Reactive Gases

Bauxite residue or Red Mud (RM) is a by-product from alumina refineries. It has a high pH of 11-13 and accumulates globally at 200 million tons yearly, totalling about 4.6 billion tons. Being an alkaline anthropogenic geomaterial, its adsorption properties and reactivity with acidic gases make it a potential sink for CO 2 and SO X emissions from the aluminium industry. It offers both research challenges and opportunities for its utilisation at an industrial scale. In particular, carbon capture and mineralisation (CCM) within RM has been demonstrated in situ and waste disposal areas through direct air trapping of atmospheric CO 2. The RM-CO 2 system is also operated in ex-situ conditions in various physical states, such as powder, wet cakes, and slurry, with yields of carbonates as CaCO 3 , Na 2 CO 3 , and FeCO 3. Our contribution as a review illuminates significant advancements made and challenges for enhancing the mineral carbonation potential of RM, thereby delineating areas necessitating further exploration. Although, researchers have primarily focused on accelerating the CCM process in RM through slurry carbonation techniques. Recent advancements in filter press technologies have favoured soda recycling and wet cake disposal of RM, creating artificial mountains of RM stacks. With changing disposal trends for RM, it is vital to understand the mechanisms that govern long-term atmospheric CO 2 trapping in RM disposal areas. Recent investigations of techniques, hydrothermal treatment and dual-stage calcification-carbonation methods have expanded the domain of CCM in RM. Given the global need to reduce CO 2 emissions, CCM using RM does offer promising insights on account of its unique physicochemical and mineralogical properties. We, although presume that RM alone will not fully offset the CO 2 emissions of the aluminium industry. Enhanced weathering and mineral carbonation could reduce over 50% of refinery emissions. Uncertainties persist regarding methods of CO 2 sequestration potential and techno-economic feasibility when tested at a field scale. Moreover, contrasting results are revealed, primarily regarding changing disposal trends, variabilities in mineralogy, and limited knowledge of micro-mechanisms of the CCM process in RM. This work elucidates existing knowledge on synthesising CO2 mineralisation, pathways, and mechanisms under various states associated with leveraging RM as a significant carbon sink in current and future climate change mitigation efforts.
Red mud
Bauxite residues
Carbon capture
Mineralisation
Sequestration potential
Carbon sink
enhanced weathering

Modelling 263 4.2.6.1 Laboratory data and the OH lifetime of greenhouse gases 263 4.2.6.2 Atmospheric measurements and modelling of photochemistry 264 4.3 Projections of Future Emissions 266 4.3.1 The Adjusted/Augmented IPCC/SRES Emission Scenarios 266 4.3.2 Shifting Regional Emissions of NO x , CO and VOC in 2100 4.3.3 Projections of Natural Emissions in 2100 4.4 Projections of Atmospheric Composition for the 21st Century 4.4.1 Introduction 4.4.2 The OxComp Workshop 4.4.3 Testing CTM Simulation of the Current (Y2000) Atmosphere 4.4.4 Model Simulations of Perturbed and Y2100 Atmospheres 4.4.5 Atmospheric Composition for the IPCC Scenarios to 2100 4.4.6 Gaps in These Projections-the Need for Coupled Models 4.4.7 Sensitivity Analysis for Individual Sectors 4.5 Open Questions 4.5.1 Chemical Processes Important on the Global Scale 4.5.1.1 Missing chemistry, representation of small scales, and changing emission patterns 4.5.1.2 Aerosol interactions with tropospheric O 3 and OH 4.5.1.3 Stratosphere-troposphere coupling 4.5.1.4 Uncertainties in the tropospheric O 3 budget 4.5.2 Impacts of Physical Climate Change on Atmospheric Chemistry 4.5.3 Feedbacks through Natural Emissions 4.6 Overall Impact of Global Atmospheric Chemistry Change References

Modelling 263 4.2.6.1 Laboratory data and the OH lifetime of greenhouse gases 263 4.2.6.2 Atmospheric measurements and modelling of photochemistry 264 4.3 Projections of Future Emissions 266 4.3.1 The Adjusted/Augmented IPCC/SRES Emission Scenarios 266 4.3.2 Shifting Regional Emissions of NO x , CO and VOC in 2100 4.3.3 Projections of Natural Emissions in 2100 4.4 Projections of Atmospheric Composition for the 21st Century 4.4.1 Introduction 4.4.2 The OxComp Workshop 4.4.3 Testing CTM Simulation of the Current (Y2000) Atmosphere 4.4.4 Model Simulations of Perturbed and Y2100 Atmospheres 4.4.5 Atmospheric Composition for the IPCC Scenarios to 2100 4.4.6 Gaps in These Projections-the Need for Coupled Models 4.4.7 Sensitivity Analysis for Individual Sectors 4.5 Open Questions 4.5.1 Chemical Processes Important on the Global Scale 4.5.1.1 Missing chemistry, representation of small scales, and changing emission patterns 4.5.1.2 Aerosol interactions with tropospheric O 3 and OH 4.5.1.3 Stratosphere-troposphere coupling 4.5.1.4 Uncertainties in the tropospheric O 3 budget 4.5.2 Impacts of Physical Climate Change on Atmospheric Chemistry 4.5.3 Feedbacks through Natural Emissions 4.6 Overall Impact of Global Atmospheric Chemistry Change References

The properties (densities of electrons and metastable argon atoms, effective electron temperature and dust charge) of argon/dust and pure argon pulsed plasmas are studied using a spatially-averaged model. The calculated time-dependencies for the densities of electrons and metastable atoms are compared with the experimental measurements and are found to be in a good qualitative agreement. It is analyzed how the plasma properties depend on the shape of the electron energy probability function (EEPF), the pulsing frequency and the duty cycle for both dust-free and dusty plasma. The analysis reveals that the agreement between theory and experiment is better with Druyvesteyn EEPF than the Maxwellian EEPF. Further, the variation in the pulsing frequency ν p differently affects the metastable density n m in a dust-free and in a dusty plasma. For large ν p, the metastable density in the dust-free pulsed plasma is larger than in the continuous-wave (CW) discharge, while the opposite is obtai...

Modelling 263 4.2.6.1 Laboratory data and the OH lifetime of greenhouse gases 263 4.2.6.2 Atmospheric measurements and modelling of photochemistry 264 4.3 Projections of Future Emissions 266 4.3.1 The Adjusted/Augmented IPCC/SRES Emission Scenarios 266 4.3.2 Shifting Regional Emissions of NO x , CO and VOC in 2100 4.3.3 Projections of Natural Emissions in 2100 4.4 Projections of Atmospheric Composition for the 21st Century 4.4.1 Introduction 4.4.2 The OxComp Workshop 4.4.3 Testing CTM Simulation of the Current (Y2000) Atmosphere 4.4.4 Model Simulations of Perturbed and Y2100 Atmospheres 4.4.5 Atmospheric Composition for the IPCC Scenarios to 2100 4.4.6 Gaps in These Projections-the Need for Coupled Models 4.4.7 Sensitivity Analysis for Individual Sectors 4.5 Open Questions 4.5.1 Chemical Processes Important on the Global Scale 4.5.1.1 Missing chemistry, representation of small scales, and changing emission patterns 4.5.1.2 Aerosol interactions with tropospheric O 3 and OH 4.5.1.3 Stratosphere-troposphere coupling 4.5.1.4 Uncertainties in the tropospheric O 3 budget 4.5.2 Impacts of Physical Climate Change on Atmospheric Chemistry 4.5.3 Feedbacks through Natural Emissions 4.6 Overall Impact of Global Atmospheric Chemistry Change References