Hydrophilic colloids and the elimination of inorganic sulfur from coal: a study employing contact angle measurements

Abstract

Selective oil agglomeration, which is an effective method of eliminating inorganic sulfur from coal, can be further improved in its efficiency by means of the addition of boiled starch. (Starch that was not boiled had a barely detectable effect.) We have measured the oil—water—solid contact angle θ s12 on coal and on iron pyrite (FeS 2) and have discovered that starch makes iron pyrite more hydrophilic without appreciable loss of hydrophobic character of the coal. Measurements of the effect of n-octanol on θ s12, and on the n-decane—water interfacial tension, were also made. The Young equation can be combined with the Gibbs equation, with a result in the form ▪ which we may call the Gibbs—Young equation. We have used this expression to show that n-octanol is more strongly adsorbed at the solid—water interface than at the solid—oil interface. We have carried out laboratory runs of the modified oil agglomeration process, and found that as much as a 55% reduction in pyritic sulfur, below the level obtained without starch, can be achieved, as well as a reduction in ash by as much as 38%.