid system eventually exists in the form of VO(2+ )and Fe(II) ions, while most of titanium precipitates to the leaching residue in the form of TiO2. The five stages countercurrent extraction test was carried out to confirm the prediction of McCabe-Thiele diagram, and the extraction efficiency of vanadium reached 98.13% under the condition of mixed extractant concentration of 15%, v(P204):v(P507) of 3, pH of 1.8 and phase ratio (O/A) of 2.0. The slope method proved that P204-P507 molecule could release two H+ ions for every vanadium ion extracted, which could be attributed to the cation exchange reaction. Finally, a high-titanium slag with a TiO2 content of 85.32% was obtained by alkaline leaching method

Recovery of Gold and Iron from Cyanide Tailings with a Combined Direct Reduction Roasting and Leaching Process

Cyanide tailings are the hazardous waste discharged after gold cyanidation leaching. The recovery of gold and iron from cyanide tailings was investigated with a combined direct reduction roasting and leaching process. The effects of reduction temperature, coal dosage and CaO dosage on gold enrichment into Au-Fe alloy (FexAu1&minus;x) were studied in direct reduction roasting. Gold containing iron powders, i.e., Au-Fe alloy, had the gold grade of 8.23 g/t with a recovery of 97.46%. After separating gold and iron in iron powders with sulfuric acid leaching, ferrous sulfate in the leachate was crystallized to prepare FeSO4&middot;7H2O with a yield of 222.42% to cyanide tailings. Gold enriched in acid-leaching residue with gold grade of 216.58 g/t was extracted into pregnant solution. The total gold recovery of the whole process reached as high as 94.23%. The tailings generated in the magnetic separation of roasted products, with a yield of 51.33% to cyanide tailings, had no toxic cyanide any more. The gold enrichment behaviors indicated that higher reduction temperature and larger dosage of coal and CaO could promote the allocation of more gold in iron phase rather than in slag phase. The mechanism for enriching gold from cyanide tailings into iron phase was proposed. This work provided a novel route to simultaneously recover gold and iron from cyanide tailings

Adsorption-photocatalytic degradation and kinetic of sodium isobutyl xanthate using the nitrogen and cerium co-doping TiO2-coated activated carbon

At present, the excessive use of sodium isobutyl xanthate (SIBX) in mineral processing has caused serious environmental problems, drawing ever-growing concern in China. A nitrogen and cerium co-doped TiO2-coated activated carbon (Ce/N-TiO2@AC) heterojunction were prepared through the sol-gel method to address these problems. The photocatalyst was characterized using XRD, TEM, SEM-EDS, PL, UV-Vis, XPS and a series of photoelectrochemical techniques. The results show that Ce/N-TiO2@AC photocatalyst possess a stable anatase phase, narrow band gap energy (2.24-2.61 eV) and high charge transport process. The photocatalytic activity of the photocatalyst was evaluated based on photodegradation kinetic studies of SIBX in aqueous solution, and it is found that it followed the Langmuir-Hinshelwood model very well. The Ce/N-TiO2@AC photocatalyst with 2% Ce appears to be the highest removal rate with 96.3% of SIBX and an apparent rate constant of 78.4 x 10(-3) min(-1). The reusability experiment for its potential applications was studied, and the removal rate of SIBX reached 95.8% after the fifth cycle. Besides, the proposed mechanism and degradation routes of SIBX were systematically studied, and certificate the concentration of SO42- ions in the final water sample was 95.9 mg/L, which was basically consistent with the theoretical value. (C) 2020 Elsevier Ltd. All rights reserved.</p

Red gypsum utilization and acidic wastewater treatment based on metal self-enrichment process

The massive accumulation of red gypsum has brought great harm to human and environment. In order to achieve low-cost and high-benefit resource utilization of red gypsum, a method of metal self-enrichment during the cycle and transformation of red gypsum was proposed. The carbon dioxide and ammonia water react with red gypsum to manufacture ammonium sulfate and solid phase products. And solid phase products neutralize pickling wastewater to produce metal-enriched red gypsum for the next cycle. After the cycle, solid phase product with one circulation (containing 39.45% Fe and 7.37% Ca) and two circulation (containing 45.79% Fe, 4.75% Ca) could be obtained, which can be used as the proportioning of metallurgical sinter. The self-enrichment process not only realizes the comprehensive utilization of red gypsum, but also solves the treatment of acidic wastewater. (C) 2019 Elsevier B.V. All rights reserved

Effect of pretreatment on the extraction of valuable metal from vanadium-bearing titanomagnetite by ammonium sulfate roasting

The paper presents the effect of pretreatment on the ammonium sulfate roasting behavior of vanadium-bearing titanomagnetite. The effects of the several parameters included pretreatment temperature, time and atmosphere upon the extraction efficiency of V, Ti and Fe were investigated. Under the conditions of a pretreatment temperature of 900 degrees C, a time of 2h and an air flow of 4 L/min, the extraction efficiency of V, Ti and Fe reached 92.56%, 11.25% and 78.72%, respectively. The study of the valence state changes of V and Fe before and after pretreatment found that pretreatment was beneficial to increase the content of acid soluble V(IV) and V(V), and enrich Ti species. XRD, SEM-EDS and FTIR were deeply clarified the influence of pretreatment on the evolution characteristics of the mineral phase. Additionally, the difficulty of pyrolysis between the intermediate Ti species and ammonium sulfate was analyzed by thermodynamic simulation

Recovery of Vanadium, Titanium, and Iron from Vanadium Titanomagnetite Concentrate Through Ammonium Sulfate Cascade Roasting with Potassium Pyrosulfate

In this study, an efficient utilization of vanadium titanomagnetite concentrate was systemically investigated through potassium pyrosulfate (K2S2O7) synergized with ammonium sulfate ((NH4)(2)SO4) cascade roasting to separate and recover vanadium, iron, and titanium. The result shows that 95.87% of vanadium and 80.13% of iron could be extracted, while that of titanium was only 9.68% under the condition of first-order temperature and time 240 degrees C and 3 h, second-order temperature and time 410 degrees C and 2 h, and the mass ratio of K2S2O7, (NH4)(2)SO4 and PVBT 0.1:4:1. Phase transformation and thermodynamic analysis reveals that the valuable metals could be converted into corresponding sulfates in situ. XRD and SEM-EDS show that the addition of K2S2O7 strongly promoted the formation of liquid phase and soluble potassium vanadate. A high-titanium slag with 85.32% titanium was obtained by the iron powder induction leaching and alkali leaching. Additionally, the additive (NH4)(2)SO4 could be recycled, achieving zero emission of waste gas. [GRAPHICS]