[Study on the occurrence of ferrum in coal by ultrasound-assisted sequential chemical extraction]

To reveal the occurrence of Ferrum in coal, seven coal samples were selected according to the different contents of ferric oxide in the coal ash, and the content of Ferric element was determined by atomic absorption spectrophotometer (AAS) using nitric acid-perchloric acid-hydrofluoric acid wet digestion. Modes of occurrence of ferrium in the seven coal samples were studied by AAS using ultrasound-assisted sequential chemical extraction experiment (SCEE). Ultrasound promoted the contact of the extraction reagent with the coal particles and enhanced the dissolution process by producing characteristic acoustic cavitations, which greatly shortened the experimental time. The total amount of ferrium obtained by sequential extraction was approximate to the result of wet digestion, which indicated the procedure of SCEE was reasonable. The results showed that the ferric element mainly occurred in forms of carbonate state, Fe-Mn oxides state, sulfide state, sialic state and organic bound Fe in these coal samples. Among the various forms of these occurrences, the content of carbonate was the least, below 3.1%, while the content of sulfide was the dominant occurrence, ranging from 40% to 81.5%.