Understanding Iron Impurities in Australian Kaolin and Their Effect on Acid and Heat Activation Processes of Clay

Abstract

Iron impurities present in the crystal structure of kaolin minerals or in accessory species are frequently encountered in clay deposits. As knowledge of the location and states of the iron is crucial when modifying the properties of clays by activation, it is important that new deposits are well characterized in terms of the amount and location of this metal. The Western Australia Noombenberry deposit has been identified as a large resource of kaolin composed largely of halloysite and kaolinite. We sampled six from one hundred drill holes and grouped them according to major mineral and iron impurities. First, we characterized them to understand the source of iron impurities. Then, we performed three physicochemical activation processes of samples involving acid treatment (by 3 M HCl), heating at 600 °C, and a combination of both. State-of-the-art tools, including X-ray diffraction, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy, and nuclear magnetic resonance, revealed the properties of kaolin, iron impurities, and the changes incurred after activation. The iron impurities were found to be linked to non-kaolin minerals, i.e., in mica or illite. Once the iron was removed mainly by acid activation, the surface area, pore volume, and negative surface charges increased, and that was significant for halloysite-rich samples. These properties helped adsorb N2 gas compared to the raw kaolin. Therefore, knowing the iron’s location and states in associated mineral species and their dissolution/retention may expand the scope of material development for gas adsorption. They are also useful in other applications like clay purification and adsorbent or additive formulations.

Characterization and treatment effects on Mutaka kaolin for additive in coatings: Mineral composition, thermal and structural modifications

“…This treatment caused dehydroxylation, producing amorphous metakaolin from the Mutaka mineral, as described by Ref. [ 33 ]. Regarding the beneficiation and untreated kaolin results, the SEM images in Fig.…”

“…After milling and particle size distribution analysis, 100 g of kaolin particles that passed through a 150 μm sieve were carefully stored as sample D, which served as an untreated sample. Another 100 g of kaolin was subjected to thermal treatment using a Carbolite Gero HTF electric furnace at a temperature of 800 °C for 4 h, without nitrogen (N2) or airflow [ 33 ]. The sample remained inside the furnace until it cooled down to approximately 100 °C, and then it was further cooled in a desiccating chamber.…”

“…Previous studies have predominantly examined treatment or beneficiation methods for the kaolin [ 15 , [24] , [25] , [26] , [27] , [28] , [29] ], but few have specifically investigated the impact of different treatment methods on kaolin and characterizing the resulting treated kaolin [ 14 , 30 , 31 ]. These processes can potentially induce changes in physical and chemical properties, including morphology, crystal structure, particle size distribution, and pH, which can subsequently affect the formation of kaolin [ 32 , 33 ]. Consequently, there is a need for a dedicated study focusing on different treatment methods of kaolin and their effects on characterization to address this research gap.…”

Synthesis of Kaolin-Supported Nickel Oxide Composites for the Catalytic Oxidative Degradation of Methylene Blue Dye

“…The results showed the peak decline of MBdye but it was not comparable with the composite. This is attributed to the adsorption capacity of kaolin toward methylene blue dye and the small catalytic removal capacity of kaolin due to the presence of metal impurities like iron oxide and titanium oxide …”

“…This is attributed to the adsorption capacity of kaolin toward methylene blue dye 37 and the small catalytic removal capacity of kaolin due to the presence of metal impurities like iron oxide and titanium oxide. 38 3.2.3. Effect of Load Amount of NiO on Kaolin.…”