Diatomaceous Earth: Characterization, thermal modification, and application

Abstract

The diatomaceous earth (DE), collected from the Mariovo region in North Macedonia, was characterized and thermally modified. The material represents a sedimentary rock of biogenic origin, soft solid that can be easily disintegrated, with white to grayish color, with bulk density of 0.51–0.55 g/cm3, total porosity of 61–63%, and specific gravity of 2.25 g/cm3. The chemical composition is as follows: SiO2, 86.03; Al2O3, 3.01; Fe2O3, 2.89; MnO, 0.06; TiO2, 0.20; CaO, 0.76; MgO, 0.28; K2O, 0.69; Na2O, 0.19; P2O5, 0.15; and loss of ignition, 5.66 (wt%). The mineralogy of the raw DE is characterized by the predominant presence of amorphous phase, followed by crystalline quartz, muscovite, kaolinite, and feldspar. Significant changes in the opal phase are observed in the 1,000–1,200°C temperature region. At 1,100°C, the entire opal underwent solid–solid transition to cristobalite. Further ramp of the temperature (1,100–1,200°C) induced formation of mullite. Scanning electron microscopy (SEM) and transmission electron microscopy depict the presence of micro- and nanostructures with pores varying from 260 to 650 nm. SEM analysis further determined morphological changes in terms of the pore diameters shrinkage to 120–250 nm in comparison to the larger pores found in the initial material. The results from this investigation improve the understanding of mechanism of silica phase transition and the relevant phase alterations that took place in DE upon calcination temperatures from 500 to 1,200°C.

Preparation and Characterization of Glass-Ceramic Foam from Clay-Rich Waste Diatomaceous Earth

“…The second weight loss in the temperature range 250-700 °C, with a distinct visible peak in the heat flow curve, resulted from dehydroxylation of kaolinite according to Equation (2) [29]. Part of the weight loss in this temperature range can also be attributed to the burn out of organic matter present in the raw material [28].…”

“…However, significant deformation due to the melting of the sample was not observed. The first major weight loss occurred in the temperature range up to 200 °C and was due to the release of physically bound water in raw diatomite [28]. The second weight loss in the temperature range 250-700 °C, with a distinct visible peak in the heat flow curve, resulted from dehydroxylation of kaolinite according to Equation (2) [29].…”

“…The dehydroxylation process continued up to 1400 • C, resulting in an additional weight loss of 0.78% in the temperature range 800-1400 • C [28]. The three exothermic peaks which are visible at 967 • C, 1142 • C and 1187 • C are likely caused by the crystallization of new phases.…”

“…The weight loss at 619 • C was likely due to the loss of structural water by the dehydroxylation of silanol groups in the opal structure of diatomite [7,28].…”

Characteristics of the Properties of Absodan Plus Sorbent and Its Ability to Remove Phosphates and Chromates from Aqueous Solutions

“…Its biogenic nature comes from the shells of diatoms that build diatomite and give the rock a porous structure. The lithological variability between deposits and even within one deposit results in differentiated porosity, density, specific surface area, and adsorption capacity of diatomite [ 35 , 36 , 37 ]. As a result, diatomite sorbents may have different properties depending on their origin.…”