Non-negligible environmental risks of typical hazardous trace elements in wastes from Chinese coal-fired industrial boilers.

ABSTRACT

Coal-fired industrial boilers (CFIBs) that provide heat for industrial production operate to produce large quantities of wastes containing hazardous trace elements (HTEs), threatening the quality of the environment. Based on the established facility-level material flow inventory of five typical HTEs (Hg, As, Cd, Cr, and Pb) of Chinese CFIBs in 2020, we explored the enrichment characteristics and environmental risks of HTEs in wastes at the regional scale from the perspective of substance flow and enrichment levels. Results showed that the shares of HTEs entering the waste stream were 2.2-16.8 % higher in the focus regions of continuous improvement of air quality compared to the non-focus regions, explained by the higher synergistic control efficiencies of their air pollution control facilities (ACPFs), at 86.6-90.4 % (Hg), 98.6-99.1 % (As), 95.1-95.9 % (Cd), 93.2-94.8 % (Cr), and 97.1-98.0 % (Pb), respectively. In addition, the national averages of HTEs in slag, fly ash, and flue gas desulphurisation (FGD) were simulated to be 0.15-0.87 g/t, 3.25-18.44 g/t, 0.30-0.96 g/t, 19.76-70.11 g/t, and 15.85-73.74 for Hg, As, Cd, Cr, and Pb, respectively. Nationally, the integrated environmental risks of the five HTEs in slag, fly ash, and FGD residue exhibited Considerable, Very High, and Very High level of environmental risk, with the cumulative environmental risk indexes of 171, 317, and 281, respectively. Hg and Cd were the major contributors to the environmental risks of slag, fly ash, and FGD residue, with environmental risk contributions ranging from 23.8 to 82.3 % and 16.0 to 66.1 %, respectively. Results can provide data support for modelling the environmental release of HTEs from wastes and formulating control strategies for environmental management agencies.