The chemical analysis of blue clay

Abstract

In a review section, the various clay minerals are described together with their origin and reactions. A special reference is given to Maltese Blue Clay deposits. A clay sample, obtained from Ġnejna, was analysed. The following species were determined, namely Calcium, Magnesium and Total Iron by Atomic Absorption Spectroscopy and Aluminium, Phosphorus, Ferrous Iron and Fluoride by UV Spectroscopy. Gravimetric determinations were carried out for Sulphur, Carbonate Carbon, Water Soluble Chloride and Total Chloride. The percentage composition of Silicon was obtained by volatilization with hydrofluoric acid while that of organic matter was obtained by titration. The water content of the sample and the pH of samples collected from points around the site from where the original sample was collected, were also determined. The following oxide form formula was deduced from the experimental results: 0.65CaO. A12O3. 4.30SiO2. 0.08Fe2O3. 0.13MgO. 0.13H2O. 0.41CO2. 0.03FeO. 0.00061P2O5. 0.011F. 0.089C1. 0.016SO3

The formula indicates the presence of a 'clay mineral mixture' probably composed of Kaolinite, Illite and Montmorillonite as the major minerals. Other minerals which may be present include Muscovite, Biotite and Apatite. The Cl : SO3 ratio varies between that in the analysed clay and that present in sea water. This is probably due to the presence of interstitial chloride and due to the sulphate being present as Gypsum or its varieties Selenite, Satin spar and Alabaster. The calcium carbonate content deduced from the experimental results shows that, by definition, the clay cannot be referred to as Marl.