Ca Phosphate Research Articles

Genomic insights into organic acid production and plant growth promotion by different species of phosphate-solubilizing bacteria.

Bacteria can solubilize phosphorus (P) through the secretion of low-molecular-weight organic acids and acidification. However, the genes involved in the production of these organic acids are poorly understood. The objectives of this study were to verify the calcium phosphate solubilization and the production of low-molecular-weight organic acids by diverse genera of phosphate solubilizing bacterial strains (PSBS); to identify the genes related to the synthesis of the organic acids in the genomes of these strains and; to evaluate growth and nutrient accumulation of maize plants inoculated with PSBS and fertilized with Bayóvar rock phosphate. Genomic DNA was extracted for strain identification and annotation of genes related to the organic acids production. A greenhouse experiment was performed with five strains plus 150mg dm- 3 P2O5 as Bayóvar rock phosphate (BRP) to assess phosphate solubilization contribution to maize growth and nutrition. Paraburkholderia fungorum UFLA 04-21 and Pseudomonas anuradhapurensis UFPI B5-8A solubilized over 60% of Ca phosphate and produced high amounts of citric/maleic and gluconic acids in vitro, respectively. Eleven organic acids were identified in total, although not all strains produced all acids. Besides, enzymes related to the organic acids production were found in all bacterial genomes. Plants inoculated with strains UFPI B5-6 (Enterobacter bugandensis), UFPI B5-8A, and UFLA 03-10 (Paenibacillus peoriae) accumulated more biomass than the plants fertilized with BRP only. Strains UFLA 03-10 and UFPI B5-8A increased the accumulation of most macronutrients, including P. Collectively, the results show that PSBS can increase maize growth and nutrient accumulation based on Bayóvar rock phosphate fertilization.

Regulation of osteogenesis and angiogenesis by cobalt, manganese and strontium doped apatitic materials for functional bone tissue regeneration

Strontium, cobalt, and manganese ions are present in the composition of bone and useful for bone metabolism, even when combined with calcium phosphate in the composition of biomaterials. Herein we explored the possibility to include these ions in the composition of apatitic materials prepared through the cementitious reaction between ion-substituted calcium phosphate dibasic dihydrate, CaHPO4·2H2O (DCPD) and tetracalcium phosphate, Ca4(PO4)2O (TTCP). The results of the chemical, structural, morphological and mechanical characterization indicate that cobalt and manganese exhibit a greater delaying effect than strontium (about 15 at.%) on the cementitious reaction, even though they are present in smaller amounts within the materials (about 0.8 and 4.5 at.%, respectively). Furthermore, the presence of the foreign ions in the apatitic materials leads to a slight reduction of porosity and to enhancement of compressive strength. The results of biological tests show that the presence of strontium and manganese, as well as calcium, in the apatitic materials cultured in direct contact with human mesenchymal stem cells (hMSCs) stimulates their viability and activity. In contrast, the apatitic material containing cobalt exhibits a lower metabolic activity. All the materials have a positive effect on the expression of Vascular Endothelial Growth Factor (VEGF) and Von Willebrand Factor (vWF). Moreover, the apatitic material containing strontium induces the most significant reduction in the differentiation of preosteoclasts into osteoclasts, demonstrating not only osteogenic and angiogenic properties, but also ability to regulate bone resorption.

The role of calcium phosphates and silicates in the storage and transport of phosphorus at the upper-to-lower mantle transition: An experimental study to 25 GPa in a model peridotitic bulk composition

Calcium (Ca) phosphates are major hosts for phosphorus, halogens and incompatible trace elements in the Earth’s crust and mantle and, by supplying almost all phosphorus to the biosphere, are indispensable for sustaining life on Earth. To better understand the role of Ca-phosphates in the deep silicate Earth portion of the global phosphorus cycle at depths of the transition zone, we performed experiments in the P-T range of 15–25 GPa and 1600–2000 °C using a moderately fertile peridotite doped with 3 % synthetic β-Ca3(PO4)2 and 1 % of a trace element mix containing a range of HFSE, LILE, REEs, Cl and Br. Tuite is stable to at least 25 GPa at which pressure its upper T-stability limit is between 1700 and 1750 °C. At 15 GPa, by comparison, the upper T-stability limit is located between 1750 and 1800 °C, indicating a negative slope of the tuite-out reaction(s). Thus, tuite is stable to at least 700-km depth with a maximum T-stability close to or slightly above the average current mantle adiabat (ACMA) at 20–25 GPa and significantly above the ACMA at 15 GPa. Beyond the P-T stability limit of majoritic garnet, tuite is the principal subsolidus phosphorus carrier in the uppermost lower mantle. Beyond the P-T stability limit of tuite, phosphorus is likely to either (i) enter a Ca3(PO4)2 polymorph with an even higher density, (ii) form an entirely new phosphate phase or (iii) be accommodated in lower mantle silicates in six-fold coordination. Within the P-T range of our experiments, the phases encountered show the following trend of phosphorus contents:Pmelt>Pmajoritic garnet > Polivine ≅ Pringwoodite > Pdavemaoite ≅ Pwadsleyite > Pclinoenstatite ≅ Pbridgmanite ≅ Pferropericlase. Even when coexisting with tuite, bridgmanite and ferropericlase show phosphorus contents < 100 µg/g, and davemaoite has phosphorus contents that do not exceed 390 µg/g, testifying to the very limited phosphorus storage capacity of the lower mantle. Model calculations based on the phosphorus contents of ocean island basalts (OIBs) compared with those of mid ocean ridge basalts (MORBs) indicate that the OIB source is significantly richer in phosphorus than the MORB source and, for a wide range of OIB phosphorus contents, is likely to contain modal apatite. The relative importance of Ca-phosphates and silicates as phosphorus carriers in the peridotitic upper and uppermost lower mantle is strongly dependent upon pressure and the bulk phosphorus content. With increasing P, phosphorus is progressively transferred from Ca-phosphates to silicates with an ensuing decrease in the modal amount of the Ca-phosphates. Dependent upon the bulk phosphorus content, this may cause the Ca-phosphates to disappear before the upper-to-lower mantle boundary is reached, leaving majoritic garnet as the major phosphorus host. Breakdown of garnet will subsequently cause tuite to re-appear in the uppermost lower mantle and to resume its role of the principal subsolidus phosphorus carrier. For sufficiently high bulk phosphorus contents, tuite will remain stable throughout the transition zone, thereby maintaining phosphorus saturation in the coexisting silicates, and will eventually be joined by the tuite newly generated by garnet breakdown.

Phosphorus speciation in manure and fertilizer impacted Mid-Atlantic coastal plain soils.

Historical applications of manures and fertilizers at rates exceeding crop P removal in the Mid-Atlantic region (United States) have resulted in decades of increased water quality degradation from P losses in agricultural runoff. As such, many growers in this region face restrictions on future P applications. An improved understanding of the fate, transformations, and availability of P is needed to manage P-enriched soils. We paired chemical extractions (i.e., Mehlich-3, water extractable P, and chemical fractionation) with nondestructive methods (i.e., x-ray absorption near edge structure [XANES] spectroscopy and x-ray fluorescence [XRF]) to investigate P dynamics in eight P-enriched Mid-Atlantic soils with various management histories. Chemical fractionation and XRF data were used to support XANES linear combination fits, allowing for identification of various Al, Ca, and Fe phosphates and P sorbed phases in soils amended with fertilizer, poultry litter, or dairy manure. Management history and P speciation were used to make qualitative comparisons between the eight legacy P soils; we also speculate about how P speciation may affect future management of these soils with and without additional P applications. With continued P applications, we expect an increase in semicrystalline Al and Fe-P, P sorbed to Al (hydro)oxides, and insoluble Ca-P species in these soils for all P sources. Under drawdown scenarios, we expect plant P uptake first from semicrystalline Al and Fe phosphates followed by P sorbed phases. Our results can help guide management decisions on coastal plain soils with a history of P application.

Influence of citrate- and phosphate-based calcium sequestering salts on the disruption of casein micelles

The disruption of casein micelles through the addition of calcium sequestering salts (CSS) disodium phosphate (DSP), disodium pyrophosphate (DSPP) and tetrasodium pyrophosphate (TSPP), sodium tripolyphosphate (STPP), sodium hexametaphosphate (SHMP) and trisodium citrate (TSC) at 10, 15, 20 and 30 mEq/L levels was investigated in 5% micellar casein isolate (MCI) solution. All the CSS, except DSPP and TSPP, showed a decrease in particle size and viscosity with increasing concentration. The addition of 10–30 mEq/L of CSS to MCI decreased the protein-bound sedimentable Ca and P at pH 6.5 10 kDa-permeable Ca decreased with increasing concentration of DSP, DSPP, TSPP, STPP and SHMP. These results indicate that orthophosphates, pyrophosphates and polyphosphates combined with Ca to form insoluble Ca phosphate complexes together with casein. Higher amount of 10 kDa permeable Ca for MCI samples with TSC confirms the formation of soluble Ca-citrate complexes.

Calcium Phosphate Brushite Cements Made of Substituted Tricalcium Phosphate Ca3(PO4)2 and Reinforced with Silicate Glass Fiber

Calcium Phosphate Brushite Cements Made of Substituted Tricalcium Phosphate Ca3(PO4)2 and Reinforced with Silicate Glass Fiber

Structural and luminescence performance of the Eu3+ doped alkaline combined metal oxide-based sodium phosphate phosphors; NaMPO4 (M = Mg, Ba, and Ca) for LED applications

The present research module is about the synthesis of Eu3+ ions-doped NaMPO4(M = Mg, Ba, and Ca) phosphate phosphors by the solution combustion synthesis method. The phase formation and chemical structures of alkaline combined metal oxide-based sodium phosphate phosphors are characterised by X-ray powder diffraction (XRD) and FT-IR measurements. Optimized crystal geometries were generated by employing VESTA software. The crystallite size was calculated from the full width at half maximum (FWHM) of the diffraction peak using the Scherrer formula. G-Fourier transformation software (G-FT) was adopted for generating electron density mapping of NaMgPO4 phosphors, 2D mapping, and 3D chicken plots showing crystal sites occupied by the compound’s constituent elements. The particle size distribution was confirmed by XRD diffraction, and SEM analysis found approximately 12 μm. UV–visible and photoluminescence spectroscopy uncover the optical traits of the prepared phosphor. Photo-emissions of Eu3+doped alkaline combined metal oxide-based sodium phosphate phosphors were monitored at possible excitation wavelengths. The orange-red peak observed at 592 nm and 598 nm occurs due to 5D0-7F1 electric dipole transitions. The peak observed at 618 nm corresponds to the forbidden f-f transitions 5D0-7F2. It is worth mentioning that absorption bands originating from the corresponding 5D0-7F2 transition widen the band region; hence, the stark effect becomes complicated. A low-intensity peak of 688 nm was observed in the NaCaPO4 phosphors, attributed to the 5D0-7F3 transition. Chromaticity coordinates and energy level transitions may determine the colour emission materials. The CIE coordinates of NaMPO4:Eu3+phosphors exhibit reddish emission and find application in light-emitting diodes (LEDs) and illuminating displays.

Magnesium Strengthening in 3D Printed TCP Scaffold Composites

This study reports the production of a Mg/15%β-tricalcium phosphate Ca3(PO4)2 composite by combining direct ink writing for the β-TCP preform and liquid infiltration technique to obtain a continuous metal matrix composite. The influence of the volume fraction of β-TCP and the in situ reaction between ceramic and metal on the microstructure and mechanical properties were investigated in detail. The β-TCP preform was uniformly distributed in the matrix, forming a continuous three-dimensional (3D) network. The obtained composite was characterized by means of relative density (He pycnometry), X-ray diffractometry (XRD), scanning electron microscopy (SEM), and electron spectroscopy (EDX). The results suggested that a highly densified composite was processed. Three phases were identified as products generated by an exothermic reaction (Mg2Ca, CaO, and MgO); based on this, the chemical reaction mechanism for MgO formation was proposed. The compression and hardness tests showed that the Mg/15%β-tricalcium phosphate Ca3 (PO4)2 composite significantly improved its mechanical properties, i.e., 27% and 15% higher than pure Mg in compressive strength and yield strength, respectively. This behavior was attributed to the high densification of the resulting composite, strong chemical interfacial bonding, phase dispersion hardening (in situ phase formation), and the geometry and continuity of the reinforcement. These provided good load transfer from the Mg matrix to the reinforcement and contributed as strengthening mechanisms. The results reported in this investigation can help to design Mg/calcium phosphate continuous composites for biomedical applications.

Natural Nitrogen-Bearing and Phosphorus-Bearing Nanoparticles in Surface Sediments of the Pearl River Estuary, China: Implications for Nitrogen and Phosphorus Cycling in Estuarine and Coastal Ecosystems

Eutrophication creates multiple environmental problems, threatening the ecological security and sustainability of estuarine and coastal ecosystems worldwide. Key nutrients of concern are nitrogen (N) and phosphorus (P), which are the main controls in eutrophication. Considering that sediments are inseparable sinks of N and P, concern has grown regarding the forms in which N and P occur in the surface sediments of estuaries and coastal areas. Nonetheless, studies on the natural N-bearing or P-bearing nanoparticles in estuarine and coastal sediments have rarely been reported. Herein, the surface sediments (0–5 cm) of the Pearl River Estuary in China were collected and subjected to analysis. Using high-resolution transmission electron microscopy (HR-TEM) analysis, numerous natural N-bearing and P-bearing nanoparticles were observed. The results revealed that there are some differences in the occurrence forms of N and P in nanoparticles, suggesting that N and P could be adsorbed by nanoparticles of minerals such as hematite, goethite, muscovite, anorthite and quartz in estuarine and coastal environments, and further form N-bearing and P-bearing nanoparticles. These nanoparticles contained small amounts of N (1.52–3.73 wt%) and P (0.22–1.12 wt%), and were mainly single crystal or polycrystalline in form, with sizes ranging from 10 nm × 50 nm to 250 nm × 400 nm. In addition, P was shown to exist in the form of Ca and Fe phosphate nanoparticles in the estuarine sediments. The Ca and Fe phosphate nanoparticles had higher phosphorus content (5.02–9.97 wt%), mainly amorphous, with sizes ranging from 50 nm × 120 nm to 250 nm × 400 nm. Moreover, N-bearing and P-bearing nanoparticles could influence the migration, precipitation and release processes of N and P, and play a certain role in the N-cycling and P-cycling of estuarine and coastal ecosystems. Furthermore, we explored the role of N-bearing and P-bearing nanoparticles in the N-cycling and P-cycling in estuarine and coastal ecosystems. Thus, this study could provide new ideas for water environment management and other related research fields.

Effects of calcium supplements on oral bioavailability of fluoride in soil based on In Vivo and In Vitro methods

Dietary calcium (Ca) intake can alleviate fluoride (F) induced fluorosis to maintain bone health. However, it is unclear whether calcium supplements can reduce the oral bioavailability of F present in contaminated soils. Here we evaluated the effects of Ca supplements on F bioavailability in three soils using an in vitro method (Physiologically Based Extraction Test) and an in vivo mouse model. Seven Ca salts, commonly used in calcium supplements, significantly reduced the F bioaccessibility in the gastric and small intestinal phases. Particularly for Ca phosphate at 150 mg Ca supplementation, F bioaccessibility in the small intestinal phase was reduced from 35.1–38.8% to 0.7–1.9% where soluble F concentrations were less than 1 mg/L. Overall, the eight Ca tablets tested in this study showed greater efficiency at decreasing F solubility. The in vitro bioaccessibility after Ca supplementation was consistent with the relative bioavailability of F. As supported by X-ray photoelectron spectroscopy, a possible mechanism is that freed F can be bound by Ca to form insoluble CaF2 and exchanged with OH groups from Al/Fe hydroxide to strongly adsorb F. These findings provide evidence of Ca supplementation in reducing health risks associated soil F exposure.

Characteristics of ceramic-like coatings obtained by plasma electrolyte oxidation on different Ti alloys

Plasma electrolyte oxidation was used to modify the surface of different Ti alloys: c.p. Ti (α hcp structure), Ti–15Nb (α′+β structure) and Ti–33Nb–33Zr (stable β cubic structure) and the influence of elements and microstructure in the TiO2-based ceramic layer formed as well as the surface properties was analyzed. The XRD patterns confirmed the presence of TiO2 (anatase and rutile) in the c.p. Ti. For Ti–15Nb (wt.%) indicated the presence the same oxides also of pentoxide niobium (Nb2O5). For Ti–33Nb–33Zr (wt.%) indicated just the presence of rutile as the stable oxide one at room temperature and dioxide zirconium (ZrO2). In addition, the formation of calcium carbonate CaCO3 and calcium phosphate Ca3(PO4)2 was detected in all 3 materials. The ceramic-like layer was more homogeneous for c.p. Ti and Ti–15Nb and more irregular hole like-pores for Ti–33Nb–33Zr. Bioactive ions used were detected in all alloys and the roughness for Ti–15Nb was higher compared to c.p. Ti. and Ti–33Nb–33Zr. The contact angle for the three samples was higher than 100°.

Hard tissue repairing potency of mesoporous borosilicate bioactive glass: An in vitro assessment

Complete repair of the fractured hard tissues remains medically challenging, wherein the bioactive glass with antibacterial characteristics can efficiently support the bone growth. Thus, mesoporous borosilicate bioactive glasses (MBGs) of composition xB2O3–(80-x)SiO2–15CaO2–5P2O5 (0≤x≤15 mol%) were prepared using the sol-gel unified evaporation-induced self-assembly (EISA) technique and characterized. In addition, in vitro bio-degradation and bioactivity potential of these MBGs were assessed by immersing them in the simulated body fluid (SBF) for different periods to measure the weight loss and solution pH change. XRD analysis of these glasses showed very weak crystallinity of calcium phosphate Ca3(PO4)2 (JCPDS 70-0364) and FESEM images confirmed their strong mesoporosity with smooth textures. The recorded nitrogen (N2) adsorption-desorption isotherms and hysteresis loops of the studied MBGs indicated their hexagonal crystalline symmetry. The highest pore area and pore volume were estimated to be 342 m2g−1 and 0.6052 cm3, respectively. FTIR spectra of glasses revealed prominent peaks at 1400 and 1500 cm−1 corresponded to the vibration modes of borate units, C-O-C and O-H on P123. With the increase of boron contents, the rate of glass dissolution was increased, indicating their fast bio-degradation essential for efficient osteointegration. In short, the proposed MBGs are asserted to be beneficial for the bio-medical implants coating.

Influence of heat treatment on the structure and properties of ceramic heat-insulating composites based on phosphate bound expanded perlite-expanded clay

The article is devoted to the production and research of composite heat-insulating porous ceramics based on common and available local raw materials in the form of perlite, expanded clay, kaolinite clays using phosphate binders. Experimental samples were obtained by semi-dry pressing and ramming, followed by heat treatment at temperatures from 600 °C to 1100 °C. The processes of structure formation occurring in the compositions during heating are characterized by X-ray diffraction and local X-ray microanalysis. The obtained results showed the formation of the crystal structure of alumophosphate AlPO4 in the form of tridimite and cristobalite in the filler grains, and calcium phosphate Ca3(PO4)2 in the binding matrix of the composite. Heating temperature increase to 1150 °C lead to an increase in the amount of melt in the areas with the largest number of impurity elements. The influence of formation methods and technological parameters on shrinkage processes, density and strength of phosphate-bonded specimens has been demonstrated. The analysis of experimental results showed that the samples containing filler (expanded perlite), clay (secondary Samarkand kaolin) and orthophosphoric acid (40 wt%) are optimal in combination of density, thermal conductivity and resistance to high temperatures.

Rare‐Earth Elements in Deep‐Sea Sediments in the South Pacific Gyre: Source Materials and Resource Potentials

AbstractDeep‐sea sediments enriched in rare‐earth elements and yttrium (REY) plus scandium (Sc), termed “REY‐rich mud,” have attracted attention as a possible resource for these critical industrial elements. Examples have been reported from the western North Pacific, central Pacific, low‐latitude South Pacific, and eastern South Pacific. Although previous studies of pelagic clay have reported the existence of highly REY‐rich mud in the ultraoligotrophic South Pacific Gyre, neither the source materials nor the resource potentials for REY and Sc of the sediment have been quantified. We analyzed the major‐ and trace‐element contents of bulk sediments in Integrated Ocean Drilling Program Holes U1365A to U1370D, drilled in the South Pacific Gyre. The elemental relationships suggest that the enrichment in REY and Sc reflects the accumulation of biogenic Ca phosphate in an environment with low sedimentation rates as well as the tectonic transition of depositional environments from hydrothermally influenced sites near the mid‐ocean ridge to distal basins far from hydrothermal vents. The maximum total REY content of 4,662 ppm at Hole U1366C is the highest value yet reported from the South Pacific Ocean. Although the REY‐ and Sc‐enriched sediment layers of most cores from the South Pacific Gyre are located deeper beneath the seafloor than those elsewhere in the Pacific Ocean, Hole U1367B demonstrates large resource potentials (1.21 × 104 t/km2 of REY oxides and 102 t/km2 of Sc) in the uppermost 6.5‐m interval, making it the most promising site for REY and Sc yet found in the South Pacific Gyre.

The Role of Urinary Modulators in the Development of Infectious Kidney Stones.

Introduction: The pathogenesis of infectious kidney stones is poorly understood. Bacteria have been implicated in promoting infectious stones via urease production; however, there is mounting evidence indicating the relationship is more complex. The aim of our study was to characterize suspected biotic and abiotic extrinsic factors that may modulate the formation of infectious stones. Materials and Methods: A high-throughput experimental model with Griffith's artificial urine was used to test a wide variety of urinary modulators and cytoplasmic enzymes present in crude cell-free extracts (CFEs) from bacterial strains to investigate how they impact struvite and calcium (Ca) phosphate crystal production. Crystal formation was evaluated with spectrophotometry and growth curve analysis. Light microscopy and scanning electron microscopy/X-ray diffraction was used for crystal structure and composition identification. Results: The acidic urinary modulators used in this study prevented crystal formation, whereas osteopontin had a significant inhibitory effect. Addition of CFEs from Proteus mirabilis 175A and 177A resulted in Ca phosphate and struvite crystals. Of interest, Klebsiella pneumoniae and Klebsiella oxytoca produced crystals including Ca phosphate and Ca oxalate, respectively. Pseudomonas aeruginosa had no urease production detected and produced Ca phosphate crystals. Discussion: Urinary modulators can have a wide variety of effects on infectious stone formation and the role of pH is important but does not guarantee robust crystal formation. Bacterial strains can produce Ca oxalate, Ca phosphate, and struvite stones with and without urease activity. Conclusion: Various urinary modulators appear to influence the process and are worthy of further evaluation as a potential therapeutic strategy to prevent infection-related urinary stone formation. Stones formed from urinary tract infections may be a result of multiple encoded metabolic pathways and discovering these would improve our understanding of the stone-bacterial relationship.

In-situ analysis of the sintering behavior of coal ash and a phosphorus-rich biomass ash under gasification condition

The relatively high contents of some ash-forming elements (Na, K, Ca, Mg, P) in biomass ash can cause serious ash-related problems (deposition, slagging, corrosion, etc.) during the co-gasification of coal and biomass, influencing the stable operation of gasifier. The sintering behavior of Jincheng coal ash (JCA) and a phosphorus-rich Jatropha seed cake ash (JSCA) were investigated by in-situ heating stage microscopy, while the sintering mechanism was revealed by phase studies employing X-ray powder diffraction and thermodynamic modelling. Results indicated that the sintering temperature of blended ashes reached the minimum at the 20 wt% blending ratio of JSCA in the coal-biomass ash mixture. The high sintering temperatures of JCA and JSCA were due to the extensive mullite and quartz crystallization in the high acidic JCA system and the widespread formation of K–Ca phosphate and K–Mg phosphate in the high basic JSCA system, respectively. The transition of the phosphorus from fluxing effect to refractory effect on the sintering of ash mixture was identified at the 20 wt% blending ratio of JSCA. It was also found that the role of mullite and quartz decreased, while the role of anorthite, gehlenite, leucite, and calcium phosphate increased with increasing JSCA content, leading to the lowest sintering temperature. Finally, the variation trend of sintering temperatures against the JSCA additions was in accord with the change of the liquidus temperatures that was calculated by thermodynamic modelling. These observations can be used for the potential prediction of the ash sintering temperature in the coal-biomass gasifier.

Eco-innovation in the conservation of built heritage: Two-steps protocol of Di-ammonium phosphate application

A new protocol for the application of the consolidating di-ammonium phosphate (DAP) has been designed and verified, to contain the decay of carbonate substrates occurring in cultural heritage. DAP reacts with carbonate substrate to produce calcium phosphate phases, generally insoluble and liable to re-establish the cohesion of the stone. The Finale and Lecce Stones have undergone the consolidation treatment by applying consecutively-two solutions with different concentrations. The first solution (0.5 wt% DAP in water) is meant to build a porous network with hardened walls, reacting with calcium carbonate substrate and producing Ca-phosphates on the pore walls without occluding them. The second solution (4 wt% DAP in water) can flow into the Ca-phosphate-coated pores, without reacting and thus reaching carbonates deeper in the substrate. The samples were characterized by multiple physical and chemical investigation techniques to detect Ca phosphates and tested for treatment effectiveness. The results showed that DAP solution attains up to 1 mm in depth, even under low concentration; the nature of Ca-phosphates is undetectable due to instrumental detection limits and to heterogeneity of the investigated substrates.

Effect of different wastewater composition on kinetics, capacities, and mechanisms of phosphorus sorption by carbonated bauxite residue

This study aims at evaluating the effect of different wastewater composition on kinetics, capacities, and mechanisms of P sorption by carbonated bauxite residues (CBR). A series of batch experiments was performed to investigate P sorption behaviors from solutions prepared with different aqueous matrices (deionized water, tap water, and real wastewater) and different initial P concentrations (from 10 to 200 mg P/L). Also, a series of sequential P extractions was performed to investigate P fractionation of CBR before and after its use in P sorption experiments, and hence to elucidate the main P removal mechanisms. The results indicate that initial P concentration is the most influential parameter controlling kinetics, capacities, and mechanisms of P removal in batch experiments. Kinetic constant of P sorption increases exponentially with decreasing initial P concentration below 100 mg P/L, thus indicating a faster achievement of P sorption equilibrium. Equilibrium P sorption capacities increase linearly from about 0.2 to about 3.9 mg P/g CBR with increasing initial P concentration from 10 to 200 mg P/L, thus indicating that P saturation of CBR was not reached. Ca phosphate precipitation is the main P removal mechanism at higher initial P concentrations (> 10 mg P/L), whereas phosphate adsorption on CBR surface becomes more relevant over the total amount of P removed at lower initial P concentrations. Overall, the findings of this study allow to evaluate kinetic constants, sorption capacities, and removal mechanisms under different operating scenarios, thus providing crucial information for the design and operation of P treatment units.

Effects of a point source of phosphorus on the arsenic mobility and transport in a small fluvial system

One of the leading causes of As release from streambed sediments into freshwater systems is competition with phosphate. Among important sources of P to the fluvial ecosystems are wastewater treatment plants (WWTP), estimated to account for 25–45% of all P in surface waters. In this paper, long-term effects of discharged phosphorus from a small WWTP on the arsenic mobility were studied in an As-enriched fluvial system (approx. 240 mg/kg) in central Czech Republic. After 7 years of elevated P (≤7.7 mg/L) in the stream water, the total As decreased by 25% and the total P increased by 40% in the sediments downstream (at a distance of 66 m). The results of the chemical extractions and mineralogical analyses indicated that the changes in the concentration were mostly due to the sorption processes in the Fe (oxyhydr)oxides (goethite and hematite). In the downstream samples, the As in these phases decreased two-fold, and P was significantly enriched by 45–140%. Phosphorus was also found precipitated as newly formed Ca phosphates. The stream water monitoring indicated that the discharged P was either sequestered when the levels of dissolved P were high (>2.3 mg/L) or released from the downstream sediments when these levels were low (<∼1.5 mg/L). Meanwhile, As was continuously mobilized from the downstream sediments likely due to (i) the ongoing As desorption from the exterior parts of the Fe (oxyhydr)oxides at high aqueous P levels and (ii) the dissolution of As-bearing Ca phosphates at low dissolved P levels. These findings clearly demonstrate that point sources of P to streams and rivers, such as WWTP, may result in the permanent and long-term release of As from contaminated streambed sediments.

Synthesis and Thermal Behaviour of Calcium Alkyl Phosphates as Bioceramic Precursors

Powders of alkyl phosphoric acids and calcium alkyl phosphates with various alkyl chains (butyl, octyl, and dodecyl) have been synthesized. The resulting powders were characterized by X-ray phase analysis, electron microscopy, and thermal analysis. It was shown that the calcium alkyl phosphates correspond to the composition of acid salts of calcium alkyl phosphates Ca(RPO4H)2, data on which are not presented in the literature. The thermal behaviour of calcium alkyl phosphates can be described as a complex phase transformation into biphasic calcium phosphate mixture (of Ca2P2O7 and Ca3(PO4)2) with the increase of the Ca to P ratio in comparison to initial materials. The powders thermally treated in the range of 400–600 °C could be recommended as single precursors of biphasic bioceramics.