Trace Metal Dynamics in Shallow Hydrothermal Plumes at the Kermadec Arc

Hydrothermal vents are a source of many trace metals to the oceans. Compared to mid-ocean ridges, hydrothermal vent systems at arcs occur in shallower water depth and are much more diverse in fluid composition, resulting in highly variable water column trace metal concentrations. However, only few studies have focused on trace metal dynamics in hydrothermal plumes at volcanic arcs. During R/V Sonne cruise SO253 in 2016/2017, hydrothermal plumes from two hydrothermally active submarine volcanoes along the Kermadec arc in the Southwest Pacific Ocean were sampled: (1) Macauley, a magmatic dominated vent site located in water depths between 300 and 680 m, and (2) Brothers, located between 1,200 and 1,600 m water depth, where hydrothermalism influenced by water rock interactions and magmatically influenced vent sites occur near each other. Surface currents estimated from satellite-altimeter derived currents and direct measurements at the sites using lowered acoustic Doppler current profilers indicate the oceanic regime is dominated by mesoscale eddies. At both volcanoes, results indicated strong plumes of dissolved trace metals, notably Mn, Fe, Co, Ni, Cu, Zn, Cd, La, and Pb, some of which are essential micronutrients. Dissolved metal concentrations commonly decreased with distance from the vents, as to be expected, however, certain element/Fe ratios increased, suggesting a higher solubility of these elements and/or their stronger stabilization (e.g., for Zn compared to Fe). Our data indicate that at the magmatically influenced Macauley and Brothers cone sites, the transport of trace metals is strongly controlled by sulfide nanoparticles, while at the Brothers NW caldera wall site iron oxyhydroxides seem to dominate the trace metal transport over sulfides. Solution stabilization of trace metals by organic complexation appears to compete with particle adsorption processes. As well as extending the generally sparse data set for hydrothermal plumes at volcanic arc systems, our study presents the first data on several dissolved trace metals in the Macauley system, and extends the existing plume dataset of Brothers volcano. Our data further indicate that chemical signatures and processes at arc volcanoes are highly diverse, even on small scales.

Microfluidic Generation of particle-stabilized water-in-water emulsions

Herein, we present a microfluidic platform that generates particle-stabilized water-in-water emulsions. The water-in-water system that we use is based on an aqueous two-phase system of polyethylene glycol (PEG) and dextran (DEX). DEX droplets are formed passively, in the continuous phase of PEG and carboxylated particle suspension, at a flow focusing junction inside a microfluidic device. As DEX droplets travel downstream inside the microchannel, carboxylated particles that are in the continuous phase partition to the interface of the DEX droplets, due to their affinity to the interface of PEG and DEX. As the DEX droplets become covered with carboxylated particles, they become stabilized against coalescence. We study the coverage and stability of the emulsions, while tuning the concentration and the size of the carboxylated particles, downstream inside the reservoir of the microfluidic device. These particle-stabilized water-in-water emulsions showcase good particle adsorption under shear, while being flowed through narrow microchannels. The intrinsic biocompatibility advantages of particle-stabilized water-in-water emulsions make them a good alternative to traditional particle-stabilized water-in-oil emulsions. To illustrate a biotechnological application of this platform, we show a proof-of-principle of cell encapsulation using this system, which with further development, may be used for immunoisolation of cells for transplantation purposes.

FLUOROQUINOLONES ANTIBIOTICS ADSORPTION ONTO POLYMER COATED MAGNETIC NANOPARTICULAR ACTIVATED CARBON

The present study investigated the adsorption of molecular fluoroquinolone (FLQ) from aqueous solution onto active carbon (AC), magnetic activated carbon (MagAC), styrene-butadiene styrene magnetic activated carbon (SBS/MagAC) and poly charbon magnetic activated carbon (PC/MagAC) as adsorbent materials. The process optimization was carried by investigating the effects of pH, temperature, solid-liquid ratio, adsorbent type and initial concentration of FLQ. The data showed that adsorption reached equilibrium in as little as one hour. The adsorption cacapcity was comparatively less at low pH values than at approximately pH 5.0. The results also showed that the polymer coated magnetic materials did not perform very well at high pH values. However, all the materials performed well at room temperature when the situation was examined in terms of kinetics. It was also observed that AC, SBS/MagAC and PC/MagAC are more effective than MagAC to remove FLQ from aqueous medium. The kinetic data support pseudo-second-order model (r2 ⩾ 0.95) but showed very poor fit for pseudo-first-order model (r2 ≤ 0.90). Intra-particle model also showed that there were two separate stages in sorption process, namely, external diffusion and the diffusion of inter-particle. Adsorption isotherms for all adsorbends were fitted to Langmuire models more effectively than Freundlich models (r2 ⩾ 0.98). Thermodynamics parameters such as; free energy (ΔG0), enthalpy (ΔH0) and entropy (ΔS0) were also calculated. In conclusion, our results revealed that FLQ can be removed more easily from the aqueous medium by using magnetic and polymeric material.

Interactions of ferro-nanoparticles (hematite and magnetite) with reservoir sandstone: implications for surface adsorption and interfacial tension reduction

There are a few studies on the use of ferro-nanofluids for enhanced oil recovery, despite their magnetic properties; hence, it is needed to study the adsorption of iron oxide (Fe2O3 and Fe3O4) nanoparticles (NPs) on rock surfaces. This is important as the colloidal transport of NPs through the reservoir is subject to particle adsorption on the rock surface. Molecular dynamics simulation was used to determine the interfacial energy (strength) and adsorption of Fe2O3 and Fe3O4 nanofluids infused in reservoir sandstones. Fourier transform infrared spectroscopy and X-ray photon spectroscopy (XPS) were used to monitor interaction of silicate species with Fe2O3 and Fe3O4. The spectral changes show the variation of dominating silicate anions in the solution. Also, the XPS peaks for Si, C and Fe at 190, 285 and 700 eV, respectively, are less distinct in the spectra of sandstone aged in the Fe3O4 nanofluid, suggesting the intense adsorption of the Fe3O4 with the crude oil. The measured IFT for brine/oil, Fe2O3/oil and Fe3O4/oil are 40, 36.17 and 31 mN/m, respectively. Fe3O4 infused with reservoir sandstone exhibits a higher silicate sorption capacity than Fe2O3, due to their larger number of active surface sites and saturation magnetization, which accounts for the effectiveness of Fe3O4 in reducing IFT.