Exploring the Thermodynamic Limits of Enhanced H2 Recovery With Inherent Carbon Removal From Low Value Aqueous Biomass Oxygenate Precursors

Rational integration of chemical pathways at the molecular scale to direct thermodynamically favorable enhanced H2 production with inherent carbon removal from low-value substrates can be guided by exploring the thermodynamic limits of feasibility. The substrates of interest are biomass oxygenates that are water-soluble and uneconomical for separation from water. In this study, we investigate the thermodynamic feasibility of recovering H2 with inherent carbon removal from biomass oxygenates such as ethanol, methanol, glycerol, ethylene glycol, acetone, and acetic acid. The influence of biomass oxygenate-to-water ratios, reaction temperature of 150°C–325°C, and CaO or Ca(OH)2 as the alkalinity source on the yields of H2, CH4, CO2, and Ca-carbonate are investigated. By maintaining the fluids in the aqueous phase under pressure, energy needs associated with vaporization are circumvented. The hypothesis that enhanced alkalinity favors the preferential formation of CO (precursor for CO2 formation) over CH4 and aids the formation of calcium carbonate is investigated. The findings from these studies inform the feasibility, design of experiments, and the tuning of reaction conditions for enhanced H2 recovery with inherent carbon removal from biomass oxygenate sources.

Visual Imaging of Benthic Carbonate-Mixed Factories in the Ross Sea Region Marine Protected Area, Antarctica

Marine biogenic skeletal production is the prevalent source of Ca-carbonate in today’s Antarctic seas. Most information, however, derives from the post-mortem legacy of calcifying organisms. Prior imagery and evaluation of Antarctic habitats hosting calcifying benthic organisms are poorly present in the literature, therefore, a Remotely Operated Vehicle survey was carried out in the Ross Sea region Marine Protected Area during the 2013–2014 austral summer. Two video surveys of the seafloor were conducted along transects between 30 and 120 m (Adelie Cove) and 230 and 260 m (Terra Nova Bay “Canyon”), respectively. We quantified the relative abundance of calcifiers vs non-calcifiers in the macro- and mega-epibenthos. Furthermore, we considered the typology of the carbonate polymorphs represented by the skeletonized organisms. The combined evidence from the two sites reveals the widespread existence of carbonate-mixed factories in the area, with an overwhelming abundance of both low-Mg and (especially) high-Mg calcite calcifiers. Echinoids, serpulids, bryozoans, pectinid bivalves and octocorals prove to be the most abundant animal producers in terms of abundance. The shallower Adelie Cove site also showed evidence of seabed coverage by coralline algae. Our results will help in refining paleoenvironmental analyses since many of the megabenthic calcifiers occur in the Quaternary record of Antarctica. We set a baseline to monitor the future response of these polar biota in a rapidly changing ocean.

Speciation of Magnesium in Aerosols Using X-ray Absorption Near-Edge Structure Related to Its Contribution to Neutralization Reactions in the Atmosphere

Aerosols, including mineral dust, are transported from China and Mongolia to Japan, particularly in spring. It has been recognized that calcium (Ca) carbonate is the main Ca species in aerosols, which reacts with acidic species such as sulfuric and nitric acids at the surface of mineral dust during its long-range transport, related to mitigation of acid depositions. The similar assumption that magnesium (Mg) originally takes the form of carbonate and contributes to the neutralization reaction and buffering effect on the acidity of aerosols has been suggested in various studies. However, few studies have confirmed this process by measuring actual Mg species in aerosols quantitatively. In this study, X-ray absorption near-edge structure (XANES) spectroscopy was employed to determine Mg species in size-fractionated aerosol samples, including mineral dust. The results showed that (i) most Mg in the mineral dust did not take the form of carbonate and its reacted species (e.g., sulfate and nitrate) produced by the neutralization reaction, but (ii) Mg was mainly found as Mg in the octahedral layer in phyllosilicates. Given that the reactivity of such Mg in phyllosilicates is much lower than those in carbonate minerals, the contribution of Mg to the neutralization reactions in the atmosphere must be lower than previously expected.

Mineral assemblage within secondary crystallized melt inclusions in olivine of mantle xenoliths from the Bultfontein kimberlite pipe (Kaapvaal craton, South Africa)

<p>For the first time, snapshots of crystallized melts in olivine of sheared garnet peridotite xenoliths from the Bultfontein kimberlite pipe have been studied. This type of xenoliths represents the deepest mantle rocks derived from the base of lithosphere (at depths from 110 to 230 km for various ancient cratons). According to different models, such type of inclusions (secondary) in mantle minerals can be interpreted as relics of the most primitive (i.e., close-to-primary) kimberlite melt that infiltrated into sheared garnet peridotites. In general, these secondary inclusions are directly related to kimberlite magmatism that finally formed the Bultfontein diamond deposits. The primary/primitive composition of kimberlite melt is poorly constrained because kimberlites are ubiquitously contaminated by xenogenic material and altered by syn/post-emplacement hydrothermal processes. Thus, the study of these inclusions helps to significantly advance in solving numerous problems related to the kimberlite petrogenesis.</p><p>The unexposed melt inclusions were studied by using a confocal Raman spectroscopy. In total, fifteen daughter minerals within the inclusions were identified by this method. Several more phases give distinct Raman spectra, but their determination is difficult due to the lack of similar spectra in the databases. Various carbonates and carbonates with additional anions, alkali sulphates, phosphates and silicates were determined among daughter minerals in the melt inclusions: calcite CaCO<sub>3</sub>, magnesite MgCO<sub>3</sub>, dolomite CaMg(CO<sub>3</sub>)<sub>2</sub>, eitelite Na<sub>2</sub>Mg(CO<sub>3</sub>)<sub>2</sub>, nyerereite (Na,K)<sub>2</sub>Ca(CO<sub>3</sub>)<sub>2</sub>, gregoryite (Na,K,Ca)<sub>2</sub>CO<sub>3</sub>, K-Na-Ca-carbonate (K,Na)<sub>2</sub>Ca(CO<sub>3</sub>)<sub>2</sub>, northupite Na<sub>3</sub>Mg(CO<sub>3</sub>)<sub>2</sub>Cl, bradleyite Na<sub>3</sub>Mg(PO<sub>4</sub>)(CO<sub>3</sub>), burkeite Na<sub>6</sub>(CO<sub>3</sub>)(SO<sub>4</sub>)<sub>2</sub>, glauberite Na<sub>2</sub>Ca(SO<sub>4</sub>)<sub>2</sub>, thenardite Na<sub>2</sub>SO<sub>4</sub>, aphthitalite K<sub>3</sub>Na(SO<sub>4</sub>)<sub>2</sub>, apatite Ca<sub>5</sub>(PO<sub>4</sub>)<sub>3</sub>(OH,Cl,F) and tetraferriphlogopite KMg<sub>3</sub>FeSi<sub>3</sub>O<sub>10</sub>(F,Cl,OH). Note that carbonates are predominant among the daughter minerals in the melt inclusions. Moreover, there are quite a lot of alkali-rich daughter minerals within the inclusions as well. During the last decade, some research groups using different approaches proposed a model of carbonate/alkali‑carbonate composition of kimberlite melts in their source regions. This model contradicts to the generally accepted ultramafic silicate nature of parental kimberlite liquids. This study is a direct support of a new model of carbonatitic composition of kimberlite melts and also shows that alkali contents in kimberlite petrogenesis are usually underestimated.</p><p>This work was supported by the Russian Foundation for Basic Research (grant No. 20-35-70058).</p>

Geothermal Fluid Variation Recorded by Banded Ca-Carbonate Veins in a Fault-Related, Fissure Ridge-Type Travertine Depositional System (Iano, southern Tuscany, Italy)

Banded Ca-carbonate veins in travertine deposits are efficient recorders of the compositional fluctuations of geothermal fluids flowing (or flowed) from deep reservoirs up to the surface, within fault zones. In this view, these veins represent key tools for decoding those factors that influenced the geochemical variations. We have analyzed veins developed in fractures channeling geothermal fluids forming travertine deposits. The studied veins cut a fossil travertine fissure ridge, near the Larderello geothermal area (Iano area, southern Tuscany) where geothermal fluid circulation is favored by NE-trending strike-to-oblique-slip faults and their intersections with NW-trending normal ones. U-Th dating indicates that fluid circulation occurred from (at least) 172 ka to 21 ka. In this time span, the geothermal fluid changed in composition, and the banded Ca-carbonate veins recorded these variations in terms of mineralogical and stable isotope composition and temperature ( T ) of deposition. We also documented for the first time the occurrence of Mn-rich black tree-shaped structures within the veins. Mineralogy coupled with stable and clumped isotope measurements allows the reconstruction of some features (i.e., crystal texture, temperature, and CO2 origin) and the inference of the processes (i.e., pH, T, and pCO2 variations) that have controlled the fluid evolution through time. Multiple-stage and one-stage deposition processes have played an important role in modifying the stable isotope composition of banded Ca-carbonate veins; temperature coupled with pCO2 also influenced their mineralogical composition. Interpreted in the context of the tectonic setting, the data show that the NW-trending faults have mainly controlled travertine deposition. Their intersection with NE-trending faults, interpreted as transfer faults, highlights the important role of transfer zones in channeling the geothermal fluids.

P1414THE PREDICTORS OF PARATHYROID HORMONE VARIABILITY IN HEMODIALYSIS PATIENTS

Background and Aims KDIGO Clinical Practice Guidelines suggest in hemodialysis (HD) patients using a dialysate calcium concentration between 1,25 and 1,5 mmol/L and maintaining serum intact parathyroid hormone (sPTH) levels in the range of approximately 2 to 9 times the upper normal limit for the assay. The aim of the study was to evaluate the predictors of PTH variability in HD patients over a 12 months period. Method The multicenter restrospective study encompassed 398 patients (256M and 142F) with the average age 59,64±13,29 years and the average HD vintage 78,63±64,26 months. Over a 12 months (M0-M12) period: serum calcium (sCa), serum phosphorus (sPi), serum alkaline phosphatase (sAPh), oral calcium-carbonate daily dose, oral calcitriol weekly dose, and dialysate Ca concentration (dCa) were monitored monthly, and sPTH at 6 months. According to PTH assay reference level (18,4-80,1 pg/ml) 3 groups of patients were categorized: patients with low sPTH<160, with target range sPTH =160-721, and with high sPTH>721. For statistical analysis chi-square test, analysis of variance with repeated measures and logistic regression analysis were performed by softver SPSS. Results Over a 12 months period the number of patients with low sPTH significantly decreased, but the number of patients with target range sPTH and high sPTH increased (Chi square=269,45; p<0.001). On the basis of overall pattern of sPTH fluctuation over a 12 months period six subgroups of patients were observed: consistently low in 20,6% of patients, consistently within the target range in 22,1%, consistently high in 14,07%, low-amplitude fluctuation with low and target range sPTH levels (LAL) in 31,4%, low-amplitude fluctuation with target range and high sPTH levels (LAH) in 10,55%, and high-amplitude fluctuation (HA) subgroup with low, target range and high sPTH levels in 1,25%. In 35 patients constantly hemodialyzed over a 12 months period with dCa=1,25 mmol/L due to high sCa the significant increase of sPTH (M0=797±657 vs M12=1030±740 pg/ml; p=0.001) and no significant changes of sCa (M0=2,44± vs M12=2,34± mmol/L; n.s.), sPi (M0=1,81±0,49 vs M12=1,68±0,49 mmol/L; n.s.), Ca-carbonate daily dose (M0=1,88±1,54 vs M12=2,22±1,53 g/d; n.s.) and calcitriol weekly dose (M0=0,84±1,38 vs M12=1,1±1,41 ucg/w; n.s.) were observed. In 24 patients constantly hemodialyzed with dCa=1,75 mmol/L due to low sCa the significant decrease of sPTH (M0=518±582 vs M12=391±530 pg/ml; p=0.037) and no significant changes of sCa (M0=2,17±0,19 vs M12=2,18±0,17 mmol/L; n.s.), sPi (M0=1,3±0,34 vs M12=1,36±0,52 mmol/L; n.s.), Ca-carbonate daily dose (M0=2,53±1,58 vs M12=2,1±1,91 g/d; n.s.) and calcitriol weekly dose (M0=1,33±1,23 vs M12=1,42±1,69 ucg/w; n.s.) were observed. In 195 patients constantly hemodialyzed with dCa=1,5 mmol/L no significant changes of sPTH (M0=388±421 vs M12=434±459 pg/ml; n.s.), sCa (M0=2,29±0,18 vs M12=2,27±0,15 mmol/L; n.s.), sPi (M0=1,48±0,41 vs M12=1,52±0,41 mmol/L; n.s.), Ca-carbonate daily dose (M0=2,42±1,4 vs M12=2,57±1,2 g/d; n.s.) and calcitriol weekly dose (M0=0,47±0,72 vs M12=0,38±0,68 ucg/w; n.s.) were observed. By model of logistic regression analysis dCa=1,75 (OR=8,33), increased sCa (OR=7,7), and presence of diabetes mellitus (OR=2,44) were the most significant predictors of low sPTH<160 (Chi square=116,27; p<0.001), but the increased sCa (OR=6,88), dCa=1,25 (OR=5,08), and the increased sPi (OR=2,72) were the most significant predictors of high sPTH>721 (Chi square=72,475; p<0.001). Conclusion The prolonged use of dCa=1,25 in patients with high sCa led to significant sPTH increase likely due to net negative calcium balance, but prolonged use of dCa=1,75 in patients with low sCa led to significant sPTH decrease likely due to net positive calcium balance.