Correct Calcium Carbonate Structure

With Inline Conductivity Measurements

Correct calcium carbonate structure is essential for achieving the desired performance characteristics in a wide range of industrial applications. Calcium carbonate is one of the most widely used industrial minerals, with product quality heavily influenced by particle size and crystal structure. Precise process control and reliable in-line conductivity measurements help manufacturers maintain consistency, optimize production efficiency, and achieve target product specifications.

Background

Calcium carbonate (limestone) is a widely abundant natural mineral with a diverse range of uses from additives for paints, plastics, ce ments and papers, to an ingredient in foodstuffs and pharmaceuticals. In many applications the particle size and molecular structure of the car bonate is critical for its use. In order to fulfill these requirements, precipitated calcium carbon ate (PCC) is produced with specific physical char acteristics in both particle size as well as molec ular arrangement.

Process

The raw material for PCC is mined limestone, which naturally has a wide range of particle sizes and configurations as well as significant bulk and trace contaminants. The first step in PCC production is the processing of the limestone to calcium hydroxide. Powdered limestone is calcined at 1000 ° C, which breaks down the carbonate to lime (CaO) and carbon dioxide (CO₂). The CO₂ is collected for reuse downstream. Adding water to the lime produces a calcium hydroxide solution. This solution goes through a purification step where unwanted species are removed.

Finally, the calcium hydroxide is reintroduced to the collected CO₂, which results in precipitation of pure calcium carbonate (now referred to as PCC) with particle size and molecular configuration that are dependent on the process conditions.

Different PCC particle shapes result in different bulk densities and surface areas. In comparison to ground calcium carbonate (GCC), PCC has smaller particles sizes as well as a narrower size distribution. Smaller particles are ideal for impact resistance in plastic, and a narrow distribution is desired in oil absorption applications.

Conductivities

Possible PCC structures include prismatic and scalenohedral forms as well as cubic or cuboidal arrangement. In the past, cubic and cuboidal types were the only forms possible. Later, it was discovered that crystal seeding could produce scalenohedral and prismatic types. It has since been found that different types can be produced through controlling conductivity and without the need for crystal seeding. Within the range of 100 – 1200 μS / cm, scaleonohedral structure will be produced, and be tween 1200 – 6000 μS / cm prismatic or colloidal structures will be favored.

The conductivity is defined by the species that have the ability to transfer electrical charge, namely calcium and hydroxide ions. Another influencing factor is the hardness of the water used (conducting species such as Ca²⁺ and Mg²⁺), so acceptable ranges are dependent on the process conditions at any time. Measuring the conductivity is thus vital to ensuring that the solution has the proper characteristics for the desired products. Using an inline conductivity measurement system becomes of increased importance, as conductivity can vary widely and change quickly, so real - time measurement is essential.

Conductivity measurement in such slurries requires a rugged sensor design. The InPro® 7250 HT is ideal. Its inductive measurement method means that no electrodes are in contact with the process, and all measurement elements are protected by a sealed PEEK covering. This durable material exhibits strong mechanical characteristics, ideal for use in slurries with significant abrasive solids contact, is inert to harsh chemicals, and is extremely resistant to fouling.

With simple installation through a flange plate, the InPro 7250 HT is a fit - and - forget sensor. Easy commissioning with minimal maintenance means it will measure reliably for many months without requiring any servicing. The probe also includes a Pt 1000 temperature sensor built into the robust PEEK body for temperature compensation. A METTLER TOLEDO M400 transmitter is highly suited to the process and for outputting the measurement signal to a DCS system.

InPro 7250 HT conductivity sensor

Inductive technology with wide measurement range
Chemically resistant PEEK body
Fit-and-forget installation

Learn more about the InPro7250 HT

M400 Ind Cond transmitter

2-wire loop-powered transmitter
Integrated signal diagnostics
cFMus/ATEX/NEPSIEx - approved for hazardous areas

Learn more about the M400 Ind Cond Transmitter

Now that you have learned how inline conductivity measurements help control calcium carbonate crystal structure, maintain product consistency, and improve process efficiency in precipitated calcium carbonate (PCC) production, download the full Application Note for a more detailed overview of the process, key conductivity challenges, and the benefits of continuous real-time monitoring.

Discover how accurate conductivity measurements can help achieve the desired particle characteristics, optimize process control, reduce production variability, and support consistent PCC quality across a wide range of industrial applications.