Solid-solution aqueous-solution reactions between jarosite (KFe3(SO4)2(OH)6) and its chromate analog

被引:60
作者
Baron, D [1 ]
Palmer, CD
机构
[1] Calif State Univ Bakersfield, Dept Phys & Geol, Bakersfield, CA 93311 USA
[2] Idaho Natl Lab, Idaho Falls, ID 83415 USA
关键词
D O I
10.1016/S0016-7037(02)00880-3
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
The sulfate mineral jarosite (KFe3(SO4)(2)(OH)(6)), its chromate analog (KFe3(CrO4)(2)(OH)(6)), and seven precipitates with intermediate compositions (KFe3(CrXS(1-X)O4)(2)(OH)(6)) were synthesized.. The unit cell volume of the precipitates is closely represented by a linear function of composition, suggesting a continuous solid solution. This solid solution dissolves stoichiometrically according to KFe3(CrXS(1-X)O4)(2)(OH)(6) + 6H(+) <----> K+ + 3Fe(3+) + 2X CrO42- + (2-2X)SO42- + 6H(2)O and reaches stoichiometric saturation after approximately 40 d. Log K-SS values calculated from samples taken after 1090 d are consistently lower than what would be expected for an ideal solid solution, indicating that the excess free energy of mixing, G(E), is negative. G(E) calculated from the log K,, values can be closely modeled by the one-parameter Guggenheim expansion G(E) = X-CrJar X-Jar RT a(0) where a, is -4.9+/-0.8, X-CrJar and X-Jar are the mole fractions of KFe3(CrO4)(2)(OH)(6) and KFe3(SO4)(2)(OH)(6) in the solids, R is the gas constant, and T the absolute temperature. Based on the calculated excess free energy, a Lippmann diagram with a modified abscissa was constructed. Copyright (C) 2002 Elsevier Science Ltd.
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页码:2841 / 2853
页数:13
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