Synthesis of porous carbon derived from coal tar residue via bimetallic salt activation for effective and selective adsorption of thallium(I)

As a highly toxic rare metal, the removal of thallium (Tl) from wastewater has been widely investigated, and adsorption is considered one of the most promising treatment technologies for Tl-containing contaminated water because of its cost-effectiveness, convenience, and high efficacy. In this work, coal tar residue (CTR)-based porous carbon was synthesized through K2FeO4 activation, and applied in adsorbing Tl(I). K2FeO4 could synergistically produce porosity and load iron oxide on the produced porous carbon surface because of the catalytic cracking and oxidative etching during the activation of CTR. The adsorbent was synthesized at 800℃ with a mass ratio of K2FeO4/CTR being 3 (PC3-800) showed optimal Tl(I) adsorption performance. The removal efficiency and distribution coefficient of PC3-800 were above 95% and 104 mL/g, respectively, in a wide pH range (4-10). Furthermore, the selection and reusability of PC3-800 were favorable. The adsorption was a spontaneous, exothermic, and entropy increase process. The adsorption process was dominated by electrostatic attraction, surface complexation, and surface oxidation. The results suggested that removing Tl(I) from contaminated water via CTR-based porous carbon was feasible. Environmental Implication Thallium (Tl) is classified as one of the 13 USEPA priority metals. Recently, Tl pollution has occurred in several sources and river basins worldwide. As an emerging contaminant, its toxicity to human health and ecological environment is higher than cadmium, lead, copper, zinc, and mercury. In this study, porous carbon was generated from extracted residue in coal tar residue via bimetallic salt activation, and the porous carbon possesses excellent adsorption capacity and high selectivity for Tl(I) in aqueous solution. Furthermore, the possible adsorption mechanism of Tl(I) is discussed.