Biochar is an emerging low-cost sorbent used for removing trace metals from water. In this study, we evaluated the removal potential of aqueous hexavalent chromium (Cr(VI)) by biochars produced from ...soybean (Glycinemax L.) and burcucumber (Sicyos angulatus L.) residues. The highest Cr(VI) removal from solution occurred at low pH values (pH2–5), and adsorption decreased approximately tenfold when the pH increased from 2 to 10. Synchrotron-based X-ray absorption spectroscopy (XAS) investigations showed that Cr(VI) species were reduced to trivalent chromium (Cr(III)) at the biochar surface following Cr(VI) adsorption. Linear combination fitting (LCF) of X-ray absorption near edge structure (XANES) data indicated that approximately 90% of the total Cr(VI) (962μM) was reduced to Cr(III). Extended X-ray absorption fine structure (EXAFS) fitting results yielded interatomic chromium (CrCr) distances consistent with the formation of Cr(III) precipitates as Cr(OH)3. Trivalent chromium is far less soluble than Cr(VI) and typically precipitates as amorphous Cr(III) solids. Thus, biochars produced by soybean and burcucumber residues are a promising technique for both adsorbing and reductively immobilizing Cr(VI) from aqueous solutions.
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•Removal potential of aqueous Cr(VI) by biochar was evaluated.•The highest Cr(VI) removal occurred at low pH values.•Cr(VI) species can be reduced to Cr(III) at the biochar surface.•Biochar properties determine the coordination environment of Cr(III) products.
Biochar has been touted as a promising sorbent for the removal of inorganic contaminants, such as uranium (U), from water. However, the molecular-scale mechanisms of aqueous U(VI) species adsorption ...to biochar remain poorly understood. In this study, two approaches, grounded in equilibrium thermodynamics, were employed to investigate the U(VI) adsorption mechanisms: (1) batch U(VI) adsorption experiments coupled to surface complexation modeling (SCM) and (2) isothermal titration calorimetry (ITC), supported by synchrotron-based X-ray absorption spectroscopy (XAS) analyses. The biochars tested have considerable proton buffering capacity and most strongly adsorb U(VI) between approximately pH 4 and 6. FT-IR and XPS studies, along with XAS analyses, show that U(VI) adsorption occurs primarily at the proton-active carboxyl (−COOH) and phenolic hydroxyl (−OH) functional groups on the biochar surface. The SCM approach is able to predict U(VI) adsorption behavior across a wide range of pH and at varying initial U(VI) and biochar concentrations, and U adsorption is strongly influenced by aqueous U(VI) speciation. Supporting ITC measurements indicate that the calculated enthalpies of protonation reactions of the studied biochar, as well as the adsorption of U(VI), are consistent with anionic oxygen ligands and are indicative of both inner- and outer-sphere complexation. Our results provide new insights into the modes of U(VI) adsorption by biochar and more generally improve our understanding of its potential to remove radionuclides from contaminated waters.
Water contamination by ammonium (NH4+) can present considerable risks to natural ecosystems. This work evaluates the potential application of biochar, produced from the pyrolysis of digested sludge, ...to remove ammonium from water. Anaerobic digester sludge was collected from a municipal wastewater treatment plant in Alberta, Canada, and individual biochars were produced at 50 °C temperature increments between 350 °C and 550 °C. The chemical characteristics of the resulting biochars were determined using elemental analysis, scanning electron microscopy (SEM), BET surface area analysis, and Fourier transform infrared spectroscopy (FTIR). Our findings demonstrate that the biochar yield decreased with increasing pyrolysis temperature, and biochar produced at 450 °C (BC450) had the highest ammonium removal capacity due to its higher surface area and functional group density. The Langmuir isotherm best described the observed ammonium removal capacity by the biochars, indicating that monolayer chemical adsorption may be the dominating mechanism. Biochar ammonium removal capacity was 1.2 mg NH4N per gram of biochar in municipal wastewater, which is lower than that observed in parallel experiments using a synthetic ammonium solution (1.4 mg NH4+-N/g biochar). This phenomenon is likely due to competition between ammonia and other containments for sorption to biochar surface sites. Our results demonstrate for the first time ever that biochar produced from digester sludge is a promising adsorbent for ammonium removal from municipal wastewater.
While numerous studies have investigated metal uptake from solution by biochar, few of these have developed a mechanistic understanding of the adsorption reactions that occur at the biochar surface. ...In this study, we explore a combined modeling and spectroscopic approach for the first time to describe the molecular level adsorption of Ni(II) and Zn(II) to five types of biochar. Following thorough characterization, potentiometric titrations were carried out to measure the proton (H+) reactivity of each biochar, and the data was used to develop protonation models. Surface complexation modeling (SCM) supported by synchrotron-based extended X-ray absorption fine structure (EXAFS) was then used to gain insights into the molecular scale metal–biochar surface reactions. The SCM approach was combined with isothermal titration calorimetry (ITC) data to determine the thermodynamic driving forces of metal adsorption. Our results show that the reactivity of biochar toward Ni(II) and Zn(II) directly relates to the site densities of biochar. EXAFS along with FT-IR analyses, suggest that Ni(II) and Zn(II) adsorption occurred primarily through proton-active carboxyl (−COOH) and hydroxyl (−OH) functional groups on the biochar surface. SCM-ITC analyses revealed that the enthalpies of protonation are exothermic and Ni(II) and Zn(II) complexes with biochar surface are slightly exothermic to slightly endothermic. The results obtained from these combined approaches contribute to the better understanding of molecular scale metal adsorption onto the biochar surface, and will facilitate the further development of thermodynamics-based, predictive approaches to biochar removal of metals from contaminated water.
The fate and transport of cesium (Cs+) is strongly related to the presence of clay minerals in soils, and their weathering due to natural cycles of wetting and drying. In this study, the adsorption ...characteristics of Cs+ under repeated wetting and drying conditions were investigated using the 1:1 lattice clay mineral, kaolinite, the non-expanding 2:1 lattice clay mineral, illite, and the expanding 2:1 lattice clay minerals, hydrobiotite and montmorillonite. Unlike the cation exchange capacity of clay minerals (montmorillonite > hydrobiotite > illite > kaolinite), the amount of Cs+ adsorbed followed the order of hydrobiotite > montmorillonite > illite > kaolinite. The expanding 2:1 lattice clay minerals (hydrobiotite and montmorillonite) displayed a fixed d-spacing when Cs+ was adsorbed and dried, after which they had a structure similar to that of illite. The desorption efficiency of Cs+ in illite and montmorillonite also was lowered after drying at 80 °C. Desorption efficiencies of Cs+ in clay minerals were in the order of kaolinite > illite > montmorillonite > hydrobiotite. Therefore, there are differences on desorption efficiencies of Cs according to clay minerals due to each clay mineral structure and characteristics.
•Cs was fixed in the interlayer of montmorillonite by drying.•Wetting and drying cycles changed structure of montmorillonite into illite-like structure.•Desorption of Cs from expanding minerals hardly occurred.
Pericoronary adipose tissue (PCAT) attenuation and low-attenuation noncalcified plaque (LAP) burden can both predict outcomes.
This study sought to assess the relative and additive values of PCAT ...attenuation and LAP to predict future risk of myocardial infarction.
In a post hoc analysis of the multicenter SCOT-HEART (Scottish Computed Tomography of the Heart) trial, the authors investigated the relationships between the future risk of fatal or nonfatal myocardial infarction and PCAT attenuation measured from coronary computed tomography angiography (CTA) using multivariable Cox regression models including plaque burden, obstructive coronary disease, and cardiac risk score (incorporating age, sex, diabetes, smoking, hypertension, hyperlipidemia, and family history).
In 1,697 evaluable participants (age: 58 ± 10 years), there were 37 myocardial infarctions after a median follow-up of 4.7 years. Mean PCAT was −76 ± 8 HU and median LAP burden was 4.20% (IQR: 0%-6.86%). PCAT attenuation of the right coronary artery (RCA) was predictive of myocardial infarction (HR: 1.55; P = 0.017, per 1 SD increment) with an optimum threshold of −70.5 HU (HR: 2.45; P = 0.01). In multivariable analysis, adding PCAT-RCA of ≥−70.5 HU to an LAP burden of >4% (the optimum threshold for future myocardial infarction; HR: 4.87; P < 0.0001) led to improved prediction of future myocardial infarction (HR: 11.7; P < 0.0001). LAP burden showed higher area under the curve compared to PCAT attenuation for the prediction of myocardial infarction (AUC = 0.71 95% CI: 0.62-0.80 vs AUC = 0.64 95% CI: 0.54-0.74; P < 0.001), with increased area under the curve when the 2 metrics are combined (AUC = 0.75 95% CI: 0.65-0.85; P = 0.037).
Coronary CTA–defined LAP burden and PCAT attenuation have marked and complementary predictive value for the risk of fatal or nonfatal myocardial infarction.
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•Modified four step sequential extraction method suitable for pyrolyzed materials.•Untreated biochar may easily release alkaline earth and transition metals.•Wood biochar releases metals more readily ...than does sewage sludge biochar.
A modified Community Bureau of Reference (CBR) sequential extraction method was tested to assess the composition of untreated pyrogenic carbon (biochar) and oil sands petroleum coke. Wood biochar samples were found to contain lower concentrations of metals, but had higher fractions of easily mobilized alkaline earth and transition metals. Sewage sludge biochar was determined to be less recalcitrant and had higher total metal concentrations, with most of the metals found in the more resilient extraction fractions (oxidizable, residual). Petroleum coke was the most stable material, with a similar metal distribution pattern as the sewage sludge biochar. The applied sequential extraction method represents a suitable technique to recover metals from these materials, and is a valuable tool in understanding the metal retaining and leaching capability of various biochar types and carbonaceous petroleum coke samples.
BACKGROUND:The future risk of myocardial infarction is commonly assessed using cardiovascular risk scores, coronary artery calcium score, or coronary artery stenosis severity. We assessed whether ...noncalcified low-attenuation plaque burden on coronary CT angiography (CCTA) might be a better predictor of the future risk of myocardial infarction.
METHODS:In a post hoc analysis of a multicenter randomized controlled trial of CCTA in patients with stable chest pain, we investigated the association between the future risk of fatal or nonfatal myocardial infarction and low-attenuation plaque burden (% plaque to vessel volume), cardiovascular risk score, coronary artery calcium score or obstructive coronary artery stenoses.
RESULTS:In 1769 patients (56% male; 58±10 years) followed up for a median 4.7 (interquartile interval, 4.0–5.7) years, low-attenuation plaque burden correlated weakly with cardiovascular risk score (r=0.34; P<0.001), strongly with coronary artery calcium score (r=0.62; P<0.001), and very strongly with the severity of luminal coronary stenosis (area stenosis, r=0.83; P<0.001). Low-attenuation plaque burden (7.5% 4.8–9.2 versus 4.1% 0–6.8; P<0.001), coronary artery calcium score (336 62–1064 versus 19 0–217 Agatston units; P<0.001), and the presence of obstructive coronary artery disease (54% versus 25%; P<0.001) were all higher in the 41 patients who had fatal or nonfatal myocardial infarction. Low-attenuation plaque burden was the strongest predictor of myocardial infarction (adjusted hazard ratio, 1.60 (95% CI, 1.10–2.34) per doubling; P=0.014), irrespective of cardiovascular risk score, coronary artery calcium score, or coronary artery area stenosis. Patients with low-attenuation plaque burden greater than 4% were nearly 5 times more likely to have subsequent myocardial infarction (hazard ratio, 4.65; 95% CI, 2.06–10.5; P<0.001).
CONCLUSIONS:In patients presenting with stable chest pain, low-attenuation plaque burden is the strongest predictor of fatal or nonfatal myocardial infarction. These findings challenge the current perception of the supremacy of current classical risk predictors for myocardial infarction, including stenosis severity.
REGISTRATION:URLhttps://www.clinicaltrials.gov; Unique identifierNCT01149590.
The reactivity of clay mineral surfaces exerts a fundamental control on elemental cycling in environmental systems. However, the effect of solution ionic strength (IS) on their reactivity is poorly ...understood. Here we quantified the effect of changes in IS on clay mineral reactivity through the application of surface complexation modeling (SCM) based on acid-base titration data for three different clay minerals (kaolinite, illite, and montmorillonite). The results demonstrate that the acidity constants (Ka values) for proton interactions on the clay surface vary linearly as a logarithmic function of solution IS, and that proton binding ability is inversely related to solution IS. Two possible explanations for the observed relationship are proposed: (1) solution electrolytes (e.g., Na+) competitively bind to clay surface sites relative to protons, and (2) that the surface electrostatic field is attenuated by solution electrolytes. We conclude that the impact of increasing solution IS on clay surface reactivity is the result of a weakening negative surface electric field that impacts the surface potential. This mechanism ultimately leads to different adsorption behavior for cations and anions under changing IS conditions. The empirical relationship between K values and IS provided here can be applied to predict clay surface reactivity under varied environmental IS conditions and has specific implications for trace metal behavior in environments, such as estuaries, where changes in IS can be significant.
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•Using acid-base potentiometric titration, we studied the K values of clay minerals change with IS.•Log K values of kaolinite, illite, and montmorillonite change linearly with log IS.•The shielding of surface electrostatic field is the mechanism of IS impact on clay.•With increasing IS, cation adsorption on clay surfaces will decrease, while anion will increase.
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