Daidai Wu

Recycling of typical difficult-to-treat e-waste: Synthesize zeolites from waste cathode-ray-tube funnel glass

The disposal of waste cathode ray-tubes (CRTs) from old televisions and discarded computer monitors has become a major environmental concern worldwide. In this work, an open-loop recycling method was developed to synthesize zeolites using CRT funnel glass as the raw material. The effects of hydrothermal temperatures and pressure, n(SiO2/Al2O3) molar ratios and hydrothermal time on the resulting products were investigated. The results indicated that hydrothermal temperatures and pressure played critical roles in zeolite synthesis. Amorphous phases were detected at lower temperatures (80-100°C) and pressure (0.47-1.01bar) with n(SiO2/Al2O3)=2.0. At the temperature of 110°C (pressure 1.43bar), NaA formed with a mixture of NaP1 and Faujasite. With further increase in the temperature and pressure, the unstable NaA and Faujasite disappeared, and Hydroxysodalite developed. The influence of n(SiO2/Al2O3) ratios on resulting products revealed a single phase of NaA was formed at the ratio of 1.5 and a mixture of NaA and Faujasite at the ratio of 2.0. Prolonging hydrothermal time, however, could promote zeolite crystallization, and NaA gradually developed with an increase in the time from 2 to 6h at n(SiO2/Al2O3)=1.5. By comparison, crystallization phases were observed only when the time was longer than 8h at n(SiO2/Al2O3)=2.0.

Early Diagenesis Records and Pore Water Composition of Methane-Seep Sediments from the Southeast Hainan Basin, South China Sea

Several authigenic minerals were identified by XRD and SEM analyses in shallow sediments from the Southeast Hainan Basin, on the northern slope of South China Sea. These minerals include miscellaneous carbonates, sulphates, and framboidal pyrite, and this mineral assemblage indicates the existence of gas hydrates and a methane seep. The assemblage and fabric features of the minerals are similar to those identified in cold-seep sediments, which are thought to be related to microorganisms fostered by dissolved methane. Chemical composition of pore water shows that the concentrations of SO42-, Ca2

Methane seepage intensities traced by sulfur isotopes of pyrite and gypsum in sediment from the Shenhu area, South China Sea

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 (δ34S) of pyrite vary greatly (from–46.6‰ to–12.3‰ 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 δ34S 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–25‰ to–20.7‰) is much lower than that of the seawater sulfate, indicating the existence of a 34S-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 δ34S values of gypsum at greater depth are lower than those of the associated pyrite, revealing downward diffusion of 34S-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.

Alcohol compounds in Azolla imbricata and potential source implication for marine sediments

This study investigated the composition of long-chain alkyl diols, triols, sec-alcohols, hydroxyl acids, and other hydroxylated compounds in Azolla imbricata and compared the organic alcohol components of Azolla filiculoides, Azolla microphylla, and South China Sea (SCS) sediments in order to investigate the possible indication of Azolla being the biological source of diols and triols in SCS sediment. Large amounts of diols, monohydroxy acids, and sec-alcohols with internal hydroxy groups at ω20 were detected in the three types of Azolla. Among these, 1,ω20-diol and ω20-hydroxy acid exhibited strong even-odd predominance distribution, whereas ω20-sec-alcohol exhibited strong odd-even predominance distribution. In addition, small amounts of diols, triols, and dihydroxy acids with internal hydroxy groups at 9, 10 or ω9, ω10 were detected, among which the chain length of C29 was predominate. Compounds having similar structures as those in Azolla reflected a similar biosynthetic pathway: ω20-hydroxy acid exhibiting even-odd predominance distribution is decarboxylated to ω20-sec-alcohol exhibiting odd-even predominance distribution and converted to 1, ω20-diol with even-odd predominance distribution by acyl reduction; ω9, ω10-hydroxy acid is converted to 1,20,21(1, ω9, ω10)-triol by acyl reduction, and then converted to 9,10-diol by hydrogenation and dehydration. The alcohol components in A. imbricata were clearly not the biological source of 1,13/1,14/1,15-C28, 30, 32 diols and 1,3,4-C27-29 triols in the SCS sediment. Certain marine diatoms might be the source of 1,14-C28, 30 diol in inshore sediment, but the biological source of diols and triols in the SCS sediment requires further investigation.

GEOCHEMICAL SEDIMENTARY EVIDENCE FROM CORE 973-2 FOR METHANE ACTIVITY NEAR THE JIULONG METHANE REEF IN THE NORTHERN SOUTH CHINA SEA

The Jiulong Methane Reef, located on the northern slope of the South China Sea (SCS), is characterized by a number of features, such as bottom simulating reflections (BSRs) and authigenic carbonates, which are indicative of methane seeps that are currently occurring as well as those that occurred in the past. However, to date, the effect that these methane seeps have on the sedimentary environment is still not completely clear. To provide further insights into the biogeochemical processes involved in methane seeps, a 6.73-m piston core (973-2) was retrieved from this area in 2011 to perform an in-depth analysis. The chronology of the core has been established by AMS14C dating, and sedimentary events since the last glacial period have been recorded. The results show abnormally low abundance and diversity, as well as high infaunal percentages of benthic foraminiferal assemblages in the lower part of the core from 673 to 350 cmbsf (centimeters below the sea floor), indicating impacts from methane activities....