HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Levy, R. Articles by Tanji, K. K. Search for Related Content PubMed Articles by Levy, R. Articles by Tanji, K. K. Agricola Articles by Levy, R. Articles by Tanji, K. K.

Ionic Activity Products and Crystal Forms of Calcium and Magnesium Carbonates Precipitated from Calcium-Magnesium Bentonites¹

ABSTRACT

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 NaHCO₃. Equilibrium solution concentrations of Ca, Mg, Na, HCO₃, 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 NaHCO₃-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.

¹ Contribution from the Department of Land, Air and Water Resources, Univ. of California, Davis. The research was supported by a grant from the University of California Kearney Foundation of Soil Science.

² Soil Scientist and Professors of Soil Science and Water Science, respectively. The Senior Author was on sabbatical leave from the Institute of Soils and Water, Volcani Center, Bet-Dagan, Israel.

Received for publication August 17, 1981. Accepted for publication January 17, 1982.