Micronized CaCO3: a feasible alternative to limestone filtration for conditioning and (re)mineralization of drinking water?

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Worldwide limestone filtration is used in many treatment plants for the conditioning and (re)mineralization of drinking water to increase concentrations of Ca2+ and HCO3−, pH and saturation index, thereby improving the quality of the water regarding corrosion control, buffering and taste. Typical applications include (very) soft groundwater with (very) low alkalinity and desalinated water. In Norway, some plants use a product made of ground natural limestone, called micronized CaCO3 slurry (MCCS), which is dosed as slurry of fine particles (1–2 μm) into the raw water. In this study the potential of MCCS as an alternative to limestone filtration was investigated. Experiments were performed to determine the dissolution kinetics of MCCS and other CaCO3-products, including natural limestone grains and two precipitated CaCO3 powders. As expected from theory, the dissolution kinetics are strongly influenced by the particle size of the CaCO3 and the driving force towards the chemical equilibrium. However, all CaCO3-products needed substantial detention times (30 min and more) to dissolve completely. It is concluded that MCCS is generally not a feasible alternative for limestone filtration as a stand-alone option for the conditioning and (re)mineralization of drinking water. Applications of MCCS are limited and should either be found in combinations with coagulation/filtration or with other conditioning and (re)mineralization methods.

Keywords: conditioning, dissolution kinetics, limestone filtration, micronized CaCO3, (re)mineralization

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