The Experts below are selected from a list of 123 Experts worldwide ranked by ideXlab platform
J J Helble - One of the best experts on this subject based on the ideXlab platform.
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reaction of arsenic vapor species with fly ash compounds kinetics and speciation of the reaction with Calcium silicates
Chemosphere, 2003Co-Authors: R O Sterling, J J HelbleAbstract:Abstract In coal combustion systems, the partitioning of arsenic between the vapor and solid phases is determined by the interaction of arsenic vapors with fly ash compounds under post-combustion conditions. This partitioning is affected by gas–solid reactions between the Calcium components of the ash particles and arsenic vapors. In this study, bench scale experiments were conducted with Calcium compounds typical of coal-derived fly ash to determine product formation, the extent of reaction and reaction rates when contacted by arsenic oxide vapors. Experiments conducted with arsenic trioxide (As 4 O 6(g) ) vapors in contact with Calcium oxide, di-Calcium silicate and mono-Calcium silicate over the temperature range 600–1000 °C indicated that these solids were capable of reacting with arsenic vapor species in both air and nitrogen. Calcium Arsenate was the observed reaction product in all the samples analyzed. Maximum capture of arsenic occurred at 1000 °C with Calcium oxide being the most effective of the three solids over the range of temperatures studied. Using a shrinking core model for a first order reaction and the results from intrinsic kinetic experiments conducted in air, the reaction rate constants were found to be 1.4×10 −3 exp(−2776/ T ) m/s for Calcium oxide particles, 7.2×10 −3 exp(−3367/ T ) m/s for di-Calcium silicate particles and 5.5×10 −3 exp(−3607/ T ) m/s for mono-Calcium silicate particles. These results therefore suggest that any Calcium present in fly ash can react with arsenic vapor and capture the metal in water-insoluble forms of the less hazardous As(V) oxidation state.
R O Sterling - One of the best experts on this subject based on the ideXlab platform.
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reaction of arsenic vapor species with fly ash compounds kinetics and speciation of the reaction with Calcium silicates
Chemosphere, 2003Co-Authors: R O Sterling, J J HelbleAbstract:Abstract In coal combustion systems, the partitioning of arsenic between the vapor and solid phases is determined by the interaction of arsenic vapors with fly ash compounds under post-combustion conditions. This partitioning is affected by gas–solid reactions between the Calcium components of the ash particles and arsenic vapors. In this study, bench scale experiments were conducted with Calcium compounds typical of coal-derived fly ash to determine product formation, the extent of reaction and reaction rates when contacted by arsenic oxide vapors. Experiments conducted with arsenic trioxide (As 4 O 6(g) ) vapors in contact with Calcium oxide, di-Calcium silicate and mono-Calcium silicate over the temperature range 600–1000 °C indicated that these solids were capable of reacting with arsenic vapor species in both air and nitrogen. Calcium Arsenate was the observed reaction product in all the samples analyzed. Maximum capture of arsenic occurred at 1000 °C with Calcium oxide being the most effective of the three solids over the range of temperatures studied. Using a shrinking core model for a first order reaction and the results from intrinsic kinetic experiments conducted in air, the reaction rate constants were found to be 1.4×10 −3 exp(−2776/ T ) m/s for Calcium oxide particles, 7.2×10 −3 exp(−3367/ T ) m/s for di-Calcium silicate particles and 5.5×10 −3 exp(−3607/ T ) m/s for mono-Calcium silicate particles. These results therefore suggest that any Calcium present in fly ash can react with arsenic vapor and capture the metal in water-insoluble forms of the less hazardous As(V) oxidation state.
Marco Pasero - One of the best experts on this subject based on the ideXlab platform.
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the crystal structure of turneaureite ca5 aso4 3cl the Arsenate analog of chlorapatite and its relationships with the Arsenate apatites johnbaumite and svabite
American Mineralogist, 2017Co-Authors: Cristian Biagioni, Ferdinando Bosi, Ulf Halenius, Marco PaseroAbstract:The crystal structure of turneaureite, ideally Ca 5 (AsO 4 ) 3 Cl, was studied using a specimen from the Brattfors mine, Nordmark, Varmland, Sweden, by means of single-crystal X-ray diffraction data. The structure was refined to R 1 = 0.017 on the basis of 716 unique reflections with F o > 4σ( F o ) in the P 6 3 / m space group, with unit-cell parameters a = 9.9218(3), c = 6.8638(2) A, V = 585.16(4) A 3 . The chemical composition of the sample, determined by electron-microprobe analysis, is (in wt%; average of 10 spot analyses): SO 3 0.22, P 2 O 5 0.20, V 2 O 5 0.01, As 2 O 5 51.76, SiO 2 0.06, CaO 41.39, MnO 1.89, SrO 0.12, BaO 0.52, PbO 0.10, Na 2 O 0.02, F 0.32, Cl 2.56, H 2 O calc 0.58, O(≡F+Cl) −0.71, total 99.04. On the basis of 13 anions per formula unit, the empirical formula corresponds to (Ca 4.82 Mn 0.17 Ba 0.02 Sr 0.01 ) ∑ 5.02 (As 2.94 P 0.02 S 0.02 Si 0.01 ) ∑ 2.99 O 12 [Cl 0.47 (OH) 0.42 F 0.11 ] ∑ 1.00 . Turneaureite is topologically similar to the other members of the apatite supergroup: columns of face-sharing M 1 polyhedra running along c are connected through T O 4 tetrahedra with channels hosting M 2 cations and X anions. Owing to its particular chemical composition, the studied turneaureite can be considered as a ternary Calcium Arsenate apatite; consequently it has several partially filled anion sites within the anion columns. Polarized single-crystal FTIR spectra of the studied sample indicate stronger hydrogen bonding and less diverse short-range atom arrangements around (OH) groups in turneaureite as compared to the related minerals johnbaumite and svabite. An accurate knowledge of the atomic arrangement of this apatite-remediation mineral represents an improvement in our understanding of minerals able to sequester and stabilize heavy metals such as arsenic in polluted areas.
Kyoungphile Nam - One of the best experts on this subject based on the ideXlab platform.
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stabilization mechanism of arsenic in mine waste using basic oxygen furnace slag the role of water contents on stabilization efficiency
Chemosphere, 2018Co-Authors: Sang Hyun Kim, Seulki Jeong, Hyeonyong Chung, Kyoungphile NamAbstract:Abstract Arsenic stabilization mechanism in a mine waste was investigated using a basic oxygen furnace (BOF) slag. A lab-scale batch test was carried out to stabilize As in the mine waste samples for 1 h, where various amounts of the BOF slag and distilled water were introduced. Different stabilization efficiencies were observed depending on the stabilizing conditions (i.e., BOF slag content and water to mine waste (L/S) ratio). The stabilization efficiencies ranged 75–92% and 92–95% for 5% (w-slag/w-mine waste) and 10% BOF slag treated mine waste samples, respectively. Interestingly, a notable effect of the L/S ratio on the stabilization efficiency was observed (78% at 0.05 L/kg, and 23% at 1.0 L/kg) at the 3% BOF slag treatment. The point of zero charge and the stabilizing pH indicated that the BOF slag surface was negatively charged. Based on the comparison of fresh and Ca-reduced BOF slags, As stabilization mechanism was determined to be adsorption through cation bridges by Ca2+. The Surface analysis using X-ray photoelectron spectroscopy (XPS) and the stabilization experiment conducted at lower pH provided evidence that the hindrance of As adsorption resulted from Ca(OH)2 precipitation on the BOF slag surface when excess water (1.0 L/kg) was added. Such effect of water content seemed to be overcome by providing an excessive amount of the BOF slag. When an ample amount of Ca2+ is provided and pH is maintained around 11, not only As adsorption but also Calcium Arsenate precipitation occur, and both contributed to the stabilization mechanisms of As.
Cristian Biagioni - One of the best experts on this subject based on the ideXlab platform.
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the crystal structure of turneaureite ca5 aso4 3cl the Arsenate analog of chlorapatite and its relationships with the Arsenate apatites johnbaumite and svabite
American Mineralogist, 2017Co-Authors: Cristian Biagioni, Ferdinando Bosi, Ulf Halenius, Marco PaseroAbstract:The crystal structure of turneaureite, ideally Ca 5 (AsO 4 ) 3 Cl, was studied using a specimen from the Brattfors mine, Nordmark, Varmland, Sweden, by means of single-crystal X-ray diffraction data. The structure was refined to R 1 = 0.017 on the basis of 716 unique reflections with F o > 4σ( F o ) in the P 6 3 / m space group, with unit-cell parameters a = 9.9218(3), c = 6.8638(2) A, V = 585.16(4) A 3 . The chemical composition of the sample, determined by electron-microprobe analysis, is (in wt%; average of 10 spot analyses): SO 3 0.22, P 2 O 5 0.20, V 2 O 5 0.01, As 2 O 5 51.76, SiO 2 0.06, CaO 41.39, MnO 1.89, SrO 0.12, BaO 0.52, PbO 0.10, Na 2 O 0.02, F 0.32, Cl 2.56, H 2 O calc 0.58, O(≡F+Cl) −0.71, total 99.04. On the basis of 13 anions per formula unit, the empirical formula corresponds to (Ca 4.82 Mn 0.17 Ba 0.02 Sr 0.01 ) ∑ 5.02 (As 2.94 P 0.02 S 0.02 Si 0.01 ) ∑ 2.99 O 12 [Cl 0.47 (OH) 0.42 F 0.11 ] ∑ 1.00 . Turneaureite is topologically similar to the other members of the apatite supergroup: columns of face-sharing M 1 polyhedra running along c are connected through T O 4 tetrahedra with channels hosting M 2 cations and X anions. Owing to its particular chemical composition, the studied turneaureite can be considered as a ternary Calcium Arsenate apatite; consequently it has several partially filled anion sites within the anion columns. Polarized single-crystal FTIR spectra of the studied sample indicate stronger hydrogen bonding and less diverse short-range atom arrangements around (OH) groups in turneaureite as compared to the related minerals johnbaumite and svabite. An accurate knowledge of the atomic arrangement of this apatite-remediation mineral represents an improvement in our understanding of minerals able to sequester and stabilize heavy metals such as arsenic in polluted areas.