Effects of the Fluxing Agents on the Formation of Crystalline Silica Phases
During Calcination of Kieselguhr
MBAA TQ vol. 42, no. 4, 2005, pp.
290-296 |
VIEW ARTICLE
Dominik Antoni (1), Winfried Russ (1), Roland Meyer-Pittroff (1), and
Heinrich M�rtel (2). 1. Chair of Energy and Environmental Technology of the Food
Industry, Technical University of Munich. 2. Department of Materials Science
Glass and Ceramics, Friedrich-Alexander University of Erlangen-N�rnberg.
Abstract
Flux-calcined kieselguhr contains cristobalite, which is classified as a
carcinogenic material, thereby causing concerns with occupational health and the
disposal of the spent material. The formation of the crystalline phases can be
prevented by the use of potassium carbonate instead of sodium carbonate as the
fluxing agent in the manufacturing process. In this test, samples of kieselguhr
containing different levels of potassium carbonate or sodium carbonate as
fluxing agents were calcined at temperatures between 800 and 1000�C. The fluxing
agents were used as powders as well as aqueous solutions. These samples were
analyzed using X-ray diffraction, laser diffraction, and scanning electron
microscopy. The permeabilities were tested. Based on these experiments, it was
determined that calcination could be accomplished in the presence of potassium
ions and with an adapted process even at high temperatures without the formation
of cristobalite and other crystalline silica modifications.
Keywords: cristobalite, diatomaceous earth, filtration, kieselguhr
S�ntesis
Kieselgur (tierra diatom�cea) calcinado con �flux� contiene cristobalito, que
es clasificado como material cancer�geno. Esto es causa de preocupaci�n en
cuanto a la salud de quienes lo manejan y a la eliminaci�n del kieselgur usado.
La formaci�n de las fases cristalinas en el proceso de manufactura puede ser
obviada utilizando carbonato de potasio en lugar de carbonato de sodio como
�flux�. En este estudio, muestras de kieselgur con diferentes niveles de
carbonato de potasio o carbonato de sodio fueron calcinadas a temperaturas entre
800 y 1000�C. Los �flux� fueron usados tanto como polvos como tambi�n como
soluciones acuosas. El kieselgur resultante fue examinado mediante difracci�n de
rayos-X, difracci�n con laser y por microscopio de escaneo por electrones; sus
permeabilidades tambi�n fueron examinadas. Estos experimentos demostraron que
era factible, con un proceso modificado, calcinar en la presencia de iones de
potasio inclusive a altas temperaturas, sin la formaci�n de cristobalito u otras
modificaciones cristalinas de la s�lice.
Palabras claves: cristobalita, tierra diatom�cea, filtraci�n, kieselgur
