Magnesia-Based Cements: A Journey of 150 Years, and Cements for the Future?

This review examines the detailed chemical insights that have been generated through 150 years of work worldwide on magnesium-based inorganic cements, with a focus on both scientific and patent literature. Magnesium carbonate, phosphate, silicate-hydrate, and oxysalt (both chloride and sulfate) cements are all assessed. Many such cements are ideally suited to specialist applications in precast construction, road repair, and other fields including nuclear waste immobilization. The majority of MgO-based cements are more costly to produce than Portland cement because of the relatively high cost of reactive sources of MgO and do not have a sufficiently high internal pH to passivate mild steel reinforcing bars. This precludes MgO-based cements from providing a large-scale replacement for Portland cement in the production of steel-reinforced concretes for civil engineering applications, despite the potential for CO2 emissions reductions offered by some such systems. Nonetheless, in uses that do not require steel reinforcement, and in locations where the MgO can be sourced at a competitive price, a detailed understanding of these systems enables their specification, design, and selection as advanced engineering materials with a strongly defined chemical basis

Characterisation and disposability assessment of multi-waste stream in-container vitrified products for higher activity radioactive waste

Materials from GeoMelt® In-Container Vitrification (ICV)™ of simulant UK nuclear wastes were characterised to understand the partitioning of elements, including inactive surrogates for radionuclide species of interest, within the heterogeneous products. Aqueous durability analysis was performed to assess the potential disposability of the resulting wasteforms. The vitrification trial aimed to immobilise a variety of simulant legacy waste streams representative of decommissioning operations in the UK, including plutonium contaminated material, Magnox sludges and ion-exchange materials, which were vitrified upon the addition of glass forming additives. Two trials with different wastes were characterised, with the resultant vitreous wasteforms comprising olivine and pyroxene crystalline minerals within glassy matrices. Plutonium surrogate elements were immobilised within the glassy fraction rather than partitioning into crystalline phases. All vitrified products exhibited comparable or improved durability to existing UK high level waste vitrified nuclear wasteforms over a 28 day period

A risk management approach to the design of contraceptive implants

Key message points - Appreciation of human factors can provide useful insights into the reduction of risks through intuitive device design and the management of contributory factors in the environment. - Risks of implants relate to the way in which devices are designed and used rather than to their pharmacological properties. - The risks associated with the use of contraceptive implants include non-insertion and deep insertio

A discussion of the papers “ Impact of hydrated magnesium carbonate additives on the carbonation of reactive MgO cements ” and “ Enhancing the carbonation of MgO cement porous blocks through improved curing conditions ”, by C. Unluer & A. Al-Tabbaa

This paper is a discussion of two recent papers by Unluer & Al-Tabbaa which analysed accelerated carbonation of reactive MgO blocks. We suggest that the authors have incorrectly analysed key data, leading to overstated claims of MgO carbonation. Based on the reassignment of their X-ray diffraction data, it is proposed that little MgO carbonation occurred in the samples discussed in those papers, with CaCO3 instead forming during accelerated carbonation. We also draw attention to the thermodynamic instability of nesquehonite under ambient conditions, which calls into question the long-term stability of these binders

Legal aspects of contraceptive implants

Key message points - There has been litigation in relation to the three types of harm associated with contraceptive implants: non-insertion, deep insertion and nerve injury. - Recommendations for safe clinical practice can be derived from analysis of legal cases and published case reports. - Nerve injury has invariably been caused by clinicians without upper limb surgical skills attempting difficult removals. - The launch of the updated single-rod implant (Nexplanon®) may hold the best possibility for harm reduction. - Litigation in relation to side effects can lead to the withdrawal of safe and effective contraceptive products, so reducing choice for wome

Fenton and Fenton-like wet oxidation for degradation and destruction of organic radioactive wastes

AbstractFenton or Fenton-like oxidation for treatment of organic radioactive wastes is a promising technology with applications to a range of organic wastes. This review details this process; exploring potential challenges, pitfalls and opportunities for industrial usage with radioactive wastes. The application of this process to real radioactive wastes within pilot-plant settings has been documented, with key findings critically assessed in the context of future waste production. Although this oxidation process has not found mainstream success in treatment of radioactive wastes, a lower temperature oxidation system bring certain benefits, specifically for higher volume or problematic organic wastestreams.</jats:p

Thermal treatment of Cs-exchanged chabazite by hot isostatic pressing to support decommissioning of Fukushima Daiichi Nuclear Power Plant

Ion exchange materials are used widely for the removal of radionuclides from contaminated water at nuclear licensed sites, during normal operating procedures, decommissioning and in accident clean-up, such as the ongoing recovery operation at the Fukushima Daiichi nuclear power plant. Framework silicate inorganic ion exchange materials, such as chabazite ((Na0.14K1.03Ca1.00Mg0.17)[Al3.36Si8.53O24]•9.7H2O), have shown particular selectivity towards 137Cs uptake, but their safe storage poses a number challenges requiring conditioning into passively safe waste packages of minimal volume. We demonstrate the transformation of Cs-exchanged chabazite into a glass-ceramic wasteform by hot isostatic pressing to produce a durable consolidated monolith. The application of heat and pressure resulted in the collapse of the chabazite framework, forming crystalline Cs-substituted leucite (Cs0.15(3)K0.57(4)Al0.90(4)Si2.24(5)O6) incorporated within a K2O-CaO-MgO-Al2O3-SiO2 glass. The Cs partitioned preferentially into the Cs/K-feldspar which incorporated ~77% of the Cs2O inventory. Analysis of the chemical durability of the glass-ceramic wasteform revealed that the Cs release rates were comparable or lower than those reported for vitrified high level and intermediate level wastes. Overall, hot isostatic pressing was demonstrated to be an effective processing technology for conditioning spent inorganic ion exchange materials by yielding durable and passively safe wasteforms.</p

Temperature transformation of blended magnesium potassium phosphate cement binders

In this study, a multi-technique approach was utilised to determine the high temperature performance of magnesium potassium phosphate cement (MKPC) blended with fly ash (FA) or ground granulated blast furnace slag (GBFS) with respect to nuclear waste immobilisation applications. Conceptual fire conditions were employed (up to 1200 °C, 30 min) to simulate scenarios that could occur during interim storage, transportation or within a final geological disposal facility. After exposure up to 400 °C, the main crystalline phase, struvite-K (MgKPO4·6H2O), was dehydrated to poorly crystalline MgKPO4 (with corresponding volumetric and mass changes), with MgKPO4 recrystallisation achieved by 800 °C. XRD and SEM/EDX analysis revealed reaction occurred between the MgKPO4 and FA/GBFS components after exposure to 1000–1200 °C, with the formation of potassium aluminosilicate phases, leucite and kalsilite (KAlSi2O6 and KAlSiO4), commensurate with a reduced relative intensity (or complete elimination) of the dehydrated struvite-K phase, MgKPO4. This was further supported by solid-state NMR (27Al and 29Si MAS), where only residual features associated with the raw FA/GBFS components were observable at 1200 °C. The high temperature phase transformation of blended MKPC binders resulted in the development of a glass/ceramic matrix with all existing porosity infilled via sintering and the formation of a vitreous phase, whilst the physical integrity was retained (no cracking or spalling). This study demonstrates that, based on small-scaled specimens, blended MKPC binders should perform satisfactorily under fire performance parameters relevant to the operation of a geological disposal facility, up to at least 1200 °C.</p