Determination of Gallium in Coal Fly Ash by Inductively Coupled Plasma-Optical Emission Spectrometry with Microwave Digestion

BACKGROUND The content of gallium in coal fly ash is 12-230μg/g. The determination of gallium in coal fly ash is crucial to realize the high-value-added utilization of coal fly ash. As a sample pretreatment method, the conventional open wet digestion method has limitations including a large amount of hydrofluoric acid, corrosion of analytical instruments, long dissolution time, the loss of elements, and environmental pollution. Microwave digestion has the advantages of complete digestion, minimal loss, and short digestion time, which can effectively solve the shortcomings of the open wet digestion method. OBJECTIVES To develop a good method for the determination of gallium in coal fly ash. METHODS The coal fly ash was collected from a power plant in Inner Mongolia. The sample was digested with nitric acid (5.0mL), hydrofluoric acid (1.0mL), hydrochloric acid (5.0mL) and perchloric acid (1.0mL) by microwave digestion and then determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). RESULTS The results showed that gallium could be leached totally using HNO3-HF-HCl-HClO4 (5:1:5:1, V/V) when the temperature was 190℃, the time 30 minutes and the microwave power 1400W. The limit of detection was 0.004mg/L. The relative standard deviation (RSD) was 1.7% with the recoveries ranging from 95.1% to 100.9%. CONCLUSIONS ICP-OES with microwave digestion method adds hydrochloric acid and reduces the amount of hydrofluoric acid, thus shortening the time of removing fluoride and reducing the damage to instruments. The method is easy to be used for the determination of trace gallium in coal fly ash.