Arsenic removal from coal by ferric chloride enhanced leaching under ultraviolet irradiation during flue gas desulphurization with coal slurry.

During coal combustion, the harmful element arsenic can be released into environment and cause potential significant harm to human beings. Therefore, it is very important to study the removal of arsenic from coal before combustion. In this work, simulated SO₂-containing flue gas was used to leach arsenic from coal in a 1 L UV photoreactor. The effects of FeCl₃, ultraviolet (UV), pH and the Cl^-/Fe³⁺ molar ratio on arsenic leaching and SO₂ removal were experimentally investigated and the enhancing mechanism was analysed. Experimental results demonstrated that FeCl₃ and UV could efficiently increase iron and arsenic leaching percentages and SO₂ removal efficiency. UV irradiation could induce the oxidation of most trivalent arsenic. The arsenic leaching percentage was significantly larger than that of iron. Low pH was favourable for iron and arsenic leaching. The optimal Cl^-/Fe³⁺ molar ratio was determined to be 3:1. The introduced ferric chloride could not only increase the concentrations of free radicals and ferric iron oxidants, the chloride ion might also impede the formation of passive coatings, thus increasing the arsenic leaching percentage, intensifying the oxidation of trivalent arsenic and enhancing the removal of SO₂.