Process Intensification Routes for Mineral Carbonation

Mineral carbonation is a realistic route for capture and storage of carbon dioxide. The principal advantages of this approach are the chemical stability and storage safety of mineral carbonates, the opportunities for process integration available, and the potential for conversion of low-value materials into useful products. In this work the valorisation of alkaline waste materials from thermal processes by mineral carbonation utilizing intensified and integrated mineral carbonation routes is explored. Process intensification is the chemical engineering of the 21st century, and aims at providing the paradigm-shifting techniques that will revolutionize the industry. The combination of process intensification and process integration strategies has the potential to produce economically feasible and industrially acceptable carbonation technologies that can soon be implemented at large-scale, several examples of which are already proven at the laboratory scale and are herein discussed

Preliminary investigation of a CFD-assisted virtual reality experience in engineering education

Virtual reality has become a significant asset to diversify tools in the support of engineering education and training. The cognitive and behavioral advantages of virtual reality (VR) can help lecturers reduce entry barriers to concepts that students struggle with. Computational fluid dynamics (CFD) simulations are imperative tools intensively utilized in the design and analysis of chemical engineering problems. Although CFD simulation tools can be directly applied in engineering education, they bring several challenges in the implementation and operation for both students and lecturers. In this study, to tackle these challenges, we developed the “Virtual Garage” as a taskcentered educational VR application with CFD simulations. The Virtual Garage is composed of a holistic immersive experience to educate students through a real-life engineering problem solved with CFD simulation data using a VR headset. The prototype is tested by graduate students (n=24). Participants assessed usability, user experience, task load and cybersickness via standard questionnaires together with self-reported questions and a semi-structured interview. Preliminary results reflect that the Virtual Garage is well-received by participants. We identify features that can further enhance the usability and user experience

Synthesis of Pure Aragonite by Sonochemical Mineral Carbonation.

The objective of this work was to promote the formation of the aragonite polymorph of calcium carbonate, which has some valuable applications in industry, via the mineral carbonation route. The combination of ultrasound with magnesium ions promoted the formation of pure aragonite crystals at optimum conditions. It was possible to synthesize high purity aragonite precipitates at temperatures ranging from 24 oC to 70 oC, with the resulting powders possessing varying particle size distributions (from sub-micron up to 20 μm) and crystal morphologies (from acicular needles to novel hubbard squash-like particles). Several process parameters were found to influence the produced calcium carbonate polymorph ratios (aragonite over calcite). Higher values of magnesium-to-calcium ratio, intermediate ultrasound amplitude (60%), continuous ultrasound application (100% cycle), introduction of ultrasound pre-breakage, lowering of the CO2 flow rate, and increase in the relative concentration (g/L Ca(OH)2), all promoted aragonite formation. A potential route for industrial production of this material has been identified via a fed-batch process, which effectively reutilizes magnesium chloride while maintaining high aragonite yield. The results presented herein are significantly superior to aragonite formation using only single promoting techniques, typically found in literature, and go beyond by focusing on pure (\u3e99%) aragonite formation

Sustainable Materialization of Residues from Thermal Processes into Products (SMaRT-Pro²).

Sustainable use of solid residues and carbon dioxide, the two largest and most important waste products from thermal processes, is an urgent issue both for the industry involved and society as a whole, considering the financial and environmental repercussions of their production. This Knowledge Platform focuses on three types of waste-to-product valorisation: production of a carbon sink, construction materials, or sorbents. Thermal processes constitute a bulk activity in metals production, waste incineration, glass industry, etc. They generally produce major amounts of solid waste materials, such as slag and fly ash, containing oxides of silicon, calcium, magnesium, aluminium and iron, together with a multitude of heavy metals, chlorides and/or sulphates. Rising prices of raw materials and growing awareness for environmental issues lead to a change in perception of these materials from waste to a potential product. Thermal processes also generate a vast amount of carbon dioxide which they emit into the atmosphere. The discussion concerning carbon dioxide is evolving rapidly, but it is clear that the emission of this greenhouse gas will become ever more regulated in the future. Mineral carbon sequestration is currently mainly investigated on primary materials such as olivine and serpentine. Sequestration in alkaline waste materials, however, provides an interesting alternative because of high reactivity, on-site production and low cost. In addition, the reaction with carbon dioxide stabilizes the waste materials and often improves environmental properties. The concept of producing construction materials from waste materials is only slowly coming of age despite the obvious benefit of transforming low-cost input materials into potentially high-value products. The production of another high-value product, a sorbent to remove pollutants from liquid streams, has only very recently been investigated for some of the waste materials studied in this project, and is a promising industrial application for in-house treatment of waste streams. A successful approach requires a broad consortium with relevant expertise for the scientific investigation, but which at the same time can be easily tailored to a particular valorisation option that emerges. The Platform aims at this dual objective by bringing together all expertise involved and by focusing on the challenging aim of valorising solid materials and/or carbon dioxide in high-value products by intensified processes and with clear prospects on the economic and legislative feasibility, ecological benefits and societal relevance.Waste valorisation; Sustainability;

Recent Developments and Perspectives on the Treatment of Industrial Wastes by Mineral Carbonation - a Review

Besides producing a substantial portion of anthropogenic CO2 emissions, the industrial sector also generates significant quantities of solid residues. Mineral carbonation of alkaline wastes enables the combination of these two by-products, increasing the sustainability of industrial activities. On top of sequestering CO2 in geochemically stable form, mineral carbonation of waste materials also brings benefits such as stabilization of leaching, basicity and structural integrity, enabling further valorization of the residues, either via reduced waste treatment or landfilling costs, or via the production of marketable products. This paper reviews the current state-of-the-art of this technology and the latest developments in this field. Focus is given to the beneficial effects of mineral carbonation when applied to metallurgical slags, incineration ashes, mining tailings, asbestos containing materials, red mud, and oil shale processing residues. Efforts to intensify the carbonation reaction rate and improve the mineral conversion via process intensification routes, such as the application of ultrasound, hot-stage processing and integrated reactor technologies, are described. Valorization opportunities closest to making the transition from laboratory research to commercial reality, particularly in the form of shaped construction materials and precipitated calcium carbonate, are highlighted. Lastly, the context of mineral carbonation among the range of CCS options is discussed

Distinguishing Between Carbonate and Non-carbonate Precipitates From the Carbonation of Calcium-containing Organic Acid Leachates

Two organic acids were trialled for the extraction of calcium from steelmaking blast furnace slag for the purpose of precipitated calcium carbonate (PCC) production: succinic and acetic acids. While the leaching performance of succinic acid was superior, carbonation of its leachate did not result in the production of PCC, but rather the precipitation of calcium succinate, and only after the use of pH buffering agents (sodium hydroxide or bicarbonate). In contrast, carbonation of the acetic acid leachate resulted in the production of PCC, also with the aid of buffering agents. This discrepancy highlights the need for a combination of chemical, mineralogical and morphological analytical techniques for the accurate characterization of carbonation precipitates for future publications in this field. Additional effects observed in this study were the low atom-efficiency of the acids for calcium leaching, at ~20–30% of the stoichiometric value, the low extraction selectivity but high carbonation selectivity between calcium and magnesium, and the contamination of the formed PCC’s with small amounts of co-leached aluminium and silicon. Further work is warranted on the purification of this PCC synthesis route

Comparative Study of Ageing, Heat Treatment and Accelerated Carbonation for Stabilization of Municipal Solid Waste Incineration Bottom Ash in View of Reducing Regulated Heavy Metal/metalloid Leaching

This study compared the performance of four different approaches for stabilization of regulated heavy metal and metalloid leaching from municipal solid waste incineration bottom ash (MSWI-BA): (i) short term (three months) heap ageing, (ii) heat treatment, (iii) accelerated moist carbonation, and (iv) accelerated pressurized slurry carbonation. Two distinct types of MSWI-BA were tested in this study: one originating from a moving-grate furnace incineration operation treating exclusively household refuse (sample B), and another originating from a fluid-bed furnace incineration operation that treats a mixture of household and light industrial wastes (sample F). The most abundant elements in the ashes were Si (20 to 27 wt.%) and Ca (16 to 19 wt.%), followed by significant quantities of Fe, Al, Na, S, K, Mg, Ti, and Cl. The main crystalline substances present in the fresh ashes were Quartz, Calcite, Apatite, Anhydrite and Gehlenite, while the amorphous fraction ranged from 56 to 73 wt.%. The leaching values of all samples were compared to the Flemish (NEN 7343) and the Walloon (DIN 38414) regulations from Belgium. Batch leaching of the fresh ashes at natural pH showed that seven elements exceeded at least one regulatory limit (Ba, Cr, Cu, Mo, Pb, Se and Zn), and that both ashes had excess basicity (pH \u3e 12). Accelerated carbonation achieved significant reduction in ash basicity (9.3–9.9); lower than ageing (10.5–12.2) and heat treatment (11.1–12.1). For sample B, there was little distinction between the leaching results of ageing and accelerated carbonation with respect to regulatory limits; however carbonation achieved comparatively lower leaching levels. Heat treatment was especially detrimental to the leaching of Cr. For sample F, ageing was ineffective and heat treatment had marginally better results, while accelerated carbonation delivered the most effective performance, with slurry carbonation meeting all DIN limits. Slurry carbonation was deemed the most effective treatment process, achieving consistently significant leaching stabilization, while also effectively washing out Cl ions, a requirement for the utilization of the ashes in construction applications. The benefits of carbonation were linked to the formation of significant quantities of Ca-carbonates, including appreciable quantities of the Aragonite polymorph formed in the slurry carbonated samples

Ultrasound-Intensified Mineral Carbonation

Several aspects of ultrasound-assisted mineral carbonation were investigated in this work. The objectives were to intensify the CO2 sequestration process to improve reaction kinetics and maximal conversion. Stainless steel slags, derived from the Argon Oxygen Decarburization (AOD) and Continuous Casting / Ladle Metallurgy (CC/LM) refining steps, were used for assessing the technical feasibility of this concept, as they are potential carbon sinks and can benefit from reduction in alkalinity (pH) by mineral carbonation. Ultrasound was applied by use of an ultrasound horn into the reaction slurry, where mineral carbonation reaction took place at 50 oC for up to four hours; comparison was made to solely mechanically mixed process. It was found that sonication increases the reaction rate after the initial stage, and permits achieving higher carbonate conversion and lower pH. AOD slag conversion increased from 30% to 49%, and pH decreased from 10.6 to 10.1; CC slag conversion increased from 61% to 73% and pH decreased from 10.8 to 9.9. The enhancement effect of ultrasound was attributed to the removal of passivating layers (precipitated calcium carbonate and depleted silica) that surround the unreacted particle core and inhibit mass transfer. Significant particle size reduction was observed for sonicated powders, compared to particle size growth in the case of stirring only; D[4,3] values increased without sonication by 74% and 50%, and decreased with sonication by 64% and 52%, respectively for AOD and CC slags. Considerations on scale-up of this technology, particularly with regards to energy efficiency, are also discussed