Diatomaceous Earth (DE) is a soft, siliceous sedimentary rock crumbled into a fine powder. This material consists of the fossilized remains of diatoms, which are ancient, hard-shelled microalgae that accumulated over millions of years. Diatomaceous Earth is not water soluble; it does not truly dissolve in water, which is crucial to its function.
The Difference Between Dissolving and Dispersing
When a substance is truly water soluble, it breaks down at a molecular level into individual ions or molecules, forming a homogeneous solution. Diatomaceous Earth does not undergo this chemical change when added to water. Instead, the fine powder simply disperses, meaning the solid particles are temporarily suspended in the liquid.
This mixing creates a temporary suspension, sometimes called a slurry, where the tiny DE particles are scattered throughout the water. The mixture is not stable, and if left undisturbed, the particles will inevitably settle out of the liquid due to gravity. This physical separation, often confused with true solubility, demonstrates that chemical dissolution has not occurred.
The Chemical Reason: Diatomaceous Earth Composition
The insolubility of Diatomaceous Earth is directly related to its chemical makeup and physical structure. DE is predominantly composed of amorphous silicon dioxide, or silica, accounting for 80–90% of the material. This silica forms the intricate, porous exoskeletons, or frustules, of the fossilized diatoms.
Silica is characterized by a strong, three-dimensional covalent network structure, making it highly resistant to breaking apart in neutral water. The energy required to break the strong bonds between silicon and oxygen atoms exceeds the energy released by interaction with water molecules. While silica can be dissolved under extreme conditions, such as in highly alkaline solutions or at very high temperatures, it remains inert and insoluble in the neutral pH of water.
How Insolubility Affects Common Uses
The insolubility of Diatomaceous Earth is fundamental to its many applications. In filtration systems for water or beverages, the solid DE particles form a porous “filter cake.” This cake physically traps insoluble contaminants like dirt and algae. If DE were soluble, it would pass through the filter, rendering it useless for separating solids from liquids.
In pest control, the material works as a mechanical insecticide, relying on the abrasive, solid structure of the silica particles. When an insect crawls over the dry powder, the sharp edges damage the waxy outer layer of the exoskeleton, causing dehydration. This mechanical action requires DE to remain a dry, solid powder.
For food-grade Diatomaceous Earth used as a dietary supplement, its insolubility ensures it passes through the digestive tract essentially unchanged. The material does not break down and get absorbed into the bloodstream. This is a safety factor that allows it to be used as an internal cleansing agent or anti-caking additive.