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4 results on '"calcium arsenates"'

1. Solubility and Stability of Calcium Arsenates at 25∘C.

Author

Zhu, Y. N., Zhang, X. H., Xie, Q. L., Wang, D. Q., and Cheng, G. W.

Subjects
SOLUBILITY, STABILITY (Mechanics), CALCIUM, ARSENATES, PRECIPITATION (Chemistry), HYDROGEN-ion concentration, INDUSTRIAL contamination
Abstract

The solubility and stability of calcium arsenates at 25 ∘C was determined by both precipitation and dissolution experiments. Ca3(AsO4)2⋅ 3H2O(c), Ca3(AsO4)2⋅ 21/4H2O(c), Ca5(AsO4)3(OH)(c) and Ca4(OH)2(AsO4)2⋅ 4H2O(c) were identified in our experiment over a wide range of pH and for Ca/As molar ratios between 1.25 and 4.0. The solids precipitated at pH = 3 ∼ 7 and Ca/As = 1.5 were phase-pure and well-crystallized Ca3(AsO4)2⋅ xH2O(c) and had relatively larger grain size than those formed at pH > 7. Based on the analytical results and using the computer program PHREEQC, the solubility products for Ca3(AsO4)2⋅ 3H2O(c), Ca3(AsO4)2⋅ 21/4H2O(c), Ca5(AsO4)3(OH)(c) and Ca4(OH)2(AsO4)2⋅ 4H2O(c) were calculated as K sp of 10− 21.14(10− 20.01 ∼ 10− 22.02), 10− 21.40(10− 20.08 ∼ 10− 21.98), 10− 40.12(10− 37.53 ∼ 10− 42.72) and 10− 27.49(10− 26.10 ∼ 10− 28.91), respectively. Correspondingly, the free energies of forming (Δ G f ) of these calcium arsenates were calculated to be −3787.87 kJ/mol, −3611.50 kJ/mol, −5096.47 kJ/mol and −4928.86 kJ/mol. [ABSTRACT FROM AUTHOR] o ) of these calcium arsenates were calculated to be −3787.87 kJ/mol, −3611.50 kJ/mol, −5096.47 kJ/mol and −4928.86 kJ/mol. [ABSTRACT FROM AUTHOR]

Published
2006
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3. Theoretical assessment of calcium arsenates stability:Application in the treatment of arsenic contaminated waste

Author

Raičević, Slavica, Stanić, Vojislav, and Kaluđerović-Radoičić, Tatjana

Subjects
cohesive energy, calcium arsenates, waste, stability, arsenate apatite
Abstract

Several approaches for immobilization of arsenic (As) based on the transformation of its soluble forms (compounds) into highly insoluble arsenate apatite Ca-5(AsO4)(3)OH have been proposed. These immobilization techniques are successfully applied in treatment of industrial waste containing As. Quite the contrary, treatment of soil contaminated with As by apatite amendments, instead of immobilization of this toxic element, increases its mobility and bioavailability. The mechanism underlying these opposite effects still remains elusive. Here, the stability analysis of different calcium arsenates: Ca-5(AsO4)(3)OH, Ca-4(AsO4)(2)(OH)(2), Ca-3(AsO4)(2) Ca5H2(AsO4)(2) and CaHASO(4) was performed, which is based on the calculation of the ion-ion interaction potential (IIIP). It has been demonstrated earlier that HIP, representing the main term of the cohesive energy, is a suitable parameter for assessment of mineral stability. According to the results of this analysis, arsenate apatite with IIIP value of -0.578 Ry represents the most stable chemical form among analyzed compounds. Based on this finding, we proposed a mechanism of formation of arsenate apatite in the presence of hydroxyapatite. This mechanism can explain the suitability of this approach for the treatment of industrial waste and its limitations for in situ treatment of soil and water contaminated with As. Research Trends in Contemporary Materials Science, 8th Conference of the Yugoslav-Materials-Research-Society (Yu-MRS), Sep 04-08, 2006, Herceg Novi, Montenegro

Published
2007

4. Theoretical assessment of calcium arsenates stability: Application in the treatment of arsenic contaminated waste

Author

Vojislav Stanić, Tanja Kaludjerović-Radoičić, and Slavica Raičević

Subjects
Materials science, Cohesive energy, Inorganic chemistry, 0211 other engineering and technologies, chemistry.chemical_element, 02 engineering and technology, Calcium, Industrial waste, Apatite, chemistry.chemical_compound, Arsenate apatite, General Materials Science, Arsenic, 021110 strategic, defence & security studies, Mineral, Mechanical Engineering, Arsenate, Contamination, 021001 nanoscience & nanotechnology, Condensed Matter Physics, 6. Clean water, Bioavailability, chemistry, Mechanics of Materials, Waste, visual_art, visual_art.visual_art_medium, 0210 nano-technology, Stability, Calcium arsenates
Abstract

Several approaches for immobilization of arsenic (As) based on the transformation of its soluble forms (compounds) into highly insoluble arsenate apatite Ca5(AsO4)3OH have been proposed. These immobilization techniques are successfully applied in treatment of industrial waste containing As. Quite the contrary, treatment of soil contaminated with As by apatite amendments, instead of immobilization of this toxic element, increases its mobility and bioavailability. The mechanism underlying these opposite effects still remains elusive. Here, the stability analysis of different calcium arsenates: Ca5(AsO4)3OH, Ca4(AsO4)2(OH)2, Ca3(AsO4)2 Ca5H2(AsO4)2 and CaHAsO4 was performed, which is based on the calculation of the ion-ion interaction potential (IIIP). It has been demonstrated earlier that IIIP, representing the main term of the cohesive energy, is a suitable parameter for assessment of mineral stability. According to the results of this analysis, arsenate apatite with IIIP value of -0.578 Ry represents the most stable chemical form among analyzed compounds. Based on this finding, we proposed a mechanism of formation of arsenate apatite in the presence of hydroxyapatite. This mechanism can explain the suitability of this approach for the treatment of industrial waste and its limitations for in situ treatment of soil and water contaminated with As.

Published
2007

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