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A passive treatment process using sulfate-reducing bacteria (SRB) is known to be effective in removing heavy metals from acid mine drainage (AMD), though there has been little discussion of the mechanism involved to date. In this work, a sulfate-reducing column test was carried out using supplementary ethanol as an electron donor for microorganisms, and the reaction mechanism was examined using geochemical modeling and X-ray absorption fine structure (XAFS) analysis. The results showed that Cu was readily removed from the AMD on the top surface of the column (0–0.2 m), while Zn and Cd depletion was initiated in the middle of the column (0.2–0.4 m), where sulfide formation by SRB became noticeable. Calculations by a developed geochemical model suggested that ethanol decomposition by aerobic microbes contributed to the reduction of Cu, while sulfide produced by SRB was the major cause of Zn and Cd removal. XAFS analysis of column residue detected ZnS, ZnSO4 (ZnS oxidized by atmospheric exposure during the drying process), and CuCO3, thus confirming the validity of the developed geochemical model. Based on these results, the application of the constructed geochemical model to AMD treatment with SRB could be a useful approach in predicting the behavior of heavy metal removal. [ABSTRACT FROM AUTHOR]

Grinding is a unit of operation of a pure mechanical process. An attritor is a grinder able to be used for fine or selective grinding. However, few studies have reported on the optimum design for the attritor. The attritor's grinding characteristics and grinding effect depend not only on the operating conditions, but also on the geometry of the agitator. Therefore, we investigated the effect of the agitator shape on the grinding efficiency from the viewpoint of experiments, kinetic analysis, and discrete element method (DEM) simulations. We conducted grinding experiments with two different agitators. One was Agitator A, a traditional design with two pairs of 90° staggered mixing arms at the middle and bottom of the mixing shaft. The other was Agitator B, with a lower mixing arm inclined by 10° along the horizontal direction. We found that the grinding rate constant of Agitator B was approximately 40% greater than that of Agitator A. Although the size distribution of the particles was relatively dispersed after grinding with Agitator B, the distribution was concentrated mainly within two ranges (<0.5 mm and 2–4 mm) with Agitator A. These results and an elemental analysis of each size fraction suggested that the dominating grinding mode in Agitator A was surface grinding, whereas in Agitator B, it was bulk grinding. In terms of the influence of the agitator shape, the DEM simulation results showed that the kinetic energy of the grinding media in Agitator B was 0.0046 J/s, i.e., larger than the 0.0035 J/s obtained for Agitator A. A collision energy analysis showed that the dominating collision was between the media and wall in the tangential direction for both models. The collision energy of the media in Agitator B was larger than that of that in Agitator A. The results from the DEM simulation can help us evaluate the experimental results and infer the reasons why the grinding rate constant in Agitator B is larger than that in Agitator A. [ABSTRACT FROM AUTHOR]

Seafloor massive sulphide (SMS) deposits, modern analogues of volcanogenic massive sulphide (VMS) deposits on land, represent future resources of base and precious metals. Studies of VMS deposits have proposed two emplacement mechanisms for SMS deposits: exhalative deposition on the seafloor and mineral and void space replacement beneath the seafloor. The details of the latter mechanism are poorly characterised in detail, despite its potentially significant role in global metal cycling throughout Earth's history, because in-situ studies require costly drilling campaigns to sample SMS deposits. Here, we interpret petrographic, geochemical and geophysical data from drill holes in a modern SMS deposit and demonstrate that it formed via subseafloor replacement of pumice. Samples from the sulphide body and overlying sediment at the Hakurei Site, Izena Hole, middle Okinawa Trough indicate that sulphides initially formed as aggregates of framboidal pyrite and matured into colloform and euhedral pyrite, which were replaced by chalcopyrite, sphalerite and galena. The initial framboidal pyrite is closely associated with altered material derived from pumice, and alternating layers of pumiceous and hemipelagic sediments functioned as a factory of sulphide mineralisation. We infer that anhydrite-rich layers within the hemipelagic sediment forced hydrothermal fluids to flow laterally, controlling precipitation of a sulphide body extending hundreds of meters. [ABSTRACT FROM AUTHOR]

CO2 sequestration into saline aquifers is considered to be one of the most promising options for reducing industrial CO2 emissions to the atmosphere. However, there are still many uncertainties regarding the storage of CO2 in the subsurface because of a lack of knowledge about CO2-water-rock interaction within CO2 reservoirs and the potential risk of CO2 leakage. In this study, we construct a semi-open type experimental system that can reproduce the interactions under conditions close to those of actual CO2 reservoirs. Using the system, we conduct CO2-water-rock interaction experiments for 8 months to monitor the long-term reaction and the mobilization of harmful metal elements. Altered tuffaceous rock is used in the experiment because these tuffaceous rock formations (called 'Green Tuff') are a potential candidate for CO2 storage in Japan. The results show that the major-element water composition will converge to the point where host rock dissolution and secondary mineral precipitation are balanced; then, the interaction will proceed under a certain groundwater composition. In addition, we found that groundwater contamination by some metal elements (Ni, Ba, and Mn) may reach unsafe levels for drinking water as a result of CO2-water-rock interaction. [ABSTRACT FROM AUTHOR]

We conducted CO 2 –water–rock interaction experiments to elucidate the dissolution characteristics and geochemical trapping potential of three different altered andesitic to rhyolitic tuffaceous rocks (Tsugawa, Ushikiri and Daijima tuffaceous rock) relative to fresh mid-ocean ridge basalt. The experiments were performed under 1 MPa CO 2 pressure to reproduce the water–rock–CO 2 interactions in CO 2 storage situations. Basalt showed high acid neutralization potential and rapid dissolution of silicate minerals. Two of the tuffaceous rocks (Ushikiri and Daijima) showed relatively high solubility trapping potential, mainly due to the dissolution of carbonate minerals in the andesitic Ushikiri tuffaceous rock and the ion-exchange reaction with zeolite minerals in the rhyolitic Daijima tuffaceous rock. The mineral trapping potential of the Ushikiri tuffaceous rock was found to be relatively high, due to the rapid dissolution of Mg- and Ca-bearing silicate minerals. Our experimental results suggest that regions of porous and andesitic tuffaceous rock hold global promise as CO 2 storage sites. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mechanochemical degradation experiments of TBBPA were conducted with a ball mill. • TBBPA was successfully decomposed into unharmful substances. • The collision energies in the ball mill were calculated by DEM simulation. • Normal collision energy was clearly correlated with the degradation rate of TBBPA. • The degradation rate of TBBPA can be predicted accurately based on DEM simulation. Persistent organic pollutants (POPs) have been banned from production and use. The brominated flame retardant TBBPA is a type of POP and has been widely used in plastics to enhance their fire resistance. However, because the natural degradation of TBBPA is a difficult process, it is particularly important to propose an appropriate treatment method. Hence, the mechanochemical degradation of TBBPA is a feasible method because it does not require high temperature heating and does not produce secondary pollutants after the reaction is completed. In this study, we performed a series of TBBPA degradation experiments with a planetary ball mill and confirmed the degradation efficiency and the rate under various conditions. Then, we conducted a discrete element method (DEM) simulation to compute the collision energies in the ball mill. By comparing the degradation rate and collision energies, we revealed that the mechanochemical degradation rate of TBBPA can be predicted by a normal collision energy computed by DEM simulation. This kinetic approach enables us to predict the rate constant and consequently, the energy consumption for the mechanochemical treatment. The predictability of these parameters will encourage the further application of mechanochemical reaction in the field of POPs treatment. [ABSTRACT FROM AUTHOR]

There has been an increasing interest in seafloor exploitation such as mineral mining in deep-sea hydrothermal fields, but the environmental impact of anthropogenic disturbance to the seafloor is poorly known. In this study, the effect of such anthropogenic disturbance by scientific drilling operations (IODP Expedition 331) on seabed landscape and megafaunal habitation was surveyed for over 3 years using remotely operated vehicle video observation in a deep-sea hydrothermal field, the Iheya North field, in the Okinawa Trough. We focused on observations from a particular drilling site (Site C0014) where the most dynamic change of landscape and megafaunal habitation was observed among the drilling sites of IODP Exp. 331. No visible hydrothermal fluid discharge had been observed at the sedimentary seafloor at Site C0014, where Calyptogena clam colonies were known for more than 10 years, before the drilling event. After drilling commenced, the original Calyptogena colonies were completely buried by the drilling deposits. Several months after the drilling, diffusing high-temperature hydrothermal fluid began to discharge from the sedimentary subseafloor in the area of over 20 m from the drill holes, ‘artificially’ creating a new hydrothermal vent habitat. Widespread microbial mats developed on the seafloor with the diffusing hydrothermal fluids and the galatheid crab Shinkaia crosnieri endemic to vents dominated the new vent community. The previously soft, sedimentary seafloor was hardened probably due to barite/gypsum mineralization or silicification, becoming rough and undulated with many fissures after the drilling operation. Although the effects of the drilling operation on seabed landscape and megafaunal composition are probably confined to an area of maximally 30 m from the drill holes, the newly established hydrothermal vent ecosystem has already lasted 2 years and is like to continue to exist until the fluid discharge ceases and thus the ecosystem in the area has been altered for long-term. [ABSTRACT FROM AUTHOR]

Arsenic contamination of groundwater is a serious issue in many countries. We investigated the removal mechanism of arsenite (As(III)) through coprecipitation with ferrihydrite to establish an optimum wastewater treatment method. We conducted adsorption and coprecipitation experiments with different As/Fe molar ratios to identify the differences between the adsorption and coprecipitation processes. Precipitates from these experiments were analyzed by using X-ray diffraction and X-ray absorption fine structure analysis to determine local structural changes of ferrihydrite during coprecipitation. As(III) removal via coprecipitation with ferrihydrite was caused by surface complexation at a lower initial As/Fe molar ratio (< 1.0). Surface complexation and amplification of the octahedral structure of the ferrihydrite were the removal mechanisms at higher initial As/Fe molar ratios (> 1.0). Our results contribute to developing a more efficient wastewater treatment method for As(III) removal. [Display omitted] • As(III) removal mechanism during coprecipitation with ferrihydrite was investigated. • Coprecipitation was more efficient than adsorption for As(III) removal. • Incorporation of As(III) ions causes structural changes in ferrihydrite. • Amplification of octahedral structure in ferrihydrite promotes As(III) removal. [ABSTRACT FROM AUTHOR]

• A new technique for the removal of sulfate (gypsum) from CaF 2 sludge is proposed. • Shrinking core model can account for the dissolution kinetics of gypsum and fluorite. • Gypsum in CaF 2 sludge was selectively carbonated in Na 2 CO 3 solution. • Sulfate content in CaF 2 sludge easily decreased under 1 % with the proposed method. Reusing wastewater and sludge containing CaF 2 has become important for ensuring a stable supply of fluorine resources. Because sulfate in CaF 2 resources causes equipment corrosion, an effective technique for sulfate removal from CaF 2 resources is critically needed for CaF 2 sludge reuse. In this study, we proposed a new technique for the purification of CaF 2 sludge by selectively carbonating sulfate contaminants (mainly gypsum). First, we demonstrated the dissolution of gypsum and fluorite in Na 2 CO 3 solution and examined the dissolution kinetics by adapting a shrinking core model. In both cases, the rate limiting factor for the dissolution phenomenon changed from a dissolution to a diffusion reaction after only a few minutes. Additionally, the diffusion rate constant for fluorite was 500,000 times slower than that for gypsum because of the textural differences of the formed calcite. Then, sulfate removal experiments with the gypsum-fluorite mixed sludge sample with Na 2 CO 3 solution were conducted. In these experiments, we confirmed that almost all of the gypsum was selectively replaced by CaCO 3 and that the gypsum content in the sludge sample decreased from 21.2% to 0.8% in 180 min at 75 °C without any loss of fluorite. Therefore, we concluded that selective carbonation is an effective purification technique for sulfate containing CaF 2 sludge. [ABSTRACT FROM AUTHOR]

Meteorite impacts have caused catastrophic perturbations to the global environment and mass extinctions throughout the Earth's history. Here, we present petrographic and geochemical evidence of a possible impact ejecta layer, dating from about 11 Ma, in deep-sea clayey sediment in the Northwest Pacific. This clay layer has high platinum group element (PGE) concentrations and features a conspicuous negative Os isotope anomaly (187Os/188Os as low as ~0.2), indicating an influx of extraterrestrial material. It also contains abundant spherules that include pseudomorphs suggestive of porphyritic olivine as well as spinel grains with euhedral, dendritic and spherical forms and NiO contents as great as 23.3 wt%, consistent with impact ejecta. Osmium isotope stratigraphy suggests a most plausible depositional age of ~11 Ma (Miocene) for this layer, as determined by fitting with the seawater evolution curve. No large impact crater of this age is known on land, even within the relatively large uncertainty range of the relative Os age. Thus, we suggest that an unrecognised impact event in the middle or late Miocene produced the impact ejecta layer of the Northwest Pacific. [ABSTRACT FROM AUTHOR]

Ancient hydrothermal metalliferous sediments (umber) have recently attracted attention as a new rare-earth element resource. We conducted chemical leaching experiments on three different umber ores to optimize the hydrometallurgical extraction process, especially regarding the grinding process. The three umber ore samples, which were collected from Japanese accretionary complexes (Kuminiyama and Aki umber) and Troodos ophiolite (Cyprus umber), had different chemical, mineral, and physical properties, and showed different leaching behaviors. The experimental results revealed that the physical properties (density and P-wave propagation velocity) principally controlled the extent of REY (lanthanides and yttrium) extraction from the umber ore samples, and REY extraction from umber samples clearly increased with the decrease in the density and P-wave propagation velocity. The differences in physical properties of the umber samples are attributable to the pressure and thermal history of each ore sample, and it was revealed that umber samples which underwent strong metamorphism are not suitable for actual development. The results also suggested that the optimum particle size (optimum grinding level) of umber samples is simply predictable based on the physical properties. The results of this study should be valuable for future efforts to procure these important mineral resources. [ABSTRACT FROM AUTHOR]

Whale carcasses (whale falls) deposited on the deep seafloor are associated with a distinctive biotic community. A fossil whale bone recovered from São Paulo Ridge, South Atlantic Ocean, during cruise YK13-04 Leg 1 of R/V Yokosuka was covered by a ferromanganese (Fe-Mn) crust approximately 9 mm thick. Here, we report an age constraint for this fossil bone on the basis of Os isotopic stratigraphy (187Os/188Os ratio) of the Fe-Mn crust. Major- and trace-element compositions of the crust are similar to those of Fe-Mn crusts of predominantly hydrogenous origin. Rare earth element concentrations in samples of the crust, normalized with respect to Post-Archean average Australian Shale, exhibit flat patterns with positive Ce and negative Y anomalies. These results indicate that the Fe-Mn crust consists predominantly of hydrogenous components and that it preserves the Os isotope composition of seawater at the time of its deposition. 187Os/188Os ratios of three Fe-Mn crust samples increased from 0.904 to 1.068 in ascending stratigraphic order. The value of 1.068 from the surface slice (0-3 mm depth in the crust) was identical to that of present-day seawater within error (~1.06). The value of 0.904 from the basal slice (6-9 mm) equaled seawater values from ca. 4-5 Ma. Because it is unknown how long the bone lay on the seafloor before the Fe-Mn crust was deposited, the Os stratigraphic age of ca. 5 Ma is a minimum age of the fossil. This is the first application, to our knowledge, of marine Os isotope stratigraphy for determining the age of a fossil whale bone. Such data may offer valuable insights into the evolution of the whale-fall biotic community. [ABSTRACT FROM AUTHOR]

Variations of 238 U/ 235 U ratio (δ 238 U) in sedimentary rocks have been proposed as a possible proxy for the paleo-oceanic redox conditions, although the marine δ 238 U system is not fully understood. Here we investigate the spatial variation of δ 238 U in modern ferromanganese (Fe–Mn) crusts by analyzing U isotopes in the surface (0–3 mm depth) layer of 19 Fe–Mn crusts collected from 6 seamounts in the Pacific Ocean. δ 238 U values in the surface layers show little variation and range from −0.59‰ to −0.69‰. The uniformity of δ 238 U values is consistent with the long residence time of U in modern seawater, although the δ 238 U values are lighter than that of present-day seawater by ∼0.24‰. The light δ 238 U values are consistent with the isotope offset observed in previously reported adsorption experiment of U to Mn oxide. These results indicate that removal of U from seawater to Mn oxide is responsible for the second largest U isotope fractionation in the modern marine system, and could contribute to isotopically heavy U to seawater. Depth profiles of U isotopes (δ 234 U and δ 238 U) in two Fe–Mn crusts (MR12-03_D06–R01 and MC10_CB07_B), dated by Os isotope stratigraphy, were investigated to reconstruct the evolution of the oceanic redox state during the Cenozoic. The δ 238 U depth profiles show very limited ranges (−0.57‰ to −0.67‰ for MR12-03_D06–R01 and −0.56‰ to −0.69‰ for MC10_CB07_B), and have values that are similar to those of the surface layers of Fe–Mn crusts. The absence of any resolvable variation in the δ 238 U depth profiles may suggest that the relative amounts of oxic and reducing U sinks have not varied significantly over the past 45 Myr. However, the δ 234 U depth profiles of the same samples show evidence for the possible redistribution of 234 U after deposition. Therefore, the depth profile of δ 238 U in Fe–Mn crusts may have been also overprinted by later chemical exchange with pore-water or seawater, and may not reflect the paleo-oceanic environmental changes. To assess the potential role of U removal by Mn oxides on seawater δ 238 U, we calculated seawater δ 238 U with different U sink fluxes into Mn oxides using a simple mass balance model. The results of these calculations suggest that seawater δ 238 U could have varied significantly throughout Earth’s history due to changes in the accumulation rate of Mn oxides. [ABSTRACT FROM AUTHOR]

Gold (Au), as one of the most precious metal resources that is used for both industrial products and private ornaments, is a global investment target, and mining companies are making huge investments to discover new Au deposits. Here, we report in situ Au adsorption in an acidic hot spring by a unique adsorption sheet made from blue-green algae with a high preferential adsorption ability for Au. The results of in situ Au adsorption experiments conducted for various reaction times ranging from 0.2 h to 7 months showed that a maximum Au concentration of 30 ppm was adsorbed onto the blue-green algal sheet after a reaction time of 7 months. The Au concentration in the hot spring water was below the detection limit (< 1 ppt); therefore, Au was enriched by preferential adsorption onto the blue-green algal sheet by a factor of more than ~ 3 × 10 7 . Thus, our gold recovery method has a high potential to recover Au even from an Au-poor solution such as hot spring water or mine wastewater with a low impact on the environment., (© 2024. The Author(s).)

Potential risks of supply shortages for critical metals including rare-earth elements and yttrium (REY) have spurred great interest in commercial mining of deep-sea mineral resources. Deep-sea mud containing over 5,000 ppm total REY content was discovered in the western North Pacific Ocean near Minamitorishima Island, Japan, in 2013. This REY-rich mud has great potential as a rare-earth metal resource because of the enormous amount available and its advantageous mineralogical features. Here, we estimated the resource amount in REY-rich mud with Geographical Information System software and established a mineral processing procedure to greatly enhance its economic value. The resource amount was estimated to be 1.2 Mt of rare-earth oxide for the most promising area (105 km 2  × 0-10 mbsf), which accounts for 62, 47, 32, and 56 years of annual global demand for Y, Eu, Tb, and Dy, respectively. Moreover, using a hydrocyclone separator enabled us to recover selectively biogenic calcium phosphate grains, which have high REY content (up to 22,000 ppm) and constitute the coarser domain in the grain-size distribution. The enormous resource amount and the effectiveness of the mineral processing are strong indicators that this new REY resource could be exploited in the near future.