Formation Of Secondary Minerals Research Articles

Filling the gaps of uranium oxide hydrates with magnesium(II) ions: unique layered structures and the role of additional sodium(I) ions.

Alkaline earth metal ions play an important role in the formation of secondary uranium minerals due to their abundance in the Earth's crust. Although uranium oxide hydrate (UOH) minerals and synthetic phases with calcium, strontium and barium ions have been investigated, their counterparts with magnesium ions are much less studied. In this work, synthetic UOH materials with magnesium ions have been investigated with three new compounds being synthesised and characterised. Compound Mg2(H3O)2(H2O)6[(UO2)3O4(OH)]2 (U-Mg1 with a U : Mg ratio of 3 : 1) crystallises in the monoclinic P21/c space group having a layered crystal structure, constructed by β-U3O8 layers with 6-fold coordinated Mg2+ ions as interlayer cations. Compound Na2Mg(H2O)4[(UO2)3O3(OH)2]2 (U-Mg2p with U : Mg : Na ratios of 6 : 1 : 2) crystallises in the triclinic P1̄ space group having a layered structure, constructed by a unique type of uranium oxide hydroxide layer containing both α-U3O8 and β-U3O8 features, with alternating layers of 6-fold coordinated Mg2+ and 6-/8-fold coordinated Na+ interlayer cations. Compound Na2Mg(H2O)4[(UO2)4O3(OH)4]2 (U-Mg2n with U : Mg : Na ratios of 8 : 1 : 2) crystallises in the triclinic P1̄ space group having a corrugated layer structure, constructed by a unique type of uranium oxide hydroxide layer with mixed 6-fold coordinated Mg2+ and 7-fold coordinated Na+ interlayer cations. The structural diversity in the UOH-Mg system was achieved by adjusting the solution pH using NaOH, highlighting the importance of solution pH control and the additional Na+ ions in the formation of UOH phases. The extra structural flexibility offered by the Na+ ions emphasizes the opportunity for synthesising UOHs with dual-cations to further improve our understanding of the alteration products of spent nuclear fuel under geological disposal.

Anaerobic syntrophic system composed of phosphate solubilizing bacteria and dissimilatory iron reducing bacteria induces cadmium immobilization via secondary mineralization

Secondary mineralization is a promising method for remediating cadmium (Cd) pollution in sediments, but the poor stability of Cd-containing secondary minerals is a bottleneck that limits the development of this approach. The existence of phosphate can enhance the formation of stable secondary minerals and points a new direction for Cd immobilization. In this research, a novel syntrophic system composed of phosphate solubilizing bacteria (PSB) and dissimilatory iron reducing bacteria (DIRB) was established and the effect and mechanism of Cd immobilization in the system were also explored. The results showed that under the conditions of DIRB:PSB (V:V)= 3:1, syntrophic bacteria dosage of 5% and glucose dosage of 5 g/L, Cd incorporated in the secondary minerals could account for about 60% of the total Cd. In the pH range of 5–9, alkaline environment was conducive to the immobilization of Cd and the percentage of combined Cd was up to 58%, while the combined Cd in secondary minerals decreased from 62% to 56% with the increase of initial Cd concentration from 0.1 to 0.3 mmol/L. In addition, XRD, XPS, Mössbauer and other characterization results showed that secondary minerals, such as Cd exchange hydroxyapatite (Cd-HAP) and kryzhanovskite (Fe3(PO4)2(OH)3) were formed in this new system. The established syntrophic system of PSB and DIRB is thus a prospective bioremediation technology for Cd immobilization in sediments and can avoid the potential risk might be caused by the addition of phosphorus-containing materials.

Mineral carbonation of New Caledonian ultramafic mine slag: Effect of glass and secondary silicates on the carbonation yield

New Caledonian nickel (Ni) mines produces ∼12 million metric tons of mine slag every year, that are considered undesired and uneconomic waste materials. However, due to the high content of Mg2+ and Fe2+, these slags exhibit a potential of carbon dioxide (CO2) storage by ex-situ aqueous mineral carbonation. We conducted laboratory batch experiments at 200 °C/ 150 bar, 250 °C/ 300 bar, 300 °C/ 300 bar, in CO2-saturated water to better understand the slag dissolution, secondary mineral formation at the fluid-mineral interface, and the effect of the secondary silicates on the carbonation yield. The slag contains olivine (45 wt%) and glass (55 wt%). Olivine in the slag dissolves faster than glass, contributing to carbonate precipitation (Fe-rich magnesite) at 200 °C/150 bar. At 250 °C/ 300 bar, olivine is almost completely dissolved while glass dissolves only partially, both contributing to the highest recorded carbonation yields of the slag of 44 wt%. Although both olivine and glass are completely dissolved at 300 °C/ 300 bar, the carbonate yield drops at a value half of that at 250 °C/ 300 bar. This is due to formation of large quantity of Mg-bearing phyllosilicates that reduces the amount of Mg2+ available for carbonation. These results emphasize that increasing temperature above 250 °C would not increase the carbonate yield of New Caledonian mine slags. However, as glass only partially reacts at T < 250 °C, mobilizing Mg2+ in glass could potentially increase the carbonation yield, for example by adding suitable organic ligands. Mg-bearing phyllosilicates and amorphous silica that are formed in these experiments do not exhibit passivation properties, and therefore do not affect the carbonation rate.

Microanalytical Investigation of Prehistoric Colorants from Uralian Rock Art (Ignatievskaya Cave and Idrisovskaya II and Zmiev Kamen’ Pictographs)

Uralian parietal and rock art (cave paintings and pictographs, or “pisanitsy”) represents a unique archaeological and cultural phenomenon, comprising 90 sites stretching for more than 800 km from north to south, which date from the Paleolithic era extending into the present Holocene epoch. The identification of the nature of prehistoric colorants provides an insight into their provenance, manufacture and utilization, as well as contributing to the conservation and restoration of drawings. The studies of mineral, elemental and organic phase composition of the colorant micro-samples from the drawings of Ignatievskaya cave and Idrisovskaya II and Zmiev Kamen’ pictographs (Southern and Middle Urals, Russia) discussed in the present work were carried out using a special set of microspectroscopic methods (SEM-EDS and Raman spectroscopy) offering high spatial resolution. The fatty acid composition of the organic phase was analyzed by GC–MS. The technology of colorant manufacture could have included thorough grinding and mixing of unheated hematite with an organic binder made from animal fat and a clayey extender in order to achieve the desired hue and intensity of the color. It is possible that the colorant was applied in layers (Idrisovskaya II and Zmiev Kamen’ pictographs). The development of authigenic phosphate and sulfate (gypsum) mineralization, which is observed in all studied sites, as well as oxalate encrustation on the Idrisovskaya II pictograph, indicates the conditions and processes of secondary mineral formation.

Rare-earth elements in salt lakes of Southeastern Transbaikalia

It was shown that with increasing salinity of waters, it was determined that concentrations of dissolved heavy HREEs and medium MREEs increase in soda lakes. It was determined that sulfatreduction and secondary mineral formation can influence the migration of lanthanides in lakes. Sulfatreduction leads to accumulation of lanthanides of medium MREEs and heavy HREEs subgroups in lake waters. The content of lanthanides of the light LREE subgroup is controlled mainly by secondary mineral formation. Thermodynamic calculations show that the degree of saturation in parasite CaCe0.95La0.6Nd0.35Pr0.1(CO3)3F2 and bastnesite CeCO3(OH)F is higher in soda lakes than in chloride lakes. The saturation of lake waters with respect to cerium hydroxide III in anaerobic and cerium hydroxide IV in aerobic conditions leads to the formation of negative cerium anomaly in lake waters of the considered lake types. It is shown that the different nature of the formation of soda and chloride lakes is the main reason for different concentrations of REEs in their waters and bottom sediments.

Microbially influenced tungsten mobilization and formation of secondary minerals in wolframite tailings

Wolframite [(Fe,Mn)WO4] tailings represent a hazardous waste that can pose a threat to the environment, humans, animals and plants. The present study aims to conduct a high-resolution depth profile characterization of wolframite tailings from Wolfram Camp, North Queensland, Australia, to understand the biogeochemical influences on W mobilization. Several indigenous Fe- and S-oxidizing bacteria (e.g., Streptococcus pneumoniae and Thiomonas delicata) in wolframite tailings were found highly associated with W, As, and rare earth elements. Biooxidation of metal sulfides, i.e., pyrite, molybdenite and bismuthinite, produced sulfuric acid, which accelerated the weathering of wolframite, mobilizing tungstate (WO42-). Using synchrotron-based X-ray fluorescence microscopy (XFM) and W L-edge X-ray absorption near-edge spectroscopy (µ-XANES) analysis, wolframite was initially transformed into Na- and Bi- tungstate as well as tungstic acid (partial weathering) followed by the formation of Ga- and Zn- tungstate after extensive weathering, i.e., the wolframite had disappeared. While W (VI) was the major W species in wolframite tailings, minor W(0) and W(II), and trace W(IV) were also detected. The major contaminant in the Wolfram Camp tailings was As. Though wolframite tailings are hazardous waste, the toxicity of W was unclear. Tungsten waste still has industrial value; apart from using them as substitution material for cement and glass production, there is interest in reprocessing W waste for valuable metal recovery. If the environmental benefits are taken into consideration, i.e., preventing the release of toxic metals into surrounding waterways, reprocessing may be economic.

Effects of Water–Rock Interaction on the Permeability of the Near-Well Reservoir in an Enhanced Geothermal System

During the operation of an enhanced geothermal system (EGS), the non-equilibrium temperature, pressure, and hydrochemistry caused by fluid injection intensify water–rock interactions, induce the mineral dissolution and precipitation in the reservoir near an injection well (also referred to as the near-well reservoir), and change reservoir permeability, thus affecting continuous and efficient geothermal exploitation. Based on the investigation of the M-1 injection well of the EGS in the Matouying uplift of Hebei Province, China, a THC reactive solute transport model using the TOUGHREACT program was established in this study to explore the mineral dissolution and precipitation laws of the near-well reservoir and their influencing mechanisms on the reservoir porosity and permeability in the long-term fluid injection of this well. As indicated by the results, the dissolution of primary feldspar and chlorite and the precipitation of secondary minerals (mainly dolomite and illite) occurred and water–rock interaction significantly reduced the porosity and permeability of the near-well reservoir in the long-term continuous injection process. Appropriate reduction in the injection flow rate, injection temperature, and the Mg2+ and K+ contents in the injected water can help inhibit the formation of secondary minerals and delay the plugging process of the near-well reservoir.

Metagenomic Influential Insights in the Formation of Biogenic Iron Hydroxysulfate Precipitates by Ferrous Oxidative Microbial Consortia

The formation of iron hydroxysulfate precipitated minerals by microbial bioleaching is an undesired dominant process because it decreases the solubilization efficiency of targeted metals. To date, the microbial role in forming these precipitated minerals is unclear. Herein, we compared two microbial community diversity (consortia M1-18 and M8-15) with the distinct formation of secondary iron minerals. In the case of M1-18, a 16S rRNA metagenomic analysis revealed a higher microbial diversity and a prevalence of Ferrimicrobium and Acidimicrobiacea. This consortium also showed a slightly higher oxidation capacity and a remarkably higher particulate precipitate capacity of secondary minerals. In contrast, the consortium M8-15 showed lower diversity and poor precipitate capacity. XRD, EDS, and FE-SEM analysis of secondary iron minerals showed that the microbial consortia promote the mineralogical formation of the secondary iron precipitates in the form of schwertmannite, an early metastable phase that can be easily transformed to jarosite.

Mixed-Layer Illite-Smectite Illitization under Supercritical CO2 Conditions

The long-term safe storage of CO2 in geological reservoirs requires the understanding of the impact of CO2 on clay-rich sealing cap rocks. The reactivity of the mixed layer of illite-smectite was investigated to determine the reaction pathways under conditions of supercritical CO2 (scCO2) conditions in the context of geological CO2 storage. A common clay (blue marl from the Guadalquivir Tertiary basin, southern Spain) was tested under brine scCO2 conditions (100 bar and 35 °C) for 120 and 240 h. The clay sample (blue marl) contains calcite, quartz, illite, smectite, and the corresponding mixed-layer and kaolinite. X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and inductively coupled plasma optical emission spectroscopy (ICP-OES) analyses were performed. The illitization of mixed-layer illite-smectite was observed by XRD and confirmed by a variation in the content of different elements (K, Mg, Na, Ca, and Fe) of the transformation, as well as an increase in the specific surface (SSA) of the clay (36.1 to 38.1 m2/g by N2, 14.5 to 15.4 m2/g by CO2 adsorption). Furthermore, these reactions lead to mineral dissolution and secondary mineral formation along the CO2–water–clay intercalations of the source rock were responsible for a change in porosity (7.8 to 7.0 nm pore size). The implications of illitisation, mineral destruction, and precipitation processes on CO2 storage and clay layer integrity should be explored before deciding on a geological storage location.

Experimental insights into the formation of secondary minerals in acid mine drainage-polluted karst rivers and their effects on element migration

Acid mine drainage (AMD) threatens the water quality and safety of karst river water (KRW), and the formation of secondary iron or aluminum-bearing minerals during the mixing of AMD with KRW plays a crucial role in the migration of elements. However, the variations in the mineralogical, morphological and elemental compositions of secondary minerals and their influences on the migration of elements during AMD–KRW mixing have not been systematically studied. In this study, we mixed different proportions of AMD and KRW in a laboratory experiment to simulate seasonal hydrological conditions in a river to understand the major and trace elemental distributions in the mixed water and in precipitates and we discuss the formation process for the secondary minerals. The results showed that AMD can lead to a decrease in pH and DO and an increase in heavy metals and rare earth elements (REEs) in KRW. With the biological or chemical oxidation of Fe2+, Fe3+ combines with SO42− to form schwertmannite or hydrolyzes to form Fe(OH)3(s) and FeOOH(s), accompanied by the formation of amorphous Al hydroxide, resulting in a decrease in pH and an increase in Eh. Schwertmannite had strong adsorption and coprecipitation effects on Mn, Cr, Cu and As, so the adsorption and coprecipitation effects of schwertmannite on REEs were inhibited, while the migration of REEs were mainly affected by Al hydroxides. Therefore, after the AMD mixes with KRW, it not only causes severe water and sediment pollution but also adsorbs and enriches high concentrations of heavy metals in the secondary minerals formed during the mixing process, creating a major ecological hazard that requires further attention.

Geochemical behavior of stable strontium isotopes during continental weathering process: A review

Continental weathering, an important geological process that affects the formation and evolution of the earth, involves the interaction of matter and energy among the lithosphere, atmosphere, hydrosphere, and biosphere. Stable Sr isotope (δ88/86Sr) is a novel non-traditional stable isotope. It has been widely discussed in tracing continental weathering, studying marine Sr cycle, and analyzing biogeochemical behavior in recent years. Its combination with 87Sr/86Sr can indicate the source of Sr and the mass fractionation of geological processes, which has incomparable advantages over other isotopic systems, such as Li, Mg, and Ba. However, owing to the small mass difference (2%) between 86Sr and 88Sr, fractionation is not significant, which makes the measurement of the ratio δ88/86Sr difficult and limits its application to trace continental weathering.In this study, major developments and challenges in using stable Sr isotopes to trace continental weathering are reviewed, when considering high-precision testing methods, characteristics of δ88/86Sr in natural reservoirs, and geochemical behaviors. The high-precision measurement methods currently used for stable Sr isotopes mainly include multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) and thermal ionization mass spectrometry (TIMS), both of which involve chemical purification by a cation exchange column or Sr specific resin, coupled with various methods for quality discrimination correction. The present analytical precision for the determination of δ88/86Sr in geological samples is 0.02‰ ∼ 0.08‰. The δ88/86Sr varies widely in natural reservoirs. In particular, the range of δ88/86Sr values in extraterrestrial reservoirs, the biosphere, the lithosphere, and the hydrosphere are -1.73‰ to +0.66‰, -0.87‰ to +0.85‰, -0.20‰ to +0.53‰ and -0.45‰ to +0.66‰, respectively. Stable Sr isotope fractionation occurs in the processes of differential dissolution of primary minerals (Δ88/86Sr = -0.13‰), formation and adsorption of secondary minerals (Δ88/86Sr = -0.15‰), precipitation of carbonate (Δ88/86Sr = -0.20‰), and biological processes (Δ88/86Sr = -0.15‰), which causes the δ88/86Sr in fluid (solid) phase to δ88/86Sr increases (decrease). Previous research on the fractionation mechanisms and constraint conditions of stable Sr isotopes during continental weathering is insufficient. Thus, promoting a wide application of stable Sr isotopes to trace continental weathering through the combination of field profiles, laboratory experiments and theoretical calculation is urgently warranted.

Hydrogen isotope behavior during rhyolite glass hydration under hydrothermal conditions

The diffusion of molecular water (H2Om) from the environment into volcanic glass can hydrate the glass up to several wt% at low temperature over long timescales. During this process, the water imprints its hydrogen isotope composition (δDH2O) to the glass (δDgl) offset by a glass-H2O fractionation factor (ΔDgl-H2O = δDgl – δDH2O) which is approximately −33‰ at Earth surface temperatures. Glasses hydrate much more rapidly at higher, sub-magmatic temperatures as they interact with H2O during eruption, transport, and emplacement. To aid in the interpretation of δDgl in natural samples, we present hydrogen isotope results from vapor hydration experiments conducted at 175–375 °C for durations of hours to months using natural volcanic glasses. The results can be divided into two thermal regimes: above 250 °C and below 250 °C. Lower temperature experiments yield raw ΔDgl-H2O values in the range of −33 ± 11‰. Experiments at 225 °C using both positive and negative initial ΔDgl-H2O values converge on this range of values, suggesting this range represents the approximate equilibrium fractionation for H isotopes between glass and H2O vapor (103lnαgl-H2O) below 250 °C. Variation in ΔDgl-H2O (−33 ± 11‰) between different experiments and glasses may arise from incomplete hydration, analytical uncertainty, differences in glass chemistry, and/or subordinate kinetic isotope effects. Experiments above 250 °C yield unexpectedly low δDgl values with ΔDgl-H2O values of ≤–85‰. While alteration alone is incapable of explaining the data, these run products have more extensive surface alteration and are not interpreted to reflect equilibrium fractionation between glass and H2O vapor. Fourier transform infrared spectroscopy (FTIR) shows that glass can hydrate with as much as 5.9 wt% H2Om and 1.0 wt% hydroxl (OH−) in the highest P-T experiment at 375 °C and 21.1 MPa. Therefore, we employ a 1D isotope diffusion–reaction model of glass hydration to evaluate the roles of equilibrium fractionation, isotope diffusion, water speciation reactions internal to the glass, and changing boundary conditions (e.g. alteration and dissolution). At lower temperatures, the best fitting model results to experimental data for low silica rhyolite (LSR) glasses require only an equilibrium fractionation factor and yield 103lnαgl-H2O values of −33‰ ± 5‰ and −25‰ ± 5‰ at 175 °C and 225 °C, respectively. At higher temperatures, ΔDgl-H2O is dominated by boundary layer effects during glass hydration and glass surface alteration. The modeled bulk δDgl value is highly responsive to changes in the δDgl boundary condition regardless of the magnitude of other kinetic effects. Observed glass dissolution and surficial secondary mineral formation are likely to impose a disequilibrium boundary layer that drives extreme δDgl fractionation with progressive glass hydration. These results indicate that the observed ΔDgl-H2O of ∼−33 ± 11‰ can be cautiously applied as an equilibrium 103lnαgl-H2O value to natural silicic glasses hydrated below 250 °C to identify hydration sources. This approximate ΔDgl-H2O may be applicable to even higher temperature glasses hydrated on short timescales (of seconds to minutes) in phreatomagmatic or submarine eruptions before H2O in the glass is primarily affected by boundary layer effects associated with alteration on the glass surface.

Secondary Mineral Formation and Carbon Dynamics during FeS Oxidation in the Presence of Dissolved Organic Matter.

Iron (Fe) minerals constitute a major control on organic carbon (OC) storage in soils and sediments. While previous research has mainly targeted Fe (oxyhydr)oxides, the impact of Fe sulfides and their subsequent oxidation on OC dynamics remains unresolved in redox-fluctuating environments. Here, we investigated the impact of dissolved organic matter (DOM) on FeS oxidation and how FeS and its oxidation may alter the retention and nature of DOM. After the anoxic reaction of DOM with FeS, FeS preferentially removed high-molecular-weight and nitrogen-rich compounds and promoted the formation of aqueous sulfurized organic molecules, according to Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR-MS) analysis. When exposed to O2, FeS oxidized to nanocrystalline lepidocrocite and additional aqueous sulfurized organic compounds were generated. The presence of DOM decreased the particle size of the resulting nano-lepidocrocite based on Mössbauer spectroscopy. Following FeS oxidation, most solid-phase OC remained associated with the newly formed lepidocrocite via a monodentate chelating mechanism (based on FTIR analysis), and FeS oxidation caused only a slight increase in the solubilization of solid-phase OC. Collectively, this work highlights the under-appreciated role of Fe sulfides and their oxidation in driving OC transformation and preservation.

Simultaneous removal of COD and NH4+-N from domestic sewage by a single-stage up-flow anaerobic biological filter based on Feammox

In recent years, Feammox has made it possible to remove NH4+-N under anaerobic conditions; however, its application in practical wastewater treatment processes has not been extensively reported. In this study, an up-flow anaerobic biological filter based on limonite (Lim-UAF) was developed to facilitate long-term and stable treatment of domestic sewage. Lim-UAF achieved the highest removal efficiency of chemical oxygen demand (COD) and NH4+-N at a hydraulic retention time (HRT) of 24 h (Stage II). Specifically, the COD and NH4+-N content decreased from 240.8 and 30.0 mg/L to about 7.5 and 0.35 mg/L, respectively. To analyze the potential nitrogen removal mechanism, the Lim-UAF was divided into three layers according to the height of the reactor. The results showed that COD and NH4+-N removal had remarkable characteristics in Lim-UAF. More than 55.0% of influent COD was removed in the lower layer (0–30 cm) of Lim-UAF, while 60.2% of NH4+-N was removed in the middle layer (30–60 cm). Microbial community analysis showed that the community structure in the middle and upper layers (60–90 cm) was relatively similar, but quite different from that of the lower layer. Heterotrophic bacteria were dominant in the lower layer, whereas iron-reducing and iron-oxidizing bacteria were enriched in the upper and middle layers. The formation of secondary minerals (siderite and Fe(OH)3) indicated that the Fe(III)/Fe(II) redox cycle occurred in Lim-UAF, which was triggered by the Feammox and NDFO processes. In summary, limonite was used to develop a single-stage wastewater treatment process for simultaneously removing organic matter and NH4+-N, which has excellent application prospects in domestic sewage treatment.

Investigation of the Ni-rich regolith in Bavanat region, Fars province, Iran: Constraints from mineralogy, geochemistry and Ni isotopes

A nickel-rich regolith outcrops discontinuously in varying thickness between the Sedimentary Zagros Orogenic (SZO) and Metamorphic Sanandaj-Sirjan (MSS) belts in Fars province, southwest Iran. It is the only known Ni-bearing regolith in the country. The laterites occur as residual and transported regolith in the Bavanat region. Profiles of the residual regolith from bottom to top include protolith, hard and soft saprolite, and oxide horizon. The parent rock is a highly serpentinized harzburgite containing relicts of olivine and orthopyroxene. From the hard saprolite to the oxide horizon, the proportions of hematite, goethite, talc, dolomite, and quartz increase, while chlorite, olivine, serpentine, and pyroxene decrease. Hematite and goethite are the dominant mineral phases in the oxide horizon. Part of the profile of transported regolith, especially oxide horizon has moved downslope due to landslide, slip, creep, and likely faulting. The Ni concentration varies gradually along the laterite profiles, with a maximum grade of 1.2 wt% in the oxide horizon. SEM-EDS data show that Ni released from serpentine group minerals in the parent rock was concentrated in the hematite of the oxide horizon. The isotopic fractionation of Ni along the soil profiles is controlled by the circulation of meteoric water and the intensity of weathering with formation of secondary minerals.

Bioleaching of metal(loid)s from sulfidic mine tailings and waste rock from the Neves Corvo mine, Portugal, by an acidophilic consortium

Sulfidic mine waste usually contains elevated amounts of valuable and hazardous metal(loid)s, which may pose environmental risks but can also provide opportunities for resource recovery. Reprocessing of mine waste can offer both economic and environmental benefits by supplying some of the ever-growing global demand for valuable metals, as well as reducing environmental risks. The present study aimed to simultaneously recover both valuable and hazardous metal(loid)s from two sulfidic mine waste samples (waste rock (NC_01) and tailings (NC_02)) from the Neves Corvo mine, Portugal, using a novel acidophilic consortium dominated by iron-oxidizing Leptospirillum genus and Acidiphilium sp. Bioleaching results showed that over 70% of the total Zn, Co, In, As, and Cd contents of NC_01 and NC_02 were leached within 21 days, while 55%–62% Mn was leached. Copper behaved in a refractory manner, as only 33% and 21% Cu were leached from NC_01 and NC_02, respectively. X-ray diffraction (XRD) and Scanning electron microscope-based automated image analyses (SEM/MLA-GXMAP) of the bioleached residues revealed an almost complete absence of residual pyrite in NC_01 and a reduction of pyrite in NC-02, as well as the formation of secondary minerals, especially jarosite. In most cases, the biogenic jarosite co-precipitated some of the leached elements again, e.g., Cu and Pb. In conclusion, a synchronized method for bioleaching valuable and hazardous metal(loid)s was developed using a novel acidophilic consortium, thereby demonstrating the potential for the generation of economic value and environmental risk reduction for sulfidic mine waste samples.

Activation of persulfate via Mn doped Mg/Al layered double hydroxide for effective degradation of organics: Insights from chemical and structural variability of catalyst.

Considerable interest has been focusing on the activation of peroxydisulfate (PDS) by layered double hydroxide (LDH) for degradation of organic pollutants. However, understanding the structure and chemistry of LDH by which the activation of PDS could achieve a high degradation efficiency of organic compounds is an unsolved and fundamental question in advanced oxidation processes (AOPs), and one which, if harnessed, could enable the rational design of LDH with desired material properties. In this work, Mg/Al-LDH was synthesized with variable structures and compositions through doping different proportions of Mn2+. We advanced to understand this question of how LDH by these characteristics can affect the activation of PDS for degradation of organic pollutants. At a relatively low dosage of Mn (˂ 1%) in Mg/Al-LDH, the degradation rate of phenol by LDH activated PDS increased with the increase content of Mn, which was achieved by an increase of catalytic sites in Mg/Al-LDH interlayer. Rather, higher content of Mn (˃ 1%) significantly lowered the degradation performance of phenol as the decrease of interlayer space resulted in reduction of PDS intercalation in LDH and the formation of secondary Mn-related minerals (i.e., Mn3O4) led to meaningless consumption of PDS. Finally, the degradation of phenol by LDH activated PDS followed a non-radical (1O2) mechanism. Our ability to quantify how the chemical and structural variability of LDH influence the activation of PDS for organic degradation could mark an important step toward synthesis strategies for advanced catalysts.

Hydration products and microstructural properties analysis of magnesium phosphate cement comprising with industrial residues

Cavities, micro-cracks and micro-pores are formed in the microstructures of magnesium phosphate cement (MPC) due to the rapid hydration process. For increasing the structural solidity, formation of secondary minerals is necessary through filling the micro-cracks and micro-pores. In addition, existence of optimum level of intermediate crystals increases the microstructural density as well as strength performance of MPC compounds. To attain the high-quality microstructures of MPC for water stability, present study added four different pozzolanic properties based industrial by products namely fly ash (FA), silica fume (SF), bauxite (BX) and phosphogypsum (PG) were introduced by means of their optimum dosages. The 1d aged SEM micrographs with high magnifications shown that free particles of magnesia and phosphate salts reacted with the used all supplementary cementitious materials and formed huge secondary crystals. In addition, presence of intermediate crystals was detected by EDS and X-ray diffraction tests in the powder specimens at 1d age, which are Enstatite, Mullite, Lizardite, Berlinite, kaolinite, kyanite, CSH and ettringite. It has been noted from crystallinity analytical results that MPC specimens comprising with BX and PG including FA exposed the higher intermediate crystal amounts around 34.3% and 41.6% at 1d; 49% and 47.6% at 28d, respectively. In the similar way, amorphous contents were significantly reduced with the passages of hydration ages. Furthermore, all the nominated blends with SCMs unveiled the well heat resistance and lost structural water at higher temperature as compared to control mix. The outcomes of present research might be applicable to design MPC matrices for higher strength and water structures.

Acid generation potential and kinetics of metal(loid) release from resuspended sulfidic mine waste

Sulfidic mine waste exposed to oxidizing conditions can generate acidity and leach metal(loid)s into the environment, posing a risk to surrounding ecosystems. In the present study, four sulfidic mine waste samples were investigated using both kinetic and static experiments to determine the acid generation potential and mobilization of metal(loid)s. A long-term resuspension experiment of 821 days was performed to study the effect of oxidation on the acid generation and the release of metal(loid)s from the mine waste samples. The mineralogy of the mine waste after 821 days of oxidation was determined and compared with the original sample. A kinetic study of a pH-dependent leaching test was also performed to study the influence of time on metal(loid) release. Additionally, a static acid-base accounting test was used to gain more insight into the acid generation and neutralization potentials. The mineralogical study revealed the presence of sulfide minerals (e.g., pyrite, and sphalerite) both as free particles and embedded within other minerals (e.g., quartz). The mine waste samples exhibited a high acid generation potential, where the pH of all samples decreased to pH< 3 after 272 days. The resuspension of the mine wastes also resulted in a considerable release of As, Cd, Cu, and Zn (up to 4500, 100, 4000, and 11,500 mg/kg, respectively). However, Pb exhibited low leaching levels, due to the formation of secondary Pb-bearing minerals (i.e., beudantite and/or plumbojarosite). Overall, the samples pose an environmental risk based on the high acid generation potential and high release of metal(loid)s.

Culture-dependent and culture-independent methods reveal microbe-clay mineral interactions by dissimilatory iron-reducing bacteria in an integral oilfield

Fe(III) may be reasonably considered as one of the most important electron acceptors in petroleum reservoir ecosystems. The microbial mineralization of clay minerals, especially montmorillonite, is also of great significance to the exploration of petroleum and gas reservoirs. The bioreduction mechanisms of iron-poor minerals in petroleum reservoirs have been poorly investigated. This study investigated the bioreduction of montmorillonite by dissimilatory iron-reducing bacteria (DIRB) in petroleum reservoirs based on culture-independent and culture-dependent methods. Microbial diversity analysis revealed that Halolactibacillus, Bacillus, Alkaliphilus, Shewanella, Clostridium, and Pseudomonas were the key genera involved in the bioreduction of Fe(III). Through the traditional culture-dependent method, most of the key genera were isolated from the samples collected from petroleum reservoirs. Traditional culture-dependent methods can be used to reveal the metabolic characteristics of microorganisms (such as iron-reduction efficiency) to further elucidate the roles of different species (B. subtilis and B. alkalitelluris) in the environment. Moreover, many species with high iron-reduction efficiencies and relatively low abundances in the samples, such as Tessaracoccus and Flaviflexus, were isolated from petroleum reservoirs for the first time. The combination of culture-dependent and culture-independent methods can be used to further the understanding of the microbial communities and the metabolic characteristics of DIRB in petroleum reservoirs. Structural alterations that occurred during the interactions of microorganisms and montmorillonite were revealed through scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray powder diffraction (XRD). The physical and chemical analysis results demonstrated that microorganisms from petroleum reservoirs can dissolve iron-poor montmorillonite and promote the release of interlayer water. The secondary minerals illite and clinoptilolite were observed in bioreduced smectite. The formation of secondary minerals was closely related to the dissolution degrees of minerals based on iron reduction.