The influence of some naturally occurring minerals on the precipitation ofcalcium carbonate polymorphs

In this work precipitation of calcium carbonates, influenced by the additio n of suspended mineral particles (quartz, kaolinite or montmorillonite) is reported. In the investigated systems the initial concentrations of calcium and carbonate species, as well as the concentration of NaCl, were similar to those in seawater. In the reference system, to which no mineral particle s were added, vaterite was the only solid phase precipitating. Quartz and k aolinite had no influence on precipitation, while the addition of calcium m ontmorillonite caused an instantaneous precipitation of calcite. This was t aken as an indication that montmorillonite is a suitable substrate for the overgrowth of this polymorph. The progress of precipitation was followed by measuring the pH value of the solution, while the solid phases were analyzed by means of X-ray diffracti on and FT-IR spectroscopy. The samples of calcite were additionally charact erized by means of the electron spin resonance spectroscopy, which revealed distortions of the crystal lattice of the calcite epitaxially grown on mon tmorillonite. (C) 1999 Elsevier Science Ltd. All rights reserved.