The solubility of rhodochrosite (MnCO3) and siderite (FeCO3) in anaerobic aquatic environments |
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| Affiliation: | 1. Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River), Ministry of Agriculture, Hubei Key Laboratory of Soil Environment and Pollution Remediation, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, Hubei Province, China;2. Department of Chemistry, University of Connecticut, 55 North Eagleville Road, Storrs, CT 06269-3060, United States;1. College of Materials and Energy, South China Agricultural University, Guangzhou, Guangdong 510642, China;2. College of Science, Yanbian University, Yanji, Jilin 133002, China |
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| Abstract: | Natural groundwaters are often reported to be highly supersaturated with the carbonate minerals siderite (FeCO3) and rhodochrosite (MnCO3). The kinetics of precipitation and dissolution were determined in the light of new determinations of the solubility products of siderite and rhodochrosite. Laboratory experiments showed that the precipitation kinetics of siderite and rhodochrosite were much slower than that of calcite, and also much slower than their dissolution kinetics. Experiments with supersaturated solutions failed to reach steady state within 474 days in the case of siderite, whereas steady state for rhodochrosite was reached after 140 days. Suspensions of siderite and rhodochrosite crystals reached steady state after 10 and 80 days, respectively. The solubility product of siderite (−log KS0(FeCO3)) was 11.03 ± 0.10 for dried crystals and 10.43 ± 0.15 for wet crystals. For rhodochrosite the solubility product (−log KS0(MnCO3)) was 11.39 ± 0.14 for dried crystals and 12.51 ± 0.07 for wet crystals. The solubility product determined from supersaturated solutions was −log KS0(MnCO3)=11.65 ± 0.14. The observed slow precipitation kinetics of siderite and rhodochrosite might explain the apparent supersaturation that is often reported for anaerobic aquatic environments. |
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