Distribution of As species in WFGD and WESP system

Coal combustionprocess causes As release and As can migrate to gypsum when entering the wet flue gas desulfurization (WFGD) system.It is of great significance to get a better understanding on the partitioning and species of As in a WFGD system. The partitioning and species of As in a WFGD system are determined by high performance liquid chromatography-hydride generation-atomic fluorescence spectrometry (HPLC-HG-AFS) technique. In addition,the mineral composition and chemical composition in the process of gypsum production are characterized by X-ray diffraction (XRD) and X-ray fluorescence (XRF),respectively. The results show that the main mineral composition in gypsum sampleis gypsum,the main chemical composition are CaO and SO₃,and the total content of which is in the range 89.97%-95.34%. The concentration of As in limestone is 1. 30 μg/g with As (Ⅲ) accounting for 24%.As (Ⅲ) can be oxidized by forced oxidation process resulting As (Ⅲ)proportion 10% decrease. A small amount of As is transported to gypsum,which contribute to the separation function from the hydrocyclone. The concentration of As in gypsum is determined as 1.28 μg/g where the proportion of As (Ⅲ) and As(Ⅴ) are 14%and 86%,respectively. The concentration of As in the solid fraction and liquid fraction of desulfurization effluent are 8.3 μg/g and 0.006 μg/L,respectively.Nearly all the As in solid fraction is removed by effluent treatment process,andalso 16.7%of As in liquid fraction is removed,resulting in that the As concentration in desulfurization effluent is over 4-5 times higher than that in gypsum. An enrichment of As in desulfurization effluent treatment process is addressed,whereAs concentration in neutralization tank,precipitation tank,and flocculation tank are 5.96,6.13 and 6.70 μg/g,respectively. Most As in this product is determined as As(Ⅴ) with proportion over 87%.As is strongly enriched in wet electrostatic precipitators (WESP) ash,where As(V)is predominant existence as residual form and is difficult to leach to the environment.