ABSTRACT
Kaolin or china clay is a versatile industrial mineral with wide technological applications and is
abundantly available in India. The major mineral in kaolin is kaolinite (Al2O3.2SiO2.2H2O). The
common ancillary / impurity minerals occurring with kaolin include parent rocks like feldspar
and mica, quartz, ferruginous, titanoferrous and carbonaceous materials. The most deleterious
impurities in kaolin are iron minerals which imparts colour to the white kaolin. Iron exists as
oxides, hydroxides, oxy hydroxides, sulphides and carbonates along with iron stained
quartz/anatase and mica in kaolin. Kaolin finds extensive applications in paper, paint, rubber,
ceramics, plastics etc. One of the highest value additions for kaolin is as pigment in paper and
paint industries. The optical properties are important for pigment applications and removal of
the iron impurity is very important to improve this property. Extensive research has been carried
out on the nature of iron impurities present in kaolin, which leads to the conclusion that iron is
present as a part of the kaolinite or ancillary mineral (mica or titania) structure, which can be
termed as “structural iron” or as independent iron minerals such as oxides, hydroxides, oxyhydroxides, sulphides and carbonates, which can be termed as “free iron” [1]. The present
paper discusses the iron speciation studies carried out on a typical china clay sample collected
from Koraput district of Orissa State in the Union of India. Studies have shown that the major
impurity mineral species is in “pyritic” (Iron sulphide) form along with other hydroxides, oxyhydoxides and oxides of Iron. Presence of limonite is also observed in the sample. The
identification/quantification of the impurity minerals have played a crucial role in the selection /
modification and sequentialisation of beneficiation processes and subsequent processing studies
have shown that the sample can be value added to ceramic grade.