Effect of Iron Ions on the Crystal Growth Kinetics and Microstructure of Calcium Carbonate

Abstract

In the present work, calcium carbonate was precipitated at 28 °C in the presence of iron ions using an accelerated scale method based on CO2 repelling from the solution. The polymorphism and morphology of the obtained precipitates were investigated using scanning electron microscopy, X-ray diffraction, and Fourier transform infrared analyses. At high solution supersaturations, iron ions did not have a significant effect on the inhibition of calcium carbonate crystallization. However, at relatively low solution supersaturations, iron ions addition retards the nucleation of calcium carbonate. Past the onset of nucleation, iron ions increased the CaCO3 growth rate, and most of calcium carbonate amounts precipitated in the bulk solution rather than on the cell walls, decreasing, therefore, risks of scaling. The inhibiting effectiveness of iron ions was explained by a three-step calcium carbonate formation mechanism involving calcium carbonate interaction with siderite.

Effect of Operating Parameters and Foreign Ions on the Crystal Growth of Calcium Carbonate during Scale Formation: An Overview

“…This agrees with the results of Korchef [16] who showed that vaterite was the predominant polymorph at 28°C, for a supersaturation in the range 4-14, and calcite was not detected, because of the low initial calcium concentration (4 Â 10 À3 M). Thus, for a solution supersaturated with respect to calcite ($15-62), aragonite (4-17) and vaterite , vaterite was favored for an initial calcium concentration 4 Â 10 À3 M(<10 À2 M), a precipitation pH in the range 8.4-8.8 and a temperature of 28°C [16]. [36]).…”

“…Several techniques, such as mechanical stirring [29], aeration [30], electrochemical precipitation [31], magnetic water treatment [32] have been used in laboratories to assess the effectiveness of chemical or physical treatment, and the influence of certain parameters on scale formation over time. However, the most interesting method used for CaCO 3 precipitation is the CO 2 repelling method [16,17,33] where the CO 2 containing solution is air bubbled which increases the solution pH and provokes the CaCO 3 precipitation (Figure 3). Indeed, this method is an accelerated simulation of the natural scaling phenomenon in which the precipitation of CaCO 3 takes place, in a short experiment time that do not exceed 90 min, following the removal of the dissolved CO 2 by the atmospheric air, according to the following reaction [16,17]:…”

“…However, the most interesting method used for CaCO 3 precipitation is the CO 2 repelling method [16,17,33] where the CO 2 containing solution is air bubbled which increases the solution pH and provokes the CaCO 3 precipitation (Figure 3). Indeed, this method is an accelerated simulation of the natural scaling phenomenon in which the precipitation of CaCO 3 takes place, in a short experiment time that do not exceed 90 min, following the removal of the dissolved CO 2 by the atmospheric air, according to the following reaction [16,17]:…”

“…Vaterite was favored in moderate (S < 6.5) to enhanced supersaturation solutions [28,44] and smaller vaterite crystals were obtained when supersaturation increased [28]. High supersaturations in the range 4À14 prevented the transformation of vaterite into calcite and increased the crystal growth rate [16,23].…”

“…However, these processes are generally of large-scale consumers of energy and confronted with various problems, such as corrosion and scale formation (Figure 1) which cause enormous energy losses. In most cases, scales are made of the sparingly soluble salt CaCO 3 [13][14][15][16][17][18][19]. Because of its poor thermal conductivity and its good adherence to the walls, CaCO 3 decreases the heat transfer rate, reduces the water flow rate, and even shortens equipment life by corrosion [20,21].…”