Pathways to Accelerated Carbon Mineralization in Mine Tailings

Alkaline waste generated from mining of magnesium silicate rocks reacts spontaneously with atmospheric carbon dioxide (CO2) to precipitate carbon in solid mineral form. The total capacity of these mine tailings to sequester carbon is about ten times greater than greenhouse gas emissions of associated mining and mineral processing. Waste from mining activity globally has capacity to sequester 100-200 Mt of CO2 per year. However passive, or unintentional, CO2 mineralization at individual mine sites is modest (1-50 kt/yr), and typically limited by CO2 supply. Acceleration of these reactions represents an opportunity to generate considerable greenhouse gas offsets for the industry, and to develop expertise in carbon mineralization that is relevant to accelerated weathering at Earth’s surface and mineral trapping in low temperature aquifers and reservoirs. Experimental acceleration of carbon mineralization is readily achieved through enhanced delivery of CO2, wherein reaction rates are limited by rates of cation (e.g., Mg2+) supply from mineral dissolution. Further acceleration requires optimization of mineral dissolution processes. Continuous-flow dissolution experiments on minerals and mine tailings exhibit rapid, transient cation release rates that decay to slower rates indicative of conventional steady-state bulk mineral dissolution processes (Fig. 1A). The transient initial phase of the experiments can release a significant amount (5-10%) of the total cation content of the material. It reflects the dissolution of highly soluble trace minerals, and surface processes in sheet silicate minerals which together we take to represent the labile cation capacity of the material. Longer-term steady-state cation release is much slower and represents recalcitrant cation capacity indicative of bulk mineral dissolution. The labile cation content represents the carbon mineralization capacity of alkaline mine wastes accessible with existing low-cost technologies while recalcitrant cation content is unlikely to be tapped at existing carbon prices (Fig. 1B). Measured labile cation content of mine tailings varies substantially between and within deposits, with implications for how carbon mineralization capacity should be characterized and how carbonation intervention would be incorporated into mine operations. Specific mines and specific alteration types with high labile cation content, which for some mines is sufficient to offset total mine greenhouse gas emissions, should be the focus of pilot scale carbon mineralization projects. Please click Additional Files below to see the full abstract

The Implicit Relational Assessment Procedure (IRAP) as a measure of implicit relative preferences: A first study

The Implicit Relational Assessment Procedure (IRAP) was designed to examine implicit beliefs or attitudes. In Experiment 1, response latencies obtained from Irish participants on the IRAP showed a strong preference for Irish over Scottish and American over African. In contrast, responses to explicit Likert measures diverged from the IRAP performance in indicating Irish equally likeable to Scottish and African more likeable than American. Using a similar IRAP, Experiment 2 showed that participants from the United States showed strong implicit preferences for American over Irish, Irish over Scottish, and Scottish over African; the explicit Likert measures again diverged from the IRAP. The findings provide preliminary support for the IRAP as a useful measure of implicit beliefs

The Implicit Relational Assessment Procedure (IRAP) as a measure of implicit relative preferences: A first study

The Implicit Relational Assessment Procedure (IRAP) was designed to examine implicit beliefs or attitudes. In Experiment 1, response latencies obtained from Irish participants on the IRAP showed a strong preference for Irish over Scottish and American over African. In contrast, responses to explicit Likert measures diverged from the IRAP performance in indicating Irish equally likeable to Scottish and African more likeable than American. Using a similar IRAP, Experiment 2 showed that participants from the United States showed strong implicit preferences for American over Irish, Irish over Scottish, and Scottish over African; the explicit Likert measures again diverged from the IRAP. The findings provide preliminary support for the IRAP as a useful measure of implicit beliefs

Offsetting of CO₂ emissions by air capture in mine tailings at the Mount Keith Nickel Mine, Western Australia: Rates, controls and prospects for carbon neutral mining

The hydrated Mg-carbonate mineral, hydromagnesite [Mg₅(CO₃)₄(OH)₂•4H₂O], precipitates within mine tailings at the Mount Keith Nickel Mine, Western Australia as a direct result of mining operations. We have used quantitative mineralogical data and δ¹³C, δ¹⁸O and F¹⁴C isotopic data to quantify the amount of CO₂fixation and identify carbon sources. Our radiocarbon results indicate that at least 80% of carbon stored in hydromagnesite has been captured from the modern atmosphere. Stable isotopic results indicate that dissolution of atmospheric CO₂ into mine tailings water is kinetically limited, which suggests that the current rate of carbon mineralization could be accelerated. Reactive transport modeling is used to describe the observed variation in tailings mineralogy and to estimate rates of CO₂ fixation. Based on our assessment, approximately 39,800 t/yr of atmospheric CO₂ are being trapped and stored in tailings at Mount Keith. This represents an offsetting of approximately 11% of the mine's annual greenhouse gas emissions. Thus, passive sequestration via enhanced weathering of mineral waste can capture and store a significant amount of CO₂. Recommendations are made for changes to tailings management and ore processing practices that have potential to accelerate carbonation of tailings and further reduce or completely offset the net greenhouse gas emissions at Mount Keith and many other mines

My School? Critiquing the abstraction and quantification of education

This paper draws upon and critiques the Australian federal government's website My School as an archetypal example of the current tendency to abstract and quantify educational practice. Arguing in favour of a moral philosophical account of educational practice, the paper reveals how the My School website reduces complex educational practices to simple, supposedly objective, measures of student attainment, reflecting the broader 'audit' society/culture within which it is located. By revealing just how extensively the My School website reduces educational practices to numbers, the paper argues that we are in danger of losing sight of the 'internal' goods of Education which cannot be readily and simply codified, and that the teacher learning encouraged by the site marginalises more active and collective approaches. While having the potential to serve some beneficial diagnostic purposes, the My School website reinforces a view of teachers as passive consumers of information generated beyond their everyday practice

An investigation of capacitance-voltage hysteresis in metal/high-k/In0.53Ga0.47As metal-oxide-semiconductor capacitors

In this work, we present the results of an investigation into charge trapping in metal/high-k/In0.53Ga0.47As metal-oxide-semiconductor capacitors (MOS capacitors), which is analysed using the hysteresis exhibited in the capacitance-voltage (C-V) response. The availability of both n and p doped In0.53Ga0.47As epitaxial layers allows the investigation of both hole and electron trapping in the bulk of HfO2 and Al2O3 films formed using atomic layer deposition (ALD). The HfO2/In0.53Ga0.47As and Al2O3/In0.53Ga0.47As MOS capacitors exhibit an almost reversible trapping behaviour, where the density of trapped charge is of a similar level to high-k/In0.53Ga0.47As interface state density, for both electrons and holes in the HfO2 and Al2O3 films. The experimental results demonstrate that the magnitude of the C-V hysteresis increases significantly for samples which have a native oxide layer present between the In0.53Ga0.47As surface and the high-k oxide, suggesting that the charge trapping responsible for the C-V hysteresis is taking place primarily in the interfacial oxide transition layer between the In0.53Ga0.47As and the ALD deposited oxide. Analysis of samples with a range of oxide thickness values also demonstrates that the magnitude of the C-V hysteresis window increases linearly with the increasing oxide thickness, and the corresponding trapped charge density is not a function of the oxide thickness, providing further evidence that the charge trapping is predominantly localised as a line charge and taking place primarily in the interfacial oxide transition layer located between the In0.53Ga0.47As and the high-k oxide. (C) 2013 AIP Publishing LLC

Associations between APOE and low-density lipoprotein cholesterol genotypes and cognitive and physical capability: the HALCyon programme

The APOE ε2/3/4 genotype has been associated with low-density lipoprotein cholesterol (LDL-C) and Alzheimer disease. However, evidence for associations with measures of cognitive performance in adults without dementia has been mixed, as it is for physical performance. Associations may also be evident in other genotypes implicated in LDL-C levels. As part of the Healthy Ageing across the Life Course (HALCyon) collaborative research programme, genotypic information was obtained for APOE ε2/3/4, rs515135 (APOB), rs2228671 (LDLR) and rs629301 (SORT1) from eight cohorts of adults aged between 44 and 90+years. We investigated associations with four measures of cognitive (word recall, phonemic fluency, semantic fluency and search speed) and physical capability (grip strength, get up and go/walk speed, timed chair rises and ability to balance) using meta-analyses. Overall, little evidence for associations between any of the genotypes and measures of cognitive capability was observed (e.g. pooled beta for APOE ε4 effect on semantic fluency z score=- 0.02; 95% CI=- 0.05 to 0.02; p value=0.3; n=18,796). However, there was borderline evidence within studies that negative effects of APOE ε4 on nonverbal ability measures become more apparent with age. Few genotypic associations were observed with physical capability measures. The findings from our large investigation of middle-aged to older adults in the general population suggest that effects of APOE on cognitive capability are at most modest and are domain- and age-specific, while APOE has little influence on physical capability. In addition, other LDL-C-related genotypes have little impact on these traits. © The Author(s) 2014