Sustainability

The US National Academy of Sciences has reported that CO₂ mineral carbonation is among the largest, most energy-efficient CO₂ utilization technologies closest to commercial scale due to its thermodynamic favorability and end-product market size. However, the natural rate of reaction is generally slow in terms of kinetics, whereby only by dramatically increasing the CO₂ dissolution rate can a major impact on the rate of reaction for CO₂ mineral carbonation happen. Hence, despite the clear advantages of CO₂ mineral carbonation over other options in Carbon Capture and Sequestration CCS technologies, the current research gaps highlighted here should be addressed to ensure future technology deployment success. Therefore, this study investigated the feasibility of the design, operation and experimental improvement of a continuous high-pressure CO₂ reactor in producing and optimizing high-quality precipitated calcium carbonates PCC synthesized for consumer and industrial application. A novel mineral carbonation reactor is hereby proposed, in which, by incorporating the application of a high-pressure or supercritical CO₂ phase into the reactor, CO₂ diffusion can be increased into the continuously fine-sprayed aqueous reaction media within the reactor to form PCC. The effective reactor volume can be simultaneously decreased from the reduced high-pressure CO₂ volume. Next, by incorporating a backpressure regulator, a continuous flow of the liquid phase in and out of the reactor can be controlled. The initial reactor design had undergone successful start-up, but experimental improvement alone was unable to provide the anticipated particle size of the calcium carbonate precipitate PCC. Optimized design of the new reactor to limit internal dead flow zones was proven to successfully reduce the particle size of precipitated calcium carbonate PCC from an initially P50/P90 of 87/131 μm to 3.8/9.1 μm. Additionally, a continuous 100 h stable run was successfully executed to thoroughly investigate the three main factors influencing the quality of PCC synthesized, in which the reactant flow rate and feedstock concentration were found to be significant, with the exception of CO₂ gas pressure. The overall 3D surface trend of the particle size spread P50/P90 of the PCC synthesized was plotted over the experimental range and found to meet most of the industrial requirements and technical specifications, except for TiO₂ replacement which requires sub-micron quality. Instantaneous electricity power consumption was also measured at various operating points. Performance-wise, the continuous high-pressure CO₂ mineral carbonation reactor in this work was calculated to be able to process a maximum of 4200 g/h lime CaO feedstock at a lime concentration of 7 g/L and flow rate of 10 g/L, using a 40 L internal volume vessel, effectively increasing the productivity of lime CaO production by several fold from what was reported by peer studies assuming similar electricity costs were used for all productivity factors under consideration.

This study aimed to jointly characterize destination diversification and revealed competitiveness in the international shrimp and prawn trade of Ecuador, India, Vietnam, and Indonesia during 2020–2024. A quantitative, descriptive–comparative approach was applied using annual free-on-board values at the exporter–destination level obtained from Trade Map (International Trade Centre). Destination diversification was proxied by the Herfindahl–Hirschman Index, while market-level competitiveness was measured through the Normalized Revealed Comparative Advantage index. Results show that Ecuador expanded exports while maintaining persistently high destination concentration. India exhibited broad revealed comparative advantage across multiple markets, yet remained highly concentrated, with episodes of deconcentration that were not sustained. Vietnam recorded relative stagnation, moderate concentration, and heterogeneous competitiveness across destinations. Indonesia experienced contraction with extremely high concentration, characterized by a pronounced advantage in the United States alongside disadvantages in alternative markets. Overall, a positive NRCA did not necessarily coincide with a low HHI, and configurations in which revealed advantage is concentrated in a small set of anchor markets are associated with higher exposure and may entail more limited reorientation options under shocks.

Hydrothermal carbonised waste (hydrochar) is increasingly considered a sustainable soil amendment within circular economy frameworks; however, its toxicity to the environment limits its safe application. Ageing and pyrolysis may be prospective treatments to mitigate hydrochar toxicity on soil organisms and plants, but their effectiveness is unresolved since available studies did not investigate the predominantly toxic hydrochars, those produced at high reaction temperatures (>200 °C). In this study, toxic hydrochars produced at hydrothermal carbonisation (HTC) temperature of 260 °C from biosolids, chicken manure and rice straw were post-treated by in situ ageing in soil for 30 days or by pyrolysis at 400 °C for 30 min, and their toxicity was assessed on wheat growth and earthworm (Eisenia fetida) avoidance. Untreated hydrochars did not affect wheat (Triticum aestivum L.) germination, but reduced wheat growth by 23–33%, and caused 82–94% earthworm avoidance. The ageing of hydrochar reduced phytotoxicity in biosolids and chicken manure hydrochar treatments, as indicated by improved wheat biomass (25–71%; compared to untreated hydrochar). Ageing of hydrochar also mitigated toxicity to earthworms, as indicated by the reduced avoidance of 19–31% across all feedstocks. The persistent phytotoxicity with aged rice straw hydrochar was due to toxic organic compounds that could not be fully detoxified after 30 days of ageing. Pyrolysis of hydrochar mitigated phytotoxicity as indicated by increased wheat biomass (43–93%), and reduced toxicity to earthworms (39–51%) across all feedstocks. Findings indicate that while both ageing and pyrolysis are appropriate hydrochar post-production treatments, ageing of hydrochar for only 30 days in soil may not fully alleviate the phytotoxic effect of all hydrochars.