Development of potentiometric titration method for assessing coals’ oxidation degree

Abstract

Oxidation of coal leads to some unwanted consequences, such as losses of products quality and increase in proneness to spontaneous combustion. One of the indicators of coals' oxidation is changing in amount and composition of active functional groups in organic matter. On using a wide number of samples and adjusting the experimental procedure, a method was developed for coals' oxidation degree evaluation by potentiometric titration based on evaluation of contents of total acidic groups (a sum of phenol and carboxyl groups). It was shown that potentiometric titration is not applicable for determination of phenol and carboxyl groups in coals separately. A phenomenon of appearance of two waves at titration curve was connected with absorption of CO 2 from air into the alcohol-alkaline solution. For coals with vitrinite reflectance varying in 2 range of 0.5-0.72 %., total acidic groups amount decrease with rank growth, whereas for higher rank coals such an alteration is less pronounced. It is shown that it is expedient to use the developed method of potentiometric titration together with the petrographic method for determining the oxidation degree. On the basis of the proposed method of coals' oxidation degree determination by potentiometric titration, a National standard of the Russian Federation GOST R 59012-2020 has been introduced. According to it, the oxidation degree is determined by the increase of the total amount of acidic groups -phenolic and carboxyl hydroxyls in coal as compared to the content of total acidic groups in the control sample, which is used as a seam sample of coal taken outside the oxidation zone, or coal taken when laying the pile, or coal received for benefication, sorting or moving.