Solubility of KFe3(CrO4)(2)(OH)(6) at 4 to 35 degrees C

被引:44
作者
Baron, D [1 ]
Palmer, CD [1 ]
机构
[1] OREGON GRAD INST SCI & TECHNOL,DEPT ENVIRONM SCI & ENGN,PORTLAND,OR 97291
关键词
D O I
10.1016/0016-7037(96)00206-2
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 solubility of KFe3(CrO4)(2)(OH)(6), the chromate analog of the sulfate mineral jarosite, was studied in a series of dissolution experiments. Experiments were conducted at 4 to 35 degrees C and pH values between 1.5 and 3.0 using synthetic KFe3(CrO4)(2)(OH)(6). The solids were kept in the reaction vessel for up to 6 months. Equilibrium was established in the experiments between 2 and 4 months. The log K-SP for the dissolution reaction of KFe3(CrO4)(2)(OH)(6) KFe3(CrO4)(2)(OH)(6) + 6H(+) reversible arrow K+ + 3Fe(3+) + 2CrO(4)(2+) + 6H(2)O at 25 degrees C is -18.3 +/- 0.6. Based on this measured solubility product, the free energy of formation, Delta G(f,298)degrees, is -3305.5 +/- 3.4 kJ mol(-1). The dissolution experiments at 25 degrees C indicate the formation of a FeCrO4+ complex. The dissolution experiments combined with previously published spectroscopic data between 0 and 25 degrees C yield a formation constant of the form 2.303log K-FeCrO4+ = - Delta H degrees/RT + Delta S degrees/R, where Delta H degrees = 19.1 +/- 2.2 kJ mol(-1) and Delta S degrees = 214 +/- 8 J K-1 mol(-1). At 25 degrees C, log K-FeCrO4+ is 7.8 +/- 0.5. The equilibrium ion activity products calculated from the experiments at 4, 15, 25, and 35 degrees C do not show a statistically significant trend indicating a weak temperature dependence of the solubility product over the temperature range of the experiments. The rate of the dissolution reaction can be described by a first-order model. The measured solubility indicates that the chromate analog of jarosite is stable over a wide range of conditions and could form in large parts of a Cr(VI)-contaminated aquifer.
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页码:3815 / 3824
页数:10
相关论文
共 42 条
[1]  
ALLISON JD, 1990, MINTEQA2PRODEFA2 GEO
[2]  
Alpers CN, 1989, SCI GEOL B, V42, P281, DOI [DOI 10.3406/SGEOL.1989.1829, 10.3406/sgeol.1989.1829]
[3]  
APHA, 1985, STAND METH EX WAT WA
[4]   Solubility of jarosite at 4-35 degrees C [J].
Baron, D ;
Palmer, CD .
GEOCHIMICA ET COSMOCHIMICA ACTA, 1996, 60 (02) :185-195
[5]   Identification of two iron-chromate precipitates in a Cr(VI)-contaminated soil [J].
Baron, D ;
Palmer, CD ;
Stanley, JT .
ENVIRONMENTAL SCIENCE & TECHNOLOGY, 1996, 30 (03) :964-968
[6]   CHROMIUM CYCLING IN SOILS AND WATER - LINKS, GAPS, AND METHODS [J].
BARTLETT, RJ .
ENVIRONMENTAL HEALTH PERSPECTIVES, 1991, 92 :17-24
[7]  
BONNIN A, 1966, CR ACAD SCI C CHIM, V262, P1782
[8]  
Breemen N. Van, 1973, Publication, International Institute for Land Reclamation and Improvement, Wageningen, P66
[9]  
BROPHY GP, 1965, AM MINERAL, V50, P112
[10]   ASSOCIATION OF CHROMIUM(VI) WITH NEPTUNIUM(IV) AND THORIUM(IV) IN PERCHLORATE SOLUTION [J].
BURKHART, MJ ;
THOMPSON, RC .
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1972, 94 (09) :2999-&