Water, Air, and Soil Pollution

, Volume 169, Issue 1, pp 221–238

Solubility and Stability of Calcium Arsenates at 25C

Authors

    • Department of Resources and Environmental EngineeringGuilin University of Technology
  • X. H. Zhang
    • Department of Resources and Environmental EngineeringGuilin University of Technology
  • Q. L. Xie
    • Department of Resources and Environmental EngineeringGuilin University of Technology
  • D. Q. Wang
    • Department of Resources and Environmental EngineeringGuilin University of Technology
  • G. W. Cheng
    • Department of Resources and Environmental EngineeringGuilin University of Technology
Article

DOI: 10.1007/s11270-006-2099-y

Cite this article as:
Zhu, Y.N., Zhang, X.H., Xie, Q.L. et al. Water Air Soil Pollut (2006) 169: 221. doi:10.1007/s11270-006-2099-y

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 Ksp 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 Gfo) 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.

Keywords

calcium arsenatesfree energies of formingsolubility productsstability

Copyright information

© Springer Science + Business Media, Inc. 2006