DORFNER Analysenzentrum und Anlagenplanungsgesellschaft mbH
Scharhof 1, 92242 Hirschau
Fon: +49 9622 82-162
E-Mail: anzaplan@dorfner.com
brown natural diatomite powder
Natural diatomite powder
SEM micrograph, natural diatomite
SEM micrograph of natural diatomite before treatment
white flux calcined diatomite powder
Flux calcined diatomite powder
SEM micrograph, flux calcined diatomite
SEM micrograph of flux calcined diatomite particles

Diatomite Processing

The aim of diatomaceous earth processing is to meet international industry standards for permeability, brightness, particle size distribution, etc. and chemistry, by removal of impurities, whilst conserving the commercially important characteristic physical properties of diatomite such as microporosity and particle shape.

Depending on the application of diatomite different processes may be used. The first processing steps consist of disagglomeration, degritting and, as run-of-mine diatomaceous earth may contain 40-60 wt% moisture, drying. The dry powder is classified to produce natural grade diatomite e.g. for vegetable oil filtration. For advanced filtration applications, e.g. beer filtration, natural grade diatomite is calcined in gas or oil-fired rotary calciners, with or without addition of a fluxing reagent.

Thermal processing at 700-1,100°C removes organic matter, partially fuses micropores, and increases particle size owing to the formation of structured clusters with larger pores and reduced surface area – an enhanced benefit for filter applications. Straight calcined, mostly pink, diatomite is used as a medium flow rate filter aid. In order to adjust the grain size distribution after calcination, milling and classification is undertaken.

The top-level quality is flux calcined diatomite. A 2-5% addition of a fluxing agent during calcination at up to 1,200°C reacts with iron-containing impurities to yield a white product for paint filler applications. Flux calcination also improves filtration properties and the release of cations from diatomite during filtration.

At the same time cristobalite is formed. Conventional flux calcined diatomites may contain up to 60% cristobalite. Owing to health considerations regarding free crystalline silica processes developed by ANZAPLAN are now available for the production of low-cristobalite diatomite products as an alternative to conventionally processed material.

The coarse product, after milling and classifying, is used as a filtration aid where high flow rates are required. Owing to the brightness and matting properties of the fine product this fraction is used as high-end filler in paints and plastics.

For some applications in the pharmaceutical industry, chemical treatment such as acid washing is applied to obtain a very pure and bright diatomite product.

Besides laboratory scale testing, ANZAPLAN provides a local test plant for the production of samples. This allows the customer to test different processing options on their specific raw diatomite. ANZAPLAN’s complete evaluation procedure - milling, classification, straight and flux calcinations, and further refinement techniques - is geared to highly-specified customer requests.

Read more:

> Diatomite: Pilot Plant Processing