RELATIONSHIP BETWEEN SURFACE POTENTIAL AND FUNCTIONAL GROUPS OF COALS

Abstract

The ζ-potentials of five kinds of Chinese typical steam coals with different ranks in aqueous solution with different pH values and the effects of H_2O_2-oxidation on ζ-potential of the corresponding coals were measured.The pH values at the isoelectric point (IEP) of the coals were determined.The functional groups related to the coal surface potentials and their changes by H_2O_2-oxidation were quantitatively characterized using FTIR.The adsorption energy of H~+ on different coal surface, along with correlated chemical bond length, order, and net charge distribution were obtained by means of ZINDO quantum chemical calculation of model compounds.According to a comprehensive analysis of ζ-potential, FTIR spectra and the results of ZINDO calculation,the following conclusions were reached.Coal surface is negatively charged in aqueous system.IEP rise regularly with increase in coal rank,(—OH) is the main negative functional group closely related to ζ-potential on coal surface.After H_2O_2-oxidation, the contents of (—OH),C[ZJZS;ZX;LX,Y]()()O,(—COOH) groups and negativity of coal surface increase.Chemical adsorption of H~+ occurrs on coal surface, and the adsorption energy increases with increase in coal rank.