Precipitation of calcium carbonate from magnetically treated sodium carbonate solution

Using a commercial 'magnetizer' with two S-S poles of the magnet 0.1 T each, the magnetic field (MF) effect on the in situ precipitated calcium carbonate have been investigated via MF treatment of the Na2CO3 solution prior to the precipitation. The MF was applied perpendicularly to Na2CO3 solution flowing in a silicone tube. In the second series, the MF was applied in quiescent conditions, where a plastic tube with the solution was placed between the poles. The S-S arrangement of the magnetizer poles caused MF strength close to zero in the middle of the tube. The MF treatment time was 5, 20, and 70 min. After that calcium carbonate was precipitated from equimolar volumes of Na2CO3 and CaCl2 (8 10(-3) M) solutions at 20 degreesC or 30 degreesC and the light absorbance at 543.2 nm and pH of the suspension were recorded as a function of time, up to 30 min. Within this time in most cases the light absorbance dropped to zero. For each tested system 3-4 replicas of the experiment were made and then average results were taken. It was found that MF effect on in situ precipitated calcium carbonate from Na2CO3 treated in the flowing conditions generally appeared in a slower nucleation and sedimentation rates of the precipitate and also in some differences in pH changes of the suspensions after the solutions mixing. When CaCO3 was precipitated from MF-treated Na2CO3 solution in quiescent environment the maximum absorbance of the light was reduced relative to the reference system by 15, 22, and 37%, for 51 20, and 70 min MF treatment time (at 30 degreesC), respectively. The reduction of the absorbance might result from smaller number of the crystals and a larger their size. (C) 2003 Elsevier B.V. All rights reserved.