Diatomaceous earth, often abbreviated as DE, is a naturally occurring, soft, siliceous sedimentary rock that can be crumbled into a fine powder. It forms from the fossilized remains of tiny, hard-shelled aquatic organisms known as diatoms. This material is primarily composed of silica, typically 80% to 90% silica in its oven-dried form. Diatomaceous earth finds widespread application across various industries, including use as a filtration aid, a mild abrasive, and a mechanical insecticide. The journey of diatomaceous earth from microscopic life to a commercially valuable product involves intricate biological, geological, and industrial processes.
The Microscopic Architects: Diatoms
Diatoms are single-celled algae that thrive in both freshwater and marine environments across the globe. These microscopic organisms are unique for their rigid and intricately patterned cell walls, which are made of hydrated silica, a form of amorphous silicon dioxide. Diatoms actively extract dissolved silica from the surrounding water to construct these protective outer shells, known as frustules. The formation of these elaborate silica structures results in a remarkable diversity of shapes and patterns unique to each diatom species. This ability to create biogenic silica makes diatoms significant contributors to the global silicon cycle.
The process of forming these silica shells involves diatoms absorbing silicic acid from the water, which is then transported to a specialized internal compartment. Within this compartment, silica monomers polymerize and are extruded to form the cell wall. The intricate and porous nature of these silica shells is a fundamental characteristic that contributes to the unique properties of diatomaceous earth.
From Ancient Waters to Earth’s Crust
The formation of diatomaceous earth begins when diatoms, after completing their life cycle, die and their lightweight silica shells, or frustules, sink to the bottom of the aquatic environments they inhabit. Over millions of years, these durable silica remains slowly accumulate on ancient lakebeds or ocean floors. This slow accumulation forms vast sedimentary deposits of what is often referred to as diatomaceous ooze.
For these delicate silica shells to be preserved and form significant deposits, specific environmental conditions are necessary. Conditions such as cool, alkaline water and minimal organic matter help prevent the dissolution of the silica. Low sedimentation rates and temperatures also play a role in their preservation. Over geological timescales, the accumulated diatom shells become compressed and solidified under the weight of overlying sediments, gradually transforming into the soft, porous diatomaceous earth rock that is mined today.
Harvesting and Refining for Commercial Use
The journey of diatomaceous earth from a geological deposit to a usable product involves several industrial steps. Commercial deposits of diatomaceous earth are typically extracted through open-pit mining operations. Heavy equipment is used to remove the overlying soil and expose the diatomite layer. The crude diatomite, often containing significant moisture, is then transported to processing facilities.
Upon arrival, the raw material undergoes an initial drying process to remove moisture, which can be as high as 40% or more. This is commonly achieved using specialized dryers to reduce the moisture content. After drying, the material is subjected to milling or grinding to break down the large pieces into a fine powder. Careful milling is important to preserve the intricate, porous structure of the individual diatom frustules, which is essential for the material’s functionality.
Following milling, the powder is typically classified or sifted to sort particles by size, removing impurities and achieving the desired particle size distribution for specific applications. A significant processing step for some diatomaceous earth products is calcination, which involves heating the material to high temperatures, often around 1000°C (1800°F). This heat treatment can alter the properties of the diatomaceous earth.
There are typically two main commercial grades that result from processing: natural/food-grade and filter-grade. Natural or food-grade diatomaceous earth is either uncalcined or minimally processed, retaining its amorphous silica structure and containing very low levels of crystalline silica. This grade is used in applications where its amorphous nature is suitable, such as in pest control or as an anti-caking agent.
In contrast, filter-grade diatomaceous earth often undergoes calcination, sometimes with the addition of a fluxing agent. This high-temperature treatment causes some of the amorphous silica to transform into crystalline forms, such as cristobalite. The addition of a fluxing agent helps fuse diatom particles, increasing particle size and improving permeability for filtration. Filter-grade DE can contain significantly higher levels of crystalline silica, which makes it unsuitable for internal use but highly effective for industrial filtration applications like those in beer or wine production.