Extraction of Metallic Lead from Cathode Ray Tube (CRT) Funnel Glass by Thermal Reduction with Metallic Iron

A novel and effective process of thermal reduction treatment with the addition of metallic iron (Fe(0)) to recover lead from cathode ray tube (CRT) funnel glass is introduced. The key technological breakthrough of this process is the use of a relatively lower temperature and an inexpensive reducing agent to extract the metallic lead. The influences of temperature, the reducing agent content, and the holding time for lead reduction were examined to determine the optimal extraction efficiency. The lead extraction efficiency first increased and then decreased with increasing temperature. The maximum lead extraction efficiency occurred at 700 °C. The growth of crystalline lead first increased significantly with an increase in the Fe content, reaching maximum growth at an Fe addition of 50 wt %. The most effective treatment time was determined to be 30 min, as the vitrification of lead back to the glass matrix occurred under longer treatment times. The experimentally derived results indicate that a 58 wt % lead extraction can be achieved with the optimized operational parameters (50 wt % Fe addition, heating at 700 °C for 30 min) in a single extraction operation

Mineralization Behavior of Fluorine in Perfluorooctanesulfonate (PFOS) during Thermal Treatment of Lime-Conditioned Sludge

The fate and transport of the fluorine in perfluorooctanesulfonate (PFOS) during the thermal treatment of lime-conditioned sludge were observed using both qualitative and quantitative X-ray diffraction techniques. Two main fluorine mineralization mechanisms leading to the substantial formation of CaF₂ and Ca₅(PO₄)₃F phases were observed. They had a close relationship with the thermal treatment condition and the PFOS content of the sludge. At low temperatures (300–600 °C), CaF₂ dominated in the product and increases in treatment time and temperature generally enhanced the fluorine transformation. However, at higher temperatures (700–900 °C), increases in treatment time and temperature had a negative effect on the overall efficiency of the fluorine crystallization. The results suggest that in the high temperature environment there were greater losses of gaseous products such as HF and SiF₄ in the transformation of CaF₂ to Ca₅(PO₄)₃F, the hydrolysis of CaF₂, and the reaction with SiO₂. The quantitative analysis also showed that when treating sludge with low PFOS content at high temperatures, the formation of Ca₅(PO₄)₃F may be the primary mechanism for the mineralization of the fluorine in PFOS. The overall results clearly indicate the variations in the fate and transport of fluorine in PFOS when the sludge is subject to different PFOS contents and treatment types, such as heat drying or incineration

Cu₂O-promoted degradation of sulfamethoxazole by <i>α</i>-Fe₂O₃-catalyzed peroxymonosulfate under circumneutral conditions: synergistic effect, Cu/Fe ratios, and mechanisms

<p>To promote the application of iron oxides in sulfate radical-based advanced oxidation processes, a convenient approach using Cu₂O as a catalyst additive was proposed. Composite catalysts based on <i>α</i>-Fe₂O₃ (CTX%Cu₂O, <i>X</i> = 1, 2.5, 5, and 10) were prepared for peroxymonosulfate (PMS) activation, and sulfamethoxazole was used as a model pollutant to probe the catalytic reactivity. The results show that a synergistic catalytic effect exists between Cu₂O and <i>α</i>-Fe₂O₃, which was explained by the promoted reduction of Fe(III) by Cu(I). Iron K-edge X-ray absorption spectroscopy investigations indicated that the promoted reduction probably occurred with PMS acting as a ligand that bridges the redox centers of Cu(I) and Fe(III). The weight ratio between Cu₂O and <i>α</i>-Fe₂O₃ influenced the degradation of sulfamethoxazole, and the optimal ratio depended on the dosage of PMS and catalysts. With 40 mg L^–1 PMS and 0.6 g L^–1 catalyst, a pseudo-first-order constant of ∼0.019 min^–1 was achieved for CT2.5%Cu₂O, whereas only 0.004 min^–1 was realized for <i>α</i>-Fe₂O₃. Nearly complete degradation of the sulfamethoxazole was achieved within 180 min under the conditions of 40 mg L^–1 PMS, 0.4 g L^–1 CT2.5%Cu₂O, and pH 6.8. In contrast, less than 20% degradation was realized with <i>α</i>-Fe₂O₃ under similar conditions. The CT2.5%Cu₂O catalyst had the best stoichiometric efficiency of PMS (0.317), which was 4.5 and 5.8 times higher than those of Cu₂O (0.070) and <i>α</i>-Fe₂O₃ (0.054), respectively. On the basis of the products identified, the cleavage of the S–N bond was proposed as a major pathway for the degradation of sulfamethoxazole.</p

Iron Atom Exchange between Hematite and Aqueous Fe(II)

Aqueous Fe­(II) has been shown to exchange with structural Fe­(III) in goethite without any significant phase transformation. It remains unclear, however, whether aqueous Fe­(II) undergoes similar exchange reactions with structural Fe­(III) in hematite, a ubiquitous iron oxide mineral. Here, we use an enriched ⁵⁷Fe tracer to show that aqueous Fe­(II) exchanges with structural Fe­(III) in hematite at room temperature, and that the amount of exchange is influenced by particle size, pH, and Fe­(II) concentration. Reaction of 80 nm-hematite (27 m² g^–1) with aqueous Fe­(II) at pH 7.0 for 30 days results in ∼5% of its structural Fe­(III) atoms exchanging with Fe­(II) in solution, which equates to about one surface iron layer. Smaller, 50 nm-hematite particles (54 m² g^–1) undergo about 25% exchange (∼3× surface iron) with aqueous Fe­(II), demonstrating that structural Fe­(III) in hematite is accessible to the fluid in the presence of Fe­(II). The extent of exchange in hematite increases with pH up to 7.5 and then begins to decrease as the pH progresses to 8.0, likely due to surface site saturation by sorbed Fe­(II). Similarly, when we vary the initial amount of added Fe­(II), we observe decreasing amounts of exchange when aqueous Fe­(II) is increased beyond surface saturation. This work shows that Fe­(II) can catalyze iron atom exchange between bulk hematite and aqueous Fe­(II), despite hematite being the most thermodynamically stable iron oxide

Combined Quantitative X‑ray Diffraction, Scanning Electron Microscopy, and Transmission Electron Microscopy Investigations of Crystal Evolution in CaO–Al₂O₃–SiO₂–TiO₂–ZrO₂–Nd₂O₃–Na₂O System

Glass-ceramics, with a specific crystalline phase assembly, can combine the advantages of glass and ceramic and avoid their disadvantages. In this study, both cubic-zirconia and zirconolite-based glass-ceramics were obtained by the crystallization of SiO₂–CaO–Al₂O₃–TiO₂–ZrO₂–Nd₂O₃–Na₂O glass. Results show that all samples underwent a phase transformation from cubic-zirconia to zirconolite when crystallized at 900, 950, and 1000 °C. The size of the cubic-zirconia crystal could be controlled by temperature and dwelling time. Both cubic-zirconia and zirconolite crystals/particles show dendrite shapes, but with different dendrite branching. The dendrite cubic-zirconia showed highly oriented growth. Scanning electron microscopy images show that the branches of the cubic-zirconia crystal had a snowflake-like appearance, while those in zirconolite were composed of many individual crystals. Rietveld quantitative analysis revealed that the maximum amount of zirconolite was ∼19 wt %. A two-stage crystallization method was used to obtain different microstructures of zirconolite-based glass-ceramic. The amount of zirconolite remained approximately 19 wt %, but the individual crystals were smaller and more homogeneously dispersed in the dendrite structure than those obtained from one-stage crystallization. This process-control feature can result in different sizes and morphologies of cubic-zirconia and zirconolite crystals to facilitate the design of glass-ceramic waste forms for nuclear wastes

Anaerobic Transformation of DDT Related to Iron(III) Reduction and Microbial Community Structure in Paddy Soils

We studied the mechanisms of microbial transformation in functional bacteria on 1,1,1-trichloro-2,2-bis­(<i>p</i>-chlorophenyl)­ethane (DDT) in two different field soils, Haiyan (HY) and Chenghai (CH). The results showed that microbial activities had a steady dechlorination effect on DDT and its metabolites (DDx). Adding lactate or glucose as carbon sources increased the amount of <i>Desulfuromonas</i>, <i>Sedimentibacter</i>, and <i>Clostridium</i> bacteria, which led to an increase in adsorbed Fe­(II) and resulted in increased DDT transformation rates. The electron shuttle of anthraquinone-2,6-disulfonic disodium salt resulted in an increase in the negative potential of soil by mediating the electron transfer from the bacteria to the DDT. Moreover, the DDT-degrading bacteria in the CH soil were more abundant than those in the HY soil, which led to higher DDT transformation rates in the CH soil. The most stable compound of DDx was 1,1-dichloro-2,2-bis­(<i>p</i>-chloro-phenyl)­ethane, which also was the major dechlorination metabolite of DDT, and 1-chloro-2,2-bis-(<i>p</i>-chlorophenyl)­ethane and 4,4′-dichlorobenzo-phenone were found to be the terminal metabolites in the anaerobic soils

Biostimulation of Indigenous Microbial Communities for Anaerobic Transformation of Pentachlorophenol in Paddy Soils of Southern China

This study explored biostimulation mechanisms with an electron donor and a shuttle for accelerating pentachlorophenol (PCP) transformation in iron-rich soils. The results indicated that indigenous microbial communities are important for PCP transformation in soils. Biostimulation of indigenous microbial communities by the addition of lactate and anthraquinone-2,6-disulfonate (AQDS) led to the enhanced rates of PCP dechlorination by the dechlorinating- and iron-reducing bacteria in soils. The electrochemical studies using cyclic voltammograms and microbial current measurements confirmed the high reduction potential and the large amount of electrons generated under biostimulation conditions, which were responsible for the higher rates of PCP transformation. After biostimulation treatments by the additions of lactate and/or AQDS during PCP dechlorination processes, microbial community analysis by the terminal restriction fragment length polymorphism (T-RFLP) method showed the abundance terminal restricted fragments (T-RFs), an indicator of bacterial abundance, which represents the dechlorinating- and iron-reducing bacteria, suggesting their critical roles in PCP dechlorination in soils