Microstructural Characteristics of Geopolymers Based on Alkali-Activated Fly Ash

Aluminosilicate geopolymers with a high silica molar ratio have been prepared by mixing Croatian coal-ash (ASTM Class F) and sodium silicate solution (water glass, technical grade). The samples were cured at 85 °C for 8 h and 24 h in different experimental conditions. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM/EDS) have been used to identify the new phases formed in geopolymeric binders, and to follow the progress of their formation. It was observed that the glassy component of fly ash used reacted with water glass. The main reaction product formed in the geopolymeric materials was amorphous alkali aluminosilicate gel that induces a shift in the T–O (T=Si or Al) asymmetric stretching band towards lower frequency (1074.58 cm–1) in relation to the ones in the original fly ash. SEM/EDS detected a highly inhomogeneous glass-like matrix, constituted mainly of Na-Si-Al phases in a bulk region, together with unreacted spheres of fly ash particles

Modelling of L-DOPA Oxidation Catalyzed by Laccase

Enzymatic oxidation of 3,4-dihydroxyphenyl-L-alanine (L-DOPA) with laccase from Trametes versicolor was investigated. The highest enzyme activity at pH 5.4 and at 25 ºC was found. The reaction kinetics and the effect of dissolved oxygen concentration on the reaction rate were evaluated. A mathematical model, comprised of double-substrate Michealis-Menten kinetics and mass balances for L-DOPA and dissolved oxygen concentrations, was developed in order to describe and predict the process of L-DOPA oxidation. Kinetic parameters, , and were estimated and experimentally verified by a set of experiments with constant additional aeration for different initial concentrations of L-DOPA and dissolved oxygen. A significant increase in reaction rate was established at a higher oxygen concentration in the inlet gas. The developed model was used to investigate the influence of dissolved oxygen concentration on L-DOPA conversion

Modelling of L-DOPA Oxidation Catalyzed by Laccase

Enzymatic oxidation of 3,4-dihydroxyphenyl-L-alanine (L-DOPA) with laccase from Trametes versicolor was investigated. The highest enzyme activity at pH 5.4 and at 25 ºC was found. The reaction kinetics and the effect of dissolved oxygen concentration on the reaction rate were evaluated. A mathematical model, comprised of double-substrate Michealis-Menten kinetics and mass balances for L-DOPA and dissolved oxygen concentrations, was developed in order to describe and predict the process of L-DOPA oxidation. Kinetic parameters, , and were estimated and experimentally verified by a set of experiments with constant additional aeration for different initial concentrations of L-DOPA and dissolved oxygen. A significant increase in reaction rate was established at a higher oxygen concentration in the inlet gas. The developed model was used to investigate the influence of dissolved oxygen concentration on L-DOPA conversion

Mass distributions and morphological and chemical characterization of urban aerosols in the continental Balkan area (Belgrade)

This work presents characteristics of atmospheric aerosols of urban central Balkans area, using a size-segregated aerosol sampling method, calculation of mass distributions, SEM/EDX characterization, and ICP/MS analysis. Three types of mass distributions were observed: distribution with a pronounced domination of coarse mode, bimodal distribution, and distribution with minimum at 1 μm describing the urban aerosol. SEM/EDX analyses have shown morphological difference and variation in the content of elements in samples. EDX spectra demonstrate that particles generally contain the following elements: Al, Ca, K, Fe, Mg, Ni, K, Si, S. Additionally, the presence of As, Br, Sn, and Zn found in air masses from southeast segment points out the anthropogenic activities most probably from mining activities in southeastern part of Serbia. The ratio Al/Si equivalent to the ratio of desert dust was associated with air masses coming from southeastern and southwestern segments, pointing to influences from North Africa and Middle East desert areas whereas the Al/Si ratio in other samples is significantly lower. In several samples, we found high values of aluminum in the nucleation mode. Samples with low share of crustal elements in the coarse mode are collected when Mediterranean air masses prevailed, while high share in the coarse mode was associated with continental air masses that could be one of the approaches for identification of the aerosol origin. Graphical abstract ᅟ.This work presents characteristics of atmospheric aerosols of urban central Balkans area, using a size-segregated aerosol sampling method, calculation of mass distributions, SEM/EDX characterization, and ICP/MS analysis. Three types of mass distributions were observed: distribution with a pronounced domination of coarse mode, bimodal distribution, and distribution with minimum at 1 mu m describing the urban aerosol. SEM/EDX analyses have shown morphological difference and variation in the content of elements in samples. EDX spectra demonstrate that particles generally contain the following elements: Al, Ca, K, Fe, Mg, Ni, K, Si, S. Additionally, the presence of As, Br, Sn, and Zn found in air masses from southeast segment points out the anthropogenic activities most probably from mining activities in southeastern part of Serbia. The ratio Al/Si equivalent to the ratio of desert dust was associated with air masses coming from southeastern and southwestern segments, pointing to influences from North Africa and Middle East desert areas whereas the Al/Si ratio in other samples is significantly lower. In several samples, we found high values of aluminum in the nucleation mode. Samples with low share of crustal elements in the coarse mode are collected when Mediterranean air masses prevailed, while high share in the coarse mode was associated with continental air masses that could be one of the approaches for identification of the aerosol origin

Outcomes from elective colorectal cancer surgery during the SARS-CoV-2 pandemic

This study aimed to describe the change in surgical practice and the impact of SARS-CoV-2 on mortality after surgical resection of colorectal cancer during the initial phases of the SARS-CoV-2 pandemic

Recovery of critical metals from dilute leach solutions – Separation of indium from tin and lead

The strategic metal indium is recovered from solutions containing tin and lead that are typical of those obtained from leach solutions of metal component fractions of electronic waste including the leach solutions from indium tin oxide thin film conductive layers that contain only indium and tin. Almost total recovery of the metals can be achieved from nitric, perchloric and acetic acid leach solutions using a novel cylindrical mesh electrode electrolysis cell under appropriate conditions. The optimum separation of indium from tin and lead is achieved by a novel three-stage process from nitric acid media in the presence of SCN− as a complexing agent. Lead is removed from dilute indium-tin-lead solutions in the first stage from 0.1 mol L−1 nitric acid solution by electrodeposition over an 8 h period in the absence of SCN− to give a residual solution containing a maximum of 2 mg L−1 of lead (97% recovery). Tin is removed in the second stage by electrodeposition over an 8 h period from the solution after addition of 0.02 mol L−1 SCN− to give a maximum residual electrolyte tin concentration of 3 mg L−1 (94% recovery). In the third stage indium is recovered at the anode of the cylindrical mesh electrode cell as an oxy-hydroxide phase by increasing the SCN− concentration to 0.1 mol L−1 and carrying out the electrolysis for a period of 24 h to give a residual solution containing 1 mg L−1 of indium (98% recovery).We acknowledge the support of an EPSRC/LINK WMR3 grant (GR/L03217) with Fluid Dynamics International Limited. We wish to thank Aleppo University for a scholarship to NY and Professor. J. D. Donaldson for all his advice and support

Trace elements in size-segregated urban aerosol in relation to the anthropogenic emission sources and the resuspension

Size segregated particulate samples of atmospheric aerosols in urban site of continental part of Balkans were collected during 6 months in 2008. Six stages impactor in the size ranges: Dp ≤ 0.49 μm, 0.49 < Dp ≤ 0.95 μm, 0.95 < Dp ≤ 1.5 μm, 1.5 < Dp ≤ 3.0 μm, 3.0 < Dp ≤ 7.2 μm, and 7.2 < Dp ≤ 10.0 μm was applied for sampling. ICP-MS was used to quantify elements: Al, As, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, K, Li, Na, Ni, Mg, Mn, Pb, Sb, V, and Zn. Two main groups of elements were investigated: (1) K, V, Ni, Zn, Pb, As, and Cd with high domination in nuclei mode indicating the combustion processes as a dominant sources and (2) Al, Fe, Ca, Mg, Na, Cr, Ga, Co, and Li in coarse mode indicating mechanical processes as their main origin. The strictly crustal origin is for Mg, Fe, Ca, and Co while for As, Cd, K, V, Ni, Cu, Pb, and Zn dominates the anthropogenic influence. The PCA analysis has shown that main contribution is of resuspension (PC1, σ2 ≈ 30 %) followed by traffic (PC2, σ2 ≈ 20 %) that are together contributing around 50 % of elements in the investigated urban aerosol. The EF model shows that major origin of Cd, K, V, Ni, Cu, Pb, Zn, and As in the fine mode is from the anthropogenic sources while increase of their contents in the coarse particles indicates their deposition from the atmosphere and soil contamination. This approach is useful for the assessment of the local resuspension influence on element’s contents in the aerosol and also for the evaluation of the historical pollution of soil caused by deposition of metals from the atmosphere

An interlaboratory comparison of aerosol inorganic ion measurements by ion chromatography : Implications for aerosol pH estimate

Water-soluble inorganic ions such as ammonium, nitrate and sulfate are major components of fine aerosols in the atmosphere and are widely used in the estimation of aerosol acidity. However, different experimental practices and instrumentation may lead to uncertainties in ion concentrations. Here, an intercomparison experiment was conducted in 10 different laboratories (labs) to investigate the consistency of inorganic ion concentrations and resultant aerosol acidity estimates using the same set of aerosol filter samples. The results mostly exhibited good agreement for major ions Cl-, SO2-4, NO-3, NHC4 and KC. However, F-, Mg2C and Ca2C were observed with more variations across the different labs. The Aerosol Chemical Speciation Monitor (ACSM) data of nonrefractory SO2-4, NO-3 and NHC4 generally correlated very well with the filter-analysis-based data in our study, but the absolute concentrations differ by up to 42 %. Cl-from the two methods are correlated, but the concentration differ by more than a factor of 3. The analyses of certified reference materials (CRMs) generally showed a good detection accuracy (DA) of all ions in all the labs, the majority of which ranged between 90 % and 110 %. The DA was also used to correct the ion concentrations to showcase the importance of using CRMs for calibration check and quality control. Better agreements were found for Cl-, SO2-4, NO-3, NHC4 and KC across the labs after their concentrations were corrected with DA; the coefficient of variation (CV) of Cl-, SO2-4, NO-3, NHC4 and KC decreased by 1.7 %, 3.4 %, 3.4 %, 1.2 % and 2.6 %, respectively, after DA correction. We found that the ratio of anion to cation equivalent concentrations (AE/CE) and ion balance (anions-cations) are not good indicators for aerosol acidity estimates, as the results in different labs did not agree well with each other. In situ aerosol pH calculated from the ISORROPIA II thermodynamic equilibrium model with measured ion and ammonia concentrations showed a similar trend and good agreement across the 10 labs. Our results indicate that although there are important uncertainties in aerosol ion concentration measurements, the estimated aerosol pH from the ISORROPIA II model is more consistent

Microstructural Characteristics of Geopolymers Based on Alkali-Activated Fly Ash

Aluminosilicate geopolymers with a high silica molar ratio have been prepared by mixing Croatian coal-ash (ASTM Class F) and sodium silicate solution (water glass, technical grade). The samples were cured at 85 °C for 8 h and 24 h in different experimental conditions. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM/EDS) have been used to identify the new phases formed in geopolymeric binders, and to follow the progress of their formation. It was observed that the glassy component of fly ash used reacted with water glass. The main reaction product formed in the geopolymeric materials was amorphous alkali aluminosilicate gel that induces a shift in the T–O (T=Si or Al) asymmetric stretching band towards lower frequency (1074.58 cm–1) in relation to the ones in the original fly ash. SEM/EDS detected a highly inhomogeneous glass-like matrix, constituted mainly of Na-Si-Al phases in a bulk region, together with unreacted spheres of fly ash particles