Des diatomées à la diatomite et à la terre de diatomée, diversité des utilisations

Diatomite is a light-colored, fine-grained, friable, and powdery siliceous sedimentary rock composed of 90% siliceous diatom frustules, agglomerated together and easily detached to form a fine white powder that settles and adheres to all surfaces. From a geological perspective, diatomite is therefore a sedimentary rock composed of a hydrated, biogenic silica mineral of the opalescent type. Diatomite floats like volcanic pumice, but unlike pumice, which retains its positive buoyancy, it eventually sinks within 1 to 2 minutes. How can we explain this characteristic of diatomite that accounts for its use in numerous industrial, agri-food, pharmaceutical, medical, and domestic fields? I - Diatomite, a siliceous biosedimentary rock formed by the accumulation of diatom frustules Observations: Macroscopic images of diatomite and diatomaceous earth Microscopic images of modern diatoms: Coscinodiscus under LM vs. SEM Microscopic images of a diatomite smear: Coscinodiscus under LM vs. SEM II - Diatomite, a micro- and nanoporous rock with exceptional physicochemical properties Siliceous (SiO2) Chemically inert Unalterable: acid test Micro- and nanoporous High S/V ratio Absorbent and filtering: buoyancy test Low density (d=0.2 to 0.3) Thermally inert Insulating Hardness of 6 Mild Abrasive III - Exploitation and Uses of Diatomite and Diatomaceous Earth Industry: Construction, paints, abrasives, insulation Food Processing: Liquid filtration, anti-caking agent E551 in food, fertilizer coating… Biochemistry, Pharmacology: Reactive surface in enzymology… Household Use: Insecticide, absorbent, filter IV - Dangers by Inhalation and Ingestion Hervé Kempf November 2022