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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 Mörtel (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-Nürnberg.

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

 

Síntesis
Kieselgur (tierra diatomácea) calcinado con “flux” contiene cristobalito, que es clasificado como material cancerígeno. Esto es causa de preocupación en cuanto a la salud de quienes lo manejan y a la eliminación del kieselgur usado. La formación 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 también como soluciones acuosas. El kieselgur resultante fue examinado mediante difracción de rayos-X, difracción con laser y por microscopio de escaneo por electrones; sus permeabilidades también 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 formación de cristobalito u otras modificaciones cristalinas de la sílice.
Palabras claves: cristobalita, tierra diatomácea, filtración, kieselgur

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