Evaluation of adsorption potential of bamboo biochar for metal-complex dye: equilibrium,kinetics and artificial neural network modeling

Metal-complex dyes are widely used in textile industry, but harmful to the environment and human health due to aromatic structure and heavy metal ions. The objective of this work was to evaluate the adsorption potential of bamboo biochar for the removal of metal-complex dye acid black 172 from solutions. Freundlich model was more suitable for the adsorption process of bamboo biochar than Langmuir isotherm, indicating multilayer adsorption of acid black 172 on a heterogeneous bamboo biochar surface. Adsorption kinetics analysis of pseudo-second-order and Weber–Morris models revealed that intraparticle transport was not the only rate-limiting step. The bamboo biochar exhibited a good adsorption performance even at high ionic strength. Analysis based on the artificial neural network indicated that the temperature with a relative importance of 29 % appeared to be the most influential parameter in the adsorption process for dye removal, followed by time, ionic strength, pH and dye concentration.     

Ca-H-Al exchanges and aluminium mobility in two Chinese acidic forest soils: a batch experiment

Exchange reactions between Ca²⁺, H⁺ and Al species and their effects on the aluminium mobility in two Chinese acidic forest soils were studied. The study was based on a batch experiment using extractant solutions with different base cation (calcium) concentrations and pH. The experimental data showed that increased Ca²⁺ concentrations increased the release of soil hydrogen—and aluminium ions, especially from the more acid soil. In agreement with a cation exchange process, the treatment with Ca²⁺ extracts gave significantly decreased soil aluminium saturation (AlS) and increased calcium saturation (CaS) on the ion exchanger. Geochemical calculation using AlCHEMI program showed that activities of Al³⁺ in the extracts were all strongly under-saturated with respect to any gibbsite mineral in the studied pH region (i.e. below 4.1). There were instead apparently two different mechanisms controlling the activities of Al³⁺ in extracts. At pH between about 4.1 and 3.7, the Al³⁺ activity did not change significantly with pH. This is especially the case in the more acid soil. Apparently there are no sizeable pools available to release Al in this pH region. At pH below 3.7 (induced by higher Ca²⁺concentration) the activity of Al³⁺ increased with H⁺ though not in a pattern that complies with a gibbsite solubility control. An increase of base cation deposition would therefore mainly enhance the release of hydrogen ions between pH 4.1 and 3.7 and aluminium ions below pH 3.7 from Chinese mature acidic soils. This will cause an increased acidity of soil water in the short term and a decrease in the soil acidity in the long term. More attention should be paid to this fact in Chinese acid rain studies and control options.     

The strain‐dependent spatial evolution of garnet in a high‐P ductile shear zone from the Western Gneiss Region (Norway): a synchrotron X‐ray microtomography study

Reaction and deformation microfabrics provide key information to understand the thermodynamic and kinetic controls of tectono‐metamorphic processes, however, they are usually analysed in two dimensions, omitting important information regarding the third spatial dimension. We applied synchrotron‐based X‐ray microtomography to document the evolution of a pristine olivine gabbro into a deformed omphacite–garnet eclogite in four dimensions, where the 4^th dimension is represented by the degree of strain. In the investigated samples, which cover a strain gradient into a shear zone from the Western Gneiss Region (Norway), we focused on the spatial transformation of garnet coronas into elongated garnet clusters with increasing strain. The microtomographic data allowed quantification of garnet volume, shape and spatial arrangement evolution with increasing strain. The microtomographic observations were combined with light microscope and backscatter electron images as well as electron microprobe (EMPA) and electron backscatter diffraction (EBSD) analysis to correlate mineral composition and orientation data with the X‐ray absorption signal of the same mineral grains. With increasing deformation, the garnet volume almost triples. In the low‐strain domain, garnet grains form a well interconnected large garnet aggregate that develops throughout the entire sample. We also observed that garnet coronas in the gabbros never completely encapsulate olivine grains. In the most highly deformed eclogites, the oblate shapes of garnet clusters reflect a deformational origin of the microfabrics. We interpret the aligned garnet aggregates to direct synkinematic fluid flow, and consequently influence the transport of dissolved chemical components. EBSD analyses reveal that garnet shows a near‐random crystal preferred orientation that testifies no evidence for crystal plasticity. There is, however evidence for minor fracturing, neo‐nucleation and overgrowth. Microprobe chemical analysis revealed that garnet compositions progressively equilibrate to eclogite facies, becoming more almandine‐rich. We interpret these observations as pointing to a mechanical disintegration of the garnet coronas during strain localization, and their rearrangement into individual garnet clusters through a combination of garnet coalescence and overgrowth while the rock was deforming.     

Removal of Cr(VI) and phenol coupled with the reduction of sulfate by sulfate-reducing bacteria sludge

Biological treatment of industrial wastewater containing heavy metal and organic pollutant has attracted extensive attention. In this study, Cr(VI) reduction coupled with phenol degradation was investigated by the sulfate-reducing bacteria (SRB) sludge with addition of zero-valent iron (ZVI). The results showed that the SRB wet sludge (SWS) had a good bioactivity in the reduction of Cr(VI) only when the initial concentration of Cr(VI) was below 60 mg L^?1. The addition of ZVI significantly enhanced the bioactivity and reusability of SWS, and the reduction percentage of Cr(VI) achieved 98% after SWS was successively used for seven cycles. SWS coupled with ZVI showed a high activity in phenol degradation, with more than 94% phenol being degraded in each cycle. However, in the simultaneous removal of Cr(VI) and phenol, phenol degradation was inhibited due to the toxicity of Cr(VI) to phenol degrading microbes in SWS. On the other hand, reduction of sulfate and Cr(VI) was not affected by the presence of phenol, with more than 95% of sulfate and Cr(VI) being removed at the end of the 5th cycle. This study enriches our understanding on the applications of the SRB sludge in the removal of organic and inorganic contaminants in wastewater.     

Dye adsorption on electrochemical exfoliated graphene oxide nanosheets: pH influence,kinetics and equilibrium in aqueous solution

Graphene oxide nanosheets were synthesized by electrochemical exfoliation. X-ray diffraction, scanning electron microscopy, atomic force microscopy, Raman spectrometry and Fourier transform infrared spectrometry were used to characterize crystal structure, particle size, thickness and function groups of the nanosheets. The nanosheets were examined for adsorption of methyl orange, an anionic dye, in aqueous solution at different pHs and temperatures. The maximum adsorption capacity of methyl orange on graphene oxide nanosheets obtained from the Langmuir isotherm was 138.69 mg/g at pH 2.0, which is larger than that of other carbonaceous adsorbents. The large adsorption affinity of graphene oxide nanosheets to methyl orange might be due to the presence of hydrogen bonding and π–π interaction between methyl orange and graphene oxide nanosheets. Adsorption kinetics followed a pseudo-second-order kinetic model, and the isotherm adsorption results were fitted with Langmuir isotherm model in a monolayer adsorption manner. The thermodynamic studies indicated that the adsorption reaction was a spontaneous physisorption process.     

An Eocene magmatic belt across central Tibet: mantle subduction triggered by the Indian collision?

Mountain domes rising to ≈ 6600 m along Tibet's Tanggula range herald the Eocene intrusion of calcalkaline granites into terranes accreted much earlier. Together with coeval, cogenetic volcanics, such intrusives, which have similar crystallization and cooling ages, may be part of an ESE-trending belt cutting central Tibet in half. This magmatic belt may have marked a former northern boundary of the plateau, testifying to S-directed subduction of the Asian mantle. Such subduction would have developed soon after India's collision but long before the rise of the plateau's present rims, along one of central Tibet's Mesozoic sutures.     

Impacts of surface runoff and sediment on nitrogen and phosphorus loss in red soil region of southern China

Surface runoff plays an important role in the process of nitrogen (N) and phosphorus (P) loss. It has two common evaluation indicators, runoff and sediment, which are greatly affected by the contributing factors. To study the impacts of surface runoff and sediment on N and P loss, 36 simulated rainfalls were applied on fields with different conditions (three rainfall intensities, three coverage ratios, and two slopes) at laboratory scale with two replicates. It was found that: (1) loss modulus of both the total nitrogen and total phosphorus decreased with runoff occurrence time; (2) runoff modulus had a closer relationship with undissolved N and P than dissolved N and P; (3) N loss was more affected by runoff than P loss; (4) both N and P loss modulus followed the consistent changes with the sediment content. At last, suggestions were provided to reduce the harm of N and P loss in red soil region of southern China in different areas with different conditions.     

Geology,geochemistry, and geochronology of the Miaowan ophiolite,Yangtze craton: Implications for South China's amalgamation history with the Rodinian supercontinent

We report the presence of a Grenvillian ophiolite on the northern margin of the Yangtze craton, drastically changing current ideas about South China's role in plate reconstructions of the Rodinia supercontinent. Strongly deformed amphibolites that locally show relict pillow lavas, isotropic and layered metagabbro, diabase dikes, serpentinized dunite and harzburgite with podiform chromite are dated at circa 1100–985 Ma (U–Pb zircon). The ophiolite is structurally dismembered and thrust over the Proterozoic shelf sequence that covers the north margin of the Yangtze craton, and overrode a flysch to conglomerate-wildflysch unit shed from the ophiolite and a magmatic arc terrane and deposited on the older Yangtze carbonate platform. The youngest clasts in the conglomerate are circa 861–813 Ma (U–Pb zircon), giving a maximum age for ophiolite emplacement. Fine-grained layered amphibolites exhibit slightly depleted-flat type REE curves with no obvious Eu anomalies, and are N-MORB type tholeiites. Metagabbro has typical cumulate textures, flat REE distributions and obvious positive Eu anomalies. The REE characteristics of serpentinized dunites show a U-shape of slight loss of middle REE, representing cumulates metasomatized by LREE slightly enriched mantle. All these features indicate that the metamafic–ultramafic rocks from the Proterozoic Miaowan Formation form a structurally dismembered ophiolite resting above an ophiolitic wildflysch, sitting on top of the Proterozoic shelf sequence on the Yangtze craton. The ophiolite is contemporaneous with an arc sequence preserved to the north on the edge of the Yangtze craton, suggesting that the entire ophiolitic forearc–arc was accreted to the Yangtze craton between 1000 and 850 Ma. Xenocrystic zircons in granite clasts in the basal wildflysch unit have ages consistent with Australian affinity, and detrital zircons in the arc sequence also show derivation from Australia, suggesting that the arc formed on the Australian segment of Rodinia before collision with the Yangtze craton. The discovery of the Proterozoic Miaowan ophiolite supplies important evidence for the existence of a Neoproterozoic oceanic basin on the north margin of the Yangtze craton, and demonstrates that the Yangtze craton first collided with Rodinia on its northern margin, with subsequent accretion of the Cathaysian block on the southern margin of the craton.