Diatomite (also known as diatomaceous earth, D.E., kieselgur/kieselguhr)
WHAT IS DIATOMITE/DIATOMACEOUS EARTH?
Diatomaceous earth is a powder produced from diatomite, a sedimentary rock composed of the skeletal remains of single-cell aquatic plants called diatoms. As one diatom generation is replaced by another over millions of years, the skeletons began to collect on the sea bed and on the bottom of lakes to form diatomite deposits. The remarkably complex skeletons are unusual in that they are composed of natural silica with a high degree of unique structure. The combination of the natural silica composition, the overall structure of the diatom particles, and the network of holes in the structure are responsible for the unique properties of these multi-functional mineral products.
Our deposits are numerous and include one of the world’s largest worked mine and only marine deposit in Lompoc, California. Marine diatom species are more varied than their freshwater cousins, and the profusion of shapes results in an extremely light density diatomaceous earth powder, with excellent filtration characteristics.
|Typical MOH Hardness||3-5|
|Moisture (max %)||0.1-9|
|*The data quoted are determined by the use of IMERYS Standard Test Methods|
THE CHEMISTRY & STRUCTURE
Although silica is a common feature in the Earth’s crust, very little exists in the lakes & oceans. Even less is apparent when considering the amount contained in living organisms. Diatomite represents a very rare occurrence – a mineral silica that has an elaborate structure worked by nature into a labyrinth of tiny holes.
No other silica source that is mined or chemically prepared has such a structure. The key to the exceptional properties of diatomite lies more in the microstructure – each diatom is peppered with thousands of holes, usually of three distinct sizes, ranging from a few microns in diameter down to submicron diameters.
It is the combination of the pure silica composition, the overall structure of the broken diatom particles, and the network of holes in the structure that are responsible for the unique properties of diatomaceous earth products.
The mineralogy and chemistry of the diatomite ore is scrupulously analyzed prior to extraction. Even the types of species found in the deposit are characterized, with each mine usually containing at least three different diatomite shapes. In fact, the different diatom species are mined separately, where possible. By doing so, these ore products may then be blended in certain proportions, to enable production of a diatomaceous earth powder with the specific properties required.
All diatomite is processed near the mine from which it was extracted. The result is a range of finished diatomaceous earth products adapted for a variety of industrial applications. Processing of the diatomite ore usually fractures the individual diatom skeletons.
Without additional processing, the resulting powder, composed of mainly broken diatom pieces, is referred to as “natural” diatomaceous earth. Such powders are limited in their use because the particle sizes are too small for the majority of applications. For most uses the diatoms have to be fused into larger particle sizes. This is done by a process of kilning or “calcination”. The outside of the diatom particles are softened by heat (at about 1000°C), so they literally glue themselves together. The temperature and time of heating is carefully controlled to prevent the total mass of the diatoms being melted and the consequent loss of the structure. To create even larger particle agglomerations, an adaptation of the calcining process has to be made to prevent melting of the structure. To do this a “flux” is added, usually sodium carbonate, during the kilning process. The sodium carbonate lowers the melting point of the surface of the diatom pieces. This allows better fusion between particles, and leaves the internal structure untouched by the heat. The resulting agglomerated diatom pieces are known as “fluxcalcined” grades.
Imerys has an extensive network of operations. See map of operations.
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