Dissolution-precipitation Reactions Research Articles

Fabrication and Histological Evaluation of a Fully Interconnected Porous CO3Ap Block Formed by Hydrate Expansion of CaO Granules.

Carbonate apatite (CO3Ap) fabricated by a dissolution-precipitation reaction from a precursor exhibits excellent osteoconductivity and is readily replaced by bone. In the present study, a fully interconnected porous CO3Ap block was fabricated by hydrate expansion and carbonation of CaO granules, and the resulting CaCO3 was then converted to CO3Ap. When CaO granules were exposed to 100% humidity CO2 in a closed vessel, the CaO granules were hydrated and expanded to form a porous Ca(OH)2 block. The block was then carbonated to form a porous CaCO3 block, which was then immersed in a Na2HPO4 solution to convert it to a porous CO3Ap block. The resulting CO3Ap block possessed a fully interconnected porous structure. Histological analyses 4 and 8 weeks after implantation in rabbits revealed that the porous CO3Ap block resulted in more significant material resorption and bone formation than the dense CO3Ap block. Therefore, it was concluded that a fully interconnected porous CO3Ap block fabricated by the hydrate expansion of CaO granules has potential value as a bone substitute.

Corona formation around monazite and xenotime during greenschist-facies metamorphism and deformation

Abstract. Epidote/allanite–fluorapatite coronae around monazite and xenotime are investigated in Permian pegmatites deformed under greenschist-facies conditions during Alpine tectonometamorphism in the Austroalpine basement, Eastern Alps. The aim was to evaluate the replacement reactions involved in the formation of a corona microstructure, its age and relation to deformation. In the corona core, monazite and xenotime single crystals show domains with different composition and age. Monazite (Mnz1) and xenotime (Xen1) dating by electron microprobe (EPM) reveals an age of 250–287 Ma, consistent with the Permian magmatic age of the pegmatites. These are partly replaced by secondary monazite (Mnz2) and xenotime (Xen2) compositions yielding younger Mesozoic (170–210 Ma) and Alpine (30–120 Ma) ages. The same crystallographic orientation of the primary and secondary monazite and xenotime indicates interface-coupled dissolution–precipitation reactions. Allanite U–Th–Pb dating by laser ablation inductively coupled mass spectrometry in the corona revealed an age of 60±6 Ma, interpreted as the age of corona formation. The coronae around monazite consist of an inner zone of equant fluorapatite grains surrounded by prismatic allanite, which are surrounded by epidote enriched in heavy rare earth elements (HREEs) and REE-poor epidote grains. Compared to coronae around monazite, fluorapatite has higher REE contents and no allanite occurs in the coronae surrounding the xenotime. General reactions for monazite and xenotime breakdown can be written as follows: Mnz1+(Si,Ca,Al,Fe,F)fluid→Mnz2+LREE-Ap+Aln+HREE-Ep+Ep+(Th,U)O2+(Th,U)SiO4,Xen1+(Si,Ca,Al,Fe,F)fluid→Xen2+HREE-Ap+HREE-Ep+Ep+(Th,U)O2. The amount of replacement (judged by the relative proportions of monazite and fluorapatite) is low for monazite included in tourmaline but high within the mylonitic foliation. This dependence on the degree of replacement on the local surrounding microfabric indicates that fluid availability along grain boundaries in the matrix and cracks controlled reaction advancement, allowing the elementary mass transfer required for corona formation (e.g. input of Ca, Al, Si, Fe, F). The oblate shape of the coronae aligned within the foliation of the pegmatites and the deflected foliation around the coronae, without an outer rim of prismatic epidote showing signs of deformation, indicate that the main stage of corona formation took place during deformation and reactions were still ongoing after the main stage of deformation. The corona microstructure documents replacement reactions of a single reactant into multiple distinct mineral growth zones by dissolution and precipitation processes at non-isostatic, greenschist-facies conditions, which prevailed in the area to the north of the Defereggen–Antholz–Vals shear zone between the middle Cretaceous and the Oligocene. These reactions ceased before being completed, and REE gradients within single grains within the corona and on the thin-section scale are preserved, which suggests restricted and/or episodic transport of REE in the fluid phase and/or availability of fluid.

A new concept for pore-scale precipitation-dissolution modelling in a lattice Boltzmann framework – Application to portlandite carbonation

Modelling of combined dissolution-precipitation at the pore scale requires the conceptualization of mineral precipitation and crystal growth, the formation of a protective diffusive layer by precipitants and slow reaction kinetics that are all coupled with alterations of the microstructure. In this work, we propose an improved approach for handling these challenges in a pore-scale coupled reactive transport model and apply it to portlandite carbonation. The model combines mineral geometry update as a consequence of dissolution-precipitation reactions during diffusive transport through a saturated porous medium, thermodynamic equilibrium chemistry and dissolution kinetics. Transport of ions is calculated by the lattice Boltzmann transport solver YANTRA. Transport and reaction processes are incorporated at different spatial length scales with the multilevel approach, i.e. mixed liquid-solid nodes in a pore-scale model, which accounts for processes at scales below the model spatial resolution. Instead of defining arbitrary values such as threshold or residual porosities to initiate or halt precipitation, information on crystal shapes, packing and solubility in nano-pores based on interfacial surface energy is used to control precipitation. Additionally, the sensitivity study has been performed on model parameters such as portlandite dissolution kinetics, interfacial surface energy, calcite crystal size, CO2 partial pressure on the rate of carbonation and on the calcite layer properties such as residual porosity and thickness. From the comparison between the modelled calcite growth and the experimental data it has been found that low diffusivity of calcite layer decreases the effect of portlandite dissolution kinetics rate in case of carbonation and diminishes the effect of CO2 partial pressure. Also differences in the structure of the calcite layer were observed for carbonation of portlandite at low and high CO2 partial pressures.

Effect of Particle Size of Quartz Sand Filler on Microstructure and Strength of Alkali-Activated Slag-Based Materials

Interaction between quartz sand and water glass has been investigated and characterized by using the Si/Na molar ratio to determine the role of silica in the polycondensation rate and mechanical properties of the synthesized materials as a function of quartz sand particle size. Results of atomic emission spectroscopy, SEM and compressive strength tests show that interactions between sodium silicate solution and quartz sand depend on the degree of dispersibility that determines the degree of amorphization of quartz sand. When using ordinary quartz sand sodium silicate solution acts as a thin layer of glue covering the grains of sand and weakly binds them to each other, while using finely ground quartz sand in the mixture there is a dissolution–precipitation reaction that modifies the surface layers of the particles and more strongly consolidating the granular system. The increase in the molar ratio of Si/Na in sodium silicate solution containing finely ground quartz sand occurs due to the increase in the proportion of amorphous quartz (according to XRD) and corresponds to the described mechanism. Then, samples of alkali-activated slag-based materials with a coarse ordinary quartz sand and finely ground quartz sand were synthesized, compared in terms of strength and the latter characterized by SEM, porosimetry, XRD. The increase of dispersibility and amorphization of quartz sand is established to favors to form consolidated of low-temperature curing materials based on alkali-activated slag and quartz sand with the significantly increased compressive strength from 30–44 MPa for mixtures based on ordinary coarse quartz sand to 95–140 MPa for finely ground slag/sand blended mixture.

Removal of Phenolic Compounds from Synthetic Solution and Oil Mill Waste Water by Adsorption onto Nanoparticles Synthesized from Phosphate Rock

In this work, we studied the elimination of phenol compounds from phenolic solutions and Oil Mill Waste Water (OMWW) by adsorption method. The adsorbents used are natural phosphate rock coming from Khouribga phosphate mine (Morocco) and an Apatite synthesized from this phosphate by a dissolution–precipitation reactions. Results obtained showed that the structure of natural phosphate and synthesized apatite are respectively Ca9.55(PO4)4.96F1.96 (CO3)1.283 and (Ca10(OH)2(PO4)6). Synthesized apatite has a higher specific surface than natural phosphate (193.62m2/g). The adsorption study showed that the synthesized apatite can be used as an adsorbent to remove phenol from water with very fast reaction kinetics (about 10 min) and an adsorption capacity equal to 15mg/g. The optimal adsorption capacity was found in low values of temperature and in neutral pH. Adsorption kinetics of phenol solution on the two adsorbents can be described by an equation corresponding to a pseudo second order. Freundlich model fitted well with the adsorption isotherms more than the Langmuir model. Characterization of olive mill wastewater shows that, phenol index equal to 0.39 g/l and chemical oxygen demand COD equal to 158 g/l. The treatment of OMWW by adsorption method on the two adsorbents shows that the use of natural phosphate as adsorbent reduced phenol index by 23% and (COD) by 35% while using synthesized apatite reduced phenol index by 30% and COD by 38%.

Hydrogen Phosphate (HPO42-) ions Substitution in Hydrated Layers of OCP by Dicarboxylate ions to Hexagonal HAP Nanocrystals System

The octacalcium phosphate (OCP) crystals are apatite bases with hydrated layers in producing of needle or plate-shaped hydroxyapatite (HAP) nanocrystals, which prepared by a dissolution precipitation reaction. The reaction led to a hexagonal HAP nanocrystals formation under hydrothermal condition via OCP at 180? for 3h with pH of solution adjusted to 5.5 with incorporating dicarboxylate or succinate ions having Ca/P molar ratio is expected to be 1.56±0.02, where the morphology of OCP are retained. During incorporating of succinate ions in OCP crystals, the hydrogen phosphate (HPO42-) ions in the hydrated layers of OCP are being substituted by succinate ions. These organically modified OCP which generated to HAP with unique nanostructures have been characterized by using of SEM, FTIR and X-ray diffraction analysis. Since the crystal system of HAP is hexagonally and its crystalline size in the direction of various (a,b,c) axes depending on the thickness of the plate-shaped HAP crystals where their size as perpendicular to the (100) plane is calculated by using of Scherrer equation D100 = K?/(? cos?). The formed hexagonal HAP are used in soft and hard tissue engineering system for biomedical application.

Formation of Natural Silicate Hydrates by the Interaction of Alkaline Seepage and Sediments Derived from Serpentinized Ultramafic Rocks at Narra, Palawan, the Philippines

In radioactive waste disposal facilities, low-permeability engineered barrier materials are important for inhibiting radionuclide migration. However, dissolution–precipitation reactions under alkaline conditions change the permeability of engineered barriers. To understand long-term dissolution–precipitation reactions under alkaline conditions in chemically complex systems, trenches and drill holes were excavated at Narra in Palawan, where alkaline fluids (pH > 11) have been naturally produced, seeping into clastic sediments derived from serpentinized ultramafic rocks and gabbro of Palawan ophiolite. Interaction between the alkaline seepage and clastic sediments, which have been deposited since 15,000 radiocarbon years before present (14C yr BP), led to dissolution of minerals and the precipitation of Si-bearing phases which were divided into two main categories: Fe-Mg-Si infillings and Ca-Si infillings. The former category was composed of iron-magnesium-silicate-hydrate (F-M-S-H) and a nontronite-like mineral and was widely recognized in the clastic sediments. The nontronite-like mineral likely formed by interaction between silicates and alkaline seepage mixed with infiltrated seawater, whereas F-M-S-H formed by the reaction of silicates with alkaline seepage in the absence of seawater infiltration. Ca-Si infillings included 14 Å tobermorite and were precipitated from alkaline seepage combined with the Ca and Si supplied by the dissolution of calcite and silicates in the clastic sediments.

Utilization of produced water baseline as a groundwater monitoring tool at a CO2-EOR site in the Permian Basin, Texas, USA

Carbon dioxide (CO2) enhanced oil recovery (EOR) provides a pathway for economic reuse and storage of CO2, a greenhouse gas. One challenge with this practice is ensuring CO2 injection does not result in target reservoir fluids migrating into overlying shallow (<1000 m) groundwater formations. Effective monitoring for leakage from storage formations could involve measuring sensitive chemical indicators in overlying groundwater units and within the producing formation itself for evidence of deviation from an initial state. In this study, produced waters and overlying groundwaters were monitored over a five-year period to evaluate which geochemical signals may be useful to ensure that oilfield produced waters did not impact overlying groundwaters. During this five-year period, a mature carbonate oil reservoir in the Permian Basin transitioned from a waterflooding operation to a water-alternating-gas injection (WAG), in which the formation was flooded with CO2 and various mixtures of produced water. Significant increases in dissolved inorganic constituents [alkalinity, TDS, Na+, Cl−, SO42−] were observed in produced waters following CO2 injection; however, carbonate reservoir dissolution-precipitation reactions appear to be minimal and injected CO2 appears to be stored via solubility trapping. Although there are statistically significant geochemical variations following CO2 injection, applying isometric log-ratios to certain parameters establishes a narrow range for post-CO2 injection produced waters. This narrow range can be considered a baseline for post-CO2 injection produced waters; this baseline can be utilized to monitor overlying local groundwaters for produced water intrusion. Additionally, certain parameters [Na+, Ca2+, K+, Cl−, alkalinity, and TDS] display large concentration disparities between produced water and overlying groundwaters; these parameters would be sensitive indicators of produced water intrusion into overlying groundwaters.

Hydration mechanisms of Ba-doped ye'elimite: Effect of Ba/Ca ratio on hydration behavior

Ba-doped ye'elimite, abbreviated as C4-xBxA3$ (x>0), presents even more satisfactory hydration properties than stoichiometric one. However, the hydration mechanism is not well understood, in particular for the effect of Ba/Ca ratio on hydration behavior. To shed light on this issue, high purity C4-xBxA3$ samples with designed element compositions (C4A3$, C3.5B0.5A3$, and C3BA3$) were prepared and their hydration processes were investigated. The results reveal that Ba-doped ye’elimite reacts faster than the stoichiometric ye’elimite. With the increase of Ba/Ca ratio, it can gradually increase the intensity of the initial peak, shorten the dormant period and reduce the total hydration heat. The phase composition evolution based on Rietveld/XRD method demonstrates that the dissolution rate of the C3.5B0.5A3$ and C3BA3$ are about 19% and 28% higher than that of C4A3$ in 6h. Moreover, the hydration sequences and main products varied significantly. The AFt is absent for the system with barium incorporation and AFm tends to be less with the increase of Ba/Ca ratio. This paper also proposes a new acceleration mechanism of Ba-doped ye'elimite. It is summarized as a higher rate of dissolution-precipitation reaction stemmed from higher ion precipitation of BaSO4 and a combination of extra surface for the nucleation sites provided by BaSO4.

Using natural systems evidence to test models of transformation of montmorillonite

Safety functions for the clay buffer in a repository for high-level radioactive waste (HLW) are fulfilled if the presence of montmorillonite with high swelling capacity and low permeability is maintained in the long-term. The transformation of montmorillonite to the non-swelling mineral illite is addressed in most safety assessments by using simple semi-empirical kinetic models, but this approach contrasts with all other near-field geochemical modelling activities that employ a full description of thermodynamic and kinetic mineral-fluid processes. The consistency of these two modelling approaches has been studied by simulating the montmorillonite to illite transformation in the marine sediment profile penetrated by the Ocean Drilling Program (ODP) Site 1174, offshore Japan. Illite in mixed-layer smectite-illite increases from 20% at <700 m below seafloor (mbsf) to 89% at 1100 mbsf. Illitization of smectite at Site 1174 using the semi-empirical approach has been shown by previous authors to provide a satisfactory match to the gradual change of illite content with depth, albeit with significant differences between model variants.In comparison, the approach used in the current study was to simulate the mineralogical and fluid chemical evolution of a ‘packet’ of a typical fluid-saturated sediment using a model involving full kinetic and thermodynamic treatment of mineral dissolution-precipitation reactions, along a temperature-time burial curve defined by published thermal conductivity data for Site 1174. The results of these simulations showed that the onset of illitization at a depth of 700 mbsf could be matched, but that the overall rate of conversion was significantly more rapid than observed, or as modelled by the simple semi-empirical kinetic approach. The onset and rate of illite growth was strongly linked to the rate of transformation of amorphous silica to quartz. Geochemical model simulations therefore err on the side of conservatism, but may produce unrealistic estimates of illitization. This comparison demonstrates that models involving full kinetic and thermodynamic treatment of mineral dissolution-precipitation reactions must be carefully applied to simulate other transformation reactions of montmorillonite relevant to the geological disposal of HLW, such as those arising from the interaction of montmorillonite with iron/steel, cement and/or groundwater.

Fabrication of three-dimensional interconnected porous blocks composed of robust carbonate apatite frameworks

In scaffolds used for bone regeneration, osteogenic ability increases and mechanical strength decreases with increasing porosity. To ensure both mechanical strength and osteogenesis, an optimal pore architecture is necessary. Porous glass has high porosity and high mechanical strength, as it is framed with a rigid interconnected silica network and void interspaces in the silica network. In this context, based on the porous structure of glass, we fabricated porous blocks composed of carbonate apatite (CO3Ap), which is the major component of human bone mineral, with both high mechanical strength and high porosity. To fabricate the CO3Ap blocks, first, calcite-polymethyl methacrylate (PMMA) mixture granules were prepared. Next, the calcite-PMMA granules were allowed to join together in the mold by fusing PMMA, resulting in the formation of porous blocks composed of interconnected calcite-PMMA granules. Next, PMMA was thermally removed and the resultant interconnected calcite granules were partially sintered. Finally, the composition of the interconnected granules was converted from calcite to CO3Ap in a dissolution-precipitation reaction. Consequently, CO3Ap blocks with a continuous pore architecture were successfully fabricated. The porosity and diametral tensile strength were controllable within the range of 60‒70% and 1.0‒1.5 MPa, respectively, by filling the space between the calcite-PMMA granules. As these values are suitable for clinical use, the porous CO3Ap blocks have potential applications as scaffolds for bone regeneration.

Replacement reactions of copper sulphides at moderate temperature in acidic solutions

Understanding mineral transformations of composite copper sulphide ores and the associated reaction mechanism at low to medium temperatures in acidic solutions with oxidant restriction is important for in situ recovery operations because natural ore bodies typically comprise multiple sulphide species and their dissolution is oxidant consuming. Here we present experimental observations on mineral replacement reactions of coarse-grained natural bornite (Cu5FeS4)–chalcocite (Cu2S) samples in acidic solutions at 90 °C and in the absence of oxidant. Transformations were found to follow a three-stage reaction sequence for bornite and one stage for chalcocite. Bornite replacement commenced with the formation of digenite (Cu1.8S) along fractures and surfaces. Bornite–digenite interfaces are sharp and digenite rims contain nanochannels that connect to the original bornite. When copper dissolution exceeded 30%, copper-deficient lamellae exsolved from the bornite by solid-state diffusion; this texture appeared only in stronger acidic solutions with extended times and did not occur in the heating experiments without fluid. Chalcocite that was present together with bornite in the unreacted samples transformed into digenite characterized by laminar replacement textures. Finally, all phases were replaced by covellite (CuS) accompanied by the formation of porosity. These replacements showed the concomitant operation of fluid-induced solid-state diffusion and fluid-mediated mineral replacement by coupled dissolution–precipitation reactions. The textures found in the resulting covellite showed a promising increase in porosity that could be beneficial for hard-rock in situ recovery and suggests a pathway for refractory sulfide processing by acid pre-treatment.

Challenges to rutile-based geoscientific tools: low-temperature polymorphic TiO2 transformations and corresponding reactive pathways

Rutile, a common accessory mineral in a wide variety of rocks, is the most stable naturally occurring TiO2 polymorph. The relationship between its trace element composition and formation conditions has provided geoscientists with discriminant tools for fingerprinting geological processes, such as magmatic evolution and subduction zone metamorphism, alongside applications to the study of sediment provenance. In the present work, volcaniclastic rock samples belonging to Fara and Saiq Formations, outcropping in Jebel Akhdar mountains, Oman, are studied with Raman spectroscopy and Electron Microprobe (EMP) aiming: of (i) the identification of different naturally-occurring TiO2 polymorphs, (ii) the evaluation of their trace element contents in relation with hydrothermal alteration features, and (iii) the analysis of the mineral reactive pathways behind the observed textural relationships. Raman investigations demonstrated that interstitial, fine-grained TiO2 corresponds to anatase, whereas rutile occurs as isolated single grains. EMP determinations further revealed that an identified Nb-enrichment in anatase is coupled with a corresponding Nb-depletion in rutile. The combination of the obtained results with petrographic observations enabled unravelling the TiO2 reactive pathways affecting the studied samples. Thus, a coupled polymorphic dissolution-precipitation reaction assisting rutile-to-anatase conversion has been defined, together with the role of Nb in further stabilizing the structure of the lower temperature polymorph. Semi-quantitative thermometric considerations suggest that rutile substrates are likely of magmatic origin, whereas anatase formation is clearly associated with a lower temperature aqueous environment. The gathered results raise fundamental questions concerning the application of commonly used rutile-based geochemical and thermometric tools.

The contribution of aqueous catechol-silica complexes to silicification during carbonate diagenesis

Pore-filling and carbonate-replacing silica is exceedingly common in carbonates, but the fundamental geochemical mechanisms that drive these silicification reactions during diagenesis remain poorly understood. An existing model has proposed that carbonate silicification proceeds through an interface-coupled dissolution-precipitation reaction, but it lacks a mechanism that enables pore fluids to reach the requisite level of supersaturation with respect to silica to allow nucleation and growth. Here, we present a sequence of batch experiments ranging in duration from 7 to 49 days designed to test the hypothesis that these reactions are facilitated by the formation and destruction of organo-silica complexes during diagenesis. Our results illustrate that the stability of organo-silica complexes is dependent upon the concentration of organic molecules in solution, as well as pH, salinity, and solution redox state. Together, these results allow us to present the following scheme for organo-silica complex mediation of silicification reactions: Firstly, the breakdown of organic matter in the presence of siliceous material creates organo-silica complexes, leading to silica-enriched pore fluids, a process which is enhanced by the anoxic conditions accompanying sediment burial. Then, as environmental conditions evolve (fO2, salinity, light, fCO2, pH…), the stability of the organo-silica complexes diminishes, and the organo-silica complexes break down. Simultaneously, the pore fluids become intensely silica-supersaturated, in direct proportion to the amount of organic material remaining in solution. The resulting supersaturation drives carbonate silicification via the precipitation of silica minerals, a process which is aided by the presence of silica “nuclei” (such as sponge spicules). This study contributes new data and a conceptual model that will aid in the ongoing quest to understand carbonate silicification reactions and their potential applications in hydrocarbon exploitation and geologic CO2 storage. Moreover, it helps to explain the common association between silica precipitates and organic mineral in the sedimentary rock record.

Membrane‐Free Zn/MnO2 Flow Battery for Large‐Scale Energy Storage

AbstractThe traditional Zn/MnO2 battery has attracted great interest due to its low cost, high safety, high output voltage, and environmental friendliness. However, it remains a big challenge to achieve long‐term stability, mainly owing to the poor reversibility of the cathode reaction. Different from previous studies where the cathode redox reaction of MnO2/MnOOH is in solid state with limited reversibility, here a new aqueous rechargeable Zn/MnO2 flow battery is constructed with dissolution–precipitation reactions in both cathodes (Mn2+/MnO2) and anodes (Zn2+/Zn), which allow mixing of anolyte and catholyte into only one electrolyte and remove the requirement for an ion selective membrane for cost reduction. Impressively, this new battery exhibits a high discharge voltage of ≈1.78 V, good rate capability (10C discharge), and excellent cycling stability (1000 cycles without decay) at the areal capacity ranging from 0.5 to 2 mAh cm‐2. More importantly, this battery can be readily enlarged to a bench scale flow cell of 1.2 Ah with good capacity retention of 89.7% at the 500th cycle, displaying great potential for large‐scale energy storage.

Zinc and chromium co-doped calcium hydroxyapatite: Sol-gel synthesis, characterization, behaviour in simulated body fluid and phase transformations

In this study for the synthesis of zinc and chromium co-doped calcium hydroxyapatite (Ca10(PO4)6(OH)2:Zn,Cr; CHAp:Zn,Cr) an aqueous sol-gel processing has been used. The substitution effects on the sinterability, phase purity and morphological properties of CHAp:Zn, Cr were investigated in the present work. The proposed synthesis route is suitable for the preparation of monophasic calcium hydroxyapatite doped with zinc and chromium up to 7%. Single-phase CHAp:Zn, Cr samples were immersed into simulated body fluid (SBF) solution for one month. The formation of low crystalline CHAp in SBF possibly via dissolution-precipitation reaction was observed. This simple synthetic approach offered a feasible way to obtain highly homogeneous zinc and chromium co-doped CHAp bioceramics with possible application in medicine. The synthesis products were characterized using X-ray powder diffraction (XRD) analysis, infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The content of Ca, P, Zn and Cr was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES).

Synthesis of B-type carbonated hydroxyapatite by a new dissolution-precipitation method

Carbonated hydroxyapatite (C-HAp) is one of the most attractive biomaterials for bone tissue engineering due to its compositional and biological similarity to the mineral part of human bone. In the present work, we have used a two-step fabrication process to precipitate a poorly crystalline Carbonated Hydroxyapatite (C-HAp) with nano-size particles at room temperature (20 °C) through the dissolution-precipitation process. For the first time, stoichiometric hydroxyapatite (S-HAp) was used as a precursor. The obtained C-HAp was evaluated for its structure; chemical composition and particle size using numerous analytical tools, including Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), Thermogravimetric analysis (TGA), and Scanning Electron Microscopy (SEM). The chemical composition, carbonate content, and molar ratio (Ca/P) of the C-HAp phase was investigated by the corresponding X-ray energy dispersive spectrometer (EDX). Therefore, the dissolution-precipitation reaction was confirmed to be useful to transform S-HAp to C-HAp.

Comparative study on physicochemical properties of alpha-TCP / calcium sulphate dihydrate biomicroconcretes containing chitosan, sodium alginate or methylcellulose

Recently, the attention has been drawn to complex systems - biomicroconcretes composed of a bone cement matrix and resorbable granules or microspheres. This paper presents novel bone substitutes composed of α-tricalcium phosphate (α-TCP; cement matrix), calcium sulphate dihydrate granules (GCSD; aggregates in biomicroconcrete) and various polymers (chitosan, sodium alginate, methylcellulose) used for the improvement of material properties. The aim of this work was to study α-TCP-GCSD-polymer interactions and to compare the impact of organic additives on the physicochemical properties of biomicroconcretes. Scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), X-ray diffractometry (XRD) as well as universal testing machine (INSTRON), Gilmore apparatus and pH/ conduct-meter were used. The chemical bonding between α-TCP matrix and CSD granules resulted in a compressive strength appropriate for low-load bearing applications (7-12 MPa) and clinically relevant setting times (8-33 min). Biomicroconcretes consisting of sodium alginate possessed the highest mechanical strength (12 ± 2 MPa). It has also been found that the dissolution-precipitation reactions of the α-TCP were retarded with the addition of chitosan and acetic acid. This effect was not observed in the case of methylcellulose and sodium alginate. Chemical stability and bioactivity of materials were demonstrated during in vitro studies in simulated body fluid. Materials containing calcium sulphate-based granules were surgically handy, possessed promising physicochemical properties and are supposed to ensure desired macroporosity as well as gradual resorption in vivo. It has been demonstrated that the presence of CSD granules and polymers influenced the physicochemical properties of composites.

Coupled dissolution–precipitation reactions of tennantite-tetrahedrite minerals in the Darasun gold deposit (Eastern Transbaikalia, Russia)

Heterogeneous rhythmic-zonal aggregates of tennantite-IV replaced partly or completely early homogeneous Zn-tetrahedrite-I and euhedral (Fe-Zn)-tennantite-I crystal were found in ores of the Darasun gold deposit. Different replacement stages of fahlore were observed. It initiates at grain boundaries and is terminated by a complete transformation into pseudomorphic newly formed (Zn-Fe)-tennantite-IV aggregates rimed with Zn-tetrahedrite-IV. These aggregates associated intimately with bournonite and galena and their deposition initiated the pseudomorph formation. EMPA revealed that (Fe-Zn)-tetrahedrite richer in As relative to Zn-tetrahedrite-I was deposited at initial stage. Tennantite with wide variation in Sb/(Sb + As) and Fe/(Fe + Zn) ratios predominantes in heterogenous zonal aggregates of (Fe-Zn)-tetrahedrite-tennantite-IV. A negative correlation between the Sb/(Sb + As) and Fe/(Fe + Zn) was found in these minerals. In each site at the contact between Zn-tetrahedrite-I and newly formed (Fe-Zn)-tetrahedrite-tennantite-IV a miscibility gap between As and Sb a sharp drop in the Sb/(Sb + As) ratio and an increase in Fe/(Fe + Zn) ratio occur. Sharp saw-shape boundaries between Zn-tetrahedrite-I and tennantite-IV and voids in newly formed aggregates are considered to be evidence for couple dissolution-precipitation reactions. The dissolution was initiated due disequilibrium between Zn-tetrahedrite-I and an undersaturated fluid resulted from deposition of galena and bournonite. Precipitation of tetrahedrite-tennantite-IV occurred under oscillation in Sb/(Sb + As) and Fe/(Fe + Zn) ratios due to the metal and semimetal contents in the fluid. Crystallization temperature of zonal-heterogenous tennantite-IV aggregates was calculated by sphalerite-fahlore geothermometer which shows (134161) 20 С. Instability of early Zn-tetrahedrite-I resulted from fluid cooling, decreasing in fluid salinity, changing in tetrahedrite and tennantite solubility due to an evolution of migration conditions of semimetals.

Fabrication of porous carbonate apatite granules using microfiber and its histological evaluations in rabbit calvarial bone defects.

Carbonate apatite (CO3 Ap) granules are known to show good osteoconductivity and replaced to new bone. On the other hand, it is well known that a porous structure allows bone tissue to penetrate its pores, and the optimal pore size for bone ingrowth is dependent on the composition and structure of the scaffold material. Therefore, the aim of this study was to fabricate various porous CO3 Ap granules through a two-step dissolution-precipitation reaction using CaSO4 as a precursor and 30-, 50-, 120-, and 205-μm diameter microfibers as porogen and to find the optimal pore size of CO3 Ap. Porous CO3 Ap granules were successfully fabricated with pore size 8.2-18.7% smaller than the size of the original fiber porogen. Two weeks after the reconstruction of rabbit calvarial bone defects using porous CO3 Ap granules, the largest amount of mature bone was seen to be formed inside the pores of CO3 Ap (120) [porous CO3 Ap granules made using 120-μm microfiber] followed by CO3 Ap (50) and CO3 Ap (30). At 4 and 8 weeks, no statistically significant difference was observed based on the pore size, even though largest amount of mature bone was formed in case of CO3 Ap (120). It is concluded, therefore, that the optimal pore size of the CO3 Ap is that of CO3 Ap (120), which is 85 μm.