Ultra-deep Removal of Metal Ions from Coal Tar by Complexation: Experimental Studies and Density Functional Theory Simulations

As one of the important aspects of upgrading coal tar, the ultra-deep removal of metal ions via the complexation method was investigated by screening four complexing agents and performing density functional theory (DFT) simulations. Analysis of the compositions and contents of the metallic compounds in the coal tar revealed that the main components were iron and calcium naphthenates. Direct filtration reduced the mechanical impurity content from 0.24% to 0.0752%, indicating that most of the large particles could be easily removed. Among the four complexing agents, namely, acetic acid, oxalic acid, citric acid, and ethylenediaminetetraacetic acid, oxalic acid exhibited the best demetallization performance. The DFT simulations suggested that the high performance of oxalic acid originated from its 1:1 coordination mode, rigid dicarboxyl structure, and greater binding energy.