Crystal structure of radium sulfate: An X-ray powder diffraction and density functional theory study

Actinium-225 photonuclear production in nuclear reactors using a mixed radium-226 and gadolinium-157 target

BACKGROUND

Actinium-225 is one of the most promising radionuclides for targeted alpha therapy. Its limited availability significantly restricts clinical trials and potential applications of 225Ac-based radiopharmaceuticals.

METHODS

In this work, we examine the possibility of 225Ac production from the thermal neutron flux of a nuclear reactor. For this purpose, a target consisting of 1.4 mg of 226Ra(NO3)2 (T1/2 = 1600 years) and 115.5 mg of 90 % enriched, stable 157Gd2O3 was irradiated for 48 h in the Breazeale Nuclear Reactor with an average neutron flux of 1.7·1013 cm-2·s-1. Gadolinium-157 has one of the highest thermal neutron capture cross sections of 0.25 Mb, and its neutron capture results in emission of high-energy, prompt γ-photons. Emitted γ-photons interact with 226Ra to produce 225Ra according to the 226Ra(γ, n)225Ra reaction. Gadolinium debulking and separation of undesirable, co-produced 227Ac from 225Ra was achieved in one step by using 60 g of branched DGA resin. After 225Ac ingrowth from 225Ra (T1/2 = 14.8 d), 225Ac was extracted from the 226Ra and 225Ra fraction using 5 g of bDGA resin and then eluted using 5 mM HNO3.

RESULTS

Measured activity of 225Ac showed that 6(1) kBq or 0.16(3) μCi (1σ) of 225Ra was produced at the end of bombardment from 0.9 mg of 226Ra.

CONCLUSION

The developed 225Ac separation is a waste-free process which can be used to obtain pure 225Ac in a nuclear reactor.

Structure and bonding of a radium coordination compound in the solid state

The structure and bonding of radium (Ra) is poorly understood because of challenges arising from its scarcity and radioactivity. Here we report the synthesis of a molecular Ra2+ complex using 226Ra and the organic ligand dibenzo-30-crown-10, and its characterization in the solid state by single-crystal X-ray diffraction. The crystal structure of the Ra2+ complex shows an 11-coordinate arrangement comprising the 10 donor O atoms of dibenzo-30-crown-10 and that of a bound water molecule. Under identical crystallization conditions, barium (Ba2+) yielded a 10-coordinate 'Pac-Man'-shaped structure lacking water. Furthermore, the bond distance between the Ra centre and the O atom of the coordinated water is substantially longer than would be predicted from the ionic radius of Ra2+ and by analogy with Ba2+, supporting greater water lability in Ra2+ complexes than in their Ba2+ counterparts. Barium often serves as a non-radioactive surrogate for radium, but our findings show that Ra2+ chemistry cannot always be predicted using Ba2+.

Occurrence state of fluoride in barite ore and the complexation leaching process

Barite ore is typically associated with difficult-to-remove vein minerals, but commercial barite products require a high BaSO4 content. We investigated the occurrence state of fluoride in barite ore using various analytical techniques, which indicated that elemental fluorine in barite predominantly exists as fluorite. Fluoride was then leached from barite ore via complexation. The effects of HCl and AlCl3 concentrations, temperature, time, and liquid-solid ratio on the leaching rate were examined, and the leaching conditions were optimized using an orthogonal array method. The fluorine leaching rate approached 93.11% after stirring for 30 min at 90 °C and 300 rpm with 3 mol/L HCl, 0.4 mol/L AlCl3, a liquid-solid ratio of 10:1 mL/g, and an ore sample size of -75 μm + 48 μm. According to the leaching kinetics, the process conformed to the solid membrane diffusion control model at a high temperature and the joint chemical reaction-diffusion control model at a low temperature. The apparent activation energy was 56.88 kJ/mol. Furthermore, aluminum and fluorine coordination numbers increased with increasing Al3+/F- molar concentration ratios. Competing complexation reactions of Al3+, H+, and F- occurred at three levels. This complexation approach effectively leaches fluoride from barite, improves barite product quality, and reduces environmental pollution.

Extended X-ray absorption fine structure spectroscopy measurements and ab initio molecular dynamics simulations reveal the hydration structure of the radium(II) ion

Radium is refocused from the viewpoint of an environmental pollutant and cancer therapy using alpha particles, where it mainly exists as a hydrated ion. We investigated the radium hydration structure and the dynamics of water molecules by extended X-ray absorption fine structure (EXAFS) spectroscopy and ab initio molecular dynamics (AIMD) simulation. The EXAFS experiment showed that the coordination number and average distance between radium ion and the oxygen atoms in the first hydration shell are 9.2 ± 1.9 and 2.87 ± 0.06 Å, respectively. They are consistent with those obtained from the AIMD simulations, 8.4 and 2.88 Å. The AIMD simulations also revealed that the water molecules in the first hydration shell of radium are less structured and more mobile than those of barium, which is an analogous element of radium. Our results indicate that radium can be more labile than barium in terms of interactions with water.

Sulfate mineral scaling: From fundamental mechanisms to control strategies

Sulfate scaling, as insoluble inorganic sulfate deposits, can cause serious operational problems in various industries, such as blockage of membrane pores and subsurface media and impairment of equipment functionality. There is limited article to bridge sulfate formation mechanisms with field scaling control practice. This article reviews the molecular-level interfacial reactions and thermodynamic basis controlling homogeneous and heterogeneous sulfate mineral nucleation and growth through classical and non-classical pathways. Common sulfate scaling control strategies were also reviewed, including pretreatment, chemical inhibition and surface modification. Furthermore, efforts were made to link the fundamental theories with industrial scale control practices. Effects of common inhibitors on different steps of sulfate formation pathways (i.e., ion pair and cluster formation, nucleation, and growth) were thoroughly discussed. Surface modifications to industrial facilities and membrane units were clarified as controlling either the deposition of homogeneous precipitates or the heterogeneous nucleation. Future research directions in terms of optimizing sulfate chemical inhibitor design and improving surface modifications are also discussed. This article aims to keep the readers abreast of the latest development in mechanistic understanding and control strategies of sulfate scale formation and to bridge knowledge developed in interfacial chemistry with engineering practice.

Distribution of uranium and thorium chains radionuclides in different fractions of phosphogypsum grains

This work presents results obtained using gamma spectrometry measurements of phosphogypsum samples on a non-fractionated (native) and fractionated phosphogypsum byproduct. The phosphogypsum was divided into particles size fractions within the range of < 0.063, 0.063-0.090, 0.090-0.125, 0.125-0.250, and over 0.250 mm and analyzed after reaching radioactive equilibrium using high-resolution gamma spectrometry technique. It was found that there is no significant differentiation between ²²⁶Ra distribution among particular grain size fractions of this material; however, tendency for preferential retention of radionuclides in particular grain size fractions is observed. The detailed analysis of results revealed that radium is preferentially retained in smaller grain size fractions, whereas lead and thorium in coarse fractions. The results indicate that overall ²²⁶Ra activity concentrations between particular fractions of phosphogypsum vary globally between - 34 and + 47% regarding non-fractionated material, and for ²¹⁰Pb activity concentration, fluctuations are found between - 26 up and + 38%. Presumably, the mechanism of radium incorporation into gypsum phase is based on a sequence of radium bearing sulfate phases formation followed by a surface adsorption of these phases on the calcium sulfate crystals, whereas for lead and thorium ions, rather incorporation into crystal lattice should be expected as more likelihood process.

Alpha emitter NORM crystal scales in industrial pipelines: A study case

Radioactive related pollution due to suspended particulate matter dispersion is an important workplace and health care issue. Recycling oil production ducts and contaminated production equipment, represent a health hazard to workers and public alike. Radioactive plate-out NORM scales with crystal deposit is analyzed by different techniques; results provide proper information on physico-chemical features and emitted alpha particles. Recommendations for handling and recycling procedures are included in relation to health risk and radiological hazard.

Barium and Radium Complexation with Ethylenediaminetetraacetic Acid in Aqueous Alkaline Sodium Chloride Media

The speciation of Ra²⁺ and Ba²⁺ with EDTA was investigated at 25 °C in aqueous alkaline NaCl media as a function of ionic strength (0.2–2.5 mol·L⁻¹) in two pH regions where the EDTA⁴⁻ and HEDTA³⁻ species dominate. The stability constants for the formation of the [BaEDTA]²⁻ and [RaEDTA]²⁻ complexes were determined using an ion exchange method. Barium-133 and radium-226 were used as radiotracers and their concentrations in the aqueous phase were measured using liquid scintillation counting and gamma spectrometry, respectively. The specific ion interaction theory (SIT) was used to account for [NaEDTA]³⁻ and [NaHEDTA]²⁻ complex formation, and used to extrapolate the logarithms of the apparent stability constants (log₁₀K) to zero ionic strength (BaEDTA²⁻: 9.86 ± 0.09; RaEDTA²⁻: 9.13 ± 0.07) and obtain the Ba²⁺ and Ra²⁺ ion interaction parameters: [ε(Na⁺, BaEDTA²⁻) = − (0.03 ± 0.11); ε(Na⁺, RaEDTA²⁻) = − (0.10 ± 0.11)]. It was found that in the pH region where HEDTA³⁻ dominates, the reaction of Ba²⁺ or Ra²⁺ with the HEDTA³⁻ ligand also results in the formation of the BaEDTA²⁻ and RaEDTA²⁻ complexes (as it does in the region where the EDTA⁴⁻ ligand dominates) with the release of a proton. Comparison of the ion interaction parameters of Ba²⁺ and Ra²⁺ strongly indicates that both metal ions and their EDTA complexes have similar activity coefficients and undergo similar short-range interactions in aqueous NaCl media.