Precursor Minerals Research Articles

Synthesis and Characterization of Metakaolin–Wollastonite Geopolymer Foams for Removal of Heavy Metal Ions from Water

Over the past few decades, researchers have focused on developing new compositions and preparation techniques for geopolymers, as multifunctional products, to optimize their characteristics for use in multiple applications. Therefore, this paper investigates metakaolin geopolymer foam and introduces new geopolymer foams based on hybrid metakaolin and wollastonite mineral precursors for water purification. The geopolymer foams were prepared using an alkaline activator, mineral-based powders (wollastonite and metakaolin), a foaming agent (aluminum powder), and a foam stabilizer (olive oil). In addition to mechanical tests and assessments of the adsorption capacity of heavy metal ions, the geopolymer foams were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The geopolymer foams exhibited unique pore structures, containing four classes of pore networks with diameters around 1000 µm, 25 µm, 3 µm, and a well-arranged mesopore network of 50 nm. The utilization of wollastonite (CaSiO3) alongside metakaolin as a hybrid precursor led to fundamental changes in the composition of the geopolymer binders: a new crystal phase, Ca5(SiO4)2(OH)2, was formed, and the Si-Al-Na crystal phase disappeared, which led to an increase in the amorphous phase from 87% to 92%. The adsorption rate of heavy metal ions, namely Cr, Co, Cu, Zn, Pd, and As, increased upon introducing wollastonite as a precursor, with absorption rates ranging from 11% to 68%. The findings also revealed that wollastonite significantly increased the geopolymers foams’ compressive strength and elastic modulus from 30 KPa to 67 KPa and from 31 MPa to 126 MPa, respectively.

REVISITING THE PHYSICAL AND CHEMICAL NATURE OF THE MINERAL COMPONENT OF BONE.

The physico-chemical characteristics of bone mineral remain heavily debated. On the nanoscale, bone mineral resides both inside and outside the collagen fibril as distinct compartments fused together into a cohesive continuum. On the micrometre level, larger aggregates are arranged in a staggered pattern described as crossfibrillar tessellation. Unlike geological and synthetic hydroxy(l)apatite, bone mineral is a unique form of apatite deficient in calcium and hydroxyl ions with distinctive carbonate and acid phosphate substitutions (CHAp), together with a minor contribution of amorphous calcium phosphate as a surface layer around a crystalline core of CHAp. In mammalian bone, an amorphous solid phase has not been observed, though an age-dependent shift in the amorphous-to-crystalline character is observed. Although octacalcium phosphate has been postulated as a bone mineral precursor, there is inconsistent evidence of calcium phosphate phases other than CHAp in the extracellular matrix. In association with micropetrosis, magnesium whitlockite is occasionally detected, indicating pathological calcification rather than a true extracellular matrix component. Therefore, the terms 'biomimetic' or 'bone-like' should be used cautiously in descriptions of synthetic biomaterials. The practice of reporting the calcium-to-phosphorus ratio (Ca/P) as proxy for bone mineral maturity oversimplifies the chemistry since both Ca2+ and PO43- ions are partially substituted. Moreover, non-mineral sources of phosphorus are ignored. Alternative compositional metrics should be considered. In the context of bone tissue and bone mineral, the term 'mature' must be used carefully, with clear criteria that consider both compositional and structural parameters and the potential impact on mechanical properties. STATEMENT OF SIGNIFICANCE: Bone mineral exhibits a unique hierarchical structure and is classified as intrafibrillar and extrafibrillar mineral compartments with distinct physico-chemical characteristics. The dynamic nature of bone mineral, i.e., evolving chemical composition and physical form, is poorly understood. For instance, bone mineral is frequently described as "hydroxy(l)apatite", even though the OH- content of mature bone mineral is negligible. Moreover, the calcium-to-phosphorus ratio is often taken as an indicator of bone mineral maturity without acknowledging substitutions at calcium and phosphate sites. This review takes a comprehensive look at the structure and composition of bone mineral, highlighting how experimental data are misinterpreted and unresolved concerns that warrant further investigation, which have implications for characterisation of bone material properties and development of bone repair biomaterials.

Characterization of geopolymer with 100% thermoactivated construction spoil powder: Effects of alkali dosage, silicate modulus and curing temperature

The traditional landfilling and stockpiling methods for disposing of construction waste have caused a series of environmental issues, and thus, recycling construction waste in a sustainable approach is a challenging issue within the resource utilization of construction waste. Utilizing thermoactivated construction spoil powder (TCSP) as a precursor for sustainable geopolymer production provides a novel approach to reusing construction spoil and reduces the need for traditional mineral precursors. This study is developed to quantify the effects of alkali dosage, silicate modulus and curing temperature on the properties of TCSP-based geopolymer which is made with 100% TCSP as precursor. The TCSP, after 800 °C thermal activation, contains active metakaolin, CaO and C2S, showing a good alkali-activated activity. Substituting an appropriate dosage of TCSP for metakaolin can enhance the micro-structure and macro-properties of metakaolin-based geopolymer, and replacing metakaolin with 100% TCSP causes a degeneration in the performance of TCSP-based geopolymer. However, the 100% TCSP-based geopolymer still shows a dense micro-structure and good compressive strength (55.97 MPa). A moderate rise in alkali dosage and silicate modulus causes an improvement of the micro-structure of TCSP-based geopolymer. When the alkali dosage-silicate modulus is 1.2M-8%, 1.4M-8%, 1.4M-4%, the MIP-measured porosity of TCSP-based geopolymer paste is 16.06%, 13.91% and 26.37%, respectively. An appropriate rise in alkali dosage and silicate modulus can enhance the strength and permeability resistance of TCSP-based geopolymer mortar, but the further rise in alkali dosage and silicate modulus does not cause an obvious performance improvement. Elevating curing temperature from 20 °C to 95 °C, as well as reducing the water to binder ratio, are two effective methods for improving the micro-structure, strength and permeability resistance of TCSP-based geopolymer.

Organic macromolecules transport a significant proportion of the calcium precursor for nacre formation

The mechanism of nacre formation in gastropods involves a vesicular system that transports organic and mineral precursors from the mantle epithelium to the mineralization chamber. Between them lies the surface membrane, a thick organic structure that covers the mineralization chamber and the forming nacre. The surface membrane is a dynamic structure that grows by the addition of vesicles on the outer side and recedes by the formation of interlamellar membranes on the inner side. By using a combination of electron microscopy imaging and spectroscopy, we have monitored the journey of the vesicles from the mantle epithelium to the mineralization chamber, focusing on the elemental composition of the organic structures at each stage. Our data reveal that transport occurs in lipid bilayer vesicles through exocytosis from the outer mantle epithelium. After release into the surface membrane, chitin undergoes a process of self-assembly and interaction with proteins, resulting in progressive changes of the internal structure of the surface membrane until the final structure of the interlamellar membranes is acquired. Finally, these detach from the inner side of the surface membrane. Elemental analysis revealed the transport of a considerable amount of calcium bound to proteins, likely forming calcium-protein complexes. Statement of significanceThe formation of nacre tablets occurs through the incorporation of organic and mineral precursors extruded from the mantle epithelium. Although much attention has been paid to the presence of amorphous phases in recent decades, the calcium transport system has not yet been elucidated. We have monitored the packaging of organic and mineral precursors in the form of vesicles from the mantle epithelium to the mineralization chamber. We have shown that the surface membrane represents the zone where chitin and protein polymerization takes place, acquiring the final structure for the formation of interlamellar membranes. Interestingly, these organic structures transport a considerable amount of organic calcium into the mineralization chamber, which support a transport system based on acidic calcium-binding proteins.

Role of metasomatism in formation of the Yichun rare-metal deposit, China

What role post-magmatic processes have played in the development and mineralization of rare-metal peraluminous granites and how important that role can be, are questions that researchers have been wrestling with for decades. The Yichun Li-Ta-Nb deposit is an example that has been the subject of such a debate. The granitic appearance of rocks, the inert nature of tantalum, and the scarcity of mineralization in country rocks have been taken to suggest that fluid overprints were limited to within the granites and were unimportant in rock- and ore-forming processes. In this study, the identification of two types of abundant Li- and Cs-rich pseudomorphs in both the topaz-lepidolite granite and overlying pegmatite, the only two mineralized units at Yichun, suggests that extensive metasomatism was involved in rock and ore formation. The textural and chemical similarities of lepidolite in comparable mineral assemblages from a variety of occurrences, including lepidolite in pseudomorphs, veins, and miarolitic cavities from both the topaz-lepidolite granite and pegmatite, suggest that all lepidolite at Yichun is metasomatic and largely inherited its chemical signatures from a magmatic-hydrothermal transitional fluid, rich in Li, Cs, and Ta, derived possibly from the Li-muscovite granite that lies beneath the topaz-lepidolite granite. We propose that this transitional liquid, composition of which lies between a silicate melt and aqueous fluid, was not in equilibrium with the original igneous mineralogy, thus bringing about significant metasomatism along its infiltration and evolution upwards. Variations in the trace-element composition of lepidolite likely reflect the influence on mineral compositions by precursor minerals. The ambiguous boundary between the topaz-lepidolite and Li-muscovite granites, combined with the intensely metasomatized nature of the former, is most consistent with the topaz-lepidolite granite being the extensively altered upper portion of the Li-muscovite granite, which is itself somewhat metasomatized. Although magmatic fractionation played a key role in the initial concentration of Nb, Li, and Ta in both granite and pegmatite formation, the Li-Ta-Nb-Cs mineralization and its host rocks were largely formed through magmatic-hydrothermal rejuvenation and re-enrichment.

Detrital clay mineral input reconstructed based on weathering records and its influence on organic matter enrichment: A case study of the Paleogene Shahejie Formation in the Dongpu Sag, Bohai Bay Basin

As major components of shales, clay minerals are important for investigating unconventional petroleum geology. However, there are few quantitative methods for investigating possible inputs of clay minerals during sedimentary processes. In this study, shales from the Shahejie Formation in the Dongpu Sag, Bohai Bay Basin, were chosen for investigating clay mineral inputs. The shales are abundant in a variety of clay minerals. The shales, uniformly derived from felsic igneous rocks, underwent mild K metasomatism. Thus, the detrital clay mineral input was primarily influenced by weathering intensity. Accordingly, representative samples subjected to varying weathering intensities were selected to identify detrital and diagenetic clay minerals. Kaolinite and chlorite are of detrital origin. Illite and illite/smectite mixed layers (I/S) have both detrital and diagenetic origins. The precursor minerals of diagenetic minerals can be identified based on their morphological and elemental characteristics. After quantifying the area proportions of various clay minerals, the detrital clay mineral compositions of selected samples were calculated. Further analysis indicated that the detrital illite content and the detrital chlorite content are closely related, while the detrital smectite content correlates well with the chemical index of alteration (CIA). Based on the preceding analysis, the fitting formulas were established to quantitatively characterize the input of detrital clay minerals. The shales from the north sag had a high input of detrital smectite, whereas the shales from the south sag had a high input of detrital illite. Consequently, the shales from the north sag contain more organic matter than those from the south sag.

Synthesis of Alpha Ferrous Oxalate Dihydrate from Ferrotitaniferous Mineral Sands via Hot Pressurized Aqueous Oxalic Acid: Kinetics and Characterization

Ferrous oxalate dihydrate is a versatile organic mineral with applications across fields. However, little is known about the feasibility of its synthesis directly from iron-bearing minerals using binary subcritical water (sCW) systems and its associated kinetics. In this study, the sCW+oxalic acid system at either 115 °C or 135 °C was investigated as a reaction medium for ferrous oxalate dihydrate (α-FeC2O4∙2H2O) synthesis, starting from ferrotitaniferous sands. The kinetics of the synthesis reaction were studied, and the physicochemical characterization of the as-synthetized ferrous oxalates was performed. Overall, the sCW synthesis was temperature-dependent, following second-order reaction kinetics according to the proposed precipitation pathway. A high reaction rate constant, significantly high yields (up to 89%), and reduced reaction times (2–8 h) were evident at 135 °C. The as-synthetized product corresponded to the monoclinic α-FeC2O4∙2H2O, showed relatively high specific surface areas (from 31.9 to 33.7 m2∙g−1), and exhibited band gap energies within the visible light range (~2.77 eV). These results suggest that α-FeC2O4∙2H2O can be synthesized using an organic dicarboxylic acid and iron-rich, widely available, low-cost mineral precursors. In addition, the as-prepared α-FeC2O4∙2H2O could be further optimized and tested for catalytic and visible light photocatalytic applications.

Comparative study on preparation and hydration mechanism of composite cementitious materials containing copper slag

Copper slag (CS) is a kind of non-ferrous solid waste with low content of aluminosilicate and relatively high content of iron oxide. In this paper, the feasibility and mechanism of CS as the mineral admixture and precursor of alkali activated cementitious material were studied. The effects of CS on mechanical properties were studied and the hydration products were determined by several characterization methods. Scanning Electron Microscopy (SEM) and Mercury Injection Porosimetry (MIP) were performed to characterize the microstructure. The results show that CS composite fly ash (FA) has more advantages than CS alone, but its application as a mineral admixture is limited by the low activity. The alkali activated cementitious material prepared by CS and FA as precursor has excellent mechanical properties. The compressive strength of specimen at 28 days age can reach the maximum of 81.3 MPa when the dosage of CS is 30 %. The 3d and 28d compressive strength of the specimen contained 60 % CS obtained 57.7 MPa and 70.7 MPa, respectively. The research exhibits great potential for the future utilization of CS.

Effect of Prolonged Action of Mineral Fertilizers under Conditions of Temperature Stress on Silage Maize Yield in the Steppe Zone of the Southern Urals

In modern agriculture in the Southern Urals, an important agronomic technique is to counteract drought. Of particular importance in increasing the feed base is the cultivation of maize for silage, which ensures maximum yields in extreme conditions. The aim of the study was to determine the potential possibilities of increasing the yield of green mass of maize for silage under the influence of temperature stress in conjunction with the prolonged action of mineral fertilizers and precursors in arid conditions. The study was carried out in the central zone of the Orenburg region from 1993 to 2022 on a stationary site with the southern carbonate heavy loamy chernozem soils with a humus content of 3.2–4.0%. The experiment was carried out with and without mineral fertilizers. The content of nitrate nitrogen in the soil was determined by the ionometric method of Tyurin, mobile phosphorus – by Machigin, exchangeable potassium – by Maslova. A thermostatic-weight method was used to determine soil moisture. On average, over 30 years of research, when cultivating maize for silage in a 6-field crop rotation, an increase in yield was noted with the use of mineral fertilizers from 0.23 to 0.84 t/ha. The annual application of mineral fertilizers in permanent sowing of maize provided an increase in the yield of green mass of 2.51 t/ha. In years with severe aridity, the yield of leaf-stem mass on a fertilized background decreased by an average of 1.61 t/ha. In very dry years, maize plants consumed less nitrate nitrogen (by 2 or more times) than in years with different humidity, but at the same time, potassium consumption increased.

The giant Baerzhe rare-earth-element–Nb–Zr–Be deposit, Inner Mongolia, China, an Early Cretaceous analogue of the Strange Lake rare-metal deposit, Quebec

The Baerzhe deposit represents world-class mineralization of rare metals, in particular rare earth elements (REEs) and Nb, and shares mineralogical and geochemical similarities with the Strange Lake deposit in Canada. However, the mechanisms responsible for the rare-metal enrichment at Baerzhe are still under debate. Mineralization at Baerzhe is characterized by multiple stages of dissolution, re-precipitation and enrichment of rare-metal elements, as with the Strange Lake deposit. Zirconium was concentrated during magmatic fractionation of elpidite in a transsolvus agpaitic granite (Stage I), and was redistributed into zircon–quartz pseudomorphs during Na-metasomatism (Stage II). Rare earth elements, Nb and Be occur as a variety of mineral assemblages, mainly as pseudomorphs after complete replacement of unknown precursor minerals that are disseminated through the hematized transsolvus granites and were precipitated in three sequential stages (Stages III–V): Stage III is characterized by the mineralization of hingganite, aeschynite-(Y), columbite-(Fe) and euxenite-group minerals, accompanied by hematite alteration; the following Stage IV is defined mainly by monazite-(Ce) crystallization, and Stage V by the preceding REE minerals being replaced by light REE minerals (i.e. bastnäsite-(Ce) and fluocerite-(Ce)). The formation of various pseudomorphs as replacement for precursor minerals is also a common feature documented at Strange Lake. Our results call for a re-evaluation of the timing and role of meteoric waters at Baerzhe, which were suggested by previous researchers to have entered the ore-forming system prior to the mineralization of zircon. New in situ O isotopic analyses on pseudomorph-hosted mineral pairs and investigation of silicate melt–fluoride melt immiscibility through observations and analyses of melt inclusions could provide further insights into the nature of the Baerzhe system.

Influence of mineral nutrition and precursor crops on the linear growth of spring barley

Influence of mineral nutrition and precursor crops on the linear growth of spring barley

Episodic hydrothermal supply and microbial anaerobic Fe(II) oxidation in early Archean ocean: Insights from precursor mineral compositions of the 3.46 Ga Marble Bar Chert, Pilbara Craton, Western Australia

The 3.46 Ga Marble Bar Chert (MBC) from the Pilbara Craton in Western Australia is known as the oldest chert on Earth. The origin of its Fe minerals was investigated to decipher the geochemistry and redox conditions of the early Archean ocean, as well as to explore the possible microbial contribution to the earliest sedimentary processes on Earth. However, the composition of the precursor minerals in the MBC remains poorly understood, giving rise to controversies on its genesis. Here we performed high-resolution petrographic, laser Raman, Mössbauer, X-ray diffraction, and Mn K-edge X-ray absorption near edge structure spectroscopic studies on two typical types of finely laminated MBC, grey-black chert and red chert. The grey-black chert contains considerable amounts of siderite, carbonaceous materials, and minor phyllosilicates and hematite. By contrast, the red chert contains high hematite and silicates, minor siderite and rare carbonaceous materials. Microcrystals in the cores of chert polyhedral are among the earliest mineral phases without signs of alterations, recrystallisation, erosion or replacement histories. Ferrihydrite, greenalite, siderite, and green rust are possible precursors of Fe-bearing minerals in the MBC. Their respective proportion in each lamina was regulated by pH, Fe(II)-oxidation rate, DIC, and Fe(II) content in the seawater. Approximately half Fe in the MBC primary minerals existed as Fe(III), indicating the existence of indigenous Fe(II)-oxidation in the Paleoarchean seawater. The element Mn in the MBC is primarily Mn(II) coordinated with O, suggesting a reduced depositional environment and hence implying the involvement of anaerobic microbial Fe(II)-oxidation in the formation of the MBC. Collectively, the grey-black laminae with abundant carbonaceous materials reflect limited Fe(II)-oxidation and increased dissolved inorganic carbon content likely due to enhanced hydrothermal CO2 supply, while the red laminae with considerable hematite represent substantial Fe(III)-supply due to rapid indigenous anaerobic Fe(II)-oxidation.

Structural Defects of Heavy Rare Earth Element Minerals in Granite Accelerate Their Decomposition and Facilitate Mineralization During Weathering

Abstract Heavy rare earth elements (HREEs), an indispensable resource for modern industry, are extracted mainly from clays in ion adsorption deposits (IADs) in South China. The HREEs in IADs are derived from accessory minerals in parental granites. These precursor HREE phases have low solubility in aqueous environments, and unraveling the mechanism of their decomposition during weathering is critical to understanding how IADs form. Here, we report the micro- to nanoscale structural characteristics of HREE precursor minerals in parental granites from the large Zudong and Zhaibei IADs. High-resolution transmission electron microscopy shows that these minerals are characterized by abundant structural defects that range from lattice dislocations to submicro- to nanoscale crystallite aggregates with a variable proportion of amorphous material. Ubiquitous structural defects make the precursor HREE minerals unstable during weathering, resulting in their rapid decomposition, thereby facilitating the development of clay-hosted mineralization.

Predictive Models for Detrital Titanite Provenance With Application to the Nanga Parbat—Haramosh Syntaxial Massif, Western Himalaya

AbstractTitanite is a versatile recorder of crystallization age, temperature, and host lithology, via the U–Pb system, the Zr‐in‐Ttn thermometer, and elemental composition, respectively. The paragenesis of titanite renders it especially useful for tracing detritus derived from lithologies that are infertile for the commonly used detrital zircon U‐Pb chronometer, such as sub‐anatectic metamorphism of calc‐silicates. Despite these advantages, detrital titanite analysis is underemployed, in part because the U–Pb system in titanite is often complicated by the incorporation of both inherited radiogenic Pb from precursor minerals during metamorphic reactions, and also bulk crustal common‐Pb. Recent systematic analyses of large titanite compositional data sets from diverse source rocks have revealed that the elemental composition of titanite is provenance‐specific. Here, we apply a workflow that incorporates a machine‐learning classifier to a large and representative compositional database for titanite, encompassing >11,000 analyses, with c. 6,700 points passed to our model. Only medians of the subcompositions for 205 rocks are used for our model. We reliably discriminate (>90%) between metamorphic and igneous titanite. Application of this classifier to a detrital case study from the Nanga Parbat‐Haramosh syntaxial massif of the western Himalaya reveals that titanite of different compositions formed during different orogenic events. Furthermore, titanite with significant common Pb solely derives from medium/low grade metasedimentary rocks. The method described here offers a pathway to increase the specificity of the provenance information derived from titanite; however, the published corpus of titanite data will have to be much larger before multi‐class source‐rock discrimination can be achieved reliably.

In Situ Geochemical Evaluation of Retrograde Hydration Effects in the Peri-Siberian Forearc Mantle (Khara-Nur and Alag-Khadny Peridotite Complexes)

In order to assess the geochemical effects of retrograde metamorphic rehydration, fluid metasomatism, and the fluid-mobile elements (FMEs) budget in the case of oceanic and continental subduction, we report the petrography, bulk, and in situ LA-ICP-MS trace-element data for the two poorly studied ophiolites in the northern (Khara-Nur, Eastern Sayan, Russia) and central (Alag-Khadny accretionary wedge, SW Mongolia) parts of the peri-Siberian orogenic framing. Both complexes are relics of the ancient oceanic mantle, which was subjected to processes of partial melting, metasomatism, and retrograde metamorphism. Typical mineral assemblages include olivine + orthopyroxene + chlorite + tremolite ± secondary olivine (640–800 °C), olivine + antigorite ± secondary clinopyroxene (<640 °C), and olivine + chrysotile ± secondary clinopyroxene (<250 °C) and are stable at pressures up to 2 GPa. Hydration and partial serpentinization of mantle peridotites lead to tremolite formation after orthopyroxene, followed by olivine replacement by antigorite. Serpentine-group minerals (antigorite and chrysotile) were distinguished by Raman spectroscopy, and the contents of incompatible elements (mobile and immobile in fluids) in metamorphic minerals (tremolite, antigorite, and chrysotile) were examined in situ by LA-ICP-MS. The behavior of conservative HFSE (Zr, Nb, Ta, and Ti) and—in part—HREE does not distinguish between the two types (oceanic and continental) of subduction environments. Different patterns of FMEs (Cs, Rb, Ba, U, Sb, Pb, Sr, and LREE) enrichment in metaperidotites reflect variations in the slab fluid composition, which was primarily governed by the contrasting nature of subducted lithologies. The affinity of Alag-Khadny to the subduction of a continental margin is recorded by increased FME contents and selective enrichment by some moderately mobile elements, such as U, Th, and LREE, with respect to the oceanic-type subduction environment of Khara-Nur. Distinct patterns of FME enrichment in tremolite and antigorite from two complexes indicate different sequences of fluid-induced replacement, which was controlled by Opx composition. We demonstrate that evaluation of the initial composition of precursor minerals affected by multi-stage melting and melt metasomatism should be considered with care to estimate the differential fluid overprint and associated elemental uptake from subduction fluids.

Transformation of Precursor Iron(III) Minerals in Diagenetic Fluids: Potential Origin of Gray Hematite at Vera Rubin Ridge

AbstractCoarse‐grained (>3–5 μm) gray hematite particles occur at Vera Rubin ridge (VRR) within Gale crater, Mars. VRR has likely undergone multiple episodes of diagenesis, at least one of which resulted in the formation of gray hematite. The precursor mineralogy and nature of the diagenetic fluids that produced coarse‐grained hematite remain unknown. Analog laboratory experiments were performed on a variety of iron(III) minerals to assess the potential fluid conditions and precursor mineralogy that form coarse‐grained hematite. Gray hematite formed from the transformation of jarosite after 20 days at 200°C. Conversion was complete in chloride‐rich fluids; however, modeling indicates that at lower jarosite‐to‐water ratios, conversion is complete even in chloride‐free, sulfate‐rich conditions. No transformations of jarosite occurred when aged at 98°C. All other precursor minerals (akaganeite, ferrihydrite, goethite, and schwertmannite) did not transform or produced red, fine‐grained hematite under all conditions assessed. Additionally, seeding precursor iron(III) phases with red hematite and coarsening pre‐existing red hematite failed to produce gray hematite. These results suggest that jarosite could have been the precursor of gray hematite at VRR and that transformation is possible in both sulfate‐bearing and chloride‐bearing fluids. Jarosite produces gray hematite because the acidic conditions it generates yield both a low degree of hematite supersaturation, producing few nuclei, and high dissolved iron concentrations, enabling rapid hematite growth. Gray hematite readily forms under oxic conditions and its occurrence at VRR is not a marker for a redox interface. The associated diagenetic event was thus unlikely to have generated substantial new chemical energy for life.

Citrate Improves Biomimetic Mineralization Induced by Polyelectrolyte-Cation Complexes Using PAsp-Ca&Mg Complexes.

Magnesium ions are highly enriched in early stage of biological mineralization of hard tissues. Paradoxically, hydroxyapatite (HAp) crystallization is inhibited significantly by high concentration of magnesium ions. The mechanism to regulate magnesium-doped biomimetic mineralization of collagen fibrils has never been fully elucidated. Herein, it is revealed that citrate can bioinspire the magnesium-stabilized mineral precursors to generate magnesium-doped biomimetic mineralization as follows: Citrate can enhance the electronegativity of collagen fibrils by its absorption to fibrils via hydrogen bonds. Afterward, electronegative collagen fibrils can attract highly concentrated electropositive polyaspartic acid-Ca&Mg (PAsp-Ca&Mg) complexes followed by phosphate solution via strong electrostatic attraction. Meanwhile, citrate adsorbed in/on fibrils can eliminate mineralization inhibitory effects of magnesium ions by breaking hydration layer surrounding magnesium ions and thus reduce dehydration energy barrier for rapid fulfillment of biomimetic mineralization. The remineralized demineralized dentin with magnesium-doped HAp possesses antibacterial ability, and the mineralization mediums possess excellent biocompatibility via cytotoxicity and oral mucosa irritation tests. This strategy shall shed light on cationic ions-doped biomimetic mineralization with antibacterial ability via modifying collagen fibrils and eliminating mineralization inhibitory effects of some cationic ions, as well as can excite attention to the neglected multiple regulations of small biomolecules, such as citrate, during biomineralization process.

Designed Microbial Biosynthesis of Hierarchical Bone-Mimetic Biocomposites in 3D-Printed Soft Bioreactors.

The creation of 3D biomimetic composite structures has important applications in tissue engineering, lightweight structures, drug delivery, and sensing. Previous approaches in fabricating 3D biomimetic composites have relied on blending or assembling chemically synthesized molecules or structures, making it challenging to achieve precise control of the size, geometry, and internal structure of the biomimetic composites. Here, we present a new approach for the creation of 3D bone-mimetic biocomposites with precisely controlled shape, hierarchical structure, and functionalities. Our approach is based on the integration of programmable microbial biosynthesis with 3D printing of gas-permeable and customizable bioreactors. The organic and inorganic components are bacterial cellulose and calcium hydroxyapatite via a mineral precursor, which are generated by Komagataeibacter xylinus and Bacillus simplex P6A, respectively, in 3D-printed silicone bioreactors in consecutive culturing cycles. This study is of high significance to biocomposites, biofabrication, and tissue engineering as it paves the way for the synergistic integration of microbial biosynthesis and additive manufacturing.

Effect of calcium-coacervate infiltration of artificial enamel caries lesions in de- and remineralizing conditions

ObjectivesCalcium-coacervate emulsions (CC) might be considered as mineral precursors to foster remineralization of carious dental hard tissues. This study analyzed the instant effect of repeated infiltration of artificial caries lesions with a CC emulsion as well as the effects of subsequent exposure of CC-infiltrated lesions to demineralizing and remineralizing environments. MethodsBovine enamel specimens were partly covered with varnish to leave three exposed windows. Artificial enamel caries lesions were created (pH 4.95, 17d). Baseline controls (BL) were obtained by preparing a thin section of each specimen. Specimens were allocated to five groups. In three groups lesions were etched with 37 % phosphoric acid gel, infiltrated with dipotassium hydrogen phosphate and subsequently with a calcium coacervate emulsion, prepared by mixing CaCl2 ⋅ 2H2O with polyacrylic acid sodium salt (PAA-Na). Subsequently, the infiltration effect was either analyzed immediately (Inf.) or after exposition to either de- (Inf.+DS) or remineralizing solution (Inf.+RS) for 10 or 20 days, respectively. In two control groups specimens were exposed to either DS or RS, respectively without prior CC infiltration. Integrated mineral loss [ΔZ(vol%×µm)] was analyzed using transverse microradiography (TMR). ResultsInfiltration of enamel caries lesions with coacervate solution resulted in only subtle immediate mineral gain even if repeated. When exposed to demineralizing conditions, infiltrated lesions showed significantly less mineral loss compared to untreated controls (p < 0.05; Kruskal Wallis) and exhibited characteristic mineral depositions within the lesion body. ConclusionsWhile immediate mineral gain by infiltration was only modest, the CC-emulsion might be able to prevent demineralization in acidic conditions. Clinical significanceCalcium coacervates might act protective against further demineralization when infiltrated into enamel caries lesions.

Self-Healing Efficiency of Cementitous Mortar Using Different Bacteria Protection Methods and Mineral Precursors

Self-Healing Efficiency of Cementitous Mortar Using Different Bacteria Protection Methods and Mineral Precursors