Seasonal variability in carbon:234thorium ratios of suspended and sinking particles in coastal Antarctic waters: Field data and modeling synthesis

238U-234Th disequilibrium is a powerful tool for investigating particle cycling and carbon export associated with the ocean's biological carbon pump. However, the interpretation of this method is complicated by multiple processes that can modify carbon:thorium ratios over small spatial scales. We investigated seasonal variability in the thorium and carbon cycles at a coastal site in the Western Antarctic Peninsula. Throughout the ice-free summer season, we quantified carbon and 234Th vertical flux, total water column 234Th, particulate 234Th, and the C:234Th ratios of sinking material and bulk suspended material. Simultaneous identification and separation of fecal pellets from sinking material showed that fecal pellets (primarily from krill) contributed 56% of carbon flux and that as a result of lower C:234Th ratios than suspended particles, these fecal pellets were primary drivers of variability in the C:234Th ratios of sinking material. Bulk suspended particles had highly variable C:234Th ratios and were consistently elevated in the euphotic zone relative to deeper waters. The fraction of 234Th adsorbed onto particles was positively correlated with chlorophyll and particulate organic carbon (POC) concentrations. The C:234Th ratios of suspended particles were positively correlated with POC, although during the spring diatom bloom C:234Th ratios were lower than would have been predicted based on POC concentrations alone. We hypothesize that diatom production of transparent exopolymers may have led to enhanced rates of thorium adsorption during the bloom, thus decreasing the C:234Th ratios. We used a Bayesian model selection approach to develop and parameterize mechanistic models to simulate thorium sorption dynamics. The best model incorporated one slowly-sinking POC pool and rapidly-sinking fecal pellets, with second-order sorption kinetics. The model accurately simulated temporal patterns in the C:234Th ratios of sinking and suspended particles and the fraction of 234Th adsorbed to particles. However, it slightly over-estimated C:234Th ratios during the spring (diatom-dominated) bloom and underestimated C:234Th ratios during the fall (mixed-assemblage) bloom. Optimized model parameters for thorium sorption and desorption were 0.0047 +/- 0.0002 m3 mmol C-1 d-1 and 0.017 +/- 0.008 d-1, respectively. Our results highlight the important role that specific taxa can play in modifying the C:234Th ratio of sinking and suspended particles and provide guidance for future studies that use 234Th measurements to investigate the functional relationships driving the efficiency of the biological pump.

Study of Sorption Kinetics of Doxycycline on pH Sensitive Hydrogel-based Graft Copolymers of Chitosan/Arabinogalactan/ Gummiarabic with Vinyl Monomers

Graft copolymers of natural polysaccharides chitosan (Chs), gummi-arabic (GA) and arabinogalactan (AG) were synthesized with N-vinylpyrrolidone (VPr) (4-vinylpyridine and N-vinylpyrrolidone used as comonomers for chitosan grafting), and then pH-sensitive hydrogels were designing by cross-linked them with N,N-methylene-bis-acrylamide. Effective sorption of doxycycline from aqueous solutions with water-swelling gels has been studied experimentally. The effect of gel dose, initial concentration of doxycycline, pH medium and solution ionic strength of the sorption rate and capacity of the antibiotic was systematically studied. The surface and volume absorption kinetics and isotherms of the process have also been investigated. It was found that the max sorption capacity for swellable gels varies between Chs-graft-VPr/4VPAG/graft-VPrGA/graft-VPr. It has been shown that the sorption mechanism is mainly dominated by physical sorption and to some extent hydrogen bonds and electrostatic interactions.

REMOVAL OF BERYLLIUM (Be2+) FROM WATER SAMPLES BY SORPTION PROCESS: A REVIEW

Beryllium (Be2+) is an important industrial metal because of its unusual material properties: it is lighter than aluminium and six times stronger than steel. Beryllium is a strategic metal due to its low density combined with its strength, low neutron absorption, high melting point and high modulus of elasticity. Beryllium is often alloyed with other metals such as copper and is an important component of materials used in the aerospace, automotive, energy, defense, medical, and electronics industries. However, beryllium and its compounds are very toxic, especially to the lungs, skin, and eyes. Beryllium compounds are known carcinogens based on sufficient evidence of carcinogenicity in humans from human studies. Toxic effects of beryllium include immunotoxic, allergic, mutagenic, and carcinogenic effects. Mammalian tissues do not excrete it, so the effects are cumulative and can lead to death at high concentrations. Therefore, removal of Be2+ is important. In this review, the removal of Be2+ from water samples by sorption processes using different sorbents was summarized. The effects of process parameters on the removal of Be2+ have been summarized. The work discussed showed that ion exchange resins, various modified biosorbents metal oxides can be used for the removal of Be2+. The results showed that the pH of the solution has an important effect on the removal rate. Sorption kinetics vary from 3 minutes to 48h. When the functional groups are on the surface of the sorbent, the sorption process is rapid. However, if the surface of the sorbent is covered with oxides such as magnetite, it takes longer to reach equilibrium. Published work shows that more than 99 % of Be2+ can be removed from solution.

Evaluation of Physical Characteristics and Sorption of Cement Mortars with Recycled Ceramic Aggregate

The subjects of this study were mortars with varying amounts of recycled ceramic aggregate (RCA). As part of the fine aggregate, the RCA volume share is 10%, 20%, 30%, 50% and 100%. First, fresh mixture parameters were evaluated, such as consistency and air content measurement by pressure method. Next, specimens were molded for compressive strength and flexural strength tests after 7, 28 and 56 days of curing. The thermo-humidity parameters of the composites, i.e., coefficient of capillary action and thermal conductivity coefficient were also investigated using nonstationary method. Sorption kinetics of the mortars at different moisture conditions at 20 °C were also evaluated. Sorption tests were carried out using two methods: TM and DVS. The sorption isotherms were plotted on the basis of equilibrium moisture content for the materials tested. The isotherms obtained by the two methods were evaluated. The results allowed us to draw conclusions on the physical and mechanical parameters of the composites with different amounts of RCA and to evaluate the ability to absorb moisture from the environment by these types of materials. A clear decrease in the compressive strength after 28 days of curing compared to the reference mortar was recorded after using 30% to 100% of RCA (approx. 26% to approx. 39%). Changes in flexural strength were significantly smaller, reaching no more than approx. 7.5%. It was shown that the amount of RCA translates into the ability to sorb moisture, which may affect the application of this type of composites. The amount of RCA translates also into the thermal conductivity coefficient, which decreased with increasing amount of RCA.

Analysis of the Influence of Coal Petrography on the Proper Application of the Unipore and Bidisperse Models of Methane Diffusion

The analysis of phenomena related to gas transport in hard coal is important with regard to the energetic use of coal bed methane (CBM), the reduction of greenhouse gas emissions to the atmosphere (CO2) and the prevention of natural hazards such as methane hazards and gas and rock outbursts. This article presents issues concerning the feasibility and scope of applying the unipore and bidisperse diffusion models to obtain knowledge concerning the kinetics of methane sorption and its diffusion in the carbon structure, depending on its petrography. Laboratory tests were carried out on coal samples which varied in terms of petrography. Quantitative point analyses were carried out, based on which content of groups of macerals was determined. The degree of coalification of coal samples was also determined based on measurements of vitrinite reflectivity R0 and the volatile matter content Vdaf. Sorption kinetics were also investigated, and attempts were made to adjust the unipore and bidisperse models to the real sorption kinetic courses. This allowed the identification of appropriate coefficients controlling the course of sorption in mathematical models. An attempt was also made to assess the possibility of applying a given model to properly describe the phenomenon of methane sorption on hard coal.

REDUCTION OF METAL CATIONS CONTENT FROM THE AQUEOUS SOLUTIONS BY SORBENTS

The article presents the results of research on reducing the concentration of heavy metals, such as copper and nickel, on natural zeolite in comparison with synthetic zeolite and chemically treated natural zeolite. The reduction of the content of specific types of heavy metals from aqueous solutions was investigated by the method of sorption kinetics. The results indicate the ability of natural zeolites to compete with synthetic zeolites.

Dependence on Film Thickness of Guest-Induced c Perpendicular Orientation in PPO Films

For poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) films exhibiting nanoporous-crystalline (NC) phases, c^ orientation (i.e., crystalline polymer chain axes being preferentially perpendicular to the film plane) is obtained by crystallization of amorphous films, as induced by sorption of suitable low-molecular-mass guest molecules. The occurrence of c^ orientation is relevant for applications of NC PPO films because it markedly increases film transparency as well as guest diffusivity. Surprisingly, we show that the known crystallization procedures lead to c^ oriented thick (50–300 μm) films and to unoriented thin (£20 μm) films. This absence of crystalline phase orientation for thin films is rationalized by fast guest sorption kinetics, which avoid co-crystallization in confined spaces and hence inhibit formation of flat-on lamellae. For thick films exhibiting c^ orientation, sigmoid kinetics of guest sorption and of thickening of PPO films are observed, with inflection points associated with guest-induced film plasticization. Corresponding crystallization kinetics are linear with time and show that co-crystal growth is poorly affected by film plasticization. An additional relevant result of this study is the linear relationship between WAXD crystallinity index and DSC melting enthalpy, which allows evaluation of melting enthalpy of the NC α form of PPO (DHmo = 42 ± 2 J/g).

Water Vapour Sorption and Moisture Transport in and Across Fibre Direction of Wood

Water vapour sorption experiments are frequently used to characterise the absorption and desorption of water in wood during transient conditions in relative humidity. When interpreting such experiments, it is still unclear to what extend the resulting time-dependent change of sample mass (i.e. sorption kinetics) is influenced by moisture transport, sorption and sorption related processes. To evaluate the impact of water vapour diffusion under such transient conditions, this study investigates the sorption kinetics of small wood samples with different lengths of transport pathways in and across fibre direction. For this purpose, water vapour sorption experiments on Norway spruce ( Picea abies ) samples were performed under identical climatic conditions at ambient air pressure and ambient standard temperature. The results showed that sample thickness has an impact on the sorption kinetics along the whole tested range of relative humidity. Differences between the sorption kinetics for samples in and across fibre direction were considerable at low relative humidity, indicating the relevance of water vapour diffusion through the lumen-pit-ray system. In contrast at high relative humidity, differences between the sorption kinetics for samples in and across fibre direction started to disappear while the impact of sample thickness was still considerable. Therefore, it seems as if an additional or modified process that depends on the number of sorption sites becomes relevant at an increased moisture content of wood. This process, as well as the increasing uptake and release of water across fibre direction, should be further investigated to gain a better understanding of the absorption and desorption of water in wood.