Hg Droplets Research Articles

Formation of Mercury Droplets at Ambient Conditions through the Interaction of Hg(II) with Graphene Quantum Dots

Unlike other metals, Hg forms droplets at ambient conditions when a Hg(II) salt interacts with hydroxyl-enriched graphene quantum dots (HEGQDs). The hydroxylation of GQD surface is evident from FT-IR, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) techniques. The scanning electron microscopy images of Hg(II)-HEGQDs incubated for 0, 1, 24, and 168 h show Hg droplets with the size of 0.1, 0.3, 0.8, and 2 μm, respectively. The XPS studies confirm the presence of Hg(0) and also reveal a noticeable decline in the composition percentage of C-O, whereas a marked increase is observed in the C═O composition percentage. The pathway for the formation of droplets induces immediate reduction of Hg(II) to Hg(0) by both hydroxyl groups and π electron cloud present on the surface of HEGQDs, followed by coalescence. The formed Hg(0) is then strongly adsorbed on the hollow sites of graphene and acts as a nucleation site for the growth of droplets. The kinetics of the reaction obeys LaMer Burst nucleation followed by coalescent growth in addition to autocatalytic reduction and finally follows the Oswald ripening mechanism. The internal pressure of Hg droplets gradually decreases as the radius of the drop increases over the incubation time and liquid-rhombohedral transformation is likely to take place at a radius of 0.8 nm.

Metal redistribution during cementation of historic processing residues, Macraes gold mine, New Zealand

ABSTRACT Roasted residues from historic gold mine processing at the Golden Point historic reserve were thoroughly cemented by surfical processes. The cements are composed mainly of oxidised and acidic Fe–As–S minerals with varying particle size and crystallinity. Bukovskyite (Fe2[AsO4][SO4][OH].7H2O) and scorodite (FeAsO4.2H2O) are the most prominent of these minerals, but a range of As and S bearing ferric iron oxyhydroxide compounds are also abundant, including K-jarosite and schwertmannite. Arsenolite (As2O3) is a minor component, either persisting from original roasting or precipitated via local reduction in the cement. After the historic roasting the residues were treated with liquid Hg to extract gold, and some of that Hg remains in the residues. This Hg now occurs as microcrystalline schuetteite (Hg3[SO4]O2), remobilised nano-scale liquid Hg droplets, and as micron-scale Hg-rich layers in ferric iron oxyhydroxide compounds in the cements. Tungsten mobilised from primary ore scheelite is contained in ferric iron oxyhydroxide and as Fe-meymacite (WO3.xFe2O3.nH2O) in the cements. The cementation processes have effectively confined metals within the residues.

Unidirectional Self-Driving Liquid Droplet Transport on a Monolayer Graphene-Covered Textured Substrate.

Controllable directional transport of liquid droplets on a functionalized surface has been a challenge in the field of microfluidics because it does not require energy supply, and the physical mechanism of such self-driving transport exhibits extraordinary contribution to fundamental understanding of some biological processes and the design of microfluidic apparatus. In this paper, we report a novel design of a surface microstructure that can realize unidirectional self-driving liquid mercury (Hg) droplet transport on a graphene-covered copper (Cu) substrate with a three-dimensional surface microstructure. We have demonstrated that a liquid Hg droplet spontaneously propagates on a grooved Cu substrate covered by a monolayer graphene without any external force fields. Classical molecular dynamics results provide a profound insight on the self-driving process of Hg droplets. It shows that the Hg droplet undergoes acceleration, deceleration, and return stages successively from the narrow to wide ends of the gradient groove. Intriguingly, Hg droplets can move continuously and unidirectionally on the three-dimensional graphene-covered surface microstructure when they accumulate enough kinetic energy from the gradient groove to break the energy barrier at the step junctions between the two neighboring unit cells. The design of the zigzag textured surface covered by a monolayer graphene artfully uses the facts; (1) the monolayer graphene can effectively reduce the droplet pinning on the textured surface, (2) the hydrophobic graphene layer reduces the friction between Hg droplets and the substrate, and (3) the textured surface can permeably interact with the droplets through the monolayer graphene to achieve a continuous self-driving process. The findings reported here open a door to explore the graphene-covered functional surface to directional transport of liquid droplets and provide an in-depth understanding of the self-driving mechanism for liquid droplets on graphene-covered textured substrates.

Micropatterned, macroporous polymer springs for capacitive energy harvesters

We realised spring/spacer elements, which are crucial components of capacitive energy harvesters, by syringe printing of polyurethane diacrylate and ethylhexyl acrylate based high (HIPE) and medium (MIPE) internal phase emulsion templates followed by UV polymerisation. The resulting micropatterned poly(merised)H/MIPEs are very flexible and reversibly compressible to a strain of 50% as cyclic compression test revealed. Dynamic mechanical analysis has shown constant mechanical behaviour of the macroporous polymer springs under a loading/unloading at a frequent of 2 Hz for 10 h, proving the practical durability of the springs. Within a prototype harvester the micropatterned macroporous springs allowed to compartmentalise Hg droplets and provided the required restoring force to operate the device successfully; the capacitive change of the device within one compression-recovery cycle reached 570 pF.

Evolution of Conformational Order During Self-Assembly of n-Alkanethiols on Hg Droplets: An Infrared Spectromicroscopy Study

This Letter describes Fourier-transform infrared spectroscopy evidence for the evolution of conformational order and coverage during the formation of n-alkanethiol monolayers on microdroplets of mercury from the solution phase. At the highest coverages obtained by self-assembly, the monolayer is characterized by predominantly all-trans conformational order. For partial monolayers obtained at arbitrarily quenched incubation periods, we find a continuous evolution of the chain conformational order with monolayer coverage. Analyzing these results in light of previously reported models from X-ray scattering reveals a complex self-assembly process in which the density-dependent evolution of the chain conformational order is coupled with that of molecular orientation and density.

Mercury speciation in a tropical soil association; Consequence of gold mining on Hg distribution in French Guiana

Mercury (Hg) speciation was compared in French Guiana pristine soils and in Hg-contaminated soils impacted by former (~ 1950's) gold mining activities which used Hg for gold amalgamation. Four selective extractions were performed on soil samples to assess the fraction of Hg present as Hg(II) and bond to organic matter (extracted by NH 4OH and KOH), to amorphous iron oxides (ascorbate) and to soil components other than refractory minerals (HCl/HNO 3). In addition, pyrolysis was used to quantify the content of elemental Hg in contaminated soils. X-ray diffraction (XRD) and X-ray fluorescence micro-mapping (µXRF) were used in combination to selective extractions to assess the nature of targeted components, the possible overlaps between the different extraction procedures and the spatial correlation between Si, K, Fe, Au and Hg. In soil profiles from pristine toposequences, Hg concentrations (0.01–0.49 µg·g − 1 ) decreased with increasing depth in soil matrix. Hg concentrations also decreased from ferralsols to acrisols and further to gleysols. In pristine soil matrix, Hg was mainly associated to the clay-size fraction (< 2 µm) which was mainly constituted of amorphous and crystalline Fe oxides (Al-substituted goethite and hematite), gibbsite and fine organic matter (OM), whose relative abundances vary along the soil association. Total Hg concentration was positively correlated with sulfurs and organic carbon suggesting the association of Hg with OM sulfur-bearing functional groups. Gleysols were depleted in Hg because of the prevailing reducing conditions that lead to the dissolution of iron oxides. In the same soil profiles, Hg concentrations in ferruginous nodules, which make up most of the soil coarse fraction (> 2 mm), were similar to those reported in the pristine soil matrix. These nodules mainly contained Al-substituted hematite and goethite and were especially abundant upslope in ferralsols and acrisols. Gold-mined gleysols were strongly disorganized by former activities as neither the original structure nor the texture was preserved. Soil granulometry was dominated by gravels, sands and silts. Hg concentrations (0.09–9.22 µg·g − 1 ) largely exceeded those in pristine soils. µXRF allowed the identification of Au-amalgamated Hg and of elemental Hg droplets. Pyrolysis confirmed Hg to be mainly present in its elemental form in contaminated soils. Selective extractions showed additional minor contributions of Hg(II) associated to OM, and to Al or Fe oxides. The combination of selective extractions with XRD and µXRF data showed that extraction efficiency is strongly dependent on the soil type, and that this efficiency needs to be determined on a soil-by-soil basis for Hg speciation studies. KOH extraction was especially delicate as crystalline and amorphous oxides were extracted together with organic matter.

Native Hg liq in the metalliferous sediments of the East Pacific Rise (21°S)

Native Hg droplets, documented here for the first time in mid-ocean ridge metalliferous sediments, were found in the surface sediment of a magmatically robust and ultra-fast spreading mid-ocean ridge, the East Pacific Rise. The surface sediment and Fe–Mn micronodules in it are enriched in Hg. Two different processes can produce Hg 0 liq in this environment: hydrothermal and biogenic. Bio-transfer of ionic Hg dissolved in the hydrothermal fluids into Hg 0 in the sediment can account for the eventual native Hg occurrences in the close vicinity of the hydrothermal vents. The Hg 0 liq occurrences in the distal metalliferous sediments most probably have originated directly from the hydrothermal fluids and been transported by hydrothermal plumes away from the vents. Condensation of Hg 0 liq from Hg 0 vap in the vent fluids subjected to near critical phase separation seems the most plausible mode of origin of the native Hg occurrences. The high-temperature vents at the global spreading ridge chain introduce an assessed amount of 1.62–4.86 × 10 3 t/yr Hg 0 liq into the ocean. With time, the deposited Hg 0 liq will likely be dissolved in the overlaying seawater and will not survive in the geologic record.

Effective cluster model of dielectric enhancement in metal-insulator composites.

The electrical permittivity of a suspension of conducting spheres at high volume loading exhibits a large enhancement above the value predicted by the Clausius-Mossotti approximation. The permittivity enhancement is a dielectric anomaly accompanying a metallization transition that occurs when conducting particles are close packed. In disordered suspensions, close encounters can cause a permittivity enhancement at any volume loading. We attribute the permittivity enhancements typically observed in monodisperse disordered suspensions of conducting spheres to local metallized regions of high density produced by density fluctuations. We model a disordered suspension as a mixture, or mesosuspension, of isolated spheres and random close-packed spherical clusters of arbitrary size. Multipole interactions within the clusters are treated exactly. External interactions between clusters and isolated spheres are treated in the dipole approximation. Model permittivities are compared with Guillien's experimental permittivity measurements [Ann. Phys. (Paris) Ser. 11, 16, 205 (1941)] on liquid suspensions of Hg droplets in oil and with Turner's conductivity measurements [Chem. Eng. Sci. 31, 487 (1976)] on fluidized bed suspensions of ion-exchange resin beads in aqueous solution. New permittivity measurements at 10 GHz on solid suspensions of monodisperse metal spheres in polyurethane are presented and compared with the model permittivities. The effective spherical cluster model is in excellent agreement with the experiments over the entire accessible range of volume loading.