Phosphate Impurities Research Articles

Effect of phosphate impurities on the properties of β-hemihydrate gypsum pastes plasticized by polycarboxylate superplasticizer

This study aims to investigate the effect of HPO42-/PO43- on the working performance and mechanical strength of β-hemihydrate gypsum pastes containing polycarboxylate superplasticizer (PCE) and reveal its underlying mechanism. The results showed that HPO42-/PO43- has a detrimental effect on the fluidity, compressive strength, and softening coefficient of β-hemihydrate gypsum pastes. However, in the presence of PCE, all properties were improved compared to the blank group when the HPO42-/PO43- content was less than 0.3 %. The fluidity and compressive strength of the pastes can be increased by up to 95 % and 32 %, respectively. It was found that HPO42-/PO43- reacted with Ca2+ to form insoluble calcium phosphate salt (ICPS), and the adsorption of PCE on the surface of ICPS increased the total adsorption amount, thereby enhancing the dispersion ability of PCE and increasing the fluidity of fresh slurry. In addition, the adsorption behavior of PCE on the surface of ICPS weakened its inhibitory effect on the hydration of hemihydrate gypsum, which was confirmed by TG-DSC. The increased hydration products and reduced water requirements significantly improved mechanical properties. These findings enhance the understanding of the interaction between phosphorus impurities and PCE, which can guide the improvement of the performance of β-HPG and promote the resource utilization of phosphogypsum.

Effect of HPO42− and brushite on gypsum reactivity and implications for utilization of phosphogypsum in plaster production

The implementation of a sustainable development strategy holds the potential to enhance productivity, profitability, and overall efficiency by leveraging by-products from other industries. In plaster manufacturing the substitution of natural gypsum with synthetic gypsum is worth exploring. Phosphogypsum (PG) represents a significant fraction of synthetic gypsum production, arising as a by-product of phosphoric acid manufacturing. However, the presence of impurities in PG, particularly phosphorus, poses challenges to its use as a plaster material. To identify the phases present in PG, quantify their occurrences and understand their effects on dehydration and hydration processes, our study aimed to examine simplified models. These models are specifically designed to provide insights into the underlying mechanisms governing the hydration reactivity of hemihydrate. Pure gypsum and brushite were synthesized, and mechanical mixing was carried out to explore how brushite affects the characteristics of gypsum. Additionally, a solid solution of Ca(SO4)1-x(HPO4)x·2H2O, where 0 < x < 1, was prepared to characterize and quantify the syncrystallized HPO42− as well as the effects of this impurity on typical gypsum use cases. The synthesized materials underwent physical and chemical characterization using SEM, XRD, IR spectroscopy, DSC, pH and conductivity measurements, and ion chromatography. The results demonstrated that the HPO42− ions can substitute for sulfate ions in gypsum to form solid solutions. The maximum quantity of HPO42− ions in the gypsum lattice is approximately 10%, leading to the crystallization of gypsum into sand rose shape rather than needle crystals. As the concentration of HPO42− ions increases, a new phase known as ardealite (Ca(SO4)1-x(HPO4)x·2H2O) with 0.42 < x < 0.54 emerges, followed by brushite (CaHPO4·2H2O). During the calcination of brushite at 160 °C, a mixture of brushite and monetite formed that exhibits different properties compared to its natural counterpart. In the presence of syncrystallized HPO42− ions, the transformation from anhydrite III to anhydrite II occurred at higher temperatures than for pure gypsum. The reactivity of calcined samples indicate that HPO42− ions from the dehydration products of brushite caused a delay in hydration, with the maximum delay observed at a calcination temperature of 160 °C. At this temperature, monetite begins to crystallize, and it is characterized by its inert nature, exhibiting no reactivity with water. This explains the observed decrease in setting times as the calcination temperature rises. Moreover, syncrystallized HPO42− ions induced a significant delay in the hydration process. Our research revealed that adjusting the calcination temperature can mitigate the retarding effect associated with this impurity, suggesting an industrial tendency to use the lowest possible temperature during the calcination process of PG containing syncrystallized phosphate impurity. In addition, we have observed that adjusting the pH of the mixing water to lower values can significantly accelerate setting times.

Deep removal of phosphate impurities in phosphogypsum by two-step crystal transformation for use as Portland cement retarder

The phosphate impurities in phosphogypsum (PG) were removed efficiently by a novel two-step crystal transformation approach, and the mechanism of the two-step transformation method for removing phosphate and metal impurities from PG was described. The effects of modified PG, natural gypsum, and PG as Portland cement retarders on the cement properties were compared and analyzed by XRD, SEM, and hydration heat analyses. Results indicated an optimal sulfuric acid concentration of 30% H2SO4 during the first crystal transformation and a liquid-to-solid ratio of 7:1 during the second crystal transformation. The content of total P2O5 in the modified PG was 0.02%, and part of heavy metal elements was also removed. The first-step crystal transformation removed the intercrystalline and insoluble phosphate impurities by breaking the crystal lattice of gypsum. The second-step crystal transformation rebuilt the crystal lattice of gypsum. The effect of phosphate impurities in the modified PG on cement hydration was significantly reduced, the setting time of the cement prepared with the modified PG was normal, and the strength was increased. The effect of the modified PG was better than that of PG as a cement retarder. The two-step crystal transformation approach provided a cost-effective method for PG purification.

Investigating the novel process for thorough removal of eutectic phosphate impurities from phosphogypsum

Phosphogypsum is the major component in solid waste of phosphoric acid manufacturing. After purification, phosphogypsum can be used as an alternative material to natural gypsum. Phosphate impurities, especially eutectic phosphorus, are challenging to be removed thoroughly from phosphogypsum. In this work, we reported a novel phosphogypsum purification process, in which the phase transition activation by calcination was combined with sulfuric acid dissolution during hydration. The two critical parameters, activation temperature and H2SO4 concentration were optimized for this process. Moreover, powder X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), X-ray photoelectron spectrometer (XPS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) were used to determine the purification efficiency for removing eutectic phosphate impurity from phosphogypsum. The comprehensive characterization results suggested that this novel process can remove eutectic phosphate impurities through the mutual transformation of different crystalline forms of calcium sulfate combined with sulfuric acid dissolution. Under the optimal purification condition (165 °C activation and 1.0 wt% H2SO4), the removal rate of eutectic phosphorus reached up to 98.3%, corresponding to overall eutectic phosphorus content decreasing from 0.58% to 0.01%. Meanwhile, the water-soluble phosphorus and insoluble phosphorus were also completely removed. Thus, 99.4% of phosphate impurity (as P2O5) was removed from phosphogypsum after the two-step treatment. The findings of this paper indicated that this novel process could separate phosphate impurity in an efficient and thorough manner, enabling sustainable utilization of phosphogypsum.

The sponge effect of phosphogypsum-based cemented paste backfill in the atmospheric carbon capture: Roles of fluorides, phosphates, and alkalinity

The use of cement for solid waste solidification/stabilization is one of the most practised methods but is under scrutiny due to its substantial emission of greenhouse gases. However, the dual role of cement-immobilized solid waste may serve as a CO2sink and promisingly reabsorb a great content of atmospheric CO2, which is hitherto unexplored. In this study, we detail the inherent potential sponge effect of phosphogypsum (PG) based cemented paste backfill (PCPB), finding that, at a high PG utilization rate, the PCPB application may produce 16.7 Mt/year of CO2 in China, whereas a reduction of 5.76 Mt/year could promisingly reach up when considering the future reabsorption. However, industrial applications are limited by the remained impurities and the maintenance of alkalinity. The results suggest that the phosphate impurities within PG have an adverse effect on CO2 uptake, which inhibits the precipitation of hydration products and inversely favors the formation of calcium-phosphate species that retard the dissolution of cement particles. By contrast, the fluorides imply an acceleration of the hydration reactions and accordingly hasten the carbonation process. Furthermore, geochemical modeling suggests that maintaining a basic pH condition of the system is another significant factor in promoting the CO2 capture capacity, of which a 35% increase in CO2 uptake can be acquired with a continuous low concentration NaOH supply, but this enhancement will require the widespread deployment of future validation. From the perspectives of CO2 balance, environmental requirements, and technological feasibility, PCPB is an effective way for in situ immobilizing PG with scalable potential. These new observations are expected to provide a deeper understanding and reliable guidance for the sustainable management of dumped PG and the zero emissions of the phosphorus fertilizer industry.

Removal of impurity Metals as Phosphates from Lithium-ion Battery leachates

Recovery of critical materials from end-of life (EOL) lithium-ion batteries (LIB) is gaining interest as demands for materials grows. Hydrometallurgical processes start with an intermediate product known as black mass which contains critical materials of interest (Co, Ni, Li, and graphite) as well as impurities such as Cu, Al, and Fe. These impurities are deleterious to downstream separation processes, as well as impact functionality of the final products. These impurities effectively compete with most solvent extraction (SX) and metal recovery processes to diminish the overall yields of the desired materials. In this work, a process flowsheet is presented where a previously reported electrochemical leaching (ECL) process is followed by selective precipitation using diammonium hydrogen phosphate (DAP) to remove Cu, Al, and Fe from LIB leachate solutions. The electrochemical leach process removes Cu and produces a pH-adjusted leachate, ca. pH 2, without requiring an extra Cu extraction step. The addition of the precipitant DAP to leachate by slightly adjusting the pH to 3–4 at 45 °C, precipitates 95–99% of Al and Fe as their phosphates and the leachate retains >95% of Co, Ni and Li. After the filtration of phosphate impurities, the solution is ready for further processing, such as SX. As an unexpected result from the leachate processing, 20–30% of the Ni and Co co-crystalize as the double salt after cooling to room temperature, which could provide a shorter route to their recovery.

Phytate-Induced Dose-Response Auto-Activation of Enzyme in Commercial Recombinant Phytase From Escherichia coli.

Microbial phytase is one of the most widely used enzymes in food industries like cattle, poultry, and aquaculture food. Therefore, understanding the kinetic properties of the enzyme is very important to evaluate and predict its behavior in the digestive system of livestock. Working on phytase is one of the most challenging experiments because of some problems, including free inorganic phosphate (FIP) impurity in phytate (substrate) and interference reaction of the reagent with both phosphates (product and phytate impurity). In the present study, FIP impurity of phytate was removed, and then it was shown that the substrate (phytate) has a dual role in enzyme kinetics: substrate and activator. phytate impurity was decreased by two-step recrystallization prior to the enzyme assay. The impurity removal was estimated by the ISO30024:2009 method and confirmed by Fourier-transform infrared (FTIR) spectroscopy. The kinetic behavior of phytase activity was evaluated using the purified phytate as substrate by non-Michaelis-Menten analysis, including Eadie-Hofstee, Clearance, and Hill plots. The possibility of an allosteric site on phytase was assessed by molecular docking. The results showed a 97.2% decrease in FIP due to recrystallization. The phytase saturation curve had a sigmoidal appearance, and Lineweaver-Burk plot with a negative y-intercept indicated the positive homotropic effect of the substrate on the enzyme activity. A right-side concavity of Eadie-Hofstee plot confirmed it. Hill coefficient was calculated to be 2.26. Molecular docking also showed that Escherichia coli phytase molecule has another binding site for phytate very close to the active site, called "allosteric site". The observations strongly propose the existence of an intrinsic molecular mechanism in Escherichia coli phytase molecules to be promoted for more activity by its substrate, phytate (positive homotropic allosteric effect). In silico analysis showed that phytate binding to the allosteric site caused new substrate-mediated inter-domain interactions, which seems to lead to a more active conformation of phytase. Our results provide a strong basis for animal feed development strategies, especially in the case of poultry food and supplements, regarding a short food passage time in their gastrointestinal tract and variable concentration of phytate along with it. Additionally, the results strengthen our understanding of phytase auto-activation as well as allosteric regulation of monomeric proteins in general.

The Effects of Phosphate Impurity on Recovered LiNi0.6Co0.2Mn0.2O2 Cathode Material via a Hydrometallurgy Method.

From portable electronics to electric vehicles, lithium-ion batteries have been deeply integrated into our daily life and industrial fields for a few decades. The booming field of battery manufacturing could lead to shortages in resources and massive accumulation of battery waste, hindering sustainable development. Therefore, hydrometallurgy-based approaches have been widely used in industrial recycling to recover cathode materials due to their high efficiency and throughput. Impurities have always been a great challenge for hydrometallurgical recycling, introducing challenges to maintain the consistency of product quality because of potential unintended effects caused by impurities. Herein, after comprehensive investigation, we first report the impacts of phosphate impurity on a recycled LiNi0.6Co0.2Mn0.2O2 ("NCM622") cathode via a hydrometallurgy method. We demonstrate that a passivation layer of Li3PO4 is formed at grain boundaries during sintering, which significantly raises the activation barrier and hinders lithium diffusion. In addition, the distinct degradation of cathode electrochemical properties is observed from poor particle morphology and high cation mixing as a result of phosphate impurity. Cathode powders with 1 at. % phosphate impurity retain a capacity of 146 mAh/g after 100 cycles at 0.33C, 6% less than that of a virgin cathode. Furthermore, cathodes with higher phosphate concentrations perform even worse in electrochemical tests. Therefore, phosphate impurities are detrimental to the hydrometallurgical recycling of NCM cathode materials and need to be excluded from the recycling process.

Dissolution Behavior of Sodium Phosphate in a Na3PO4–Na2WO4–NaOH Solution System

Sodium hydroxide autoclaving is the main method for smelting scheelite in China. In this method, sodium phosphate is added as an additive to realize the highly efficient decomposition of scheelite, and a crude sodium tungstate solution containing sodium phosphate and sodium hydroxide is obtained. In the subsequent process of ion exchange, phosphorus ions in the solution compete with the resin adsorption of tungstate, which reduces the adsorption capacity of the resin and endangers the purity of the subsequent sodium tungstate solution. To remove the phosphorus from crude sodium tungstate solution, a chemical purification method is usually adopted. The principle of the chemical purification method is to use chemical reagents to react with impurities to form precipitates to achieve the purpose of impurity removal. Because of the advantages of simple industrial implementation and high impurity removal efficiency, it has been widely used in phosphorus removal from crude sodium tungstate solution. However, in the process of phosphate removal in a crude sodium phosphate solution, the chemical purification method has some disadvantages. First, the additional cost of chemical reagents is required, and other metal impurities from chemical reagents would be introduced to crude sodium tungstate solution. Second, phosphate impurity removed by the chemical precipitation method is usually sedimented in other forms but sodium phosphate, which makes the phosphate resource unable to be recycled for tungsten smelting. Therefore, a novel phosphorus removal method needs to be developed. The dissolution behavior of sodium phosphate in a Na3PO4–Na2WO4–NaOH system was investigated in this paper. The results showed that in binary or ternary solution systems of sodium phosphate, sodium tungstate, and sodium hydroxide, the common-ion effect and salt effect exist simultaneously. The common-ion effect decreases the solubility of sodium phosphate, while the salt effect increases the solubility of sodium phosphate. Increasing the concentration of sodium hydroxide or sodium tungstate and lowering the temperature of the solution can greatly reduce the phosphorus concentration in crude sodium tungstate solution, making the crude sodium tungstate solution meet industrial requirements of ion exchange. The results of the study lay a theoretical foundation for the development of new phosphorus removal methods.

The improvement of the water-resistance of the phosphogypsum by adding waste metallurgical sludge

The solution of the phosphogypsum ecological problem consist in its utilisation. The purpose of the study is to improve the water-resistance of the phosphogypsum to make it a suitable and green alternative to cement. Hence, a waste metallurgical sludge from a ship-repairing yard was added in amounts of 0.1 to 0.5%. The modifier reduced the harmful water-soluble phosphate by 15 times and maintained the high hydration degree of the specimens. The compressive strength was tested for both the dry and the previously immersed in water specimens. The addition of 0.1–0.3% metallurgical sludge improved their water-resistance by 2 times. • The content of soluble phosphate impurities in PG is reduced by the MS by 15 times. • The MS modifier enhances the water resistance of the PG specimens by 2 times. • The proposed composite material is a completely ecological solution. • The MS additive gives new possibilities to PG, improving its applicability.

Metal Phosphides Embedded with In Situ‐Formed Metal Phosphate Impurities as Buffer Materials for High‐Performance Potassium‐Ion Batteries

AbstractAs anodes for metal‐ion batteries, metal phosphides usually suffer from severe capacity degradation because of their huge volume expansion and unstable solid electrolyte interphase (SEI), especially for potassium‐ion batteries (PIBs). To address these issues, this study proposes amorphous phosphates acting as buffer materials. Ten types of metal phosphide composites embedded with in situ‐formed amorphous phosphates are prepared by one‐step ball milling using red phosphorus (RP) and the corresponding metal oxides (MOs) as starting materials. A zinc phosphide composite is selected for further study as a PIB anode. Benefitting from the effective suppression of volume variation, a KF‐rich SEI is formed on the electrode surface in the KFSI‐based electrolyte. The zinc phosphide composite exhibits a high reversible specific capacity and outstanding long‐term cycling stability (476 mAh g−1 over 350 cycles at 0.1 A g−1 after going through a rate capability test and 177 mAh g−1 after 6000 cycles at 1.0 A g−1) and thus achieves the best cycling performance among all reported metal phosphide‐based anodes for PIBs. This study highlights a low‐cost and effective strategy to guide the development of metal phosphides as high‐performance anodes for PIBs.

Effect of phosphogypsum on the properties of magnesium phosphate cement paste with low magnesium-to-phosphate ratio

The incorporation of phosphogypsum (PG) in magnesium potassium phosphate cement (MPPC) can promote the utilization of PG not only by utilising the phosphate impurity in PG, but also by immobilising the heavy metals with MPPC. This paper investigates the feasibility of the incorporation of PG in preparing MPPC. Both early age properties, including workability and setting time, and hardened properties of compressive strength and microstructure, of PG-incorporated MPPC paste were investigated, and the hydration mechanism was explored. The results indicated that the addition of PG increased the workability of MPPC and extended the setting time of MPPC. However, incorporation of 20% PG slightly reduced the compressive strength because higher PG content led to the loose microstructure. Moreover, the addition of PG did not change the formation of hydration product, while it only reduced the hydration heat. Finally, compared to PG, the concentration of leached heavy metals of MPPC with PG was significantly reduced after 28 days curing.

Recycling of waste gypsum in preparation of magnesium oxychloride cement (MOC)

Phosphogypsum (PG) and flue gas desulfurization gypsum (FGDG) are industrial by-products with an annual production of about 30 million tons in China. They are usually treated as solid waste instead of being recycled efficiently. In this study, MgO powder was replaced with waste gypsum by weight of 10%–30% to prepare magnesium oxychloride cement (MOC). The effect of PG and FGDG on the workability and mechanical performance of MOC was evaluated with final setting time, flowability, compressive strength, water resistance, water absorption and volume stability. The hydration mechanism influenced by PG and FGDG was analyzed using X-ray diffraction method and scanning electron microscope. Results showed that PG and FGDG replacement increased the flowability and retarded the setting of the paste, but decreased the compressive strength. PG incorporation effectively improved the water resistance of MOC. The main hydration product in gypsum-free MOC was 5 Mg(OH)2·MgCl2·8H2O (phase 5). The addition of PG and FGDG induced the formation of 3 Mg(OH)2·MgCl2·8H2O (phase 3). Microstructure observations confirmed that phosphate impurities in untreated PG promoted the nucleation of phase 5 and phase 3 and improved their water stability. The untreated PG showed a better compatibility in MOC system than FGDG. This study could contribute to using waste gypsum to produce a green cementitious material with good performance, thus helping improve the waste resource recycling and achieve the goal of environmental protection.

Removal of Major Phosphate Impurities by Flotation using DTAB Collector

Abstract Removal of phosphate impurities is a prerequisite for using phosphate ores in different applications. The flotation process is one of the most promising processes that have been used to improve the phosphate grade. However, the flotation performance depends on the type of the associated impurities to valuable minerals due to their different flotation behaviour that needs more attention. In this paper, the flotation response of impurities at different pH and dodecyl tri-methyl ammonium bromide (DTAB) collector concentrations was investigated using the statistical design of experiments. The results indicated that some impurities were completely removed such as silica and alumina while others are only partially removed at about 72% and 38%, respectively. Thus, based on the impurities response to flotation and their rejection by flotation using DTAB collector, they are classified into two groups. The first group is SiO2, MgO, and Al2O3, while the second group includes only sulphide mineral (FeS2). The lowest rejection percentage for pyrite is due to its chemical composition as a sulphide mineral that has a different interaction with DTAB collector in comparison to first group minerals.

CHARACTERIZATION OF OSELTAMIVIR PHOSPHATE API AND SIMULTANEOUS QUANTIFICATION AND VALIDATION OF ITS IMPURITIES BY UPLC

Objective: The purpose of the study is to develop a high sensitive and short runtime method to quantify oseltamivir phosphate impurities (C and D) and characterization of oseltamivir phosphate API.&#x0D; Methods: The active pharmaceutical ingredient (API) characterization was done using spectroscopic techniques such as mass, infrared spectroscopy (IR), differential scanning calorimetry (DSC), proton nuclear magnetic resonance (H-NMR), phosphorus nuclear magnetic resonance (P-NMR), carbon-13 nuclear magnetic resonance (C13-NMR), and two-dimensional nuclear magnetic resonance (2D-NMR). The impurities (C and D) quantification was done using ACQUITY UPLC BEH C18- 100 mm × 2.1 mm, 1.7 μm column connected to ACQUITY UPLC with PDA detector. The optimized chromatographic conditions were achieved at 0.3 mL/min flow rate using gradient system with 0.1% orthophosphoric acid in water and acetonitrile as mobile phase. Both impurities are measured at λmax 210 nm at 30°C column temperature.&#x0D; Results: The finalized method has given good peak shape and resolution for impurity-C and impurity-D at Rt = 3.39 and 4.33 min, respectively, and the quantification method is linear and its r2 &gt; 0.999 as a correlation coefficient. The recoveries of impurity-C and impurity-D were found in the range of 100±15% at 0.05, 0.1, and 0.15 and limit of quantitation (LOQ) % concentration levels. The other validation parameters such as specificity, system precision, sensitivity, method precision, ruggedness, robustness, and solution stability were established for this method, and the results are satisfactory as per International Council for Harmonization (ICHQ2).&#x0D; Conclusion: The characterization data confirm the structure of oseltamivir phosphate active pharmaceutical ingredient (API). The validated method shall be used for regular analysis as well as release analysis in quality control (QC).

Efficient removal of phosphate impurities in waste phosphogypsum for the production of cement

Phosphogypsum (PG) is an industry solid waste produced from phosphoric acid manufacture. To reduce environmental pollution of the PG, H2C2O4 was employed to purify it, which then can be used for cement production. The optimal concentration of H2C2O4 for PG purification was determined. In addition, differential thermal analysis (DTA), X-ray photoelectron spectroscopy (XPS) and X-ray fluorescence (XRF) were used to determine the removal of phosphate impurity in PG. The effects of purified PG on cement hydration and the environmental implications were also investigated. The results demonstrate that H2C2O4 can remove the intercrystalline phosphate impurities by destroying the part of the crystal structure of gypsum. With the best treatment concentration of 1% H2C2O4, 77.7% of phosphate impurity (as P2O5) was removed from PG, which subsequently shortened the final setting time down to 220min and successfully met the national standard (GB 175-1999). Portland cement prepared by the 1% H2C2O4 treated PG possessed a comparable 3d compressive strength of 20.8MPa and a 28d compressive strength of 44.6MPa. It is concluded that PG purified by 1% H2C2O4 treatment can be used for cement production. Meanwhile, this H2C2O4 treatment can effectively reduce the environmental pollution from PG and offer a sustainable method for the utilization of PG.

Insight into Ion Diffusion Dynamics/Mechanisms and Electronic Structure of Highly Conductive Sodium-Rich Na3+xLaxZr2-xSi2PO12 (0 ≤ x ≤ 0.5) Solid-State Electrolytes.

Solid-state electrolytes (SSEs) have attracted considerable attention as an alternative for liquid electrolytes to improve safety and durability. Sodium Super Ionic CONductor (NASICON)-type SSEs, typically Na3Zr2Si2PO12, have shown great promise because of their high ionic conductivity and low thermal expansivity. Doping La into the NASICON structure can further elevate the ionic conductivity by an order of magnitude to several mS/cm. However, the underlying mechanism of ionic transportation enhancement has not yet been fully disclosed. Herein, we fabricate a series of Na3+xLaxZr2-xSi2PO12 (0 ≤ x ≤ 0.5) SSEs. The electronic and local structures of constituent elements are studied via synchrotron-based X-ray absorption spectroscopy, and the ionic dynamics and Na-ion conduction mechanism are investigated by solid-state nuclear magnetic resonance spectroscopy. The results prove that La3+ ions exist in the form of phosphate impurities such as Na3La(PO4)2 instead of occupying the Zr4+ site. As a result, the increased Si/P ratio in the NASICON phase, accompanied by an increase in the sodium ion occupancy, makes a major contribution to the enhancement of ionic conductivity. The spin-lattice relaxation time study confirms the accelerated Na+ motions in the altered NASICON phase. Modifications on the Si/P composition can be a promising strategy to enhance the ionic conductivity of NASICON.

A method to prepare a high-strength building material from press-formed phosphogypsum purified with waste zeolite

The production of by-product phosphogypsum is very problematic. In order to recycle the phosphogypsum into a building material, its harmful acidic impurities (especially the soluble phosphate) should be purified, and the mechanical properties improved. Therefore, in this study, a novel method of processing the phosphogypsum is proposed. It consists in the addition of waste zeolite to adsorb the phosphate impurities, and in the application of press-forming processing to improve the compressive strength of the hardened specimens. The zeolite additive has proven to be an efficacious adsorbent, which reduced the soluble phosphate content by 3.2–7.5 times and surprisingly improved the hydration degree of the phosphogypsum. Moreover, the press-forming of phosphogypsum by applying 15 and 20 MPa pressure produced specimens with a compressive strength over 50 MPa.

Recovery of struvite from hydrothermally processed algal biomass cultivated in urban wastewaters

A mixotrophic algal wastewater treatment system capable of reducing biochemical oxygen demand (BOD), ammoniacal nitrogen (NH4+-N), and phosphate (PO43−-P) in primary effluent in a single step has been demonstrated previously. Downstream processing of the resulting algal biomass by hydrothermal liquefaction (HTL) to recover its energy-content as biocrude oil has also been demonstrated. The current study evaluated the feasibility of recovering struvite from the two byproducts of HTL– a solid residue, rich in PO43–P; and an aqueous phase, rich in NH4+–N, for use as fertilizer. Results of this feasibility study and a preliminary mass balance model show that the proposed pathway can potentially yield ~2.5 kg struvite per 100 m3 of wastewater treated, recovering nearly 73% of PO43–P and 6% of NH4+–N in the primary effluent. Chemical and microscopic analysis of the wastewater-derived struvite revealed its composition to be close to that of pure struvite, with more than 12% P-content by weight. Scanning electron microscopy images depicted uniformly distributed sizes of irregular crystals in the wastewater-derived struvite. Low calcium content of this struvite indicated minimum amorphous calcium phosphate (ACP) impurities. Trace metal analysis showed that heavy metal levels in the recovered struvite were below current guidelines. This study confirmed the feasibility of recovering high-quality struvite from wastewaters, warranting further process optimization and characterization of the recovered struvite.

Hibrid biomaterials based on hydroxyapatite and blood components

Hybrid biomaterials based on amorphous hydroxyapatite and blood components (fibrin, citrate plasma) were developed by chemical precipitation of hydroxyapatite in a biopolymer matrix (pH 11; Ca/P ratio 1.67) and by mixing 6–14 wt.% of hydroxyapatite gel (pH 7.0–7.2) with bipolymers. Chemically precipitated hydroxyapatite in biopolymer matrices is single phase or contains ticalcium phosphate impurity up to 30 %, mainly α-modification in fibrin matrix and β-modification in citrate plasma. The interaction of hydroxyapatite gel into the fibrin leads to significant amorphization of hydroxyapatite and an increase in its bioresorbability. Holding the composites with hydroxyapatite obtained by chemical precipitation in the Simulated Body Fluid model solution for 75 days leads to their partial resorption and simultaneous increase of biomimetic apatite, with its greater weight gain on composites with a fibrin. Hybrid biomaterials based on a fibrin obtained from the patient’s blood and hydroxyapatite gel showed positive result during implantation, allowing to form an adequate configuration of the defect, expanding the possibilities of ENT surgery.