Mass transport release of heavy metal oxyanions from solidified/stabilized co-disposed flue gas desulfurization brine and coal fly ash monoliths

Abstract

The coal-fired power industry faces pressing needs to improve disposal practices for the generated flue gas desulfurization (FGD) wastewater and coal fly ash (CFA). Zero-liquid-discharge (ZLD) strategies are gaining significant interest and can be achieved by co-disposing the concentrated FGD wastewater brine with CFA and Portland cement in a solidification/stabilization (S/S) process-a novel strategy that manages two wastes simultaneously. In this study, the stability of such S/S solids produced by utilizing bituminous CFA was evaluated for the mass transport release of major components (Ca2+, Cl-, Mg2+, Na+, and SO42-) and heavy metal oxyanions (As, Cr, and Se) in long-term leaching tests. Particularly, the impact of FeSO4 (FS) addition to the S/S mixture for the purpose of enhancing heavy metal immobilization was assessed. Results showed that FS addition to the S/S process decreased the solid's cumulative release and flux at shorter leaching times for the major components Ca2+, Cl-, Mg2+, Na+, and SO42-, but this effect was diminished over time. However, FS addition significantly decreased release of oxyanions As, Cr, and Se throughout the prolonged leaching time, indicating that FS addition could increase the likelihood of successful long-term disposal of S/S solids of concentrated FGD brines containing these heavy metal oxyanions. Results of this study can help the power industry to further assess and optimize the co-disposal ZLD strategy to minimize environmental risks.