Speciation analysis of arsenic in coal and its combustion by-products in coal-fired power plants

The speciations of Arsenic (As) in coal will inevitably convert during the combustion process. The As speciations in coal and its by-products are closely related to human health and environmental safety which is urgent to be identified. However, there is a lack of pretreatment procedure and analysis method on the As species in coal-related products in power plants. In this study, the As species in coal, fly ash (FA), and gypsum were successfully determined by high performance liquid chromatography coupled with hydride generation atomic fluorescence spectrometry (HPLC-HG-AFS). The instrument parameters, extract reagents, and pretreatment methods (i.e. ultrasound and microwave-assisted) were optimized. The whole separation time of inorganic As was shorten to 7 min after optimization, with the detection limit of 1.8 and 4.6 ng/g for As(Ⅲ) and As(Ⅴ), respectively. The efficient As extract reagent was the mixture of 1.0 mol/L H₃PO₄ and 0.1 mol/L ascorbic acid solution. Microwave-assisted (2000 W, 80 ℃, 40 min) and ultrasound-assisted (40 kHz, 20 ℃, 40 min) schemes were the optimal extraction methods for coal/FA and gypsum samples, respectively. Under the proposed microwave and ultrasound extraction procedure, the recovery of As(Ⅲ) and As(Ⅴ) could reach to 95.8%/104.5% and 90.6%/89.7%, respectively. The dominant occurrence of As species in coal was As(Ⅴ) with a small percentage of As(Ⅲ), while As(Ⅴ) was the only occurrence form observed in FA and gypsum. It is indicated that revealing the transformation of As(Ⅲ) to As(Ⅴ) is the key for gaseous As capture. The As species distribution investigation provides a scientific insight to the controlling of As emission from power plant.