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

Abstract

Due to the insufficiency of freshwater resources and to supply the drinking water populations, many desalination processes such as reverse osmosis, electrodialysis and distillation are widely used. However, these processes are of large-scale consumers of energy and confronted with various problems such as corrosion and scale formation. In most cases, scales are made of calcium carbonate CaCO3. In the present chapter, an overview on the effect of operating parameters such as temperature, pH and supersaturation on the precipitation kinetics, microstructure, and polymorphism of CaCO3 is given. Additionally, I put special emphasis on the effect of foreign ions such as magnesium, sulphate, and iron ions on CaCO3 precipitation since they are present at significant concentrations in natural waters. Also, the mechanisms by which these ions affect the crystal growth of CaCO3 were pointed out. Knowledge about these operating parameters as well as the effects of foreign ions allow elucidating the polymorphs growth during water treatment. The control of these operating parameters allows reducing scale formation during drinking water and wastewater treatment. The economic impact is of greatest importance since this favorably affects the treatment costs, increases the equipment life, and allows enhanced product water recovery.

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“…Contrary to the above suggestion (easy replacement of Ca by Fe ions) many experimental studies [37] agreed that, in an aqueous phase, and in the presence of minute amounts of ferrous iron Fe +2 calcite will not occur at all or only marginally. Calcite phase is the most stable form of crystalline calcium carbonate and very difficult to dissolve as soon as it nucleates and grows at the walls of pipelines.…”

“…Studies on the interference of iron on the crystallization of CaCO3 has immediate economic importance as the scales of CaCO 3 occludes pipes in water treatment systems, desalination plants, mineral, and crude oil pipelines, etc. Contrary to the above suggestion (easy replacement of Ca by Fe ions) many experimental studies [37] agreed that, in an aqueous phase, and in the presence of minute amounts of ferrous iron Fe +2 calcite will not occur at all or only marginally. Calcite phase is the most stable form of crystalline calcium carbonate and very difficult to dissolve as soon as it nucleates and grows at the walls of pipelines.…”

“…However ferrous ion presence does not prevent the nucleation and growth of aragonite. The reason for this behavior is not yet clearly understood but it has been observed since the problem caught the attention of scientists [37, 38].…”