Determination of total Cl in incinerator fly ashes utilized as cement raw materials

To utilize incinerator fly ashes (IFAs) as cement raw materials, the knowledge of their total Cl content is indispensible, hence a process which can digest IFA samples completely becomes critical. This study describes a two-stage microwave-assisted digestion process in which various acids and a set of terminal temperatures of 180-210 °C are applied. In the first stage, three types of acids are utilized, namely, concentrated HNO3, concentrated HF, and a mixture of concentrated HNO3 and HF. In the second stage, saturated H3BO3 is added to the cooled sample residues, and the temperature programming applied is the same as that of the first stage. Results indicate that a complete digestion can only be achieved if the two-stage digestion process is operated at a terminal temperature of 210 °C, coupled with a mixture of concentrated HNO3 and HF. Although the microwave-assisted digestion process operated at 180 °C is sanctioned by both USA and Taiwan environmental authorities, IFA samples treated accordingly often leave a considerable amount of undissolved residues.