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Ionic Activity Products and Crystal Forms of Calcium and Magnesium Carbonates Precipitated from Calcium‐Magnesium Bentonites
Author(s) -
Levy Rachel,
Whittig L. D.,
Tanji K. K.
Publication year - 1982
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1982.03615995004600030010x
Subject(s) - solubility , calcite , magnesium , chemistry , calcium carbonate , carbonate , bentonite , precipitation , crystallization , inorganic chemistry , calcium , mineralogy , geology , organic chemistry , paleontology , physics , meteorology
A series of laboratory experiments were conducted to study quantities, mineral forms, and solubility of alkaline earth carbonates precipitated from Ca‐Mg‐bentonite systems. The effects of Mg on carbonate precipitation and solubility were assessed in isolation from other carbonate precipitation inhibitors commonly found in soils. Five bentonite systems were preconditioned by saturation with different proportions of exchangeable Ca and Mg. Calcium/magnesium ratios ranged from 99:1 to 8:92. Portions of each system were seeded with calcite, and both seeded and unseeded systems were equilibrated with deionized water or NaHCO 3 . Equilibrium solution concentrations of Ca, Mg, Na, HCO 3 , and Cl and also pH served as input data to the WATEQF solution chemistry computer program for calculations of ion strength, ion pairs, ion activities, and carbonate ionic activity products (IAP). The data obtained from the series of experiments clearly demonstrated that solubility characteristics of calcium carbonate in the Ca‐Mg‐bentonite systems were influenced by incongruent properties of freshly precipitated carbonate surfaces. The data further show that Mg inhibited crystallization and increased solubility of calcium carbonate and that high concentrations of Mg in the NaHCO 3 ‐bentonite precipitation medium induced crystallization of Mg calcite. In some systems, Mg was precipitated in forms which were not identified by either x‐ray diffraction analysis or IAP characteristics.