Evaluation of various microwave-assisted acid digestion procedures for the determination of major and heavy metal elements in municipal solid waste incineration fly ash

Abstract

Municipal solid waste incineration (MSWI) generates large amounts of fly ash, which requires proper disposal due to containing high levels of toxic elements. Accurate determination of the contents of these elements is crucial to its further treatment and utilization. Microwave-assisted acid digestion is a widely used approach for elemental determination in MSWI fly ash. The digestion procedure affects the analytical results of element contents. This study compares various procedures for microwave-assisted acid digestion of MSWI fly ash in the literature and standard methods. Factors including four common acid combinations and sample mass (from 25 to 250 mg) were investigated, and the analytical results for major and heavy metal element contents were evaluated. The effects of HF and HClO4 in acid combinations were studied in detail. The results showed that acid combinations and sample mass significantly affect analytical results for Ca, Mg, Al, Ba, and Sr. HF is essential to the total digestion of MSWI fly ash, but can lead to loss of Ca, Mg, Al, Ba, and Sr. Loss of elements was caused by the precipitation of Ca and HF as well as complex co-precipitation reactions during digestion. Reducing sample mass and using HClO4 can mitigate loss of element and facilitate the determination of elements in MSWI fly ash.