A Novel Flux That Determines the Physico-Chemical Properties of Calcined Diatomite in Its Industrial Use as a Filler and Filter Aid: Thenardite (Na2SO4)

Abstract

Diatomite needs to go through the flux-calcination process in order to increase its functionality in some specific applications such as filter aids. In this study, the effects of the thenardite, which was used for the first time as a flux in the calcination of diatomite, and widely used soda ash on the industrially important physico-chemical properties of diatomite were investigated. Samples taken from two diatomite deposits in the Aegean region of Turkey (Seydiler diatomite from Afyon and Sarayköy diatomite from Denizli) were used in this study. In raw and calcined diatomite samples, geochemical and mineralogical composition and parameters such as colour, grain size, morphology, specific surface area, permeability and wet cake density were characterized. It was found that thenardite was more effective than traditionally used soda ash in improving whiteness (L* = 98.20) and filtrate clarity (wet cake density = 0.378 g/cm3). However, higher permeability (k), i.e., higher filtration rate, was obtained in diatomite calcined with soda ash (k = 0.97 µm2). Fluxes had different effects on different diatomite species. The necessity of choosing flux type depending on the application area and the desired properties from diatomite was demonstrated.