Diatomaceous Earth (DE) is a fine, powdery substance composed of the fossilized remains of ancient, hard-shelled microalgae known as diatoms. These microscopic fossils accumulated over millions of years, forming deposits that are now mined. DE is not soluble in water under normal conditions, a property that stems directly from its unique chemical structure.
The Chemical Reason Diatomaceous Earth Does Not Dissolve
The primary component of Diatomaceous Earth is silicon dioxide, or silica, which typically makes up 80 to 90 percent of its composition. The silica in DE exists in an amorphous state, meaning it lacks the highly ordered, crystalline structure of materials like quartz. This amorphous silica forms a strong, continuous lattice where silicon atoms are bonded tightly to oxygen atoms in a three-dimensional network.
True dissolution occurs when water molecules break apart the bonds holding a substance together. However, the silicon-oxygen bonds within the silica framework are too robust for water molecules to effectively break at standard temperatures and pressures. The solubility of amorphous silica in water is considered negligible at temperatures below 200 degrees Celsius.
Physical Behavior When Mixed with Water
Because Diatomaceous Earth is chemically non-soluble, mixing it with water results in a physical change, not a chemical one. The fine powder will initially form a temporary mixture known as a suspension. In this state, the microscopic particles are dispersed throughout the liquid, giving the water a cloudy or milky appearance.
The particles of Diatomaceous Earth are denser than water, causing them to eventually separate from the liquid phase. This leads to rapid sedimentation, where the powder settles out of the suspension and collects at the bottom of the container. While it does not dissolve, DE is extremely porous and highly absorbent, allowing it to soak up water into its microscopic structure. This absorption does not change its fundamental nature; the water simply fills the voids within the fossilized diatom shells.
Implications for Common Uses
The non-solubility and physical properties of Diatomaceous Earth have direct consequences for its most common applications. In pest control, DE works by physically abrading and dehydrating insects. When Diatomaceous Earth gets wet, the water coats the microscopic, sharp edges of the particles, which temporarily neutralizes their ability to pierce an insect’s exoskeleton.
Once the water evaporates and the Diatomaceous Earth dries out, the powder regains its physical efficacy against pests. Conversely, its non-dissolving nature is a benefit in filtration systems, such as in swimming pool filters. The particles form a porous “filter cake” on a screen, which remains stable and traps microscopic impurities as the water passes through.