An Experimental Study of the Decomposition and Carbonation of Magnesium Carbonate for Medium Temperature Thermochemical Energy Storage

Synthesis of Novel Hierarchical Rod-like Mg-Al bimetallic oxides for enhanced removal of uranium (VI) from wastewater

As one of the most frequently used nuclides for nuclear fuel and toxic heavy metal in polluted solutions, the removal and recovery of U(VI) from wastewater is significant both for nuclear energy and human health. Herein, the novel hierarchical Mg-Al bimetallic oxides (Mg/Al-BOs) were successfully synthesized by a facile hydrothermal-lyophilization-calcination method for enhanced removal of uranium (U(VI)) from wastewater. The as-synthesized Mg/Al-BOs adsorbents were characterized by a variety of techniques including SEM-EDS, XRD, high temperature in-situ XRD, TG-DSC, N₂ adsorption-desorption isotherm and XPS. Batch experiments including the effects of pH, hydration species, interfering ions on U(VI) removal, adsorption kinetics, isotherms and recyclability were systematically studied. Results showed that calcined Mg/Al-BO-24 inherited the hierarchical structure from its hydrotalcite-like precursor and grew the bimetallic oxides of Al₂O₃/MgO into a 3D rod-like and mesoporous network with the large BET surface area (472.4 m²∙g-¹), which presented abundant binding sites on the surface and contributed to preventing the aggregation of Al₂O₃/MgO nanoparticles, allowing the fast uptake of U(VI) for equilibrium within 180 min and the significant increase of maximum adsorption capacity to 411.5 mg∙g-¹. The uptake kinetics and isotherms of U(VI) removal could be well represented by the pseudo-second-order and Langmuir models, respectively. Further, it was demonstrated that U(VI) removal by Mg/Al-BO-24 was less influenced by coexisting cations and the regeneration cycles, indicating the excellent selectivity and reusability for U(VI) by the as-prepared composites. Based on the XPS analysis results, the mechanisms for U(VI) sorption onto the Mg/Al-BO-24 were mainly ascribed to the synergistic surface complexation and electrostatic interaction. These results suggested that Mg/Al-BO-24 prepared by the method reported here was available for developing other multiple metal oxides and would be a promising material for the effective treatment of wastewater with U(VI)-contamination.

Biogenic preparation of biphasic calcium phosphate powder from natural source of snail shells: bioactivity study

In this present work, carbonated apatite powder (CAP) and β-tricalcium phosphate (β-TCP) were prepared from waste snail shells via thermal decomposition followed by chemical precipitation method with phosphoric acid in a one step process. The CAP produced was thereafter reacted with a pore forming agent solution of ammonium bicarbonate to formed carbonated apatite powder- ammonium bicarbonate scaffold composites (CAP-AMB) and was deployed in a bioactivity experiment with simulated body fluid (SBF) media. The phase purity, crystallinity, particle size, thermal behaviour, elemental composition, morphology as well as the functional groups of snail shells, synthesized CAP and CAP-AMB scaffold were assessed by XRD, FE-SEM, TGA, EDX, TEM and FT-IR. XRD and selected area electron diffraction (SAED) results confirmed the synthesized apatite as pure amorphous powder which upon heat treatment, transformed to polycrystalline powder. Analysis of FT-IR results revealed that the apatite produced from snail shells (SS) contains phosphates and hydroxyl functional groups. Furthermore, the formation of carbonated apatite was also confirmed from the FT-IR result with peaks which appeared at 882 and 1484 cm−1 respectively, thus depicting a B-type apatite. Microscopy analyses by FE-SEM and TEM indicated that the prepared apatite is composed of different morphologies in the range of 5 to 200 nm long. The presence of trace elements such as K, C, Na, Mg and Mg which could play crucial functions in biological applications were detected by EDX measurement alongside Ca and P. The mixture of CAP with AMB produced interconnected pores structure with porosity in the range of 35–67%. The bioactivity study of the SBF treated CAP-AMB composite confirmed apatite formation on the scaffold surface which totally covered the pores after seven days of incubation. Thus, waste biomaterial of snail shells origin can be use for the production of pure apatite that could be useful in medical application.

Graphical abstract

Development of Thermochemical Heat Storage Based on CaO/CaCO3 Cycles: A Review

Due to the inconsistency and intermittence of solar energy, concentrated solar power (CSP) cannot stably transmit energy to the grid. Heat storage can maximize the availability of CSP plants. Especially, thermochemical heat storage (TCHS) based on CaO/CaCO3 cycles has broad application prospects due to many advantages, such as high heat storage density, high exothermic temperature, low energy loss, low material price, and good coupling with CSP plants. This paper provided a comprehensive outlook on the integrated system of CaO/CaCO3 heat storage, advanced reactor design, heat storage conditions, as well as the performance of CaO-based materials. The challenges and opportunities faced by current research were discussed, and suggestions for future research and development directions of CaO/CaCO3 heat storage were briefly put forward.