FöRFATTARE
Millqvist, Theresa

DATUM
2000-12-20

INSTITUTION
Kemi och metallurgi / Mineralteknik

SAMMANFATTNING
Diatomite (diatomaceous earth, kiselguhr) is a sedimentary rock of marine or lacustrine deposition. This microscopic single celled algae belonging to the class Bacillarieae consist mainly of an accumulation of siliceous frustules or skeletons of diatoms. Chemically, diatomite is essentially amorphous hydrated or opaline silica with varying amounts of contaminants, such as silica sand, clay minerals, metal salts and organic matter. Diatomite can be considered as inert due to the chemical composition, which imply that diatomite does not affect taste, smell or colour.

Filtration is one of the most widely used operations in industrial processing, and diatomite has been an indispensable filter aid material for more than 60 years. Nowadays the diatomite industry faces many challenges as traditional end-use markets, especially filtration, move towards other technologies. However new applications, particularly in biotechnology could pave the way for a recovery.

In this Master thesis diatomite from the state of Bahia was investigated. A pilot plant scale was built up and the diatomite was hydro classified and calcined in a rotary kiln. Ciemil, a company situated in Bahia, which produces diatomite to filtration and filler, supplied the diatomite, which was investigated. The results from this work will be handed to Ciemil and will in the future be the foundation of improvement of the diatomite process at Ciemil.

The aim of this Master thesis was to investigate the effect of the retention time, temperature and addition of Na2CO3 on the filtration properties of calcined diatomite. To investigate the influence of calcination on the filtration properties, literature studies, sample preparation, mineralogical characterization, chemical analysis, desegregating, sand and clay removal by hydro classification, drying, particle size analysis, filtration tests was made.

It is concluded that the particle size is increasing and the filtration rates are increasing when the diatomite is calcined. An improvement of the filtration rate is achieved with Na2CO3 addition.

ISSN 1402-1617 / ISRN LTU-EX--01/009--SE / NR 2001:009