Geochemical and industrial properties of the Kejal kaolin deposit, NW Iran

Abstract

The Kejal kaolin deposit, situated in the northwest of Iran, is considered a small part of the Hashtjin hydrothermal zone. The kaolinization process in this deposit has occurred in ignimbritic and volcanic tuff parent rocks in different grades such that severely kaolinized samples can be found in the middle section of the kaolinization profile. Kaolinite is the most abundant clay mineral in the studied samples. Quartz and cristobalite are the main minerals while anatase is the minor mineral of the kaolin samples. Among the major oxides, SiO2, Al2O3, and TiO2 show the highest concentrations in kaolin samples. The mass change calculations based on Ti show enrichment of Si, Al, Sr, and LREEs and depletion of alkali and alkali earth elements, HREEs, and HFSEs. The evaluation of REEs normalized to chondrite represents the higher concentration of LREEs comparing to HREEs. A remarkable positive Gd anomaly is seen in spider diagrams, which can be attributed to the primary CaO in the composition of ignimbritic precursor and also the Gd release due to the decomposition of Gd complexes and adsorption by clay minerals. The Eu negative anomaly is the other obvious characteristic of the studied samples and is most likely related to the alteration of feldspars, decomposition of plagioclase, and Eu liberation from the system. The significant positive correlations between REEs and Al2O3, TiO2, and P2O5 demonstrate the important role of clay minerals, REE-bearing phosphate minerals such as monazite, and titanium minerals like anatase and rutile in the kaolinization process and REE transport and establishment. The performed particle size test based on the hydrometer method shows about 20% of particles <2 μm and 36%-42% of particles <25 μm, which reveals a dominant medium particle size for these kaolin samples. Furthermore, the chemical composition of the analyzed samples represents around 20% alumina. Based on the obtained physicochemical evaluations, the Kejal kaolin deposit is medium- to low-grade kaolin, which is useable after simple processing in the paper industry as filler and in the ceramic industry as floor tiles.