Ex-situ mineral carbonation: resources, process and environmental assessment (Carmex project)

This article presents the main results of the Carmex project (2009-2012), whose purpose was to review the feasibility of ex-situ mineral carbonation in terms of resource availability, performance of the aqueous mineral carbonation process and life cycle analysis criteria. This collaborative project looked at a wide range of generic issues about this CO2 mitigation option, with particular views on assessing its potential in the context of New-Caledonia. Indeed, insularity and local abundance of 'carbonatable' rocks and industrial wastes (i.e. rich in MgO, CaO, if not Fe(II)O), coupled with significant GHG emissions from first-class nickel pyrometallurgical industries, make it a potential candidate for application of ex-situ mineral carbonation. The project conducted a worldwide analysis of the potential of ex-situ mineral carbonation using a dedicated SIG-based tool. Using a variety of materials the project also reviewed a number of critical issues associated with the aqueous mineral carbonatation process itself, with promising perspectives. Finally, through life cycle analysis of the system as a whole, ex-situ mineral carbonation was compared to mainstream CSC solutions. It was concluded that the viability of this CO2 storage option is located at the level of the process itself and lies with the optimisation of its operating conditions

About the foundations of direct aqueous carbonation with dissolution enhancing organic salts

Direct aqueous carbonation is a promising mineral carbonation route. Under mildly acidic conditions, this single-step carbonation process aims to simultaneously dissolve Ca/Mg-bearing silicates or wastes and precipitate Ca/Mg carbonates. By and large, since mineral dissolution is rate limiting due to the lack of protons at near-neutral pH, research has mainly been concerned with the issue of enhancing dissolution. By analysing the liquid phase, it has been established that polyacid organic salts can significantly enhance silicate dissolution under such unfavourable conditions. Comparatively little attention has been paid to the investigation of the very basis of the whole process, i.e. the concomitance of silicate dissolution and carbonate precipitation. By taking a close look at the solid phases in lizardite and olivine slurries, this work confirms the co-occurrence of magnesium silicate dissolution and magnesite precipitation inside a stirred reactor operating at 120°C, 20 bar of CO2 and 0.1M disodium oxalate, thereby bringing indisputable evidence that supports the foundation of direct aqueous carbonation with organic salts

Comprehensive analysis of direct aqueous mineral carbonation using dissolution enhancing organic additives.

Direct aqueous mineral carbonation using organic anions has been presented by many as a promising strategy for mineral carbonation, on the basis that additives such as oxalate increase the rate and extent of dissolution of magnesium silicates several folds. Through geochemical modelling and detailed solid characterization, this paper discusses and extends our current understanding of this process. The role of disodium oxalate as a dissolution enhancing agent for olivine is thoroughly examined through experiments in which all phases are carefully analysed. We show that under 20 bar of CO2 pressure formation of strong oxalate-magnesium complexes in solution and precipitation of MgC2O4,2H2O (glushinskite) impede any chance of obtaining significant amounts of magnesium carbonate. Other promising ligands from a dissolution perspective, namely citrate and EDTA salts, are also investigated. Contrary to oxalate, these ligands do not form any solid by-products with magnesium, and yet they do not produce better carbonation results, thereby casting strong doubts on the possibility of developing a direct aqueous mineral carbonation process using organic salts. Geochemical modelling permits successful simulation of the dissolution kinetics of magnesium silicate using a shrinking particle model that accounts for the precipitation of glushinskite, amorphous silica and a magnesium phyllosilicate at advanced stages of the dissolution process

Screening for Staphylococcal Superantigen Genes Shows No Correlation with the Presence or the Severity of Chronic Rhinosinusitis and Nasal Polyposis

BACKGROUND: Staphylococcus aureus secretes numerous exotoxins which may exhibit superantigenic properties. Whereas the virulence of several of them is well documented, their exact biological effects are not fully understood. Exotoxins may influence the immune and inflammatory state of various organs, including the sinonasal mucosa: their possible involvement in chronic rhinosinusitis has been suggested and is one of the main trends in current research. The aim of this study was to investigate whether the presence of any of the 22 currently known staphylococcal exotoxin genes could be correlated with chronic rhinosinusitis. METHODOLOGY/PRINCIPAL FINDINGS: We conducted a prospective, multi-centred European study, analysing 93 Staphylococcus aureus positive swabs taken from the middle meatus of patients suffering from chronic rhinosinusitis, with or without nasal polyposis, and controls. Strains were systematically tested for the presence of the 22 currently known exotoxin genes and genotyped according to their agr groups. No direct correlation was observed between chronic rhinosinusitis, with or without nasal polyposis, and either agr groups or the presence of the most studied exotoxins genes (egc, sea, seb, pvl, exfoliatins or tsst-1). However, genes for enterotoxins P and Q were frequently observed in nasal polyposis for the first time, but absent in the control group. The number of exotoxin genes detected was not statistically different among the 3 patient groups. CONCLUSIONS/SIGNIFICANCE: Unlike many previous studies have been suggesting, we did not find any evident correlation between staphylococcal exotoxin genes and the presence or severity of chronic rhinosinusitis with or without nasal polyposis

The Vam6 GEF controls TORC1 by activating the EGO complex

The target of rapamycin complex 1 (TORC1) is a central regulator of eukaryotic cell growth that is activated by a variety of hormones (e.g., insulin) and nutrients (e.g., amino acids) and is deregulated in various cancers. Here, we report that the yeast Rag GTPase homolog Gtr1, a component of the vacuolar-membrane-associated EGO complex (EGOC), interacts with and activates TORC1 in an amino-acid-sensitive manner. Expression of a constitutively active (GTP-bound) Gtr1GTP, which interacted strongly with TORC1, rendered TORC1 partially resistant to leucine deprivation, whereas expression of a growth inhibitory, GDP-bound Gtr1GDP, caused constitutively low TORC1 activity. We also show that the nucleotide-binding status of Gtr1 is regulated by the conserved guanine nucleotide exchange factor (GEF) Vam6. Thus, in addition to its regulatory role in homotypic vacuolar fusion and vacuole protein sorting within the HOPS complex, Vam6 also controls TORC1 function by activating the Gtr1 subunit of the EGO complex

Ex situ mineral carbonation for CO2 mitigation: Evaluation of mining waste resources, aqueous carbonation processability and life cycle assessment (Carmex project)

This article presents the main outputs from the multidisciplinary Carmex project (2009–2012), which was concerned with the possibility of applying ex situ mineral carbonation concepts to mafic/ultramafic mining wastes. Focus points of the project included (i) matching significant and accessible mining wastes to large CO2 emitters through a dedicated geographical information system (GIS), (ii) analysis of aqueous carbonation mechanisms of mining waste and process development and (iii) environmental assessment of ex situ mining waste carbonation through life cycle assessment (LCA) methodology. With a number of materials associated with the mining sector, the project took a close look at the aqueous carbonation mechanisms for these materials and obtained unexpected carbonation levels (up to 80%) by coupling mechanical exfoliation and reactive carbonation. Results from this work support the possibility of processing serpentine-rich peridotites without applying the classical first step of heat activation. Perspectives are also given for the carbonation of Ni-pyrometallurgical slag available closed to ultramafic mining residues. LCA of the mining waste carbonation system as a whole made it clear that the viability of this CO2 storage option lies with the carbonation process itself and optimisation of its operating conditions. By combining the body of knowledge acquired by this project, it is concluded that New Caledonia, with its insularity and local abundance of ‘carbonable’ rocks and industrial wastes coupled with significant greenhouse gas (GHG) emissions from world-class nickel pyro and hydrometallurgical industries stands out as a strong potential candidate for application of ex situ mineral carbonation