Neutron diffraction measurements of the double molybdate Cs₃Na(MoO₄)₂ have been performed for the first time in this work and the crystal structure refined using the Rietveld method. The thermal expansion of this trigonal phase, in space group P3¯m1, measured using high temperature X-ray diffraction (XRD), remains moderate: α_a=31·10⁻⁶K⁻¹ and α_c=24·10⁻⁶K⁻¹ in the temperature range T = (298−723) K. The melting temperature of this compound has been determined at T_fus= (777 ± 5) K using Differential Scanning Calorimetry (DSC). No phase transition was detected, neither by DSC, nor by high temperature XRD or high temperature Raman spectroscopy, which disagrees with the literature data of Zolotova et al. (2016), who reported a reversible phase transition around 663 K. Finally, thermodynamic equilibrium calculations have been performed to assess the probability of formation of Cs₃Na(MoO₄)₂ inside the fuel pin of a Sodium cooled Fast Reactor by reaction between the cesium molybdate phase Cs₂MoO₄, which forms at the pellet rim at high burnup, the fission product molybdenum (either as metallic or oxide phase), and the liquid sodium coolant in the accidental event of a breach of the stainless steel cladding and sodium ingress in the failed pin.

Kinetics of iron reduction, formation of vivianite and the microbial community in activated sludge from two sewage treatment plants (STPs) with low (STP Leeuwarden, applying enhanced biological phosphate removal, EBPR) and high (STP Cologne, applying chemical phosphate removal, CPR) iron dosing were studied in anaerobic batch experiments. The iron reduction rate in CPR sludge (2.99 mg-Fe g VS ⁻¹ h ⁻¹ ) was 3-times higher compared to EBPR sludge (1.02 mg-Fe g VS ⁻¹ h ⁻¹ ) which is probably caused by its 3-times higher iron content. Accordingly, first order rate constants in both sludges are comparable (0.06 ± 0.001 h ⁻¹ in EBPR vs 0.05 ± 0.007 h ⁻¹ in CPR sludge), thus potential rates in both sludges are comparable. The measured Fe(III) reduction rates suggest that all iron in STP Leeuwarden and STP Cologne can be turned over within 15 h and 44 h respectively. Mössbauer spectroscopy and X-ray diffraction (XRD) indicated vivianite formation within 24 h in both sludges. After 24 h, 53% and 34% of all iron were bound in vivianite in the EBPR and CPR sludge respectively. Next generation sequencing (NGS) showed that the microbial community in the CPR sludge comprised more genera with iron-oxidizing and iron-reducing bacteria. Iron reduction and vivianite formation commence once activated sludge is exposed to oxygen free conditions. Our study reveals that the biogeochemistry of iron in STPs is very dynamic. By understanding the interactions between iron and phosphate crucial processes in modern sewage treatment, such as chemical phosphate removal or phosphate recovery from sewage sludge, can be optimized.

To prevent eutrophication of surface water, phosphate needs to be removed from sewage. Iron (Fe) dosing is commonly used to achieve this goal either as the main strategy or in support of biological removal. Vivianite (Fe(II) ₃ (PO ₄ ) ₂ * 8H ₂ O) plays a crucial role in capturing the phosphate, and if enough iron is present in the sludge after anaerobic digestion, 70–90% of total phosphorus (P) can be bound in vivianite. Based on its paramagnetism and inspired by technologies used in the mining industry, a magnetic separation procedure has been developed. Two digested sludges from sewage treatment plants using Chemical Phosphorus Removal were processed with a lab-scale Jones magnetic separator with an emphasis on the characterization of the recovered vivianite and the P-rich caustic solution. The recovered fractions were analyzed with various analytical techniques (e.g., ICP-OES, TG-DSC-MS, XRD and Mössbauer spectroscopy). The magnetic separation showed a concentration factor for phosphorus and iron of 2–3. The separated fractions consist of 52–62% of vivianite, 20% of organic matter, less than 10% of quartz and a small quantity of siderite. More than 80% of the P in the recovered vivianite mixture can be released and thus recovered via an alkaline treatment while the resulting iron oxide has the potential to be reused. Moreover, the trace elements in the P-rich caustic solution meet the future legislation for recovered phosphorus salts and are comparable to the usual content in Phosphate rock. The efficiency of the magnetic separation and the advantages of its implementation in WWTP are also discussed in this paper.

Phosphate recovery from sewage sludge is essential in a circular economy. Currently, the main focus in centralized municipal wastewater treatment plants (MWTPs) lies on struvite recovery routes, land application of sludge or on technologies that rely on sludge incineration. These routes have several disadvantages. Our study shows that the mineral vivianite, Fe₂(PO₄)₃ × 8H₂O, is present in digested sludge and can be the major form of phosphate in the sludge. Thus, we suggest vivianite can be the nucleus for alternative phosphate recovery options. Excess and digested sewage sludge was sampled from full-scale MWTPs and analysed using x-ray diffraction (XRD), conventional scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), environmental SEM-EDX (eSEM-EDX) and Mössbauer spectroscopy. Vivianite was observed in all plants where iron was used for phosphate removal. In excess sludge before the anaerobic digestion, ferrous iron dominated the iron pool (≥50%) as shown by Mössbauer spectroscopy. XRD and Mössbauer spectroscopy showed no clear correlation between vivianite bound phosphate versus the iron content in excess sludge. In digested sludge, ferrous iron was the dominant iron form (>85%). Phosphate bound in vivianite increased with the iron content of the digested sludge but levelled off at high iron levels. 70–90% of all phosphate was bound in vivianite in the sludge with the highest iron content (molar Fe:P = 2.5). The quantification of vivianite was difficult and bears some uncertainty probably because of the presence of impure vivianite as indicated by SEM-EDX. eSEM-EDX indicates that the vivianite occurs as relatively small (20–100 μm) but free particles. We envisage very efficient phosphate recovery technologies that separate these particles based on their magnetic properties from the complex sludge matrix.

The relation between the microstructure and the magnetic properties of Fe₂P-type (Mn,Fe)₂(P,Si,B) based materials has been systematically investigated by changing the annealing temperature and time. X-ray diffraction, Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy measurements show that the alloys contain the main Fe₂P-type phase and two impurity phases of (Fe,Mn)₅Si₃-type and Fe₂MnSi-type. Boron appears to facilitate the formation of the Fe₂P-type phase during the arc-melting progress. Upon increasing the annealing temperatures from 1123 to 1423 K, the Curie temperature (T_C) decreases from 302.0 to 270.5 K in the Mn_1.15Fe_0.85P_0.55Si_0.45 alloys and the magnetic-entropy change (ΔS_M) increases linearly with annealing temperature. For the Mn_1.15Fe_0.85P_0.52Si_0.45B_0.03 alloys annealed at 1423 K for different times, T_C decreases from 263.8 and 232.8 K with increasing annealing time and ΔS_M reaches a maximum value after annealing for 48 h. The differences in the annealing temperature and time influence the Si content in the Fe₂P-type phase of the alloys and determine T_C, the thermal hysteresis and the magneto-elastic transition.

Paracetamol [N-(4-hydroxyphenyl)acetamide, C₈H₉NO₂] has several polymorphs, just like many other drugs. The most stable polymorphs, denoted Forms I and II, can be obtained easily and their crystal structures are known. Crystals of the orthorhombic, less stable, room-temperature Form III are difficult to grow; they need a special recipe to crystallize and suffer from severe preferred orientation. A crystal structure model of Form III has been proposed and solved from a combination of structure prediction and powder X-ray diffraction (PXRD) [Perrin et al. (2009). Chem. Commun.22, 3181-3183]. The final R_wp value of 0.138 and the corresponding considerable residual trace were reasons to check its validity. A new structure determination of Form III using new high-resolution PXRD data led to a final R_wp value of 0.042 and an improvement of the earlier proposed model. In addition, a reversible phase transition was found at 170-220 K between the orthorhombic Form III and a novel monoclinic Form III-m. The crystal structure of Form III-m has been determined and refined from PXRD data to a final R_wp value of 0.059.

The structure of α-Cs₂Mo₂O₇ (monoclinic in space group P2₁/c), which can form during irradiation in fast breeder reactors in the space between nuclear fuel and cladding, has been refined in this work at room temperature from neutron diffraction data. Furthermore, the compounds' thermal expansion and polymorphism have been investigated using high temperature X-ray diffraction combined with high temperature Raman spectroscopy. A phase transition has been observed at T_tr(α→β)=(621.9±0.8) K using Differential Scanning Calorimetry, and the structure of the β-Cs₂Mo₂O₇ phase, orthorhombic in space group Pbcm, has been solved ab initio from the high temperature X-ray diffraction data. Furthermore, the low temperature heat capacity of α-Cs₂Mo₂O₇ has been measured in the temperature range T=(1.9–313.2) K using a Quantum Design PPMS (Physical Property Measurement System) calorimeter. The heat capacity and entropy values at T=298.15 K have been derived as C_p,m ^o(Cs₂Mo₂O₇,cr,298.15K)=(211.9±2.1)JK⁻¹mol⁻¹ and S_m ^o(Cs₂Mo₂O₇,cr,298.15K)=(317.4±4.3)JK⁻¹mol⁻¹. When combined with the enthalpy of formation reported in the literature, these data yield standard entropy and Gibbs energy of formation as Δ_fS_m ^o(Cs₂Mo₂O₇,cr,298.15K)=−(628.2±4.4)JK⁻¹mol⁻¹ and Δ_fG_m ^o(Cs₂Mo₂O₇,cr,298.15K)=−(2115.1±2.5)kJmol⁻¹. Finally, the cesium partial pressure expected in the gap between fuel and cladding following the disproportionation reaction 2Cs₂MoO₄=Cs₂Mo₂O₇+2Cs(g)+ 1/2 O₂(g) has been calculated from the newly determined thermodynamic functions.

Given the potential applications of (Mn,Fe₂(P,Si))-based materials for room-temperature magnetic refrigeration, several research groups have carried out fundamental studies aimed at understanding the role of the magneto-elastic coupling in the first-order magnetic transition and further optimizing this system. Inspired by the beneficial effect of the addition of boron on the magnetocaloric effect of (Mn,Fe₂(P,Si))-based materials, we have investigated the effect of carbon (C) addition on the structural properties and the magnetic phase transition of Mn _1.25Fe _0.70P _0.50Si _0.50C _z and Mn _1.25Fe _0.70P _0.55Si _0.45C _z compounds by x-ray diffraction, neutron diffraction and magnetic measurements in order to find an additional control parameter to further optimize the performance of these materials. All samples crystallize in the hexagonal Fe ₂P -type structure (space group P-62m), suggesting that C doping does not affect the phase formation. It is found that the Curie temperature increases, while the thermal hysteresis and the isothermal magnetic entropy change decrease by adding carbon. Room-temperature neutron diffraction experiments on Mn _1.25Fe _0.70P _0.55Si _0.45C _z compounds reveal that the added C substitutes P/Si on the 2c site and/or occupies the 6k interstitial site of the hexagonal Fe ₂P -type structure.

The high theoretical energy density of Li-O₂ batteries as required for electrification of transport has pushed Li-O₂ research to the forefront. The poor cyclability of this system due to incomplete Li₂O₂ oxidation is one of the major hurdles to be crossed if it is ever to deliver a high reversible energy density. Here we present the use of nano seed crystallites to control the size and morphology of the Li₂O₂ crystals. The evolution of the Li₂O₂ lattice parameters during operando X-ray diffraction demonstrates that the hexagonal NiO nanoparticles added to the activated carbon electrode act as seed crystals for equiaxed growth of Li₂O₂, which is confirmed by scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDX) elemental maps also showing preferential formation of Li₂O₂ on the NiO surface. Even small amounts of NiO (∼5 wt %) particles act as preferential sites for Li₂O₂ nucleation, effectively reducing the average size of the primary Li₂O₂ crystallites and promoting crystalline growth. This is supported by first principle calculations, which predict a low interfacial energy for the formation of NiO-Li₂O₂ interfaces. The eventual cell failure appears to be the consequence of electrolyte side reactions, indicating the necessity of more stable electrolytes. The demonstrated control of the Li₂O₂ crystallite growth by the rational selection of appropriate nano seed crystals appears to be a promising strategy to improve the reversibility of Li-air electrodes.

Iron is an important element for modern sewage treatment, inter alia to remove phosphorus from sewage. However, phosphorus recovery from iron phosphorus containing sewage sludge, without incineration, is not yet economical. We believe, increasing the knowledge about iron-phosphorus speciation in sewage sludge can help to identify new routes for phosphorus recovery. Surplus and digested sludge of two sewage treatment plants was investigated. The plants relied either solely on iron based phosphorus removal or on biological phosphorus removal supported by iron dosing. Mössbauer spectroscopy showed that vivianite and pyrite were the dominating iron compounds in the surplus and anaerobically digested sludge solids in both plants. Mössbauer spectroscopy and XRD suggested that vivianite bound phosphorus made up between 10 and 30% (in the plant relying mainly on biological removal) and between 40 and 50% of total phosphorus (in the plant that relies on iron based phosphorus removal). Furthermore, Mössbauer spectroscopy indicated that none of the samples contained a significant amount of Fe(III), even though aerated treatment stages existed and although besides Fe(II) also Fe(III) was dosed. We hypothesize that chemical/microbial Fe(III) reduction in the treatment lines is relatively quick and triggers vivianite formation. Once formed, vivianite may endure oxygenated treatment zones due to slow oxidation kinetics and due to oxygen diffusion limitations into sludge flocs. These results indicate that vivianite is the major iron phosphorus compound in sewage treatment plants with moderate iron dosing. We hypothesize that vivianite is dominating in most plants where iron is dosed for phosphorus removal which could offer new routes for phosphorus recovery.