Journal of Colloid and Interface Science 281 (2005) 377–388 www.elsevier.com/locate/jcis The magnetic field influence on the polymorph composition of CaCO 3 precipitated from carbonized aqueous solutions Sergej Knez a,∗ , Ciril Pohar b a Faculty for Natural Sciences and Technology, Askerceva 12, 1000 Ljubljana, Slovenia b Department of Chemistry and Biochemistry, Faculty for Chemistry and Chemical Technology, Askerceva 5, 1000 Ljubljana, Slovenia Received 17 March 2004; accepted 12 August 2004 Available online 2 October 2004 Abstract One of the most debated effects the magnetic fields exert on aqueous solutions and dispersions is their influence on the crystal structure of the main scale component, CaCO 3 . This study presents the results of an experimental program performed to quantitatively evaluate influence of the key magnetic treatment parameters—magnetic induction, exposure time, and fluid velocity—on the polymorph composition of CaCO 3 , precipitated from carbonized aqueous solutions. The results show that magnetic treatment favored the precipitation of aragonite. The key treatment parameters affecting the aragonite content were the magnetic induction and the exposure time, while the fluid velocity exerted no significant influence. The magnetic field has no significant influence on the zeta potential of the precipitated particles in any stage of the treatment. These experimental findings indicate that the magnetic field influence on the crystal structure of CaCO 3 cannot be attributed to the magnetohydrodynamic influence on the charge distribution within the electrical double layer of the forming crystallites. The results rather suggest that the magnetic fields influence the CaCO 3 polymorph phase equilibrium either by influencing the CO 2 /water interface or through the hydration of CO 2− 3 ions prior to the formation of stable crystal nuclei in the solution.  2004 Elsevier Inc. All rights reserved. Keywords: Crystal structure; Crystal morphology; Nucleation; Zeta potential; Magnetic fields; Calcium carbonate 1. Introduction Judging by the increasing number of papers published in numerous scientific journals in recent years, magnetic field (MF) effects in aqueous solutions and dispersions have be- come one of the more popular fields of research, despite (or because of) the aura of controversy surrounding these phe- nomena. Much of the controversy and interest in this field are due to its relation to magnetic water treatment (MWT), where the MF is applied as a means of controlling/preventing the deposition of scale from hard water. Even after several decades of practical application in domestic and industrial water systems, most of the scientific community remains skeptical about the viability of this water treatment method. * Corresponding author. Fax: +386(01)4704560. E-mail address: sergej.knez@uni-lj.si (S. Knez). The most commonly raised criticism revolves around the low reproducibility of the results, especially those reported in various industrial studies, and the fact that the mecha- nism(s) through which the MF exerts its influence(s) on the processes of scale formation and the characteristics of scal- ing compounds is as yet not adequately explained. This is not to say that the fundamental laboratory studies have gen- erally yielded negative results of the MF influences. Quite to the contrary, numerous studies performed by researchers around the world indicate MF influences on • crystallization processes in solutions—nucleation and/or crystal growth rate [1–7]; • the crystal structure of the precipitated CaCO 3 —the main scale component [1,4,5,8,9]; • electrokinetic zeta potential of colloidal particles in electrolyte solutions [1,4,5,10,11]; • colloidal stability of aqueous dispersions [10,12–15]; 0021-9797/$ – see front matter  2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2004.08.099