Ge. Christidis et Pw. Scott, PHYSICAL AND CHEMICAL-PROPERTIES OF BENTONITE DEPOSITS OF MILOS ISLAND, GREECE, Transactions - Institution of Mining and Metallurgy. Section B. Applied earth science, 105, 1996, pp. 165-174
Citations number
40
Categorie Soggetti
Mining & Mineral Processing","Geosciences, Interdisciplinary",Mineralogy
The bentonite deposits of Miles Island, Aegean, Greece, which formed f
rom low-temperature alteration of pyroclastic rocks, have been investi
gated to determine physical and chemical properties and group them acc
ordingly. These properties include the cation exchange capacity, swell
ing capacity, pH, rheological properties and some important foundry pr
operties, such as the green and dry compressive strengths, shatter ind
ex, wet tensile strength, compactability and permeability. In principl
e, deposits with abundant opal-CT develop poor physical properties. Th
e rheological and swelling properties are influenced mainly by the ben
tonite grade (smectite content) and the degree of disaggregation of th
e smectite quasi-crystals. The latter might have been caused by such f
actors as the nature of the interlayer cation, the smectite layer char
ge and its localization, the degree of oxidation of iron and the type
of smectite-opal-CT interaction. Deposits in which opal-CT forms aggre
gates separated from smectite develop viscous suspensions, but their g
rade is low. Only deposits of high grade that are free of opal-CT deve
lop good foundry properties. Both the foundry and the rheological prop
erties are influenced by swelling, since only bentonites of high swell
ing capacity form viscous suspensions and develop good bonding propert
ies. Moreover, viscous fluids result after the smectite flakes have sw
ollen beyond a certain degree. Hydrothermal alteration is detrimental
to the physical and chemical properties of bentonites in that it decre
ases the smectite content and the pH and changes the smectite layer ch
arge and the lattice dimensions.