Abstract
Abstract The ion-exchange properties of low-rank coals have been studied with a view to obtaining optimum conditions for the determination of carboxyl groups in the presence of phenolic groups. The effect of pH, temperature, and atmosphere on the exchange has been examined. Alternative procedures for estimating the carboxyl content following the initial exchange were assessed, eg titration of acid released, estimation of cation in the exchanged coal and of acid consumed in the back-exchange. It was concluded that exchange with barium acetate at pH 8.25 under reflux (single for 4 h) followed by potentiometric titration to pH 8.25 in the presence of the coal provided the most reliable approach. No evidence was obtained to support suggestions in the literature that exchange with the acetate of a bivalent cation (eg Ca ++ , Ba ++ ) can lead to formation of the half salt where one atom of cation is associated with only one carboxyl group.
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