The Competing Effects between Magnetic Field and Impurity on Growth Rate of Aragonite

Magnetic treatment device has been installed to suppress the scale formation in heat exchanger and boiler for many years; however, positive and negative effects have been reported. This treatment technique remains controversial, because the scientific mechanism is unclear and may be complicated. The process water generally contains impurities, which would influence the nucleation and growth of CaCO3. For this reason, the aim of this study was to explore the competing effects between the magnetic field and impurityhis report presents a study of how the solution conditions, including iron concentration, strontium concentration, activity ratio, relative supersaturation influence the effectiveness of magnetic field on the growth of aragonite. The solution was pumped through the Descal-A-Matic DC-1 and then back to the tank for 20h to make sure it was fully magnetized. The aragonite growth rates in the jacketed stirred tank were measured using a constant composition method. nder the conditions of pH=9.0, I=0.018M, R=5.54, T=25οC without magnetic field, the aragonite seeds growth rate approached to zero over a wide range of supersaturation (σara=0.73 to1.42). Under the same operating conditions, we found that aragonite started growing in the presence of magnetic field. It is conjectured that the structure of CaCO3 clusters in the supersaturation solution became similar to that of aragonite under the influence of magnetic field.ithout magnetic field and with the same operating conditions, we found that aragonite seeds started growing in the presence of ferrous ion (Fe(Ⅱ)) .But the surface of aragonite seed transformed into calcite morphology at high supersaturation and then stopped growing (i.e., σara> 1.33). In the presence of a small quantity strontium (Sr+2), the aragonite seed surface transformed to calcite and its growth rate is similar to that of calcite. nder the magnetic field, the Fe(Ⅱ) will cause a synergetic effect on the crystal growth of aragonite even at high supersaturation. At σ=1.42, the increasing of aragonite growth rate was about 4.6 fold of that obtained without Fe(Ⅱ). Under the influence of Sr+2, the growth rate of aragonite was significantly lower when the magnetic field was present. It is because the magnetic field were unable to suppress the conversion of aragonite to calcite, and the structure of clusters is similar to aragonite.n the presence of magnetic field, the aragonite growth rate still exhibited a minimum value at R=1.00 as the case without magnetic field. These experimental results suggest that R=1.00 is a condition that favors the formation of clusters with a structure that is similar to calcite in a supersaturated solution.