Hydroxide Minerals Research Articles

Impact of evaporation on groundwater salinity in the arid coastal aquifer, Western Saudi Arabia

Understanding groundwater salinization and pollution in the arid coastal aquifer is crucial due to complex geochemical processes and sources. This study intends to evaluate the impact of evaporation on groundwater salinity in the arid coastal aquifer, Al Lusub basin, Saudi Arabia using geochemical and multivariate statistical tools. Groundwater samples were collected (n = 52) and analysed for major and minor ions. Groundwater is brackish and shallow wells have higher salinity compared to deeper ones. Hierarchical cluster analysis (HCA) classified the wells into three groups (CG1, CG2, CG3). In these cluster groups, salinity is in the order of CG1(1448 mg/l) < CG2 (3704 mg/l) < CG3(11018 mg/l). PHREEQC modelling reveals that groundwater in this basin is saturated with carbonate, sulphate (CG2, CG3), fluorite (CG3) and silicate minerals, and under-saturated with chloride and hydroxide minerals. Thermodynamic stability diagrams confirm the silicate weathering and kaolinite equilibrium. Precipitation of carbonate minerals at high salinity due to evaporation reduces Ca activity in the groundwater, which triggered the solubility of gypsum and fluorite through common ion effect. Pearson correlation analysis, principal component analysis, ionic ratios (Na/Cl, Cl/Br and F/Cl) and ionic deltas (+ΔBr, +ΔF, +ΔCa, +ΔSO4, +ΔNO3, −ΔNa and −ΔK) justified that non-saline sources and processes, namely evaporation, reverse ion exchange, mineral dissolution and wastewater infiltration predominantly affected the water chemistry in this aquifer. Repeated irrigation practice with high salinity groundwater leads to salt accumulation in the vadose zone due to evaporation, which flushed by the subsequent irrigation events and resulted in higher salinity and NO3− in the groundwater. Hence, sustainable groundwater management and smart irrigation should be implemented.

A Comparative Study on Cure Kinetics of Layered Double Hydroxide (LDH)/Epoxy Nanocomposites

Layered double hydroxide (LDH) minerals are promising candidates for developing polymer nanocomposites and the exchange of intercalating anions and metal ions in the LDH structure considerably affects their ultimate properties. Despite the fact that the synthesis of various kinds of LDHs has been the subject of numerous studies, the cure kinetics of LDH-based thermoset polymer composites has rarely been investigated. Herein, binary and ternary structures, including [Mg0.75 Al0.25 (OH)2]0.25+ [(CO32−)0.25/2∙m H2O]0.25−, [Mg0.75 Al0.25 (OH)2]0.25+ [(NO3−)0.25∙m H2O]0.25− and [Mg0.64 Zn0.11 Al0.25 (OH)2]0.25+ [(CO32−)0.25/2∙m H2O]0.25−, have been incorporated into epoxy to study the cure kinetics of the resulting nanocomposites by differential scanning calorimetry (DSC). Both integral and differential isoconversional methods serve to study the non-isothermal curing reactions of epoxy nanocomposites. The effects of carbonate and nitrate ions as intercalating agents on the cure kinetics are also discussed. The activation energy of cure (Eα) was calculated based on the Friedman and Kissinger–Akahira–Sunose (KAS) methods for epoxy/LDH nanocomposites. The order of autocatalytic reaction (m) for the epoxy/Mg-Al-NO3 (0.30 and 0.254 calculated by the Friedman and KAS methods, respectively) was smaller than that of the neat epoxy, which suggested a shift of the curing mechanism from an autocatalytic to noncatalytic reaction. Moreover, a higher frequency factor for the aforementioned nanocomposite suggests that the incorporation of Mg-Al-NO3 in the epoxy composite improved the curability of the epoxy. The results elucidate that the intercalating anions and the metal constituent of LDH significantly govern the cure kinetics of epoxy by the participation of nitrate anions in the epoxide ring-opening reaction.

Preliminary Study of Mining Material Prospects Based on Hydrothermal Alteration Distribution Using Composite and Density Slicing of Landsat 8 Image in Ulubongka Regency, Central Sulawesi

Difficult access to the field in Central Sulawesi causes the process of identifying prospects for mining minerals requires a relatively large time and cost. Therefore, the remote sensing approach can be carried out as a preliminary study to determine the distribution of hydrothermal alterations that characterize the presence of mine minerals. This study utilizes Landsat 8 imagery to obtain the distribution of alteration minerals, especially the group of ferrous mineral oxide and hydroxide minerals, clay and carbonate minerals and Ferromagnesian minerals. The method used is composite (RGB) 4/2, 6/7, 5 and 4/2, 6/7, 10 to detect the distribution of alteration minerals. Whereas the Density Slicing method uses 4/2, 5/6 and 6/7 ratio images to detect Ferrugitation, Ferromagnesian, clay and carbonate minerals. The results of the analysis showed the distribution of iron oxide and hydroxide minerals (Ferrugination) dominated the area in alluvium and opiolite rocks. This alteration distribution is interpreted as a prospect of further studies of the presence of mining minerals such as nickel and iron. Whereas ferromagnesian minerals, clays and carbonates dominate in conglomerate and limestone rocks.

New insights into the genesis of IOCG deposits: From a case study of the Yinachang deposit in SW China

The Yinachang Fe-Cu-Au-U-REE deposit is hosted by the lower part of the Paleoproterozoic Kunyang Group in the central Yunnan Province of SW China in an area known to contain iron-oxide Cu-Au mineralisation. The deposit includes: (i) the sulphide assemblage chalcopyrite – pyrite – magnetite – cobaltite – molybdenite – cassiterite; (ii) Rare Earth Element assemblage bastnaesite – parasite – fergusonite – xenotime – monazite; (iii) the uranyl hydroxide mineral vandendriesscheite; (iv) gold commonly hosted by ankerite; and (v) the gangue mineral assemblage apatite – biotite – fluorspar – quartz – calcite. The ore is commonly massive, disseminated, banded, or in calcite veins. The banded mineralisation contains high concentration of Au, Co, Mo, U, Fe, Cu and REE, and the vein-type mineralisation has abundant REE minerals of bastnaesite, parisite, fergusonite and xenotime. Monazite exists as inclusions in apatite or as discrete grains on the surface of magnetite, and the uranium is associated with chalcopyrite. The mineralising process can be divided into an initial Na-alteration followed by the ore-forming assemblages of Fe-REE and Cu-Au-U-REE mineralisation. The average δ18OH2O values in the quartz and calcite change are between 3.5 and 10.7‰, with δDV-SMOW values ranging between −98.2 and −47.7‰. The calcite, siderite and ankerite have δ13C isotope composition ranges from –14 to +1‰ and δ18O compositions of +6.9 to +22‰. The H–O–C isotope systematics indicate that the mineralising fluids have mixed magmatic and metamorphic sources, whereas the carbon is sourced from marine carbonate, and the low temperature alternation of polyphase mantle material. In situ δ34S sulphide value ranges between 1.1 and 11.9‰, and the bulk δ34S value ranges between −4.7 and 10.5‰. In situ Pb isotopes of sulphide samples have 206Pb/204Pb values of 18.58–18.76, 207Pb/204Pb values of 15.51–15.66 and 208Pb/204Pb values of 37.47–38.06. These values plot in the upper crust Pb-evolution curve, indicative of a complex source of Pb in the deposit. The Pb is interpreted to have a deep-seated magmatic source with a contribution from the crust. It is also proposed that the REE-mineralised fluids are derived from a late stage of alkaline magma differentiation. The 40Ar-39Ar biotite date indicates that the Precambrian rocks in the Kangdian region were regionally metamorphosed at ca. 900 Ma. The Yinachang Fe-Cu-Au-U-REE deposit is interpreted as an IOCG deposit based on geological and isotopic studies. The banded ore and vein type ore are the main exploration targets for uranium, gold and REE. This study helps us better understand IOCG deposits in China.

Nanoscale constraints on the in situ transformation of Ru–Os–Ir sulfides to alloys at low temperature

We report new results of a combined focused ion beam high-resolution transmission electron microscopy (FIB/HRTEM) investigation of two grains of platinum-group minerals (PGM) corresponding to the laurite (RuS2)-erlichmanite (OsS2) solid solution series. The grains are included within unaltered chromite and the serpentine-dominant matrix of the mantle-hosted chromitite body of Monte Bueno in eastern Cuba. At the micron-scale, the grain hosted in unaltered chromite preserves magmatic features including a complex oscillatory zoning defined by a core of erlichmanite surrounded by alternating bands of Os-rich/Os-poor laurite, revealed by conventional field emission scanning electron microscopy (FE-SEM) and X-ray mapping by electron microprobe analyzer (EPMA). Combining high-magnification (HMEM), high angle-annular dark field (HAADF) images and the corresponding Energy Dispersive Spectra (EDS), the elemental mappings acquired using HRTEM showed that the oscillatory zoning occurs at both the micron and nano scales. A specific feature highlighted by HRTEM observations is the rather complex structure of the erlichmanite core, consisting of an aggregation of much smaller cores (<1 µm) characterized by an oscillatory zoning linked to bands thinner than 10 nm that are not detectable when the whole grain is imaged using conventional FE–SEM and X–ray EPMA elemental mapping. The nanotextural features identified in this study suggest: (1) formation of the PGM grains characterized by the coalescence of laurite/erlichmanite nuclei that originally formed independently and coalesced in the silicate magma, (2) growth and crystal zoning of compositionally different bands as a result of sudden changes in T, fS2, fO2 and composition of the melt. These thermodynamic and chemical changes also allowed the segregation of nano-sized Fe–Ni–S solid particles/droplets from the silicate magma, which are now found within the PGM grain as nanoparticles of pentlandite of <100 nm in size and had potential implications for laurite nucleation. On the other hand, backscattered FESEM images and X-ray EPMA mapping of the altered PGM grain associated with the silicate matrix of the chromitite revealed a magmatic sector zoned core, which is surrounded by a rim of S-deficient laurite (i.e., desulfurized laurite) that hosts Ru-Os-Ir alloys. The FIB/HRTEM observations on the rim of desulfurized laurite ± Os–Ir–Ru alloys revealed an intergrowth of nano-sized (<5 nm) laurite with ad Ru-Os-Ir-(S-As) and Ru-Os-Ir alloys (50–100 nm) within a Fe-Mn oxide/hydroxide matrix. This microstructure and the coexistence of these nanoparticles within the Fe-Mn oxide/hydroxide matrix illustrates an alteration sequence whereby magmatic laurite was desulfurized and decomposed into smaller laurite nanoparticles, which in turn were progressively transformed to Ru-Os-Ir-(S-As) particles and, finally, to Ru-Os-Ir nanoalloys. Self-reorganization (coarsening) of the desulfurizing laurite within a matrix transforming to Fe-Mn oxide/hydroxide matrix resulted in the formation of nanoscale intergrowths of Ru-Os-Ir-(S-As) particles and Ru-Os-Ir alloys with the Fe-Mn oxide/hydroxide . This took place concomitant to incorporation/oxidation of Fe and Mn by relatively more oxidizing fluids. These alteration fluids were generated during to serpentinization/ocean-floor metamorphism that affected the chromitite body. The observations provided here are relevant to the current debate about the platinum-group element (PGE) mobilization and the possible existence of PGE oxides and hydroxides minerals

Routes of iron entry into, and exit from, the catalytic ferroxidase sites of the prokaryotic ferritin SynFtn.

Ferritins are multimers comprised of 4 α-helical bundle monomers that co-assemble to form protein shells surrounding an approximately spherical internal cavity. The assembled multimers acquire Fe2+ from their surroundings by utilising channels that penetrate the protein for the transportation of iron to diiron catalytic centres buried within the monomeric units. Here oxidation of the substrate to Fe3+ is coupled to the reduction of O2 and/or peroxide to yield the precursor to a ferric oxy hydroxide mineral that is stored within the internal cavity. The rhombic dodecahedral quaternary structure results in channels of 4-fold and 3-fold symmetry, located at the vertices, which are common to all 24mer-ferritins. Ferritins isolated from higher eukaryotes have been demonstrated to take up Fe2+via the 3-fold channels. One of the defining features of ferritins isolated from prokaryotes is the presence of a further 24 channels, the B-channels, and these are thought to play an important role in Fe2+ uptake in this sub-family. SynFtn is an unusual ferritin isolated from the marine cyanobacterium Synechococcus CC9311. The reported structure of SynFtn derived from Fe2+ soaked crystals revealed the presence of a fully hydrated Fe2+ associated with three aspartate residues (Asp137 from each of the three symmetry related subunits) within each three-fold channel, suggesting that it might be the route for Fe2+ entry. Here, we present structural and spectro-kinetic data on two variants of SynFtn, D137A and E62A, designed to assess this possibility. Glu62 is equivalent to residues demonstrated to be important in the transfer of iron from the inner exit of the 3-fold channel to the catalytic centre in animal ferritins. As expected replacing Asp137 with a non-coordinating residue eliminated rapid iron oxidation by SynFtn. In contrast the rate of mineral core formation was severely impaired whilst the rate of iron transit into the catalytic centre was largely unaffected upon introducing a non-coordinating residue in place of Glu62 suggesting a role for this residue in release of the oxidised product. The identification of these two residues in SynFtn maps out major routes for Fe2+ entry to, and exit from, the catalytic ferroxidase centres.

Preference of Co over Al for substitution of Fe in goethite (α-FeOOH) structure: Mechanism revealed from EXAFS, XPS, DFT and linear free energy correlation model

Goethite is the most stable iron hydroxide mineral in geological environments, and it is usually crystallized with more than one type of substituent. However, the synergetic or antagonistic effects of coexisting cations on substitution for lattice Fe in gothite are unclear. In this study, a series of Co-, Al-, and Co + Al co-substituted goethite samples were synthesized at room temperature and then investigated by powder XRD, X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure spectroscopy (XAFS), density function theory (DFT) calculations, and acid dissolution experiments. All the obtained samples were pure goethite, except the one with a high total content of Co + Al that contained a portion of 2-line ferrihydrite. Lattice parameter a of Co + Al co-substituted goethite was linearly decreased with the final Co content, lattice parameter b and calculated crystal density had the best negatively linear relationships with Al content while lattice parameter c, cell volume, average edge-sharing Fe − Me (Me = Fe, Al, and Co) distances along c⁎ and b⁎ axis (E′ and E) and average corner-sharing Fe − Me (DC) distances had the best linear correlations with the total contents of Co + Al. Aluminum and Co were found to be evenly distributed in goethite structure, and both reduced the mineral particle size. Co coexisted in a mixed valance of +2 and +3, and the proportion of Co3+ increased with the increase of Co content in Co-substituted goethite owing to relatively high electric potential energy and decreased with the increase of coexisting Al3+ content in Co + Al co-substituted goethites because of relatively low alkalinity in local environments around Co2+. Incorporation of Co greatly promoted the mineral dissolution in 2 M HCl solution at 298 K. Fe K-edge EXAFS analysis indicated almost constant local order around Fe in these samples. Coexisting Al had almost no effect on Co incorporation into goethite structure but Co suppressed Al substitution for lattice Fe. This preference of Co over Al to substitute for Fe was explained by the predicted partition coefficients (Kd) of common trivalent substituents in goethite by using the linear free energy relationship. It highlights the necessity to take into consideration not only the substituent physical properties (size and charge) but also their chemical properties (chemical bonding energy and chemical potential). These results enhanced our understanding of the incorporation of exotic cations into the iron oxide structures and the mutual effects of coexisting cations on substitution for lattice Fe.

Using Ca[sbnd]Fe layered double hydroxide transformation to optimise phosphate removal from waste waters

Single phase CaFe layered double hydroxide (LDH) minerals containing Cl− species in the interlayer was synthesized by coprecipitation with a CaII: FeIII ratio of 2: 1. In both phosphate (PO4) free water and at low aqueous PO4 concentration, the LDH was fully transformed into a mixture of a “ferrihydrite-like” material, calcite and soluble calcium species. Mössbauer spectroscopy and transmission electron microscopy showed that phosphate was removed by the “ferrihydrite like” phase that contained a significant quantity of Ca. At high phosphate concentration the Ca species released from the LDH precipitated to form hydroxyapatite leading to a maximal removal capacity of ~ 130 mg P-PO4 g−1. The CaFe LDH was deposited onto a pozzolana volcanic rock in order to perform a column experiment under hydrodynamic conditions for 70 days. A high removal capacity was observed, a qB of ~ 4 mg P-PO4 g−1 was measured at the breakthrough of the column, however the pH in the outflow was measured to be higher than 11. Such an increase was due to the very high solubility of the CaFe LDH.

Linkage of sulfur isotopic enrichment to sulfur and arsenic release in the coastal aquifers of southwestern Taiwan

High arsenic concentration in groundwater is influenced by redox reactions in As-bearing iron (oxy)hydroxide minerals and elevated total organic carbon, resulting in arsenic contamination and enrichment in groundwater after introduction of seawater into an aquifer. In this study, hydrochemical and isotopic (S, O and C) techniques were used to relate arsenic contamination and seawater flooding/intrusion in groundwater aquifers in the Chianan Plain, southwestern Taiwan. Thirty-three samples (30 from groundwater and 3 from river water) were collected from April–June of 2014. Most of the groundwater samples collected from the Chianan Plain were dominated by As(III), indicating that reducing conditions prevailed within the aquifers. The δ18O-δD plots of most of the groundwater samples from the Chianan Plain are generally lined on the global meteoric water line (GMWL), but the δ18O and δD isotopic compositions of the river water samples show enriched signals. Salinity and sulfate concentrations of river water and shallow groundwater have been found to increase after seawater flooding/intrusion. The δ18O and δD isotopic compositions of the river water showed a gradual trend toward those of seawater. The trend in the isotopic compositions of the river and groundwater samples indicated a mixing of seawater and meteoric water. Up to the present, the groundwater levels in the coastal areas of the Chianan Plain have dropped to zero meters in elevation parallel to sea level due to excessive groundwater withdrawal, resulting in seawater intrusion into the aquifers in Budai, Yichu, and Beimen in the Plain. Moreover, high salinity (48.1‰) occurred only in the Beimen 2B shallow groundwater at a depth of 60 m is a result of seawater flooding infiltration from the nearby salinized Pachang River. The δ34S[SO4]/δ18O[SO4] isotopic ratios (2.63–2.82) of low-As (concentration < 50 μg/L) river water samples were similar to those of marine sulfate minerals dissolved in seawater, but were variable (0 − 2.93) among the high-As (concentration ≧ 50 μg/L) groundwater samples from the Chianan Plain. Sulfates in seawater were introduced into the coastal aquifers of the Chianan Plain under the Holocene marine transgression, wherein the mixing of paleo- and modern-sulfates due to seawater intrusion might have occurred or are occurring. The release of sulfur and arsenic (mostly arsenite) in the Chianan Plain groundwater under reducing environments indicating redox reactions in sulfates and iron (oxy)hydroxide minerals may change the isotopic (S and O in sulfate) compositions in groundwater, resulting in enrichment of δ34S[SO4] and δ18O[SO4]. Salinity can promote arsenic release in groundwater and thus enrich the δ34S[SO4] and δ18O[SO4] isotopic compositions, in which 6.0–22.8‰ δ34S[SO4] and 9.3–15.5‰ δ18O[SO4]occur in shallow fresh groundwater (depth < 60 m) but up to 27.7‰ δ34S[SO4] and 20.4‰ δ18O[SO4] occur in shallow saline groundwater, in comparison to 0‰ δ34S[SO4] and 5.4–6.5‰ δ18O[SO4] in deep fresh groundwater (depth between 60 and 318 m) and up to 38.5‰ δ34S[SO4] and 18.7‰ δ18O[SO4] in deep brackish groundwater. This study provides insights suggesting that the As-containing iron(II) minerals are oxidized to iron(III) minerals and then re-reduced to iron(II) which leads to As release.

Regenerative Endodontic Procedures Using Contemporary Endodontic Materials

Calcium hydroxide apexification and Mineral Trioxide Aggregate (MTA) apexification are classical treatments for necrotic immature permanent teeth. The first tend to fail for lack of compliance given the high number of sessions needed; the second has technical difficulties such as material manipulation and overfilling. With both techniques, the root development is interrupted leaving the tooth with a fragile root structure, a poor crown-to-root ratio, periodontal breakdown, and high risk of fracture, compromising long-term prognosis of the tooth. New scientific literature has described a procedure that allows complete root development of these specific teeth. This regenerative endodontic procedure (REP) proposes the use of a combination of antimicrobials and irrigants, no canal walls instrumentation, induced apical bleeding to form a blood clot and a tight seal into the root canal to promote healing. MTA is the most used material to perform this seal, but updated guidelines advise the use of other bioactive endodontic cements that incorporate calcium and silicate in their compositions. They share most of their characteristics with MTA but claim to have fewer drawbacks with regards to manipulation and aesthetics. The purpose of the present article is to review pertinent literature and to describe the clinical procedures protocol with its variations, and their clinical application.

Reactivity of redox cycled Fe-bearing subsurface sediments towards hexavalent chromium reduction

Abstract Structural Fe(II) in clay minerals and natural sediments is known to reduce Cr(VI) to Cr(III), but the effect of redox-cycled Fe-bearing natural sediments on Cr(VI) reduction kinetics is poorly understood. The objective of this study was to understand the kinetics and mechanisms of Cr(VI) reduction by Fe(II) in redox cycled natural sediment. Fe-bearing sediment was collected from the Ringold formation in the 300 area of Hanford, Washington, United States. Fe redox cycling of the sediment was accomplished via four cycles of bioreduction of structural Fe(III) in Hanford sediment and air oxidation of the resulting Fe(II). Bio-produced Fe(II) in Hanford sediment from each redox cycle was utilized to reduce Cr(VI) at three temperatures (10, 20 and 30 °C). The initial rate of Cr(VI) reduction generally increased with each redox cycle, which was more pronounced at high temperatures. The amount of Fe(II) oxidized to the amount of Cr(VI) reduced was close to the expected stoichiometric ratio of 3. Aqueous concentrations of Si, Al, and Fe revealed some dissolution of the sediment after reaction with Cr(VI). X-ray diffraction (XRD) and scanning electron microscopy (SEM) detected secondary mineral formation. Mossbauer data showed that the oxidation of Fe(II) was coupled with the reduction of Cr(VI) but no Fe-oxides/oxyhydroxides formed. Transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), XANES, and EXAFS were performed for representative reduced Cr solids that formed from reduction of Cr(VI) by sediment-associated Fe(II) at 30 °C. TEM revealed that the d-spacing of Cr-reacted montmorillonite at 30 °C, a dominant Fe-bearing mineral in Hanford sediment, expanded from 10 A to 13 A. This layer expansion was likely due to intercalation of reduced Cr(III) into the interlayer space of the montmorillonite structure. EELS exhibited an L2 absorption peak at 586.0 eV and an L3 absorption peak at 577.0 eV, suggestive of Cr(III) in a hydroxide mineral phase. Similarly, XANES and EXAFS analyses confirmed Cr(VI) reduction to Cr(OH)3 at 30 °C and indicated an edge-sharing coordination of the Cr(III) octahedra to 2–3 other Cr or metal ions. This study has important implications for understanding the reactivity of clay-rich sediment towards Cr(VI) reduction at contaminated sites and the stability of the reduced Cr(III).

Redox and pH gradients drive amino acid synthesis in iron oxyhydroxide mineral systems.

Iron oxyhydroxide minerals, known to be chemically reactive and significant for elemental cycling, are thought to have been abundant in early-Earth seawater, sediments, and hydrothermal systems. In the anoxic Fe2+-rich early oceans, these minerals would have been only partially oxidized and thus redox-active, perhaps able to promote prebiotic chemical reactions. We show that pyruvate, a simple organic molecule that can form in hydrothermal systems, can undergo reductive amination in the presence of mixed-valence iron oxyhydroxides to form the amino acid alanine, as well as the reduced product lactate. Furthermore, geochemical gradients of pH, redox, and temperature in iron oxyhydroxide systems affect product selectivity. The maximum yield of alanine was observed when the iron oxyhydroxide mineral contained 1:1 Fe(II):Fe(III), under alkaline conditions, and at moderately warm temperatures. These represent conditions that may be found, for example, in iron-containing sediments near an alkaline hydrothermal vent system. The partially oxidized state of the precipitate was significant in promoting amino acid formation: Purely ferrous hydroxides did not drive reductive amination but instead promoted pyruvate reduction to lactate, and ferric hydroxides did not result in any reaction. Prebiotic chemistry driven by redox-active iron hydroxide minerals on the early Earth would therefore be strongly affected by geochemical gradients of Eh, pH, and temperature, and liquid-phase products would be able to diffuse to other conditions within the sediment column to participate in further reactions.

Comparison between calcium hydroxide mixtures and mineral trioxide aggregate in primary teeth pulpotomy: a randomized controlled trial.

Objectives:To evaluate the effect of calcium hydroxide (CH) associated with two different vehicles as a capping material for pulp tissue in primary molars, compared with mineral trioxide aggregate (MTA).Methodology:Forty-five primary mandibular molars with dental caries were treated by conventional pulpotomy using one of the following materials: MTA only (MTA group), CH with saline (CH+saline group) and CH with polyethylene glycol (CH+PEG group) (15 teeth/group). Clinical and periapical radiographic examinations of the pulpotomized teeth were performed 3, 6, and 12 months after treatment. Data were tested by chi-squared analysis and a multiple comparison post-test.Results:The MTA group showed both clinical and radiographic treatment success in 14/14 teeth (100%), at all follow-up appointments. By clinical evaluation, no teeth in the CH+saline and CH+PEG groups had signs of mobility, fistula, swelling or inflammation of the surrounding gingival tissue. However, in the CH+saline group, radiographic analysis detected internal resorption in up to 9/15 teeth (67%), and inter-radicular bone resorption and furcation radiolucency in up to 5/15 teeth (36%), from 3 to 12 months of follow-up. In the CH+PEG group, 2/11 teeth (18%) had internal resorption and 1/11 teeth (9%) presented bone resorption and furcation radiolucency at all follow-up appointments.Conclusion:CH with PEG performed better than CH with saline as capping material for pulpotomy of primary teeth. However, both combinations yielded clinical and radiographic results inferior to those of MTA alone.

Behavior of Sulfide Ore Elements in the Oxidation of Concentration Tailings under Cryogenic Conditions (Dalnegorsk District, Far East)

Oxidation processes in the sulfide component of the concentration located in the Dalnegorsk district were modeled in the range from–25 to 0°C. The modeling showed crystallization of the following minerals from the model solutions: hypergene Fe, Cu, Pb, Zn, Al, Mg, and Ca sulfate, arsenate, silicate, oxide, and hydroxide minerals at the tailing dumps of the Central concentrating mill and hypergene Fe, Pb, Sb, and Ca sulfate, carbonate, oxide, and hydroxide minerals at the tailing dumps of the Krasnorechensk concentrating mill. The concentrations of sulfide ore elements in the solution in the negative temperature range are much higher compared to those at positive temperatures. This takes place, because the most part of the solution passes to the solid phase (ice), and the volume of the liquid phase decreases. As a result, the hydrosphere of the district is experiencing severe anthropogenic impact from the elements of sulfide ores (S, Zn, Cu, Pb, Fe, Ag, As, and Sb) and their host rocks (Mg, K, Na, Ca, Si and Al).

Iron- and aluminium-induced depletion of molybdenum in acidic environments impedes the nitrogen cycle.

Anthropogenic nitrate contamination is a serious problem in many natural environments. Nitrate removal by microbial action is dependent on the metal molybdenum (Mo), which is required by nitrate reductase for denitrification and dissimilatory nitrate reduction to ammonium. The soluble form of Mo, molybdate (MoO4 2- ), is incorporated into and adsorbed by iron (Fe) and aluminium (Al) (oxy) hydroxide minerals. Herein we used Oak Ridge Reservation (ORR) as a model nitrate-contaminated acidic environment to investigate whether the formation of Fe- and Al-precipitates could impede microbial nitrate removal by depleting Mo. We demonstrate that Fe and Al mineral formation that occurs as the pH of acidic synthetic groundwater is increased, decreases soluble Mo to low picomolar concentrations, a process proposed to mimic environmental diffusion of acidic contaminated groundwater. Analysis of ORR sediments revealed recalcitrant Mo in the contaminated core that co-occurred with Fe and Al, consistent with Mo scavenging by Fe/Al precipitates. Nitrate removal by ORR isolate Pseudomonas fluorescens N2A2 is virtually abolished by Fe/Al precipitate-induced Mo depletion. The depletion of naturally occurring Mo in nitrate- and Fe/Al-contaminated acidic environments like ORR or acid mine drainage sites has the potential to impede microbial-based nitrate reduction thereby extending the duration of nitrate in the environment.

Comment on “Application of Analytical Diffusion Models to Outcrop Observations: Implications for Mass Transport by Fluid Flow Through Fractures” by Antonellini et al. (2017)

AbstractAntonellini et al. (2017, https://doi.org/10.1002/2016WR019864) presented a detailed analysis of alteration halos observed in outcrops of a fractured rock system. We point out here the need for a critical discussion on the low value of dissolved oxygen concentration used in the boundary water of their analytical models. Moreover, we argue that the model used by Antonellini et al. (2017) to evaluate the time for fracture filling is not consistent with the hypotheses used by the same authors to analyze the alteration halos. We propose here an alternative explanation along with an alternative model for fracture filling by precipitation of hydroxide minerals. Unlike the model used by Antonellini et al. (2017), in the model presented here, the time for fracture filling, defined as the time when the relative fracture aperture is equal to a given minimum threshold, does not depend on the initial fracture aperture.

Biological Characteristics and Concentrations of Extractable Fe, Al, and Si Compounds in Spruce Rhizosphere in Podzolic Soil

Some biological properties and concentrations of extractable Fe, Al, and Si compounds in the samples of the AOEL horizon of podzolic soil taken in five replicates from the rhizosphere of 15- to 20-year-old spruce and from the nonrhizosphere soil are discussed. The soil mass of the rhizosphere is characterized by a significantly higher total number of bacteria, more abundant and diverse saprotrophic bacterial complex, greater length of fungal mycelium, and higher content of benzenecarboxylic acids dominated by benzoic acid in comparison with the nonrhizosphere soil. The soil mass of the rhizosphere and the fraction of 1–5 µm isolated from it are also characterized by significantly higher concentrations of Fe and Al extracted by the Tamm and Bascomb reagents because of the accumulation of Fe-organic and Al-organic complexes. For extractable Al compounds in the rhizosphere, this finding is confirmed by the high coefficient of correlation between the amount of Al in the extracts and the Corg content in the bulk soil mass and in the fraction 1–5 µm. Such a correlation is absent in the nonrhizosphere soil. The content of iron compounds extracted by the Mehra–Jackson reagent from the rhizosphere and nonrhizosphere soils is significantly higher than that extracted by the Tamm and Bascomb reagents; in the nonrhizosphere samples, it is significantly higher than in the rhizosphere. This difference can be explained by the fact that the content of Fe oxides and hydroxides minerals decreased in the soil mass of the rhizosphere due to more active dissolution processes under the conditions of more acid medium and higher concentration of organic ligands, so that the mobilized Fe enters Fe–organic complexes.

Hydrotalcites and hydrated Mg-carbonates as carbon sinks in serpentinite mineral wastes from the Woodsreef chrysotile mine, New South Wales, Australia: Controls on carbonate mineralogy and efficiency of CO2 air capture in mine tailings

Carbon mineralisation of ultramafic mine tailings can reduce net emissions of anthropogenic carbon dioxide by reacting Mg-silicate and hydroxide minerals with atmospheric CO2 to produce carbonate minerals. We investigate the controls on carbonate mineral formation at the derelict Woodsreef chrysotile mine (New South Wales, Australia). Quantitative XRD was used to understand how mineralogy changes with depth into the tailings pile, and shows that hydromagnesite [Mg5(CO3)4(OH)2·4H2O], is present in shallow tailings material (<40 cm), while coalingite [Mg10Fe3+2(CO3)(OH)24·2H2O] and pyroaurite [Mg6Fe3+2(CO3)(OH)16·4H2O] are forming deeper in the tailings material. This indicates that there may be two geochemical environments within the upper ∼1 m of the tailings, with hydromagnesite forming within the shallow tailings via carbonation of brucite in CO2-rich conditions, and pyroaurite and coalingite forming under more carbon limited conditions at depth. Radiogenic isotope results indicate hydromagnesite and pyroaurite have a modern (F14C > 0.8) atmospheric CO2 source. Laboratory-based anion exchange experiments, conducted to explore stable C isotope fractionation in pyroaurite, shows that pyroaurite δ13C values change with carbon availability, and 13C-depleted signatures are typical of hydrotalcites in C-limited environments, such as the deep tailings at Woodsreef. Quantitative XRD and elemental C data estimates that Woodsreef absorbs between of 229.0–405.1 g CO2 m−2 y−1.

Phosphorus recovery through adsorption by layered double hydroxide nano-composites and transfer into a struvite-like fertilizer

Phosphorus (P) recovery from waste streams is attracting more attention due to the twin problems of aquatic eutrophication and global phosphorus scarcity. Layered double hydroxide mineral materials are promising phosphate adsorbents due to their excellent anion-exchange abilities and large surface area. In this study, the adsorption isotherms estimated the saturation capacity of calcined layered double hydroxide (LDH) nano-composites for phosphate as 100.7 mg-P/g-adsorbent. Ion exchange is proposed as the major mechanism in the sorption process. The commonly utilized desorption method via sodium hydroxide was found to cause recrystallization of LDH particles in increased crystal size based on the dissolution-reprecipitation (D-R) mechanism. Ammonia solution was used to desorb P from LDH adsorbent. However, struvite crystallization occurred during the desorption process because struvite has a higher precipitation tendency than LDH with sufficient NH4+ ions. The comparison of P leaching behavior among P-adsorbed LDH, ammonia-treated LDH, and pure struvite samples demonstrates that ammonia desorption probably weakened the interaction between phosphate species and LDH cationic layers, thus enhancing the bioavailability of P in LDH adsorbents. The ammonia-treated LDH has a high potential to serve like struvite as a P slow-releasing fertilizer.

The interfacial reactivity of arsenic species with green rust sulfate (GRSO4)

Arsenic (As) contamination in groundwater is a significant health and environmental concern worldwide because of its wide distribution and toxicity. The fate and mobility of As is greatly influenced by its interaction with redox-active mineral phases, among which green rust (GR), an FeII-FeIII layered double hydroxide mineral, plays a crucial role. However, the controlling parameters of As uptake by GR are not yet fully understood. To fill this gap, we determined the interfacial reactions between GR sulfate (GRSO4) and aqueous inorganic As(III) and As(V) through batch adsorption experiments, under environmentally-relevant groundwater conditions. Our data showed that, under anoxic conditions, GRSO4 is a stable and effective mineral adsorbent for the removal of As(III) and As(V). At an initial concentration of 10 mg L−1, As(III) removal was higher at alkaline pH conditions (~95% removal at pH 9) while As(V) was more efficiently removed at near-neutral conditions (>99% at pH 7). The calculated maximum As adsorption capacities on GRSO4 were 160 mg g−1 (pH 8–9) for As(III) and 105 mg g−1 (pH 7) for As(V). The presence of other common groundwater ions such as Mg2+ and PO43− reduces the efficiency of As removal, especially at high ionic strengths. Long-term batch adsorption experiments (up to 90 days) revealed that As-interacted GRSO4 remained stable, with no mineral transformation or release of adsorbed As species. Overall, our work shows that GRSO4 is one of the most effective As adsorbents among iron (oxyhydr)oxide phases.