Pyrolysis treatment of nonmetal fraction of waste printed circuit boards : Focusing on the fate of bromine

Advanced thermal treatment of electronic waste offers advantages of volume reduction and energy recovery. In this work, the pyrolysis behaviour of nonmetallic fractions of waste printed circuit boards was studied. The fate of a bromine and thermal decomposition pathway of nonmetallic fractions of waste printed circuit boards were further probed. The thermogravimetric analysis showed that the temperatures of maximum mass loss were located at 319°C and 361°C, with mass loss of 29.6% and 50.6%, respectively. The Fourier transform infrared Spectroscopy analysis revealed that the spectra at temperatures of 300°C–400°C were complicated with larger absorbance intensity. The nonmetallic fractions of waste printed circuit boards decomposed drastically and more evolved products were detected in the temperature range of 600°C–1000°C. The gas chromatography–mass spectrometry analysis indicated that various brominated derivates were generated in addition to small molecules, such as CH4, H2O and CO. The release intensity of CH4 and H2O increased with temperature increasing and reached maximum at 600°C–800°C and 400°C–600°C. More bromoethane (C2H5Br) was formed as compared with HBr and methyl bromide (CH3Br). The release intensity of bromopropane (C3H7Br) and bromoacetone (C3H5BrO) were comparable, although smaller than that of bromopropene (C3H5Br). More dibromophenol (C6H4Br2O) was released than that of bromophenol (C6H5BrO) in the thermal treatment. During the thermal process, part of the ether bonds first ruptured forming bisphenol A, propyl alcohol and tetrabromobisphenol A. Then, the tetrabromobisphenol A decomposed into C6H5BrO and HBr, which further reacted with small molecules forming brominated derivates. It implied debromination of raw nonmetallic fractions of waste printed circuit boards or pyrolysis products should be applied for its environmentally sound treating.© 2020 Sage. The article is protected by copyright and reuse is restricted to non-commercial and no derivative uses. Users may also download and save a local copy of an article accessed in an institutional repository for the user's personal reference.fi=vertaisarvioitu|en=peerReviewed

Distribution and isotopic composition of foraminifera at cold-seep Site 973-4 in the Dongsha area, northeastern South China Sea

A 1375-cm-long gravity core (Site 973-4) was acquired from the Dongsha cold seep area of the northeastern South China Sea (SCS). We measured its stable isotopes of planktonic foraminifera and investigated benthic foraminiferal assemblage compositions. Accelerator mass spectrometry C-14 analysis of planktonic foraminifera shows that some intervals are dated to Marine Isotope Stage (MIS) 3. Pulleniatina obliquiloculata has positive delta C-13 (0.25-1.25 parts per thousand) except for a negative carbon isotopic excursion (up to delta C-13 = 1.15 parts per thousand), but its light -carbon sources remain elusive. The benthic delta C-13 values (Uvigerina) of non -seep and cold-seep boreholes from the SCS have no systematic difference. Therefore, the benthic delta C-13 at Site 973-4 did not record the enhanced seepage activities (if occurred) during the last sea-level lowstand in the Dongsha area. In the pre-Holocene sediments, the foraminiferal assemblages have lower diversities, Shannon-Wiener indices, evenness indices, Simpson indices and higher calcareous proportions like typical cold-seep settings. The changes in oxygen levels (lower in the glacial period than those in the Holocene) indicated by foraminiferal indices reflect either bottom-water oxygen variations on the glacial-interglacial scale or enhanced seepage activities during the last glacial period

Kinetic modeling study on the combustion treatment of cathode from spent lithium-ion batteries

Thermal treatment offers an alternative method for the separation of aluminum foil and cathode materials during spent lithium-ion batteries recycling. In this work, the combustion kinetic of cathode was studied based on six model-free (isoconversional) methods, namely Flynn-Wall-Ozawa (FWO), Friedman, Kissinger-Akahira-Sunose, Starink, Tang, and Boswell methods. The possible decomposition mechanism was also probed using a master-plots method (Criado method). Thermogravimetric analysis showed that the whole thermal process could be divided into three stages with temperatures of 37-578 degrees C, 578-849 degrees C, and 849-1000 degrees C. The activation energy (E alpha) derived from these model-free methods displayed the same trend, gradually increasing with a conversion range of 0.002-0.013, and significantly elevating beyond this range. The coefficients from the FWO method were larger, and the resulted E alpha fell into the range of 10.992-40.298 kJ/mol with an average value of 20.228 kJ/mol. Comparing the theoretical master plots with an experimental curve, the thermal decomposition of cathode could be better described by the geometric contraction models

Experimental and Numerical Simulation of the Formation of Cold Seep Carbonates in Marine Sediments

Cold seep emissions of low temperature fluid from the marine sediment basins are mainly comprised of methane and other hydrocarbons. A series of biogeochemical processes related to methane lead to the formation of authigenic carbonate minerals. In this study, a self-built experimental device was used to study the formation process of carbonate minerals under cold seep conditions. The concentrations of pore water chemicals, HCO3− and Ca2+ at different heights of the reactor under flow conditions can be observed. According to the experimental results, the formation process of carbonate minerals under cold seep conditions was estimated, that 1 m carbonate growth needs 12,000 and 7000 years, respectively, under fast (5 mL·min−1) and slow emission (1 mL·min−1) conditions. Furthermore, TOUGHREACT was used to simulate the diagenesis process. A 1D unsteady react-transport model was developed, and the experimental data was used to constrain the simulation. The results of simulation show that the carbonates need 17,000 and 9700 years to grow 1 m under the condition of fast and slow flow scenarios, respectively. The results of this work will contribute to the study of foundation on the formation of authigenic minerals in cold seep areas, and for the physical properties of sedimentary media as well

Fatty-acids and their delta C-13 characteristics of seep carbonates from the northern continental slope of Gulf of Mexico

Here we reported the fatty-acids and their delta C-13 values in seep carbonates collected from Green Canyon lease block 185 (GC 185; Sample GC-F) at upper continental slope (water depth:similar to 540 m), and Alaminos Canyon lease block 645 (GC 645; Sample AC-E) at lower continental slope (water depth: similar to 2200 m) of the Gulf of Mexico. More than thirty kinds of fatty acids were detected in both samples. These fatty acids are maximized at C-16. There is a clear even-over-odd carbon number predominance in carbon number range. The fatty acids are mainly composed of n-fatty acids, iso-/anteiso-fatty acids and terminally branched odd-numbered fatty acids (iso/anteiso). The low delta C-13 values (-39.99aEuro degrees to.32.36aEuro degrees) of n-C-12:0, n-C-13:0, i-C-14:0 and n-C-14:0 suggest that they may relate to the chemosynthetic communities at seep sites. The unsaturated fatty acids n-C-18:2 and C-18:1 Delta(9) have the same delta C-13 values, they may originate from the Beggiatoa/Thioploca. Unlike other fatty acids, the terminally branched fatty acids (iso/anteiso) show lower delta C-13 values (as low as -63.95aEuro degrees) suggesting a possible relationship to sulfate reducing bacteria, which is common during anaerobic oxidation of methane at seep sites

Zone of metal-driven anaerobic oxidation of methane is an important sink for phosphorus in the Taixinan Basin, South China Sea

Phosphorus (P) is an important nutrient and has an important impact on global primary productivity. Presently, the dynamics of the P cycle in low sulfate, anoxic settings are largely unknown. In this study, the adsorption-desorption behavior of Fe-bound P, organic-P, loosely-bund P, detrital apatite P, and refractory P was described in the sulfate and methane transition zone (SMTZ) at site 973-4 in the cold-seep area of the Taixinan Basin, South China Sea. Results showed that the Fe-bound P and organic-P were influenced by sulfate-driven anaerobic oxidation of methane (SD-AOM) and metal-driven anaerobic oxidation of methane (MD-AOM), and subsequently, the Fe-bound P and organic-P were released as HPO42- into the pore water. Meanwhile, significant increases were detected in authigenic carbonate fluorapatite (P-C(FA)) and vivianite within the MD-AOM zone, which indicate that this zone is an important P-sink area. The MD-AOM plays an important role in the formation of P CFA and vivianite because MD-AOM provide the necessary HPO42- and Fe2+ for the formation of these minerals. Our findings have major implications for understanding the P cycle in low sulfate, anoxic settings and are important for understanding the influence of MD-AOM on the phosphate cycle

Source and implication of fatty acids in surface sediments from the Pearl River Mouth Basin, South China Sea

1528-1539Present study consists the fatty acid composition of five samples of Site 4B surface sediment from the Pearl River Mouth Basin in the South China Sea. Total fatty acid (TFA) content of the ranged from 5.14 μg/g to 8.99 μg/g (μg FA/g dry sediment), and the carbon number ranged from C12 to C32. The fatty acids detected in the five surface samples include the normal saturated fatty acids, branched-chain fatty acids, monounsaturated fatty acids, polyunsaturated fatty acids, and isoprenoid acids. Short-chain fatty acids in the normal saturated fatty acids were mainly from the marine microorganisms, whereas the long-chain fatty acids were from terrigenous higher plants. The higher concentration of short-chain fatty acids relative to the long-chain fatty acids indicates that the input from marine microorganisms in the surface sediment is far greater than that from terrigenous higher plants. The branched-chain fatty acids i/a15:0, i/a17:0, and 10me16:0 and the monounsaturated fatty acids 18:1ω9 and 16:1ω9 were mainly synthesized by sulfate-reducing bacteria, whereas 16:1ω7 was from the sulfur-oxidizing bacteria. Relative content of the different fatty acids indicate that the surface sediment is dominated by a reductive environment. In addition, eight isoprenoid acids including phytanic acid, 17β(H),21β(H)-32-bi-homohopanoic acid, and pristane acid were detected in the surface sediment, and they mainly originated from chlorophyll a and bacteria

methaneseepageintensitiestracedbysulfurisotopesofpyriteandgypsuminsedimentfromtheshenhuareasouthchinasea

The northern slope of the South China Sea is a gas-hydrate-bearing region related to a high deposition rate of organic-rich sediments co-occurring with intense methanogenesis in subseafloor environments. Anaerobic oxidation of methane (AOM) coupled with bacterial sulfate reduction results in the precipitation of solid phase minerals in seepage sediment, including pyrite and gypsum. Abundant aggregates of pyrites and gypsums are observed between the depth of 667 and 850 cm below the seafloor (cmbsf) in the entire core sediment of HS328 from the northern South China Sea. Most pyrites are tubes consisting of framboidal cores and outer crusts. Gypsum aggregates occur as rosettes and spheroids consisting of plates. Some of them grow over pyrite, indicating that gypsum precipitation postdates pyrite formation. The sulfur isotopic values (delta S-34) of pyrite vary greatly (from-46.6aEuro degrees to-12.3aEuro degrees V-CDT) and increase with depth. Thus, the pyrite in the shallow sediments resulted from organoclastic sulfate reduction (OSR) and is influenced by AOM with depth. The relative high abundance and delta S-34 values of pyrite in sediments at depths from 580 to 810 cmbsf indicate that this interval is the location of a paleo-sulfate methane transition zone (SMTZ). The sulfur isotopic composition of gypsum (from-25aEuro degrees to-20.7aEuro degrees) is much lower than that of the seawater sulfate, indicating the existence of a S-34-depletion source of sulfur species that most likely are products of the oxidation of pyrites formed in OSR. Pyrite oxidation is controlled by ambient electron acceptors such as MnO2, iron (III) and oxygen driven by the SMTZ location shift to great depths. The delta S-34 values of gypsum at greater depth are lower than those of the associated pyrite, revealing downward diffusion of S-34-depleted sulfate from the mixture of oxidation of pyrite derived by OSR and the seawater sulfate. These sulfates also lead to an increase of calcium ions from the dissolution of calcium carbonate mineral, which will be favor to the formation of gypsum. Overall, the mineralogy and sulfur isotopic composition of the pyrite and gypsum suggest variable redox conditions caused by reduced seepage intensities, and the pyrite and gypsum can be a recorder of the intensity evolution of methane seepage

Evolution of gas hydrates inventory and anaerobic oxidation of methane (AOM) after 40ka in the Taixinan Basin, South China Sea

Gas hydrates are the largest carbon sink on the earth and have an important impact on global climate and the environment. We studied the delta S-34,delta C-13, major trace elements and P -Fe dates at station 973-4 which acquired from the cold seep area of the Taixinan Basin. The results showed that during the Last Glacial Maximum (LGM), Younger Dryas (YD), and the Last Deglaciation, Gas hydrate inventory (GHI) was significantly reduced. And during the LGM, anaerobic oxidation of methane played an important role in preventing methane from leaking into seawater and the atmosphere. Because that there was no acidification of seawater or increase in Pun. Meanwhile, rapid rate of sediment accumulation caused by isobaric flow provided accumulated material for Anaerobic Oxidation of Methan (AOM) during the LGM. The rapid rate of sediment accumulation also created a good environment for the formation of Pm and vivianite below the sulfate methane transition zone (SMTZ). And according to changes of elements with depth, we conclude that the effect of methane anaerobic oxidation on redistribution of elemental P-Fe is divided into three processes: SMTZ rapid movement (material accumulation); SMTZ gradually stable; and SMTZ fixation process. In this paper, the effects of sedimentary evolution and hydrate evolution on AOM are studied in detail, which is of great significance for further understanding of anaerobic oxidation of methane

Geochemical Evidence of Metal-Driven Anaerobic Oxidation of Methane in the Shenhu Area, the South China Sea

Anaerobic oxidation of methane (AOM) is a common biochemical process in the ocean and it plays an important role in global climate change, elemental circulation, and atmospheric evolution over geological time. In this paper, we analyzed of delta S-34, Fe, Mn, Ca/Ti, and Sr/Ti ratios, and the date of carbon and sulfur from the site SH3 of Shenhu area. Result showed that (1) 0-6 mbsf (meter blow the sea floor) was mainly affected by OSR (anaerobic oxidation of organic matters) and 7-15 mbsf was a paleo-SMTZ (sulfate-methane transition zone) position. The modern SMTZ was mainly distributed at 19-25 mbsf. The barium sulfate precipitation above the modern SMTZ indicating that the current methane leakage was stable and lasted longer during geological history. (2) By studying the change of magnetic and the different carbonate minerals, results showed that there were two AOM stages. During the early stage, Fe2+ were mainly produced by sulfide abiotic reductive dissolution. During the later stage, Fe2+ were mainly produced by the metal-AOM. (3) Study of the mineral characteristics of the paleo-SMTZ and the modern SMTZ showed that the modern SMTZ carbonate minerals were mainly low-Mg calcite and aragonite, while the paleo-SMTZ carbon minerals were mainly high Mg minerals. The reason for this difference is that the modern SMTZ layer was only experienced the first stage of anaerobic oxidation of methane. In the paleo-SMTZ layer, it has experienced two stage of anaerobic oxidation of methane. During the last stage of metal-AOM, the low Mg carbonate minerals were converted into high Mg carbonate minerals. This research confirms the presence of metal-driven methane anaerobic oxidation at the bottom of sulfate-driven methane anaerobic oxidation and during the metal-driven methane anaerobic oxidation, methane and metal oxides or hydroxides would couple to convert the in situ metal oxides or hydroxides into metal ions, meanwhile the phosphorus adsorbed on the surface of the metal oxides is released into adjacent pore water, and convert to new P-bearing minerals under suitable conditions