Biotite Dissolution Research Articles

The influence of metal cations on the dissolution and transformation of biotite

The influence of metal cations on the dissolution and transformation of biotite

A combination of physiology, metabolomics, and genetics reveals the two-component system ResS/ResR-mediated Fe and Al release from biotite by Pseudomonas pergaminensis F77

Understanding of the mechanisms on bacteria-regulated mineral dissolution functions is important for further insight into mineral-microbe interactions. The functions of the two-component system have been studied. However, the molecular mechanisms involved in bacterial two-component system-mediated mineral dissolution are poorly understood. Here, the two-component regulatory system ResS/ResR in the mineral-solubilizing bacterium Pseudomonas pergaminensis F77 was characterized for its involvement in biotite dissolution. Strain F77 and the F77ΔresS, F77ΔresR, and F77ΔresS/R mutants were constructed and compared for the ResS/ResR system-mediated Fe and Al release from biotite in the medium and the mechanisms involved. After 3 days of incubation, the F77ΔresS, F77ΔresR, and F77ΔresS/R mutants significantly decreased the Fe and Al concentrations in the medium compared with F77. The F77ΔresS/R mutant had a greater impact on Fe and Al release from biotite than did the F77ΔresS or F77ΔresR mutant. The F77∆resS/R mutant exhibited significantly reduced Fe and Al concentrations by 21–61 % between 12 h and 48 h of incubation compared with F77. Significantly increased pH values and decreased cell counts on the mineral surfaces were found in the presence of the F77∆resS/R mutant compared with those in the presence of F77 between 12 h and 48 h of incubation. Metabolomic analysis revealed that the extracellular metabolites associated with biotite dissolution were downregulated in the F77ΔresS/R mutant. These downregulated metabolites included GDP-fucose, 20-carboxyleukotriene B4, PGP (16:1(9Z)/16:0), 3′,5′-cyclic AMP, and a variety of acidic metabolites involved in carbohydrate, amino acid, and lipid metabolisms, glycan biosynthesis, and cellular community function. Furthermore, the expression levels of the genes involved in the production of these metabolites were downregulated in the F77ΔresS/R mutant compared with those in F77. Our findings suggested that the ResS/ResR system in F77 contributed to mineral dissolution by mediating the production of mineral-solubilizing related extracellular metabolites and bacterial adsorption on mineral surface.

Biotite dissolution kinetics at pH 4 and 6.5 under anaerobic conditions and the release of dissolved Fe(II)

Dissolution of biotite, the main Fe-bearing mineral in granitic bedrock, is of particular importance for the remediation of reducing conditions after the ingress of oxygen, such as after mining activities or the construction of deep repositories for toxic waste. This study investigated the leaching of biotite of size fraction 0.053–0.075 mm under anaerobic conditions at room temperature and pH 4 and 6.5 for a maximum of 160 days. The changes in the concentrations of the major elements in the leaching solutions were monitored. In addition, Fe(II) was analysed separately. pH-independent rate coefficients kH+ were 4.8∙10−10, 6.9∙10−10, 6.3∙10−11, and 1.0∙10−12 mol1-n m−2 s-1, for Fe, Fe(II), Mn, and Si, respectively. The corresponding proton reaction orders nH+ were 0.61, 0.63, 0.33, and 0.09, respectively. The corresponding parameters for Al were not evaluated because of a suspected gibbsite precipitation at pH 6.5. The dissolution of biotite was found to be incongruent (non-stoichiometric) with respect to both the dissolving elements and the pH value. At pH 4, the dissolution was dominated by the octahedral layer element Fe, whereas at pH 6.5, the dissolution of the tetrahedral element Si dominated. There was no evidence of secondary phase formation, and the biotite leaching rates were consistent with those reported in previous studies conducted under aerobic conditions. In addition, the Fe(III)/Fetot ratio of biotite remained essentially unchanged before and after the experiment. This indicates that the anaerobic conditions alone have little effect on the rate and nature of biotite dissolution, although they may influence vermiculite formation. Therefore, biotite dissolution rates previously obtained under aerobic conditions may also be valid under anaerobic conditions.

Iron mobility in subduction zone fluids at forearc depths and implications for mantle redox heterogeneity

The mobility of redox sensitive elements such as iron, carbon and sulfur in subduction zone fluids is important for redox transfer between the subducting slab and mantle wedge. However, the speciation of Fe during its mobility in subduction zone fluids at forearc depths is still unclear. Here, we studied the Fe isotope compositions of high-pressure (HP) fluid-metasomatized rocks (Mg-rich leucophyllite and gneiss, which is mineralogically transitional between leucophyllite and metagranite) from the Eastern Alps and found evidence for two distinct types of Fe species during Fe mobility in subduction zone fluids. The protolith of both types of rocks is metagranite, which shows δ56Fe values of 0.12–0.25‰. Compared to the metagranite, the transitional gneiss shows slightly higher Fe2O3t contents, lower Fe3+/∑Fe ratios and significantly lower δ56Fe values of −0.03–0.16‰, whereas the leucophyllite exhibits much lower Fe2O3t contents, comparable or slightly lower Fe3+/∑Fe ratios and generally higher δ56Fe values of up to 0.55‰. These observations indicate that the granitic protolith has experienced two types of fluid metasomatism. Combined with previous results, we infer the mobility of Fe in subduction zone fluids at forearc depths via two kinds of Fe species, Fe2+-(CO3), and Fe2+-(HS) or Fe2+-Cl. The Fe mobility was dominant in the form of the Fe2+-(CO3) complex in a carbonate-rich fluid during the formation of transitional gneiss, consistent with reported radiogenic Sr and isotopically light Mg isotope compositions, whereas Fe loss in the form of Fe2+-(HS) or Fe2+-Cl complexes via dissolution of biotite and phlogopite can account for the formation of leucophyllites. According to the tectonic evolution of the Eastern Alps, both types of fluids possibly originated from the dehydration of the sediment-serpentinite mélange produced by the subducting oceanic slab of the Alpine Penninic unit. The diversity of ferrous iron species in the subduction zone fluids at forearc depths probably reflects the variation in the redox properties of fluids derived from carbonate-rich sediment and serpentinite under such conditions. Our results provide an excellent example of tracing Fe mobility with distinct Fe species in subduction zone fluids.

Process and optimum pH for permeability enhancement of fractured granite through selective mineral dissolution by chelating agent flooding

Chemical stimulation of geothermal reservoirs via selective mineral dissolution with eco-friendly chelating agents has been recently proposed as a novel method complementary to hydraulic stimulation. In our previous study, we demonstrated rapid and significant permeability enhancement accompanied by the creation of voids due to the selective dissolution of biotite in fractured granite at 200 °C under confining stress. However, the process of permeability enhancement and its optimum pH have not been investigated yet. In this study, we present the results of the stimulation experiments conducted on fractured granite at 200 °C under confining stress using a 20 wt% aqueous solution of the sodium salt of the chelating agent, N, N-bis(carboxymethyl)-l-glutamic acid (GLDA), at pH 1–8. The permeability enhancement was the highest at pH 4, at which preferential flow paths connecting the voids caused by biotite dissolution were observed. With decreasing and increasing pH, silica precipitation and suppressed selective dissolution of biotite, respectively, became more significant, accompanied by a decrease in permeability enhancement. Our findings suggested that the optimum pH was a combination of two pH values suitable for the creation of stress-resistant preferential flow paths by selective mineral dissolution of biotite and for the accelerated dissolution of quartz, which could not be achieved by the chelating agent. The successive use of first pH 4 and then pH 8 resulted in a more than 2-fold permeability enhancement in 4 h. Therefore, our study has strengthened the possibility and effectiveness of the new chemical stimulation method to facilitate the extensive use of enhanced geothermal systems worldwide in future.

Effect of Fluoride Ions on the Surface Dissolution of Vanadium-Bearing Biotite

In shale vanadium ore, vanadium is mainly formed as a low-V(III) homogeneous phase to partially replace Si and exists in the lattice structure of aluminosilicate minerals such as biotite. During the acid leaching of shale vanadium ore, an activator is needed to effectively extract vanadium. Using biotite as a tetrahedral structure doped with Aluminum-Silicon tetrahedron structure, the interaction between leaching-agent ions (H+), activator ions (F−), and vanadium-containing biotite surface was discussed by DFT quantum chemical calculations. The dissolution behavior of activator fluoride ions on the surface of vanadium-bearing biotite during sulfuric acid leaching was revealed. According to the simulated leaching results, the oxygen on the biotite surface first absorbed hydrogen ions to undergo complete hydroxylation, and then combined with hydrogen ions to form water molecules. However, in the presence of activator (NaF), fluoride ions were adsorbed on the surface cations, which catalyzed the formation of water molecules and promoted the dissolution of surface cations. SEM–EDS analysis showed that the surface of vanadium-bearing minerals became very irregular, and the number of voids and cracks greatly increased. At the same time, XPS showed that the addition of activator fluoride ions destroyed the Al-O tetrahedron structure. Many Al and V atoms dissolved in the solution, which improved the leaching rate of vanadium.

Hydrogeochemical modeling of the spatiotemporal variations in 87Sr/86Sr isotope ratios and Sr concentrations of spring waters in a headwater catchment (Strengbach CZO–France)

The variations in strontium (Sr) isotope ratios in river waters at a regional scale are usually discussed in terms of lithological diversity constituting the watershed bedrock. To discuss the origin of the spatiotemporal variations in Sr concentrations and isotopic compositions of spring waters at the headwater watershed scale, we analyzed the 87Sr/86Sr and 143Nd/144Nd isotopic ratios of the main constitutive minerals of the granitic bedrock of the Strengbach Critical Zone Observatory (CZO) and developed coupled hydrogeochemical modeling integrating the Sr concentration and isotopic composition. The simulation results show that the long-term (1990–2010) decrease in Sr concentrations in the CS springs of the Strengbach catchment can be explained by the response of mineral weathering along the water pathway to the pH increase that affected the incoming solutions to the weathering system during the same period. This pH increase reduces the water path proportion marked by a high flux of apatite and biotite dissolution. Thus, it reduces the Sr concentration of the outgoing spring waters. The different responses of the various CS springs to the incoming solutions' pH increase can be explained by the more or less long residence time of the water in the bedrock for the different springs. The analytical data also confirm that the 87Sr/86Sr isotope ratios of the CS springs varied little or not at all on average from 1990 to 2010. In contrast, they varied significantly during a hydrological cycle and from one spring to another. The constancy of the average 87Sr/86Sr isotope ratios over several years is explained by a granitic bedrock water path sufficiently long for soil solution pH variations to no longer influence the emergence of the spring. The simulation results also show that the isotopic variations observed in the CS springs during a hydrological cycle can be explained by differences in the transit time of the water in the substratum between high and low waters and the modifications that they entail on the degree of saturation of the water with respect to biotite and apatite. These differences do not need to be explained by differences in the mineralogy of the rocks drained by waters between high and low discharge periods. Similarly, the different average isotope ratios from one spring to another can be explained by the more or less long transit times in the bedrock of the waters feeding these different springs. Again, it is not necessary to explain them by local lithological differences from one spring to another. These different results highlight that at the scale of an upstream basin such as the Strengbach, the Sr isotopic variations observed in the CS springs should not systematically indicate lithological differences in the rock. The development of coupled isotope modeling approaches should help to disentangle the part of this process relating to hydrological processes in the isotopic variability of the spring waters.

Potassium silicate alteration in porphyry copper‑gold deposits: a case study at the giant maar-diatreme hosted Grasberg deposit, Indonesia

Potassium silicate alteration is a hallmark of the porphyry copper deposits that supply two thirds of the world's annual copper demand. These deposits formed in the cores of calc-alkaline to alkaline volcanic systems from the flux of magmatic gas that transported copper and other metals from source to the surface. The giant 3.2 Ma Grasberg CuAu deposit formed within a maar-diatreme complex following a resurgence in magmatism. The defined resources of this deposit occur from a few hundred metres depth to 1.7 km below the paleosurface which, uniquely in this deposit, is partially preserved as a section of maar tuffs.Potassium silicate alteration has commonly been interpreted as being the result of the addition of potassium to the porphyry copper host rocks via pervasive interaction with a large volume of a potassium-rich brine that is commonly presumed to be of magmatic origin. However, the data reported here show that alteration at the deposit scale is essentially isochemical with respect to the major rock-forming components and that only sulphur and the economic metals (Cu, Mo, Au, etc.) are added by flux of reactive magmatic gas containing SO2 and HCl from source intrusions at depth. Silicate solubilities are very low so that only a minor fraction of the total alkalis in the host rock are extracted by alteration reactions and then discharged at the paleo-surface. Reaction of the magmatic gas phase with plagioclase results in the coupled deposition of anhydrite (CaSO4) and disproportionation of SO2 to release H2S. The in-situ release of H2S immediately scavenges Cu and other chalcophile metals from the continuing magmatic gas flux to form the Cu-, Fe- and other sulphides that, in sufficient concentration, make up the economic reserve available to mining.The sequestration of Ca into anhydrite, along with deposition of silica into early quartz veins, increases the concentration of the other major components (K2O, Na2O, MgO, etc) in the remaining silicate assemblage within the porous host rock. The result is the development of intermingled potassium-enriched silicate and sulphur-rich (anhydrite-sulphide) sub-assemblages that constitute the mineralised phyllic or potassic alteration zones. These crystallise according to their pressure and depth into alteration assemblages dominated by potassic phyllosilicates, quartz and pyrite in the phyllic alteration zone, and alkali feldspar and phlogopitic-biotite plus minor andalusite and corundum in the central potassic zone. Dissolution and recrystallisation of primary magmatic biotite in the host rock releases K as well as Fe, the latter (along with amphibole and feldspar) providing iron for the formation of chalcopyrite, bornite and pyrite. The in-situ release of H2S through anhydrite formation, immediately scavenges Cu and other chalcophile metals from the continuing magmatic gas flux to form the CuFe sulphides that, in sufficient concentration, make up the economic reserve available to mining. Understanding of the alteration processes during porphyry copper formation also provides insights into gas-solid reactions processes inside active magmatic arc volcanoes but the magnitude of copper mineralisation is dependent on the original metal content of the source of the magmatic gas phase.

Long-term evolution of terrestrial weathering and its link to Earth's oxygenation

Terrestrial weathering releases phosphorus and other essential nutrients that fuel life in Earth's surface environments and sustain oxygenic photosynthesis. Despite previous suggestions that major changes in terrestrial chemical weathering might have played a role in the global oxygen cycle in the geological past, little is known about the Earth's weathering history. To date, the cause-and-effect relationship between weathering and the long-term evolution of atmospheric oxygen, and whether chemical weathering became more efficient after the initial rise of atmospheric oxygen in the early Paleoproterozoic, remained largely elusive. Here we report a reconstruction of the intensity of terrestrial weathering for the last 2.7 billion years, based on coupled neodymium-hafnium isotope (ΔεHf(i)CLAY) and elemental analyses of the fine-grained clay-size fraction of shales. A pronounced shift towards higher ΔεHf(i)CLAY values and rubidium/aluminium (Rb/Al) ratios indicates that preferential dissolution of phosphate-bearing minerals and biotite intensified between ∼2.5 and 2.4 billion years ago (Ga), following the emergence of continental landmasses and coinciding with the initiation of the Great Oxidation Event. After a long time interval characterized by a constant degree of low-intensity chemical weathering, between ∼2.3 to 0.7 Ga, terrestrial weathering further accelerated after the Neoproterozoic glaciations at ∼0.6 Ga, as inferred from markedly decreased Rb/Al ratios, coincident with the second rise of atmospheric oxygen. These findings support a link between the long-term intensity of chemical weathering and atmospheric oxygen level since the late Archean. We further propose that the 100-million-year-long period of enhanced terrestrial weathering from ∼2.5 Ga played a major role, via crustal recycling of phosphorus and export to the surface ocean, in the early expansion of the aerobic biosphere that ultimately led to the Great Oxidation Event.

Lithium-rich geothermal brines in Europe: An up-date about geochemical characteristics and implications for potential Li resources

Lithium (Li) is a strategic metal - especially for batteries in electric vehicles - for which worldwide demand is constantly increasing. Presently, several investigations are examining if a part of lithium could be extracted from deep European geothermal fluids. Among the data from geothermal and hydrocarbon wells found in the literature review carried out by BRGM and EIFER, only six areas stand out with deep fluids containing high Li concentrations from 125 to 480 mg/l in Italy, Germany, France and the United-Kingdom. Except the UK fluid, which has a relatively low salinity (TDS = 19 g/l) and reservoir temperature (around 52 °C), these deep Li-rich fluids are Na-Cl brines (TDS ≥ 56 g/l) with high concentrations of Na (> 18 g/l) and Cl (> 25 g/l) and high temperatures (≥ 120 °C and up to 380 °C in Italy). If high TDS and temperature values seem to be key factors for triggering high Li concentrations in such fluids, these two factors alone cannot be sufficient. Indeed, our study confirms that Li concentrations not only depend on temperature and fluid salinity, but also on the type of reservoir rock and its mineralogical constituents, as demonstrated by the good results obtained using two different Na-Li thermometric relationships existing in the literature. One fits well with the brines from low to high temperature (120–250 °C) reservoirs in deep tectonic sedimentary basins over a crystalline basement (France, Germany) and the other with the fluids from ultra-high temperature (≥ 300 °C) reservoirs in volcano-sedimentary environment (Italy). If the high chloride concentrations values in these brines mainly depend on the fluid origin (evaporated seawater or freshwater, halite dissolution, primary neutralization fluids or parent-geothermal fluids in high-temperature and -pressure volcanic environments, water mixing, etc.), the other aqueous major species are mostly controlled by hydrothermal water-rock interaction processes. At these temperatures (≥ 120 °C), the fluid-rock interaction processes are generally dominated by plagioclase and K-feldspar dissolution, followed by albitization of these minerals, dissolution of white micas and biotite, precipitation of illite, and chloritization. According to the two Na-Li thermometric relationships, existing mineralogical and isotopic data, this study suggests that the main sources of Li are white micas and biotite dissolution. Among the European areas, it shows that the Upper Rhine Graben (URG) along the French/German border is probably the most promising zone. For the URG geothermal brines, the main source and control of lithium, at about 225 °C, at reservoir depth, is probably the up to 450-m-thick micaceous continental sandstone of Triassic Buntsandstein. A minor contribution from the granite basement can also not be excluded. Though the Li concentration values of these brines (≥ 150 mg/l) seem to be favourable for geothermal Li exploitation, it is essential to make an as accurate as possible estimate of the Li resource of these brines, design the Li extraction process, and examine the economic conditions of its exploitation.

Drainage chemistry of mine tailings from a carbonatite-hosted Nb-REE deposit, Oka, Québec, Canada

Potential environmental issues associated with the mining of carbonatites are receiving increased attention due to the importance of critical metals for green technologies. This study investigates the chemistry of tailings seepage at the former Saint Lawrence Columbium mine near Oka, Québec, Canada, which produced pyrochlore concentrate and ferroniobium from a carbonatite-hosted Nb-REE deposit. Detailed field sampling and laboratory methods were used to characterize the hydraulic properties of the tailings, their bulk chemistry, mineralogy, pore water and effluent chemistries. The tailings are composed of REE-enriched calcite (64–89 wt %) and fluorapatite (2–22 wt %), as well as biotite (6–17 wt %) and chlorite (0–7 wt %). Minor minerals include ankerite, pyrite, sphalerite, molybdenite, magnetite and unrecovered pyrochlore. Secondary minerals include gypsum, barite, strontianite and rhodochrosite. Geochemical mass balance modeling, constrained by speciation modeling, was used to identify dissolution, precipitation and exchange reactions controlling the chemical evolution of pore water along its flow path through the tailings impoundment. In the unsaturated zone, these reactions include sulfide oxidation and calcite dissolution with acid neutralization. Below the water table, gypsum dissolution is followed by sulfate reduction and FeS precipitation driven by the oxidation of organic carbon in the tailings. Incongruent dissolution of biotite and chlorite releases K, Mg, Fe, Mn, Ba and F and forms kaolinite and Ca-smectite. Cation exchange reactions further remove Ca from solution, increasing concentrations of Na and K. Fluoride concentrations reach 23 mg/L and 8 mg/L in tailings pore water and effluent, respectively. These values exceed Canadian guidelines for the protection of aquatic life. In the mildly alkaline (pH 8.3) pore waters, Mo is highly mobile and reaches an average concentration of 83 μg/L in tailings effluent, which slightly exceeds environmental guidelines. Concentrations (unfiltered) of Zn reach 1702 μg/L in tailings pore water although values in effluent are usually less than 20 μg/L. At the ambient pH, Zn is strongly adsorbed by Fe–Mn oxyhydroxides. Although U forms mobile complexes in tailings pore water, concentrations do not exceed 16 μg/L due to the low solubility of its pyrochlore host. Adsorption and the low solubility of pyrochlore limit concentrations of Nb to less than 49 μg/L. Cerium, from calcite dissolution, is strongly adsorbed although it reaches concentrations (unfiltered) in excess of 1 mg/L and 100 μg/L in pore water and effluent, respectively. Results of this study show that mine tailings from carbonatite deposits are enriched in a wide variety of incompatible elements with multiple mineral hosts of varying solubility. Some of these elements, such as F and Mo, may represent contaminants of concern because of their mobility in alkaline tailings waters.

Unconformity-controlled bleaching of Jurassic-Triassic sandstones in the Ordos Basin, China

Bleaching of red beds, a type of hydrocarbon-induced alteration, is generally attributed to redox reactions between ferric iron minerals and hydrocarbon-bearing solutions. Herein, we report sandstone bleaching occurs interbedded with the coal- and dark mudstone-bearing strata at shallow depths below two unconformity surfaces separating sandstone formations of Triassic-Jurassic age in the Ordos Basin, China. Field observations, petrography, and geochemistry suggest that uplift events controlled the formation of red beds via supergene alteration and bleaching via hydrocarbon circulation. The color of sandstones below the unconformities grade from red, yellow, and white colors at shallow depths (few meters to tens of meters) to dark yellow, gray-green and gray colors at deeper depths. Organic matter (carbonaceous plant debris) and pyrite in the unaltered sandstone gave rise to the gray color. The red/yellow sandstones are characterized by the presence of extensive iron oxide/hydroxide grain coatings, exhibit intense dissolution and extensive kaolinization of detrital feldspar and biotite and lithics and are mainly composed of detrital quartz. The white, bleached sandstone presents similar petrographic characteristics as the unbleached sandstone except for a lack of iron oxide/hydroxide cements. δ18OVSMOW (9.8‰ to 15.8‰) and δDVSMOW (−103‰ to −119‰) values of kaolinite, and chemical indices of alteration of sandstones indicate a weathering origin for the kaolinite and the dissolution of labile minerals in the red and yellow sandstones. The original color of the bleached sandstone was gray during very early diagenesis and shifted to red/yellow due to the oxidation of pyrite and ferromagnesian silicate minerals (e.g., biotite) into hematite or goethite cements by the meteoric water circulation during regional uplift following the deposition of each formation. Supergene alteration associated with unconformities also created significant secondary porosity, and allowed later hydrocarbons to flow along the unconformities. The lithological properties of the weathered rocks below unconformities are highly heterogeneous both vertically and laterally and have a significant influence on fluid flow. This study provides direct evidence for hydrocarbon migration along unconformities and improves understanding of fluid-rock interaction in subsurface reservoirs.

Impact of freeze-thaw on the behaviour of flotation tailings from a rare earth deposit

The Ashram Rare Earth and Fluorspar Deposit, located in northern Quebec (Canada), contains a potential carbonatite-type rock source of rare earth elements (REE). A pilot scale pre-concentration of REE minerals produced flotation tailings. A kinetic leach column study was performed to evaluate the behaviour of these tailings in a northern context (i.e. freeze-thaw cycles). The tailings were exposed to 12 cycles (over 1 year) of leaching with deionized water under two different conditions. The first column, CW (water column), was stored at 5 °C for the duration of the experiment, while the second column, CFT (freeze-thaw column), was subjected to freeze-thaw cycling. A comparison with Quebec environmental guidelines showed that the tailings were not acid generating but deemed leachable for Cd, Pb, Zn and Mn. Leachate analysis for the CW (water column) showed that the behaviour of Ba, Ca, Sr and Mn appeared similar. These elements could originate from the dissolution of calcite [CaCO3], dolomite [CaMg(CO3)2], dolomite-Fe [Ca(Mg,Fe2+)(CO3)2] or ankerite [Ca(Fe2+,Mg,Mn)(CO3)2]. Mg, F and Si could originate from the dissolution of biotite [K2(Mg,Fe2+)6-4(Fe3+,Al,Ti)0-2(Si6-5Al2-3O20)(OH,F)2]. The release of these elements would, however, appear to come from separate minerals. The presence of fluorine in the leachate could come from the dissolution of fluorite [CaF2], apatite [Ca5(PO4)3(O,H,F,Cl)] or bastnaesite [(La,Ce)CO3F]. Mg could come from the dissolution of carbonate minerals such as magnesite [MgCO3]. Despite high Fe content (98,620 mg/kg) in the initial flotation tailings, Fe was not present in the leachate, probably because of potential precipitation in the form of iron oxides/hydroxides. Despite being only slightly soluble (<0.001% mobilized), some heavy REE (HREE), Er, Yb, Lu and Sc, have a distinct leaching behaviour compared to other REE. Overall, the freeze-thaw cycles only decreased the mobility of some elements (e.g. Ca, Ba, Sr and Mn) and, thus, the potential for environmental contamination from the tested REE tailings.

Novel chemical stimulation for geothermal reservoirs by chelating agent driven selective mineral dissolution in fractured rocks

Improving geothermal systems through hydraulic stimulation to create highly permeable fractured rocks can induce seismicity. Therefore, the technique must be applied at a moderate intensity; this has led to concerns of insufficient permeability enhancement. Adding chemical stimulation can mitigate these issues, but traditional methods using strong mineral acids have challenges in terms of achieving mineral dissolution over long distances and highly variable fluid chemistry. Here, we demonstrate a novel chemical stimulation method for improving the permeability of rock fractures using a chelating agent that substantially enhances the dissolution rate of specific minerals to create voids that are sustained under crustal stress without the challenges associated with the traditional methods. Applying this agent to fractured granite samples under confining stress at 200 °C in conjunction with 20 wt% aqueous solutions of sodium salts of environmentally friendly chelating agents (N-(2-hydroxyethyl)ethylenediamine-N, N′, N′-triacetic acid and N, N-bis(carboxymethyl)-l-glutamic acid) at pH 4 was assessed. A significant permeability enhancement of up to approximately sixfold was observed within 2 h, primarily due to the formation of voids based on the selective dissolution of biotite. These results demonstrate a new approach for chemical stimulation.

Nature of the mineralizing fluids in the Balda and Motiya W-prospects, western India: Constraints from chemical and B-isotope composition of tourmaline

In the Proterozoic tungsten belts of Balda and Motiya in western India, tungsten mineralization is hosted in tourmaline-bearing quartz veins intrusive into pelitic schists and granites. Tourmaline is a ubiquitous phase in all rock types, and in this study, we use its major, trace element and B-isotope composition to constrain the nature of the tungsten (W)-bearing hydrothermal fluid and the processes involved in the precipitation of wolframite. We have also reconstructed the compositions of the W-precipitating fluids from mineral-fluid trace element partition coefficients that were extrapolated using the Lattice Strain Model. The tourmalines from both belts are of schorl composition and have high alkali, low Ca content, and moderate X-site vacancies. High Li, Mn, Zn, and Sn in the fluid in Motiya is suggestive of relatively saline fluid possibly derived from a granitic source. The high V/Sc ratios of tourmalines in the mineralized veins and wall-rock tourmalinites indicate an important role of biotite dissolution and fluid-rock interaction that contributed Fe–Mn for the precipitation of tourmaline and wolframite. The tourmalines in the mineralized veins at Balda (δ11Btur = −10.9 ± 0.7‰, 2σ; n = 10) and those in the associated granites (δ11Btur = −11.5 ± 0.7‰, 2σ; n = 6) have similar B-isotope composition, while those of the associated topaz granites and pegmatites (−13.9 ± 0.7‰, 2σ; n = 19) are isotopically lighter than the granites. The B-isotopic variation in the granite-pegmatite-vein system can be explained by fluid exsolution with the mineralized vein forming from exsolved fluid and the topaz-bearing granites and the pegmatites crystallizing from the residual melts. The δ11B of the mineralizing fluid is estimated to be ca. −7.4‰ at Balda and ca. −7.6‰ at Motiya, and were possibly derived from granites, consistent with extensive tourmalinization and muscovitization of the adjacent wall rocks, and high concentration of elements such as F, Li, B, Sn, Mn in the tourmalines and the reconstructed fluid. The chemistry and B-isotope composition of tourmalines in both the belts support the hypothesis that W-bearing hydrothermal fluid was primarily derived from a fractionated granitic source, and that precipitation of wolframite and tourmaline involved interaction of the granitic fluid with surrounding pelitic rocks.

Experimental research on carbon storage in a CO2-Based enhanced geothermal system

Ensuring sustainable energy development and reducing CO2 emissions are two major challenges that need to be overcome to deal with the global economic crisis and to alleviate climate change. Hot dry rock is a renewable energy resource with a huge potential. CO2-based enhanced geothermal systems (CO2-EGS) can achieve both heat extraction and CO2 storage in hot dry rock. To investigate the storage rate, a heat extraction experiment involving the alternating cyclic injection of water and supercritical CO2 was conducted. The ion contents of the fracture solution of the different injection cycles were measured, and the amount of CO2 mineralization storage was calculated. In addition, changes in the mineral composition of the fracture surface were observed and analysed. The results revealed that the mineral dissolution on the fracture surface was mainly feldspars, which possibly accompanied biotite dissolution. The precipitated minerals that stored the carbon were mainly calcite and dolomite, and possibly illite and cancrinite. Many blocky carbonate minerals were distributed on the flat surface of the fracture, while many rod-shaped carbonates were distributed in the concave holes of the microfractures. The research results reveal the CO2 storage mechanism and are significant for the CO2 storage prediction in the CO2-EGS.

When zircon drowns: Elusive geochronological record of water-fluxed orthogneiss melting in the Velay dome (Massif Central, France)

Zircon U-Pb geochronology is routinely performed to unravel the timing and duration of melting events within the continental crust. A comprehensive understanding of the zircon behavior during anatexis is therefore paramount to accurately assess the impact of crustal melting on orogenic processes. We report on an anatectic system from the southern part of the Velay dome (Variscan French Massif Central) encompassing late Carboniferous migmatites developed at the expense of peraluminous orthogneisses and associated with (leuco)granite bodies intrusive at higher structural levels. Our zircon U-Pb geochronological survey (494 analyzed grains) evidences a very scant record of the Variscan anatectic event. Indeed, oscillatory-zoned melt-precipitated zircon grains extracted from metatexites, leucosomes and (leuco)granites almost systematically yielded the late Neoproterozoic crystallization age of the felsic igneous protolith. Field and petrographic observations, whole-rock geochemical signatures, phase equilibrium and thermodynamically-constrained trace element modelling collectively indicate that partial melting of the orthogneisses took place at T ~ 700 °C and was fluxed by ingress of external water. The lack of new zircon growth is ascribed to a range of processes ultimately related to the low melting temperature including limited zircon solubility in the melt phase, occlusion of zircon in non-reacting source biotite and sluggish zircon dissolution kinetics. Peraluminous orthogneisses, yet highly fusible due to their “eutectic” subsolidus mineral assemblage, exhibit a very limited zircon record of low temperature water-fluxed melting. Thus, zircon has little potential to provide reliable chronological constraints on water-fluxed melting episodes affecting such lithologies.

The influence of water\u2013rock interactions on household well water in an area of high prevalence chronic kidney disease of unknown aetiology (CKDu)

Poor drinking water quality in household wells is hypothesised as being a potential contributor to the high prevalence of chronic kidney disease of uncertain aetiology (CKDu) among the farming communities of the Medawachchiya area, Anuradhapura, Sri Lanka. One of the natural processes that can affect water quality is the dissolution of minerals contained within an aquifer by water–rock interactions (WRIs). Here we present a comprehensive assessment of WRIs and their influence on the water chemistry in household wells and spring waters in the Medawachchiya area by combining measurements of environmental isotopes, such as strontium, lithium and stable carbon isotopes and inorganic chemistry parameters, and modelling geochemical mass balance reactions between rainfall and groundwater samples. Our results reveal the presence of strontium, dissolved from both silicate and carbonate minerals, with high isotopic (87Sr/86Sr) ratios of up to 0.7316. Geochemical mass balance modelling and prior 87Sr/86Sr studies on the Wanni Complex bedrock suggest these strontium values may be the result of biotite dissolution. We also identify lithium and uranium contributed from the dissolution of silicates, albeit at concentrations too low to constitute a known health risk. In contrast, the levels of magnesium and calcium in our samples are high and demonstrate that, despite the felsic bedrock, well water chemistry in the Medawachchiya area is dominated by carbonate dissolution.

Synthesis of KAlSiO4 by Hydrothermal Processing on Biotite Syenite and Dissolution Reaction Kinetics

To make potassium from K-bearing rocks accessible to agriculture, processing on biotite syenite powder under mild alkaline hydrothermal conditions was carried out, in which two types of KAlSiO4 were obtained successfully. The dissolution-precipitation process of silicate rocks is a significant process in lithospheric evolution. Its effective utilization will be of importance for realizing the comprehensiveness of aluminosilicate minerals in nature. Two kinds of KAlSiO4 were precipitated in sequence during the dissolution process of biotite syenite. The crystal structures of two kinds of KAlSiO4 were compared by Rietveld structure refinements. The kinetics model derived from geochemical research was adopted to describe the dissolution behavior. The reaction order and apparent activation energy at the temperature range of 240–300 °C were 2.992 and 97.41 kJ/mol, respectively. The higher dissolution reaction rate of K-feldspar mainly relies on the alkaline solution, which gives rise to higher reaction order. During the dissolution-precipitation process of K-feldspar, two types of KAlSiO4 with different crystal structure were precipitated. This study provides novel green chemical routes for the comprehensive utilization of potassium-rich silicates.

Kinetics and Mechanism of Leaching Potassium from Biotite in H2SO4 Solution

AbstractBiotite is a potential potassium mineral resource and the dissolution of biotite in H2SO4 solution is a green chemistry approach for recovering potassium. To estimate the efficiency of leaching process and to understand the behavior of leaching reactors, the kinetics and mechanism of leaching potassium from biotite in H2SO4 solution were studied in this work. The leaching experiments show that leached fractions of K2O increase with the increasing of temperatures and H2SO4 concentrations, and yet with the decreasing of biotite particle sizes. According to the shrinking core model, the leached fractions of K2O were fitted better by diffusion through product layer. A kinetics expression of diffusion‐controlled model on three parameters was acquired and it is appropriate to predict the leached fractions of K2O from biotite in H2SO4 solution. The dissolution of biotite in H2SO4 solution was interpreted by electrochemical mechanism coupling with characterization of the acid‐leached residues. This research results can aid in the design of leaching process for recovering potassium sustainably from biotite.